Nuclear Theory·nucl-th

Tuesday·December 17, 2019

14 papers—6 primary·8 cross-listed

07
[Submitted on 13 Dec 2019] (cross-list from hep-ph)
A new approach to search for free neutron-antineutron oscillations using coherent neutron propagation in gas
V. Gudkov🇺🇸 · V. V. Nesvizhevsky🇫🇷 · K. V. Protasov🇫🇷 · W. M. Snow🇺🇸 · A. Yu. Voronin🇷🇺
Coherent forward neutron propagation in gas is discussed as a new approach to search for neutron-antineutron oscillations ( $n - n ˉ$ ), which violate both $B$ and $B - L$ conservation. We show that one can increase the probability of neutron - antineutron transitions to essentially the free neutron oscillation rate in the presence of a nonzero external magnetic field by tuning the density of an appropriate mixture of gases so that the neutron optical potential of the gas cancels that from an external magnetic field.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1912.06730 [pdf]
PLB(2020)·21 citations
08
[Submitted on 14 Dec 2019] (cross-list from nucl-ex)
Compton scattering from $^{4}$ He at the TUNL HI $γ$ S facility
X. Li🇺🇸 · M.W. Ahmed🇺🇸 · A. Banu🇺🇸 · C. Bartram🇺🇸 · B. Crowe🇺🇸 · E.J. Downie🇺🇸 · M. Emamian🇺🇸 · G. Feldman🇺🇸 · H. Gao🇺🇸 · D. Godagama🇺🇸 · H.W. Grießhammer🇺🇸 · C.R. Howell🇺🇸 and 17 other authors
Differential cross sections for elastic Compton scattering from $^{4}$ He have been measured with high statistical precision at the High Intensity $γ$ -ray Source at laboratory scattering angles of $5 5^{\circ}$ , $9 0^{\circ}$ , and $12 5^{\circ}$ using a quasi-monoenergetic photon beam with a weighted mean energy value of $81.3$ MeV. The results are compared to previous measurements and similar fore-aft asymmetry in the angular distribution of the differential cross sections is observed. This experimental work is expected to strongly motivate the development of effective-field-theory calculations of Compton scattering from $^{4}$ He to fully interpret the data.
Comments:
8 pages, 8 figures
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1912.06915 [pdf]
PRC(2020)·9 citations
09
[Submitted on 15 Dec 2019] (cross-list from hep-ph)
Threshold cusps and triangle singularities in hadronic reactions
Feng-Kun Guo🇨🇳 · Xiao-Hai Liu · Shuntaro Sakai🇨🇳
The spectrum of hadrons is the manifestation of color confinement of quantum chromodynamics. Hadronic resonances correspond to poles of the S-matrix. Since 2003, lots of new hadron resonant structures were discovered in the mass regions from light mesons to hadrons containing a pair of a heavy quark and an antiquark. Many of them are candidates of exotic hadrons, and they are usually observed as peaks in invariant mass distributions. However, the S-matrix also has kinematical singularities due to the on-shellness of intermediate particles for a process, such as two-body thresholds and triangle singularities, and they can produce peaks as well. On the one hand, such singularities may be misidentified as resonances; on the other hand, they can be used as tools for precision measurements. In this paper, we review the threshold cusps and various triangle singularities in hadronic reactions, paying attention to their manifestations in phenomena related to exotic hadron candidates.
Comments:
Version accepted for publication in Prog. Part. Nucl. Phys.; 84 pages, 34 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1912.07030 [pdf]
PPNP(2020)·381 citations
10
[Submitted on 16 Dec 2019] (cross-list from hep-ph)
Systematic study on production of hidden-bottom pentaquark via $γ p$ and $π^{-} p$ scatterings
Xiao-Yun Wang🇨🇳 · Jun He🇨🇳 · Xurong Chen🇨🇳
The production of hidden-bottom pentaquark $P_{b}$ states via $γ p$ and $π^{-} p$ scatterings is studied within an effective Lagrangian approach and the vector-meson-dominance mechnism. For the $P_{b}$ production in the process $γ p \to Υ p$ , the dipole Pomeron model is employed to calculate the background contribution, and the experimental data can be well described. For the process $π^{-} p \to Υ n$ , the Reggeized $t$ -channel with $π$ exchange is considered as the main background for the $P_{b}$ production. Near the threshold, two-peak structure from the states $P_{b (11080)$ and $P_{b} (11125)$ can be observed if energy bin width is chosen as 0.01 GeV, and the same result is obtained in the $π^{-} p$ scattering. Moreover, by taking the branching ratio of Br $[P_{b} \to π N] ≃ 0.05%$ , the numerical result shows that the average value of cross section from the $P_{b} (11080)$ state produced in the $γ p$ or $π^{-} p$ scattering reaches at least 0.1 nb with a bin of 0.1 GeV. Even if we reduce the branching ratio of the $P_{b}$ state into $π N$ channel by one order, the theoretical average of the cross section from $P_{b} (11080)$ production in $π^{-} p$ scattering can reach the order of 0.01 nb with a bin of 0.1 GeV, which means that the signal can still be clearly distinguished from the background. The experimental measurements and studies on the hidden-bottom pentaquark $P_{b}$ state production in the $γ p$ or $π^{-} p$ scattering near-threshold energy region around $W ≃ 11$ GeV are strongly suggested, which are accessible at COMPASS and JPARC. Particularly, the result of the photoproduction suggests that it is very promising to observe the hidden-bottom pentaquark at proposed EicC facility in China.
Comments:
7 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1912.07156 [pdf]
PRD(2020)·21 citations
11
[Submitted on 16 Dec 2019] (cross-list from hep-ex)
Two-particle azimuthal correlations as a probe of collective behaviour in deep inelastic $ep$ scattering at HERA
ZEUS Collaboration
Two-particle azimuthal correlations have been measured in neutral current deep $\mbox in e l a s t i c$ $ep$ scattering with virtuality $Q^{2} > 5$ GeV $^{2}$ at a centre-of-mass energy $s = 318$ GeV recorded with the ZEUS detector at HERA. The correlations of charged particles have been measured in the range of laboratory pseudorapidity $- 1.5 < η < 2.0$ and transverse momentum $0.1 < p_{T} < 5.0$ GeV and event multiplicities $N_{ch}$ up to six times larger than the average $⟨ N_{ch} ⟩ \approx 5$ . The two-particle correlations have been measured in terms of the angular observables $c_{n} {2} = ⟨ ⟨ cos n Δ φ ⟩ ⟩$ , where $n$ is between 1 and 4 and $Δ φ$ is the relative azimuthal angle between the two particles. Comparisons with available models of deep inelastic scattering, which are tuned to reproduce inclusive particle production, suggest that the measured two-particle correlations are dominated by contributions from multijet production. The correlations observed here do not indicate the kind of collective behaviour recently observed at the highest RHIC and LHC energies in high-multiplicity hadronic collisions.
Comments:
Updated draft after JHEP review. Fix plotting mistake in figures 3-5
Subjects:
High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1912.07431 [pdf]
JHEP(2020)·56 citations
12
[Submitted on 16 Dec 2019] (cross-list from hep-lat)
Dirac spectrum and the BEC-BCS crossover in QCD at nonzero isospin asymmetry
B. B. Brandt🇩🇪 · F. Cuteri🇩🇪 · G. Endrődi🇩🇪 · S. Schmalzbauer🇩🇪
For large isospin asymmetries, perturbation theory predicts the QCD ground state to be a superfluid phase of $u$ and $d ˉ$ Cooper pairs. This phase, which is denoted as the BCS phase, is expected to be smoothly connected to the standard phase with Bose-Einstein condensation (BEC) of charged pions at $μ_{I} \geq m_{π} /2$ by an analytic crossover. A first hint for the existence of the BCS phase, which is likely characterised by the presence of both, deconfinement and charged pion condensation, is coming from the lattice observation that the deconfinement crossover smoothly penetrates into the BEC phase. To further scrutinize the existence of the BCS phase, in this proceedings article we investigate the complex spectrum of the massive Dirac operator in 2+1-flavor QCD at nonzero temperature and isospin chemical potential. The spectral density near the origin is related to the BCS gap via a generalization of the Banks-Casher relation to the case of complex Dirac eigenvalues (derived for the zero-temperature, high-density limits of QCD at nonzero isospin chemical potential).
Comments:
6 pages, 5 figures, Proceedings of "The II International Workshop on Theory of Hadronic Matter under Extreme Conditions" - Dubna, JINR
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1912.07451 [pdf]
Particles(2020)·23 citations
13
[Submitted on 16 Dec 2019] (cross-list from hep-ph)
Pion observables with the Minkowski Space Pion Model
J. P. B. C. de Melo (Laboratório de Física Teórica e Computacional, LFTC/Universidade Cruzeiro do Sul/Universidade Cidade de São Paulo)🇧🇷 · Rômulo M. Moita🇧🇷 · Tobias Frederico (Instituto Tecnológico de Aeronáutica, DCTA 12.228-900 São José dos Campos, SP, Brazil)🇧🇷
The pion structure in Minkowski space is described in terms of an analytic model of the Bethe-Salpeter amplitude combined with Euclidean Lattice QCD results for the running quark mass. In the present work, a pion model previously proposed, which allows for a Nakanishi integral representation, is studied in order to verify the sensitivity of the pion electromagnetic form factor to small variations of the quark self-energy. In addition, we extend the previous work, providing the Nakanishi integral representation for the invariants associated with a decomposition of the pion Bethe-Salpeter amplitude.
Comments:
Use PoS style. Light Cone 2019 - QCD on the light cone: from hadrons to heavy ions - LC2019 - 16-20 September 2019 -Ecole Polytechnique, Palaiseau, France
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1912.07459 [pdf]
PoS(2019)·2 citations
14
[Submitted on 13 Dec 2019] (cross-list from hep-ph)
Drawing insights from pion parton distributions
Minghui Ding🇨🇳 · Khépani Raya🇲🇽 · Daniele Binosi🇮🇹 · Lei Chang🇨🇳 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪
A symmetry-preserving continuum approach to the two valence-body bound-state problem is used to calculate the valence, glue and sea distributions within the pion; unifying them with, inter alia, electromagnetic pion elastic and transition form factors. The analysis reveals the following momentum fractions at the scale $ζ_{2} := 2$ GeV: $⟨ x_{valence} ⟩ = 0.48 (3)$ , $⟨ x_{glue} ⟩ = 0.41 (2)$ , $⟨ x_{sea} ⟩ = 0.11 (2)$ ; and despite hardening induced by the emergent phenomenon of dynamical chiral symmetry breaking, the valence-quark distribution function, $q^{π} (x)$ , exhibits the $x ≃ 1$ behaviour predicted by quantum chromodynamics (QCD). After evolution to $ζ = 5.2$ GeV, the prediction for $q^{π} (x)$ matches that obtained using lattice-regularised QCD. This confluence should both stimulate improved analyses of existing data and aid in planning efforts to obtain new data on the pion distribution functions.
Comments:
6 pages, 1 figure. To be published as a Letter in Chinese Physics C. arXiv admin note: substantial text overlap with arXiv:1905.05208
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1912.07529 [pdf]
CPC(2020)·55 citations

Affiliations

first authorsco-authorsvia INSPIRE