A precise measurement of the cross section of the process e + e − → π + π − (γ) from threshold to an energy of 3 GeV is obtained with the initial-state radiation (ISR) method using 232 fb −1 of data collected with the BABAR detector at e + e − center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process e + e − → µ + µ − (γ)γISR, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process e + e − → π + π − (γ) is obtained with a systematic uncertainty of 0.5% in the dominant ρ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured ππ cross section from threshold to 1.8 GeV is (514.1±2.2(stat)±3.1(syst))×10 −10 .

We calculate the skewed quark distributions(SQDs) of the pion in the light-front quark model, and discuss the calculation of the nonvalence contribution to the SQDs in this model. The frame-independence of our model calculation is guaranteed by the constraint of the sum rule between the SQDs and form factor. Our numerical results show large nonvalence contributions to the SQDs at small momentum transfer region as the skewedness increases. PACS number(s): 13.40. Gp, 13.60.Fz, 12.39.Ki

A precise measurement of the cross section for the process e + e − → K + K − (γ) from threshold to an energy of 5 GeV is obtained with the initial-state radiation (ISR) method using 232 fb −1 of data collected with the BABAR detector at e + e − center-of-mass energies near 10.6 GeV. The measurement uses the effective ISR luminosity determined from the e + e − → µ + µ − (γ)γISR process with the same data set. The corresponding lowest-order contribution to the hadronic vacuum polarization term in the muon magnetic anomaly is found to be a KK,LO µ = (22.93 ± 0.18stat ± 0.22syst) × 10 −10 . The charged kaon form factor is extracted and compared to previous results. Its magnitude at large energy significantly exceeds the asymptotic QCD prediction, while the measured slope is consistent with the prediction.

We study the reactions e + e − → e + e − η (′) in the single-tag mode and measure the γγ * → η (′) transition form factors in the momentum-transfer range from 4 to 40 GeV 2 . The analysis is based on 469 fb −1 of integrated luminosity collected at PEP-II with the BABAR detector at e + e − centerof-mass energies near 10.6 GeV.

We propose † to measure the photo-production cross section of J/ψ near threshold, in search of the recently observed LHCb hidden-charm resonances P c (4380) and P c (4450) consistent with 'pentaquarks'. The observation of these resonances in photo-production will provide strong evidence of the true resonance nature of the LHCb states, distinguishing them from kinematic enhancements. A bremsstrahlung photon beam produced with an 11 GeV electron beam at CEBAF covers the energy range of J/ψ production from the threshold photo-production energy of 8.2 GeV, to an energy beyond the presumed P c (4450) resonance. The experiment will be carried out in Hall C at Jefferson Lab, using a 50 µA electron beam incident on a 9% copper radiator. The resulting photon beam passes through a 15 cm liquid hydrogen target, producing J/ψ mesons through a diffractive process in the t-channel, or through a resonant process in the s-and u-channel. The decay e + e − pair of the J/ψ will be detected in coincidence using the two highmomentum spectrometers of Hall C. The spectrometer settings have been optimized to distinguish the resonant s-and u-channel production from the diffractive t-channel J/ψ production. The s-and u-channel production of the charmed 5-quark resonance dominates the t-distribution at large t. The momentum and angular resolution of the spectrometers is sufficient to observe a clear resonance enhancement in the total cross section and t-distribution. We request a total of 11 days of beam time with 9 days to carry the main experiment and 2 days to acquire the needed t-channel elastic J/ψ production data for a calibration measurement. This calibration measurement in itself will greatly enhance our knowledge of t-channel elastic J/ψ production near threshold. † This document is an updated version of the original proposal PR12-16-007, which was approved with an 'A' rating and a 'high-impact' label by the Jefferson Lab PAC 44 in July 2016. The experiment was awarded 11 days of beam time.