Tue·Mar 10, 2020Tuesday·March 10, 2020

1. 01*

   Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ATLAS detector

   ATLAS Collaboration

   Azimuthal anisotropies of muons from charm and bottom hadron decays are measured in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. The data were collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2018 with integrated luminosities of $0.5{\mathrm{nb}}^{-1}$ and $1.4\mathrm{n}{\mathrm{b}}^{-1}$, respectively. The kinematic selection for heavy-flavor muons requires transverse momentum $4<p_{\mathrm{T}}<30$ GeV and pseudorapidity $|\eta |<2.0$. The dominant sources of muons in this $p_{\mathrm{T}}$ range are semi-leptonic decays of charm and bottom hadrons. These heavy-flavor muons are separated from light-hadron decay muons and punch-through hadrons using the momentum imbalance between the measurements in the tracking detector and in the muon spectrometers. Azimuthal anisotropies, quantified by flow coefficients, are measured via the event-plane method for inclusive heavy-flavor muons as a function of the muon $p_{\mathrm{T}}$ and in intervals of Pb+Pb collision centrality. Heavy-flavor muons are separated into contributions from charm and bottom hadron decays using the muon transverse impact parameter with respect to the event primary vertex. Non-zero elliptic ($v_2$) and triangular ($v_3$) flow coefficients are extracted for charm and bottom muons, with the charm muon coefficients larger than those for bottom muons for all Pb+Pb collision centralities. The results indicate substantial modification to the charm and bottom quark angular distributions through interactions in the quark-gluon plasma produced in these Pb+Pb collisions, with smaller modifications for the bottom quarks as expected theoretically due to their larger mass.

   nucl-exhep-exPLB(2020)·61 citations
2. 02*

   Polarization and Vorticity in the Quark Gluon Plasma

   Francesco Becattini🇮🇹 · Michael Lisa🇺🇸

   The quark-gluon plasma produced by collisions between ultra-relativistic heavy nuclei is well described in the language of hydrodynamics. Non-central collisions are characterized by very large angular momentum, which in a fluid system manifests as flow vorticity. This rotational structure can lead to a spin polarization of the hadrons that eventually emerge from the plasma, providing experimental access to flow substructure at unprecedented detail. Recently, first observations of $\Lambda$ hyperon polarization along the direction of collisional angular momentum have been reported. These measurements are in broad agreement with hydrodynamic and transport-based calculations and reveal that the QGP is the most vortical fluid ever observed. However, there remain important tensions between theory and observation which might be fundamental in nature. In the relatively mature field of heavy ion physics, the discovery of global hyperon polarization and three-dimensional simulations of the collision have opened an entirely new direction of research. We discuss the current status of this rapidly developing area and directions for future research.

   nucl-exhep-phnucl-thAnn.Rev.Nucl.Part.Sci.(2020)·305 citations
3. 03*

   Reinterpretation of classic proton charge form factor measurements

   Miha Mihovilovic🇸🇮 · Douglas W. Higinbotham🇺🇸 · Melisa Bevc🇸🇮 · Simon Sirca🇸🇮

   In 1963, a proton radius of $0.805(11)\mathrm{fm}$ was extracted from electron scattering data and this classic value has been used in the standard dipole parameterization of the form factor. In trying to reproduce this classic result, we discovered that there was a sign error in the original analysis and that the authors should have found a value of $0.851(19)\mathrm{fm}$. We additionally made use of modern computing power to find a robust function for extracting the radius using this 1963 data's spacing and uncertainty. This optimal function, the Padé $(0,1)$ approximant, also gives a result which is consistent with the modern high precision proton radius extractions.

   nucl-exphysics.data-anFront.in Phys.(2020)·7 citations
4. 04*

   Physical features of strength of isoscalar pairing interaction determined by relation between double charge change and double pair transfer

   J. Terasaki🇨🇿

   A new method has been proposed to determine the strength of the isoscalar proton-neutron pairing interaction applicable to many nuclei. The principle is the equivalence between the double charge change and the double transfer of like-particle pair, and a constraint is derived to the effective interactions used in approximations. This method was applied to the quasiparticle random-phase approximation for determining that interaction strength. In this paper, detail of this method is explained thoroughly, and applications are made to nuclei of several instances of the double-$\beta$ decays. The systematics of the strengths determined for those nuclei is understood in terms of a midshell effect. The effect of the new interaction strength is examined in two examples of the Gamow-Teller strength function with comparisons with the experimental data. The nuclear matrix elements of the neutrinoless double-$\beta$ decay are also calculated.

   ↳ nucl-thnucl-exPRC(2020)·41 citations
5. 05*

   Investigation of electroproduction of $\varphi$ mesons off protons

   Sang-Ho Kim🇰🇷 · Seung-il Nam🇰🇷

   We investigate $\varphi$-meson electroproduction off the proton target, i.e., ${\gamma }^{\ast }p\to \varphi p$, by employing a tree-level effective Lagrangian approach in the kinematical ranges of $Q^2$ = (0$-$4) ${\mathrm{GeV}}^2$, $W$ = (2$-$5) GeV, and $|t|\le 2{\mathrm{GeV}}^2$. In addition to the universally accepted Pomeron exchange, we consider various meson exchanges in the $t$ channel with the Regge method. Direct $\varphi$-meson radiations in the $s$- and $u$-channels are also taken into account. We find that the $Q^2$ dependence of the transverse (${\sigma }_{\mathrm{T}}$) and longitudinal (${\sigma }_{\mathrm{L}}$) cross sections are governed by Pomeron and $(a_0,f_0)$ scalar meson exchanges, respectively. Meanwhile, the contributions of $(\pi ,\eta )$ pseudoscalar- and $f_1(1285)$ axial-vector-meson exchanges are much more suppressed. The results of the interference cross sections (${\sigma }_{\mathrm{LT}},{\sigma }_{\mathrm{LT}}$) and the spin-density matrix elements indicate that $s$-channel helicity conservation holds at $Q^2$ = (1$-$4) ${\mathrm{GeV}}^2$. The result of the parity asymmetry yield $P\simeq 0.95$ at $W$ = 2.5 GeV, meaning that natural-parity exchange dominates the reaction process. Our numerical results are in fair agreement with the experimental data and thus the use of our effective Reggeized model is justified over the considered kinematical ranges of $Q^2$, $W$, and $t$.

   ↳ hep-phhep-exnucl-exPRC(2020)·9 citations
6. 06*

   Energy resolution and linearity of XENON1T in the MeV energy range

   E. Aprile · J. Aalbers · F. Agostini · M. Alfonsi · L. Althueser · F. D. Amaro · V. C. Antochi · E. Angelino · J. Angevaare · F. Arneodo · D. Barge · L. Baudis and 126 other authors

   Xenon dual-phase time projection chambers designed to search for Weakly Interacting Massive Particles have so far shown a relative energy resolution which degrades with energy above $\sim$200 keV due to the saturation effects. This has limited their sensitivity in the search for rare events like the neutrinoless double-beta decay of ${}^{136}$Xe at its $Q$-value, $Q_{\beta \beta }\simeq$ 2.46 MeV. For the XENON1T dual-phase time projection chamber, we demonstrate that the relative energy resolution at 1 $\sigma /\mu$ is as low as (0.80$\pm$0.02) % in its one-ton fiducial mass, and for single-site interactions at $Q_{\beta \beta }$. We also present a new signal correction method to rectify the saturation effects of the signal readout system, resulting in more accurate position reconstruction and indirectly improving the energy resolution. The very good result achieved in XENON1T opens up new windows for the xenon dual-phase dark matter detectors to simultaneously search for other rare events.

   ↳ physics.ins-detastro-ph.IMhep-exnucl-exEPJC(2020)·108 citations
7. 07*

   Effective field theory for triaxially deformed odd-mass nuclei

   Q. B. Chen🇩🇪 · N. Kaiser🇩🇪 · Ulf-G. Meißner🇩🇪 · J. Meng🇨🇳

   The effective field theory for collective rotations of triaxially deformed nuclei is generalized to odd-mass nuclei by including the angular momentum of the valence nucleon as an additional degree of freedom. The Hamiltonian is constructed up to next-to-leading order within the effective field theory formalism. The applicability of this Hamiltonian is examined by describing the wobbling bands observed in the lutetium isotopes ${}^{161,163,165,167}$Lu. It is found that by taking into account the next-to-leading order corrections, quartic in the rotor angular momentum, the wobbling energies $E_{\text{wob}}$ and spin-rotational frequency relations $\omega (I)$ are better described than with the leading order Hamiltonian.

   ↳ nucl-thhep-phnucl-ex7 citations
8. 08*

   Transverse single-spin asymmetry for very forward neutral pion production in polarized $p+p$ collisions at $\sqrt{s}=510$ GeV

   M.H. Kim🇰🇷 · O. Adriani🇮🇹 · E. Berti🇮🇹 · L. Bonechi🇮🇹 · R. D'Alessandro🇮🇹 · Y. Goto🇯🇵 · B. Hong🇰🇷 · Y. Itow🇯🇵 · K. Kasahara🇯🇵 · H. Menjo🇯🇵 · I. Nakagawa🇯🇵 · J.S. Park🇯🇵 and 13 other authors

   Transverse single-spin asymmetries of very forward neutral pions generated in polarized $p+p$ collisions allow us to understand the production mechanism in terms of perturbative and non-perturbative strong interactions. During 2017 the RHICf Collaboration installed an electromagnetic calorimeter in the zero-degree region of the STAR detector at the Relativistic Heavy Ion Collider (RHIC) and measured neutral pions produced at pseudorapidity larger than 6 in polarized $p$+$p$ collisions at $\sqrt{s}$ = 510 GeV. The large non-zero asymmetries increasing both in longitudinal momentum fraction $x_F$ and transverse momentum $p_T$ have been observed at low transverse momentum $p_T<1$ GeV/$c$ for the first time at this collision energy. The asymmetries show an approximate $x_F$ scaling in the $p_T$ region where non-perturbative processes are expected to dominate. A non-negligible contribution from soft processes may be necessary to explain the nonzero neutral pion asymmetries.

   ↳ hep-exnucl-exPRL(2020)·23 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.