Nuclear Theory·nucl-th

Thursday·December 24, 2015

14 papers—6 primary·8 cross-listed

01
Anisotropic hydrodynamics for conformal Gubser flow
Michael Strickland🇺🇸 · Mohammad Nopoush🇺🇸 · Radoslaw Ryblewski🇵🇱
In this proceedings contribution, we review the exact solution of the anisotropic hydrodynamics equations for a system subject to Gubser flow. For this purpose, we use the leading-order anisotropic hydrodynamics equations which assume that the distribution function is ellipsoidally symmetric in local-rest-frame momentum. We then prove that the SO(3)_q symmetry in de Sitter space constrains the anisotropy tensor to be of spheroidal form with only one independent anisotropy parameter remaining. As a consequence, the exact solution reduces to the problem of solving two coupled non-linear differential equations. We show that, in the limit that the relaxation time goes to zero, one obtains Gubser's ideal hydrodynamic solution and, in the limit that the relaxation time goes to infinity, one obtains the exact free streaming solution obtained originally by Denicol et al. For finite relaxation time, we solve the equations numerically and compare to the exact solution of the relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using this as our standard, we find that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches.
nucl-thhep-phNPA(2016)·24 citations
02
Multiplicity fluctuations of net protons on the hydrodynamic freeze-out surface
Lijia Jiang🇨🇳 · Pengfei Li🇨🇳 · Huichao Song (Peking U.)🇨🇳
This proceeding briefly summarizes our recent work on calculating the correlated fluctuations of net protons on the hydrodynamic freeze-out surface near the QCD critical point. For both Poisson and Binomial baselines, our calculations could roughly reproduce the energy dependent cumulant $C_{4}$ and $κ σ^{2}$ of net protons, but always over-predict $C_{2}$ and $C_{3}$ due to the positive contributions from the static critical fluctuations.
nucl-thnucl-exNPA(2016)·20 citations
03
Generalization of the model-independent Laurent-Pietarinen single-channel pole-extraction formalism to multiple channels
Alfred Svarc🇭🇷 · Mirza Hadzimehmedovic🇧🇦 · Hedim Osmanovic🇧🇦 · Jugoslav Stahov🇧🇦 · Lothar Tiator🇩🇪 · Ron L. Workman🇺🇸
A method to extract resonance pole information from single-channel partial-wave amplitudes based on a Laurent (Mittag-Leffler) expansion and conformal mapping techniques has recently been developed. This method has been applied to a number of reactions and provides a model-independent extraction procedure which is particularly useful in cases where a set of amplitudes is available only at descrete energies. This method has been generalized and applied to the case of a multi-channel fit, where several sets of amplitudes are analysed simultaneously. The importance of unitarity constraints is discussed. The final result provides a powerful, model-independent tool for analyzing partial-wave amplitudes of coupled or connected channels based entirely on the concepts of analyticity and unitarity.
nucl-thnucl-exPLB(2016)·19 citations
04
Unified description of electron-nucleus scattering within the spectral function formalism
Noemi Rocco🇮🇹 · Alessandro Lovato🇺🇸 · Omar Benhar🇺🇸
We developed a novel approach based on a generalization of factorization and nuclear spectral functions, allowing for a consistent treatment of the amplitudes involving one- and two-nucleon currents, whose contribution to the nuclear electromagnetic response in the transverse channel is known to be significant. We report the results of calculations of the inclusive electron-carbon cross section, showing that the inclusion of processes involving two-nucleon currents appreciably improves the agreement between theory and data in the dip region, between the quasi elastic and $Δ$ -production peaks. The implications for the analysis of neutrino-nucleus cross sections are discussed.
nucl-thhep-exhep-phPRL(2016)·97 citations
05
Lightening-like interactions in nuclear collisions at CERN large hadron collider
Khaled Abdel-Waged🇸🇦 · Nuha Felemban🇸🇦
A simple basic model for describing proton-nucleus (pA) and nucleus-nucleus (AA) collisions has been the intra-nuclear cascade model, where the interactions are simulated by a sequence of binary nucleon-nucleon (NN) collisions. This model helped to establish many scientific concepts and also creates the foundation for more modern simulation codes, especially at low and intermediate energies. In this paper, we present a new Monte Carlo model for pA and AA collisions at high CERN Large Hadron collider energies. The model implements HIJING code with a collective cascade recipe, that induces striking light-like effect in a large nucleus. A single collision (lightening) event is shown to be a complex process:A primary interacting nucleon passes its energy to the surrounding nucleons in a large nucleus. This new simulation code is shown to be good to reproduce the Large Hadron collider (LHC) data, especially the charged particle pseudorapidity density in p+Pb and Pb+Pb collisions at LHC energies.
nucl-thPoS(2015)·0 citations
06
Isovector spin-singlet (T=1, S=0) and isoscalar spin-triplet (T=0, S=1) pairing interactions and spin-isospin response
H. Sagawa (RIKEN, Nishina Center and University of Aizu, Japan)🇯🇵 · C.L. Bai (Sichuan University, Chengdu, China)🇨🇳 · G. Colo' (Universita' degli Studi and INFN, Milano, Italy)🇮🇹
We review several experimental and theoretical advances that emphasise common aspects of the study of T=1 and T=0 pairing correlations in nuclei. We first discuss several empirical evidences of the special role played by the T=1 pairing interaction. In particular, we show the peculiar features of the nuclear pairing interaction in the low density regime, and possible outcomes such as the BCS-BEC crossover in nuclear matter and, in an analogous way, in loosely bound nuclei. We then move to the competition between T=1 and T=0 pairing correlations. The effect of such competition on the low-lying spectra is studied in N=Z odd-odd nuclei by using a three-body model; it is shown that the inversion of the 0+ and 1+ states near the ground state, and the strong magnetic dipole transitions between them, can be considered as a clear manifestation of strong T=0 pairing correlations in these nuclei. The effect of T=0 pairing correlations is also quite evident if one studies charge-changing transitions. The Gamow-Teller (GT) states in N=Z+2 nuclei are studied here by using self-consistent HFB+QRPA calculations in which the T=0 pairing interaction is taken into account. Strong GT states are found, near the ground state of daughter nuclei; these are compared with available experimental data from charge-exchange reactions, and such comparison can pinpoint the value of the strength of the T=0 interaction. Pair transfer reactions are eventually discussed: while two-neutron transfer has been long proposed as a tool to measure the T=1 superfluidity in the nuclear ground states, the study of deuteron transfer is still in its infancy, despite its potential interest in revealing effects coming from both T=1 and T=0 interactions.
nucl-thPhys.Scripta(2016)·51 citations
07
Using Wilson flow to study the SU(3) deconfinement transition
Saumen Datta🇮🇳 · Sourendu Gupta🇮🇳 · Andrew Lytle🇮🇳
We explore the use of Wilson flow to study the deconfinement transition in SU(3) gauge theory. We use the flowed Polyakov loop as a renormalized order parameter for the transition, and use it to renormalize the Polyakov loop. We also study the flow properties of the electric and magnetic gluon condensates, and demonstrate that the difference of the flowed operators shows rapid change across the transition point.
↳ hep-lathep-phnucl-thPRD(2016)·25 citations
08
Mesons in strong magnetic fields: (I) General analyses
Koichi Hattori🇯🇵 · Toru Kojo🇨🇳 · Nan Su🇩🇪
We study properties of neutral and charged mesons in strong magnetic fields |eB|>> Lambda_QCD^2 with Lambda_QCD being the QCD renormalization scale. Assuming long-range interactions, we examine magnetic-field dependences of various quantities such as the constituent quark mass, chiral condensate, meson spectra, and meson wavefunctions by analyzing the Schwinger-Dyson and Bethe-Salpeter equations. Based on the density of states obtained from these analyses, we extend the hadron resonance gas (HRG) model to investigate thermodynamics at large B. As B increases the meson energy behaves as a slowly growing function of the meson's transverse momenta, and thus a large number of meson states is accommodated in the low energy domain; the density of states at low temperature is proportional to B^2. This extended transverse phase space in the infrared regime significantly enhances the HRG pressure at finite temperature, so that the system reaches the percolation or chiral restoration regime at lower temperature compared to the case without a magnetic field; this simple picture would offer a gauge invariant and intuitive explanation of the inverse magnetic catalysis.
↳ hep-phhep-lathep-thnucl-thNPA(2016)·75 citations
09
Modification of generalized vector form factors and transverse charge densities of the nucleon in nuclear matter
Ju-Hyun Jung🇦🇹 · Ulugbek Yakhshiev🇰🇷 · Hyun-Chul Kim🇰🇷
We investigate the medium modification of the generalized vector form factors of the nucleon, which include the electromagnetic and energy-momentum tensor form factors, based on an in-medium modified $π$ - $ρ$ - $ω$ soliton model. We find that the vector form factors of the nucleon in nuclear matter fall off faster than those in free space, which implies that the charge radii of the nucleon become larger in nuclear medium than in free space. We also compute the corresponding transverse charge densities of the nucleon in nuclear matter, which clearly reveal the increasing of the nucleon size in nuclear medium.
↳ hep-phhep-latnucl-thPRD(2016)·10 citations
10
The impact of the medium and the jet-medium coupling on jet measurements at RHIC and LHC
Barbara Betz🇩🇪 · Florian Senzel🇩🇪 · Carsten Greiner🇩🇪 · Miklos Gyulassy🇨🇳
We compare a perturbative QCD-based jet-energy loss model to the measured data of the pion nuclear modification factor and the high-pT elliptic flow at RHIC and LHC energies. This jet-energy loss model (BBMG) is currently coupled to state-of-the-art hydrodynamic descriptions. We report on a model extension to medium backgrounds generated by the parton cascade BAMPS. In addition, we study the impact of realistic medium transverse flow fields and a jet-medium coupling which includes the effects of the jet energy, the temperature of the bulk medium, and non-equilibrium effects close to the phase transition. By contrasting the two different background models, we point out that the description of the high-pT elliptic flow for a non-fluctuating medium requires to include such a jet-medium coupling and the transverse flow fields. While the results for both medium backgrounds show a remarkable similarity, there is an impact of the background medium and the background flow on the high-pT elliptic flow.
↳ hep-phhep-exnucl-th3 citations
11
Double vector meson production in $γ γ$ interactions at hadronic colliders
V. P. Goncalves🇸🇪 · B. D. Moreira🇧🇷 · F. S. Navarra🇧🇷
In this paper we revisit the double vector meson production in $γ γ$ interactions at heavy ion collisions and present, by the first time, predictions for the $ρρ$ and $J /Ψ J /Ψ$ production in proton -- nucleus and proton -- proton collisions. In order to obtain realistic predictions for rapidity distributions and total cross sections for the double vector production in ultra peripheral hadronic collisions we take into account of the description of $γ γ \to V V$ cross section at low energies as well as its behaviour at large energies, associated to the gluonic interaction between the color dipoles. Our results demonstrate that the double $ρ$ production is dominated by the low energy behaviour of the $γ γ \to V V$ cross section. In contrast, for the double $J /Ψ$ production, the contribution associated to the description of the QCD dynamics at high energies contributes significantly, mainly in $pp$ collisions. Predictions for the RHIC, LHC, FCC and CEPC - SPPC energies are shown.
↳ hep-phhep-exnucl-exnucl-thEPJC(2016)·24 citations
12
The $η^{'}$ transition form factor from space- and time-like experimental data
Rafel Escribano🇪🇸 · Sergi Gonzalez-Solis🇪🇸 · Pere Masjuan🇩🇪 · Pablo Sanchez-Puertas🇩🇪
The $η^{'}$ transition form factor is reanalyzed in view of the recent BESIII first observation of the Dalitz decay $η^{'} \to γ e^{+} e^{-}$ in both space- and time-like regions at low and intermediate energies using the Padé approximants method. The present analysis provides a suitable parameterization for reproducing the measured form factor in the whole energy region and allows to extract the corresponding low-energy parameters together with a prediction of its values at the origin, related to $Γ_{η^{'} \to γ γ}$ , and the asymptotic limit. The $η$ - $η^{'}$ mixing is reassessed within a mixing scheme compatible with the large- $N_{c}$ chiral perturbation theory at next-to-leading order, with particular attention to the OZI-rule--violating parameters. The $J / ψ$ , $Z \to η^{(')} γ$ decays are also considered and predictions reported.
↳ hep-phhep-exnucl-thPRD(2016)·105 citations
13
Heavy-flavour transport: from large to small systems
A. Beraudo🇮🇹 · A. De Pace🇮🇹 · M. Monteno🇮🇹 · M. Nardi🇮🇹 · F. Prino🇮🇹
Predictions for heavy-flavour production in relativistic heavy-ion experiments provided by the POWLANG transport setup, including now also an in-medium hadronization model, are displayed, After showing some representative findings for the Au-Au and Pb-Pb cases, a special focus will be devoted to the results obtained in the small systems formed in proton(deuteron)-nucleus collisions, where recent experimental data suggest the possible formation of a medium featuring a collective behaviour.
↳ hep-phnucl-exnucl-thNPA(2016)·1 citation
14
Jet formation and interference in a thin QCD medium
Jorge Casalderrey-Solana🇬🇧 · Daniel Pablos🇪🇸 · Konrad Tywoniuk🇪🇸
In heavy-ion collisions, an abundant production of high-energy QCD jets allows to study how these multiparticle sprays are modified as they pass through the quark-gluon plasma. In order to shed new light on this process, we compute the inclusive two-gluon rate off a hard quark propagating through a color deconfined medium at first order in medium opacity. We explicitly impose an energy ordering of the two emitted gluons, such that the "hard" gluon can be thought of as belonging to the jet substructure while the other is a "soft" emission (which can be collinear or medium-induced). Our analysis focusses on two specific limits that clarify the modification of the additional angle- and formation time-ordering of splittings. In one limit, the formation time of the "hard" gluon is short compared to the "soft" gluon formation time, leading to a probabilistic formula for production of and subsequent radiation off a quark-gluon antenna. In the other limit, the ordering of formation is reverted, which automatically leads to the fact that the jet substructure is resolved by the medium. We observe in this case a characteristic delay: the jet radiates as one color current (quark) up to the formation of the "hard" gluon, at which point we observe the onset of radiation of the new color current (gluon). Our computation supports a picture in which the in-medium jet dynamics are described as a collection of subsequent antennas which are resolved by the medium according to their transverse extent.
↳ hep-phhep-thnucl-thJHEP(2016)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE