arXiv subjects

Lisheng Geng

Publications and source records attributed to Lisheng Geng.

66 records · Page 4Linked to original sources

arXiv2019

An Improved Evaluation of the Neutron Background in the PandaX-II Experiment

In dark matter direct detection experiments, neutron is a serious source of background, which can mimic the dark matter-nucleus scattering signals. In this paper, we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach. Instead of fully relying on the Monte Carlo simulation, the overall neutron background is determined from the neutron-induced high energy signals in the data. In addition, the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator, where the correlated emission of neutron(s) and $γ$(s) in the ($α$, n) reactions and spontaneous fissions is taken into consideration. With this method, the neutron backgrounds in the Run 9 (26-ton-day) and Run 10 (28-ton-day) data sets of PandaX-II are estimated to be 0.66$\pm$0.24 and 0.47$\pm$0.25 events, respectively.

hep-ex↗

arXiv2019

Searching for Neutrino-less Double Beta Decay of $^{136}$Xe with PandaX-II Liquid Xenon Detector

We report the Neutrino-less Double Beta Decay (NLDBD) search results from PandaX-II dual-phase liquid xenon time projection chamber. The total live time used in this analysis is 403.1 days from June 2016 to August 2018. With NLDBD-optimized event selection criteria, we obtain a fiducial mass of 219 kg of natural xenon. The accumulated xenon exposure is 242 kg$\cdot$yr, or equivalently 22.2 kg$\cdot$yr of $^{136}$Xe exposure. At the region around $^{136}$Xe decay Q-value of 2458 keV, the energy resolution of PandaX-II is 4.2%. We find no evidence of NLDBD in PandaX-II and establish a lower limit for decay half-life of 2.4 $ \times 10^{23} $ yr at the 90% confidence level, which corresponds to an effective Majorana neutrino mass $m_{ββ} < (1.3 - 3.5)$ eV. This is the first NLDBD result reported from a dual-phase xenon experiment.

hep-ex↗

arXiv2019

Meson-baryon Scattering in Extend-on-mass-shell scheme at $\mathcal{O}(p^3)$

In this present work, we study the scattering of a pseudoscalar meson off one ground state octet baryon in covariant baryon chiral perturbation theory up to the next-to-next-to-leading order. We remove the power counting breaking terms with the extended-on-mass-shell scheme. We perform the first combined study of the pion-nucleon and kaon-nucleon scattering data and show that the covariant baryon Chiral perturbation theory can provide a reasonable description of the experimental data for both channels.

hep-ph↗

arXiv2018

$Ξ$(2030) and $Ξ$(2120) as $\bar{K}^*Σ$ molecular states

In this work, the molecular states from the \bar{K}^{*}Σinteraction are studied in a quasipotential Bethe-Salpeter equation approach with the one-boson-exchange potentials. We consider the exchanges of vector (ρ,ωand ϕ) mesons and pseudoscalar (πand η) mesons to describe the \bar{K}^{*}Σinteraction with the coupling constants determined by the SU(3) symmetry, The poles of the scattering amplitude are searched for to find the molecular states dynamically generated from the \bar{K}^{*}Σinteraction. A bound state with quantum number I(J^{p})=1/2(5/2^{+}) is produced, which can be associated to the Ξ(2030) baryon. Other bound states with J\le{}5/2 are also searched for and it is found that there exist bound states with quantum numbers I(J^P)=1/2(1/2^-), 1/2(3/2^{-}), and 1/2(3/2^+). The Ξ(2120) may be a candidate for one of these three bound states. In addition, we also find two bound states with isospin 3/2 and spin parities 1/2^- and 1/2^+.

hep-ph↗

arXiv2018

Scale Invariance in Heavy Hadron Molecules

We discuss a scenario in which the $P_c(4450)^{+}$ heavy pentaquark is a $Σ_c \bar{D}^*$-$Λ_{c}(2595) \bar{D}$ molecule. The $Λ_{c1} \bar{D} \to Σ_c \bar{D}^*$ transition is mediated by the exchange of a pion almost on the mass shell that generates a long-range $1/r^2$ potential. This is analogous to the effective force that is responsible for the Efimov spectrum in three-boson systems interacting through short-range forces. The equations describing this molecule exhibit approximate scale invariance, which is anomalous and broken by the solutions. If the $1/r^2$ potential is strong enough this symmetry survives in the form of discrete scale invariance, opening the prospect of an Efimov-like geometrical spectrum in two-hadron systems. For a molecular pentaquark with quantum numbers $\frac{3}{2}^{-}$ the attraction is not enough to exhibit discrete scale invariance, but this prospect might very well be realized in a $\frac{1}{2}^{+}$ pentaquark or in other hadron molecules involving transitions between particle channels with opposite intrinsic parity and a pion near the mass shell. A very good candidate is the $Λ_{c}(2595) \barΞ_b - Σ_c \barΞ_b'$ molecule. Independently of this, the $1/r^2$ force is expected to play a very important role in the formation of this type of hadron molecule, which points to the existence of $\frac{1}{2}^{+}$ $Σ_c D^*$-$Λ_{c}(2595) D$ and $1^+$ $Λ_{c}(2595) Ξ_b - Σ_c Ξ_b'$ molecules and $0^{+}$/$1^{-}$ $Λ_{c}(2595) \barΞ_b - Σ_c \barΞ_b'$ baryonia.

hep-ph↗

arXiv2018

Particle number conserving BCS approach in the relativistic mean field model and its application to $^{32-74}$Ca

A particle number conserving BCS approach (FBCS) is formulated in the relativistic mean field (RMF) model. It is shown that the so-obtained RMF+FBCS model can describe the weak pairing limit. We calculate the ground-state properties of the calcium isotopes $^{32-74}$Ca and compare the results with those obtained from the usual RMF+BCS model. Although the results are quite similar to each other, we observe an interesting phenomenon, i.e., for $^{54}$Ca, the FBCS approach can enhance the occupation probability of the $2p_{1/2}$ single particle level and slightly increases its radius, compared with the RMF+BCS model. This leads to an unusual scenario that although $^{54}$Ca is more bound with a spherical configuration but the corresponding size is not the most compact one. We anticipate that such a phenomenon might happen for other neutron rich nuclei and should be checked by further more systematic studies.

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arXiv2018

Strong and radiative decays of DΞmolecular state and newly observed $Ω_c$ states

In this work, we study strong and radiative decays of S-wave DΞmolecular state, which is related to the Ω^*_c states newly observed at LHCb. The coupling between the DΞmolecular state and its constituents D and Ξis calculated by using the compositeness condition. With the obtained coupling, the partial decay widths of the DΞmolecular state into the Ξ_c^{+}K^{-}, Ξ^{'+}_cK^{-} and Ω^{*}_c(2695)γfinal states through hadronic loop are calculated with the help of the effective Lagrangians. By comparison with the LHCb observation, the current results of total decay width support the Ω^{*}_c(3119) or Ω^{*}_c(3050) as DΞmolecule while the the decay width of the Ω^{*}_c(3000), Ω^{*}_c(3066) and Ω^{*}_c(3090) can not be well reproduced in the molecular state picture. The partial decay widths are also presented and helpful to further understand the internal structures of Ω^{*}_c(3119) and Ω^{*}_c(3050).

hep-ph↗

arXiv2016

Weak decays of heavy hadrons into dynamically generated resonances

In this review we give a perspective of the theoretical work done recently on the interpretation of results from $B$, $D$, $Λ_b$, $Λ_c$ weak decays into final states that contain interacting hadrons, and how it is possible to obtain additional valuable information that is increasing our understanding of hadron interactions and the nature of many hadronic resonances. The novelty of these processes is that one begins with a clean picture at the quark level which allows one to select the basic mechanisms by means of which the process proceeds. Finally, one has a final state described in terms of quarks. To make contact with the experiments, where mesons and baryons are observed, one must hadronize, creating pairs of $q \bar q$ and writing the new states in terms of mesons and baryons. This concludes the primary hadron production in these processes. After that, the interaction of these hadrons takes place, offering a rich spectrum of resonances and special features from where it is possible to learn much about the interaction of these hadrons and the nature of many resonances in terms of the components of their wave functions.

hep-ph↗

arXiv2013

Lowest-lying octet baryon masses in covariant baryon chiral perturbation theory

We report on a systematic study of the ground-state octet baryon masses in the covariant baryon chiral perturbation theory with the extended-on-mass-shell renormalization scheme up to next-to-next-to-next-to-leading order, taking into account the contributions of the virtual decuplet baryons. A reasonable description of the lattice results is achieved by fitting simultaneously all the publicly available $n_f = 2+1$ lattice QCD data. It confirms that the various lattice simulations are consistent with each other. We stress that a self-consistent treatment of finite-volume corrections is important to obtain a $χ^2/\rm{d.o.f.}$ about 1.

nucl-th↗

arXiv2013

Recent developments in SU(3) covariant baryon chiral perturbation theory

Baryon chiral perturbation theory (BChPT), as an effective field theory of low-energy quantum chromodynamics (QCD), has played and is still playing an important role in our understanding of non-perturbative strong interaction phenomena. In the past two decades, inspired by the rapid progress in lattice QCD simulations and the new experimental campaign to study the strangeness sector of low-energy QCD, many efforts have been made to develop a fully covariant BChPT and to test its validity in all scenarios. These new endeavours have not only deepened our understanding of some long-standing problems, such as the power-counting-breaking problem and the convergence problem, but also resulted in theoretical tools that can be confidently applied to make robust predictions. Particularly, the manifestly covariant BChPT supplemented with the extended-on-mass-shell (EOMS) renormalization scheme has been shown to satisfy all analyticity and symmetry constraints and converge relatively faster compared to its non-relativistic and infrared counterparts. In this article, we provide a brief review of the fully covariant BChPT and its latest applications in the $u$, $d$, and $s$ three-flavor sector.

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arXiv2013

Virtual decuplet effects on octet baryon masses in covariant baryon chiral perturbation theory

We extend a previous analysis of the lowest-lying octet baryon masses in covariant baryon chiral perturbation theory (ChPT) by explicitly taking into account the contribution of the virtual decuplet baryons. Up to next-to-next-to-next-to-leading order (N$^3$LO), the effects of these heavier degrees of freedom are systematically studied. Their effects on the light-quark mass dependence of the octet baryon masses are shown to be relatively small and can be absorbed by the available low-energy constants up to N$^3$LO. Nevertheless, a better description of the finite-volume corrections of the lattice QCD data can be achieved, particularly those with small $M_ϕL$ ($<4$), which is demonstrated by a careful study of the NPLQCD and QCDSF-UKQCD small-volume data. Finally, we show that the predicted pion- and strangeness-baryon sigma terms are only slightly changed by the inclusion of the virtual decuplet baryons.

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arXiv2012

Octet-baryon masses in finite space

We report on a recent study of finite-volume effects on the lowest-lying octet baryon masses using the covariant baryon chiral perturbation theory up to next-to-leading order by analysing the latest $n_f = 2 + 1$ lattice QCD results from the NPLQCD Collaboration.

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