Nuclear Theory·nucl-th

Monday·February 11, 2019

12 papers—3 primary·9 cross-listed

04
[Submitted on 7 Feb 2019] (cross-list from hep-ph)
Heavy flavour Langevin diffusion with the chromo-electromagnetic field fluctuations in the quark-gluon plasma
Ashik Ikbal Sheikh🇮🇳 · Zubayer Ahammed🇮🇳
The chromo-electromagnetic field is produced due to the motion of partons in a quark-gluon plasma created by relativistic heavy-ion collisions. The fluctuations in the produced chromo-electromagnetic field are important, since they cause heavy quarks to gain energy in the low velocity limit. We study the effect of such fluctuations on heavy quark diffusion in quark-gluon plasma within the framework of Langevin dynamics under the background matter described by the ( $3 + 1$ )-dimensional relativistic viscous hydrodynamics. Theoretical calculations of the nuclear modification factor ( $R_{AA}$ ) of heavy mesons ( $D$ and $B$ mesons), with the effect of these fluctuations, are compared with experimental measurements in $A u - A u$ collisions at $s_{N N} = 200$ GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) and $P b - P b$ collisions at $s_{N N} = 2.76$ and $5.02$ TeV by the ALICE and CMS experiments at the CERN Large Hadron Collider (LHC). We find a significant effect of these fluctuations in describing the the measured $R_{AA}$ of $D$ and $B$ mesons in both RHIC and LHC energies.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1902.02477 [pdf]
EPJA(2020)·5 citations
05
[Submitted on 7 Feb 2019] (cross-list from hep-ph)
$K^{0} Λ$ Photoproduction with Nucleon Resonances
Sang-Ho Kim🇰🇷 · Hyun-Chul Kim🇰🇷
We investigate the reaction mechanism of $K^{0} Λ$ photoproduction off the neutron target, i.e., $γ n \to K^{0} Λ$ , in the range of $W \approx 1.6 - 2.2$ GeV. We employ an effective Lagrangian method at the tree-level Born approximation combining with a Regge approach. As a background, the $K^{*}$ -Reggeon trajectory is taken into account in the $t$ channel and $Λ$ and $Σ$ hyperons in the $u$ -channel Feynman diagram. In addition, the role of various nucleon resonances listed in the Particle Data Group (PDG) is carefully scrutinized in the $s$ channel where the resonance parameters are extracted from the experimental data and constituent quark model. We present our numerical results of the total and differential cross sections and compare them with the recent CLAS data. The effect of the narrow nucleon resonance $N (1685, 1/ 2^{+})$ on cross sections is studied in detail and it turns out that its existence is essential in $K^{0} Λ$ photoproduction to reproduce the CLAS data.
Comments:
4 pages, 3 figures, Proceedings of "8th International Conference on Quarks and Nuclear Physics (QNP2018)", November 13-17, 2018, Tsukuba, Japan
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1902.02553 [pdf]
JPS Conf.Proc.(2019)·0 citations
06
[Submitted on 7 Feb 2019] (cross-list from hep-ph)
Anisotropic pressure of deconfined QCD matter in presence of strong magnetic field within one-loop approximation
Bithika Karmakar🇮🇳 · Ritesh Ghosh🇮🇳 · Aritra Bandyopadhyay🇧🇷 · Najmul Haque🇮🇳 · Munshi G Mustafa🇮🇳
Considering the general structure of the two point functions of quarks and gluons, we compute the free energy and pressure of a strongly magnetized hot and dense QCD matter created in heavy-ion collisions. In presence of strong magnetic field we found that the deconfined QCD matter exhibits a paramagnetic nature. One gets different pressure in a direction parallel and perpendicular to magnetic field due to the magnetization acquired by the system. We obtain both longitudinal and transverse pressure, and magnetization of a hot deconfined QCD matter in presence of magnetic field. We have used hard thermal loop approximation (HTL) for heat bath. We obtained completely analytic expression for pressure and magnetization under certain approximation. Various divergences appearing in free energy are regulated using appropriate counter terms. The obtained anisotropic pressure may be useful for magnetohydrodynamics description of a hot and dense deconfined QCD matter produced in heavy-ion collisions.
Comments:
37 pages, 8 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1902.02607 [pdf]
PRD(2019)·70 citations
07
[Submitted on 7 Feb 2019] (cross-list from nucl-ex)
Evidence for coexisting shapes in $^{98}$ Zr through lifetime measurements
Purnima Singh🇫🇷 · W. Korten🇫🇷 · T. W. Hagen🇳🇴 · A. Görgen🇳🇴 · L. Grente🇫🇷 · M.-D. Salsac🇫🇷 · F. Farget🇫🇷 · E. Clément🇫🇷 · G. de France🇫🇷 · T. Braunroth🇩🇪 · B. Bruyneel🇫🇷 · I. Celikovic🇫🇷 and 26 other authors
The lifetimes of first excited 2 $^{+}$ , 4 $^{+}$ and 6 $^{+}$ states in $^{98}$ Zr were measured with the Recoil-Distance Doppler Shift method in an experiment performed at GANIL. Excited states in $^{98}$ Zr were populated using the fission reaction between a 6.2 MeV/u $^{238}$ U beam and a $^{9}$ Be target. The $γ$ rays were detected with the EXOGAM array in correlation with the fission fragments identified in mass and atomic number in the VAMOS++ spectrometer. Our result shows very small B(E2;2 $_{1}^{+}$ $\to$ 0 $_{1}^{+}$ ) value in $^{98}$ Zr thereby confirming the very sudden onset of collectivity at $N = 60$ . The experimental results are compared to large-scale Monte Carlo Shell model and beyond mean field calculations. The present results indicate coexistence of two additional deformed shapes in this nucleus along with the spherical ground state.
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1902.02637 [pdf]
PRL(2018)·59 citations
08
[Submitted on 8 Feb 2019] (cross-list from hep-ph)
Heavy-quark spin and flavour symmetry partners of the X(3872) revisited: what can we learn from the one boson exchange model?
Ming-Zhu Liu🇨🇳 · Tian-Wei Wu🇨🇳 · Manuel Pavon Valderrama🇨🇳 · Ju-Jun Xie🇨🇳 · Li-Sheng Geng🇨🇳
Heavy-quark symmetry as applied to heavy hadron systems implies that their interactions are independent of their heavy-quark spin (heavy-quark spin symmetry) and heavy flavour contents (heavy flavour symmetry). In the molecular hypothesis the $X (3872)$ resonance is a $1^{++}$ $D^{*} D ˉ$ bound state. If this is the case, the application of heavy-quark symmetry to a molecular $X (3872)$ suggests the existence of a series of partner states, the most obvious of which is a possible $2^{++}$ $D^{*} D ˉ^{*}$ bound state for which the two-body potential is identical to that of the $1^{++}$ $D^{*} D ˉ$ system, the reason being that these two heavy hadron-antihadron states have identical light-spin content. As already discussed in the literature this leads to the prediction of a partner state at $4012 MeV$ , at least in the absence of other dynamical effects which might affect the location of this molecule. However the prediction of further heavy-quark symmetry partners cannot be done solely on the basis of symmetry and requires additional information. We propose to use the one boson exchange model to fill this gap, in which case we will be able to predict or discard the existence of other partner states. Besides the isoscalar $2^{++}$ $D^{*} D ˉ^{*}$ bound state, we correctly reproduce the location and quantum numbers of the isovector hidden-bottom $Z_{b} (10610)$ and $Z_{b} (10650)$ molecular candidates. We also predict the hidden-bottom $1^{++}$ $B^{*} B ˉ^{*}$ and $2^{++}$ $B^{*} B ˉ^{*}$ partners of the $X (3872)$ , in agreement with previous theoretical speculations, plus a series of other states. The isoscalar, doubly charmed $1^{+}$ $D D^{*}$ and $D^{*} D^{*}$ molecules and their doubly bottomed counterparts are likely to bind, providing a few instances of explicitly exotic systems.
Comments:
16 pages, 10 tables, corresponds to published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1902.03044 [pdf]
PRD(2019)·144 citations
09
[Submitted on 8 Feb 2019] (cross-list from hep-ph)
Chiral constraints on the isoscalar electromagnetic spectral functions of the nucleon from leading order vector meson couplings
Y. Ünal🇩🇪 · Ulf-G. Meißner🇩🇪
Using baryon chiral perturbation theory including vector mesons, we analyse various continuum contributions to the isoscalar electromagnetic spectral functions of the nucleon induced by the leading order couplings.
Comments:
12 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1902.03143 [pdf]
PLB(2019)·5 citations
10
[Submitted on 8 Feb 2019] (cross-list from hep-lat)
Symmetries of spatial meson correlators in high temperature QCD
C. Rohrhofer🇦🇹 · Y. Aoki🇯🇵 · G. Cossu🇬🇧 · H. Fukaya🇯🇵 · C. Gattringer🇦🇹 · L.Ya. Glozman🇦🇹 · S. Hashimoto🇯🇵 · C.B. Lang🇦🇹 · S. Prelovsek🇸🇮
Based on a complete set of $J = 0$ and $J = 1$ spatial isovector correlation functions calculated with $N_{F} = 2$ domain wall fermions we identify an intermediate temperature regime of $T \sim 220 - 500$ MeV ( $1.2 T_{c}$ -- $2.8 T_{c}$ ), where chiral symmetry is restored but the correlators are not yet compatible with a simple free quark behavior. More specifically, in the temperature range $T \sim 220 - 500$ MeV we identify a multiplet structure of spatial correlators that suggests emergent $S U (2)_{C S}$ and $S U (4)$ symmetries, which are not symmetries of the free Dirac action. The symmetry breaking effects in this temperature range are less than 5%. Our results indicate that at these temperatures the chromo-magnetic interaction is suppressed and the elementary degrees of freedom are chirally symmetric quarks bound into color-singlet objects by the chromo-electric component of the gluon field. At temperatures between 500 and 660 MeV the emergent $S U (2)_{C S}$ and $S U (4)$ symmetries disappear and one observes a smooth transition to the regime above $T \sim 1$ GeV where only chiral symmetries survive, which are finally compatible with quasi-free quarks.
Comments:
A new figure and discussion added. Accepted for publication in PRD
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1902.03191 [pdf]
PRD(2019)·81 citations
11
[Submitted on 8 Feb 2019] (cross-list from hep-ph)
Thermal contribution of unstable states
Pok Man Lo🇵🇱 · Francesco Giacosa🇵🇱
Within the framework of the Lee model, we analyze in detail the difference between the energy derivative of the phase shift and the standard spectral function of the unstable state. The fact that the model is exactly solvable allows us to demonstrate the construction of these observables from various exact Green functions. The connection to a formula due to Krein, Friedal, and Lloyd is also examined. We also directly demonstrate how the derivative of the phase shift correctly identifies the relevant interaction contributions for consistently including an unstable state in describing the thermodynamics.
Comments:
11 pages, 2 figures, to be submitted to EPJC
Subjects:
High Energy Physics — Phenomenology (hep-ph); Statistical Mechanics (cond-mat.stat-mech); Nuclear Theory (nucl-th)
arXiv:
1902.03203 [pdf]
EPJC(2019)·17 citations
12
[Submitted on 8 Feb 2019] (cross-list from hep-ph)
Jet quenching as a probe of the initial stages in heavy-ion collisions
Carlota Andres🇺🇸 · Néstor Armesto🇪🇸 · Harri Niemi🇫🇮 · Risto Paatelainen🇫🇮 · Carlos A. Salgado🇪🇸
Jet quenching provides a very flexible variety of observables which are sensitive to different energy- and time-scales of the strongly interacting matter created in heavy-ion collisions. Exploiting this versatility would make jet quenching an excellent chronometer of the yoctosecond structure of the evolution process. Here we show, for the first time, that a combination of jet quenching observables is sensitive to the initial stages of heavy-ion collisions, when the approach to local thermal equilibrium is expected to happen. Specifically, we find that in order to reproduce at the same time the inclusive particle production suppression, $R_{AA}$ , and the high- $p_{T}$ azimuthal asymmetries, $v_{2}$ , energy loss must be strongly suppressed for the first $\sim 0.6$ fm. This exploratory analysis shows the potential of jet observables, possibly more sophisticated than the ones studied here, to constrain the dynamics of the initial stages of the evolution.
Comments:
10 pages, 7 figures. Version to be published in PLB. Minor changes in the text and a new appendix containing 4 additional figures added
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1902.03231 [pdf]
PLB(2020)·94 citations

Affiliations

first authorsco-authorsvia INSPIRE