Two-photon exchange correction to the hyperfine splitting in muonic hydrogen

We reevaluate the Zemach, recoil and polarizability corrections to the hyperfine splitting in muonic hydrogen expressing them through the low-energy proton structure constants and obtain the precise values of the Zemach radius and two-photon exchange (TPE) contribution. The uncertainty of TPE correction to S energy levels in muonic hydrogen of 105 ppm exceeds the ppm accuracy level of the forthcoming 1S hyperfine splitting measurements at PSI, J-PARC and RIKEN-RAL.Comment: 17 pages, 4 figures, version published in Eur. Phys. J. C, 77, no. 12, 858 (2017

Subtracted dispersion relation formalism for the two-photon exchange correction to elastic electron-proton scattering: comparison with data

We apply a subtracted dispersion relation formalism with the aim to improve predictions for the two-photon exchange corrections to elastic electron-proton scattering observables at finite momentum transfers. We study the formalism on the elastic contribution, and make a detailed comparison with existing data for unpolarized cross sections as well as polarization transfer observables.Comment: 49 pages, 26 figures, version published in Eur. Phys. J. A 51, no. 2, 24 (2015

Two-photon exchange correction to muon-proton elastic scattering at low momentum transfer

We evaluate the two-photon exchange (TPE) correction to the muon-proton elastic scattering at small momentum transfer. Besides the elastic (nucleon) intermediate state contribution, which is calculated exactly, we account for the inelastic intermediate states by expressing the TPE process approximately through the forward doubly virtual Compton scattering. The input in our evaluation is given by the unpolarized proton structure functions and by one subtraction function. For the latter, we provide an explicit evaluation based on a Regge fit of high-energy proton structure function data. It is found that, for the kinematics of the forthcoming muon-proton elastic scattering data of the MUSE experiment, the elastic TPE contribution dominates, and the size of the inelastic TPE contributions is within the anticipated error of the forthcoming data.Comment: 33 pages, 15 figures, version published in Eur. Phys. J. C 76, no. 3, 125 (2016

Two-photon exchange contribution to elastic e−e^--proton scattering: Full dispersive treatment of πN\pi N states and comparison with data

We evaluate the two-photon exchange correction to the elastic electron-proton scattering cross section within a dispersive framework. Besides the elastic contribution, we account for all $\pi N$ intermediate state contributions using the phenomenological MAID fit as an input. We develop a novel method for the analytical continuation of the two-photon exchange amplitudes into the unphysical region and generalize our previous work to the momentum transfer region $0.064~\mathrm{GeV}^2 \lesssim Q^2 \lesssim 1~\mathrm{GeV}^2$. We compare our results with recent OLYMPUS, CLAS and VEPP-3 data as well as with empirical fits and estimates in the forward angular region.Comment: 43 pages, 21 figures, version published in Phys. Rev. D 96, 096001 (2017

Tau Neutrinos in the Next Decade: from GeV to EeV

Tau neutrinos are the least studied particle in the Standard Model. Thiswhitepaper discusses the current and expected upcoming status of tau neutrinophysics with attention to the broad experimental and theoretical landscapespanning long-baseline, beam-dump, collider, and astrophysical experiments.This whitepaper was prepared as a part of the NuTau2021 Workshop.<br

Scaled momentum distributions for K-S(0) and Λ /̄ Λ in DIS at HERA

Scaled momentum distributions for the strange hadrons K0S and Λ/Λ¯ were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb−1. The evolution of these distributions with the photon virtuality, Q 2, was studied in the kinematic region 10 < Q 2  < 40000 GeV2 and 0.001 < x < 0.75, where x is the Bjorken scaling variable. Clear scaling violations are observed. Predictions based on different approaches to fragmentation were compared to the measurements. Leading-logarithm parton-shower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Next-to-leading-order QCD calculations based on fragmentation functions, FFs, extracted from e + e − data alone, fail to describe the measurements. The calculations based on FFs extracted from a global analysis including e + e −, ep and pp data give an improved description. The measurements presented in this paper have the potential to further constrain the FFs of quarks, anti-quarks and gluons yielding K0S and Λ/Λ¯ strange hadrons

Fundamental Symmetries, Neutrons, and Neutrinos (FSNN): Whitepaper for the 2023 NSAC Long Range Plan

This whitepaper presents the research priorities decided on by attendees of the 2022 Town Meeting for Fundamental Symmetries, Neutrons and Neutrinos, which took place December 13-15, 2022 in Chapel Hill, NC, as part of the Nuclear Science Advisory Committee (NSAC) 2023 Long Range Planning process. A total of 275 scientists registered for the meeting. The whitepaper makes a number of explicit recommendations and justifies them in detail