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Nuclear Theory·nucl-th

Tuesday·July 13, 2021

14 papers—7 primary·7 cross-listed

All14Primary7Cross-lists7
  1. 08

    [Submitted on 8 Jul 2021] (cross-list from hep-ph)

    A Large- Expansion for Minimum Bias

    Andrew J. Larkoski🇺🇸 · Tom Melia🇯🇵

    Despite being the overwhelming majority of events produced in hadron or heavy ion collisions, minimum bias events do not enjoy a robust first-principles theoretical description as their dynamics are dominated by low-energy quantum chromodynamics. In this paper, we present a novel expansion scheme of the cross section for minimum bias events that exploits an ergodic hypothesis for particles in the events and events in an ensemble of data. We identify power counting rules and symmetries of minimum bias from which the form of the squared matrix element can be expanded in symmetric polynomials of the phase space coordinates. This expansion is entirely defined in terms of observable quantities, in contrast to models of heavy ion collisions that rely on unmeasurable quantities like the number of nucleons participating in the collision, or tunes of parton shower parameters to describe the underlying event in proton collisions. The expansion parameter that we identify from our power counting is the number of detected particles and as the variance of the squared matrix element about its mean, constant value on phase space vanishes. With this expansion, we show that the transverse momentum distribution of particles takes a universal form that only depends on a single parameter, has a fractional dispersion relation, and agrees with data in its realm of validity. We show that the constraint of positivity of the squared matrix element requires that all azimuthal correlations vanish in the limit at fixed center-of-mass energy, as observed in data. The approach we follow allows for a unified treatment of small and large system collective behavior, being equally applicable to describe, e.g., elliptic flow in PbPb collisions and the "ridge" in pp collisions.

    Comments:
    34 pages, 5 figures; v2: JHEP version, minor edits and clarified e+e- analysis is for resonance decay, while hadrons would be described by the same symmetries as pp/AA collisions
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Theory (hep-th); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2107.04041 [pdf]
    JHEP(2021)·7 citations
  2. 09

    [Submitted on 10 Jul 2021] (cross-list from quant-ph)

    Standard Model Physics and the Digital Quantum Revolution: Thoughts about the Interface

    Natalie Klco🇺🇸 · Alessandro Roggero🇺🇸 · Martin J. Savage🇺🇸

    Advances in isolating, controlling and entangling quantum systems are transforming what was once a curious feature of quantum mechanics into a vehicle for disruptive scientific and technological progress. Pursuing the vision articulated by Feynman, a concerted effort across many areas of research and development is introducing prototypical digital quantum devices into the computing ecosystem available to domain scientists. Through interactions with these early quantum devices, the abstract vision of exploring classically-intractable quantum systems is evolving toward becoming a tangible reality. Beyond catalyzing these technological advances, entanglement is enabling parallel progress as a diagnostic for quantum correlations and as an organizational tool, both guiding improved understanding of quantum many-body systems and quantum field theories defining and emerging from the Standard Model. From the perspective of three domain science theorists, this article compiles thoughts about the interface on entanglement, complexity, and quantum simulation in an effort to contextualize recent NISQ-era progress with the scientific objectives of nuclear and high-energy physics.

    Comments:
    63 pages, 5 figures
    Subjects:
    Quantum Physics (quant-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2107.04769 [pdf]
    Rept.Prog.Phys.(2022)·233 citations
  3. 10

    [Submitted on 11 Jul 2021] (cross-list from hep-ph)

    (3+1)-D viscous hydrodynamics CLVisc at finite net baryon density: identified particle spectra, anisotropic flows and flow fluctuations across BES energies

    Xiang-Yu Wu🇨🇳 · Guang-You Qin🇨🇳 · Long-Gang Pang🇨🇳 · Xin-Nian Wang🇨🇳

    To study the bulk properties of the quark-gluon-plasma (QGP) produced at the beam energy scan (BES) energies at the Relativistic Heavy Ion Collider (RHIC), we extend the (3+1)-dimensional viscous hydrodynamics CLVisc to include net baryon number conservation and Israel-Stewart-like equation for baryon diffusion with the NEOS-BQS equation of state, fluctuating initial conditions from Monte-Carlo Glauber model, and the afterburner SMASH. This integrated framework is shown to provide a good description of identified particle spectra, mean transverse momenta and anisotropic flows for different centralities and over a wide range of collision energies (7.7-62.4 GeV). It is found that the mean momenta of identified particles and anisotropic flows increases mildly with the collision energy due to larger radial flow. We further compute the multiple-particle cumulant ratio of elliptic flow across BES energies, and find that the relative fluctuations of elliptic flow are insensitive to the collision energy, consistent with the preliminary STAR data. Our model provides a benchmark for understanding the RHIC-BES data and studying the critical properties and phase structure of hot and dense QCD matter.

    Comments:
    10 pages, 6 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2107.04949 [pdf]
    PRC(2022)·101 citations
  4. 11

    [Submitted on 11 Jul 2021] (cross-list from astro-ph.HE)

    Projecting the likely importance of weak-interaction-driven bulk viscosity in neutron star mergers

    Elias R. Most🇺🇸 · Steven P. Harris🇺🇸 · Christopher Plumberg🇺🇸 · Mark G. Alford🇺🇸 · Jorge Noronha🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸 · Frans Pretorius🇺🇸 · Helvi Witek🇺🇸 · Nicolás Yunes🇺🇸

    In this work, we estimate how much bulk viscosity driven by Urca processes is likely to affect the gravitational wave signal of a neutron star coalescence. In the late inspiral, we show that bulk viscosity affects the binding energy at fourth post-Newtonian (PN) order. Even though this effect is enhanced by the square of the gravitational compactness, the coefficient of bulk viscosity is likely too small to lead to observable effects in the waveform during the late inspiral, when only considering the orbital motion itself. In the post-merger, however, the characteristic time-scales and spatial scales are different, potentially leading to the opposite conclusion. We post-process data from a state-of-the-art equal-mass binary neutron star merger simulation to estimate the effects of bulk viscosity (which was not included in the simulation itself). In that scenario, we find that bulk viscosity can reach high values in regions of the merger. We compute several estimates of how much it might directly affect the global dynamics of the considered merger scenario, and find that it could become significant. Even larger effects could arise in different merger scenarios or in simulations that include non-linear effects. This assessment is reinforced by a quantitative comparison with relativistic heavy-ion collisions where such effects have been explored extensively.

    Comments:
    12 pages, 6 figures
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
    arXiv:
    2107.05094 [pdf]
    MNRAS(2021)·129 citations
  5. 12

    [Submitted on 11 Jul 2021] (cross-list from hep-ph)

    Bremsstrahlung photons from stopping in heavy-ion collisions

    Sohyun Park🇨🇭 · Urs Achim Wiedemann🇨🇭

    We examine the spectrum of bremsstrahlung photons that results from the stopping of the initial net charge distributions in ultrarelativistic nucleus-nucleus collisions at the CERN Large Hadron Collier (LHC). This effect has escaped detection so far since it becomes sizable only at very low transverse momentum and at sufficiently forward rapidity. We argue that it may be within reach of the next-generation LHC heavy-ion detector ALICE-3 that is currently under study, and we comment on the physics motivation for measuring it.

    Comments:
    7 pages, 6 figures. v2: matches version published in PRC
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
    arXiv:
    2107.05129 [pdf]
    PRC(2021)·5 citations
  6. 13

    [Submitted on 12 Jul 2021] (cross-list from hep-ph)

    Polarization effects at finite temperature and magnetic field

    Pok Man Lo🇵🇱 · Michal Szymanski🇵🇱 · Krzysztof Redlich🇵🇱 · Chihiro Sasaki🇵🇱

    We study the screening of four-quark interaction by the ring diagram in an effective chiral quark model. This entails a medium dependent coupling which naturally reduces the chiral transition temperature in a class of models, and is capable of generating an inverse magnetic catalysis at finite temperature. These results are the first coherent description of inverse magnetic catalysis, anchored to a reliable field-theoretical basis.

    Comments:
    10 pages, 2 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
    arXiv:
    2107.05521 [pdf]
    3 citations
  7. 14

    [Submitted on 12 Jul 2021] (cross-list from hep-ph)

    An equation-of-state-meter for CBM using PointNet

    Manjunath Omana Kuttan🇩🇪 · Kai Zhou🇩🇪 · Jan Steinheimer🇩🇪 · Andreas Redelbach🇩🇪 · Horst Stoecker🇩🇪

    A novel method for identifying the nature of QCD transitions in heavy-ion collision experiments is introduced. PointNet based Deep Learning (DL) models are developed to classify the equation of state (EoS) that drives the hydrodynamic evolution of the system created in Au-Au collisions at 10 AGeV. The DL models were trained and evaluated in different hypothetical experimental situations. A decreased performance is observed when more realistic experimental effects (acceptance cuts and decreased resolutions) are taken into account. It is shown that the performance can be improved by combining multiple events to make predictions. The PointNet based models trained on the reconstructed tracks of charged particles from the CBM detector simulation discriminate a crossover transition from a first order phase transition with an accuracy of up to 99.8%. The models were subjected to several tests to evaluate the dependence of its performance on the centrality of the collisions and physical parameters of fluid dynamic simulations. The models are shown to work in a broad range of centralities (b=0-7 fm). However, the performance is found to improve for central collisions (b=0-3 fm). There is a drop in the performance when the model parameters lead to reduced duration of the fluid dynamic evolution or when less fraction of the medium undergoes the transition. These effects are due to the limitations of the underlying physics and the DL models are shown to be superior in its discrimination performance in comparison to conventional mean observables.

    Comments:
    12 pages, 7 figures. Matches published version
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2107.05590 [pdf]
    JHEP(2021)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE