Nuclear Theory·nucl-th

Friday·September 20, 2024

13 papers—7 primary·6 cross-listed

08
[Submitted on 13 Sept 2024] (cross-list from hep-ph)
Nonequilibrium Phenomenology of Identified Particle Spectra in Heavy-Ion Collisions at LHC Energies
Oleksandr Vitiuk🇵🇱 · David Blaschke🇵🇱 · Benjamin Dönigus🇩🇪 · Gerd Röpke🇩🇪
We employ the Zubarev approach of the non-equilibrium statistical operator to investigate the enhancement of the low- $p_{T}$ region of pion spectra, introducing an effective pion chemical potential to describe the overpopulation of low-energy pion states. We test a corresponding freeze-out approach by analyzing the transverse-momentum spectra of identified particles measured recently with high precision by the ALICE Collaboration in Pb+Pb collisions at CERN LHC. A blast-wave model and a blast-wave-based particle generator, coupled to a hadronic transport model, are utilized. Bayesian inference methods are applied to extract the most probable sets of thermodynamic parameters at the chemical freeze-out hypersurface. Both models for the overpopulated pion states, the hadronic transport model and the thermal model with a nonzero pion chemical potential, provide a satisfactory description of the observed pion spectra. However, both approaches contain approximations which can be improved within a systematic nonequilibrium approach. We demonstrate that the introduction of a nonequilibrium pion chemical potential offers an efficient alternative to the conventional explanation of the low- $p_{T}$ enhancement, typically attributed to resonance decays with subsequent thermalization. A similar discussion holds also for the kaon spectra.
Comments:
8 pages, 3 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2409.09019 [pdf]
PRC(2026)·3 citations
09
[Submitted on 18 Sept 2024] (cross-list from hep-ph)
$ν$ -point energy correletors with FastEEC: small- $x$ physics from LHC jets
Ankita Budhraja🇳🇱 · Hao Chen🇺🇸 · Wouter J. Waalewijn🇳🇱
In recent years, energy correlators have emerged as a powerful tool for studying jet substructure, with promising applications such as probing the hadronization transition, analyzing the quark-gluon plasma, and improving the precision of top quark mass measurements. The projected $N$ -point correlator measures correlations between $N$ final-state particles by tracking the largest separation between them, showing a scaling behavior related to DGLAP splitting functions. These correlators can be analytically continued in $N$ , commonly referred to as $ν$ -correlators, allowing access to non-integer moments of the splitting functions. Of particular interest is the $ν \to 0$ limit, where the small momentum fraction behavior of the splitting functions requires resummation. Originally, the computational complexity of evaluating $ν$ -correlators for $M$ particles scaled as $2^{2 M}$ , making it impractical for real-world analyses. However, by using recursion, we reduce this to $M 2^{M}$ , and through the FastEEC method of dynamically resolving subjets, $M$ is replaced by the number of subjets. This breakthrough enables, for the first time, the computation of $ν$ -correlators for LHC data. In practice, limiting the number of subjets to 16 is sufficient to achieve percent-level precision, which we validate using known integer- $ν$ results and convergence tests for non-integer $ν$ . We have implemented this in an update to FastEEC and conducted an initial study of power-law scaling in the perturbative regime as a function of $ν$ , using CMS Open Data on jets. The results agree with DGLAP evolution, except at small $ν$ , where the anomalous dimension saturates to a value that matches the BFKL anomalous dimension.
Comments:
16 pages, 6 figures. v2: journal version. Associated code available at: https://github.com/abudhraj/FastEEC/releases/tag/0.2
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2409.12235 [pdf]
PLB(2025)·13 citations
10
[Submitted on 18 Sept 2024] (cross-list from hep-ph)
Towards an unbiased jet energy loss measurement
Liliana Apolinário🇵🇹 · Lénea Luís🇵🇹 · José Guilherme Milhano🇵🇹 · João M. Silva🇵🇹
The modifications imprinted on jets due to their interaction with Quark Gluon Plasma (QGP) are assessed by comparing samples of jets produced in nucleus-nucleus collisions and proton-proton collisions. The standard procedure ignores the effect of bin migration by comparing specific observables for jet populations at the same reconstructed jet transverse momentum ( $p_{T}$ ). Since jet $p_{T}$ is itself modified by interaction with QGP, all such comparisons confound QGP induced modifications with changes that are simply a consequence of comparing jets that started out differently. The quantile matching procedure introduced by Brewer et al. directly estimates average fractional jet energy loss ( $Q_{AA}$ ) and can thus mitigate this $p_{T}$ migration effect. In this work, we validate the procedure in more realistic scenarios that include medium response. We study the evolution of $Q_{AA}$ with jet radius, its sensitivity to minimum particle $p_{T}$ and medium response as implemented in two different models for jet evolution in heavy-ion collisions. Further, we use this procedure to establish that the difference between inclusive jet and $γ +$ jet nuclear modification factors ( $R_{AA}$ ) is dominated by differences in the spectral shape, leaving the colour charge of the jet initiating parton with a lesser role to play. Additionally, we compare $Q_{AA}$ to an experimentally proposed proxy for fractional jet energy loss, $S_{l oss}$ , showing that both quantities are similar, although the former provides a more clear physical interpretation. Finally, we show the size of the $p_{T}$ migration correction for four different substructure observables and how to reliably use the quantile procedure experimentally to improve existing measurements.
Comments:
29 pages, 10 figures, reference added
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2409.12238 [pdf]
JHEP(2025)·7 citations
11
[Submitted on 18 Sept 2024] (cross-list from hep-ph)
Magnetized neutral 2SC color superconductivity and possible origin of the inner magnetic field of magnetars
Shuai Yuan🇨🇳 · Bo Feng🇨🇳 · Efrain J. Ferrer🇺🇸 · Alejandro Pinero🇺🇸
In this paper the neutral 2SC phase of color superconductivity is investigated in the presence of a magnetic field and for diquark coupling constants and baryonic densities that are expected to characterize neutron stars. Specifically, the behavior of the charged gluons Meissner masses is investigated in the parameter region of interest taking into account, in addition, the contribution of a rotated magnetic field. It is found that up to moderately-high diquark coupling constants the mentioned Meissner masses become tachyonic independently of the applied magnetic-field amplitude, hence signalizing the chromomagnetic instability of this phase. To remove the instability, the restructuring of the system ground state is proposed, which now will be formed by vortices of the rotated charged gluons. These vortices boost the applied magnetic field having the most significant increase for relatively low applied magnetic fields. Finally, considering that with the stellar rotational frequency observed for magnetars a field of the order of $1 0^{8}$ G can be generated by dynamo effect, we show that by the boosting effect just described the field can be amplified to $1 0^{17}$ G that is in the range of inner core fields expected for magnetars. Thus, we conclude that the described mechanism could be the one responsible for the large fields characterizing magnetars if the cores of these compact objects are formed by neutral 2SC matter.
Comments:
14 pages, 7 figures; Version appeared in PRD
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
2409.12356 [pdf]
PRD(2024)·5 citations
12
[Submitted on 19 Sept 2024] (cross-list from hep-ph)
Medium modifications of heavy-flavor jet angularities in high-energy nuclear collisions
Yao Li🇨🇳 · Shi-Yong Chen🇨🇳 · Wei-Xi Kong🇨🇳 · Sa Wang🇨🇳 · Ben-Wei Zhang🇨🇳
We present the first theoretical study of heavy-flavor jet angularities ( $λ_{α}^{κ}$ ) in Pb+Pb collisions at $s_{NN} =$ 5.02 TeV. The initial production of heavy-flavor jets is carried out using the POWHEG+PYTHIA8 prescription, while the jet evolution in the quark-gluon plasma (QGP) is described by the SHELL transport model. In p+p collisions, we observe narrower angularity distributions for D $^{0}$ -tagged jets compared to inclusive jets, consistent with the ALICE preliminary results. We then demonstrate that jet quenching in the QGP slightly widens the angularity distribution of D $^{0}$ -tagged jets in Pb+Pb collisions relative to that in p+p collisions for jet transverse momentum of $10 < p_{T, jet} < 20$ GeV/c, while the angularity distributions of inclusive and D $^{0}$ -tagged jets become narrower in Pb+Pb collisions relative to p+p at $p_{T, jet} > 20$ GeV/c due to the strong influence of the selection bias. Additionally, by comparing the average angularities $⟨ λ_{α}^{κ} ⟩$ of inclusive, D $^{0}$ -tagged and B $^{0}$ -tagged jets with varying $α$ and $κ$ , we show that the larger the quark mass is, the lower the jet's $⟨ λ_{α}^{κ} ⟩$ values are. As a result of the slenderer initial distribution, we predict that as compared to inclusive jets, the heavy-flavor jets, especially the B $^{0}$ -tagged ones, will suffer stronger modifications of $⟨ λ_{α}^{κ} ⟩$ in Pb+Pb relative to p+p at $10 < p_{T, jet} < 20$ GeV/c. For a larger jet radius, a more significant broadening of jet angularities is predicted because of the enhanced contributions of the wide-angle particles.
Comments:
8 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2409.12742 [pdf]
Chin.Phys.Lett.(2025)·9 citations
13
[Submitted on 19 Sept 2024] (cross-list from hep-ph)
Flavor Hierarchy of Jet Energy Correlators inside the Quark-Gluon Plasma
Wen-Jing Xing🇨🇳 · Shanshan Cao🇨🇳 · Guang-You Qin🇨🇳 · Xin-Nian Wang🇨🇳
Heavy flavor jets provide ideal tools to probe the mass effect on jet substructure in both vacuum and quark-gluon plasma (QGP). Energy-energy correlator (EEC) is an excellent jet substructure observable owning to its strong sensitivity to jet physics at different scales. We perform a complete realistic simulation on medium modification of heavy and light flavor jet EEC in heavy-ion collisions. A clear flavor hierarchy is observed for jet EEC in both vacuum and QGP due to the mass effect. The medium modification of inclusive jet EEC at different angular scales exhibits very rich structure: suppression at intermediate angles, and enhancement at small and large angles, which can be well explained by the interplay of mass effect, energy loss, medium-induced radiation and medium response. These unique features of jet EEC are shown to probe the physics of jet-medium interaction at different scales, and can be readily validated by upcoming experiments.
Comments:
7 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2409.12843 [pdf]
PRL(2025)·40 citations

Affiliations

first authorsco-authorsvia INSPIRE

Nonequilibrium Phenomenology of Identified Particle Spectra in Heavy-Ion Collisions at LHC Energies

ν-point energy correletors with FastEEC: small-x physics from LHC jets

Towards an unbiased jet energy loss measurement

Magnetized neutral 2SC color superconductivity and possible origin of the inner magnetic field of magnetars

Medium modifications of heavy-flavor jet angularities in high-energy nuclear collisions

Flavor Hierarchy of Jet Energy Correlators inside the Quark-Gluon Plasma

Affiliations

$ν$ -point energy correletors with FastEEC: small- $x$ physics from LHC jets