Nuclear Theory·nucl-th

Friday·May 6, 2016

6 papers—4 primary·2 cross-listed

01
[Submitted on 5 May 2016]
Improvement in a phenomenological formula for ground state binding energies
G. Gangopadhyay
The phenomenological formula for ground state binding energy derived earlier (International Journal of Modern Physics E {\bf 20} (2011) 179) has been modified. The parameters have been obtained by fitting the latest available tabulation of experimental values. The major modifications include a new term for pairing and introduction of a new neutron magic number at $N = 160$ . The new formula reduced the root mean square deviation to 363 keV, a substantial improvement over the previous version of the formula.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1605.01476 [pdf]
IJMPE(2016)·1 citation
02
[Submitted on 5 May 2016]
Structure of $^{78}$ Ni from first principles computations
G. Hagen🇺🇸 · G. R. Jansen🇺🇸 · T. Papenbrock🇺🇸
Doubly magic nuclei have a simple structure and are the cornerstones for entire regions of the nuclear chart. Theoretical insights into the supposedly doubly magic $^{78}$ Ni and its neighbors are challenging because of the extreme neutron-to-proton ratio and the proximity of the continuum. We predict the $J^{π} = 2_{1}^{+}$ state in $^{78}$ Ni from a correlation with the $J^{π} = 2_{1}^{+}$ state in $^{48}$ Ca using chiral nucleon-nucleon and three-nucleon interactions. Our results confirm that $^{78}$ Ni is doubly magic, and the predicted low-lying states of $^{79, 80}$ Ni open the way for shell-model studies of many more rare isotopes.
Comments:
8 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1605.01477 [pdf]
PRL(2016)·141 citations
03
[Submitted on 5 May 2016]
Geometrical scaling of inclusive charged hadron $p_{T}$ spectra in Pb-Pb collsions at 2.76 TeV
W. C. Zhang🇨🇳
In Pb-Pb collisions at $s_{NN}$ = 2.76 TeV, we report on a geometrical scaling in the transverse momentum ( $p_{T}$ ) spectra of inclusive charged hadrons at 0-5 $%$ , 5-10 $%$ , 10-20 $%$ , 20-30 $%$ , 30-40 $%$ , 40-50 $%$ , 50-60 $%$ , 60-70 $%$ and 70-80 $%$ centralities. This geometrical scaling is exhibited when these spectra are expressed in terms of a new scaling variable, $p_{T}^{'} = p_{T} (191.5/ N_{A})^{1/ (3 λ + 6)}$ , where $N_{A}$ is the number of participating nucleon pairs, $λ$ is the scaling parameter. With the method of ratios, this scaling parameter is determined to be 1.68. We then use a single Tsallis distribution to parameterize the spectra at different centralities, and find that the Tsallis temperature $T$ is proportional to $N_{A}^{1/ (3 λ + 6)}$ , which is exactly the prediction of the geometrical scaling. The geometrical scaling also predicts that the charged-particle density per participating nucleon pair ( $(d N_{ch} / d η) / N_{A}$ ) grows as a power of $N_{A}$ , $N_{A}^{2/ (3 λ + 6)}$ , which is confirmed by the data collected by the ALICE collaboration.
Comments:
6 pages, 5 EPS figures included. In v2, another table is added, and the fifth reference has been changed
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1605.01541 [pdf]
0 citations
04
[Submitted on 5 May 2016]
Tritium $β$ -decay in chiral effective field theory
A. Baroni🇺🇸 · L. Girlanda🇮🇹 · A. Kievsky🇮🇹 · L.E. Marcucci🇮🇹 · R. Schiavilla🇺🇸 · M. Viviani🇮🇹
We evaluate the Fermi and Gamow-Teller (GT) matrix elements in tritium $β$ -decay by including in the charge-changing weak current the corrections up to one loop recently derived in nuclear chiral effective field theory ( $χ$ EFT). The trinucleon wave functions are obtained from hyperspherical-harmonics solutions of the Schrodinger equation with two- and three-nucleon potentials corresponding to either $χ$ EFT (the N3LO/N2LO combination) or meson-exchange phenomenology (the AV18/UIX combination). We find that contributions due to loop corrections in the axial current are, in relative terms, as large as (and in some cases, dominate) those from one-pion exchange, which nominally occur at lower order in the power counting. We also provide values for the low-energy constants multiplying the contact axial current and three-nucleon potential, required to reproduce the experimental GT matrix element and trinucleon binding energies in the N3LO/N2LO and AV18/UIX calculations.
Comments:
19 pages,6 figures, corrections to Text as suggested by Referee added; Erratum: 4 pages, 3 figures, corrections to Eq.(20), Tables I, II, III, Figures 4, 5, conclusions unchanged
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1605.01620 [pdf]
PRC(2016)·72 citations
05
[Submitted on 5 May 2016] (cross-list from hep-ph)
Hunting for exotic doubly hidden-charm/bottom tetraquark states
Wei Chen🇨🇦 · Hua-Xing Chen🇨🇳 · Xiang Liu🇨🇳 · T. G. Steele🇨🇦 · Shi-Lin Zhu🇨🇳
We develop a moment QCD sum rule method augmented by fundamental inequalities to study the existence of exotic doubly hidden-charm/bottom tetraquark states made of four heavy quarks. Using the compact diquark-antidiquark configuration, we calculate the mass spectra of these tetraquark states. There are 18 hidden-charm $cc c ˉ c ˉ$ tetraquark currents with $J^{P C} = 0^{++}$ , $0^{-+}$ , $0^{--}$ , $1^{++}$ , $1^{+-}$ , $1^{-+}$ , $1^{--}$ , and $2^{++}$ . We use them to perform QCD sum rule analyses, and the obtained masses are all higher than the spontaneous dissociation thresholds of two charmonium mesons, which are thus their dominant decay modes. The masses of the corresponding hidden-bottom $bb b ˉ b ˉ$ tetraquarks are all below or very close to the thresholds of the $Υ (1 S) Υ (1 S)$ and $η_{b} (1 S) η_{b} (1 S)$ , except one current of $J^{P C} = 0^{++}$ . Hence, we suggest to search for the doubly hidden-charm states in the $J / ψ J / ψ$ and $η_{c} (1 S) η_{c} (1 S)$ channels.
Comments:
5 pages, 3 figures and 2 tables. published in PLB
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1605.01647 [pdf]
PLB(2017)·196 citations
06
[Submitted on 5 May 2016] (cross-list from astro-ph.HE)
The millisecond pulsar mass distribution: Evidence for bimodality and constraints on the maximum neutron star mass
John Antoniadis · Thomas M. Tauris · Feryal Ozel · Ewan Barr · David J. Champion · Paulo C. C. Freire
The mass function of neutron stars (NSs) contains information about the late evolution of massive stars, the supernova explosion mechanism, and the equation-of-state of cold, nuclear matter beyond the nuclear saturation density. A number of recent NS mass measurements in binary millisecond pulsar (MSP) systems increase the fraction of massive NSs (with $M > 1.8$ M $_{⊙}$ ) to $\sim 20%$ of the observed population. In light of these results, we employ a Bayesian framework to revisit the MSP mass distribution. We find that a single Gaussian model does not sufficiently describe the observed population. We test alternative empirical models and infer that the MSP mass distribution is strongly asymmetric. The diversity in spin and orbital properties of high-mass NSs suggests that this is most likely not a result of the recycling process, but rather reflects differences in the NS birth masses. The asymmetry is best accounted for by a bimodal distribution with a low mass component centred at $1.39 3_{- 0.029}^{+ 0.031}$ M $_{⊙}$ and dispersed by $0.06 4_{- 0.025}^{+ 0.064}$ M $_{⊙}$ , and a high-mass component with a mean of $1.80 7_{- 0.132}^{+ 0.081}$ and a dispersion of $0.17 7_{- 0.072}^{+ 0.115}$ M $_{⊙}$ . We also establish a lower limit of $M_{ma x} \geq 2.018$ M $_{⊙}$ at 98% C.L. for the maximum NS mass, from the absence of a high-mass truncation in the observed masses. Using our inferred model, we find that the measurement of 350 MSP masses, expected after the conclusion of pulsar surveys with the Square-Kilometre Array, can result in a precise localization of a maximum mass up to 2.15 M $_{⊙}$ , with a 5% accuracy. Finally, we identify possible massive NSs within the known pulsar population and discuss birth masses of MSPs.
Comments:
submitted to ApJ; 21 pages in aastex6 two-column format, 12 figures, 5 tables. Comments are welcome
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1605.01665 [pdf]
217 citations

Affiliations

first authorsco-authorsvia INSPIRE

Improvement in a phenomenological formula for ground state binding energies

Structure of 78Ni from first principles computations

Geometrical scaling of inclusive charged hadron pT​ spectra in Pb-Pb collsions at 2.76 TeV

Tritium β-decay in chiral effective field theory

Hunting for exotic doubly hidden-charm/bottom tetraquark states

The millisecond pulsar mass distribution: Evidence for bimodality and constraints on the maximum neutron star mass

Affiliations

Structure of $^{78}$ Ni from first principles computations

Geometrical scaling of inclusive charged hadron $p_{T}$ spectra in Pb-Pb collsions at 2.76 TeV

Tritium $β$ -decay in chiral effective field theory