Nuclear Theory·nucl-th

Monday·December 14, 2015

16 papers—9 primary·7 cross-listed

01
[Submitted on 11 Dec 2015]
Comparing the Tsallis distribution with and without thermodynamical description in p+p collisions
H. Zheng🇮🇹 · Lilin Zhu🇨🇳
We compare two types of Tsallis distribution, i.e., with and without thermodynamical description, using the experimental data from the STAR, PHENIX, ALICE and CMS Collaborations on the rapidity and energy dependence of the transverse momentum spectra in p+p collisions. Both of them can give us the similar fitting power to the particle spectra. We show that the Tsallis distribution with thermodynamical description gives lower temperatures than the ones without it. The extra factor $m_{T}$ (transverse mass) in the Tsallis distribution with thermodynamical description plays an important role in the discrepancies between the two types of Tsallis distribution. But for the heavy particles, the choice to use the $m_{T}$ or $E_{T}$ (transverse energy) in the Tsallis distribution becomes more crucial.
Comments:
9 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1512.03555 [pdf]
Adv.High Energy Phys.(2016)·90 citations
02
[Submitted on 11 Dec 2015]
Isoscalar monopole and dipole excitations of cluster states and giant resonances in $^{12}$ C
Yoshiko Kanada-En'yo
The isoscalar monopole(ISM) and dipole(ISD) excitations in $^{12}$ C are theoretically investigated with the shifted antisymmetrized molecular dynamics(AMD) plus $3 α$ -cluster generator coordinate method(GCM). The small amplitude vibration modes are described by coherent one-particle one-hole excitations expressed by small shift of single-nucleon Gaussian wave functions within the AMD framework, whereas the large amplitude cluster modes are incorporated by superposing $3 α$ -cluster wave functions in the GCM. The coupling of the excitations in the intrinsic frame with the rotation and parity transformation is taken into account microscopically by the angular-momentum and parity projections. The present calculation describes the ISM and ISD excitations in a wide energy region covering cluster modes in the low-energy region and the giant resonances in the high-energy region, though the quantitative description of the high-energy part is not satisfactory. The low-energy ISM and ISD strengths of the cluster modes are enhanced by the radial motion of $α$ clusters, and they split into a couple of states because of the angular motion of $α$ clusters. The low-energy ISM strengths exhaust 26% of the EWSR, which is consistent with the experimental data for the $^{12}$ C( $0_{2}^{+}$ ;7.65 MeV) and $^{12}$ C( $0_{3}^{+}$ ;10.3 MeV) measured by $(e, e^{'})$ , $(α, α^{'})$ , and ( $^{6}$ Li, $^{6}$ Li $^{'}$ ) scatterings. In the calculated low-energy ISD strengths, two $1^{-}$ states (the $1_{1}^{-}$ and $1_{2}^{-}$ ) with the significant strengths are obtained in $E = 10 - 15$ MeV. It is indicated that the ISD excitations can be a good probe to experimentally search for new cluster states such as the $^{12}$ C( $1_{2}^{-}$ ) obtained in the present calculation.
Comments:
13 pages, 6 figures. arXiv admin note: text overlap with arXiv:1511.08530
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1512.03619 [pdf]
PRC(2016)·31 citations
03
[Submitted on 11 Dec 2015]
Strangeness At Extremes
Laura Tolos🇪🇸 · Daniel Cabrera🇩🇪 · Kanchan Khemchandani🇧🇷 · Alberto Martinez-Torres🇧🇷 · Elena Bratkovskaya🇩🇪 · Joerg Aichelin🇫🇷 · Marina Nielsen🇧🇷 · Fernando S. Navarra🇧🇷
We study the properties of strange mesons in vacuum and in the hot nuclear medium within unitarized coupled-channel effective theories. We determine transition probabilities, cross sections and scattering lengths for strange mesons. These scattering observables are of fundamental importance for understanding the dynamics of strangeness production and propagation in heavy-ion collisions.
Comments:
4 pages, 2 figures, to appear in the proceedings of The 12th International Conference on Hypernuclear and Strange Particle Physics (HYP2015), September 7-12, 2015, Tohoku University, Sendai, Japan
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1512.03639 [pdf]
JPS Conf.Proc.(2017)·0 citations
04
[Submitted on 11 Dec 2015]
Thermal decay rate of a metastable state with two degrees of freedom: dynamical modeling versus approximate analytical formula
Igor Gontchar (Omsk State Transport University) · Maria Chushnyakova (Omsk State Technical University, Tomsk Polytechnic University)
Accuracy of the Kramers approximate formula for the thermal decay rate of the metastable state is studied for the two-dimensional potential pocket. This is done by the comparison with the quasistationary rate resulting from the dynamical modeling. It is shown that the Kramers rate is in agreement with the quasistationary rate within the statistical errors provided the absorptive border is far enough from the potential ridge restricting the metastable state. As the absorptive border (or its part) gets closer to the ridge the Kramers formula underestimate the quasistationary rate. The difference reaches approximately the factor of 2 when the absorptive border coincides with the ridge.
Comments:
12 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1512.03644 [pdf]
Pramana(2017)·4 citations
05
[Submitted on 11 Dec 2015]
Nucleon Polarizabilities: from Compton Scattering to Hydrogen Atom
Franziska Hagelstein (JGU Mainz)🇩🇪 · Rory Miskimen (UMass Amherst)🇺🇸 · Vladimir Pascalutsa (JGU Mainz)🇩🇪
We review the current state of knowledge of the nucleon polarizabilities and of their role in nucleon Compton scattering and in hydrogen spectrum. We discuss the basic concepts, the recent lattice QCD calculations and advances in chiral effective-field theory. On the experimental side, we review the ongoing programs aimed to measure the nucleon (scalar and spin) polarizabilities via the Compton scattering processes, with real and virtual photons. A great part of the review is devoted to the general constraints based on unitarity, causality, discrete and continuous symmetries, which result in model-independent relations involving nucleon polarizabilities. We (re-)derive a variety of such relations and discuss their empirical value. The proton polarizability effects are presently the major sources of uncertainty in the assessment of the muonic hydrogen Lamb shift and hyperfine structure. Recent calculations of these effects are reviewed here in the context of the "proton-radius puzzle". We conclude with summary plots of the recent results and prospects for the near-future work.
Comments:
83 pages, 51 figures, 9 tables; typos corrected; published version
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Atomic Physics (physics.atom-ph)
arXiv:
1512.03765 [pdf]
PPNP(2016)·111 citations
06
[Submitted on 11 Dec 2015]
Benchmarking mean-field approximations to level densities
Y. Alhassid · G.F. Bertsch · C.N. Gilbreth · H. Nakada
We assess the accuracy of finite-temperature mean-field theory using as a standard the Hamiltonian and model space of the shell model Monte Carlo calculations. Two examples are considered: the nucleus $^{162}$ Dy, representing a heavy deformed nucleus, and $^{148}$ Sm, representing a nearby heavy spherical nucleus with strong pairing correlations. The errors inherent in the finite-temperature Hartree-Fock and Hartree-Fock-Bogoliubov approximations are analyzed by comparing the entropies of the grand canonical and canonical ensembles, as well as the level density at the neutron resonance threshold, with shell model Monte Carlo (SMMC) calculations, which are accurate up to well-controlled statistical errors. The main weak points in the mean-field treatments are seen to be: (i) the extraction of number-projected densities from the grand canonical ensembles, and (ii) the symmetry breaking by deformation or by the pairing condensate. In the absence of a pairing condensate, we confirm that the usual saddle-point approximation to extract the number-projected densities is not a significant source of error compared to other errors inherent to the mean-field theory. We also present an alternative formulation of the saddle-point approximation that makes direct use of an approximate particle-number projection and avoids computing the usual three-dimensional Jacobian of the saddle-point integration. We find that the pairing condensate is less amenable to approximate particle-number projection methods due to the explicit violation of particle-number conservation in the pairing condensate. Nevertheless, the Hartree-Fock-Bogoliubov theory is accurate to less than one unit of entropy for $^{148}$ Sm at the neutron threshold energy, which is above the pairing phase transition.
Comments:
18 pages, 19 figures and 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1512.03773 [pdf]
PRC(2016)·36 citations
07
[Submitted on 11 Dec 2015]
$n d$ Scattering and the $A_{y}$ Puzzle to Next-to-next-to-next-to-leading Order
Arman Margaryan · Roxanne P. Springer · Jared Vanasse
Polarization observables in neutron-deuteron scattering are calculated to next-to-next-to-next-to-leading order ( $N^{3} LO$ ) in pionless effective field theory ( $EFT_{\neq π}$ ). At $N^{3} LO$ the two-body $P$ -wave contact interactions are found to be important contributions to the neutron vector analyzing power, $A_{y} (θ)$ , and the deuteron vector analyzing power, $i T_{11} (θ)$ . Extracting the two-body $P$ -wave $EFT_{\neq π}$ coefficients from two-body scattering data and varying them within the expected $EFT_{\neq π}$ theoretical errors provides results that are consistent (at the $N^{3} LO$ level) with $A_{y}$ experimental data at low energies. Cutoff dependence of the $N^{3} LO$ correction of the doublet $S$ -wave $n d$ scattering amplitude suggests the need for a new three-body force at $N^{3} LO$ , which is likely one that mixes Wigner- symmetric and Wigner-antisymmetric three-body channels.
Comments:
18 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1512.03774 [pdf]
PRC(2016)·21 citations
08
[Submitted on 11 Dec 2015]
Effective field theory in the harmonic oscillator basis
S. Binder · A. Ekström · G. Hagen · T. Papenbrock · K. A. Wendt
We develop interactions from chiral effective field theory (EFT) that are tailored to the harmonic oscillator basis. As a consequence, ultraviolet convergence with respect to the model space is implemented by construction and infrared convergence can be achieved by enlarging the model space for the kinetic energy. In oscillator EFT, matrix elements of EFTs formulated for continuous momenta are evaluated at the discrete momenta that stem from the diagonalization of the kinetic energy in the finite oscillator space. By fitting to realistic phase shifts and deuteron data we construct an effective interaction from chiral EFT at next-to-leading order. Many-body coupled-cluster calculations of nuclei up to 132Sn exhibit a fast convergence of ground-state energies and radii in feasible model spaces.
Comments:
16 pages, 6 figures; published version
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1512.03802 [pdf]
PRC(2016)·43 citations
09
[Submitted on 11 Dec 2015]
The Triton Charge Radius to Next-to-next-to-leading order in Pionless Effective Field Theory
Jared Vanasse
The triton point charge radius is calculated to next-to-next-to-leading order (NNLO) in pionless effective field theory ( $EFT (\neq π)$ ), yielding a prediction of $1.14 \pm 0.19$ fm (leading order), $1.59 \pm 0.08$ fm (next-to leading order), and $1.62 \pm 0.03$ fm (NNLO) in agreement with the current experimental extraction of $1.5978 \pm 0.040$ fm [Angeli and Marinova, At. Data Nucl. Data Tables 99, 69 (2013)]. The error at NNLO is due to cutoff variation ( $\sim$ 1%) within a reasonable range of calculated cutoffs and from a $EFT (\neq π)$ error estimate ( $\sim$ 1.5%). In addition new techniques are introduced to add perturbative corrections to bound and scattering state calculations for short range effective field theories, but with a focus on their use in $EFT (\neq π)$
Comments:
v1: 41 pages, 21 figures; v2: 47 pages, 19 figures; v3: 51 pages 19 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1512.03805 [pdf]
PRC(2017)·44 citations

Affiliations

first authorsco-authorsvia INSPIRE