Tue·Jul 19, 2022Tuesday·July 19, 2022

1. 01*

   Nuclear Modification Factor in Small System Collisions within Perturbative QCD Including Thermal Effects

   L.S. Moriggi🇧🇷 · M.V.T. Machado🇧🇷

   In this paper, dedicated to the memory of the late Prof. Jean Cleymans, the nuclear modification factors, $R_{xA}$, are investigated for pion production in small system collisions, measured by PHENIX experiment at RHIC (Relativistic Heavy Ion Collider). The theoretical framework is the transverse momentum $k_T$-factorization formalism for hard processes at small momentum fraction, $x$. Evidence for collective expansion and thermal effects for pions, produced at equilibrium, is studied based on phenomenological parametrization of blast-wave type in the relaxation time approximation. The dependencies on the centrality and on the projectile species are discussed in terms of the behavior of Cronin peak and the suppression of $R_{xA}$ at large transverse momentum, $p_T$. The multiplicity of produced particles, which is sensitive to the soft sector of the spectra, is also included in the present analysis.

   ↳ hep-phhep-exnucl-exMDPI Physics(2022)·4 citations
2. 02*

   Measurement of the Electric Dipole Moment of ${}^{171}$Yb Atoms in an Optical Dipole Trap

   T. A. Zheng · Y. A. Yang · S.-Z. Wang · J. T. Singh🇺🇸 · Z.-X. Xiong · T. Xia🇨🇳 · Z.-T. Lu🇨🇳

   The permanent electric dipole moment (EDM) of the ${}^{171}$Yb $(I=1/2)$ atom is measured with atoms held in an optical dipole trap (ODT). By enabling a cycling transition that is simultaneously spin-selective and spin-preserving, a quantum non-demolition measurement with a spin-detection efficiency of 50$\%$ is realized. A systematic effect due to parity mixing induced by a static E field is observed, and is suppressed by averaging between measurements with ODTs in opposite directions. The coherent spin precession time is found to be much longer than 300 s. The EDM is determined to be $d({}^{171}\mathrm{Yb})=(-6.8\pm 5.1_{\mathrm{stat}}\pm 1.2_{\mathrm{syst}})\times 10^{-27}e\mathrm{cm}$, leading to an upper limit of $|d({}^{171}\mathrm{Yb})|<1.5\times 10^{-26}e\mathrm{cm}$ ($95\%$ C.L.). These measurement techniques can be adapted to search for the EDM of ${}^{225}$Ra.

   ↳ physics.atom-phnucl-exquant-phPRL(2022)·37 citations
3. 03*

   Study of Thin Iron Films for Polarization Analysis of Ultracold Neutrons

   Hiroaki Akatsuka🇯🇵 · Takashi Higuchi🇯🇵 · Sean Hansen-Romu🇨🇦 · Kichiji Hatanaka🇯🇵 · Tomohiro Hayamizu · Masahiro Hino🇯🇵 · Go Ichikawa🇯🇵 · Sohei Imajo🇯🇵 · Blair Jamieson🇨🇦 · Shinsuke Kawasaki🇯🇵 · Masaaki Kitaguchi🇯🇵 · Ryohei Matsumiya🇨🇦 · Kenji Mishima

   The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) collaboration aims to search for the neutron electric dipole moment (nEDM) with unprecedented precision. One of the essential elements for the nEDM measurement is a polarization analyzer of ultracold neutrons (UCNs), whose main component is a magnetized thin iron film. Several thin iron films were deposited on aluminum and silicon ubstrates and were characterized by vibrating sample magnetometry and cold-neutron reflectometry. A magnetic field required to saturate the iron film is $\sim$12 kA/m for those on the aluminum substrates and 6.4 kA/m for the silicon substrates. The magnetic potential of the iron films on the Si substrate was estimated to be 2 T by the neutron reflectometry, which is sufficient performance for an UCN polarization analyzer of the nEDM measurement.

   ↳ physics.ins-detnucl-exJPS Conf.Proc.(2022)·4 citations
4. 04*

   Effective shear and bulk viscosities of the quark-gluon plasma: QCD versus heavy-ion data

   Fernando G. Gardim🇧🇷 · Jean-Yves Ollitrault🇫🇷

   In recent years, there has been a significant effort to extract the temperature-dependent shear ($\eta /s$) and bulk ($\zeta /s$) viscosity over entropy ratios of the quark-gluon plasma from a global comparison of heavy-ion data with results of hydrodynamic simulations. However, anisotropic flow, which is arguably the most sensitive probe of viscosity, is only sensitive to an {\it effective\/} viscosity over entropy ratio, which is obtained by taking a weighted average over the temperature, and summing the contributions of shear and bulk. We estimate this effective viscosity using existing first-principles calculations, which give $0.17<(\eta /s{)}_{\mathrm{eff}}<0.21$, and $(\zeta /s{)}_{\mathrm{eff}}<0.08$, implying that the damping of anisotropic flow at the LHC is mostly due to shear viscosity. The values extracted from global data analyses are compatible with these theory predictions.

   ↳ nucl-thhep-phnucl-exActa Phys.Polon.Supp.(2023)·3 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.