Thu·Aug 13, 2020Thursday·August 13, 2020

1. 01*

   Measurement of the Charge-Averaged Elastic Lepton-Proton Scattering Cross Section by the OLYMPUS Experiment

   J. C. Bernauer🇺🇸 · A. Schmidt🇺🇸 · B. S. Henderson🇺🇸 · L. D. Ice🇺🇸 · D. Khaneft🇩🇪 · C. O'Connor🇺🇸 · R. Russell🇺🇸 · N. Akopov🇦🇲 · R. Alarcon🇺🇸 · O. Ates🇺🇸 · A. Avetisyan🇦🇲 · R. Beck🇩🇪 and 58 other authors

   We report the first measurement of the average of the electron-proton and positron-proton elastic scattering cross sections. This lepton charge-averaged cross section is insensitive to the leading effects of hard two-photon exchange, giving more robust access to the proton's electromagnetic form factors. The cross section was extracted from data taken by the OLYMPUS experiment at DESY, in which alternating stored electron and positron beams were scattered from a windowless gaseous hydrogen target. Elastic scattering events were identified from the coincident detection of the scattered lepton and recoil proton in a large-acceptance toroidal spectrometer. The luminosity was determined from the rates of Møller, Bhabha and elastic scattering in forward electromagnetic calorimeters. The data provide some selectivity between existing form factor global fits and will provide valuable constraints to future fits.

   nucl-exPRL(2021)·16 citations
2. 02*

   A Guided Tour of Ab Initio Nuclear Many-Body Theory

   H. Hergert🇺🇸

   Over the last decade, new developments in Similarity Renormalization Group techniques and nuclear many-body methods have dramatically increased the capabilities of ab initio nuclear structure and reaction theory. Ground and excited-state properties can be computed up to the tin region, and from the proton to the presumptive neutron drip lines, providing unprecedented opportunities to confront two- plus three-nucleon interactions from chiral Effective Field Theory with experimental data. In this contribution, I will give a broad survey of the current status of nuclear many-body approaches, and I will use selected results to discuss both achievements and open issues that need to be addressed in the coming decade.

   ↳ nucl-thnucl-exFront.in Phys.(2020)·306 citations
3. 03*

   Bound-free pair production from nuclear collisions and the steady-state quench limit of the main dipole magnets of the CERN Large Hadron Collider

   Michaela Schaumann🇨🇭 · John M. Jowett🇨🇭 · Cristina Bahamonde Castro🇨🇭 · Roderik Bruce🇨🇭 · Anton Lechner🇨🇭 · Tom Mertens🇨🇭

   During its Run 2 (2015-2018), the Large Hadron Collider (LHC) operated at almost twice higher energy, and provided Pb-Pb collisions with an order of magnitude higher luminosity, than in the previous Run 1. In consequence, the power of the secondary beams emitted from the interaction points by the bound-free pair production (BFPP) process increased by a factor ~20, while the propensity of the bending magnets to quench increased with the higher magnetic field. This beam power is about 35 times greater than that contained in the luminosity debris from hadronic interactions and is focused on specific locations that fall naturally inside superconducting magnets. The risk of quenching these magnets has long been recognized as severe and there are operational limitations due to the dynamic heat load that must be evacuated by the cryogenic system. High-luminosity operation was nevertheless possible thanks to orbit bumps that were introduced in the dispersion suppressors around the ATLAS and CMS experiments to prevent quenches by displacing and spreading out these beam losses. Further, in 2015, the BFPP beams were manipulated to induce a controlled quench, thus providing the first direct measurement of the steady-state quench level of an LHC dipole magnet. The same experiment demonstrated the need for new collimators that are being installed around the ALICE experiment to intercept the secondary beams in the future. This paper discusses the experience with BFPP at luminosities very close to the future High Luminosity LHC (HL-LHC) target, gives results on the risk reduction by orbit bumps and presents a detailed analysis of the controlled quench experiment.

   ↳ physics.acc-phnucl-exPhys.Rev.Accel.Beams(2020)·27 citations
4. 04*

   Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb${}^{-1}$ of Pb+Pb data with the ATLAS detector

   ATLAS Collaboration

   This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses $2.2$ nb${}^{-1}$ of integrated luminosity collected in 2015 and 2018 at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy $E_{\mathrm{T}}^{\gamma }>2.5$ GeV, pseudorapidity $|{\eta }_{\gamma }|<2.37$, diphoton invariant mass $m_{\gamma \gamma }>5$ GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6-100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.

   ↳ hep-exnucl-exJHEP(2021)·240 citations
5. 05*

   The Sivers Asymmetry in Hadronic Dijet Production

   Zhong-Bo Kang🇺🇸 · Kyle Lee🇺🇸 · Ding Yu Shao🇺🇸 · John Terry🇺🇸

   We study the single spin asymmetry in the back-to-back dijet production in transversely polarized proton-proton collisions. Such an asymmetry is generated by the Sivers functions in the incoming polarized proton. We propose a QCD formalism in terms of the transverse momentum dependent parton distribution functions, which allow us to resum the large logarithms that arise in the perturbative calculations. We make predictions for the Sivers asymmetry of hadronic dijet production at the kinematic region that is relevant to the experiment at the Relativistic Heavy Ion Collider (RHIC). We further compute the spin asymmetries in the selected positive and negative jet charge bins, to separate the contributions from $u$- and $d$-quark Sivers functions. We find that both the sign and size of our numerical results are roughly consistent with the preliminary results from the STAR collaboration at the RHIC.

   ↳ hep-phhep-exnucl-exnucl-thJHEP(2021)·29 citations
6. 06*

   Characterization of the SIDDHARTA-2 luminosity monitor

   M. Skurzok🇵🇱 · A. Scordo🇮🇹 · S. Niedzwiecki🇵🇱 · A. Baniahmad · M. Bazzi🇮🇹 · D. Bosnar🇭🇷 · M. Bragadireanu🇷🇴 · M. Carminati🇮🇹 · M. Cargnelli🇦🇹 · A. Clozza🇮🇹 · C. Curceanu🇮🇹 · L. De Paolis🇮🇹 and 20 other authors

   A luminosity monitor, based on plastic scintillator detectors, has been developed for the SIDDHARTA-2 experiment aiming to perform high precision measurements of kaonic atoms and was installed in 2020 on the DAFNE $e^{+}{e}^{-}$ collider at LNF (Laboratori Nazionali di Frascati, INFN). The main goal of this system is to provide the~instantaneous and integrated luminosity of the DAFNE facility by measuring the rate of $K^{+}{K}^{-}$ correlated pairs emitted by the phi meson decay. This task requires an accurate timing of the DAQ signals, as well as timing resolution below 1ns, in order to disentangle the $K^{\pm }$ signals from the background minimum ionizing particles (MIPs) produced during the $e^{+}{e}^{-}$ collisions at DAFNE. In this paper the luminosity monitor concept as well as its laboratory characterization and the first results inside DAFNE are presented.

   ↳ physics.ins-detnucl-exJINST(2020)·48 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.