Nuclear Theory·nucl-th

Friday·March 3, 2017

8 papers—5 primary·3 cross-listed

06
[Submitted on 2 Mar 2017] (cross-list from nucl-ex)
Missing-mass spectroscopy with the $^{6}$ Li( $π^{-}, K^{+}$ )X reaction to search for $_{Λ}^{6}$ H
R. Honda🇯🇵 · M. Agnello🇮🇹 · J. K. Ahn🇰🇷 · S. Ajimura🇯🇵 · Y. Akazawa🇯🇵 · N. Amano🇯🇵 · K. Aoki🇯🇵 · H. C. Bhang🇰🇷 · N. Chiga🇯🇵 · M. Endo🇯🇵 · P. Evtoukhovitch🇷🇺 · A. Feliciello🇮🇹 and 54 other authors
We searched for the bound state of the neutron-rich $Λ$ -hypernucleus $_{Λ}^{6}$ H, using the $^{6}$ Li( $π^{-}, K^{+}$ )X double charge-exchange reaction at a $π^{-}$ beam momentum of 1.2 GeV/c at J-PARC. A total of $1.4 \times 1 0^{12}$ $π^{-}$ was driven onto a $^{6}$ Li target of 3.5-g/ $c m^{2}$ thickness. No event was observed below the bound threshold, i.e., the mass of $_{Λ}^{4}$ H + 2n, in the missing-mass spectrum of the $^{6}$ Li( $π^{-}, K^{+}$ )X reaction in the $2^{\circ}$ < $θ_{π K}$ < $2 0^{\circ}$ angular range. Furthermore, no event was found up to 2.8 MeV/ $c^{2}$ above the bound threshold. We obtained the the double-differential cross section spectra of the $^{6}$ Li( $π^{-}, K^{+}$ )X reaction in the angular range of $2^{\circ}$ < $θ_{π K}$ < $1 4^{\circ}$ . An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the $_{Λ}^{6}$ H hypernucleus bound state. In addition, not only the bound state region, but also the $Λ$ continuum region and part of the $Σ^{-}$ quasi-free production region of the $^{6}$ Li( $π^{-}, K^{+}$ )X reaction, were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the $Σ^{-}$ -nucleus optical potential for $Σ^{-}$ - $^{5}$ He through spectrum shape analysis.
Comments:
24 pages, 17 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1703.00623 [pdf]
PRC(2017)·16 citations
07
[Submitted on 2 Mar 2017] (cross-list from hep-ph)
String dynamics and metastability of fully-heavy tetraquarks
Jean-Marc Richard (Lyon)🇫🇷 · Alfredo Valcarce (Salamanca)🇪🇸 · Javier Vijande (Valencia)🇪🇸
Multiquark states have been advocated to explain recent experimental data in the heavy-light sector, and there are already speculations about multiquarks containing only heavy quarks and antiquarks. With a rigorous treatment of the four-body problem in current quark models, full-charm $(cc c ˉ c ˉ)$ and full-beauty $(bb b ˉ b ˉ)$ tetraquarks are found to be unbound. Thus their stability should rely on more subtle effects that are not included in the simple picture of constituent quarks. The case of $(b c b ˉ c ˉ)$ might be more favorable if the naive color-additive model of confinement is replaced by a string-inspired interaction.
Comments:
9 pages, 3 figs., to appear in Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1703.00783 [pdf]
PRD(2017)·117 citations
08
[Submitted on 2 Mar 2017] (cross-list from hep-lat)
Parallel tempering algorithm for integration over Lefschetz thimbles
Masafumi Fukuma🇯🇵 · Naoya Umeda🇯🇵
The algorithm based on integration over Lefschetz thimbles is a promising method to resolve the sign problem for complex actions. However, this algorithm often meets a difficulty in actual Monte Carlo calculations because the configuration space is not easily explored due to the infinitely high potential barriers between different thimbles. In this paper, we propose to use the flow time of the antiholomorphic gradient flow as an auxiliary variable for the highly multimodal distribution. To illustrate this, we implement the parallel tempering method by taking the flow time as a tempering parameter. In this algorithm, we can take the maximum flow time to be sufficiently large such that the sign problem disappears there, and two separate modes are connected through configurations at small flow times. To exemplify that this algorithm does work, we investigate the (0+1)-dimensional massive Thirring model at finite density and show that our algorithm correctly reproduces the analytic results for large flow times such as T=2.
Comments:
14 pages, 5 figures. v2: typos corrected, figures updated. v3: title changed, references added, typos corrected
Subjects:
High Energy Physics — Lattice (hep-lat); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1703.00861 [pdf]
PTEP(2017)·80 citations

Affiliations

first authorsco-authorsvia INSPIRE

Missing-mass spectroscopy with the 6Li(π−,K+)X reaction to search for Λ6​H

String dynamics and metastability of fully-heavy tetraquarks

Parallel tempering algorithm for integration over Lefschetz thimbles

Affiliations

Missing-mass spectroscopy with the $^{6}$ Li( $π^{-}, K^{+}$ )X reaction to search for $_{Λ}^{6}$ H