Nuclear Theory·nucl-th

Friday·May 11, 2018

10 papers—4 primary·6 cross-listed

01
Longitudinal fluctuations and decorrelations of anisotropic flows at the LHC and RHIC energies
Xiang-Yu Wu🇨🇳 · Long-Gang Pang🇺🇸 · Guang-You Qin🇨🇳 · Xin-Nian Wang🇨🇳
We perform a systematic study on the decorrelation of anisotropic flows along the pseudorapidity in relativistic heavy-ion collisions at the LHC and RHIC energies. The dynamical evolution of the QGP fireball is simulated via the CLVisc (ideal) (3+1)-dimensional hydrodynamics model, with the fully fluctuating initial condition from A-Multi-Phase-Transport (AMPT) model. Detailed analysis is performed on the longitudinal decorrelations of elliptic, triangular and quadrangular flows in terms of flow vectors, flow magnitudes and flow orientations (event planes). It is found that pure flow magnitudes have smaller longitudinal decorrelation than pure flow orientations, and the decorrelation of flow vectors is a combined effect of both flow magnitudes and orientations. The longitudinal decorrelation of elliptic flow has a strong and non-monotonic centrality dependence due to the initial elliptic collision geometry: smallest decorrelation in mid-central collisions. In contrast, the decorrelations of triangular and quadrangular flows have weak centrality dependence, slightly larger decorrelations in more peripheral collisions. Our numerical results for Pb+Pb collisions at the LHC are in good agreement with the ATLAS data, while our RHIC results predict much larger longitudinal decorrelations as compared to the LHC. We further analyze the longitudinal structures of the AMPT initial conditions and find that the final-state longitudinal decorrelation effects are strongly correlated with the lengths of the initial string structures in the AMPT model. The decorrelation effects are typically larger at lower collision energies and in more peripheral collisions due to shorter lengths of the string structures in the initial states.
nucl-thhep-phnucl-exPRC(2018)·61 citations
02
Modified Skellam, Poisson and Gaussian distributions in semi-open systems at charge-like conservation law
Yuri Sinyukov🇺🇦
A modification of the Skellam and Poisson distributions is proposed for subsystems when the constraints imposed by the charge conservation law in the complete system are taken into account. Such distributions can be applied, for example, for an analysis of the fluctuations of baryon and net baryon numbers in certain pseudo-rapidity interval in $A + A$ and $p + p$ collisions with high multiplicities. The presented modified Skellam, Poisson and Gaussian distributions can be utilized also in various branches of science, when one studies the fluctuations of the two variables related to a subsystem, as well as the distribution of the difference of these variables, while the mentioned difference in the total system is fixed.
nucl-thhep-phphysics.data-an0 citations
03
How to test path-length dependence in energy loss mechanisms: analysis leading to a new observable
Magdalena Djordjevic🇷🇸 · Dusan Zigic🇷🇸 · Marko Djordjevic🇷🇸 · Jussi Auvinen🇷🇸
When traversing QCD medium, high $p_{⊥}$ partons lose energy, which is typically measured by suppression, and also predicted by various energy loss models. A crucial test of different energy loss mechanisms is how the energy loss depends on the length of traversed medium (so-called path-length dependence). The upcoming experimental results will allow to, at least in principle, for the first time, clearly observe how the energy loss changes with the size of the medium, in particular, by comparing already available $P b + P b$ measurements with now upcoming $X e + X e$ data at the LHC. However, in practice, to actually perform such test, it becomes crucial to chose an optimal observable. With respect to this, a ratio of observed suppression for the two systems may seem a natural (and frequently mentioned) choice. We, however, show that extracting the path-length dependence from this observable would not be possible. We here provide an analytical derivation based on simple scaling arguments, as well as detailed numerical calculations based on our advanced energy loss framework, showing that a different observable is suitable for this purpose. We call this observable path-length sensitive suppression ratio ( $R_{L}^{A B}$ ) and provide our predictions before experimental data become available. This predictions also clearly show that this observable will allow a simple comparison of the related theoretical models with the experimental data, and consequently to distinguish between different (underlying) energy loss mechanisms, which is in turn crucial for understanding properties of created QCD medium.
nucl-thhep-phPRC(2019)·31 citations
04
Dissociation of heavy quarkonium states in rapidly varying strong magnetic field
Partha Bagchi🇨🇳 · Nirupam Dutta🇮🇳 · Souvik Priyam Adhya🇮🇳 · Bhaswar Chatterjee🇵🇱
In a transient magnetic field, heavy quarkonium bound states evolve non adiabatically. In presence of a strong magnetic field, $J /Ψ$ and $Υ (1 S)$ become more tightly bound than we expected earlier for a pure thermal medium. We have shown that in a time varying magnetic field, there is a possibility of moderate suppression of $J /Ψ$ through the non adiabatic transition to continuum where as the $Υ (1 S)$ is so tightly bound that can not be dissociated through this process. We have calculated the dissociation probabilities up to the first order in the time dependent perturbation theory for different values of initial magnetic field intensity.
nucl-thhep-phMod.Phys.Lett.A(2023)·13 citations
05
Lattice QCD study of the $H$ dibaryon using hexaquark and two-baryon interpolators
A. Francis🇨🇭 · J.R. Green🇩🇪 · P.M. Junnarkar🇮🇳 · Ch. Miao🇩🇪 · T.D. Rae🇩🇪 · H. Wittig🇩🇪
We present a lattice QCD spectroscopy study in the isospin singlet, strangeness $- 2$ sectors relevant for the conjectured $H$ dibaryon. We employ both local and bilocal interpolating operators to isolate the ground state in the rest frame and in moving frames. Calculations are performed using two flavors of O( $a$ )-improved Wilson fermions and a quenched strange quark. Our initial point-source method for constructing correlators does not allow for bilocal operators at the source; nevertheless, results from using these operators at the sink indicate that they provide an improved overlap onto the ground state in comparison with the local operators. We also present results, in the rest frame, using a second method based on distillation to compute a hermitian matrix of correlators with bilocal operators at both the source and the sink. This method yields a much more precise and reliable determination of the ground-state energy. In the flavor-SU(3) symmetric case, we apply Lüscher's finite-volume quantization condition to the rest-frame and moving-frame energy levels to determine the $S$ -wave scattering phase shift, near and below the two-particle threshold. For a pion mass of 960 MeV, we find that there exists a bound $H$ dibaryon with binding energy $Δ E = (19 \pm 10)$ MeV. In the 27-plet (dineutron) sector, the finite-volume analysis suggests that the existence of a bound state is unlikely.
↳ hep-lathep-phnucl-thPRD(2019)·118 citations
06
$N Ω$ interaction: meson exchanges, inelastic channels, and quasibound state
Takayasu Sekihara (JAEA, Ibaraki)🇯🇵 · Yuki Kamiya (Kyoto U., Yukawa Inst., Kyoto)🇯🇵 · Tetsuo Hyodo (Kyoto U., Yukawa Inst., Kyoto)🇯🇵
Based on a baryon-baryon interaction model with meson exchanges, we investigate the origin of the strong attraction in the $N Ω (^{5} S_{2})$ interaction, which was indicated by recent lattice QCD simulations. The long range part of the potential is constructed by the conventional mechanisms, the exchanges of the $η$ meson and of the correlated two mesons in the scalar-isoscalar channel, denoted by " $σ$ " in the literature. The short range part is represented by the contact interaction. We find that the meson exchanges do not provide sufficient attraction. This means that most of the attraction is attributed to the short range contact interaction. We then evaluate the effect of the coupled channels to the $N Ω (^{5} S_{2})$ interaction. We find that, while the $D$ -wave mixing of the $N Ω$ channel is negligible, the inelastic $ΛΞ$ , $ΣΞ$ , and $ΛΞ (1530)$ channels via the $K$ meson exchange give the attraction of the $N Ω (^{5} S_{2})$ interaction to the same level with the elastic meson exchanges. Although the elimination of these channels induces the energy dependence of the single-channel $N Ω$ interaction, this effect is not significant. With the present model parameters fitted to reproduce the scattering length of the HAL QCD result of the nearly physical quark masses, we obtain the $N Ω (^{5} S_{2})$ quasibound state with its eigenenergy $2611.3 - 0.7 i$ MeV, which corresponds to the binding energy $0.1$ MeV and width $1.5$ MeV for the decay to the $ΛΞ$ and $ΣΞ$ channels. From the analysis of the spatial structure and the compositeness, the quasibound state is shown to be the molecular state of $N Ω$ . We also construct an equivalent local potential for the $N Ω (^{5} S_{2})$ system which is useful for various applications.
↳ hep-phhep-latnucl-thPRC(2018)·43 citations
07
Relaxation Times for Chiral Transport Phenomena and Spin Polarization in Strongly Coupled Plasma
Shiyong Li🇺🇸 · Ho-Ung Yee🇺🇸
We compute the dynamical relaxation times for chiral transport phenomena in strongly coupled regime using the AdS/CFT correspondence. These relaxation times can be a useful proxy for the dynamical time scale for achieving equilibrium spin-polarization of quasi-particles in the presence of magnetic field and fluid vorticity. We identify the Kubo relations for these relaxation times and clarify some previous issues regarding time-dependence of the Chiral Vortical Effect. We study the consequences of imposing time-reversal invariance on parity-odd thermal noise fluctuations that are related to chiral transport coefficients by the fluctuation-dissipation relation. We find that time-reversal invariance dictates the equality between some of the chiral transport coefficients as well as their relaxation times.
↳ hep-thhep-phnucl-thPRD(2018)·10 citations
08
Geometrical scaling for energies available at the BNL Relativistic Heavy Ion Collider to those at the CERN Large Hadron Collider
M.Petrovici🇷🇴 · A.Lindner🇷🇴 · A.Pop🇷🇴 · M.Tarzila🇷🇴 · I.Berceanu🇷🇴
Based on the recent RHIC and LHC experimental results, the $⟨ p_{T} ⟩$ dependence of identified light flavour charged hadrons on $(\frac{d N}{d y}) / S_{⊥}$ , relevant scale in gluon saturation picture, is studied from $s_{N N}$ =7.7 GeV up to 5.02 TeV. This study is extended to the slopes of the $⟨ p_{T} ⟩$ dependence on the particle mass and the $⟨ β_{T} ⟩$ parameter from Boltzmann-Gibbs Blast Wave (BGBW) fits of the $p_{T}$ spectra. A systematic decrease of the slope of the $⟨ p_{T} ⟩$ dependence on $(\frac{d N}{d y}) / S_{⊥}$ from BES to the LHC energies is evidenced. While for the RHIC energies, within the experimental errors, the $⟨ p_{T} ⟩$ / $(\frac{d N}{d y}) / S_{⊥}$ does not depend on centrality, at the LHC energies a deviation from a linear behaviour is observed towards the most central collisions. The influence of the corona contribution to the observed trends is discussed. The slopes of the $⟨ p_{T} ⟩$ particle mass dependence and the $⟨ β_{T} ⟩$ parameter from BGBW fits scale well with $(\frac{d N}{d y}) / S_{⊥}$ . Similar systematic trends for pp at $s$ =7 TeV are in a good agreement with the ones corresponding to Pb-Pb collisions at $s_{N N}$ =2.76 TeV and 5.02 TeV pointing to a system size independent behaviour.
↳ hep-phnucl-thPRC(2018)·13 citations
09
Opacity dependence of elliptic flow in kinetic theory
Aleksi Kurkela🇨🇭 · Urs Achim Wiedemann🇨🇭 · Bin Wu🇨🇭
The observation of large azimuthal anisotropies $v_{n}$ in the particle spectra of proton-proton (pp) and proton-nucleus (pA) collisions challenges fluid dynamic interpretations of $v_{n}$ , as it remains unclear how small collision systems can hydrodynamize and to what extent hydrodynamization is needed to build up $v_{n}$ . Here, we study in a simple kinetic theory how the same physics that leads to hydrodynamization in large systems represents itself in small systems. We observe that one third to one half of the elliptic flow signal seen in fully hydrodynamized systems can be built up in collisions that extend over only one mean free path $l_{mfp}$ and that do not hydrodynamize. This is qualitatively in line with observing a sizeable $v_{2}$ in $pp$ collisions for which other characteristics of soft multi-particle production seem well-described in a free-streaming picture. We further expose a significant system size dependence in the accuracy of hybrid approaches that match kinetic theory to viscous fluid dynamics. The implications of these findings for a reliable extraction of shear viscosity are discussed.
↳ hep-phhep-exnucl-exnucl-thEPJC(2019)·88 citations
10
Third family of compact stars within a nonlocal chiral quark model equation of state
D.E. Alvarez-Castillo🇷🇺 · D.B. Blaschke🇷🇺 · A.G. Grunfeld🇦🇷 · V.P. Pagura🇪🇸
A class of hybrid compact star equations of state is investigated that joins by a Maxwell construction a low-density phase of hadronic matter, modeled by a relativistic meanfield approach with excluded nucleon volume, with a high-density phase of color superconducting two-flavor quark matter, described within a nonlocal covariant chiral quark model. We find the conditions on the vector meson coupling in the quark model under which a stable branch of hybrid compact stars occurs in the cases with and without diquark condensation. We show that these hybrid stars do not form a third family disconnected from the second family of ordinary neutron stars unless additional (de)confining effects are introduced with a density-dependent bag pressure. A suitably chosen density dependence of the vector meson coupling assures that at the same time the $2$ M $_{⊙}$ maximum mass constraint is fulfilled on the hybrid star branch. A twofold interpolation method is realized which implements both, the density dependence of a confining bag pressure at the onset of the hadron-to-quark matter transition as well as the stiffening of quark matter at higher densities by a density-dependent vector meson coupling. For three parametrizations of this class of hybrid equation of state the properties of corresponding compact star sequences are presented, including mass twins of neutron and hybrid stars at 2.00, 1.39 and 1.20 $M_{⊙}$ , respectively. The sensitivity of the hybrid equation of state and the corresponding compact star sequences to variations of the interpolation parameters at the 10% level is investigated and it is found that the feature of third family solutions for compact stars is robust against such a variation. This advanced description of hybrid star matter allows to interpret GW170817 as a merger not only of two neutron stars but also of a neutron star with a hybrid star or of two hybrid stars.
↳ hep-phnucl-thPRD(2019)·129 citations

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