14th International Workshop on e⁺e⁻ collisions from Phi to Psi 2026

8 Jun 2026, 08:30 → 11 Jun 2026, 23:25 Europe/Rome

Scuola Normale Superiore, Aula Dini, Palazzo del Castelletto (Pisa)

Alberto Lusiani (Scuola Normale Superiore & INFN, sezione di Pisa), Andrea Gurgone (University of Pisa and INFN), Angela Papa (Universita' di Pisa e INFN, sezione di Pisa), Anna Driutti (University and INFN Pisa), Lorenzo Punzi (By SerSe - Lorenzo PUNZI)

The 14th edition of the International Workshop on e⁺e^– collisions from Phi to Psi will be held in Pisa from the morning of June 8th to the end of the afternoon of June 11th, 2026. The aim of the workshop is to review the latest advances in hadron physics at low-energy accelerators and related fields. The scientific program covers the following topics:

• R measurements and Muon g-2
• Hadron Physics
• Flavour Physics
• Tau and Muon Physics
• Two-photon Physics
• Dark sector Physics

The event is hosted by Scuola Normale Superiore (SNS) with the support of Istituto Nazione di Fisica Nucleare (INFN). The program will include both invited and contributed talks.

Monday 8 June

Registration

Welcome

phipsi26-intro-08jun26.pdf

Muon g-2 theo/exp

Convener: Achim Denig

1 The Fermilab Muon g-2 Final Measurement

The 2026 Breakthrough Prize in Fundamental Physics was recently awarded to the Muon g-2 Collaborations from CERN, BNL, and Fermilab for their high-precision measurements of the anomalous magnetic moment of the muon (a_mu = (g – 2)/2) spanning six decades. This talk will present the final Fermilab results for a_mu, which achieved a precision of 127 parts per billion. Comparison with theoretical calculations of comparable precision will enable some of the most stringent tests of the Standard Model and most sensitive searches for new physics, some of which will be previewed in this presentation. So, while this result for a_mu may be the final Fermilab measurement of muon g-2, it will not be the final measurement from Fermilab Muon g-2!

Speaker: Breese Quinn (University of Mississippi)

Quinn_PhiPsi_060826.pptx

2 Status and prospects of muon g-2 theory

I will present the current status of theory for the muon g-2 standard model result. I will also give an outlook on possible paths towards matching the experimental precision.

Speaker: Christoph Lehner (University of Regensburg)

talk.pdf

Coffee Break

HVP LO theo/exp.

Convener: Andrzej Kupsc (NCBJ , Warsaw & Uppsala Univerity)

3 Hadronic contributions to muon g-2 in the dispersive approach

Measurements of the anomalous magnetic moment of the muon (muon $g-2$) are among the most precise tests of the Standard Model, but efforts to achieve an equally precise theoretical prediction are presently impeded. Significant tensions within the hadronic data inputs to the dispersive approach, and further tensions between dispersive and newer lattice values, are currently still unexplained. I will discuss these current tensions and relevant recent developments with a focus on the dispersive approach. This work constitutes a necessary step towards determining a best possible theory estimate of the muon anomalous magnetic moment and fully realising the power of the experimental measurement to constrain potential new physics.

Speaker: Aidan Wright (University of Liverpool)

AWright_PhiPsi_Pisa_2026 (2).pdf

4 Higher-order hadronic vacuum polarization contributions to the muon anomalous magnetic moment in spacelike and timelike domains

The complete set of six relations, which mutually express the spacelike and
timelike kernel functions for the hadronic vacuum polarization contributions
to the muon anomalous magnetic moment $a^{\text{HVP}}_{\mu}$ in terms of each
other, is obtained. By making use of the derived relations the explicit
expression for the next-to-leading order spacelike kernel function, which
enters the representation for $a^{\text{HVP}}_{\mu}$ involving the hadronic
vacuum polarization function, is obtained. The corresponding next-to-leading
order spacelike kernel function, which appears in the representation for
$a^{\text{HVP}}_{\mu}$ involving the Adler function, is calculated
numerically. The obtained results can be employed in the assessments of the
hadronic vacuum polarization contributions to the muon anomalous magnetic
moment in the framework of the spacelike methods, such as lattice studies,
MUonE project, and others.

Additionally, it is shown that the quark flavour thresholds of the hadronic
vacuum polarization function generate additional contributions to
$a^{\text{HVP}}_{\mu}$ expressed in terms of the Adler function and the
$R$-ratio and the explicit expressions for such contributions are obtained.
The contributions due to the heavy quark thresholds to $a^{\text{HVP}}_{\mu}$
expressed in terms of the $R$-ratio appear to be quite sizable, that can be
of a particular relevance for the data-driven method of assessment of the
hadronic part of the muon anomalous magnetic moment.

[1] A.V.Nesterenko, J.Phys.G49, 055001 (2022); arXiv:2112.05009[hep-ph].
https://doi.org/10.1088/1361-6471/ac5d0a

[2] A.V.Nesterenko, J.Phys.G50, 029401 (2023); arXiv:2209.03217[hep-ph].
https://doi.org/10.1088/1361-6471/aca3c1

[3] A.V.Nesterenko, J.Phys.G51, 015005 (2024); arXiv:2306.16392[hep-ph].
https://doi.org/10.1088/1361-6471/ad0b33

[4] A.V.Nesterenko, J.Phys.G53, 025003 (2026); arXiv:2505.10339[hep-ph].
https://doi.org/10.1088/1361-6471/ae16c4

Speaker: Alexander Nesterenko

Nesterenko_PHIPSI26.pdf

5 Recent results from the CMD-3 detector at VEPP-2000

The CMD-3 detector continues taking data at the VEPP-2000 collider. Total collected integrated luminosity exceeded 1 fb-1. At the moment next energy scan around Rho-resonance is in progress with about factor of three in the luminisity integral compare to the published results on pion form factor. Many other final state are under study in the e+e- energy range up to 2 GeV. Large accumulated data sample allowers to measure the hadronic cross sections with high precision, what some how delays obtaining final results. Preliminary new results will be presented. Some preliminary plans for the future detector modernization are discussed for the posibility to measure the pion form factor with 0.2% systematic uncertainty.

Speaker: Evgeny Solodov (Budker Institute of Nuclear Physics, Novosibirsk, Russia)

Solodov_CMD_PhiPsi2026.pdf

6 Recent results from the SND experiment at the VEPP-2000 collider

We present studies that are based on the 1 fb$^{-1}$ data, and acquired
by the SND detector with $e^+e^-$-collisions at VEPP-2000 in the
$\sqrt{s}$=0.3–2 GeV energy range. Our results of high precision
measurements of the
$e^+e^- \to \pi^+\pi^-$ and $e^+e^- \to \pi^+\pi^-\pi^0$
cross sections and the calculation of their Hadronic Contribution to the
Muon (g-2) are presented. Also we report the results of the analysis of
the $e^+e^-\to \eta\gamma$ and $e^+e^-\to \pi^0\gamma$ radiative
processes
near mass of the $\phi$-meson, the study of the cross section of
$e^+e^-\to \omega\pi^0\to\pi^0\pi^0\gamma$
process, the dalitz analysis of the $e^+e^- \to \pi^+\pi^-\pi^0$
process at
the energy range $\sqrt{s}$=1.05–2 GeV and the measurement
of the inclusive hadronic cross section at 1.8 GeV $<\sqrt{s}<$2 GeV.

Speaker: Andrey Kupich (BINP)

PHIPSI2026.pdf

R-ratio

7 Measurement of R with the KEDR Detector at the VEPP-4M Collider

This report presents precision measurements of the total cross section for $e^+e^-$ annihilation into hadrons, performed with the KEDR detector at the VEPP-4M collider. The KEDR collaboration has measured the $R$ values at 22 center-of-mass energies between 1.84 and 3.72 GeV with the highest accuracy achieved to date. In addition, the energy region from 4.56 to 6.96 GeV was scanned at 17 points, corresponding to an integrated luminosity of approximately 13.7 pb$^{-1}$. The results of this analysis are reported and discussed.

Speaker: Tatyana Kharlamova (BINP)

MeasurementR-2026-PhiPsi.pdf

Lunch

Charm & Quarkonium

8 Study of $\chi_{b1,2}(2P)\to \omega\Upsilon(1{\mathrm{S}})$ transitions in $\Upsilon(3S)\to \gamma\,\chi_{b1,2}(2P)$ decays at $BABAR$

We present the result of a study of the transitions $\chi_{b1,2}(2P)\to \omega\Upsilon(1{\mathrm{S}})$, with $\chi_b$ mesons produced in $e^+e^−\to \Upsilon(3S)\to\gamma\,\chi_{b1,2}(2P)$ reactions. The data were collected with the $BABAR$ detector at the PEP-II asymmetric-energy $e^+e^−$ collider, at the peak of the $\Upsilon(3S)$ resonance. The integrated luminosity of the data sample is 28.0 fb$^{−1}$, corresponding to $121.3\times 10^6$ $\Upsilon(3S)$ decays. Signals of $\chi_{b1,2}(2P)$ are observed over a negligible background. Improved precision measurements of branching fractions are obtained, and the first measurements of the angular distributions are performed. No evidence is found for the presence of a $\chi_{b0}(2P)\to \omega\Upsilon(1{\mathrm{S}})$ decay mode.

Speaker: Guy Wormser (IJCLab Orsay)

guy-wormser-babar_chib_v2.pdf

HVP LO theo/exp.

Convener: Graziano Venanzoni (University of Liverpool and INFN Pisa)

9 KLOE-nxt: towards a new measurement of the two-pion contribution to the anomalous magnetic moment of the muon

The uncertainty of the Standard Model dispersive prediction of the muon anomalous magnetic moment $a_\mu$ is limited by the precision of the leading-order hadronic vacuum polarization contribution $a_\mu^{HLO}$. The KLOE experiment at the DA$\Phi$NE electron-positron collider has already provided some of the most precise measurements of the two-pion contribution to $a_\mu^{HLO}$. A more precise determination of this term is essential to clarify the long standing tension between the SM dispersive prediction of $a_\mu$ and its experimental measurements. This talk will present preliminary results from a new ongoing analysis (KLOE-nxt), which aims to improve the precision of the two-pion contribution by exploiting a previously unused KLOE dataset with significantly higher statistics compared to those employed in earlier KLOE measurements.

Speaker: Lorenzo PUNZI (By SerSe - Lorenzo PUNZI)

Punzi_PHIPSI.pdf

10 BABAR precision results on e+e- -> pi+pi-gamma for g-2 HVP calculations

New $BABAR$ results, based on the full $BABAR$ dataset, are presented on the processes $e^+e^-\to \pi^+\pi^-(\gamma)$ and $e^+e^-\to \mu^+\mu^-(\gamma)$ using the Initial State Radiation method at the PEP II collider. To reduce systematic uncertainties the measurement of the $\pi^+\pi^-$ cross section is obtained through the ratio with $\mu^+\mu^-$ and the final state includes additional photons in order to be less sensitive to radiative corrections, a technique pioneered in the 2009 $BABAR$ result. The separation between the pion and muon channels is achieved by fitting the angular distribution in the two-particle system, with templates built from the individual distributions known from first principles, without relying on particle identification, which was the source of the largest systematic uncertainty in the 2009 result. The analysis is performed with multiple blinding factors on the efficiency measurements and in the fits yielding the cross sections. These $BABAR$ results, which are essentially independent from those obtained in 2009, provide an important new precision input for computing the hadron vacuum polarization contribution to the muon $g-2$ anomalous magnetic moment.

Speaker: Isabella Garzia (INFN - Ferrara and University of Ferrara)

PhiPsi2026-garzia.pdf

11 The MUonE Experiment: A Third Path to Understanding the Muon g‑2

The MUonE experiment, currently under preparation at CERN, aims to measure the running of the electromagnetic coupling $\alpha$ in the elastic $\mu e$ scattering process, from which the dominant hadronic contribution to the anomalous magnetic moment of the muon can be extracted. The method is based on collisions of 160 GeV muons from CERN’s high‑intensity M2 beam with thin, fixed targets made of low‑Z material, and represents an alternative to the traditional dispersive integral of hadronic cross sections from e+e- annihilation. The latter shows tensions with the muon g-2 measurement, depending on the input data, while the purely theoretical prediction from lattice QCD calculations agrees with the experiment. MUonE’s method, being completely independent and data‑driven, therefore constitutes a third approach. The main challenge of the MUonE measurement lies in the control of systematic effects. In the summer of 2025, a two‑month test run was carried out with a reduced but fully functional version of the apparatus. Preliminary results will be presented, and future plans will be discussed.

Speaker: Giorgia Cacciola (University of Liverpool)

MUonE_a_third_path.pdf

12 Recent Developments in Lattice QCD Calculations of the Muon $g{-}2$ HVP

The hadronic vacuum polarization contribution currently dominates the uncertainty of the Standard Model prediction for the muon anomalous magnetic moment.
In recent years, lattice QCD has reached sub-percent precision for the leading hadronic vacuum polarization contribution and now provides the basis of the updated Standard Model prediction of the muon $g{-}2$.
This talk will review the current status of lattice-QCD-based determinations of the hadronic vacuum polarization contribution, with a focus on recent developments, control of systematic uncertainties, and related quantities accessible in lattice QCD.

Speaker: Simon Kuberski (CERN)

26phipsi_kuberski.pdf

Coffee Break

HVP LO theo/exp.

Convener: Fedor Ignatov (University of Liverpool)

13 Short-Distance–Free Leptonic $g-2$

We note that the hadronic contributions to $a_e$ and $a_\mu$ are strongly correlated, which potentially allows to reduce the uncertainties associated with higher energy contributions (and address the current discrepancy between lattice and data-driven evaluations) by improved measurements of a_e and the fine-structure constant.

Speaker: Siyuan Li (Johannes Gutenberg-Universität Mainz (JGU))

SLi_phipsi26_Pisa_Jun8.pdf

R-ratio

Convener: Fedor Ignatov (University of Liverpool)

14 Inclusive R measurement at BESIII

The inclusive measurement of R, which is the ratio of the leading-order cross sections between inclusive hadronic events and a pair of muon leptons, is of great importance in the precision test of the Standard Model. For example, the determination of QED running coupling constant at the Z pole, the evaluation of the muon anomaly, and search and study of exotic hadron states. We will introduce the inclusive R measurement at BESIII, including the published results and ongoing efforts based on the energy-scan method. In addition, we will present a novel approach for R measurement that combines the advantages of the initial-state radiation technique with the inclusive method. This approach enables an inclusive determination of R over the energy range from 0.3 to 2.0 GeV, which is of significant interest to the community.

Speaker: Weiping Wang

Inclusive_R_Measurement_at_BESIII_PhiPsi26_wangwp.pdf

15 R(s) below charm threshold: theory and tensions with data

We assess the theory prediction for $R(s)$ below the charm threshold and address tensions with the existing data, notably with the 2021 BES-III results. We provide an analysis of the theory uncertainty associated with perturbative QCD in the light of renormalon calculus, and show that the perturbative series is well behaved and under good control. We provide a reliable and conservative estimate of the effect of residual quark-hadron duality violation contributions, which are shown to be sizable up to 2.5 GeV, but negligible for higher energies. Small electromagnetic and quark-mass corrections are also considered. Finally, we compare theory and data, both locally and in their contributions to the anomalous magnetic moment of the muon. Theory is compatible with a combination of all of the available experimental data but discrepancies with the BES-III data reach more than 3$\sigma$.

Speaker: Diogo Boito (University of Sao Paulo)

Boito-Ruds-phi-to-psi-Pisa-2026.pdf

Tau Physics

Convener: Fedor Ignatov (University of Liverpool)

16 $\tau$ lepton physics at Belle and Belle II

The Belle and Belle II experiments have collected a $1.6~\mathrm{ab}^{-1}$ sample of $e^+e^-$ collision data at center-of-mass energies near the $\Upsilon(nS)$ resonances. This sample contains approximately 1.3 billion $e^+e^-\to \tau^+\tau^{-}$ events. We use the Belle and Run 1 Belle II data samples to search for lepton-flavor violating decays, presenting searches for the decays $\tau \to \mu\gamma$, $\tau \to \ell\eta$, $\tau\to \ell\pi^0$, and $\tau^-\to \ell^-\alpha$, where $\ell = e$ or $\mu$ and $\alpha$ is an invisible scalar particle. Using the Belle II $600~\mathrm{fb}^{-1}$ data sample we also present new measurements including the $C\!P$ asymmetry in $\tau \to K^0 \pi\nu$ decays, the $\tau$ lifetime, and branching fractions and spectral moments of $\tau$ decays to final states with strangeness.

Speaker: Yipu Liao

PhiPsi26_tau_B1B2_YipuLiao.pdf

17 The strong coupling from hadronic $\tau$ decays including $\tau\to \pi^- \pi^0 \nu_\tau$ from Belle

Inclusive hadronic $\tau$ decays provide one of the most precise extractions of the QCD coupling, $\alpha_s$, from experimental data. For a long time, these analyses relied on ALEPH and OPAL inclusive spectral functions, which were based on measurements of the dominant decay modes but necessitated Monte Carlo simulations for subleading decay channels. We have recently demonstrated that these subleading contributions can now be obtained entirely from experiment, using CVC-related electron-positron cross-sections as well as BaBar tau-decay data. In this work, we incorporate high-statistics Belle $\tau \to \pi^-\pi^0\nu_\tau$ data to construct an updated inclusive non-strange vector spectral function. Using finite-energy sum rules, and our previously developed strategy, we determine $\alpha_s(m_Z^2) = 0.1159(14)$. We discuss why this new analysis yields a smaller central value and larger error than our previous extraction, attributing the shift primarily to updated HFLAV results for the $\pi^-3\pi^0$ branching fraction. Finally, we explore how future data could further refine this determination.

Speaker: Lucas Mansur (Johannes Gutenberg-Universität Mainz)

LMM_PhiPsi26.pdf

Welcome reception

Tuesday 9 June

Generators

Convener: Diogo Boito (University of Sao Paulo)

18 Status of Radiative Corrections and Monte Carlo Generators for low-energy e+e- into leptons and hadrons final states: the RadioMonteCarLow2 effort.

The analysis of low-energy e+e- scattering experiments at electron-positron colliders requires robust and precise Monte Carlo generators, which are essential for precision tests of the Standard Model, such as the dispersive evaluation of the hadronic vacuum polarization contribution to the muon g−2. As part of the community-driven initiative RadioMonteCarlow2, we aim to collect these Monte Carlo tools, compare them, and facilitate their access. This initiative has been working on providing the community with codes that are able to produce differential cross-section distributions for processes related to e+e- -> leptons and hadrons at center-of-mass energies of a few GeV. In this talk, I will report on the results of Phase I of this effort, published as 10.21468/SciPostPhysCommRep.9, which presents a detailed comparison of Monte Carlo codes for e+e− scattering into muon, pion, and electron pairs, both for energy-scan and radiative-return experiments. This first phase is a theoretical exercise which focuses on comparisons without reference to experimental data, aiming to clarify the importance of different physics effects and approaches in realistic experimental setups.

Speaker: Jeremy Paltrinieri (University of Liverpool)

PhiPsi_26_JP.pdf

19 Precise predictions for radiative return at flavour factories

The leading-order hadronic vacuum polarization (HVP) contribution to the muon
anomalous magnetic moment, $a_\mu = (g-2)_\mu / 2$, can be evaluated either
through $ab\,\, initio$ lattice QCD calculations or via data-driven
dispersive analyses based on low-energy $e^+e^- \to$ hadrons
cross-section measurements. In this framework, the dipion production
channel accounts for approximately $70\%$ of the total HVP contribution.
At present, the predictions obtained from these two approaches show a
significant discrepancy. Resolving this tension, commonly referred to as
the ``new muon $g-2$ puzzle'', is essential for achieving a reliable
comparison between experimental measurements and theoretical predictions.

The process $e^+e^- \to \pi^+\pi^-\gamma$ plays a key role in the
determination of the $\pi^+\pi^-$ production cross section below
$2\,\mathrm{GeV}$ at flavour factories through the radiative return
method. In this context, a precise control of theory-driven systematic
uncertainties in the simulation of the process is essential to ensure
reliable cross-section measurements.

To this aim, we present the first calculation of QED next-to-leading
order (NLO) corrections to radiative pion and muon pair production in
$e^+e^-$ annihilation, matched to a QED Parton Shower (PS) algorithm for the
fully exclusive simulation of multiphoton emission, thereby achieving
NLOPS accuracy.

For pion pair production, we consider two different approaches to the
treatment of the pion form factor in the loop calculation: the purely
factorized approach (FxsQED), in which the point-like amplitude is
multiplied by the pion form factor evaluated at the appropriate
virtuality, and the Generalized Vector Meson Dominance (GVMD) model,
where the pion form factor is incorporated directly in the loop
integration.

We present phenomenological results obtained with a new version of
the BabaYaga@NLO event generator, which includes the radiative
channels $e^+e^- \to X^+X^-\gamma$ ($X=\mu,\pi$) according to the above
theoretical approach.

Speaker: Marco Ghilardi

BabaYaga_radiative_Talk_PHIPSI-3-1.pdf

20 Recent developments in PHOKHARA

The Monte Carlo event generator PHOKHARA has been widely used to simulate electron-positron annihilation into hadrons plus a hard photon with next-to-leading-order (NLO) accuracy. It includes virtual and soft-photon corrections to single-photon emission, as well as events with two hard real photons. In this talk, we present recent progress in extending PHOKHARA beyond NLO precision. First, we report new results for the pion-pair channel, incorporating the Generalised Vector Dominance Model as an improvement over the usual point-like treatment of pions. We then present the implementation of soft-photon resummation and discuss ongoing work on additional next-to-next-to-leading-order (NNLO) corrections.

Speaker: Pau Petit Rosàs (University of Liverpool)

PhiPsiPauPetit.pdf

21 PrecisionSM: an annotated database for low-energy positron-electron hadronic cross sections

PrecisionSM is an annotated database that compiles the available data on low-energy cross sections of electron-positron collisions into hadronic channels. This database organizes and collects data samples from $e^+e^-$ experiments, which are used as input for the data-driven theoretical evaluation of the muon anomalous magnetic moment, $a_{\mu}$, serving as a precise test of the Standard Model when compared to the experimental measurements of $a_{\mu}$. The database is accessible through a custom website (https://precision-sm.github.io) which contains details about the data samples, such as the treatment of radiative corrections, as well as links to papers on INSPIRE-HEP and to tables on HEPData.
The PrecisionSM database was developed within a Joint Research Initiative in the group application of the European hadron physics community, STRONG2020, and is now incorporated into the RadioMonteCarLow2 Working Group (RMCL2 WG) activities, which have the more general goal of improving the theoretical description of scattering processes at $e^+e^-$ colliders. The results of Phase I of the new RMCL2 WG have been published in https://doi.org/10.21468/SciPostPhysCommRep.9.
In this presentation, we will report on the status of the PrecisionSM database, which currently contains a list of the dominant $2\pi$ channel as well as $3\pi$ and $\pi^0\gamma$, and on the ongoing work for the other channels and for responsive plots.

Speaker: Anna Driutti (University and INFN Pisa)

Driutti_PhiPsi26_9june256.pdf

Coffee Break

Muon g-2 theo

Convener: Aidan Wright (University of Liverpool)

22 Dispersive description of new subprocesses for tensor-meson contribution to muon g-2

The uncertainties in the muon anomalous magnetic moment are dominated by the hadronic contributions, i.e. hadronic vacuum polarization (HVP) and hadronic light-by-light (HLbL) scattering. The discrepancies among different data sets of cross section within the data-driven dispersive method and with lattice QCD are still an open problem. This presentation focuses on the dispersive evaluation of hadronic contributions and the efforts to further reduce the error on the HLbL and HVP terms. Particularly the benefits of a new scheme for the HLbL is high-lighted which will consistently allow for higher intermediate states. Current work concentrates on the sub-processes including tensor-meson and two-pion intermediate states to the $\gamma^*\gamma^*\gamma\rightarrow\pi\pi$ process in the context of the HLbL term, which will also be relevant for radiative corrections to HVP.

Speaker: Eirini Lymperiadou (PSI/UZH)

PisaPresentation2026.pdf

23 Dispersive description of the $\gamma^*T\to\pi^+\pi^-$ subprocess and its role in muon $g-2$

One of the leading sources of uncertainty in the Hadronic Light-by-Light (HLbL) contribution to the muon $g-2$ is the tower of spin-2 resonances, beginning with the $f_2(1270)$. We present progress in evaluating these effects within a new dispersive framework in triangle kinematics, which permits a description of higher-spin states with reduced model dependence by representing the muon anomaly as a sum of two unitarity cuts. A key ingredient is the analysis of the $\gamma^*T\to\pi^+\pi^-$ subprocess in the $P$ wave, identifying $T$ with the $f_2(1270)$. We derive its dispersive solution using the Muskhelishvili–Omnès (MO) representation and discuss its role in the construction of the tensor $T\to\gamma^*\gamma^*$ transition form factors (TFFs), previously measured by Belle only in the singly-virtual region. We show how the MO solution, in conjunction with the TFFs, can yield a robust estimate of the HLbL spin-2 contribution to the muon $g-2$.

Speaker: Emilis Kaziukenas (University of Vienna)

Pisa_slides_JUN2026.pdf

24 Two-potential parametrization to describe the pion vector form factor

A precise description of the pion vector form factor (VFF) requires not only high-quality data but also a consistent theoretical framework that captures the interplay of multiple hadronic channels. In this contribution, we focus on the construction of a dispersive model that explicitly incorporates inelastic effects beyond the elastic $\pi\pi$ channel, employing the two-potential formalism. It is discussed how analyticity and unitarity constraints guide the parametrization-building strategy and how they are preserved when extending the framework to include inelastic channels. By fitting multiple exclusive channels simultaneously, the approach allows for a more reliable extraction and differentiation of and between hadronic contributions relevant for the hadronic vacuum polarisation (HVP).

Speaker: Leon Heuser (HISKP - University Bonn)

VFF_TwoPotential.pdf

25 The pion vector form factor with explicit inelasticities

The pion vector form factor (VFF) offers the dominant contribution to the hadronic vacuum polarisation (HVP). The lasting tension between modern $e^+e^-$ data calls for a better theoretical understanding of the experimental situation, both in terms of accuracy and precision. To this day, most phenomenologic fits to the pion VFF are performed without explicit modelling of inelastic channels. We present a model based on dispersion relations, that inherently respects the analytic properties of the amplitudes and the unitarity of the S-matrix. The dynamics of the system include s-channel resonance exchange, in addition to background interactions to improve the lineshapes generated from a naive unitarised Gounaris–Sakurai prescription and to simulate non-resonant contributions. The model is fitted to the data from multiple exclusive channels simultaneously.

Speaker: George Chanturia (HISKP, University of Bonn)

VFF_TwoPotential.pdf

26 Calibrated study of the correlation between heavy-quark masses and HVP observables at the precision frontier

The theoretical prediction of the muon $g-2$ depends crucially on the hadronic vacuum polarization (HVP), whose evaluation relies either on experimental data through dispersive relations or on lattice QCD calculations. Since the former probes the time-like region while the latter is formulated in the space-like region, their comparison cannot be performed locally, and the origin of the differences observed in global determinations remains to be fully understood. In this work we investigate whether part of this difference could arise from sources of uncertainty that have not yet been systematically explored. We focus on the heavy-quark sector, particularly the charm contribution, which can be cleanly isolated in both approaches. Using relativistic QCD sum rules for the vector current correlator, computed in perturbative QCD up to $\mathcal{O}(\alpha_s^3)$, we determine the heavy-quark masses and their contribution to the muon anomalous magnetic moment. Treating the integration kernel as a dynamical degree of freedom, we explore its functional space and quantify how optimized kernels can reduce theoretical uncertainties while revealing the intrinsic correlation between heavy-quark mass determinations and their impact on $a_\mu$.

Speaker: Antonio Rivera (IFAE)

presentation_PsiPhi.pdf

27 Data-driven results for the light-quark connected contribution to the muon g-2

Reducing the uncertainty of the Standard Model $g-2$ determination is a crucial task. A key issue is the discrepancy between lattice-QCD and data-driven hadronic vacuum polarization (HVP) results. A path to resolve this discrepancy is the precise data-driven determination of the isospin-limit light-quark connected (lqc) and strange plus light-quark disconnected (s+lqd) components of the HVP contribution. We will present data-driven evaluations of the isospin-limit lqc and s+lqd components of the RBC/UKQCD window results for the HVP contribution to the muon g-2. The results will be compared with the most recent lattice determinations. We will discuss the role of the recent CMD-3 measurements of $e^+e^-\to \pi^+\pi^-$ and present new results based on hadronic $\tau$ decays.

Speaker: Diogo Boito (University of Sao Paulo)

Boito-lqc-g-2-phi-to-psi-2026-no-clicks.pdf

Lunch

CLFV/EDM

28 Theory overview of CLFV and EDM

Charged lepton flavor violation (CLFV) and electric dipole moments (EDMs) are among the most sensitive low-energy probes of physics beyond the Standard Model (BSM). This talk will present a theoretical overview of CLFV and EDM observables, emphasizing their role as precision probes of new sources of flavor and CP violation. The interplay among different observables, their correlations within representative BSM frameworks,
and the implications of present experimental bounds will be discussed. Particular attention will be devoted to the complementarity between CLFV searches and EDM measurements in constraining the flavor structure and CP-violating sectors of new physics models.

Speaker: Paride Paradisi (Padova U. and INFN)

Phipsi26_Paradisi.pdf

29 Status of BSM searches with the MEG II experiment

The MEG II experiment at the Paul Scherrer Institute searches for the charged lepton flavor violating decay μ⁺ → e⁺γ with a target sensitivity of 6 × $10^{-14}$, improving previous limits by an order of magnitude. This process is highly suppressed in the Standard Model, making it a sensitive probe of new physics.

Beyond its primary goal, MEG II can explore additional scenarios involving light, weakly interacting particles. In particular, axion-like particles (ALPs) may be investigated through anomalous photon signatures in muon decays. The dataset also offers potential sensitivity to exotic signals such as the proposed X17 boson, motivated by anomalies in nuclear transitions.

In this talk, I will report on the current status of data taking and analysis, and outline perspectives for future developments.

Speaker: Luca Galli (INFN Pisa)

GalliMEGII.pdf

30 The Mu3e Experiment at PSI: Recent Commissioning Results and Outlook

The Mu3e experiment at the Paul Scherrer Institute (PSI) searches for the charged lepton flavour violating decay $\mu^+ \to e^+ e^- e^+$, aiming to improve the current best limit set by the SINDRUM experiment by four orders of magnitude.

The experiment will proceed in two phases. Phase I, currently under construction at the $\pi$E5 beamline at PSI, will utilise a DC surface muon beam of $10^8\ \mu^+/\mathrm{s}$ to achieve a single-event sensitivity of $2 \times 10^{-15}$. Phase II will leverage the upcoming High-Intensity Muon Beam (HIMB) to push this further to the $10^{-16}$ regime. This improvement is made possible by combining high-intensity muon beams with a low-material-budget tracking system based on ultra-thin HV-MAPS silicon pixel detectors, fast scintillating fibre and tile detectors providing sub-ns timing resolution, and a high-rate data acquisition system. Operating in a $1\ \mathrm{T}$ solenoidal magnetic field, the detector is optimised for the $\mu^+ \to e^+ e^- e^+$ signature, enabling precise reconstruction of the decay vertex and invariant mass.

In preparation for Phase I data-taking, a crucial commissioning campaign took place in June 2025 at the PSI $\pi$E5 beamline. This campaign successfully validated essential detector components—including vertex, scintillating fibre, and tile modules—and demonstrated their integration with the high-intensity muon beamline under a $1\ \mathrm{T}$ magnetic field. These achievements mark a major milestone towards readiness for Phase I measurements.

This contribution will present first results from the 2025 commissioning run, the current status of the experiment, and an outlook on the 2026 campaign leading towards the physics run, anticipated in 2027.

Speaker: Mikio Sakurai (University College London)

Mu3e_MikioSakurai_PhiPsi2026.pdf

31 Status of the Mu2e experiment at Fermilab

The Mu2e experiment at Fermilab will search for the charged lepton flavor violating (CLFV), neutrinoless conversion of a negative muon into an electron in the field of an aluminum nucleus. This process is forbidden within the Standard Model and remains extremely suppressed in its minimal extensions. The signal would appear as a monoenergetic electron with an energy of 104.97 MeV, just below the muon rest mass. The Mu2e experiment aims to improve the current upper limit on this process by four orders of magnitude, targeting a single event sensitivity (SES) of $3 \times 10^{-17}$. The experiment employs three solenoids arranged in sequence to produce and transport an intense pulsed beam of negative muons. Approximately $10^{18}$ muons are expected to stop in an aluminum target over three years of data taking. The experiment is currently under construction in the experimental hall, and the detector systems are undergoing commissioning. This presentation will outline the physics motivations of Mu2e and describe the design of the experimental apparatus, with particular emphasis on the electromagnetic calorimeter, the main INFN contribution to the experiment. The current status of the experiment and the plans for data taking will also be presented.

Speaker: Paolo Girotti (INFN LNF)

pgirotti_mu2e_phipsi2026.pdf

32 Search for charged lepton flavor violation with the COMET experiment

Charged Lepton Flavor Violation is expected to be one of the most powerful tools to reveal physics beyond the Standard Model. The COMET experiment aims to search for the neutrinoless coherent transition of a muon into an electron in the field of a nucleus. The experimental sensitivity of this process is expected to be significantly improved by a factor of 100 to 10,000 in the coming decade. The COMET experiment will take place at Japan Proton Accelerator Research Complex (J-PARC). The construction of the beam line and superconducting magnets has been completed. The commissioning is in progress towards the forthcoming Phase-I experiment. The recent status and prospects are presented.

Speaker: Manabu Moritsu (National Institute of Technology, Akashi College)

PhiPsi2026_COMET_moritsu.pdf

Coffee Break

CLFV/EDM

Convener: Breese Quinn (University of Mississippi)

33 Search for the Muon Electric Dipole Moment: The muEDM Experiment at PSI

Non-zero electric dipole moments (EDMs) of fundamental particles intrinsically violate time-reversal (T) and CP symmetries, providing a highly sensitive probe of physics beyond the Standard Model. This talk will present the muEDM experiment at the Paul Scherrer Institute (PSI), Switzerland, which aims to measure the muon EDM using the innovative frozen-spin technique within a compact storage trap. We will outline the fundamental principles of this search and present the status and conceptual design of the experimental setup for Phase I, targeting a sensitivity of $\sigma(d) \leq 4 \times 10^{-21} \, e \cdot \mathrm{cm}$, followed by a Phase II upgrade capable of reaching $\sigma(d) \leq 6 \times 10^{-23} \, e \cdot \mathrm{cm}$.

Speaker: Lorenzo Bianco (University of Pisa)

muEDM_PhiPsi-Bianco.pdf

BSM

Convener: Breese Quinn (University of Mississippi)

34 Searching for light dark particles in η and η' decays

A new generation of precision experiments in hadron physics will soon offer new data that will provide sensitive probes to test potential New Physics including searches for dark photons, light scalars and axions, complementing worldwide efforts to detect new light particles in the MeV-GeV mass range.
In this talk, I will focus on the sensitivity offered by the $\eta$ and $\eta^{\prime}$ mesons to light dark particles and discuss experimental opportunities in this field.

Speaker: Sergi Gonzalez-Solis (Universitat de Barcelona)

PhiPsi26Pisa_Sergi.pdf

35 Search for dark sector at BESIII

The BESIII experiment is taking dat at a symmetric e+e- collider operating at c.m. energy from 2.0 to 4.95 GeV. With the world’s largest threshold production data set of J/ψ (10 billion), ψ(3686) (2.6 billion), and 20 $fb^{-1}$ of D meson pairs from ψ(3770) decay, we are able to search for various dark sectors produced in e+e- annihilation and meson decay processes. In this talk, we report the search for $K_S^0$ invisible decay, search for the massless dark photon with charm FCNC process $D^0→ωγ’$ and $D^0→γγ’$, search for the dark baryon decay in $Ξ^-→π^-$ + invisible, search for J/ψ→Φ + invisible, and search for X(17) with $ψ(3686)→X(17)χ_c^0$ and $ψ(3686)→γχ_c^0->γX(17)J/ψ$.

Speaker: Xiaoshuai Qin (Shandong University)

PHIPSI_Dark sector BESIII.pdf

36 Searches for dark sector particles at Belle and Belle II

The Belle and Belle II experiment have collected samples of $e^+e^-$ collision data at center-of-mass energies near the $\Upsilon(nS)$ resonances. These data have constrained kinematics and low multiplicity, which allow searches for dark sector particles in the mass range from a few MeV to 10 GeV. We present new searches in a $600~\mathrm{fb}^{-1}$ sample collected by Belle II, including searches for a light dark photon decaying to a pair of muons, an axion-like particle decaying to two photons, and a $Z^{\prime}$ boson that decays invisibly. Using a $711~\mathrm{fb}^{-1}$ sample collected by Belle, we search for $B\to h + \mathrm{invisible}$ decays, where $h$ is a $\pi$, $K$, $D$, $D_{s}$ or $p$, and $B\to Ka$, where $a$ is an axion-like particle.

Speaker: Ijeong Na

PhiPsi2026_Ijeong_Na_vf.pdf

Social Dinner

Wednesday 10 June

Current Facilities

37 Status and prospects of BES III

Status and prospects of BES III

Speaker: Wolfgang Gradl (JGU Mainz)

besiii-status-and-prospects.pdf

38 Recent $B$ physics results from Belle II

The Belle and Belle II experiments have collected a $1.2~\mathrm{ab}^{-1}$ sample of $e^+ e^-\to B\bar{B}$ collisions at a center-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. We present measurements of the ratios for exclusive $B\to D^{(*)}\ell \nu$ decays $R(D^{(*)})$ in decays where the other $B$ in the event is reconstructed in hadronic or semileptonic final states. We also present recent results on $B\to K^{(*)}\nu\bar{\nu}$ using an inclusive tagging technique, including the first results from Belle. We will also present a search for inclusive decays $B\to X_s\nu\bar{\nu}$, where $X_s$ is a hadronic system with strangeness. We will also present searches for the decays $B^+\to K^+\tau^+\tau^-$ and $B^0\to K^0_S\tau^+\tau^-$. The asymmetric-energy SuperKEKB collider provides a boost to the $B$ mesons in the laboratory frame, allowing measurements of time-dependent $C\!P$ violation. We present measurements of time-dependent $C\!P$ violation in both hadronic and radiative penguin $B$ decays, including measurements of the $C\!P$ asymmetries in $B\to \eta' K^0$, and the radiative decays $B\to \rho^0\gamma$ and $B\to K^0 \pi^0 \gamma$.

Speaker: Jim Libby

Belle II B physics - phi2psi - Libby - v3.pdf

Hadron Production

39 Novel Azimuthal Observables from Two-Photon Collision at e+e- Colliders

Novel Azimuthal Observables from Two-Photon Collision at e+e- Colliders

Speaker: Yajin Zhou

YZ_PHIPSI2026.pdf

40 Fragmentation function study at BESIII

Fragmentation Function (FF) plays a crucial role in describing the hadronization process, which is usually studied by investigating the inclusive production of final-state hadrons of interest. We report the measurements of normalized differential inclusive production cross, of neutral mesons $π^0$, $K_S^0$, η and charged particles $π^±$ and $K^±$, as a function of the hadron momentum at the BESIII energy region (2~5 GeV). The results, with relatively high precision and wide energy-fraction coverage, deviate from several theoretical calculations based on existing fragmentation functions. Moreover, the comparison of the production cross sections between neutral and charged π and K, at the same energy point, will be presented for a dedicated scrutiny of iso-spin symmetry.

Speaker: Isabella Garzia

Garzia_FF.pdf

Coffee Break

Hadron Production

41 Light Meson decays at BESIII

The world’s largest sample of J/ψ events accumulated at the BESIII detector offers a unique opportunity to investigate η and η′ physics via two body J/ψ radiative or hadronic decays. In recent years the BESIII experiment has made significant progresses in η/η′ decays. A selection of recent highlights in light meson decays at BESIII are reviewed in this report, including the precision measurement of Dalitz plots, transition form factor measurements, as well as the search for rare/forbidden decays of η/η′.

Speaker: Kailu Liu

PhiPsi2026_KailuLi_LZU.pdf

42 Measurement of the relative phase between strong and electromagnetic decays

The strong and electromagnetic interactions are two main decay mechanisms in charmonium decays. The relative phase between them is a basic parameter in understanding the decay dynamics, especially for the precise measurements. In this talk, we present the direct measurement with resonance scan method. By introducing the EM amplitude from continuum decay, the interference between EM and strong mechanism is measured in $J/\psi$ decays to several final states.

Speaker: Francesca De Mori (Universita' di Torino and INFN sez. di Torino)

phipsi_demori_phase_indico_def4.pdf

43 Three-body decays with Khuri-Treiman equations

One of the main issues posed by the presence of hadrons in any reaction is their final-state interactions, which are formally expressed in terms of the unitarity of the amplitude. In two-body scattering, unitarity is usually imposed in the direct channel only, as one is not sensitive to the details of the crossed channels. This is certainly not the case for a three-body decay, where the three possible two-hadron channels are physical, and one ideally wants to impose unitarity in all channels at once. The Khuri-Treiman formalism is a dispersive approach which indeed allows one to do so. In this talk, I will review the contributions made by the JPAC Collaboration to this field with focus on various important applications, e.g. $𝑉\to3\pi$ $(𝑉=\omega,\phi,𝐽/\psi)$ and the related transition form factor $𝑉\to\pi^{0}\gamma^{*}$, or the exotic $\pi_{1}(1600)\to3\pi$ decay.

Speaker: Sergi Gonzalez-Solis (Universitat de Barcelona)

PhiPsi26Pisa_Sergi_talkv2.pdf

44 Towards an improved understanding of $a_1$ and $a_2$ transition form factors

The isovector axial-vector and tensor meson states $a_1$ and $a_2$ have garnered interest in the last years since they appear as intermediate states in the hadronic light-by-light (HLbL) scattering contribution to $(g-2)_\mu$. Their dynamical behaviour, including their transition form factors, is poorly understood to this day, which also affects the uncertainty budget of the HLbL contribution.
In order to improve the situation, we construct the $a_1$ and $a_2$ as resonances in the $\rho \pi$ system, which allows us to express the relevant amplitudes in terms of known form factors. However, imaginary parts and singularities in this system need to be understood. With this, we aim to obtain a phenomenologically well motivated parameterisation of the transition form factors.

Speaker: Hannah Schäfer (Bern University)

PhiPsi26_HannahSchaefer.pdf

45 Measurement of electromagnetic transition form factors in two-photon collisions at BESIII

Electromagnetic transition form factors of light mesons are important inputs to the calculations of the hadronic light-by-light scattering contribution to the Standard Model prediction of the anomalous magnetic moment of the muon. However, data in the relevant regions of momentum transfer are scarce. The BESIII experiment at the $e^+ e^-$ collider BEPCII has collected the world's largest data sets in the tau-charm energy region, including, but not limited to more than 20 $fb^{-1}$ of data at a center-of-mass energy of 3.773 GeV/c^2. The data are analyzed for two-photon collisions in events of the type $e^+ e^-→e^+ e^- P$, with $P=π^0,η^{(') },f_1 (1285),π^0 π^0$, and $π^+ π^-$. The aim is to study the momentum dependence of the respective space-like electromagnetic transition form factors. In this presentation we discuss recent results and prospects of ongoing analyses.

Speaker: Max Lellmann

260610_PhiPsi.pdf

Charm & Quarkonium

46 Study of Charmonium-like States via e⁺e⁻ → Hidden Charm Final States at BESIII

The BESIII experiment, with its unique data samples in the √s = 4.0 – 4.95 GeV region, continues to provide inputs for understanding charmonium and exotic XYZ states. This talk presents three recent analyses of processes with hidden charm in the final state. We report the search for a charmonium-like state ψ₀(4360) J^{PC} = 0^{--} via e⁺e⁻ → ηψ₀(4360) → ηηψ(2S), conducted at the center-of-mass energies of 4.84, 4.92, and 4.95 GeV. The upper limits are provided since no significant signal has been observed. Furthermore, we present a search for the process e⁺e⁻ → ηηJ/ψ at the center-of-mass energies from 4.226 to 4.950 GeV, with two different methods, exclusively and semi-inclusively. The upper limits for the reaction channel e+e− → ηηJ/ψ also serve as limits for the existence of a possible isospin partner to the charmonium-like isospin triplet Zc(3900) which decays to J/ψη. Finally, we disclose a precision measurement of the Born cross section for e⁺e⁻ → π⁰π⁰ψ(3686) across the energy range from 4.008 to 4.951 GeV. The obtained cross sections are found to be approximately one-half of those of e+e− → π+π−ψ(3686), and a coherent fit to the dressed cross sections is performed with the vector resonances Y(4230), Y(4390), and Y(4660).

Speaker: Maoqiang Jing

PhiPsi26-MaoqiangJing-SDUT.pdf

Lunch

Excursion

Thursday 11 June

Baryon/Hyperon Physics

47 Spin effects in baryon-antibaryon pair production in electron-positron annihilation

I will give an overview of spin polarisation and correlation effects in baryon-antibaryon pair production at electron-positron colliders. General formalism and methods for measuring the polarisation of the baryons and determining the properties of the production reactions will be introduced. Precision studies of the spin properties were enabled, thanks to millions of hyperon-antihyperon pairs collected by BESIII. Such studies include the measurement of hyperon decays, electromagnetic form factors, searches for electric dipole moments, and tests of quantum mechanics.

Speaker: Andrzej Kupsc (NCBJ , Warsaw & Uppsala Univerity)

Kupsc2506Pisa.pdf

48 Hyperon physics at BESIII

With the large datasets on 𝑒+𝑒−-annihilation at the 𝐽/𝜓 and 𝜓(3686) resonances collected at the BESIII experiment, multi-dimensional analyses making use of polarization and entanglement can shed new light on the production and decay properties hyperon-antihyperon pairs. In a series of recent studies performed at BESIII, significant transverse polarization of the (anti)hyperons has been observed in 𝐽/𝜓 or 𝜓(3686) to ΛΣ-bar , ΣΣ-bar , ΞΞ-bar .The decay parameters for the most common hadronic weak decay modes were measured, and due to the non-zero polarization, the parameters of hyperon and antihyperon decays could be determined independently of each other for the first time. Comparing the hyperon and antihyperon decay parameters yields precise tests of direct, Δ𝑆 = 1 CP-violation that complement studies performed in the kaon sector.

Speaker: Weiping Wang (JGU Mainz)

HyperonPhysicsBESIII_PhiPsi2026_v05.pdf

49 Recent results of baryon electromagnetic form factors at BESIII

At BESIII, the electromagnetic form factors (EMFFs) and the pair production cross sections of various baryons have been studied. The proton EMFF ratio |GE/GM| is determined precisely and line-shape of |GE| is obtained for the first time. The recent results of neutron EMFFs at BESIII show great improvement comparing with previous experiments. Cross sections of various baryon pairs ($\Lambda, \Sigma, \Xi, \Lambda_c$) are studied from their thresholds. Anomalous enhancement behavior on the $\Lambda$ and $\Lambda_c$ pair are observed. The relative phase of EMFFs for $\Lambda$ and $\Sigma^+$ are measured for the first time.

Speaker: Hailin Song

Baryons_EMFFs_SHL_Italy.pdf

Photo

Coffee Break

Exotic hadrons

50 Exotic hadron studies at BESIII

Using the unique data samples collected with the BESIII detector at the $J/\psi$ and $\psi(3686)$ resonances, as well as fine energy-scan data in the center-of-mass energy range from 3.7 to 4.95 GeV, extensive studies of exotic hadrons in the charmonium and light-hadron sectors have been carried out. In this talk, recent highlights from BESIII on the study of exotic hadrons will be presented.

Speaker: Yuping Guo (Fudan University)

GuoYP-202606.pdf

51 Studies of hadron spectroscopy at Belle and Belle II

The Belle and Belle II experiments have collected a $1.6~\mathrm{ab}^{-1}$ sample of $e^+e^-$ collision data at center-of-mass energies near the $\Upsilon(nS)$ resonances. These data include a $19.2~\mathrm{fb}^{-1}$ sample of data collected at center-of-mass energies near the $\Upsilon(10753)$ resonance. We present several results related to the following processes: $e^+ e^-\to h_b(1P)\eta$, $e^+ e^-\to\chi_{bJ}\omega$, $e^+ e^-\to\chi_{bJ}\gamma$, and $\Upsilon$ decays to di-baryons. In addition, we present a measurement of the $B^{0}$ and $B^+$ meson mass difference, and a search for $X(3872)$ in $B^+\to (\chi_{cJ}\pi^0)K^+$ decays. We also present a study of the tetraquark $T_{c\bar{c}}(4430)^+$ and a search for the $T_{c\bar{c}}(4430)^0$, and a first study of $pp$ femtoscopy in narrow $\Upsilon(nS)$ decays.

Speaker: Federico Testa (Infn Torino)

Testa_PhiToPsi.pdf

52 Light Exotics at BESIII

Using the world’s largest samples of J/ψ and ψ(3686) events produced in e+e- annihilation, BESIII is uniquely positioned to investigate light hadrons in radiative and hadronic charmonium decays. This includes detailed studies of exotic hadron candidates such as multiquark states, hybrid mesons and glueballs. Recent highlights on the light exotics searches, including a glueball-like particle X(2370) , exotics state π1(1600), new production mode of exotics $\eta_1$(1855), as well as the new strangeonium state X(2300), will be presented.

Speaker: Emma Di Fiore (Istituto Nazionale di Fisica Nucleare)

EmmaDiFiore_PhiPsi_2026.pdf

53 Coupled-channel Omn\`es matrix for the $D$-wave isoscalar $\pi\pi/K\bar K$ system and its application to $J/\psi\to\pi^{0}\pi^{0}\gamma,\,K_{S}K_{S}\gamma$

In this work, we construct the $D$-wave isoscalar $\pi\pi/K\bar K$ coupled-channel Omn`es matrix, formulated to satisfy unitarity, analyticity, and the appropriate asymptotic behavior. We employ a two-channel $K$-matrix model containing poles associated with the $f_{2}(1270)$ and $f_{2}'(1525)$ resonances. The resulting unitary scattering matrix, which reproduces the experimental $\pi\pi\to\pi\pi$ and $\pi\pi\to K\bar K$ data and PDG information, serves as input to the homogeneous two-channel Muskhelishvili-Omn`es equation. We compare our Omn`es matrix with previous constructions based on $\pi\pi\to K\bar K$ phases extracted from sums of Breit-Wigner amplitudes. The Omn`es matrix developed here provides a reliable dispersive input for form-factor calculations and resonance studies in the tensor-meson sector. As an application, we show that it enables a simultaneous and accurate description of the BESIII $J/\psi\to\pi^{0}\pi^{0}\gamma$ and $J/\psi\to K_{S}K_{S}\gamma$ spectra in the $J=2$ electric-dipole (E1) partial wave. e-Print: 2512.23669 (accepted to PLB)

Speaker: Igor Danilkin (Johannes Gutenberg University of Mainz)

Danilkin2026_PhiPsi.pdf

Charm & Quarkonium

54 P-wave charmonium contribution to hidden-charm states from reanalysis of lattice QCD data

We reanalyze, considering the contribution of $P$-wave charmonia, lattice data for the $D \bar D$-$D_s \bar D_s$ coupled-channel of S. Prelovsek et al. [JHEP 06, 035 (2021)] and $D \bar{D}{}^\ast$ systems of S. Prelovsek et al. [Phys. Rev. Lett. 111, 192001 (2013)] with $m_{\pi}\simeq 280$ and $266$ MeV, and $L=24a/32a$ ($a\simeq 0.09$ fm) and $L=16a$ ($a\simeq0.1239(13)$ fm), respectively. The hidden-charm states with $J^{PC}=0^{++}$, $1^{++}$, and $2^{++}$ quantum numbers are then searched for. For $0^{++}$, the analysis reveals three poles in the $D\bar{D}$-$D_s \bar{D}_s$ coupled-channel amplitude, corresponding to three states. Two of these poles, located near the $D\bar{D}$ and $D_s \bar{D}_s$ thresholds, can be interpreted as mostly molecular states. A third pole above the $D_s \bar{D}_s$ threshold is originated from the $P$-wave $\chi_{c0}(2P)$ charmonium state. The number of poles found in the $D\bar D$-$D_s \bar D_s$ system is the same as that found in the original lattice analysis though the position of the third pole changes sizeably. In the $1^{++}$ sector, we find two poles in the complex energy plane. The first one is related to the molecular $X(3872)$ state, with a compositeness exceeding $90\%$, while the second one, stemming from the $\chi_{c1}(2P)$ charmonium, appears above the $D \bar{D}{}^\ast$ threshold and it likely corresponds to the recently discovered $\chi_{c1}(4010)$ state. In the $2^{++}$ sector, we also report two poles and find that the dressed $\chi_{c2}(2P)$ is lighter than the $D^*\bar{D}{}^\ast$ molecular state, with the dynamics of the latter closely related to that of the heavy-quark spin-symmetry partner of the $X(3872)$. Our exploratory study of the $1^{++}$ and $2^{++}$ sectors offers valuable insights into their dynamics, but given that the fits that we carry out are underconstrained, more lattice data are required to draw robust conclusions.

Speaker: Pan-Pan Shi (Instituto de Física Corpuscular (IFIC))

PhiPsi26.pdf

Lunch

Charm & Quarkonium

55 Measurements of charm hadrons at Belle and Belle II

The Belle and Belle II experiments have collected a $1.6~\mathrm{ab}^{-1}$ sample of $e^+e^-$ collision data at center-of-mass energies near the $\Upsilon(nS)$ resonances. These samples contain a large number of $e^+e^-\to c\bar{c}$ events that produce charmed mesons and baryons. We present new results including the observation of the radiative decay $D_s(2317)^+ \to D_s^* \gamma$, a search for the electroweak penguin decay $D^+\to \pi^+ e^+e^-$, and a partial-wave analysis of the decay $\Xi_c^+\to \Xi^-\pi^+\pi^+$. Direct $C\!P$ violation is searched for in $D^0\to \pi^+\pi^-\pi^0$ decays and $D^+\to \pi^+\pi^0$ decays. We also present results on $C\!P$ violation in the charm baryon decays $\Xi^+_c\to \Sigma^+h^+ h^-$ and $\Lambda_c^+\to ph^+ h^-$.

Speaker: Sanjeeda Bharati Das (Universita di Torino)

sanjee_PhiPsi_Pisa2026.pptx.pdf

56 Recent Progresses on η_c(1S) Decays at BESIII

The lowest-mass charmonium ground state, the η_c(1S), serves as a crucial laboratory for testing quantum chromodynamics (QCD) and understanding charmonium decay dynamics. Utilizing its world-leading data samples of J/ψ and ψ(3686) events, the BESIII experiment has recently achieved significant progresses in the study of η_c decays. This presentation will report three key results. First, we will present the first observation of the η_c → $Ξ^0 \bar{\Xi}^0$ decay, a hadronic decay mode involving a baryon-antibaryon pair. Second, we will report the first model-independent measurement of the absolute branching fraction of the η_c → γγ decay, in which a sample of 0.16 million ηc events are tagged via the channel ψ(3686) → π0 hc, hc → γηc to avoid interference effects. Third, we will discuss a high-precision study of the magnetic dipole transition J/ψ → γ η_c, where the η_c is reconstructed via its decay to p pbar. It has significantly improved our knowledge of this key transition between charmonium S-wave states.

Speaker: Xueqiang Yan

Recent Progresses on eta_c(1S) Decays at BESIII.pdf

57 Search for charm rare decays at BESIII

The BESIII experiment has collected 10 billion $J/ψ$ events and 2.7 billion $ψ(3686)$ events. The huge charmonium data samples allow us to search for rare decay processes allowed in the standard model and new physics beyond the standard model.
In this talk, we report the search for charged lepton flavor violation process ψ(3686)→eμ, charmonium weak decay processes $J/ψ→γD^0$, $J/ψ→D^0μ^+μ^-$, $J/ψ→D^0K^{0*}$, $J/ψ→D_s e ν$, $J/ψ→D_sρ/D_sπ$ and $ψ(3686)→D_sρ/D_sπ$. The search for Bose symmetry violation processes $J/ψ→K_SK_S$ and $ψ(3686)→K_SK_S$ will also be presented.

Speaker: XiaoKang Li

PHIPSI2026_lxk_v1.2.pdf

HVP LO theo/exp.

58 Hybrid calculation of the hadronic vacuum polarization contribution to the muon g−2, to 0.48%

The Muon g−2 Experiment at Fermi National Accelerator Laboratory has recently concluded its six-year data-taking campaign, delivering a measurement of the muon's anomalous magnetic moment with an unprecedented precision of 0.127 parts per billion — one of the most stringent tests of the Standard Model ever performed. However, to fully leverage this experimental tour de force in the search for new fundamental physics, a theoretical prediction of comparable accuracy is required.

In this talk, we present a first-principles calculation, by the BMW and DMZ collaborations, of the hadronic vacuum polarization contribution — the largest source of uncertainty in the Standard Model prediction. When combined with all other Standard Model contributions, the result of this calculation yields a prediction that agrees with experiment within one standard deviation, confirming the Standard Model to eleven significant digits and sharpening constraints on physics beyond it.

Speaker: Alessandro Lupo (Aix-Marseille Univ. & CNRS)

lupo_phipsi26.pdf

New Facilities

59 Status of the Muon g-2/EDM Experiment at J-PARC

The muon magnetic anomaly, $a_\mu=(g-2)/2$, is one of the most precise tests of the Standard Model and a sensitive probe for new physics.
In 2025, the Muon g−2 Experiment at Fermilab has measured a_mu with an astonishing precision of 0.127 ppm, which show a persistent tension with the theoretical predictions. In this scenario, the Muon g$-$2/EDM Experiment at J-PARC will provide an independent determination of $a_\mu$ using a novel approach based on a low-emittance muon beam stored in a compact magnetic ring. The experiment employs innovative technologies, including three-dimensional spiral injection, an MRI-type magnet with excellent field uniformity, and a positron tracking detector. The initial goal is a precision of 450 ppb on $a_\mu$ after two years of data taking, together with a sensitivity of $1.5\times10^{-21}$ e$\cdot$cm for the muon EDM. The experiment is currently in an advanced construction phase, and first beam tests have successfully demonstrated the feasibility of the new injection method. In this contribution, I will present the current status of the experiment, ongoing tests and optimizations, and plans for future improvements in experimental precision.

Speaker: Elia Bottalico (University of Liverpool)

PhiPsi2026_JPARC_Muon_g-2_110626.pdf

PhiPsi2026_JPARC_Muon_g-2_110626.pptx

Coffee Break

New Facilities

Convener: Anna Driutti (University and INFN Pisa)

60 CANTON-μ Proposal: a Next-Generation Muon g-2 Experiment at HIAF

We propose a next-generation precision measurement of the muon anomalous magnetic moment (muon g−2) at the High Intensity Heavy-Ion Accelerator Facility (HIAF) in Huizhou, China. The project, named CANTON-μ (Coherent Anomalous magNetic momenT ObservatioN with muon), describes novel experimental approaches based on HIAF's intense pulsed GeV muons, particularly for negative-muon polarity. This independent measurement with distinct systematics is designed to achieve a precision of 0.1 ppm in Phase 1, matching the latest Fermilab precision, and 0.05 ppm in Phase 2 with the HIAF upgrade. Such precision will provide an exceptionally sensitive test of the Standard Model and a powerful probe of New Physics and CPT symmetry.

Speaker: CE ZHANG (University of Liverpool (GB))

CZhang_260611_PhiPsi2026.pdf

61 Progress of the Super Tau Charm Facility project in China

The Super Tau-Charm Facility (STCF) is a new-generation high-luminosity electron-positron collider proposed in China. It will operate in an energy range of 2-7 GeV with a luminosity higher than 0.5*10^35 cm^2 s^-1 at 4 GeV. The STCF can produce a large number of hadrons and tau leptons in a clean environment, serving as a unique and powerful tool for studying how quarks form hadrons to understand the quark confinement, as well as revealing the mystery of the space-time symmetry of fundamental interactions with unprecedented precision. The STCF physics program covers a broad spectrum of physics topics, placing stringent demands on the performance of the STCF accelerator and detector. The STCF detector and accelerator conceptual designs have been completed and published. A full accelerator and detector technology R&D program was established and has been progressing rapidly. In this report, the STCF physics program will be introduced following an overview of the STCF project. The STCF accelerator and detector conceptual designs and R&D progress will then be presented.

Speaker: Xiaoshuai Qin (Shandong University)

STCF-PhiPsi26.pdf

62 Estimated reach of FCC-ee in searches for lepton flavor violation in tau decays

We present work in progress and preliminary sensitivity estimates for
lepton flavor violation searches in tau decays at FCC-ee, assuming an
expected sample of $6 \times 10^{12}$ $Z$ decays.

Speaker: Michal Kazanecki (IFJ PAN)

Estimated reach of FCC-ee in searches for lepton flavor violation in tau decays (2).pdf

63 MESA – a new linear accelerator in Mainz

The Mainz Energy-Recovering Superconducting Accelerator (MESA) is currently under construction on the campus of Johannes Gutenberg University Mainz and is scheduled to begin operation in
2027. In this talk, an overview of the operating principles and the experimental program of the MESA experiments MAGIX, P2, and DarkMESA will be presented. As will be shown, the high beam intensities of the MESA accelerator, which will accelerate an electron beam of up to 155 MeV, provide the basis for unique experiments in the fields of nuclear, hadron, and particle physics

Speaker: Achim Denig

Denig_MESA_pdf.pdf

Conclusions