Nuclear Theory·nucl-th

Friday·July 20, 2018

8 papers—4 primary·4 cross-listed

01
Penetrating probes: Jets and photons in a non-equilibrium quark-gluon plasma
Sigtryggur Hauksson🇨🇦 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦
We employ new field-theoretical tools to study photons and jets in a non-equilibrium quark-gluon plasma. Jet broadening and photon emission takes place through radiation which is suppressed by repeated and coherent interaction with the medium. We analyze this physics in an anisotropic plasma such as is created in the early stages of heavy-ion collisions. The anisotropy introduces an angular dependence in radiation and reduces its overall rate. This can affect phenomenological predictions of the rapidity dependence and angular flow of jets and photons.
nucl-thhep-phNPA(2019)·3 citations
02
Small system studies: A theory overview
Michael Strickland🇺🇸
There is now a substantial body of evidence that a deconfined quark-gluon plasma is created in ultrarelativistic collisions of heavy nuclei. Some key observables which are used to gauge the production of the quark-gluon plasma are the hadronic spectra and multiplicities across many species, azimuthal anisotropies in the production of various hadrons, jet quenching, photon/dilepton production, and heavy quarkonium suppression. A key question in the study of the quark-gluon plasma is what happens to these observables as one changes the system size. In particular, it is very interesting to study collisions of `small systems' such as pp, dA, pA, and $e^{+} e^{-}$ since naively one does not expect to produce a QGP in these cases. One of the surprises from such studies was the existence of sizable azimuthal anisotropies in the hadron spectra in the highest multiplicity classes, which led to speculations that one can generate a QGP in such relatively rare events. This interpretation, however, is complicated by the fact that there can be multiple sources of azimuthal anisotropy. I will discuss our current understanding of the different sources of azimuthal anisotropies and the multiplicity windows in which each mechanism is expected to dominate. I will also provide a critical discussion of the reliability of hydrodynamic models applied to small systems. Finally, I will briefly discuss jet quenching and heavy quarkonium suppression in small systems and discuss whether or not these observables show any indication of the production of a small QGP droplet.
nucl-thhep-phNPA(2019)·40 citations
03
Radiative pion capture in 2H, 3He and 3H
J.Golak · R.Skibinski · K. Topolnicki · H. Witala · A.Grassi · H.Kamada · A.Nogga · L.E.Marcucci
The $π^{-} +^{2} H \to γ + n + n$ , $π^{-} +^{3} He \to γ +^{3} H$ , $π^{-} +^{3} He \to γ + n + d$ , $π^{-} +^{3} He \to γ + n + n + p$ and $π^{-} +^{3} H \to γ + n + n + n$ capture reactions are studied with the AV18 two-nucleon potential and the Urbana~IX three-nucleon potential. We provide for the first time realistic predictions for the differential and total capture rates for all these processes, treating consistently the initial and final nuclear states. Our results are based on the single nucleon Kroll-Ruderman-type transition operator and concentrate on the full treatment of the nuclear final state interactions. They are compared with older theoretical predictions and experimental data.
nucl-thPRC(2018)·10 citations
04
Reliable extraction of the $d B (E1) / d E$ for $^{11}$ Be from its breakup at 520 MeV/nucleon
Laura Moschini🇧🇪 · Pierre Capel🇩🇪
We analyze the breakup of the one-neutron halo nucleus $^{11}$ Be measured at 520 MeV/nucleon at GSI on Pb and C targets within an eikonal description of the reaction including a proper treatment of special relativity. The Coulomb term of the projectile-target interaction is corrected at first order, while its nuclear part is described at the optical limit approximation. Excellent agreement with the data is obtained using a description of $^{11}$ Be, which fits the breakup data of RIKEN. This solves the apparent discrepancy between the $d B (E1) / d E$ estimations from GSI and RIKEN for this nucleus.
nucl-thPLB(2019)·32 citations
05
Proton Isovector Helicity Distribution on the Lattice at Physical Pion Mass
Huey-Wen Lin🇺🇸 · Jiunn-Wei Chen🇹🇼 · Xiangdong Ji🇨🇳 · Luchang Jin🇺🇸 · Ruizi Li🇺🇸 · Yu-Sheng Liu🇨🇳 · Yi-Bo Yang🇺🇸 · Jian-Hui Zhang🇩🇪 · Yong Zhao🇺🇸
We present a state-of-the-art calculation of the isovector quark helicity Bjorken- $x$ distribution in the proton using lattice-QCD ensembles at the physical pion mass. We compute quasi-distributions at proton momenta $P_{z} \in {2.2, 2.6, 3.0}$ ~GeV on the lattice, and match them systematically to the physical parton distribution using large-momentum effective theory (LaMET). We reach an unprecedented precision through high statistics in simulations, large-momentum proton matrix elements, and control of excited-state contamination. The resulting distribution with combined statistical and systematic errors is in agreement with the latest phenomenological analysis of the spin-dependent experimental data; in particular, $Δ u ˉ (x) > Δ d ˉ (x)$ .
↳ hep-lathep-exhep-phnucl-ex+1PRL(2018)·137 citations
06
Bottomonium suppression at RHIC and LHC
Brandon Krouppa🇺🇸 · Alexander Rothkopf🇳🇴 · Michael Strickland🇺🇸
The strong suppression of heavy quarkonia is a good indicator that one has generated a quark-gluon plasma (QGP) in an ultrarelativistic heavy ion collision. Recent advancements in first principles calculations of the heavy quark potential provide additional insight into this suppression and can be used to further pin down the in-medium properties of the QGP. Realistic 3+1d dissipative hydrodynamical models can be used to simulate the QGP and, with bottomonium as a probe, one can make inferences for the initial temperature of the QGP and other phenomenological parameters such as the shear viscosity to entropy density ratio. However, progressing to LHC $s_{N N} = 5.02$ TeV Pb-Pb collisions, one expects regeneration to have an increasingly important impact on the suppression observables. In this proceedings, we present a brief overview to set up the model and then provide model results for bottomonium suppression and regeneration, for ultrarelativistic heavy-ion collision experiments at RHIC and LHC.
↳ hep-phnucl-thNPA(2019)·11 citations
07
Distributions of the largest fragment size in multifragmentation: Traces of a phase transition
J. Brzychczyk🇵🇱 · T. Pietrzak🇵🇱 · A. Wieloch🇵🇱 · W. Trautmann🇩🇪
Distributions of the largest fragment charge are studied using the ALADIN data on fragmentation of $^{197}$ Au projectiles at relativistic energies. The statistical measures skewness and kurtosis of higher-order fluctuations provide a robust indication of the transition point, linked to a phase transition in the thermodynamic limit. Extensive comparisons with predictions of a bond percolation model corroborate the high accuracy of this model in reproducing the distributions as well as the whole fragmentation pattern as represented by the measured charge correlations. In analogy to percolation, the pseudocritical and critical points are identified in the fragmentation data. Questions concerning the distinction between different models and between first- and second-order phase transitions are discussed.
↳ nucl-exnucl-thPRC(2018)·6 citations
08
Quasi-parton distribution functions: two-dimensional scalar and spinor QCD
Xiangdong Ji🇺🇸 · Yizhuang Liu🇺🇸 · Ismail Zahed🇺🇸
We construct the quasi-parton distributions of mesons for two-dimensional QCD with either scalar or spinor quarks using the $1/ N_{c}$ expansion. We show that in the infinite momentum limit, the parton distribution function is recovered in both leading and sub-leading order in $1/ N_{c}$ .
↳ hep-phhep-thnucl-thPRD(2019)·33 citations

Affiliations

first authorsco-authorsvia INSPIRE