Nuclear Theory·nucl-th

Thursday·May 7, 2020

6 papers—1 primary·5 cross-listed

01
One fluid might not rule them all
You Zhou🇩🇰 · Wenbin Zhao🇨🇳 · Koichi Murase🇨🇳 · Huichao Song🇨🇳
In this proceeding, we present our recent investigations on hydrodynamic collectivity in high-multiplicity proton--proton collisions at $s =$ 13 TeV using the VISHNU hybrid model with different initial condition models, called HIJING, super-MC and TRENTo. We find that with carefully tuned parameters, hydrodynamic simulations can give reasonable descriptions of the measured two-particle correlations. However, multi-particle single and mixed harmonics cumulants can not be described by hydrodynamics with these three initial conditions, even for the signs in a few cases. Further studies show that the non-linear response plays an important role in the hydrodynamic expansion of the p--p systems. Such an effect can change $c_{2} {4}$ from a negative value in the initial state to a positive value in the final state. The failure of the hydrodynamic description of multi-particle cumulant triggers the questions on whether the hydrodynamics can rule all collision systems, including p--p collisions at the LHC.
nucl-thnucl-exNPA(2021)·14 citations
02
Polarized jet fragmentation functions
Zhong-Bo Kang🇺🇸 · Kyle Lee🇺🇸 · Fanyi Zhao🇺🇸
We develop the theoretical framework needed to study the distribution of hadrons with general polarization inside jets, with and without transverse momentum measured with respect to the standard jet axis. The key development in this paper, referred to as "polarized jet fragmentation functions", opens up new opportunities to study both collinear and transverse momentum dependent (TMD) fragmentation functions. As two examples of the developed framework, we study longitudinally polarized collinear $Λ$ and transversely polarized TMD $Λ$ production inside jets in both $pp$ and $e p$ collisions. We find that both observables have high potential in constraining spin-dependent fragmentation functions with sizeable asymmetries predicted, in particular, at the future Electron-Ion Collider.
↳ hep-phhep-exnucl-exnucl-thPLB(2020)·67 citations
03
Heavy quark diffusion in an overoccupied gluon plasma
K. Boguslavski🇦🇹 · A. Kurkela🇨🇭 · T. Lappi🇫🇮 · J. Peuron🇮🇹
We extract the heavy-quark diffusion coefficient \kappa and the resulting momentum broadening <p^2> in a far-from-equilibrium non-Abelian plasma. We find several features in the time dependence of the momentum broadening: a short initial rapid growth of <p^2>, followed by linear growth with time due to Langevin-type dynamics and damped oscillations around this growth at the plasmon frequency. We show that these novel oscillations are not easily explained using perturbative techniques but result from an excess of gluons at low momenta. These oscillation are therefore a gauge invariant confirmation of the infrared enhancement we had previously observed in gauge-fixed correlation functions. We argue that the kinetic theory description of such systems becomes less reliable in the presence of this IR enhancement.
↳ hep-phhep-latnucl-thJHEP(2020)·65 citations
04
Description of the newly observed $Ξ_{c}^{0}$ states as molecular states
HongQiang Zhu🇨🇳 · NaNa Ma🇨🇳 · Yin Huang🇨🇳
Very recently, three new structures $Ξ_{c} (2923)^{0}$ , $Ξ (2938)^{0}$ , and $Ξ (2964)^{0}$ at the invariant mass spectrum of $Λ_{c}^{+} K^{-}$ observed by the LHCb Collaboration triggers a hot discussion about their inner structure. In this work, we study the strong decay mode of the newly observed $Ξ_{c}$ assuming that the $Ξ_{c}$ is a $D ˉ Λ - D ˉ Σ$ molecular state. With the possible quantum numbers $J^{p} = 1/ 2^{\pm}$ and $3/ 2^{\pm}$ , the partial decay widths of the $D ˉ Λ - D ˉ Σ$ molecular state into the $Λ_{c}^{+} K^{-}$ , $Σ_{c}^{+} K^{-}$ ,and $Ξ_{c}^{+} π^{-}$ final states through hadronic loop are calculated with the help of the effective Lagrangians. By comparison with the LHCb observation, the current results of total decay width support the $Ξ (2923)^{0}$ as $D ˉ Λ - D ˉ Σ$ molecule while the decay width of the $Ξ_{c} (2938)^{0}$ and $Ξ (2964)^{0}$ can not be well reproduced in the molecular state picture. In addition, the calculated partial decay widths with $S$ wave $D ˉ Λ - D ˉ Σ$ molecular state picture indicate that allowed decay modes, $Ξ_{c}^{+} π^{-}$ , may have the biggest branching ratios for the $Ξ_{c} (2923)$ . The experimental measurements for this strong decay process could be a crucial test for the molecule interpretation of the $Ξ_{c} (2923)$ .
↳ hep-phnucl-thEPJC(2020)·18 citations
05
Transport and hydrodynamics in the chiral limit
Eduardo Grossi🇺🇸 · Alexander Soloviev🇺🇸 · Derek Teaney🇺🇸 · Fanglida Yan🇺🇸
We analyze the evolution of hydrodynamic fluctuations for QCD matter below $T_{c}$ in the chiral limit, where the pions (the Goldstone modes) must be treated as additional non-abelian superfluid degrees of freedom, reflecting the broken $S U_{L} (2) \times S U_{R} (2)$ symmetry of the theory. In the presence of a finite pion mass $m_{π}$ , the hydrodynamic theory is ordinary hydrodynamics at long distances, and superfluid-like at short distances. The presence of the superfluid degrees of freedom then gives specific contributions to the bulk viscosity, the shear viscosity, and diffusion coefficients of the ordinary theory at long distances which we compute. This determines, in some cases, the leading dependence of the transport parameters of QCD on the pion mass. We analyze the predictions of this computation, as the system approaches the $O (4)$ critical point.
↳ hep-thhep-phnucl-thPRD(2020)·50 citations
06
The global geometrical property of jet events in high-energy nuclear collisions
Shi-Yong Chen🇨🇳 · Wei Dai🇨🇳 · Shan-Liang Zhang🇨🇳 · Qing Zhang🇨🇳 · Ben-Wei Zhang🇨🇳
We present the first theoretical study of medium modifications of the global geometrical pattern, i.e., transverse sphericity ( $S_{⊥}$ ) distribution of jet events with parton energy loss in relativistic heavy-ion collisions. In our investigation, POWHEG+PYTHIA is employed to make an accurate description of transverse sphericity in the p+p baseline, which combines the next-to-leading order (NLO) pQCD calculations with the matched parton shower (PS). The Linear Boltzmann Transport (LBT) model of the parton energy loss is implemented to simulate the in-medium evolution of jets. We calculate the event normalized transverse sphericity distribution in central Pb+Pb collisions at the LHC, and give its medium modifications. An enhancement of transverse sphericity distribution at small $S_{⊥}$ region but a suppression at large $S_{⊥}$ region are observed in A+A collisions as compared to their p+p references, which indicates that in overall the geometry of jet events in Pb+Pb becomes more pencil-like. We demonstrate that for events with 2 jets in the final-state of heavy-ion collisions, the jet quenching makes the geometry more sphere-like with medium-induced gluon radiation. However, for events with $\geq 3$ ~jets, parton energy loss in the QCD medium leads to the events more pencil-like due to jet number reduction, where less energetic jets may lose their energies and then fall off the jet selection kinematic cut. These two effects offset each other and in the end result in more jetty events in heavy-ion collisions relative to that in p+p.
↳ hep-phnucl-exnucl-thEPJC(2020)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE

One fluid might not rule them all

Polarized jet fragmentation functions

Heavy quark diffusion in an overoccupied gluon plasma

Description of the newly observed Ξc0​ states as molecular states

Transport and hydrodynamics in the chiral limit

The global geometrical property of jet events in high-energy nuclear collisions

Affiliations

Description of the newly observed $Ξ_{c}^{0}$ states as molecular states