Nuclear Theory·nucl-th

Monday·June 1, 2015

8 papers—2 primary·6 cross-listed

01
Nuclear medium effects in structure functions of nucleon at moderate $Q^{2}$
H. Haider🇮🇳 · F. Zaidi🇮🇳 · M. Sajjad Athar🇮🇳 · S. K. Singh🇮🇳 · I. Ruiz Simo🇪🇸
Recent experiments performed on inclusive electron scattering from nuclear targets have measured the nucleon electromagnetic structure functions $F_{1} (x, Q^{2})$ , $F_{2} (x, Q^{2})$ and $F_{L} (x, Q^{2})$ in $^{12} C$ , $^{27} A l$ , $^{56} F e$ and $^{64} C u$ nuclei. The measurements have been done in the energy region of $1 G e V^{2} < W^{2} < 4 G e V^{2}$ and $Q^{2}$ region of $0.5 G e V^{2} < Q^{2} < 4.5 G e V^{2}$ . We have calculated nuclear medium effects in these structure functions arising due to the Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects. The calculations are performed in a local density approximation using relativistic nucleon spectral function which include nucleon correlations. The numerical results are compared with the recent experimental data from JLab and also with some earlier experiments.
nucl-thhep-phNPA(2015)·25 citations
02
Probing Shadowed Nuclear Sea with Massive Gauge Bosons in the Future Heavy-Ion Collisions
Peng Ru🇨🇳 · Ben-Wei Zhang🇨🇳 · Enke Wang🇨🇳 · Wei-Ning Zhang🇨🇳
The production of the massive bosons $Z^{0}$ and $W^{\pm}$ could provide an excellent tool to study cold nuclear matter effects and the modifications of nuclear parton distribution functions (nPDFs) relative to parton distribution functions (PDFs) of a free proton in high energy nuclear reactions at the LHC as well as in heavy-ion collisions (HIC) with much higher center-of mass energies available in the future colliders. In this paper we calculate the rapidity and transverse momentum distributions of the vector boson and their nuclear modification factors in p+Pb collisions at $s_{N N} = 63$ TeV and in Pb+Pb collisions at $s_{N N} = 39$ TeV in the framework of perturbative QCD by utilizing three parametrization sets of nPDFs: EPS09, DSSZ and nCTEQ. It is found that in heavy-ion collisions at such high colliding energies, both the rapidity distribution and the transverse momentum spectrum of vector bosons are considerably suppressed in wide kinematic regions with respect to p+p reactions due to large nuclear shadowing effect. We demonstrate that in the massive vector boson productions processes with sea quarks in the initial-state may give more contributions than those with valence quarks in the initial-state, therefore in future heavy-ion collisions the isospin effect is less pronounced and the charge asymmetry of W boson will be reduced significantly as compared to that at the LHC. Large difference between results with nCTEQ and results with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and $p_{T}$ distributions of $Z^{0}$ and $W$ in the future HIC.
nucl-thEPJC(2015)·9 citations
03
Signature of the Fragmentation of a Color Flux Tube
Cheuk-Yin Wong🇺🇸
The production of quark-antiquark pairs along a color flux tube precedes the fragmentation of the tube. Because of local conservation laws, the production of a $q$ - $q ˉ$ pair will lead to correlations of adjacently produced mesons (mostly pions). Adjacently produced mesons however can be signalled by their rapidity difference $Δ y$ falling within the window of $∣Δ y ∣$ $≲$ $1/ (d N / d y)$ , on account of the space-time-rapidity ordering of produced mesons in a flux tube fragmentation. Therefore, the local conservation laws of momentum, charge, and flavor will lead to a suppression of angular correlation function $d N / (d Δ ϕ d Δ y)$ for two mesons with opposite charges or strangeness on the near side at $(Δ ϕ, Δ y)$ $\sim$ 0, but an enhanced correlation on the back-to-back, away side at $Δ ϕ$ $\sim$ $π$ , within the window of $∣Δ y ∣$ $≲$ $1/ (d N / d y)$ . These properties can be used as signatures for the fragmentation of a color flux tube. The gross features of the signature of flux tube fragmentation for two oppositely charged mesons are qualitatively consistent with the STAR and NA61/SHINE angular correlation data for two hadrons with opposite charges in the low- $p_{T}$ region in high-energy $pp$ collisions.
↳ hep-phhep-exnucl-thPRD(2015)·7 citations
04
Holographic calculation of the QCD crossover temperature in a magnetic field
Romulo Rougemont (Sao Paulo U.)🇧🇷 · Renato Critelli (Sao Paulo U.)🇧🇷 · Jorge Noronha (Sao Paulo U. and Columbia U.)🇧🇷
Lattice data for the QCD equation of state and the magnetic susceptibility computed near the crossover transition at zero magnetic field are used to determine the input parameters of a five dimensional Einstein-Maxwell-Dilaton holographic model. Once the model parameters are fixed at zero magnetic field, one can use this holographic construction to study the effects of a magnetic field on the equilibrium and transport properties of the quark-gluon plasma. In this paper we use this model to study the dependence of the crossover temperature with an external magnetic field. Our results for the pressure of the plasma and the crossover temperature are in quantitative agreement with current lattice data for values of the magnetic field $0 \leq e B ≲ 0.3$ GeV $^{2}$ , which is the relevant range for ultrarelativistic heavy ion collision applications.
↳ hep-thhep-phnucl-thPRD(2016)·111 citations
05
First measurement of target and beam-target asymmetries in the $γ p \to π^{0} η p$ reaction
J. R. M. Annand🇬🇧 · H. J. Arends🇩🇪 · R. Beck🇩🇪 · N. Borisov🇷🇺 · A. Braghieri🇮🇹 · W. J. Briscoe🇺🇸 · S. Cherepnya🇷🇺 · C. Collicott🇨🇦 · S. Costanza🇮🇹 · E. J. Downie🇺🇸 · M. Dieterle🇨🇭 · A. Fix🇷🇺 and 55 other authors
The first data on target and beam-target asymmetries for the $γ p \to π^{0} η p$ reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the $Δ3/ 2^{-}$ amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves.
↳ nucl-exhep-exnucl-thPRC(2015)·13 citations
06
Fission barriers heights in A $\sim$ 200 mass region
K. Mahata
Statistical model analysis has been carried out for $p$ and $α$ induced fission reactions using a consistent description for fission barrier and level density in A $\sim$ 200 mass region. A continuous damping of shell correction with excitation energy have been considered. Extracted fission barriers agree well with the recent microscopic-macroscopic model. The shell corrections at the saddle point were found to be not significant.
↳ nucl-exnucl-thPramana(2015)·3 citations
07
Modelling Early Stages of Relativistic Heavy Ion Collisions: Coupling Relativistic Transport Theory to Decaying Color-electric Flux Tubes
M. Ruggieri🇮🇹 · A. Puglisi🇮🇹 · L. Oliva🇮🇹 · S. Plumari🇮🇹 · F. Scardina🇮🇹 · V. Greco🇮🇹
In this study we model early times dynamics of the system produced in relativistic heavy ion collisions by an initial color electric field which then decays to a plasma by the Schwinger mechanism, coupling the dynamical evolution of the initial color field to the dynamics of the many particles system produced by the decay. The latter is described by relativistic kinetic theory in which we fix the ratio $η / s$ rather than insisting on specific microscopic processes. We study isotropization and thermalization of the system produced by the field decay for a static box and for a $1 + 1$ D expanding geometry. We find that regardless of the viscosity of the produced plasma, the initial color electric field decays within $1$ fm/c; however in the case $η / s$ is large, oscillations of the field are effective along all the entire time evolution of the system, which affect the late times evolution of the ratio between longitudinal and transverse pressure. In case of small $η / s$ ( $η / s ≲ 0.3$ ) we find $τ_{i so t r o p i z a t i o n} \approx 0.8$ fm/c and $τ_{t h er ma l i z a t i o n} \approx 1$ fm/c in agreement with the common lore of hydrodynamics. Moreover we have investigated the effect of turning from the relaxation time approximation to the Chapman-Enskog one: we find that this improvement affects mainly the early times evolution of the physical quantities, the effect being milder in the late times evolution.
↳ hep-phnucl-thPRC(2015)·46 citations
08
Quark Nova Model for Fast Radio Bursts
Zachary Shand · Amir Ouyed · Nico Koning · Rachid Ouyed
FRBs are puzzling, millisecond, energetic radio transients with no discernible source; observations show no counterparts in other frequency bands. The birth of a quark star from a parent neutron star experiencing a quark nova - previously thought undetectable when born in isolation - provides a natural explanation for the emission characteristics of FRBs. The generation of unstable r-process elements in the quark nova ejecta provides millisecond exponential injection of electrons into the surrounding strong magnetic field at the parent neutron star's light cylinder via $β$ -decay. This radio synchrotron emission has a total duration of hundreds of milliseconds and matches the observed spectrum while reducing the inferred dispersion measure by approximately 200 cm $^{- 3}$ pc. The model allows indirect measurement of neutron star magnetic fields and periods in addition to providing astronomical measurements of $β$ -decay chains of unstable neutron rich nuclei. Using this model, we can calculate expected FRB average energies ( $\sim$ 10 $^{41}$ ergs), spectra shapes and provide a theoretical framework for determining distances.
↳ astro-ph.HEnucl-thRes.Astron.Astrophys.(2016)·27 citations

Affiliations

first authorsco-authorsvia INSPIRE