Fri·Mar 12, 2021Friday·March 12, 2021

1. 01*

   Direct TPE Measurement via $e^{+}p/e^{-}p$ Scattering at low $\epsilon$ in Hall A

   Ethan Cline🇺🇸 · Jan C. Bernauer🇺🇸 · Axel Schmidt🇺🇸

   The proton elastic form factor ratio can be measured either via Rosenbluth separation in an experiment with unpolarized beam and target, or via the use of polarization degrees of freedom. However, data produced by these two approaches show a discrepancy, increasing with $Q^2$. The proposed explanation of this discrepancy - two-photon exchange - has been tested recently by three experiments. The results support the existence of a small two-photon exchange effect but cannot establish that theoretical treatments at the measured momentum transfers are valid. At larger momentum transfers, theory remains untested, and without further data, it is impossible to resolve the discrepancy. A positron beam at Jefferson Lab allows us to directly measure two-photon exchange over an extended $Q^2$ and $ϵ$ range with high precision. With this, we can validate whether the effect reconciles the form factor ratio measurements, and test several theoretical approaches, valid in different parts of the tested $Q^2$ range. In this proposal, we describe a measurement program in Hall A that combines the Super BigBite, BigBite, and High Resolution Spectrometers to directly measure the two-photon effect. Though the limited 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 two photon exchange.

   nucl-exEPJA(2021)·6 citations
2. 02*

   Probing the Symmetry Energy with the Spectral Pion Ratio

   J. Estee🇺🇸 · W.G. Lynch🇺🇸 · C.Y. Tsang🇺🇸 · J. Barney🇺🇸 · G. Jhang🇺🇸 · M.B. Tsang🇺🇸 · R. Wang🇺🇸 · M. Kaneko🇯🇵 · J.W. Lee🇰🇷 · T. Isobe🇯🇵 · M. Kurata-Nishimura🇯🇵 · T. Murakami🇯🇵 and 51 other authors

   Many neutron star (NS) properties, such as the proton fraction within a NS, reflect the symmetry energy contributions to the Equation of State that dominate when neutron and proton densities differ strongly. To constrain these contributions at supra-saturation densities, we measure the spectra of charged pions produced by colliding rare isotope tin (Sn) beams with isotopically enriched Sn targets. Using ratios of the charged pion spectra measured at high transverse momenta, we deduce the slope of the symmetry energy to be $42<L<117$ MeV. This value is slightly lower but consistent with the $L$ values deduced from a recent measurement of the neutron skin thickness of ${}^{208}$Pb.

   nucl-exPRL(2021)·172 citations
3. 03*

   Weinberg's proposal of 1990: A very personal view

   R. Machleidt🇺🇸

   My personal encounter with Weinberg's proposal of 1990 was a really entertaining one: My collaborator David Entem and I had embarked to show that Weinberg's idea, though smart and beautiful, was essentially useless in practice (like so many of those genius ideas of the 1980s where people claimed to have "derived the nuclear force from QCD"). However, in trying to do so, we showed the opposite; namely, we showed that Weinberg's idea worked better than allowed by any reasonable means.

   ↳ nucl-thhep-phnucl-exphysics.hist-phFew Body Syst.(2021)·7 citations
4. 04*

   A cornucopia of antineutrons and hyperons from super J/psi factory for next-generation nuclear and particle physics high-precision experiments

   Chang-Zheng Yuan🇨🇳 · Marek Karliner🇮🇱

   In order to study the interactions and structure of various types of matter one typically needs to carry out scattering experiments utilizing many different particles as projectiles. Whereas beams of $e^{\pm }$, ${\mu }^{\pm }$, ${\pi }^{\pm }$, $K^{\pm }$, proton, antiproton, and of various heavy ions have been produced and have enabled many scientific breakthroughs, beams of antineutrons, hyperons ($\Lambda$, $\Sigma$ and $\Xi$) and their antiparticles are typically not easy to obtain. Here we point out and investigate a new high-quality source of these particles: a super $J/\psi$ factory with capability of accumulating trillions of $J/\psi$ decays each year. In the relevant $J/\psi$ decays the desired particle is produced together with other final state particles that can be tagged. This allows accurate determination of the flux and momentum of the projectile, enabling unprecedented precision-study of the corresponding interactions with a broad range of targets. These novel high-statistics sources of baryons and antibaryons with precisely known kinematics open fresh opportunities for applications in particle and nuclear physics, including antinucleon-nucleon interaction, nonvalence $s\bar{s}$ component of the nucleon, (anti)hyperon-nucleon interaction, OZI violation, (multi-strange) hypernuclei, exotic light hadron spectroscopy and many others, as well as calibration of Monte Carlo simulation for hadronic and medical physics.

   ↳ hep-exhep-phnucl-exnucl-thPRL(2021)·41 citations
5. 05*

   Implementation of ACTS into sPHENIX track reconstruction

   Joseph D. Osborn🇺🇸 · Anthony D. Frawley🇺🇸 · Jin Huang🇺🇸 · Sookhyun Lee🇺🇸 · Hugo Pereira Da Costa🇫🇷 · Michael Peters🇺🇸 · Chris Pinkenburg🇺🇸 · Christof Roland🇺🇸 · Haiwang Yu🇺🇸

   sPHENIX is a high energy nuclear physics experiment under construction at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory (BNL). The primary physics goals of sPHENIX are to study the quark-gluon-plasma, as well as the partonic structure of protons and nuclei, by measuring jets, their substructure, and heavy flavor hadrons in $p$$+$$p$, $p$+Au, and Au+Au collisions. sPHENIX will collect approximately 300 PB of data over three run periods, to be analyzed using available computing resources at BNL; thus, performing track reconstruction in a timely manner is a challenge due to the high occupancy of heavy ion collision events. The sPHENIX experiment has recently implemented the A Common Tracking Software (ACTS) track reconstruction toolkit with the goal of reconstructing tracks with high efficiency and within a computational budget of 5 seconds per minimum bias event. This paper reports the performance status of ACTS as the default track fitting tool within sPHENIX, including discussion of the first implementation of a time projection chamber geometry within ACTS.

   ↳ physics.ins-dethep-exnucl-exComput.Softw.Big Sci.(2021)·22 citations
6. 06*

   Ab initio computation of the longitudinal response function in ${}^{40}$Ca

   J. E. Sobczyk🇩🇪 · B. Acharya🇩🇪 · S. Bacca🇩🇪 · G. Hagen🇺🇸

   We present a consistent \emph{ab initio} computation of the longitudinal response function $R_L$ in ${}^{40}$Ca using the coupled-cluster and Lorentz integral transform methods starting from chiral nucleon-nucleon and three-nucleon interactions. We validate our approach by comparing our results for $R_L$ in ${}^4$He and the Coulomb sum rule in ${}^{40}$Ca against experimental data and other calculations. For $R_L$ in ${}^{40}$Ca we obtain a very good agreement with experiment in the quasi-elastic peak up to intermediate momentum transfers, and we find that final state interactions are essential for an accurate description of the data. This work presents a milestone towards \emph{ab initio} computations of neutrino-nucleus cross sections relevant for experimental long-baseline neutrino programs.

   ↳ nucl-thhep-exhep-phnucl-exPRL(2021)·57 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.