Nuclear Theory·nucl-th

Friday·April 19, 2019

9 papers—5 primary·4 cross-listed

01
[Submitted on 18 Apr 2019]
Mean-field potential effects in the cumulants of baryons from central Au+Au collision at $E_{l ab}$ = 1.23 GeV $/$ nucleon
Yongjia Wang🇨🇳 · Yunxiao Ye🇨🇳 · QIngfeng Li🇨🇳
The cumulants of baryon multiplicity distribution in relativistic heavy-ion collisions (HICs) have attracted considerable attention recently. It has been conjectured that they may serve as a promising observable to detect the critical end point in the QCD phase diagram, while the cumulants in HICs at intermediate energies have not been widely studied to date. How to interpret the cumulants data at intermediate energies and compare with the data at relativistic energies is now being actively discussed. Both meam-field potential and clustering are highly important to HICs at intermediate energies. In this talk, we discuss these effects on the cumulant ratios of baryon number distributions in Au+Au collisions at beam energies of 1.23 GeV $/$ nucleon which have been currently performed by the HADES Collaboration at GSI. Within the newest version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, calculations with different mean field potentials as well as without mean field potential are performed. It is found that the mean field potential enhances fluctuations in the momentum space during the expanding stage, especially in a small rapidity acceptance window. The enhancement of cumulant ratios for free protons is suppressed compared with that for all baryons.
Comments:
5 pages, 2 figures, To appear in the AIP Conference Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy (January 3 - 7, 2019, Xiamen, China)
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1904.08602 [pdf]
AIP Conf.Proc.(2019)·0 citations
02
[Submitted on 18 Apr 2019]
Two-particle angular correlations in heavy ion collisions from a multiphase transport model
Liu-Yao Zhang🇨🇳 · Jin-Hui Chen🇨🇳 · Zi-Wei Lin🇺🇸 · Yu-Gang Ma🇨🇳 · Song Zhang🇨🇳
We extend our earlier study on two-particle angular correlations in $pp$ collisions at low transverse momentum ( $p_{T}$ ) to $p$ -Pb, Pb-Pb and Au-Au collisions at RHIC and LHC energies. We mainly use the string melting version of a multiphase transport model with improved quark coalescence for this study. We start from the analysis of $π^{\pm}$ , $K^{\pm}$ and $p$ ( $p ˉ$ ) $p_{T}$ and rapidity distributions at different centralities. We then focus on two-particle angular correlations in $p$ -Pb collisions at $s_{NN} = 5.02$ TeV and Pb-Pb collisions at $s_{NN} = 2.76$ TeV. For $p$ -Pb collisions, a near side depression in the angular correlation is observed for low $p_{T}$ proton pairs and $Λ$ pairs but not for pion pairs or kaon pairs, similar to our earlier finding for $pp$ collisions at $s = 7$ TeV. This is also the case for very low multiplicity Pb-Pb and Au-Au collisions. We also find that parton interactions and the improved quark coalescence are mainly responsible for the depression feature in baryon pair angular correlations. However, no such baryon-baryon anti-correlations are observed in Pb-Pb and Au-Au collisions at higher multiplicities. Therefore our results suggest that low $p_{T}$ baryon-baryon angular anti-correlations have a strong multiplicity dependence.
Comments:
10 pages, 15 figures, submit for publication
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1904.08603 [pdf]
PRC(2019)·19 citations
03
[Submitted on 18 Apr 2019]
Medium Modification of Charm Production in Relativistic Heavy Ion Collisions due to Pre-equilibrium Dynamics of Partons at $s_{NN}$ = 0.2--5.02 TeV
Dinesh K. Srivastava · Rupa Chatterjee
We study the production dynamics of charm quarks in the parton cascade model for relativistic heavy ion collisions at RHIC and LHC energies. The model is eminently suited for a study of the pre-equilibrium dynamics of charm quarks at modest transverse momenta. The treatment is motivated by QCD parton picture and describes the dynamics of an ultra-relativistic heavy-ion collision in terms of cascading partons which undergo scattering and multiplication while propagating. We find considerable suppression of charm quarks production in $AA$ collisions compared to those for $pp$ collisions at the same $s_{NN}$ scaled by number of collisions. This may be important for an accurate determination of energy loss suffered by charm quarks while traversing the thermalized quark gluon plasma.
Comments:
8 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.08652 [pdf]
0 citations
04
[Submitted on 18 Apr 2019]
Emergence of hydrodynamical behavior in expanding quark-gluon plasmas
Jean-Paul Blaizot🇫🇷 · Li Yan🇨🇳
We use a set of simple angular moments to solve the Boltzmann equation in the relaxation time approximation for a boost invariant longitudinally expanding gluonic plasma. The transition from the free streaming regime at early time to the hydrodynamic regime at late time is well captured by the first two-moments, corresponding to the monopole and quadrupole components of the momentum distribution, or equivalently to the energy density and the difference between the longitudinal and the transverse pressures. We relate this property to the existence of fixed points in the infinite hierarchy of equations satisfied by the moments. These fixed points are already present in the two-moment truncations and are only moderately affected by the coupling to higher moments. Collisions contribute to a damping of all the non trivial moments. At late time, when the hydrodynamic regime is entered, only the monopole and quadrupole moments are significant and remain strongly coupled, the decay of the quadrupole moment being delayed by the expansion, causing in turn a delay in the full isotropization of the system. The two-moment truncation contains second order viscous hydrodynamics, in its various variants, and third order hydrodynamics, together with explicit values of the relevant transport coefficients, can be easily obtained from the three-moment truncation.
Comments:
59 pages and 20 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1904.08677 [pdf]
Annals Phys.(2020)·76 citations
05
[Submitted on 18 Apr 2019]
Excitation of the electric pygmy dipole resonance by inelastic electron scattering
V.Yu. Ponomarev · D.H. Jakubassa-Amundsen · A. Richter · J. Wambach
To complete earlier studies of the properties of the electric pygmy dipole resonance (PDR) obtained in various nuclear reactions, the excitation of the 1 $^{-}$ states in $^{140}$ Ce by $(e, e^{'})$ scattering for momentum transfers $q = 0.1 - 1.2$ ~fm $^{- 1}$ is calculated within the plane-wave and distorted-wave Born approximations. The excited states of the nucleus are described within the Quasiparticle Random Phase Approximation (QRPA), but also within the Quasiparticle-Phonon Model (QPM) by accounting for the coupling to complex configurations. It is demonstrated that the excitation mechanism of the PDR states in $(e, e^{'})$ reactions is predominantly of transversal nature for scattering angles $θ_{e} \approx 9 0^{o} - 18 0^{o}$ . Being thus mediated by the convection and spin nuclear currents, the $(e, e^{'})$ like the $(γ, γ^{'})$ reaction, may provide additional information to the one obtained from Coulomb- and hadronic excitations of the PDR in $(p, p^{'})$ , $(α, α^{'})$ , and heavy-ion scattering reactions. The calculations predict that the $(e, e^{'})$ cross sections for the strongest individual PDR states are in general about three orders of magnitude smaller as compared to the one of the lowest $2_{1}^{+}$ state for the studied kinematics, but that they may become dominant at extreme backward angles.
Comments:
Prepared for the special issue of EPJA on the topic "Giant, Pygmy, Pairing Resonances and related topics" dedicated to the memory of Pier Francesco Bortignon
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1904.08772 [pdf]
EPJA(2019)·4 citations
06
[Submitted on 29 Jan 2019] (cross-list from hep-ph)
Rare hyperon decays with missing energy
Jusak Tandean🇹🇼
We explore the strangeness-changing decays of the lightest hyperons into another baryon plus missing energy within and beyond the standard model (SM). In the SM these processes arise from the loop-induced quark transition $s \to d ν ν ˉ$ and their branching fractions are estimated to be less than $1 0^{- 11}$ . In the presence of new physics (NP) the rates of these hyperon decays with missing energy could increase significantly with respect to the SM expectations because of modifications to the SM process or contributions from additional modes with new invisible particles. Adopting a model-independent approach and taking into account constraints from the kaon sector, we find that the current data on $K \to π ν ν ˉ$ do not permit sizable NP impact on the hyperon decays via underlying operators having mainly parity-even quark parts. In contrast, NP operators with primarily parity-odd quark parts are much less restricted by the existing bounds on $K \to invisible$ and $K \to π π ν ν ˉ$ and consequently could produce substantially amplifying effects on the hyperon modes. Their NP-enhanced branching fractions could reach levels potentially observable in the ongoing BESIII experiment.
Comments:
16 pages, no figure, slightly enlarged, references added, typos corrected, matches publication
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1901.10447 [pdf]
JHEP(2019)·21 citations
07
[Submitted on 18 Apr 2019] (cross-list from hep-th)
Effective gauge theories of superfluidity with topological order
Yuji Hirono🇰🇷 · Yuya Tanizaki🇺🇸
We discuss the low-energy dynamics of superfluidity with topological order in $(3 + 1)$ spacetime dimensions. We generalize a topological $B F$ theory by introducing a non-square $K$ matrix, and this generalized $B F$ theory can describe massless Nambu-Goldstone bosons and anyonic statistics between vortices and quasiparticles. We discuss the general structure of discrete and continuous higher-form symmetries in this theory, which can be used to classify quantum phases. We describe how to identify the appearance of topological order in such systems and discuss its relation to a mixed 't Hooft anomaly between discrete higher-form symmetries. We apply this framework to the color-flavor locked phase of dense QCD, which shows anyonic particle-vortex statistics while no topological order appears. An explicit example of superfluidity with topological order is discussed.
Comments:
34 pages, no figure; v2: added discussions and Appendix D
Subjects:
High Energy Physics — Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1904.08570 [pdf]
JHEP(2019)·24 citations
08
[Submitted on 18 Apr 2019] (cross-list from hep-ph)
Nonlinear flavor development of a two-dimensional neutrino gas
Joshua D. Martin🇺🇸 · Sajad Abbar🇺🇸 · Huaiyu Duan🇺🇸
We present a numerical survey of the nonlinear flavor development of dense neutrino gases. This study is based on the stationary, two-dimensional ( $x$ and $z$ ), two-beam, monochromatic neutrino line model with a periodic boundary condition along the $x$ direction. Similar to a previous work, we find that small-scale flavor structures can develop in a neutrino gas even if the physical conditions are nearly homogeneous along the $x$ axis initially. The power diffusion from the large-scale to small-scale structures increases with the neutrino density and helps to establish a semi-exponential dependence of the magnitudes of the Fourier moments on the corresponding wave numbers. The overall flavor conversion probabilities in the neutrino gases with small initial sinusoidal perturbations reach certain equilibrium values at large distances which are mainly determined by the neutrino-antineutrino asymmetry. Similar phenomena also exist in a neutrino gas with a localized initial perturbation, albeit only inside an expanding flavor conversion region. Our work suggests that a statistical treatment may be possible for the collective flavor oscillations of a dense neutrino gas in a multi-dimensional environment.
Comments:
10 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1904.08877 [pdf]
PRD(2019)·29 citations
09
[Submitted on 18 Apr 2019] (cross-list from astro-ph.HE)
Constraining the equation of state of high-density cold matter using nuclear and astronomical measurements
M. Coleman Miller (University of Maryland) · Cecilia Chirenti (UFABC) · Frederick K. Lamb (University of Illinois)
The increasing richness of data related to cold dense matter, from laboratory experiments to neutron-star observations, requires a framework for constraining the properties of such matter that makes use of all relevant information. Here, we present a rigorous but practical Bayesian approach that can include diverse evidence, such as nuclear data and the inferred masses, radii, tidal deformabilities, moments of inertia, and gravitational binding energies of neutron stars. We emphasize that the full posterior probability distributions of measurements should be used rather than, as is common, imposing a cut on the maximum mass or other quantities. Our method can be used with any parameterization of the equation of state (EOS). We use both a spectral parameterization and a piecewise polytropic parameterization with variable transition densities to illustrate the implications of current measurements and show how future measurements in many domains could improve our understanding of cold catalyzed matter. We find that different types of measurements will play distinct roles in constraining the EOS in different density ranges. For example, better symmetry energy measurements will have a major influence on our understanding of matter somewhat below nuclear saturation density but little influence above that density. In contrast, precise radius measurements or multiple tidal deformability measurements of the quality of those from GW170817 or better will improve our knowledge of the EOS over a broader density range.
Comments:
31 pages, 14 figures, accepted in The Astrophysical Journal
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
1904.08907 [pdf]
122 citations

Affiliations

first authorsco-authorsvia INSPIRE