Nuclear Theory·nucl-th

Monday·February 22, 2016

9 papers—7 primary·2 cross-listed

01
Form Factors and Generalized Parton Distributions in Basis Light-Front Quantization
Lekha Adhikari🇺🇸 · Yang Li🇺🇸 · Xingbo Zhao🇨🇳 · Pieter Maris🇺🇸 · James P. Vary🇺🇸 · Alaa Abd El-Hady🇪🇬
We calculate the elastic form factors and the Generalized Parton Distributions (GPDs) for four low-lying bound states of a demonstration fermion-antifermion system, strong coupling positronium ( $e e ˉ$ ), using Basis Light-Front Quantization (BLFQ). Using this approach, we also calculate the impact-parameter dependent GPDs $q (x, b_{⊥})$ to visualize the fermion density in the transverse plane ( $b_{⊥}$ ). We compare selected results with corresponding quantities in the non-relativistic limit to reveal relativistic effects. Our results establish the foundation within BLFQ for investigating the form factors and the GPDs for hadronic systems.
nucl-thPRC(2016)·27 citations
02
Electromagnetic and Weak Nuclear Structure Functions $F_{1, 2} (x, Q^{2})$ in the Intermediate Region of $Q^{2}$
H. Haider🇮🇳 · F. Zaidi🇮🇳 · M. Sajjad Athar🇮🇳 · S. K. Singh🇮🇳 · I. Ruiz Simo🇪🇸
We have studied nuclear structure functions $F_{1 A} (x, Q^{2})$ and $F_{2 A} (x, Q^{2})$ for electromagnetic and weak processes in the region of $1 G e V^{2} < Q^{2} < 8 G e V^{2}$ . The nuclear medium effects arising due to Fermi motion, binding energy, nucleon correlations, mesonic contributions and shadowing effects are taken into account using a many body field theoretical approach. The calculations are performed in a local density approximation using a relativistic nucleon spectral function. The results are compared with the available experimental data. Implications of nuclear medium effects on the validity of Callan-Gross relation are also discussed.
nucl-thJPS Conf.Proc.(2016)·0 citations
03
Revisiting $ν_{μ} (ν ˉ_{μ})$ and $ν_{e} (ν ˉ_{e})$ Induced Quasielastic Scattering from Nuclei in Sub-GeV Energy Region
F. Akbar🇮🇳 · M. Rafi Alam🇮🇳 · M. Sajjad Athar🇮🇳 · S. Chauhan🇮🇳 · S. K. Singh🇮🇳 · F. Zaidi🇮🇳
We present the results of charged current quasielastic(CCQE) scattering cross sections from free as well as bound nucleons like in $^{12} C$ , $^{16} O$ , $^{40} A r$ and $^{208} P b$ nuclear targets in $E_{ν} (_{ν ˉ}) \leq$ 1 GeV energy region. The results are obtained using local Fermi gas model with and without RPA effect. The differences those may arise in the electron and muon production cross sections due to the different lepton mass, uncertainties in the axial dipole mass $M_{A}$ and pseudoscalar form factor, and due to the inclusion of second class currents have been highlighted for neutrino/antineutrino induced processes.
nucl-thJPS Conf.Proc.(2016)·0 citations
04
Effects of Nuclear Medium on the Sum Rules in Electron and Neutrino Scattering
F. Zaidi · H. Haider · M. Sajjad Athar · S. K. Singh · I. Ruiz Simo
In this work, we study the influence of nuclear medium effects on various parton model sum rules in nuclei and compare the results with the free nucleon case. We have used relativistic nucleon spectral function to take into account Fermi motion, binding and nucleon correlations. The pion and rho meson cloud contributions have been incorporated in a microscopic model. The effect of shadowing has also been considered.
nucl-thJPS Conf.Proc.(2016)·0 citations
05
Charge-changing transitions and capture strengths of pf-shell nuclei with $T_{z} = - 2$ at proton drip-line
Muneeb-Ur Rahman · Jameel-Un Nabi
Charge-changing transitions, commonly referred to as Gamow-Teller (GT) transitions, and electron capture/ $β^{+}$ -decay strengths for pf-shell nuclei with $T_{z} = - 2$ at proton drip-line have been calculated using the proton-neutron quasi-particle random phase approximation (pn-QRPA) model. The total GT $_{+}$ strength values and electron capture/ $β^{+}$ -decay rates are needed for the study of the late stages of the stellar evolution. The pn-QRPA theory is used for a microscopic calculation of GT strength distribution functions and associated stellar electron capture/ $β^{+}$ -decay rates of proton-rich pf-shell nuclei with $T_{z} = - 2$ in the mass range 46 $\leq$ A $\leq$ 56 at proton drip-line. Standard quenching factor of 0.74, usually implemented in the shell model calculation, has been incorporated for the comparison with experimental data (wherever available). The calculated GT strength of the two proton-rich nuclei, $^{52}$ Ni and $^{56}$ Zn are compared with experimental data of corresponding mirror nuclei. It has been found that the pn-QRPA results are in good agreement with the experimental data as well as shell model result. It is noted that the total GT strength increases linearly with the increase of mass number. The electron capture/ $β^{+}$ -decay rates for proton-rich nuclei are calculated on a temperature and density scale relevant to presupernova evolution of massive stars. The $β^{+}$ decay half-lives are compared with measured and other theoretical calculations.
nucl-thastro-ph.SRAstrophys.Space Sci.(2015)·1 citation
06
Spin-isospin transitions in chromium isotopes within the quasiparticle random phase approximation
Sadiye Cakmak · Jameel-Un Nabi · Tahsin Babacan · Ismail Maras
Beta decay and electron capture on isotopes of chromium are advocated to play a key role in the stellar evolution process. In this paper we endeavor to study charge-changing transitions for 24 isotopes of chromium ( $^{42 - 65}$ Cr). These include neutron-rich and neutron-deficient isotopes of chromium. Three different models from the QRPA genre, namely the pn-QRPA, the Pyatov method (PM) and the Schematic model (SM), were selected to calculate and study the Gamow-Teller (GT) transitions in chromium isotopes. The SM was employed separately in the particle-particle ( $pp$ ) and $pp$ + particle-hole ( $p h$ ) channels. To study the effect of deformation, the SM was first used assuming the nuclei to be spherical and later to be deformed. The PM was used both in $pp$ and $pp$ + $p h$ channels but only for the case of spherical nuclei. The pn-QRPA calculation was done by considering both $pp$ and $p h$ forces and taking deformation of nucleus into consideration. A recent study proved this version of pn-QRPA to be the best for calculation of GT strength distributions amongst the QRPA models. The pn-QRPA model calculated GT distributions had low-lying centroids and small widths as compared to other QRPA models. Our calculation results were also compared with other theoretical models and measurements wherever available. Our results are in decent agreement with previous measurements and shell model calculations.
nucl-thastro-ph.SRAdv.Space Res.(2015)·10 citations
07
Magnetic field-induced squeezing effect at RHIC and at the LHC
Long-gang Pang🇩🇪 · Gergely Endrődi🇩🇪 · Hannah Petersen🇩🇪
In off-central heavy-ion collisions, the quark-gluon plasma (QGP) is exposed to the strongest magnetic fields ever created in the universe. Due to the paramagnetic nature of the QGP at high temperatures, the spatially inhomogeneous magnetic field configuration exerts an anisotropic force density that competes with the pressure gradients resulting from purely geometric effects. In this paper, we simulate (3+1)-dimensional ideal hydrodynamics with external magnetic fields to estimate the effect of this force density on the anisotropic expansion of the QGP in collisions at RHIC and at the LHC. While negligible for quickly decaying magnetic fields, we find that long-lived fields generate a substantial force density that suppresses the momentum anisotropy of the plasma by up to $20%$ at the LHC energy, and also leaves its imprint on the elliptic flow $v_{2}$ of charged pions.
nucl-thPRC(2016)·55 citations
08
Precision Electron-Beam Polarimetry using Compton Scattering at 1 GeV
A. Narayan · D. Jones · J. C. Cornejo · M. M. Dalton · W. Deconinck · D. Dutta · D. Gaskell · J. W. Martin · K.D. Paschke · V. Tvaskis · A. Asaturyan · J. Benesch and 24 other authors
We report on the highest precision yet achieved in the measurement of the polarization of a low energy, $O$ (1 GeV), electron beam, accomplished using a new polarimeter based on electron-photon scattering, in Hall~C at Jefferson Lab. A number of technical innovations were necessary, including a novel method for precise control of the laser polarization in a cavity and a novel diamond micro-strip detector which was able to capture most of the spectrum of scattered electrons. The data analysis technique exploited track finding, the high granularity of the detector and its large acceptance. The polarization of the $180 μ$ A, $1.16$ ~GeV electron beam was measured with a statistical precision of $<$ ~1\% per hour and a systematic uncertainty of 0.59\%. This exceeds the level of precision required by the \qweak experiment, a measurement of the vector weak charge of the proton. Proposed future low-energy experiments require polarization uncertainty $<$ ~0.4\%, and this result represents an important demonstration of that possibility. This measurement is also the first use of diamond detectors for particle tracking in an experiment.
↳ nucl-exhep-phnucl-thphysics.acc-ph+1PRX(2016)·47 citations
09
Numerical models for stationary superfluid neutron stars in general relativity with realistic equations of state
Aurélien Sourie · Micaela Oertel · Jérôme Novak
We present a numerical model for uniformly rotating superfluid neutron stars, for the first time with realistic microphysics including entrainment, in a fully general relativistic framework. We compute stationary and axisymmetric configurations of neutron stars composed of two fluids, namely superfluid neutrons and charged particles (protons and electrons), rotating with different rates around a common axis. Both fluids are coupled by entrainment, a non-dissipative interaction which in case of a non-vanishing relative velocity between the fluids, causes the fluid momenta being not aligned with the respective fluid velocities. We extend the formalism by Comer and Joynt (2003) in order to calculate the equation of state (EoS) and entrainment parameters for an arbitrary relative velocity. The resulting entrainment matrix fulfills all necessary sum rules and in the limit of small relative velocity our results agree with Fermi liquid theory ones, derived to lowest order in the velocity. This formalism is applied to two new nuclear equations of state which are implemented in the numerical model. We are able to obtain precise equilibrium configurations. Resulting density profiles and moments of inertia are discussed employing both EoSs, showing the impact of entrainment and the dependence on the EoS.
↳ astro-ph.HEastro-ph.SRgr-qcnucl-thPRD(2016)·26 citations

Affiliations

first authorsco-authorsvia INSPIRE