Fri·Apr 16, 2021Friday·April 16, 2021

1. 01*

   Nucleon off-shell structure and the free neutron valence structure from A=3 inclusive electron scattering measurements

   E.P. Segarra🇺🇸 · J.R. Pybus🇺🇸 · F. Hauenstein🇺🇸 · T. Kutz🇺🇸 · D. Higinbotham🇺🇸 · G.A. Miller🇺🇸 · E. Piasetzky🇮🇱 · A. Schmidt🇺🇸 · M. Strikman🇺🇸 · L.B. Weinstein🇺🇸 · O. Hen🇺🇸

   Understanding the differences between the distribution of quarks bound in protons and neutrons is key for constraining the mechanisms of SU(6) spin-flavor symmetry breaking in Quantum Chromodynamics (QCD). While vast amounts of proton structure measurements were done, data on the structure of the neutron is much more spars as experiments typically extract the structure of neutrons from measurements of light atomic nuclei using model-dependent corrections for nuclear effects. Recently the MARATHON collaboration performed such an extraction by measuring inclusive deep-inelastic electron-scattering on helium-3 and tritium mirror nuclei where nuclear effects are expected to be similar and thus be suppressed in the helium-3 to tritium ratio. Here we evaluate the model dependence of this extraction by examining a wide range of models including the effect of using instant-form and light-cone nuclear wave functions and several different parameterizations of nucleon modification effects, including those with and without isospin dependence. We find that, while the data cannot differentiate among the different models of nuclear structure and nucleon modification, they consistently prefer a neutron-to-proton structure function ratio of at $x_B\to 1$ of $\sim 0.4$ with a typical uncertainty ($1\sigma$) of $\sim 0.05$ and $\sim 0.10$ for isospin-independent and isospin-dependent modification models, respectively. While strongly favoring SU(6) symmetry breaking models based on perturbative QCD and the Schwinger-Dyson equation calculation, the MARATHON data do not completely rule out the scalar di-quark models if an isospin-dependent modification exist.

   ↳ hep-phnucl-exnucl-th8 citations
2. 02*

   Jülich-Bonn-Washington Model for Pion Electroproduction Multipoles

   Maxim Mai🇺🇸 · Michael Döring🇺🇸 · Carlos Granados🇺🇸 · Helmut Haberzettl🇺🇸 · Ulf-G. Meißner🇩🇪 · Deborah Rönchen🇩🇪 · Igor Strakovsky🇺🇸 · Ron Workman🇺🇸

   Pion electroproduction off the proton is analyzed in a new framework based on a general parametrization of transition amplitudes, including constraints from gauge invariance and threshold behavior. Data with energies $1.13\mathrm{GeV}<W<1.6\mathrm{GeV}$ and $Q^2$ below $6{\mathrm{GeV}}^2$ are included. The model is an extension of the latest Jülich-Bonn solution incorporating constraints from pion-induced and photoproduction data. Performing large scale fits ($\sim 10^5$ data) we find a set of solutions with ${\chi }_{\mathrm{dof}}^2=1.69-1.81$ which allows us to assess the systematic uncertainty of the approach.

   ↳ nucl-thhep-phnucl-exPRC(2021)·46 citations
3. 03*

   Intermediate mass dileptons as pre-equilibrium probes in heavy ion collisions

   Maurice Coquet🇫🇷 · Xiaojian Du🇩🇪 · Jean-Yves Ollitrault🇫🇷 · Soeren Schlichting🇩🇪 · Michael Winn🇫🇷

   The production of dileptons with an invariant mass in the range 1 GeV < M < 5 GeV provides unique insight into the approach to thermal equilibrium in ultrarelativistic nucleus-nucleus collisions. In this mass range, they are produced through the annihilation of quark-antiquark pairs in the early stages of the collision. They are sensitive to the anisotropy of the quark momentum distribution, and also to the quark abundance, which is expected to be underpopulated relative to thermal equilibrium. We take into account both effects based on recent theoretical developments in QCD kinetic theory, and study how the dilepton mass spectrum depends on the shear viscosity to entropy ratio that controls the equilibration time. We evaluate the background from the Drell-Yan process and argue that future detector developments can suppress the additional background from semileptonic decays of heavy flavors.

   ↳ nucl-thhep-exhep-phnucl-exPLB(2021)·58 citations
4. 04*

   Global Analysis of Leptophilic Z' Bosons

   Andrzej J. Buras🇩🇪 · Andreas Crivellin🇨🇭 · Fiona Kirk🇨🇭 · Claudio Andrea Manzari🇨🇭 · Marc Montull🇨🇭

   New neutral heavy gauge bosons ($Z^{\prime }$) are predicted within many extensions of the Standard Model. While in case they couple to quarks the LHC bounds are very stringent, leptophilic $Z^{\prime }$ bosons (even with sizable couplings) can be much lighter and therefore lead to interesting quantum effects in precision observables (like $(g-2{)}_{\mu }$) and generate flavour violating decays of charged leptons. In particular, $\ell \to {\ell }^{\prime }\nu \bar{\nu }$ decays, anomalous magnetic moments of charged leptons, $\ell \to {\ell }^{\prime }\gamma$ and $\ell \to 3{\ell }^{\prime }$ decays place stringent limits on leptophilic $Z^{\prime }$ bosons. Furthermore, in case of mixing $Z^{\prime }$ with the SM $Z$, $Z$ pole observables are affected. In light of these many observables we perform a global fit to leptophilic $Z^{\prime }$ models with the main goal of finding the bounds for the $Z^{\prime }$ couplings to leptons. To this end we consider a number of scenarios for these couplings. While in generic scenarios correlations are weak, this changes once additional constraints on the couplings are imposed. In particular, if one considers an $L_{\mu }-L_{\tau }$ symmetry broken only by left-handed rotations, or considers the case of $\tau -\mu$ couplings only. In the latter setup, on can explain the $(g-2{)}_{\mu }$ anomaly and the hint for lepton flavour universality violation in $\tau \to \mu \nu \bar{\nu }/\tau \to e\nu \bar{\nu }$ without violating bounds from electroweak precision observables.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2021)·82 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.