Nuclear Theory·nucl-th

Thursday·June 23, 2016

7 papers—1 primary·6 cross-listed

02
[Submitted on 21 Jun 2016] (cross-list from hep-ph)
Elementary quantum mechanics of the neutron with an electric dipole moment
Gordon Baym🇺🇸 · D. H. Beck🇺🇸
The neutron, in addition to possibly having a permanent electric dipole moment as a consequence of violation of time-reversal invariance, develops an induced electric dipole moment in the presence of an external electric field. We present here a unified non-relativistic description of these two phenomena, in which the dipole moment operator, $D$ , is not constrained to lie along the spin operator. Although the expectation value of $D$ in the neutron is less than $1 0^{- 13}$ of the neutron radius, $r_{n}$ , the expectation value of $D^{2}$ is of order $r_{n}^{2}$ . We determine the spin motion in external electric and magnetic fields, as employed in past and future searches for a permanent dipole moment, and show that the neutron electric polarizability, although entering the neutron energy in an external electric field, does not affect the spin motion. In a simple non-relativistic model we show that the expectation value of the permanent dipole is, to lowest order, proportional to the product of the time reversal-violating coupling strength and the electric polarizability of the neutron.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1606.06774 [pdf]
Proc.Nat.Acad.Sci.(2016)·9 citations
03
[Submitted on 22 Jun 2016] (cross-list from nucl-th)
Nuclear Modification Factor Using Tsallis Non-extensive Statistics
Sushanta Tripathy🇮🇳 · Trambak Bhattacharyya🇿🇦 · Prakhar Garg🇮🇳 · Prateek Kumar🇮🇳 · Raghunath Sahoo🇮🇳 · Jean Cleymans🇿🇦
The nuclear modification factor is derived using Tsallis non-extensive statistics in relaxation time approximation. The variation of nuclear modification factor with transverse momentum for different values of non-extensive parameter, $q$ , is also observed. The experimental data from RHIC and LHC are analysed in the framework of Tsallis non-extensive statistics in a relaxation time approximation. It is shown that the proposed approach explains the $R_{AA}$ of all particles over a wide range of transverse momenta but doesn't seem to describe the rise in $R_{AA}$ at very high transverse momenta.
Comments:
Same as the published version in EPJA
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1606.06898 [pdf]
EPJA(2016)·61 citations
04
[Submitted on 22 Jun 2016] (cross-list from nucl-th)
Limiting Fragmentation in a Thermal Model with Flow
Swatantra Kumar Tiwari🇮🇳 · Raghunath Sahoo🇮🇳
The property of limiting fragmentation of various observables such as rapidity distributions ( $d N / d y$ ), elliptic flow ( $v_{2}$ ), average transverse momentum ( $⟨ p_{T} ⟩$ ) etc. of charged particles is observed when they are plotted as a function of rapidity ( $y$ ) shifted by the beam rapidity ( $y_{b e am}$ ) for a wide range of energies from AGS to RHIC. Limiting fragmentation (LF) is a well studied phenomenon as observed in various collision energies and colliding systems experimentally. It is very interesting to verify this phenomenon theoretically. We study such a phenomenon for pion rapidity spectra using our hydrodynamic-like model where the collective flow is incorporated in a thermal model in the longitudinal direction. Our findings advocate the observation of extended longitudinal scaling in the rapidity spectra of pions from AGS to lower RHIC energies, while it is observed to be violated at top RHIC and LHC energies. Prediction of LF hypothesis for Pb+Pb collisions at $s_{N N}$ =5.02 TeV is given.
Comments:
Published version in EPJA
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1606.06906 [pdf]
EPJA(2016)·2 citations
05
[Submitted on 22 Jun 2016] (cross-list from hep-ph)
Neutron-skin effect in direct-photon and charged hadron-production in Pb+Pb collisions at the LHC
Ilkka Helenius🇸🇪 · Hannu Paukkunen🇫🇮 · Kari J. Eskola🇫🇮
A well-established observation in nuclear physics is that in neutron-rich spherical nuclei the distribution of neutrons extends farther than the distribution of protons. In this work, we scrutinize the influence of this so called neutron-skin effect on the centrality dependence of high- $p_{T}$ direct-photon and charged-hadron production. We find that due to the estimated spatial dependence of the nuclear parton distribution functions, it will be demanding to unambiguously expose the neutron-skin effect with direct photons. However, when taking a ratio between the cross sections for negatively and positively charged high- $p_{T}$ hadrons, even centrality-dependent nuclear-PDF effects cancel, making this observable a better handle on the neutron skin. Up to 20~\% effects can be expected for the most peripheral collisions.
Comments:
7 pages, 3 figures, corresponds to the published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1606.06910 [pdf]
EPJC(2017)·22 citations
06
[Submitted on 22 Jun 2016] (cross-list from hep-ph)
Charged current quasi elastic scattering of muon neutrino with nuclei
Kapil Saraswat🇮🇳 · Prashant Shukla🇮🇳 · Vineet Kumar🇮🇳 · Venktesh Singh🇮🇳
We present a study on the charge current quasi elastic scattering of $ν_{μ}$ from nucleon and nuclei which gives a charged muon in the final state. To describe nuclei, the Fermi Gas model has been used with proposed Pauli suppression factor. The diffuseness parameter of the Fermi distribution has been obtained using experimental data. We also investigate different parametrizations for electric and magnetic Sach's form factors of nucleons. Calculations have been made for CCQES total and differential cross sections for the cases of $ν_{μ} - N$ , $ν_{μ} -^{12} C$ and $ν_{μ} -^{56} F e$ scatterings and are compared with the data for different values of the axial mass. The present model gives excellent description of measured differential cross section for all the systems.
Comments:
14 pages, 14 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1606.06916 [pdf]
Indian J.Phys.(2018)·4 citations
07
[Submitted on 22 Jun 2016] (cross-list from hep-lat)
Axial, Scalar and Tensor Charges of the Nucleon from 2+1+1-flavor Lattice QCD
Tanmoy Bhattacharya🇺🇸 · Vincenzo Cirigliano🇺🇸 · Saul Cohen🇺🇸 · Rajan Gupta🇺🇸 · Huey-Wen Lin🇺🇸 · Boram Yoon🇺🇸
We present results for the isovector axial, scalar and tensor charges $g_{A}^{u - d}$ , $g_{S}^{u - d}$ and $g_{T}^{u - d}$ of the nucleon needed to probe the Standard Model and novel physics. The axial charge is a fundamental parameter describing the weak interactions of nucleons. The scalar and tensor charges probe novel interactions at the TeV scale in neutron and nuclear $β$ -decays, and the flavor-diagonal tensor charges $g_{T}^{u}$ , $g_{T}^{d}$ and $g_{T}^{s}$ are needed to quantify the contribution of the quark electric dipole moment (EDM) to the neutron EDM. The 9 ensembles, generated by the MILC Collaboration using the HISQ action with 2+1+1 dynamical flavors, span three lattice spacings $a \approx 0.06, 0.09$ and 0.12 fm and light-quark masses corresponding to the pion masses $M_{π} \approx 135, 225$ and 315 MeV. High-statistics estimates on five ensembles using the all-mode-averaging method allow us to quantify all systematic uncertainties and perform a simultaneous extrapolation in the lattice spacing, lattice volume and light-quark masses for the connected contributions. Our final estimates, in the $MS$ scheme at 2 GeV, of the isovector charges are $g_{A}^{u - d} = 1.195 (33) (20)$ , $g_{S}^{u - d} = 0.97 (12) (6)$ and $g_{T}^{u - d} = 0.987 (51) (20)$ . The first error includes statistical and all systematic uncertainties except that due to the extrapolation Ansatz, which is given by the second error estimate. Combining our estimate for $g_{S}^{u - d}$ with the difference of light quarks masses $(m_{d} - m_{u})^{QCD} = 2.67 (35)$ MeV given by FLAG, we obtain $(M_{N} - M_{P})^{QCD} = 2.59 (49)$ MeV. Estimates of the connected part of the flavor-diagonal tensor charges of the proton are $g_{T}^{u} = 0.792 (42)$ and $g_{T}^{d} = - 0.194 (14)$ . Combining our new estimates with precision low-energy experiments, we update constraints on novel scalar and tensor interactions, $ϵ_{S, T}$ , at the TeV scale.
Comments:
Published Version
Subjects:
High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1606.07049 [pdf]
PRD(2016)·205 citations

Affiliations

first authorsco-authorsvia INSPIRE

Elementary quantum mechanics of the neutron with an electric dipole moment

Nuclear Modification Factor Using Tsallis Non-extensive Statistics

Limiting Fragmentation in a Thermal Model with Flow

Neutron-skin effect in direct-photon and charged hadron-production in Pb+Pb collisions at the LHC

Charged current quasi elastic scattering of muon neutrino with nuclei

Axial, Scalar and Tensor Charges of the Nucleon from 2+1+1-flavor Lattice QCD

Affiliations