Tue·Apr 27, 2021Tuesday·April 27, 2021

1. 01*

   Measuring two photon exchange in elastic nuclear scattering with $e^{+}/e^{-}$ charge asymmetries

   Tyler Kutz🇺🇸 · Axel Schmidt🇺🇸

   Measurements of nuclear $\beta$-decay are commonly used to extract elements of the quark-mixing Cabibbo-Kobayashi-Maskawa (CKM) matrix. The precision of these measurements is currently limited by theoretical uncertainties in electroweak radiative corrections (EWRC) arising from so-called box diagrams, which involve the exchange of two gauge bosons. Two photon exchange (TPE) is the most experimentally accessible of such processes, making it a natural choice for providing constraints on the theoretical frameworks used for calculating EWRC. The cross section asymmetry between elastic $e^{+}/e^{-}$ scattering is directly sensitive to this, as the TPE contribution to the cross section has opposite sign for electrons and positrons. While charge asymmetry measurements have been performed on proton targets, no such data exists for nuclear targets. Proposed here is a measurement of the $e^{+}/e^{-}$ charge asymmetry on various nuclei relevant to $\beta$-decay measurements used for CKM matrix extraction. Determining the size of TPE through these processes can provide important constraints on EWRC.

   nucl-ex1 citation
2. 02*

   Polarization transfer in ${\vec{e}}^{+}p\to e^{+}\vec{p}$ scattering using the Super BigBite Spectrometer

   A. J. R. Puckett🇺🇸 · J. C. Bernauer🇺🇸 · A. Schmidt🇺🇸

   The effects of multi-photon-exchange and other higher-order QED corrections on elastic electron-proton scattering have been a subject of high experimental and theoretical interest since the polarization transfer measurements of the proton electromagnetic form factor ratio $G_E^p/G_M^p$ at large momentum transfer $Q^2$ conclusively established the strong decrease of this ratio with $Q^2$ for $Q^2\gtrsim 1$ GeV${}^2$. This result is incompatible with previous extractions of this quantity from cross section measurements using the Rosenbluth Separation technique. Much experimental attention has been focused on extracting the two-photon exchange (TPE) effect through the unpolarized $e^{+}p/e^{-}p$ cross section ratio, but polarization transfer in polarized elastic scattering can also reveal evidence of hard two-photon exchange. Furthermore, it has a different sensitivity to the generalized TPE form factors, meaning that measurements provide new information that cannot be gleaned from unpolarized scattering alone. Both $ϵ$-dependence of polarization transfer at fixed $Q^2$, and deviations between electron-proton and positron-proton scattering are key signatures of hard TPE. A polarized positron beam at Jefferson Lab would present a unique opportunity to make the first measurement of positron polarization transfer, and comparison with electron-scattering data would place valuable constraints on hard TPE. Here, we propose a measurement program in Hall A that combines the Super BigBite Spectrometer for measuring recoil proton polarization, with a non-magnetic calorimetric detector for triggering on elastically scattered positrons. Though the reduced beam current of the positron beam will restrict the kinematic reach, this measurement will have very small systematic uncertainties, making it a clean probe of TPE.

   nucl-exEPJA(2021)·4 citations
3. 03*

   Alpha-decay spectroscopy of ${}^{257}$Rf

   K. Hauschild · A. Lopez-Martens · R. Chakma · O. Dorvaux · B. Gall · M.L. Chelnokov · V.I. Chepigin · A.V. Isaev · I.N. Izosimov · D.E. Katrasev · A.A. Kuznetsova · O.N. Malyshev and 9 other authors

   The decay properties of the ground state and excited states of ${}^{257}$Rf have been investigated with the detector array GABRIELA at the FLNR, Dubna. The electromagnetic decay of a new excited state in ${}^{253}$No has been observed. The state lies 750 keV above the ground state and is favourably populated in the alpha decay of the low-lying spin isomer of ${}^{257}$Rf. It decays to the 9/2${}^{-}$ ground state by an M1 transition and is assigned the 11/2${}^{-}$[725] Nilsson configuration. The presence of this state suggests a possible reinterpretation of the decay of the high-K isomer in ${}^{253}$No.

   nucl-exEPJA(2022)·10 citations
4. 04*

   Helicity Evolution at Small $x$: the Single-Logarithmic Contribution

   Yuri V. Kovchegov🇺🇸 · Andrey Tarasov🇺🇸 · Yossathorn Tawabutr🇺🇸

   We calculate single-logarithmic corrections to the small-$x$ flavor-singlet helicity evolution equations derived recently in the double-logarithmic approximation. The new single-logarithmic part of the evolution kernel sums up powers of ${\alpha }_s\ln (1/x)$, which are an important correction to the dominant powers of ${\alpha }_s{\ln }^2(1/x)$ summed up by the double-logarithmic kernel at small values of Bjorken $x$ and with ${\alpha }_s$ the strong coupling constant. The single-logarithmic terms arise separately from either the longitudinal or transverse momentum integrals. Consequently, the evolution equations we derive employing the light-cone perturbation theory simultaneously include the small-$x$ evolution kernel and the leading-order polarized DGLAP splitting functions. We further enhance the equations by calculating the running coupling corrections to the kernel.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2022)·53 citations
5. 05*

   Symmetry energy extracted from the S$\pi$RIT pion data in Sn+Sn systems

   Gao-Chan Yong🇨🇳

   With the improved particular Isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model (impIBUU) including the nucleon-nucleon short-range correlations, the ratios and yields of ${\pi }^{-}$ and ${\pi }^{+}$ in Sn+Sn systems with different asymmetries at 270 MeV/nucleon are studied. It is found that the yields of ${\pi }^{-}$ and ${\pi }^{+}$ and their ratios in Sn+Sn systems characterized by different neutron to proton ratios obtained from the very recent S$\pi$RIT pion data, are quite well described by the model, especially when a soft symmetry energy with $L({\rho }_0)$ = 66.75$\pm$24.75 MeV is used. The calculations also clearly demonstrate that the high-momentum tail of the nucleon initialization in momentum space strongly affects the yields and ratios of pion production in Sn+Sn systems with different asymmetries near or below threshold. In addition, given many insoluble theoretical uncertainties in transport models, multi-system experimental measurements with various N/Z asymmetries are proposed to extract the symmetry energy less model-dependently by using heavy-ion collisions.

   ↳ nucl-thnucl-exPRC(2021)·24 citations
6. 06*

   Mapping Dirac--Hartree--Fock approach onto relativistic mean field model

   S. Gmuca🇸🇰 · K. Petrik🇸🇰 · J. Leja🇸🇰

   The exchange part of energy density of the linear Dirac--Hartree--Fock (DHF) model in symmetric nuclear matter is evaluated in a parameter--free closed form and expressed as density functional. After the rearranging terms the relativistic mean-field approach with density-dependent couplings may be recovered with density dependence coming from the Fock exchange. The formalism developed, is then extended to the nonlinear DHF approximation with field self-couplings allowed. The nonlinear self--interactions result in essential density dependence (medium modification) of effective couplings that are decoupled from the Fock ones.

   ↳ nucl-thhep-thnucl-ex0 citations
7. 07*

   The multiple-charm hierarchy in the statistical hadronization model

   Anton Andronic🇩🇪 · Peter Braun-Munzinger🇩🇪 · Markus K. Köhler🇩🇪 · Aleksas Mazeliauskas🇨🇭 · Krzysztof Redlich🇵🇱 · Johanna Stachel🇩🇪 · Vytautas Vislavicius🇩🇰

   In relativistic nuclear collisions the production of hadrons with light (u,d,s) quarks is quantitatively described in the framework of the Statistical Hadronization Model (SHM). Charm quarks are dominantly produced in initial hard collisions but interact strongly in the hot fireball and thermalize. Therefore charmed hadrons can be incorporated into the SHM by treating charm quarks as 'impurities' with thermal distributions, while the total charm content of the fireball is fixed by the measured open charm cross section. We call this model SHMc and demonstrate that with SHMc the measured multiplicities of single charm hadrons in lead-lead collisions at LHC energies can be well described with the same thermal parameters as for (u,d,s) hadrons. Furthermore, transverse momentum distributions are computed in a blast-wave model, which includes the resonance decay kinematics. SHMc is extended to lighter collision systems down to oxygen-oxygen and includes doubly- and triply-charmed hadrons. We show predictions for production probabilities of such states exhibiting a characteristic and quite spectacular enhancement hierarchy.

   ↳ hep-phnucl-exnucl-thJHEP(2021)·132 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.