Nuclear Theory·nucl-th

Tuesday·January 17, 2017

11 papers—4 primary·7 cross-listed

01
Revealing long-range multi-particle collectivity in small collision systems via subevent cumulants
Jiangyong Jia🇺🇸 · Mingliang Zhou🇺🇸 · Adam Trzupek🇵🇱
Multi-particle azimuthal cumulants, often used to study collective flow in high-energy heavy-ion collisions, have recently been applied in small collision systems such as $pp$ and $p$ +A to extract the second-order azimuthal harmonic flow $v_{2}$ . Recent observation of four-, six- and eight-particle cumulants with "correct sign" $c_{2} {4} < 0, c_{2} {6} > 0, c_{2} {8} < 0$ and approximate equality of the inferred single-particle harmonic flow, $v_{2} {4} \approx v_{2} {6} \approx v_{2} {8}$ , have been used as strong evidence for a collective emission of all soft particles produced in the collisions. We show that these relations in principle could be violated due to the non-Gaussianity in the event-by-event fluctuation of flow and/or non-flow. Furthermore, we show, using $pp$ events generated with the PYTHIA model, that $c_{2} {2 k}$ obtained with standard cumulant method are dominated by non-flow from dijets. An alternative cumulant method based on two or more $η$ -separated subevents is proposed to suppress the dijet contribution. The new method is shown to be able to recover a flow signal as low as 4\% imposed on the PYTHIA events, independently of how the event activity class is defined. Therefore the subevent cumulant method offers a more robust way of studying collectivity based on the existence of long-range azimuthal correlations between multiple distinct $η$ ranges. The prospect of using the subevent cumulants to study collective flow in A+A collisions, in particular its longitudinal dynamics, is discussed.
nucl-thnucl-exPRC(2017)·174 citations
02
$Λ_{c}$ Semileptonic Decays in a Quark Model
Md Mozammel Hussain🇺🇸 · Winston Roberts🇺🇸
Hadronic form factors for semileptonic decay of the $Λ_{c}$ are calculated in a nonrelativistic quark model. The full quark model wave functions are employed to numerically calculate the form factors to all relevant orders in ( $1/ m_{c}$ , $1/ m_{s}$ ). The form factors obtained satisfy relationships expected from the heavy quark effective theory (HQET). The differential decay rates and branching fractions are calculated for transitions to the ground state and a number of excited states of $Λ$ . The branching fraction of the semileptonic decay width to the total width of $Λ_{c}$ has been calculated and compared with other theoretical estimates and experimental results. The branching fractions for $Λ_{c} \to Λ^{*} l^{+} ν_{l} \to Σ π l^{+} ν_{l}$ and $Λ_{c} \to Λ^{*} l^{+} ν_{l} \to N K ˉ l^{+} ν_{l}$ are also calculated. Apart from decays to the ground state $Λ$ (1115), it is found that decays through the $Λ (1405)$ provide a significant portion of the branching fraction $Λ_{c} \to X_{s} l ν_{l}$ . A new estimate for $f = B (Λ_{c}^{+} \to Λ l^{+} ν_{l}) / B (Λ_{c}^{+} \to X_{s} l^{+} ν_{l})$ is obtained.
nucl-thhep-phPRD(2017)·18 citations
03
Nonmesonic Weak Decay of $Λ$ Hypernuclei: The Three--Nucleon Induced Mode
E. Bauer🇦🇷 · G. Garbarino🇮🇹 · C. A. Rodríguez Peña🇦🇷
The nonmesonic weak decay of $Λ$ hypernuclei is studied within a microscopic diagrammatic approach which is extended to include the three--nucleon induced mechanism. We adopt a nuclear matter formalism which, through the local density approximation, allows us to model finite hypernuclei, a one--meson--exchange weak transition potential and a Bonn nucleon--nucleon strong potential. One--, two-- and three--nucleon induced weak decay rates are predicted for $_{Λ}^{12}$ C by including ground state correlations up to second order in the nucleon--nucleon potential and the recoil of the residual nucleus. Three--nucleon stimulated decays, $Λ N N N \to n N N N$ ( $N = n$ or $p$ ), are considered here for the first time. The obtained decay rates compare well with the latest KEK and FINUDA data. The three--nucleon induced rate turns out to be dominated by $nn p$ -- and $n pp$ --induced decays, it amounts to $\sim$ 7\% of the total nonmesonic rate and it is $\sim 1/2$ of the neutron--induced decay rate. The reduction effect of the nuclear recoil is particularly relevant for the three--nucleon induced rates ( $\sim$ 15\%), less important for the two--nucleon induced rates ( $\sim$ 4\%) and negligible for the one--nucleon induced rates. Given the non--negligible size of the three--nucleon induced contribution and consequently its importance in the precise determination of the complete set of decay rates, new measurements and/or experimental analysis are encouraged.
nucl-thPLB(2017)·4 citations
04
Production of $ρ^{0}$ meson with large $p_{T}$ at NLO in heavy-ion collisions
Wei Dai🇨🇳 · Ben-Wei Zhang🇨🇳 · Enke Wang🇨🇳
Production of large transverse momentum $ρ^{0}$ meson in high-energy nuclear collisions is investigated for the first time at the next-leading-order in the QCD improved parton model. The $ρ^{0}$ fragmentation functions (FFs) in vacuum at any scale $Q$ are obtained, by evolving a newly developed initial parametrization of $ρ^{0}$ FFs at a scale $Q_{0}^{2} = 1.5 Ge V^{2}$ from a broken SU(3) model through NLO DGLAP equations. The numerical simulations of $p_{T}$ spectra of $ρ^{0}$ meson in the elementary $p + p$ collisions at NLO give a decent description of STAR $p + p$ data. In $A + A$ reactions the jet quenching effect is taken into account with the higher-twist approach by the medium-modified parton FFs due to gluon radiation in the quark-gluon plasma, whose space-time evolution is described by a (3+1D) hydrodynamical model. The nuclear modification factors for $ρ^{0}$ meson and its double ratio with $π^{\pm}$ nuclear modification in central $Au + Au$ collisions at the RHIC are calculated and found to be in good agreement with STAR measurement. Predictions of $ρ^{0}$ nuclear modification and the yield ratio $ρ^{0} / π^{0}$ in central Pb+Pb at the LHC are also presented. It is shown that the ratio $ρ^{0} / π^{0}$ in central Pb+Pb will approach to that in p+p reactions when $p_{T} > 12$ ~GeV.
nucl-thnucl-exPRC(2018)·10 citations
05
Rotating NSs/QSs and recent astrophysical observations
Ang Li🇨🇳 · Jianmin Dong🇨🇳
Both fast and slow configurations of rotating neutron stars (NSs) are studied with the recently-constructed unified NS EoSs. The calculations for pure quark stars (QSs) and hybrid stars (HSs) are also done, using several updated quark matter EoSs and Gibbs construction for obtaining hadron-quark mixed phase. All three types of EoSs fulfill the recent 2-solar-mass constrain. By confronting the glitch observations with the theoretical calculations for the crustal moment of inertia (MoI), we find that the glitch crisis is still present in Vela-like pulsars. An upcoming accurate MoI measurement (eg., a possible 10\% accuracy for pulsar PSR J0737-3039A) could distinguish QSs from NSs, since the MoIs of QSs are generally $>\sim 1.5$ times larger than NSs and HSs, no matter the compactness and the mass of the stars. Using tabulated EoSs, we compute stationary and equilibrium sequences of rapidly rotating, relativistic stars in general relativity from the well-tested $r n s$ code, assuming the matter comprising the star to be a perfect fluid. All three observed properties of the short gamma-ray bursts (SGRBs) internal plateaus sample are simulated using the rotating configurations of NSs/QSs as basic input. We finally argue that for some characteristic SGRBs, the post-merger products of NS-NS mergers are probably supramassive QSs rather than NSs, and NS-NS mergers are a plausible location for quark deconfinement and the formation of QSs.
↳ astro-ph.HEastro-ph.SRnucl-thJ.Phys.Conf.Ser.(2017)·0 citations
06
Upper limit set by causality on the tidal deformability of a neutron star
Eric D. Van Oeveren🇺🇸 · John L. Friedman🇺🇸
A principal goal of gravitational-wave astronomy is to constrain the neutron star equation of state (EOS) by measuring the tidal deformability of neutron stars. The tidally induced departure of the waveform from that of point-particle (or spinless binary black hole (BBH)) increases with the stiffness of the EOS. We show that causality (the requirement that the speed of sound is less than the speed of light for a perfect fluid satisfying a one-parameter equation of state) places an upper bound on tidal deformability as a function of mass. Like the upper mass limit, the limit on deformabity is obtained by using an EOS with $v_{so u n d} = c$ for high densities and matching to a low density (candidate) EOS at a matching density of order nuclear saturation density. We use these results and those of [B.D. Lackey et al., Phys. Rev. D 89, 043009 (2014)] to estimate the resulting upper limit on the gravitational-wave phase shift of a black hole-neutron star (BHNS) binary relative to a BBH. Even for assumptions weak enough to allow an maximum mass of $4 M_{⊙}$ (a match at nuclear saturation density to an unusually stiff low-density candidate EOS), the upper limit on dimensionless tidal deformability is stringent. It leads to a still more stringent estimated upper limit on the maximum tidally induced phase shift prior to merger. We comment in an appendix on the relation between causality, the condition $v_{so u n d} < c$ , and the condition $d p / d ϵ < 1$ for the effective EOS governing the equilibrium star.
↳ gr-qcastro-ph.HEnucl-thPRD(2017)·42 citations
07
The Sun as a probe of Fundamental Physics and Cosmology
Ilídio Lopes🇵🇹
The high quality data provided by helioseismology, solar neutrino flux measurements, spectral determination of solar abundances, nuclear reactions rates coefficients among other experimental data, leads to the highly accurate prediction of the internal structure of the present Sun - the standard solar model. In this talk, I have discussed how the standard solar model, the best representation of the real Sun, can be used to study the properties of dark matter, for which two complementary approaches have been developed: - to limit the number of theoretical candidates proposed as the dark matter particles, this analysis complements the experimental search of dark matter, and - as a template for the study of the impact of dark matter in the evolution of stars, which possibly occurs for stellar populations formed in regions of high density of dark matter, such as stars formed in the centre of galaxies and the first generations of stars.
↳ astro-ph.COastro-ph.SRnucl-exnucl-thJ.Phys.Conf.Ser.(2016)·3 citations
08
Observing a scale anomaly and a universal quantum phase transition in graphene
O. Ovdat · Jinhai Mao · Yuhang Jiang · E. Y. Andrei · E. Akkermans
One of the most interesting predictions resulting from quantum physics, is the violation of classical symmetries, collectively referred to as anomalies. A remarkable class of anomalies occurs when the continuous scale symmetry of a scale free quantum system is broken into a discrete scale symmetry for a critical value of a control parameter. This is an example of a (zero temperature) quantum phase transition. Such an anomaly takes place for the quantum inverse square potential known to describe 'Efimov physics'. Broken continuous scale symmetry into discrete scale symmetry also appears for a charged and massless Dirac fermion in an attractive $1/ r$ Coulomb potential. The purpose of this article is to demonstrate the universality of this quantum phase transition and to present convincing experimental evidence of its existence for a charged and massless fermion in an attractive Coulomb potential as realised in graphene.
↳ cond-mat.mes-hallnucl-thNature Commun.(2017)·16 citations
09
Gluonic Lorentz violation and chiral perturbation theory
J. P. Noordmans🇵🇹
By applying chiral-perturbation-theory methods to the QCD sector of the Lorentz-violating Standard-Model Extension, we investigate Lorentz violation in the strong interactions. In particular, we consider the CPT-even pure-gluon operator of the minimal Standard-Model Extension. We construct the lowest-order chiral effective Lagrangian for three as well as two light quark flavors. We develop the power-counting rules and construct the heavy-baryon chiral-perturbation-theory Lagrangian, which we use to calculate Lorentz-violating contributions to the nucleon self energy. Using the constructed effective operators, we derive the first stringent limits on many of the components of the relevant Lorentz-violating parameter. We also obtain the Lorentz-violating nucleon-nucleon potential. We suggest that this potential may be used to obtain new limits from atomic-clock or deuteron storage-ring experiments.
↳ hep-phnucl-thPRD(2017)·17 citations
10
Investigating the impact of the gluon saturation effects on the momentum transfer distributions for the exclusive vector meson photoproduction in hadronic collisions
V. P. Goncalves🇧🇷 · F. S. Navarra🇧🇷 · D. Spiering🇧🇷
The exclusive vector meson production cross section is one of the most promising observables to probe the high energy regime of the QCD dynamics. In particular, the squared momentum transfer ( $t$ ) distributions are an important source of information about the spatial distribution of the gluons in the hadron and about fluctuations of the color fields. In this paper we complement previous studies on exclusive vector meson photoproduction in hadronic collisions presenting a comprehensive analysis of the $t$ - spectrum measured in exclusive $ρ$ , $ϕ$ and $J /Ψ$ photoproduction in $pp$ and $P b P b$ collisions at the LHC. We compute the differential cross sections taking into account gluon saturation effects and compare the predictions with those obtained in the linear regime of the QCD dynamics. Our results show that gluon saturation suppresses the magnitude of the cross sections and shifts the position of the dips towards smaller values of $t$ .
↳ hep-phhep-exnucl-exnucl-thPLB(2017)·25 citations
11
Quark-Nuclear Hybrid EoS with Excluded Volume Effects
Mark Alexander Randolph Kaltenborn🇺🇸 · Niels-Uwe Friedrich Bastian🇵🇱 · David Bernhard Blaschke🇵🇱
A two-phase description of the quark-nuclear matter hybrid equation of state that takes into account the effect of excluded volume in both the hadronic and the quark matter phases is introduced. The nuclear phase manifests a reduction of the available volume as density increases, leading to a stiffening of the matter. The quark matter phase displays a reduction of the effective string tension in the confining density functional from available volume contributions. The nuclear equation of state is based upon the relativistic density functional model DD2 with excluded volume. The quark matter is based upon a mean-field modification to the free fermi gas and will be discussed in greater detail. The interactions are decomposed into mean scalar and vector components. The scalar interaction is motivated by a string potential between quarks, whereas the vector interaction potential is motivated by higher order interactions of quarks leading to an increased stiffening at high densities. As an application, we consider matter under compact star constraints of electric neutrality and $β$ -equilibrium. We obtain mass-radius relations for hybrid stars that form a third family, disconnected from the purely hadronic star branch, and fulfill the $2 M_{⊙}$ constraint.
↳ astro-ph.HEhep-phnucl-thPRD(2017)·117 citations

Affiliations

first authorsco-authorsvia INSPIRE