International Journal of Modern Physics: Conference Series

The impact of improved measurements of the cross section for electron-positron annihilation into hadrons in the charm threshold region is discussed. Two aspects are studied in detail: i.) A significant reduction of the experimental error of the electronic width of the narrow resonances J/ψ and ψ′ and of the continuum cross section from the open charm threshold up to 4.6 GeV will lead to a correspondingly improved determination of the charmed quark mass; ii) A high luminosity measurement with 24 pb^-1 at three points and with a spacing of 2 MeV around may allow to observe the direct, resonant production of χ_c1.

The VEPP-2000 electron-positron collider was commissioned in 2010. About 60 pb^-1 were collected so far by CMD-3 detector in the whole available c.m. energy range from 0.32 GeV to 2.0 GeV. The preliminary results of data analysis for various modes of e⁺e⁻ → hadrons are discussed.

The preliminary results on multihadron processes obtained with the SND detector at the e⁺e⁻ collider VEPP-2000 in the energy range from 1 to 2 GeV are presented. The results are interesting in connection with their contribution to the total hadronic cross section, the muon g-2 and a possibility to study excited vector mesons properties. The nucleon anti-nucleon production was also studied.

The KLOE experiment at the DAΦNE ϕ-factory in Frascati was the first to use Initial State Radiation to precisely determine the e⁺e⁻ → π⁺π⁻(γ) cross section below 1 GeV. This measurement is particularly important to test the Standard Model calculation for the anomalous magnetic moment of the muon, (g-2), where a long standing 3σ discrepancy between measurement and theory is observed. In 2005 and 2008 KLOE published two measurements of the π⁺π⁻ cross section with the photon emitted at small angle. In 2011 an independent measurement of the π⁺π⁻ cross section with the photon emitted at large angle was published using data at a collision energy of 1 GeV, 20 MeV below the ϕ-peak. A new analysis, published in 2013, derives the pion form factor directly from the bin-by-bin π⁺π⁻γ/μ⁺μ⁻γ ratio significantly reducing the systematic uncertainty, while the previous measurements were normalized to the DAΦNE luminosity using large angle Bhabha scattering. We present the final result of this measurement, as well as a preliminary value for the combined result of all KLOE hadronic cross section measurements, and evaluate the hadronic contribution to the muon anomaly.

The MEG experiment started taking data in 2009 looking for the Standard Model suppressed decay μ → e + γ, which, if observed, can reveal Beyond Standard Model physics. It makes use of state-of-the art detectors optimized for operating in conditions of very high intensity, rejecting as much background as possible. The data taking ended August 2013 and an upgrade R&D is started to push the experimental sensitivity. The present upper limit on the decay Branching Ratio (BR) is presented, obtained with the subset of data from 2009 to 2011 run, together with a description of the key features of the upgraded detector.

The status of the theoretical predictions for processes with flavor violation in the charged lepton sector is discussed in the light of the recent determination of the reactor angle θ₁₃, as well as the improved limit set by MEG on BR(μ → eγ).

Searches for physics Beyond the Standard Model (BSM) can be carried out with precise and GeV-energy-range experiments. In many string theories, a Hidden Sector, decoupled to the SM, foresees the existence of a new massive boson, the A′ or heavy photon, that weakly couples to the electromagnetic current. A new particle with mass in the range of 1 MeV - 1 GeV could explain many astro-particle observations (e.g. positron excess seen by PAMELA and AMS experiments) and some anomalies not yet fully understood (e.g. muon g - 2 factor). The search for A′ has motivated intense experimental activities in almost every accelerator facility using different techniques: colliding beam, fixed target experiments, meson rare decays. Jefferson Lab, a world-leading nuclear physics laboratory, is planning a set of fixed target experiments aiming to discover the A′ or set new limits in its mass and coupling, with an unprecedented sensitivity and reach capability. In this contribution, after reviewing the physics case and some experimental evidences, I will report on the program of measurements planned at Jefferson Lab for the next years.

The existence of a light dark force mediator has been tested with the KLOE detector at DAΦNE. This particle, the dark photon U, has been searched for in three different processes and four different final states: a) Φ → ηU, with U → e⁺e⁻, η → π⁺π⁻π⁰ and η → π⁰π⁰π⁰; b) e⁺e⁻ → Uγ with U → μ⁺μ⁻; c) e⁺e⁻ → Uh′ (dark Higgsstrahlung), U → μ⁺μ⁻, where h′ is a Higgs-like particle responsible for the breaking of the hidden symmetry.

We did not find any evidence of the processes above and set upper limits on the parameters of the model, for different M_U (and M_h′) mass ranges, depending on the considered final state.

The lepton-charge (L_e, L_μ, L_τ) nonconserving interaction leads to the mixing of the electron, muon and tau neutrinos, which manifests itself in spatial oscillations of a neutrino beam, and also to the mixing of the electron, negative muon and tau lepton, which, in particular, may be the cause of the "forbidden" radiative decay of the negative muon into the electron and γ quantum. Under the assumption that the nondiagonal elements of the mass matrices for neutrinos and ordinary leptons, connected with the lepton charge nonconservation, are the same, and by performing the joint analysis of the experimental data on neutrino oscillations and experimental restriction for the probability of the decay μ^- → e^- + γ per unit time, the following estimate for the lower bound of neutrino mass has been obtained: .

Photon-photon interactions have been studied at the ϕ-factory DAΦNE with the detector KLOE operating the machine at GeV, without tagging of the final leptons. The results about the γγ → η process and the evidence for γγ → π⁰π⁰ production at low π⁰π⁰ invariant mass are reviewed. The process γγ → π⁰ will be studied at KLOE-2 running the machine at ϕ-peak thanks to new lepton tagger detectors. In particular, the possibility to measure the two-photon width of π⁰ and the π⁰γ*γ transition form factor in the low (space-like) Q² region is considered.

We report a high-statistics measurement of the differential cross section of the process with the Belle detector. We study spectroscopy of light-quark resonances and charmonia and test QCD models using the data. We summarize our systematic measurements of different processes of γγ → meson-pair production based on the parameterization of the cross sections and comparison with QCD models. We also report on the measurement of the two-photon π⁰ transition form factor at Belle.

The process γπ → ππ, in the limit of vanishing photon and pion energies, is determined by the chiral anomaly. This reaction can be investigated experimentally using Primakoff reactions, as currently done at COMPASS. We derive a dispersive representation that allows one to extract the chiral anomaly from cross-section measurements up to 1 GeV, where effects of the ρ resonance are included model-independently via the ππ P-wave phase shift. We discuss how this amplitude serves as an important input to a dispersion-theoretical analysis of the π⁰ transition form factor, which in turn is a vital ingredient to the hadronic light-by-light contribution to the anomalous magnetic moment of the muon.

The η and η′ transition form factors in the space-like region are analyzed at low and intermediate energies in a model-independent way through the use of rational approximants. The slope and curvature parameters of the form factors as well as their values at infinity are extracted from experimental data. The impact of these results on the mixing parameters of the η-η′ system are also discussed.

A representation of the amplitude γ*(q²) → γππ is proposed which combines large N_c chiral resonance Lagrangian modelling with general unitarity and analyticity properties. The amplitude is constrained from γγ scattering results and e⁺e⁻ → γπ⁰π⁰ measurements by the CMD-2 and SND collaborations. As an application, the contribution of the ππ + γ states in the HVP contribution to the muon g - 2 are reconsidered, taking into account the effect of the strong S-wave ππ rescattering in a model independent way.

Based on analyticity, unitarity, and Lorentz invariance the contribution from hadronic vacuum polarization to the anomalous magnetic moment of the muon is directly related to the cross section of e⁺e⁻ → hadrons. We review the main difficulties that impede such an approach for light-by-light scattering and identify the required ingredients from experiment. Amongst those, the most critical one is the scattering of two virtual photons into meson pairs. We analyze the analytic structure of the process γ*γ* → ππ and show that the usual Muskhelishvili–Omnès representation can be amended in such a way as to remain valid even in the presence of anomalous thresholds.

The light-by-light contribution to the anomalous magnetic moment of muon is estimated in the framework of nonlocal quark model. The partial contribution from contact diagrams and mesonic exchanges is discussed.

A short description of generators used in low energy experiments measuring the hadronic cross section with scan and radiative return methods is presented.

The final state interaction in the processes and close to the threshold is discussed. It is shown that, due to the Coulomb interaction, the contribution of the d wave to the cross section does not vanish even at zero relative velocity of produced particles. This results in the nonzero anisotropy in angular distribution at the threshold. We use the Paris nucleon-antinucleon optical potential for explanation of experimental data in the process near threshold. It follows from our consideration that the isoscalar form factor is much larger than the isovector one.

The g - 2 experiment at Fermi National Laboratory is planned to refine previous measurements of the anomalous magnetic moment of the muon, reducing systematic errors and generate constraints on possible physics beyond the standard model. This paper describes some of the ways in which a four-fold reduction in systematic errors will be achieved.

The contributions from the standard model interactions to the anomalous magnetic moments of the two lightest charged leptons, the electron and the muon, are reviewed. Comparison with the very accurately measured experimental values is made, using the most recent high-precision determination of the fine structure constant.

The status of the hadronic vacuum polarisation contributions to g - 2 of the muon and to the running QED coupling is briefly reviewed. The role of recent hadronic cross section measurements and remaining puzzles are discussed.

A number of production cross sections for electron-positron annihilation to a hadronic final state have been measured using the Belle dataset, which is possible given the general purpose design of the Belle detector and its large solid-angle coverage. The cross section measurements predominantly fall above 3 GeV, which still leaves the opportunity for using the dataset to systematically measure cross sections below 3 GeV. These low-energy cross sections are important for improving the precision of the Standard Model prediction for the muon anomalous magnetic moment.

Measurements of the R ratio are closely related to two pre quantities, the anomalous magnetic moment of the muon (g - 2), and the value of the electromagnetic fine structure constant . Hadronic contributions to both quantities can be derived via dispersion integrals, using experimental R data as input. For the phenomenological evaluations of these contributions, different energy ranges of hadronic cross section data are required. At BES-III, Initial State Radiation (ISR) from an existing Ψ(3770) dataset will be used for measurements of hadronic cross sections below , while for higher energies a dedicated energy scan program will be performed up to .

Using the field-theory-inspired expression for the pion electromagnetic form factor F_π, a good description of the data in the range -10 < s < 1 GeV² is obtained upon taking into account the pseudoscalar-pseudoscalar (PP) loops. When the vector-pseudoscalar (VP) and the axial vector-pseudoscalar (AP) loops are taken into account in addition to the PP ones, a good description of the BABAR data on the reaction e⁺e⁻ → π⁺π⁻ is obtained at energies up to 3 GeV. The inclusion of the VP and AP loops demands the treatment of the reactions e⁺e⁻ → ωπ⁰ and e⁺e⁻ → π⁺π⁻π⁺π⁻. This task is performed with the SND data on ωπ⁰ production and the BABAR data on π⁺π⁻π⁺π⁻ production, both in e⁺e⁻ annihilation, by taking into account ρ(770) and the heavier ρ(1450), ρ(1700), and ρ(2100) resonances. The problems arising from including of the VP and AP loops are pointed out and discussed.

We will discuss the particle physics opportunities at IRIDE (Interdisciplinary Research Infrastructure based on a Dual Electron Linac et Laser), a new multipurpose facility based on a combination of a high duty cycle radio-frequency superconducting electron linac (SC RF LINAC) and of high energy laser, presently under consideration at INFN.

The 12 GeV upgrade to the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab will enable a new generation of experiments in hadronic nuclear physics, seeking to address fundamental questions in our understanding of QCD. The existence of exotic states, suggested by both quark models and lattice calculations, would allow gluonic degrees of freedom to be explored, and may help explain the role played by gluons in the QCD interaction. This article will review the meson spectroscopy program being planned at the lab following the 12 GeV upgrade, utilising real and quasi-real photon beams in two of the lab's four experimental halls, whose distinct capabilities will enable an extensive set of spectroscopy experiments to be performed at the same facility.

We present a selection of recent charm results from the BESIII Collaboration. The topics include measurements of strong phase in D⁰ → Kπ decay and y_CP, decay constant f_D⁺ measurement from D⁺ → μ⁺ν, form-factors measurement in D⁰ → K⁻e⁺ν, π⁻e⁺ν, Dalitz plot analysis of , search for D⁰ → γγ rare decay and D_s decays.

CP violation in charm decays is expected to be very small in the Standard Model, at the level of 0.1% or less. A sizable excess of CP violation with respect to the Standard Model predictions could be a signature of new physics. We report on recent searches for CP violation in charm meson decays at BABAR and Belle experiments. In particular we report a lifetime ratio analysis of D⁰ → K⁺K⁻, π⁺π⁻ with respect to D⁰ → K⁻π⁺ decays, which is sensitive to mixing and CP violation. We report also on searches for CPV in the 3-body D⁺ → K⁺K⁻π⁺ decay and for decay modes with a in the final state, such as .

Recent results on mixing, CP violation and rare decays in charm physics from the LHCb experiment are presented. Study of "wrong-sign" D⁰ → K⁺π^- decays provides the highest precision measurements to date of the mixing parameters x′² and y′, and of CP violation in this decay mode. Direct and indirect CP violation in the D⁰ system are probed to a sensitivity of around 10^-3 using D⁰ → K⁺K⁻ and D⁰ → π⁺π⁻ decays and found to be consistent with zero. Searches for the rare decays , and D⁰ → μ⁺μ⁻ find no evidence of signal, but set the best limits on branching fractions to date. Thus, despite many excellent results in charm physics from LHCb, no evidence for physics beyond the Standard Model is found.

Recent measurements of charm production at HERA are presented. They include measurements of charm fragmentation fractions, of charm production in DIS and of inelastic and exclusive J/ψ photoproduction. Charm measurements have been combined and analysed in the framework of a QCD fit to inclusive and charm data.

Relying on a global fit based on the HLS model suitably broken, we show that the recent π⁺π⁻ data samples collected by KLOE behave in full consistency with the corresponding scan data and also with the physics associated with the e⁺e⁻ annihilations to the π⁺π⁻π⁰, π⁰ γ, ηγ, and K⁺K⁻ final states. Their impact on the estimate of the muon g - 2 is shown to increase sensitively the difference with the measurement performed at BNL.

In this contribution we present recent four-loop results for the muon anomalous magnetic moment based on analytic methods. In particular, fermionic corrections involving two or more closed electron loops or at least one tau lepton loop are discussed.

We review some of the issues that arise in attempts to compute the hadronic corrections to the muon anomalous magnetic moment using Lattice QCD. We concentrate on the dominant contribution, which requires an accurate evaluation of the hadronic vacuum polarization.

Recent progress on the (g - 2)_μ prediction is presented. In the SM, the Higgs-boson mass dependent contributions have been evaluated exactly up to the two-loop level and consistently combined with leading three-loop effects. Thus, the currently most accurate value including a detailed error analysis for the SM electroweak contributions has been obtained. The SUSY two-loop corrections from fermion/sfermion-loop insertions have been computed; they are generally large and logarithmically enhanced for heavy squarks.

The KLOE experiment at the Frascati e⁺e⁻ collider DAΦNE, operating at the ϕ peak, provides unique opportunities for precision measurements of kaon branching ratios. We present the upper limit on the branching ratio of the CP violating decay K_S → 3π⁰ obtained with 1.7 fb^-1 of e⁺e⁻ collisions collected by the KLOE detector. We also present the new preliminary result of the branching ratio for K⁺ → π⁺π⁻π⁺(γ) using approximately 10% of all KLOE data.

The NA48/2 experiment presents preliminary measurements of the form factors of the charged kaon semileptonic decays. The Ke3 and Kμ3 results are in good agreement allowing for a combined result which matches the precision of the current world average on the vector and scalar form factors. Recent study of the rare decay K^± → π^±γγ from the NA48/2 and NA62 data samples is also reported.

Rare kaon decays provide unique opportunity to test the Standard Model and probe its possible extensions. The primary goal of the NA62 experiment is the measurement of the decay with a precision of 10% in two years of data taking. The detector setup together with the analysis technique is described.

During the last three lustra nucleon form factors experiments have lived a golden age, full of interesting results, that likely will continue and culminate when new data will come from BESIII, SND, CMD3 and PANDA, in the time-like region and, Jefferson Lab and A1 in the space-like region. On the other hand, from theoretical point of view, mainly concerning the possibility of descriptions in all kinematical regions, no great breakthrough has been made.

During years 2011 and 2012 data taking runs have been carried out at VEPP-2000 e⁺e^- collider to measure the production of the nucleon-antinucleon pairs near threshold. In this talk the preliminary results on the nucleon timelike electromagnetic form factors (FF) and the |G_E/G_M| ratio are presented.

The process has been studied in the mass range from threshold to 6.5 GeV/c² using the initial-state-radiation technique with both detected and undetected photon. The analysis is based on 469 fb^-1 of integrated luminosity collected with the BABAR detector at the PEP-II collider at e⁺e^- center-of-mass energies near 10.6 GeV.

The electric and magnetic form factors are defined as basic observables which reflect the composite nature of the nucleon. They have long been studied in electron scattering, and now we are here to discuss opportunities that can come from an e⁺e^- collider (in the time-like region) at moderate energies where exclusive cross sections can be measured. With largest data samples and better resolutions, we discuss the status of baryon form factors and a bright opportunity of measurement at BESIII.

The physics of the nucleon form factors is the basic part of the Jefferson Laboratory program. We review the achievements of the 6-GeV era and the program with the 12-GeV beam with the SBS spectrometer in Hall A, with a focus on the nucleon ground state properties.

The recent results about charmonium and charmonium-like spectroscopy and decays from BESIII are presented in this talk. We report the observation of X(3872) from Y(4260) radiative transition, π⁺π^-h_c line shape measurement and Z_c states. In addition, the accurate measurement of η_c parameters, the analysis on h_c exclusive decays into γη_c, and the first observation of the M1 transition ψ′ → γη_c(2S) are included in this talk.

We report results of experiments performed with the KEDR detector at the VEPP-4M e⁺e^- collider. They include final results for the mass and other parameters of the J/ψ, ψ(2S) and ψ(3770) and J/ψ → γη_c branching fraction determination.

We report recent results related to spectroscopy of heavy quarks obtained with the LHCb detector. They include a study of the X(3872) produced in continuum and B decays, precise measurements of the D and D_s masses, a study of the properties of D_J mesons and excited B_s states as well as the first observation of the decay.

This talk summarizes recent developments in quarkonium spectroscopy. I comment on the relation between the Z_b(10610) and Z_b(10650) and recently observed Z_c(3900) and Z_c(4025) states. Then I discuss a number of calculations using non-relativistic effective field theory for the X(3872), Z_b(10610), and Z_b(10650), under the assumption that these are shallow molecular bound states of charm or bottom mesons.

During the last three years strong experimental evidence from B and charm factories has been accumulating for the existence of exotic hadronic quarkonia, narrow resonances which cannot be made from a quark and an antiquark. Their masses and decay modes show that they contain a heavy quark-antiquark pair, but their quantum numbers are such that they must also contain a light quark-antiquark pair. The main theoretical challenge has been to determine the nature of these resonances. The main possibilities are that they are either "genuine tetraquarks", i.e. two quarks and two antiquarks within one confinement volume, or "hadronic molecules" of two heavy-light mesons. In the last few months there is more and more evidence in favor of the latter. I discuss the experimental data and its interpretation and provide fairly precise predictions for masses and quantum numbers of the additional exotic states which are naturally expected in the molecular picture but have yet to be observed. I also provide arguments in favor of the existence of an even more exotic state – a hypothetical deuteron-like bound state of two heavy baryons.

A novel method to perform a direct T (or CPT) symmetry test in the neutral kaon system is presented. This is based on the comparison of suitable transition probabilities, where the required interchange of in ↔ out states for a given process is obtained exploiting the Einstein-Podolsky-Rosen correlations of neutral kaon pairs produced at a ϕ-factory.

The possibility to perform these tests with the KLOE-2 experiment at DAΦNE, the Frascati ϕ-factory, is also briefly discussed.

Measurement of the difference of the decay times of neutral kaon pairs produced in an antisymmetric entangled state allows for the search of possible violation of CPT symmetry and Lorentz invariance. In this paper we present the recently announced results based on the reaction ϕ → K_SK_L → π⁺π^-π⁺π^- measured at the KLOE experiment. Obtained parameters in the Standard Model Extension (SME) are:

A microwave spectroscopy experiment of muonium atoms are being prepared at J-PARC in Japan, aiming at an improved relative precision at a level of 10^-8 in determination of the muonic magnetic moment. A major improvement of statistical uncertainty is due to higher muon intensity of the pulsed beam at J-PARC, while further improvements are expected for systematic uncertainties. Reduction of sources of systematic uncertainties are being studied: those arising from microwave power fluctuations, magnetic field inhomogeneity, muon stopping distribution and gas-density shift of resonance frequencies. Status and prospects of studies and developments of the experiment is presented in this paper.

The ratio of the leptonic charged kaon decays R_K = Γ(K^± → e^±ν)/Γ(K^± → μ^±ν) is sensitive to the structure of the weak interactions and can be precisely calculated within the Standard Model. Presence of New Physics can introduce a shift on its value of the order of a percent. The NA62 experiment at CERN SPS used data from a dedicated run in 2007 to perform a measurement of this ratio and probe the lepton universality. The data analysis technique and the final results are presented.

Simple dynamics, few available decay channels, and highly controlled radiative and loop corrections, make pion and muon decays a sensitive means of exploring details of the underlying symmetries. We review the current status of the rare decays: π⁺ → e⁺ν (π_e2), π⁺ → e⁺νγ (π_e2γ), π⁺ → π⁰e⁺ν (π_e3), and . For the latter we report new preliminary values for the branching ratio B(E_γ > 10 MeV, θ_eγ > 30°) = 4.365 (9)_stat (42)_syst × 10^-3, and the decay parameter , both in excellent agreement with standard model predictions. We review recent measurements, particularly by the PIBETA and PEN experiments, and near-term prospects for improvement. These and other similar precise low energy studies complement modern collider results materially.

The new experiment at BESIII aims at the uncertainty less than 0.1 MeV, or 5.6 × 10^-5 for the relative error. To make full use of machine time, the optimization study is performed to acquire the best strategy of data taking. The results of m_τ based on the test scan sample at BESIII are presented.

We report recent results on τ lepton physics obtained with the Belle detector. They include a search for lepton-flavor-violating decays τ → lhh′, a high-precision measurement of the τ lepton lifetime and a study of the hadronic decays with the in the final state.

We report recent measurements on τ leptons obtained by the BABAR collaboration using the entire recorded sample of electron-positron collisions at and around the Υ(4S) (about 470fb^-1). The events were recorded at the PEP-II asymmetric collider at the SLAC National Accelerator Laboratory. The measurements include high multiplicity τ decay branching fractions with 3 or 5 charged particles in the final state, a search for the second class current the τ decay τ → πη′ν, τ branching fractions into final states containing two K_S mesons, , with h = π, K, and preliminary measurements of hadronic spectra of τ decays with three hadrons (τ^- → h^-h⁺h^-ν_τ decays, where h = π, K). The results improve the experimental knowledge of the τ lepton properties and can be used to improve the precision tests of the Standard Model.

Recent analyses of flavor-breaking hadronic-τ-decay-based sum rules produce values of |V_us| ~ 3σ low compared to 3-family unitarity expectations. An unresolved systematic issue is the significant variation in |V_us| produced by different prescriptions for treating the slowly converging D = 2 OPE series. We investigate the reliability of these prescriptions using lattice data for various flavor-breaking correlators and show the fixed-scale prescription is clearly preferred. Preliminary updates of the conventional τ-based, and related mixed τ-electroproduction-data-based, sum rule analyses incorporating B-factory results for low-multiplicity strange τ decay mode distributions are then performed. Use of the preferred FOPT D = 2 OPE prescription is shown to significantly reduce the discrepancy between 3-family unitarity expectations and the sum rule results.

In the extraction of α_s from hadronic τ decay data several moments of the spectral functions have been employed. Furthermore, different renormalization group improvement (RGI) frameworks have been advocated, leading to conflicting values of α_s. Recently, we performed a systematic study of the perturbative behavior of these moments in the context of the two main-stream RGI frameworks: Fixed Order Perturbation Theory (FOPT) and Contour Improved Perturbation Theory (CIPT). The yet unknown higher order coefficients of the perturbative series were modelled using the available knowledge of the renormalon singularities of the QCD Adler function. We were able to show that within these RGI frameworks some of the commonly employed moments should be avoided due to their poor perturbative behavior. Furthermore, under reasonable assumptions about the higher order behavior of the perturbative series FOPT provides the preferred RGI framework.

We present an analysis of the isospin-one V – A correlator based on our successful simultaneous description of the OPAL V and A non-strange tau spectral data. We discuss the values obtained for the Chiral Perturbation Theory low-energy constants L₁₀ and C₈₇ as well as the dimension-six and eight condensates and compare them with those in the literature.

The status of the main ongoing analyses on light-meson spectroscopy at KLOE are presented. In particular, the most recent upgrades for the ϕ → ηe⁺e^- analysis, in both charged (η → π⁺π^-π⁰) and neutral (η → π⁰π⁰π⁰) channels of η decay, as well as the preliminary studies of the ϕ → π⁰e⁺e^- process are reported. Latest upgrades on η → π⁺π^-π⁰ Dalitz plot analysis are also shown. All the analyses are based on data collected at DAΦNE collider with the KLOE detector during the 2004/2005 data taking campaign.

We present a selection of recent results on light hadron spectroscopy from the BESIII collaboration. The topics include the full partial wave analysis on J/ψ radiative decays, including J/ψ → γηη and γωϕ. Besides, we also cover the topics about baryon spectroscopy, including the partial wave analysis of and .

Detailed experimental studies of the decays and interactions of light mesons, such as π⁰, η and ω, are highly needed as precision tests for theoretical models.

The Wide Angle Shower Apparatus (WASA) detector is one of the available experimental set-ups optimized for studying production and decays of light mesons. In contrast to the focus of this workshop, the mesons are produced through proton-proton or proton-deuteron collisions using a fixed target.

This paper will present status of studies performed by the WASA-at-COSY collaboration in the field of light meson interactions.

We study the mechanism of production of the light scalar mesons in the decays: , and compare it with the mechanism of production of the light pseudoscalar mesons in the decays: . We show that the transition is negligibly small in comparison with the one. As for the the f₀(980) meson, the intensity of the transition is not more thirty percent from the intensity of the () transition. So, the decay supports the previous conclusions about a dominant role of the four-quark components in the σ(600) and f₀(980) mesons.

In this report the overview of activity at existing and future electron-positron high energy colliders at BINP is presented. VEPP-2000 and VEPP-4M electron-positron colliders are currently being in operation at the Budker Institute of Nuclear Physics in Novosibirsk. These two machines cover a wide collision energy range: from 0.32 GeV to 2 GeV (VEPP-2000) and from 1.8 GeV to 11 GeV (VEPP-4M). Both complexes will be upgraded after successful start of operation in 2013 of the new electron-positron injector complex VEPP-5, which should supply both facilities by much more intense beams. Super-tau-charm factory waits for the final government's approval being considered as one of 6 mega-science project in Russia.

The current status of the SuperKEKB/Belle II project which is under construction now at KEK is reported. Main motivations and goals of this project are discussed as well.

We report preliminary results on the measurement of the cross section of the process e⁺e^- → K⁺K^-π⁺π^- in the c.m. energy range from 1.5 GeV to 2 GeV. It is shown that the cross section is dominated by the contributions of several intermediate states K⁺K^-ρ, K*Kπ, ϕπ⁺π^- and K*K*.

The intensity of scalar a₀(980), f₀(980) and tensor a₂(1320), f₂(1270) mesons production at VEPP-2000 (BINP, Novosibirsk) and the upgraded DAΦNE (Frascati, Italy) in the processes e⁺e^- → a₀(f₀, a₂, f₂)γ is calculated.

Using the technique of helicity amplitudes, the electromagnetic process e⁺e^- → μ⁺μ^-(τ⁺τ^-) is theoretically studied in the one-photon approximation. The structure of the triplet states of the final (μ⁺μ^-) system is analyzed. It is shown that in the case of unpolarized electron and positron the final muons are also unpolarized, but their spins are strongly correlated. Explicit expressions for the components of the correlation tensor of the (μ⁺μ^-) system are derived. The formula for the angular correlation at the decays of final muons μ⁺ and μ^- is obtained. It is demonstrated that spin correlations of muons in the considered process have the purely quantum character, since one of the Bell-type incoherence inequalities for the correlation tensor components is always violated.

The spin structure of the process γγ → e⁺e^- is theoretically investigated. It is shown that, if the primary photons are unpolarized, the final electron and positron are unpolarized as well but their spins are strongly correlated. For the final (e⁺e^-) system, explicit expressions for the components of the correlation tensor are derived, and the relative fractions of singlet and triplet states are found. It is demonstrated that in the process γγ → e⁺e^- one of the Bell-type incoherence inequalities for the correlation tensor components is always violated and, thus, spin correlations of the electron and positron in this process have the strongly pronounced quantum character. Analogous consideration can be wholly applied as well to the two-photon processes γγ → μ⁺μ^- and γγ → τ⁺τ^-, which become possible at considerably higher energies.

A study of the light-meson couplings to the single photon in the framework of the covariant oscillator quark model (COQM) is reported. The transition rates of {ρ(770), b₁(1235), a₁(1260), a₂(1320), π₂(1670), ρ₃(1690), ρ(1700)}^± into π^±γ, being expected to be measured by the COMPASS collaboration in their Primakoff-reaction experiments, are calculated. It could be useful not only for understanding the internal structures of observed light-quark mesons and their quark-model classification but also for the ongoing experimental studies by COMPASS.

Using the Skyrme model for nucleons we test the possibility to obtain time-like form factors by analytic continuation of space-like ones. We present a method based on a direct computation of the space-like form factors in the Breit frame, where they are defined as Fourier transform of electromagnetic current. A Padé approximation of the current is implemented in order to solve the integral. The results are compared to data both in space-like and time-like region.

We give an update on the status of the hadronic light-by-light scattering contribution to the muon g – 2. We review recent work, list some open problems and give an outlook on how to better control the uncertainty of this contribution. We think the estimate still gives a fair description of the current situation.

We report preliminary results on the measurement of the cross section with the CMD-3 detector at the VEPP-2000 electron-positron collider based on 4.5 pb^-1 of integrated luminosity collected in the c.m. energy range 1.92 - 2.0 GeV. Event selection using information from the Drift Chamber and Calorimeters provides a clean sample of events. The obtained results are in good agreement with the previous measurements.

The NA48/2 experiment has collected the largest samples to date of semi-leptonic charged kaon decays in the (K^± → π⁺π^-e^±ν) and (K^± → π⁰π⁰e^±ν) modes. From 1.1 million decays, form factors in the S- and P-wave have been extensively studied. Branching ratio and form factors have been measured at unprecedented precision. From ~ 66000 decays, preliminary values of the Branching ratio and form factor have been obtained at a percent level precision. The comparison of Branching ratio and form factor values in both K_e4 modes sheds new light on isospin symmetry breaking effects. Form factor measurements are major inputs to the study of low energy QCD and are powerful tests of Chiral Perturbation Theory predictions.

The aim of this paper is to present an effective field theory description of the conversion transition of the vector meson V into the pseudoscalar P and the lepton-pair l⁺l^-. The normalized form factor for ω → π⁰γ* transition is presented and compared to the available data and to the predictions of other models.

We study the phenomenology of the τ^- → π^-ν_τℓ⁺ℓ^- decays (ℓ = e, μ), predicting the respective branching ratios and di-lepton invariant-mass spectra. In addition to the model-independent (QED) contributions, we investigate the structure-dependent (SD) terms, encoding features of the hadronization of QCD currents. The relevant form factors are evaluated by supplementing Chiral Perturbation Theory with the inclusion of the lightest (axial-)vector resonance multiplet as dynamical fields. The Lagrangian couplings are fully predicted requiring the known QCD asymptotic behavior to the relevant Green functions and associated form factors in the limit of an infinite number of colours. As a consequence we predict that the τ^- → π^-ν_τe⁺e^- decays should be discovered soon while this is not granted for the ℓ = μ case.

Dispersion-theoretical analyses of transition form factors are stepping stones to a model-independent determination of the light-by-light scattering contribution to (g - 2)_μ. We extend a calculation of the conversion decays of the lightest isoscalar vector mesons, ω/ϕ → π⁰ℓ⁺ℓ^-, that builds on a previous dispersive analysis of the ω/ϕ → 3π partial-wave amplitudes and the pion vector form factor as its sole ingredients. We construct a good parametrization of e⁺e^- → 3π that, together with information on the anomalous process γπ → ππ, allows us to obtain a description of the π⁰ transition form factor measured in e⁺e^- → π⁰γ.

Since 2004 the KEDR detector at the VEPP-4M collider has taken several data sets in the ψ(2S) region, acquiring total luminosity of about 7 pb^-1, which corresponds to more than 3.5 × 10⁶ψ(2S).

We report the preliminary value of Γ_ee × Γ_μμ/Γ = 19.4 ± 0.4 ± 1.1 eV for ψ(2S).

We determine the magnetic dipole moment of the rho meson using preliminary data from the BaBar Collaboration for the e⁺e^- → π⁺π^-2π⁰ process, in the center of mass energy range from 0.9 to 2.2 GeV. We describe the γ* → 4π vertex using a vector meson dominance model, including all intermediate resonance contributions. We find that μ_ρ = 2.1 ± 0.5 [e/2m_ρ].