Tue·Jan 14, 2020Tuesday·January 14, 2020

1. 01*

   Longitudinal flow decorrelations in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV with the ATLAS detector

   ATLAS Collaboration

   The first measurement of longitudinal decorrelations of harmonic flow amplitudes $v_n$ for $n=2$, 3 and 4 in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV is obtained using 3 $\mu {\text{b}}^{-1}$ of data with the ATLAS detector at the LHC. The decorrelation signal for $v_3$ and $v_4$ is found to be nearly independent of collision centrality and transverse momentum ($p_{\mathrm{T}}$) requirements on final-state particles, but for $v_2$ a strong centrality and $p_{\mathrm{T}}$ dependence is seen. When compared with the results from Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, the longitudinal decorrelation signal in mid-central Xe+Xe collisions is found to be larger for $v_2$, but smaller for $v_3$. Current hydrodynamic models reproduce the ratios of the $v_n$ measured in Xe+Xe collisions to those in Pb+Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe+Xe and Pb+Pb. The results on the system-size dependence provide new insights and an important lever-arm to separate effects of the longitudinal structure of the initial state from other early-time and late-time effects in heavy-ion collisions.

   nucl-exhep-exPRL(2021)·68 citations
2. 02*

   Direct determination of neutron lifetime in $\beta$-decay

   Valerius V. Vasiliev

   The neutron lifetime is determined for now most accurately by two methods --the so-called "beam method" and the method of neutron storage in a trap. The goal of this research is to obtain the neutron lifetime with a higher precision by eliminating the traditional systematic errors. A new feature is extracting the neutron lifetime only from the set of electron counting rates with their errors. The newly received neutron lifetime value is $${\tau }_{NT}=883.31\pm 0.02(stat.)\pm 0.02(sys.)\text{mbox}s.$$ The obtained neutron lifetime is the weighted average of two lifetimes, defined for different subsets of neutrons providing the well-known effect of the asymmetry in the neutron $\beta$-decay. Simple calculations predict the values of these lifetimes and show their correspondence to the known asymmetry parameters of neutron decay. The arithmetic mean (central) value for the two newly introduced neutron lifetimes was determined. The resulting weighted value ${\tau }_{NT}$ is in a good agreement with the lifetimes in the first and second methods in limits of their double errors, but exceeds them significantly in precision. In addition, estimates of the new lifetimes, which are called here as $L$-neutron lifetime and $R$-neutron lifetime, are fulfilled. The estimation results correspond to the known parameters of the neutron decay asymmetry. \keywords{neutron \and decay \and channel \and lifetime \and electron \and trap} \PACS{06.30.-k \and 12.90+b \and 13.30Ce \and 14.20.Dh \and 28.20-V \and 29.40 Cs}

   nucl-exphysics.data-an0 citations
3. 03*

   Bayesian inference of the incompressibility, skewness and kurtosis of nuclear matter from empirical pressures in relativistic heavy-ion collisions

   Wen-Jie Xie🇨🇳 · Bao-An Li🇺🇸

   Within the Bayesian statistical framework we infer the incompressibility $K_0$, skewness $J_0$ and kurtosis $Z_0$ parameters of symmetric nuclear matter (SNM) at its saturation density ${\rho }_0$ using the constraining bands on the pressure in cold SNM in the density range of 1.3${\rho }_0$ to 4.5${\rho }_0$ from transport model analyses of kaon production and nuclear collective flow in relativistic heavy-ion collisions. As the default option assuming the $K_0$, $J_0$ and $Z_0$ have Gaussian prior probability distribution functions (PDFs) with the means and variances of $235\pm 30$, $-200\pm 200$ and $-146\pm 1728$ MeV, their posterior most probable values are narrowed down to 192${}_{-16}^{+12}$ MeV, -180${}_{-110}^{+100}$ MeV and 200${}_{-250}^{+250}$ at 68\% confidence level, respectively. The results are largely independent of the prior PDFs of $J_0$ and $Z_0$ used. However, if one adopts the strong belief that the incompressibility $K_0$ has a uniform prior PDF within its absolute boundary of 220-260 MeV as one can find easily in the literature, the posterior most probable values of $K_0$, $J_0$ and $Z_0$ shift to $K_0=220_{-0}^{+6}$ MeV, $J_0=-390_{-70}^{+60}$ MeV and $Z_0=600_{-200}^{+200}$ MeV, respectively. While the posterior PDFs of the SNM EOS parameters depend somewhat on the prior PDF of $K_0$ used, the results from using different prior PDFs are qualitatively consistent. The uncertainties of all three parameters are significantly reduced especially for the $J_0$ and $Z_0$ parameters compared to their current values.

   ↳ nucl-thastro-ph.HEastro-ph.SRnucl-exJ.Phys.G(2021)·35 citations
4. 04*

   Mean Field Quarks on the Light Front

   Christopher Leon🇺🇸 · Misak Sargsian🇺🇸

   We present a new approach for the calculation of the valence quark distributions in the nucleon based on the scenario in which the spectrum of the valence quarks at x>0.05 is generated through three main mechanisms: interaction of valence quarks with the mean field generated by the residual nucleon system, two and three quark short range interactions through gluon exchanges. In the current report we present the first phase of the project in which we develop a non-perturbative model for valence quark interaction in the mean field of the nucleonic interior to describe their distribution in the moderate x region (0.05 < x < 0.4). The short range quark-quark interaction effects in our approach generate the high x tail of valence quark distributions. The presented non-perturbative model is based on the picture in which three relativistic valence quarks occupy the nucleon core at distances of $\le 0.5$ Fm while interacting in the mean field generated by the residual nucleon system. The calculations are based on the assumption of the a factorization of the internal interaction of short-range three valence quarks with the long-range interaction of these quarks with the residual system. The theoretical approach is based on effective light-front diagrammatic approach which allows us to introduce the valence quark and residual system wave functions in a consistent way The parameters of these wave functions are fixed by the position of the peak of the xf_q(x) distribution of valence quarks at Q_0 corresponding to the charm-quark mass. With few parameters we achieved a very reasonable description of the up and down valence quark distributions in the moderate x region (x < 0.4), where one expects the mean field dynamics to dominate. The model, however, systematically underestimates the high $x$ region where enhanced contributions from partonic short-range correlations are expected.

   ↳ hep-phhep-exnucl-exnucl-thPoS(2020)·4 citations
5. 05*

   Nuclear effects in high-energy neutrino interactions

   Spencer R. Klein🇺🇸 · Sally A. Robertson🇺🇸 · Ramona Vogt🇺🇸

   Neutrino telescopes like IceCube, KM3NeT and Baikal-GVD offer physicists the opportunity to study neutrinos with energies far beyond the reach of terrestrial accelerators. These neutrinos are used to study high-energy neutrino interactions and to probe the Earth through absorption tomography. Current studies of TeV neutrinos use cross sections which are calculated for free nucleons with targets which are assumed to contain equal numbers of protons and neutrons. Here we consider modifications of high-energy neutrino interactions due to two nuclear effects: modifications of the parton densities in the nucleus, referred to here as shadowing, and the effect of non-isoscalar targets, with unequal numbers of neutrons and protons. Both these effects depend on the interaction medium. Because shadowing is larger for heavier nuclei, such as iron, found in the Earth's core, it introduces a zenith-angle dependent change in the absorption cross section. These modifications increase the cross sections by 1-2\% at energies below 100 TeV (antishadowing), and reduce it by 3-4\% at higher energies (shadowing). Nuclear effects also alter the inelasticity distribution of neutrino interactions in water/ice by increasing the number of low inelasticity interactions, with a larger effect for $\nu$ than $\bar{\nu }$. These effects are particularly large in the energy range below a few TeV. These effects could alter the cross sections inferred from events with tracks originating within the active detector volume as well as the ratio $\nu /\bar{\nu }$ inferred from inelasticity measurements. The uncertainties in these nuclear effects are larger than the uncertainties on the free-proton cross sections and will thus limit the systematic precision of future high-precision measurements at neutrino telescopes.

   ↳ hep-phastro-ph.HEnucl-exnucl-thPRC(2020)·23 citations
6. 06*

   Determination of centrality in nuclear collisions by using hadron calorimeter

   A. Kurepin (1)🇷🇺 · A. Litvinenko (2)🇷🇺 · E. Litvinenko (2) ((1) Institute for Nuclear Research RAS, Moscow, (2) Joint Institute for Nuclear Research, Dubna)🇷🇺

   The determination of the centrality of nuclear collision or the value of the impact parameter of heavy nuclei is of great importance for the analysis of all experimental data and comparison with theory. One method is to measure the number of spectators using a hadron calorimeter located at a small angle to the nuclear beam. It is shown that with an achievable resolution of the hadron calorimeter in energy, the accuracy of determining the impact parameter is insufficient for using the calorimeter in the MPD / NICA and CBM / FAIR projects. The error reaches 35 % at a beam energy of 2.5 GeV even for peripheral collisions. Secondary processes during the passage of spectators through the nucleus give an additional contribution to the error for central collisions and at medium centralities.

   ↳ hep-exnucl-exPhys.Atom.Nucl.(2020)·4 citations
7. 07*

   Probing impact-parameter dependent nuclear parton densities from double parton scatterings in heavy-ion collisions

   Hua-Sheng Shao🇫🇷

   We propose a new method to determine the spatially or impact-parameter dependent nuclear parton distribution functions (nPDFs) using the double parton scattering (DPS) processes in high-energy heavy-ion (proton-nucleus and nucleus-nucleus) collisions. We derive a simple generic DPS formula in nuclear collisions by accommodating both the nuclear collision geometry and the spatially dependent nuclear modification effect, under the assumption that the impact-parameter dependence of nPDFs is only related to the nuclear thickness function. While the geometric effect is widely adopted, the impact of the spatially dependent nuclear modification on DPS cross sections has been overlooked so far, which can, however, be significant when the initial nuclear modification is large. In turn, the DPS cross sections in heavy-ion collisions can provide useful information on the spatial dependence of nPDFs. They can be, in general, obtained in minimum-bias nuclear collisions, featuring the virtue of independence of Glauber modeling.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2020)·25 citations
8. 08*

   Charged particle track reconstruction with S$\pi$RIT Time Projection Chamber

   J.W. Lee🇰🇷 · G. Jhang🇺🇸 · G. Cerizza🇺🇸 · J. Barney🇺🇸 · J. Estee🇺🇸 · T. Isobe🇯🇵 · M. Kaneko🇯🇵 · M. Kurata-Nishimura🇯🇵 · W.G. Lynch🇺🇸 · T. Murakami🇯🇵 · C.Y. Tsang🇺🇸 · M.B. Tsang🇺🇸 and 9 other authors

   In this paper, we present a software framework, S$\pi$RITROOT, which is capable of track reconstruction and analysis of heavy-ion collision events recorded with the S$\pi$RIT time projection chamber. The track-fitting toolkit GENFIT and the vertex reconstruction toolkit RAVE are applied to a box-type detector system. A pattern recognition algorithm which performs helix track finding and handles overlapping pulses is described. The performance of the software is investigated using experimental data obtained at the Radioactive Isotope Beam Facility (RIBF) at RIKEN. This work focuses on data from ${}^{132}$Sn + ${}^{124}$Sn collision events with beam energy of 270 AMeV. Particle identification is established using $⟨dE/dx⟩$ and magnetic rigidity, with pions, hydrogen isotopes, and helium isotopes.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2020)·16 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.