Nuclear Theory·nucl-th

Wednesday·June 23, 2021

10 papers—3 primary·7 cross-listed

01
[Submitted on 21 Jun 2021]
Determining the jet transport coefficient $q^$ of the quark-gluon plasma using Bayesian parameter estimation
J. Mulligan🇺🇸 · A. Angerami · R. Arora · S. A. Bass · S. Cao · Y. Chen · J. Coleman · L. Cunqueiro · T. Dai · L. Du · R. Ehlers · H. Elfner and 37 other authors
We present a new determination of $q^$ , the jet transport coefficient of the quark-gluon plasma. Using the JETSCAPE framework, we use Bayesian parameter estimation to constrain the dependence of $q^$ on the jet energy, virtuality, and medium temperature from experimental measurements of inclusive hadron suppression in Au-Au collisions at RHIC and Pb-Pb collisions at the LHC. These results are based on a multi-stage theoretical approach to in-medium jet evolution with the MATTER and LBT jet quenching models. The functional dependence of $q^$ on jet energy, virtuality, and medium temperature is based on a perturbative picture of in-medium scattering, with components reflecting the different regimes of applicability of MATTER and LBT. The correlation of experimental systematic uncertainties is accounted for in the parameter extraction. These results provide state-of-the-art constraints on $q^$ and lay the groundwork to extract additional properties of the quark-gluon plasma from jet measurements in heavy-ion collisions.
Comments:
contribution to the 2021 QCD session of the 55th Recontres de Moriond
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2106.11348 [pdf]
2 citations
02
[Submitted on 22 Jun 2021]
Optimizing multilayer Bayesian neural networks for evaluation of fission yields
Zi-Ao Wang · Junchen Pei
The Bayesian machine learning is a promising tool for the evaluation of nuclear fission data but its potential capability has not been fully realized. We attempt to optimize the performances of the multilayer Bayesian neural networks for evaluations of fission yields. The influences of adjustments of learning data, activation functions, network structures have been studied. In particular, negative values of net functions have been penalized to avoid non-physical inferences of fission yields. Presently the network with double hidden layers has optimal performances compared to the single-layer or deeper networks. These studies are essential for further developments of precise evaluation methods.
Comments:
5 pages and 5 figures. arXiv admin note: text overlap with arXiv:2102.09314
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2106.11746 [pdf]
PRC(2021)·24 citations
03
[Submitted on 22 Jun 2021]
Diagnosing the Quark-Gluon Plasma
Berndt Müller🇺🇸
Brief review of the hadronic probes that are used to diagnose the quark-gluon plasma produced in relativistic heavy ion collisions and interrogate its properties. Emphasis is placed on probes that have significantly impacted our understanding of the nature of the quark-gluon plasma and confirmed its formation.
Comments:
Prize lecture presented on April 19, 2021 at the Spring Meeting of the American Physical Society
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2106.11923 [pdf]
7 citations
04
[Submitted on 18 Jun 2021] (cross-list from hep-ph)
The photon PDF within the CT18 global analysis
Keping Xie🇺🇸 · T. J. Hobbs🇺🇸 · Tie-Jiun Hou🇨🇳 · Carl Schmidt🇺🇸 · Mengshi Yan🇨🇳 · C.-P. Yuan🇺🇸
Building upon the most recent CT18 global fit, we present a new calculation of the photon content of the proton based on an application of the LUX formalism. In this work, we explore two principal variations of the LUX ansatz. In one approach, which we designate "CT18lux," the photon PDF is calculated directly using the LUX formula for all scales, $μ$ . In an alternative realization, "CT18qed," we instead initialize the photon PDF in terms of the LUX formulation at a lower scale, $μ \sim μ_{0}$ , and evolve to higher scales with a combined QED+QCD kernel at $O (α), O (α α_{s})$ and $O (α^{2})$ . While we find these two approaches generally agree, especially at intermediate $x$ ( $1 0^{- 3} ≲ x ≲ 0.3$ ), we discuss some moderate discrepancies that can occur toward the end-point regions at very high or low $x$ . We also study effects that follow from variations of the inputs to the LUX calculation originating outside the pure deeply-inelastic scattering (DIS) region, including from elastic form factors and other contributions to the photon PDF. Finally, we investigate the phenomenological implications of these photon PDFs for the LHC, including high-mass Drell-Yan, vector-boson pair, top-quark pair, and Higgs associated with vector-boson production.
Comments:
45 pages, 27 figures, and 5 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2106.10299 [pdf]
PRD(2022)·55 citations
05
[Submitted on 18 Jun 2021] (cross-list from nucl-ex)
Improved neutron lifetime measurement with UCN $τ$
F. M. Gonzalez · E. M. Fries · C. Cude-Woods · T. Bailey · M. Blatnik · L. J. Broussard · N. B. Callahan · J. H. Choi · S. M. Clayton · S. A. Currie · M. Dawid · E. B. Dees and 33 other authors
We report an improved measurement of the free neutron lifetime $τ_{n}$ using the UCN $τ$ apparatus at the Los Alamos Neutron Science Center. We counted a total of approximately $38 \times 1 0^{6}$ surviving ultracold neutrons (UCN) after storing in UCN $τ$ 's magneto-gravitational trap over two data acquisition campaigns in 2017 and 2018. We extract $τ_{n}$ from three blinded, independent analyses by both pairing long and short storage-time runs to find a set of replicate $τ_{n}$ measurements and by performing a global likelihood fit to all data while self-consistently incorporating the $β$ -decay lifetime. Both techniques achieve consistent results and find a value $τ_{n} = 877.75 \pm 0.2 8_{stat} + 0.22/ - 0.1 6_{syst}$ ~s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.
Comments:
7 pages, 2 figures, 3 tables
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2106.10375 [pdf]
PRL(2021)·194 citations
06
[Submitted on 21 Jun 2021] (cross-list from hep-ph)
Spectral function of fermions in a highly occupied non-Abelian plasma
Kirill Boguslavski🇦🇹 · Tuomas Lappi🇫🇮 · Mark Mace🇫🇮 · Sören Schlichting🇩🇪
We develop a method to obtain fermion spectral functions non-perturbatively in a non-Abelian gauge theory with high occupation numbers of gauge fields. After recovering the free field case, we extract the spectral function of fermions in a highly occupied non-Abelian plasma close to its non-thermal fixed point, i.e., in a self-similar regime of the non-equilibrium dynamics. We find good agreement with hard loop perturbation theory for medium-induced masses, dispersion relations and quasiparticle residues. We also extract the full momentum dependence of the damping rate of the collective excitations.
Comments:
13 pages, 6 figures; v2: minor revision, data and plot files attached, published in Phys. Lett. B
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2106.11319 [pdf]
PLB(2022)·19 citations
07
[Submitted on 21 Jun 2021] (cross-list from hep-ph)
The strong CP problem solved by itself due to long-distance vacuum effects
Y. Nakamura🇯🇵 · G. Schierholz🇩🇪
The vacuum of quantum chromodynamics has an incredibly rich structure at the nonperturbative level, which is intimately connected with the topology of gauge fields, and put to a test by the strong CP problem. We investigate the long-distance properties of the theory in the presence of the topological $θ$ term. This is done on the lattice, using the gradient flow to isolate the long-distance modes in the functional integral measure and tracing it over successive length scales. The key point is that the vacuum splits into disconnected topological sectors with markedly different physical characteristics, which gives rise to a nontrivial behavior depending on $θ$ . We find that the color fields produced by quarks and gluons are screened, and confinement is lost, for bare vacuum angles $∣ θ ∣ > 0$ , thus providing a natural solution of the strong CP problem. The renormalized vacuum angle $θ$ is found to flow to zero in the infrared limit, leading to a self-consistent solution within QCD.
Comments:
22 pages, 15 figures, typos corrected, meets journal version in Nucl. Phys. B
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2106.11369 [pdf]
NPB(2023)·40 citations
08
[Submitted on 21 Jun 2021] (cross-list from hep-ph)
Model dependence of the polarization asymmetries in weak pion production off the nucleon
Krzysztof M. Graczyk🇵🇱 · Beata E. Kowal🇵🇱
The work presents the studies of the polarization observables in the single pion production (SPP) induced by the interaction of the muon neutrino (antineutrino) with nucleons. The SPP cross-sections and spin asymmetries are computed within two phenomenological models. One is basing on the nonlinear sigma model \cite{Hernandez:2007qq}; the other has origin in linear sigma model~\cite{Fogli:1979cz}. Firstly, we show that the final nucleon polarization and target spin asymmetries are good observables to obtain information about the $C_{5}^{A}$ axial form factor. Secondly, we demonstrate that the nucleon polarization and the target spin asymmetries are sensitive to the relative phase between resonance and nonresonance amplitudes. We conclude that the polarization of the final nucleon and the target spin asymmetry are promising observables for testing SPP models, including studies of the axial content of $Δ (1232)$ resonance and unitarization procedures.
Comments:
17 pages, 11 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2106.11383 [pdf]
PRD(2021)·6 citations
09
[Submitted on 21 Jun 2021] (cross-list from cond-mat.stat-mech)
Beyond the relaxation time approximation
Grzegorz Wilk🇵🇱 · Zbigniew Włodarczyk🇵🇱
The relaxation time approximation (RTA) is a well known method of describing the time evolution of a statistical ensemble by linking distributions of the variables of interest at different stages of their temporal evolution. We show that if all the distributions occurring in the RTA have the same functional form of a quasi-power Tsallis distribution the time evolution of which depends on the time evolution of its control parameter, nonextensivity $q (t)$ , then it is more convenient to consider only the time evolution of this control parameter.
Comments:
5 pages, 3 figures. To be published in Eur. Phys. J. A
Subjects:
Statistical Mechanics (cond-mat.stat-mech); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2106.11777 [pdf]
EPJA(2021)·4 citations
10
[Submitted on 22 Jun 2021] (cross-list from hep-ph)
Doubly Heavy Tetraquark Resonant States
Qi Meng🇨🇳 · Masayasu Harada🇯🇵 · Emiko Hiyama🇯🇵 · Atsushi Hosaka🇯🇵 · Makoto Oka🇯🇵
Spectrum of the doubly heavy tetraquarks, $bb q ˉ q ˉ$ , is studied in a constituent quark model. Four-body problem is solved in a variational method where the real scaling technique is used to identify resonant states above the fall-apart decay thresholds. In addition to the two bound states that were reported in the previous study we have found several narrow resonant states above the $B B^{*}$ and $B^{*} B^{*}$ thresholds. Their structures are studied and are interpreted by the quark dynamics. A narrow resonance with spin-parity $J^{P} = 1^{+}$ is found to be a mixed state of a compact tetraquark and a $B^{*} B^{*}$ scattering state. This is driven by a strong color Coulombic attraction between the $bb$ quarks. Negative-parity excited resonances with $J^{P} = 0^{-}$ , $1^{-}$ and $2^{-}$ form a triplet under the heavy-quark spin symmetry. It turns out that they share a similar structure to the $λ$ -mode of a singly heavy baryon as a result of the strongly attractive correlation for the doubly heavy diquark.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2106.11868 [pdf]
PLB(2022)·40 citations

Affiliations

first authorsco-authorsvia INSPIRE