Nuclear Theory·nucl-th

Friday·December 16, 2016

13 papers—7 primary·6 cross-listed

01
Process-independent strong running coupling
Daniele Binosi🇮🇹 · Cedric Mezrag🇺🇸 · Joannis Papavassiliou🇪🇸 · Craig D. Roberts🇺🇸 · Jose Rodriguez-Quintero🇪🇸
We unify two widely different approaches to understanding the infrared behaviour of quantum chromodynamics (QCD), one essentially phenomenological, based on data, and the other computational, realised via quantum field equations in the continuum theory. Using the latter, we explain and calculate a process-independent running-coupling for QCD, a new type of effective charge that is an analogue of the Gell-Mann--Low effective coupling in quantum electrodynamics. The result is almost identical to the process-dependent effective charge defined via the Bjorken sum rule, which provides one of the most basic constraints on our knowledge of nucleon spin structure. This reveals the Bjorken sum to be a near direct means by which to gain empirical insight into QCD's Gell-Mann--Low effective charge.
nucl-thhep-lathep-phnucl-exPRD(2017)·178 citations
02
Shear viscosity from nuclear stopping
Brent Barker (Roosevelt U) · Pawel Danielewicz (NSCL MSU)
Within a Boltzmann transport model, we demonstrate correlation between stopping observables and shear viscosity in central nuclear collisions at intermediate energies (on the order of 10 to 1000 MeV/nucleon). The correlation allows us to assess the viscosity of nuclear matter, by tuning the in-medium nucleon-nucleon cross section in our transport model to agree with nuclear stopping data. We also calculate the ratio of shear viscosity to entropy density to determine how close the system is to the universal quantum lower limit proposed in the context of ultrarelativistic heavy ion collisions.
nucl-thnucl-exPRC(2019)·30 citations
03
The $d^{*}$ (2380) dibaryon resonance width and decay branching ratios
Avraham Gal🇮🇱
Attempts to reproduce theoretically the relatively small width, $Γ_{d^{*}} = 80 \pm 10$ MeV, of the $I (J^{P}) = 0 (3^{+})$ $d^{*}$ (2380) dibaryon resonance established by the WASA-at-COSY Collaboration are discussed. The validity of associating the $d^{*}$ (2380) in quark-based models primarily with a tightly bound $ΔΔ$ configuration is questioned. The $d^{*}$ (2380) width and decay branching ratios into $N N π π$ , $N N π$ and $N N$ final states are studied within the Gal-Garcilazo hadronic model in which the $d^{*}$ (2380) is a $π N Δ$ resonance embedded in the $N N π π$ continuum some 80 MeV below the $ΔΔ$ threshold. In particular, predictions are made for the branching ratios of the unobserved yet $d^{*} (2380) \to N N π$ decays which are suppressed in a purely- $ΔΔ$ dibaryon model. Comments are also made on a possible connection of the ABC effect observed in the $p n \to d^{*} \to d π^{0} π^{0}$ resonance reaction to the $d^{*}$ (2380) dibaryon.
nucl-thhep-phnucl-exPLB(2017)·50 citations
04
Holographic Photon Production and Anisotropic Flow
Ioannis Iatrakis🇳🇱 · Elias Kiritsis🇬🇷 · Chun Shen🇨🇦 · Di-Lun Yang🇯🇵
The thermal-photon emission from strongly coupled gauge theories at finite temperature via the bottom-up models in holographic QCD in the deconfined phase is studied. The models are constructed to approximately reproduce the electric conductivity obtained from lattice simulations for the quark gluon plasma (QGP). The emission rates are then embedded in hydrodynamic simulations combined with prompt photons and hadronic contributions to analyze the spectra and anisotropic flow of direct photons in RHIC and LHC. In general, the holographic models enhance the yield and improve the agreement in spectra, while they reduce the flow in low $p_{T}$ and increase it in high $p_{T}$ .
nucl-thhep-phhep-thNucl.Part.Phys.Proc.(2017)·3 citations
05
Medium Recoils and background subtraction in JEWEL
Raghav Kunnawalkam Elayavalli🇺🇸 · Korinna Christine Zapp🇵🇹
\textsc{Jewel} is a fully dynamical event generator for jet evolution in a dense QCD medium, which has been validated for multiple jet and jet-like observables. Jet constituents (partons) undergo collisions with thermal partons from the medium, leading to both elastic and radiative energy loss. The recoiling medium scattering centers carry away energy and momentum from the jet. Keeping track of these recoils is essential for the description of intra-jet observables. Since the thermal component of the recoils is part of the soft background activity, comparison with data on jet observables requires the implementation of a background subtraction procedure. We will show two independent procedures through which background subtraction can be performed and discuss the impact of the medium recoil on jet shape observables and jet-background correlations. Keeping track of the medium recoil significantly improves the \textsc{Jewel} description of jet shape measurements.
nucl-thhep-phNucl.Part.Phys.Proc.(2017)·5 citations
06
Correlated stopping, proton clusters and higher order proton cumulants
Adam Bzdak🇵🇱 · Volker Koch🇺🇸 · Vladimir Skokov🇺🇸
We investigate possible effects of correlations between stopped nucleons on higher order proton cumulants at low energy heavy-ion collisions. We find that fluctuations of the number of wounded nucleons $N_{part}$ lead to rather nontrivial dependence of the correlations on the centrality; however, this effect is too small to explain the large and positive four-proton correlations found in the preliminary data collected by the STAR collaboration at $s = 7.7$ GeV. We further demonstrate that, by taking into account additional proton clustering, we are able to qualitatively reproduce the preliminary experimental data. We speculate that this clustering may originate either from collective/multi-collision stopping which is expected to be effective at lower energies or from a possible first-order phase transition, or from (attractive) final state interactions. To test these ideas we propose to measure a mixed multi-particle correlation between stopped protons and a produced particle (e.g. pion, antiproton).
nucl-thhep-exhep-phnucl-exEPJC(2017)·47 citations
07
Model-independent determination of the two-photon exchange contribution to hyperfine splitting in muonic hydrogen
Clara Peset🇪🇸 · Antonio Pineda🇪🇸
We obtain a model-independent prediction for the two-photon exchange contribution to the hyperfine splitting in muonic hydrogen. We use the relation of the Wilson coefficients of the spin-dependent dimension-six four-fermion operator of NRQED applied to the electron-proton and to the muon-proton sectors. Their difference can be reliably computed using chiral perturbation theory, whereas the Wilson coefficient of the electron-proton sector can be determined from the hyperfine splitting in hydrogen. This allows us to give a precise model-independent determination of the Wilson coefficient for the muon-proton sector, and consequently of the two-photon exchange contribution to the hyperfine splitting in muonic hydrogen, which reads $δ E ˉ_{p μ, HF}^{TPE} (n S) = - \frac{1}{n ^{3}} 1.161 (20)$ meV. Together with the associated QED analysis, we obtain a prediction for the hyperfine splitting in muonic hydrogen that reads $E_{p μ, HF}^{th} (1 S) = 182.623 (27)$ meV and $E_{p μ, HF}^{th} (2 S) = 22.8123 (33)$ meV. The error is dominated by the two-photon exchange contribution.
nucl-thhep-phphysics.atom-phJHEP(2017)·35 citations

Affiliations

first authorsco-authorsvia INSPIRE

Process-independent strong running coupling

Shear viscosity from nuclear stopping

The d∗(2380) dibaryon resonance width and decay branching ratios

Holographic Photon Production and Anisotropic Flow

Medium Recoils and background subtraction in JEWEL

Correlated stopping, proton clusters and higher order proton cumulants

Model-independent determination of the two-photon exchange contribution to hyperfine splitting in muonic hydrogen

Affiliations

The $d^{*}$ (2380) dibaryon resonance width and decay branching ratios