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
08
Jet axes and universal transverse-momentum-dependent fragmentation
Duff Neill🇺🇸 · Ignazio Scimemi🇪🇸 · Wouter J. Waalewijn🇳🇱
We study the transverse momentum spectrum of hadrons in jets. By measuring the transverse momentum with respect to a judiciously chosen axis, we find that this observable is insensitive to (the recoil of) soft radiation. Furthermore, for small transverse momenta we show that the effects of the jet boundary factorize, leading to a new transverse-momentum-dependent (TMD) fragmentation function. In contrast to the usual TMD fragmentation functions, it does not involve rapidity divergences and is universal in the sense that it is independent of the type of process and number of jets. These results directly apply to sub-jets instead of hadrons. We discuss potential applications, which include studying nuclear modification effects in heavy-ion collisions and identifying boosted heavy resonances.
↳ hep-phnucl-thJHEP(2017)·68 citations
09
Threshold effects in P-wave bottom-strange mesons
Pablo G. Ortega🇪🇸 · Jorge Segovia🇩🇪 · David R. Entem🇪🇸 · Francisco Fernández🇪🇸
Using a nonrelativistic constituent quark model in which the degrees of freedom are quark-antiquark and meson-meson components, we have recently shown that the $D^{(*)} K$ thresholds play an important role in lowering the mass of the physical $D_{s 0}^{*} (2317)$ and $D_{s 1} (2460)$ states. This observation is also supported by other theoretical approaches such as lattice-regularised QCD or chiral unitary theory in coupled channels. Herein, we extend our computation to the lowest $P$ -wave $B_{s}$ mesons, taking into account the corresponding $J^{P} = 0^{+}$ , $1^{+}$ and $2^{+}$ bottom-strange states predicted by the naive quark model and the $B K$ and $B^{*} K$ thresholds. We assume that mixing with $B_{s}^{(*)} η$ and isospin-violating decays to $B_{s}^{(*)} π$ are negligible. This computation is important because there is no experimental data in the $b s ˉ$ sector for the equivalent $j_{q}^{P} = 1/ 2^{+}$ ( $D_{s 0}^{*} (2317)$ , $D_{s 1} (2460)$ ) heavy-quark multiplet and, as it has been seen in the $c s ˉ$ sector, the naive theoretical result can be wrong by more than $100 MeV$ . Our calculation allows to introduce the coupling with the $D$ -wave $B^{*} K$ channel and to compute the probabilities associated with the different Fock components of the physical state.
↳ hep-phhep-exhep-latnucl-thPRD(2017)·49 citations
10
Dynamics, nucleosynthesis, and kilonova signature of black hole - neutron star merger ejecta
Rodrigo Fernández · Francois Foucart · Daniel Kasen · Jonas Lippuner · Dhruv Desai · Luke F. Roberts
We investigate the ejecta from black hole - neutron star mergers by modeling the formation and interaction of mass ejected in a tidal tail and a disk wind. The outflows are neutron-rich, giving rise to optical/infrared emission powered by the radioactive decay of $r$ -process elements (a kilonova). Here we perform an end-to-end study of this phenomenon, where we start from the output of a fully-relativistic merger simulation, calculate the post-merger hydrodynamical evolution of the ejecta and disk winds including neutrino physics, determine the final nucleosynthetic yields using post-processing nuclear reaction network calculations, and compute the kilonova emission with a radiative transfer code. We study the effects of the tail-to-disk mass ratio by scaling the tail density. A larger initial tail mass results in fallback matter becoming mixed into the disk and ejected in the subsequent disk wind. Relative to the case of a disk without dynamical ejecta, the combined outflow has lower mean electron fraction, faster speed, larger total mass, and larger absolute mass free of high-opacity Lanthanides or Actinides. In most cases, the nucleosynthetic yield is dominated by the heavy $r$ -process contribution from the unbound part of the tidal tail. A Solar-like abundance distribution can however be obtained when the total mass of the dynamical ejecta is comparable to the mass of the disk outflows. The kilonova has a characteristic duration of 1 week and a luminosity of ~ $1 0^{41}$ erg/s, with orientation effects leading to variations of a factor ~2 in brightness. At early times (< 1 day) the emission includes an optical component from the (hot) Lanthanide-rich material, but the spectrum evolves quickly to the infrared thereafter.
↳ astro-ph.HEastro-ph.SRgr-qcnucl-thClass.Quant.Grav.(2017)·115 citations
11
Prospects for neutrino oscillation parameters
Patrick Huber🇺🇸
In this contribution we discuss the future of the global long-baseline neutrino oscillation program. The case is made that our current lack of understanding of neutrino-nucleus interactions is a serious challenge which will need to be met with new experimental initiatives in neutrino scattering.
↳ hep-phhep-exnucl-thPoS(2017)·2 citations
12
$p_{t}$ -Angular power spectrum in ALICE events
Felipe J. Llanes-Estrada🇪🇸 · Jose L. Muñoz Martinez (Univ. Complutense de Madrid)🇪🇸
We study the particles emitted in the fireball following a Relativistic Heavy Ion Collision with the traditional angular analysis employed in cosmology and earth sciences, producing Mollweide plots of the p_t distribution of a few actual, publically released ALICE-collaboration events and calculating their angular power spectrum. With the limited statistics at hand, we do not find evidence for acoustic peaks but a decrease of C_l that is reminiscent of viscous attenuation, but subject to a strong effect from the rapidity acceptance which probably dominates (so we also subtract the m=0 component). As an exercise, we still extract a characteristic Silk damping length (proportional to the square root of the viscosity over entropy density ratio). The absence of acoustic-like peaks is also compatible with a crossover from the QGP to the hadron gas (because a surface tension at domain boundaries would effect a restoring force that could have driven acoustic oscillations). Presently an unexpected depression appears in the l=6 multipole strength, which should be revisited by the ALICE collaboration with full statistics to confirm or discard it.
↳ hep-phnucl-exnucl-thNPA(2018)·8 citations
13
A shoving model for collectivity in hadronic collisions
Christian Bierlich🇸🇪 · Gösta Gustafson🇸🇪 · Leif Lönnblad🇸🇪
An extension of the rope hadronization model, which has previously provided good descriptions of hadrochemistry in high multiplicity pp collisions, is presented. The extension includes a dynamically generated transverse pressure, produced by the excess energy from overlapping strings. We find that this model can qualitatively reproduce soft features of Quark Gluon Plasma in small systems, such as higher $⟨ p_{⊥} ⟩$ for heavier particles and long range azimuthal correlations forming a ridge. The effects are similar to those obtained from a hydrodynamic expansion, but without assuming a thermalized medium.
↳ hep-phnucl-th83 citations

Affiliations

first authorsco-authorsvia INSPIRE