Nuclear Theory·nucl-th

Monday·November 28, 2016

18 papers—7 primary·11 cross-listed

01
Equation of state dependence of directed flow in a microscopic transport model
Yasushi Nara🇯🇵 · Harri Niemi🇩🇪 · Jan Steinheimer🇩🇪 · Horst Stoecker🇩🇪
We study the sensitivities of the directed flow in Au+Au collisions on the equation of state (EoS), employing the transport theoretical model JAM. The EoS is modified by introducing a new collision term in order to control the pressure of a system by appropriately selecting an azimuthal angle in two-body collisions according to a given EoS. It is shown that this approach is an efficient method to modify the EoS in a transport model. The beam energy dependence of the directed flow of protons is examined with two different EoS, a first-order phase transition and crossover. It is found that our approach yields quite similar results as hydrodynamical predictions on the beam energy dependence of the directed flow; Transport theory predicts a minimum in the excitation function of the slope of proton directed flow and does indeed yield negative directed flow, if the EoS with a first-order phase transition is employed. Our result strongly suggests that the highest sensitivity for the critical point can be seen in the beam energy range of $4.7 \leq \srtNN \leq 11.5$ GeV.
nucl-thhep-phnucl-exPLB(2017)·56 citations
02
Vorticity in the QGP liquid and hyperon polarization at the RHIC BES energies
Iu. Karpenko🇮🇹 · F. Becattini🇮🇹
We calculate the polarization of $Λ$ hyperons in Au-Au collisions at RHIC Beam Energy Scan range $s_{NN} = 7.7, \dots, 200$ GeV in a state-of-the-art 3+1 dimensional cascade + viscous hydro model vHLLE+UrQMD. We find that the polarization of $Λ$ in the out-of-plane direction decreases substantially with collision energy. We explore the connection between the polarization signal and thermal vorticity and discuss the feed-down and hadronic rescattering effects on the mean polarization of all produced $Λ$ hyperons.
nucl-thJ.Phys.Conf.Ser.(2017)·5 citations
03
Extracting kinetic freeze-out temperature and radial flow velocity from an improved Tsallis distribution
Hai-Ling Lao🇨🇳 · Fu-Hu Liu🇨🇳 · Roy A. Lacey🇺🇸
We analyze the transverse momentum ( $p_{T}$ ) spectra of identified particles ( $π^{\pm}$ , $K^{\pm}$ , $p$ , and $p ˉ$ ) produced in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions over a $s_{N N}$ (center-of-mass energy per nucleon pair) range from 14.5 GeV [one of the Relativistic Heavy Ion Collider (RHIC) energies] to 2.76 TeV [one of the Large Hadron Collider (LHC) energies]. For the spectra with a narrow $p_{T}$ range, an improved Tsallis distribution which is in fact the Tsallis distribution with radial flow is used. For the spectra with a wide $p_{T}$ range, a superposition of the improved Tsallis distribution and an inverse power-law is used. Both the extracted kinetic freeze-out temperature ( $T_{0}$ ) and radial flow velocity ( $β_{T}$ ) increase with the increase of $s_{N N}$ , which indicates a higher excitation and larger expansion of the interesting system at the LHC. Both the values of $T_{0}$ and $β_{T}$ in central collisions are slightly larger than those in peripheral collisions, and they are independent of isospin and slightly dependent on mass.
nucl-thhep-exhep-phnucl-exEPJA(2017)·51 citations
04
Leading order relativistic chiral nucleon-nucleon interaction
Xiu-Lei Ren🇨🇳 · Kai-Wen Li🇨🇳 · Li-Sheng Geng🇨🇳 · Bing-Wei Long🇨🇳 · Peter Ring🇨🇳 · Jie Meng🇨🇳
Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the need for a relativistic chiral force in relativistic nuclear structure studies, we explore a new relativistic scheme to construct the nucleon-nucleon interaction in the framework of covariant chiral effective field theory. The chiral interaction is formulated up to leading order with covariant power counting and a Lorentz invariant chiral Lagrangian. We find that the relativistic scheme induces all six spin operators needed to describe the nuclear force. A detailed investigation of the partial wave potentials shows a better description of the $^{1} S_{0}$ and $^{3} P_{0}$ phase shifts than the leading order Weinberg approach, and similar to that of the next-to-leading order Weinberg approach. For the other partial waves with angular momenta $J \geq 1$ , the relativistic results are almost the same as their leading order non-relativistic counterparts.
nucl-thhep-phCPC(2018)·90 citations
05
Nuclear fragmentation and charge-exchange reactions induced by pions in the $Δ$ -resonance region
Zhao-Qing Feng🇨🇳
Dynamics of the nuclear fragmentations and the charge exchange reactions in pion-nucleus collisions near the $Δ$ (1232) resonance energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. An isospin, momentum and density-dependent pion-nucleon potential is implemented in the model, which influences the pion dynamics, in particular the kinetic energy spectra, but weakly impacts the fragmentation mechanism. The absorption process in pion-nucleon collisions to form the $Δ$ (1232) resonance dominates the heating mechanism of target nucleus. The excitation energy transferred to the target nucleus increases with the pion kinetic energy and is similar for both $π^{-}$ and $π^{+}$ induced reactions. The magnitude of fragmentation of target nucleus weakly depends on the pion energy. The isospin ratio in the pion double charge exchange is influenced by the isospin ingredient of target nucleus.
nucl-thPRC(2016)·17 citations
06
Ab initio calculation of the potential bubble nucleus $^{34}$ Si
T. Duguet🇫🇷 · V. Somà🇫🇷 · S. Lecluse🇧🇪 · C. Barbieri🇬🇧 · P. Navrátil🇨🇦
The possibility that an unconventional depletion in the center of the charge density distribution of certain nuclei occurs due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. We report on ab initio self-consistent Green's function calculations of one of such candidates, $^{34}$ Si, together with its Z+2 neighbour $^{36}$ S. Binding energies, rms radii and density distributions of the two nuclei as well as low-lying spectroscopy of $^{35}$ Si, $^{37}$ S, $^{33}$ Al and $^{35}$ P are discussed. The interpretation of one-nucleon removal and addition spectra in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input inter-nucleon interactions. The prediction regarding the (non-)existence of the bubble structure in $^{34}$ Si varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root mean square radius of $^{36}$ S are well reproduced, along with $^{34}$ Si and $^{36}$ S binding energies, only leaves the NNLO $_{sat}$ Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of $^{34}$ Si, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the 1/2 $^{-}$ -3/2 $^{-}$ splitting in the spectrum of $^{35}$ Si as compared to $^{37}$ S.
nucl-thnucl-exPRC(2017)·74 citations
07
Flow anisotropy due to momentum deposition in ultra-relativistic nuclear collisions
Boris Tomasik🇸🇰 · Martin Schulc🇨🇿
Minijets and jets are produced in large numbers in nuclear collisions at TeV energies, so that there are many of them in a single fireball. They deposit non-negligible amount of momentum and energy into the hydrodynamically expanding bulk and cause anisotropies of the expansion. Moreover, due to their multiple production in a single event the resulting anisotropies are correlated with the collision geometry and thus contribute positively also to event-averaged anisotropies in non-central collisions. Using simulations with three-dimensional ideal hydrodynamic model we demonstrate the importance of this effect. It must be taken into account if conclusions about the properties of the hot matter are to be drawn.
nucl-thhep-phEPJ Web Conf.(2017)·0 citations
08
Backward charmonium production in $π N$ collisions
B. Pire🇫🇷 · K. Semenov-Tian-Shansky🇷🇺 · L. Szymanowski🇵🇱
The QCD collinear factorization framework allows to describe exclusive backward production of a $J / ψ$ meson in pion-nucleon collisions in terms of pion-to-nucleon transition distribution amplitudes. We calculate the scattering amplitude at the leading order in the strong coupling constant and estimate the cross section of this reaction in the backward kinematical region for a medium energy pion beam available at the J-Parc experimental facility.
↳ hep-phhep-exnucl-exnucl-thPRD(2017)·13 citations
09
Renormalization Group Flow, Stability, and Bulk Viscosity in a Large N Thermal QCD Model
Keshav Dasgupta🇨🇦 · Maxim Emelin🇨🇦 · Charles Gale🇨🇦 · Michael Richard🇨🇦
The ultraviolet completion of a large N QCD model requires introducing new degrees of freedom at certain scale so that the UV behavior may become asymptotically conformal with no Landau poles and no UV divergences of Wilson loops. These UV degrees of freedom are represented by certain anti-branes arranged on the blown-up sphere of a warped resolved conifold in a way that they are separated from the other set of branes that control the IR behavior of the theory. This separation of the branes and the anti-branes creates instability in the theory. Further complications arise from the curvature of the ambient space. We show that, despite these analytical hurdles, stability may still be achieved by switching on appropriate world-volume fluxes on the branes. The UV degrees of freedom, on the other hand, modify the RG flow in the model. We discuss this in details by evaluating the flow from IR confining to UV conformal. Finally we lay down a calculational scheme to study bulk viscosity which, in turn, would signal the inherent non-conformality in this model.
↳ hep-thhep-phnucl-thPRD(2017)·3 citations
10
Parity- and Time Reversal-Violating Pion Nucleon Couplings: Higher Order Chiral Matching Relations
Chien-Yeah Seng🇺🇸 · Michael Ramsey-Musolf🇺🇸
Parity- and time reversal-violating (PVTV) pion-nucleon couplings govern the magnitude of long-range contributions to nucleon and atomic electric dipole moments. When these couplings arise from chiral symmetry-breaking CP-violating operators, such as the QCD $θ$ -term or quark chromoelectric dipole moments, one may relate hadronic matrix elements entering the PVTV couplings to nucleon and pion mass shifts by exploiting the corresponding chiral transformation properties at leading order (LO) in the chiral expansion. We compute the higher-order contributions to the lowest order relations arising from chiral loops and next-to-next-to leading order (NNLO) operators. We find that for the QCD $θ$ -term the higher order contributions are analytic in the quark masses, while for the quark chromoelectric dipole moments and chiral symmetry-breaking four-quark operators, the matching relations also receive non-analytic corrections. Numerical estimates suggest that for the isoscalar PVTV pion-nucleon coupling, the higher order corrections may be as large as $\sim 20%$ , while for the isovector coupling, more substantial corrections are possible.
↳ hep-phnucl-thPRC(2017)·20 citations
11
Gauge cooling for the singular-drift problem in the complex Langevin method --- an application to finite density QCD
Keitaro Nagata🇯🇵 · Hideo Matsufuru🇯🇵 · Jun Nishimura🇯🇵 · Shinji Shimasaki🇯🇵
We study full QCD at finite density and low temperature with light quark mass using the complex Langevin method. Since the singular drift problem turns out to be mild on a $4^{3} \times 8$ lattice we use, the gauge cooling is performed only to control the unitarity norm in this exploratory study. We report on our preliminary data obtained from the complex Langevin simulation up to certain Langevin time. While the data are still noisy due to lack of statistics, the onset of the baryon number density seems to occur at larger $μ$ than half the pion mass, which is the value for the phase quenched QCD. The validity of our simulation is tested by the recently proposed criterion based on the probability distribution of the drift term.
↳ hep-lathep-thnucl-thPoS(2016)·17 citations
12
Accessing Generalized Parton Distributions in Exclusive Photoproduction of a $γ ρ$ Pair with a Large Invariant Mass
R. Boussarie🇵🇱 · B. Pire🇫🇷 · L.Szymanowski🇵🇱 · S. Wallon🇫🇷
We propose and study the photoproduction of a $γ ρ$ pair with a large invariant mass and a small transverse momentum of the final nucleon, as a way to access generalized parton distributions. In the kinematics of JLab 12-GeV, we demonstrate the feasibility of this measurement.
↳ hep-phhep-exnucl-exnucl-thAIP Conf.Proc.(2017)·0 citations
13
Influence of broken flavor and C and P symmetry on the quark propagator
Axel Maas🇦🇹 · Walid Ahmed Mian🇦🇹
Embedding QCD into the standard model breaks various symmetries of QCD explicitly, especially C and P. While these effects are usually perturbatively small, they can be amplified in extreme environments like merging neutron stars or by the interplay with new physics. To correctly treat these cases requires fully backcoupled calculations. To pave the way for later investigations of hadronic physics, we study the QCD quark propagator coupled to an explicit breaking. This substantially increases the tensor structure even for this simplest correlation function. To cope with the symmetry structure, and covering all possible quark masses, from the top quark mass to the chiral limit, we employ Dyson-Schwinger equations. While at weak breaking the qualitative effects have similar trends as in perturbation theory, even moderately strong breakings lead to qualitatively different effects, non-linearly amplified by the strong interactions.
↳ hep-phnucl-thEPJA(2017)·2 citations
14
Double quarkonium production at high Feynman- $x$
Sergey Koshkarev🇪🇪 · Stefan Groote🇪🇪
In this paper we give estimates for the proton--proton cross sections into pairs of quarkonium states $J / ψ$ , $ψ (2 S)$ , $Υ (1 S)$ and $Υ (2 S)$ at the scheduled AFTER@LHC energy of $115$ GeV. The estimates are based on the intrinsic heavy flavor mechanism which is observable for high values of $x_{F}$ , a range outside the dominance of single parton and double parton scattering.
↳ hep-phnucl-thNPB(2017)·6 citations
15
Bulk viscous corrections to screening and damping in QCD at high temperatures
Qianqian Du🇨🇳 · Adrian Dumitru🇺🇸 · Yun Guo🇨🇳 · Michael Strickland🇺🇸
Non-equilibrium corrections to the distribution functions of quarks and gluons in a hot and dense QCD medium modify the "hard thermal loops" (HTL). The HTLs determine the retarded, advanced, and symmetric (time-ordered) propagators for gluons with soft momenta as well as the Debye screening and Landau damping mass scales. We compute such corrections to a thermal as well as to a non-thermal fixed point.The screening and damping mass scales are sensitive to the bulk pressure and hence to (pseudo-) critical dynamical scaling of the bulk viscosity in the vicinity of a second-order critical point. This could be reflected in the properties of quarkonium bound states in the deconfined phase and in the dynamics of soft gluon fields.
↳ hep-phhep-thnucl-thJHEP(2017)·32 citations
16
From $J / ψ$ to LHCb pentaquark
F. Fernández🇪🇸 · D. R. Entem🇪🇸 · P. G. Ortega🇪🇸 · J. Segovia🇩🇪
The original charmonium two-body problem, like the $c c ˉ$ structure of the $J / ψ$ meson, has become more involved in the last few years with the discovery of new resonances such as the tentative molecular state $X (3872)$ or the possible pentaquark one $P_{c} (4380)^{+}$ . We discuss herein how these exotic states (and others) can be described in a unified way adding higher Fock state components to the naive quark model picture. In particular, we present our theoretical results on the pentaquark states $P_{c} (4380)^{+}$ and $P_{c} (4450)^{+}$ , and on the new charmonium-like resonances $X (4140)$ , $X (4274)$ , $X (4500)$ and $X (4700)$ that have been reported in $2016$ by the LHCb Collaboration.
↳ hep-phhep-exhep-latnucl-th0 citations
17
From $J / ψ$ to LHCb pentaquarks
F. Fernández🇪🇸 · D. R. Entem🇪🇸 · P. G. Ortega🇪🇸 · J. Segovia🇩🇪
The two exotic $P_{c}^{+} (4380)$ and $P_{c}^{+} (4450)$ discovered in $2015$ by the LHCb Collaboration, together with the four resonances $X (4140)$ , $X (4274)$ , $X (4500)$ and $X (4700)$ , reported in $2016$ by the same collaboration, are described in a constituent quark model which has been able to explain the properties of charmonium states from the $J / ψ$ to the $X (3872)$ . Using this model we found a $D ˉ Σ_{c}^{*}$ bound state with $J^{P} = \frac{3}{2}^{-}$ that may be identified with the $P_{c}^{+} (4380)$ . In the $D ˉ^{*} Σ_{c}$ channel we found three possible candidates for the $P_{c}^{+} (4450)$ with $J^{P} = \frac{1}{2}^{-}$ , $\frac{3}{2}^{-}$ and $\frac{3}{2}^{+}$ with almost degenerated energies. The $X (4140)$ resonance appears as a cusp in the $J / ψ ϕ$ channel due to the near coincidence of the $D_{s}^{\pm} D_{s}^{*\pm}$ and $J / ψ ϕ$ mass thresholds. The remaining three $X (4274)$ , $X (4500)$ and $X (4700)$ resonances appear as conventional charmonium states with quantum numbers $3^{3} P_{1}$ , $4^{3} P_{0}$ and $5^{3} P_{0}$ , respectively; and whose masses and widths are slightly modified due to their coupling with the corresponding closest meson-meson thresholds.
↳ hep-phhep-exhep-latnucl-thPoS(2016)·2 citations
18
Event Shape Sorting: selecting events with similar evolution
Boris Tomasik🇸🇰 · Renata Kopecna🇩🇪
We present novel method for the organisation of events. The method is based on comparing event-by-event histograms of a chosen quantity Q that is measured for each particle in every event. The events are organised in such a way that those with similar shape of the Q-histograms end-up placed close to each other. We apply the method on histograms of azimuthal angle of the produced hadrons in ultrarelativsitic nuclear collisions. By selecting events with similar azimuthal shape of their hadron distribution one chooses events which are likely that they underwent similar evolution from the initial state to the freeze-out. Such events can more easily be compared to theoretical simulations where all conditions can be controlled. We illustrate the method on data simulated by the AMPT model.
↳ physics.data-anhep-exhep-phnucl-ex+1EPJ Web Conf.(2017)·0 citations

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