Production of charmonium pentaquarks from b-baryon and B-meson decays:SU(3)analysis

Here,we study the production of charmonium pentaquarks cc¯qqq from bottom baryon and B-meson decays under the flavor SU(3)symmetry.Decay amplitudes for various processes are parameterized in terms of SU(3)irreducible nonperturbative amplitudes.Numerous relations between decay widths are deduced.Moreover,the strong decays of pentaquarks are considered.Our results can be tested in future measurements at LHCb,Belle II,and CEPC.Once decay branching fractions are measured,this study will be useful for the exploration of new decay channels and pentaquark states.

QCD sum rule study for hidden-strange pentaquarks

Inspired by the LHCb observations of hidden-charm Pc(s)states,we study their hidden-strange analog Psstates in both the[udu][■s]and[uds][■u]configurations.We investigate Ps pentaquark states in the pη′,pφ,ΛK,ΣK,andΣ*K*structures with JP=1/2-andΣ*K andΣK*with JP=3/2-and calculate their masses in the framework of QCD sum rules.Our numerical results show that the extracted hadron masses for all the pη′,pφ,ΛK,ΣK,andΣ*K*structures are significantly higher than theΣK mass threshold,and the masses forΣ*K andΣK*are also higher than the threshold of the corresponding hadron;hence,no bound state exists in such channels,which is consistent with the current experimental status.

The pentaquarks observed by the LHCb experiment

In 1964, Murray Gell-Mann [1], the Nobel Prize winner in Physics, and George Zweig [2] separately proposed the quark model.The model revealed for the first time that a class of particles, baryons including protons and neutrons, were not elementary, instead were formed by three quarks (qqq), and another class, mesons,were made of quark-antiquark pairs (qqà). The quark model can successfully describe all the baryons and mesons (collectively referred to as hadrons) observed in the last century, thereby helps to explain how the strong force binds the quarks to form a particle.

Investigation of quark distributions in a family of pentaquarks using the Thomas-Fermi quark model

Using the Thomas-Fermi quark model,a collective,spherically symmetric density of states is created to represent a gas of interacting fermions with various degeneracies at zero temperature.Over a family of pentaquarks,uudcc,color interaction probabilities were obtained after averaging over all the possible configurations.Three different functions are developed for light,charm,and anti-charm quarks and are assumed to be linearly related by some proportionality constants.Interesting patterns of quark distributions are observed while analyzing the quark function consistency conditions for such constants.

Possible strange hidden-charm pentaquarks from Σ_c^((*))_s~* and Ξ_c^((',*))~* interactions

Using the one-boson-exchange model, we investigate the Λcs^＊, Σcs^＊, Σc^＊s^＊, Ξc^＊, Ξ＇c^＊, and Ξc^＊^＊ interactions by considering the one-eta-exchange and/or one-pion-exchange contributions. We further predict the existence of hidden-charm molecular pentaquarks. Promising candidates for hidden-charm molecular pentaquarks include a Ξ＇cD^＊ state with 0（（1/2）^-） and the Ξc^＊D^＊ states with 0（1/2^-） and 0（3/2^-）. Experimental searches for these predicted hidden-charm molecular pentaquarks are an interesting future research topic for experiments like LHCb.

Revisiting hidden-charm pentaquarks from QCD sum rules

We revisit hidden-charm pentaquark states P_c(4380) and P_c(4450) using the method of QCD sum rules by requiring the pole contribution to be greater than or equal to 30% in order to better that the one-pole parametrization is valid. We find two mixing currents, and our results suggest that P_c(4380) and P_c(4450) can be identified as hiddencharm pentaquark states having J^P= 3/2^-and 5/2^+, respectively. However, there still exist other possible spin-parity assignments, such as J^P = 3/2^+ and J^P = 5/2^-, which must be clarified in further theoretical and experimental studies.

The Masses of P_c* (4380) and P_c* (4450) as Di-Hadronic States

The masses of the recently reported by LHCb two pentaquark charmonium states Pc* (4380) and Pc* (4450) which are suggested to possess pentaquark configuration () have been estimated considering a dihadronic state consisting of a meson? and a baryon (uud). The binding energies of the states have been estimated with a van der Walls type of molecular interaction between the hadrons. A spin interaction has also been considered. Masses of these two states are well reproduced with the aforesaid molecular interaction which indicates that the multiquarks Pc* (4380) and Pc* (4450) can be well described as meson-baryon bound states.

Second Thoughts about the <i>τ-θ</i>Puzzle

The new parity value of π0 was determined according to the hypothesis of conservation of particle number. The theo-retical pentaquark proton’s parity value was also determined, and it was found that the conservation of parity is account nicely for the τ-θ puzzle.

Strong decays of the P_(c)(4312) and its isospin cousin via the QCD sum rules

In this study,considering the conservation of isospin in the strong decays,we investigate the strong decays of the pentaquark molecule candidate P_(c)(4312)and its possible higher isospin cousin P_(c)(4330)in the framework of the QCD sum rules.Further,the pole residue of theΔbaryon with isospin eigenstate|II3>=|3/21/2)is obtained.If the possible pentaquark molecule candidate P_(c)(4330)could be determined,it would shed light on the interpretations of the P_(c) states in future experiments.

利用机器学习研究隐粲五夸克态的性质

机器学习已经在生物、医学、生产等多个领域广泛应用并展现了其优势.最近,机器学习在物理领域也开始逐渐兴起并展现出其独特的优点.该文旨在探索机器学习在强子物理中的应用潜力.作者以隐粲五夸克态Pc(4312)、Pc(4440)和Pc(4457)为例,在强子分子态图像下研究它们的性质.研究表明,神经网络方法和基于χ2的拟合方法都能够阐明基于领头阶接触势的基本物理性质.然而,χ2拟合方法无法区分Pc(4440)和Pc(4457)的量子数,神经网络方法则可以.由此,作者进一步分析了每个实验数据点对于神经网络预测的影响,以及在拟合方法中每个数据点对于关键物理参数的重要性.通过对比研究,作者发现神经网络方法可以多维度地利用实验数据信息,在强子物理中具有巨大的应用前景.

Molecular states in D_(s)^(*)+=^_(c)^(′,*)systems^(*)

The possible hadronic molecules in D_(S)^(∗)+Ξ_(c)(′,∗)systems with J^(P)=1/2−,3/2−,and 5/2−are investigated with interactions described by light meson exchanges.By varying the cutoff in a phenomenologically reasonable range of 1−2.5 GeV,we find ten near-threshold(bound or virtual)states in the single-channel case.After introducing the coupled-channel dynamics of D_(+)^(s)Ξ_(c)-D_(s)^(+)Ξ′c-D_(s)^(∗+)Ξ_(c-)D_(s)^(+)Ξ_(c)^(*)-D_(s)^(∗)+sΞ′_(c)-D_(s)^(∗)Ξ_(c)^(∗)systems,these states,except those below the lowest channels in each JP sector,move into the complex energy plane and become resonances in the mass range 4.43−4.76 GeV.Their spin-parities and nearby thresholds are 1/2−(D_(s)^(+)Ξ′_(c)),1/2^(−)(D_(s)^(++)Ξ_(c)^(*)),1/2−(D_(s)^(∗+)Ξ_(c)),1/2−(D_(s)^(∗+)Ξ_(c)^(′)),1/2−(D_(s)^(∗+)Ξ_(c)^(∗)),3/2−(D_(s)^(∗+)(Ξc),3/2−(D_(s)^(+)Ξ_(c)),3/2−(D_(s)^(∗+)Ξ′c),3/2−(D_(+s)^(∗)Ξ_(c)^(∗)),and 5/2−(D_(s)^(∗+)Ξ_(c)^(∗)).The impact of theδ(r)-term in the one-boson-exchange model on these states is presented.SettingΛ=1.5 GeV as an illustrative value,it is found that 1/2−(D_(s)^(*+)Ξ_(c))is a stable bound state(becoming unstable if the coupling to lower channels is turned on),1/2−(D∗+sΞc)and 3/2−(D_(s)^(∗+)Ξ_(c))are physical resonances in cases where theδ(r)-term is included or excluded,and the other seven states are physical resonances or"virtual-state-like"poles near thresholds,depending on whether theδ(r)-term is included.In addition,the partial decay widths of the physical resonances are provided.These double-charm hidden-strangeness pentaquark states,as the partners of the experimentally observed Pc and Pcs states,can be searched for in the D(∗)Λ_(c)final states in the future.

Analysis of Pcs(4338) and related pentaquark molecular states via QCD sum rules

In this study,we tentatively identify Pcs(4338)■Ξc molecular state and distinguish the isospins of current operators to explore in detail the■Ξc,■Λc,■sΞc,■sΛc,■*Ξc,■*Λc,■*sΞc,and■*sΛcmolecular states without strange,with strange,and with double strange in the framework of QCD sum rules.The present exploration favors identifying Pcs(4338)(Pcs(4459))as the■Ξc(■*Ξc)molecular state with the spin-parity JP=1/2-(3/2-)and(I,I3)=(0,0),and the observation of their cousins with the isospin(I,I3)=(1,0)J/ψΣ0/ηcΣ0in the invariant mass distributions would decipher their inner structures.

Pentaquark^+的介质效应

在密度相关的相对论平均场理论基础上,假定^+通过交换有效的同位旋标量介子σ和ω与其他重子发生相互作用,研究了强子在包含^+的奇异核物质中的性质改变。讨论并计算了介质中的^+和核子有效质量及其对重子密度的依赖关系,分析了^+在核物质中包含的成分大小以及核子的同位旋效应对奇异核物质性质的影响,进一步计算了不同重子组成比例下奇异核物质的标量密度ρ_S和矢量密度ρ_B的对应曲线。

Pentaquark■^+对核物质状态方程的影响

假定■^+通过交换有效的同位旋标量介子σ和ω与核子和它本身发生相互作用,在密度相关的相对论平均场理论基础上研究了{p,n,■^+}系统状态方程和可能形成的亚稳定态．讨论了在不同的重子密度下质子中子同位旋比值以及Pentaquark ■^+成分对系统单个重子能的影响．计算结果表明,在单个重子能取极小时,■^+有可能在核物质中束缚存在．

A new hadron spectroscopy

QCD-motivated models for hadrons predict an assortment of ＂exotic＂ hadrons that have structures that are more complex than the quark-antiquark mesons and three-quark baryons of the original quark-parton model. These include pentaquark baryons： the six-quark H-dibaryon~ and tetraquark, hybrid and glueball mesons. Despite extensive experimental searches, no unambiguous candidates for any of these exotic configurations have been identified. On the other hand, a number of meson states, one that seems to be a proton-antiproton bound state, and others that contain either charmed- anticharmed quark pairs or bottom-antibottom quark pairs, have been recently discovered that neither fit into the quark-antiquark meson picture nor match the expected properties of the QCD- inspired exotics. Here I briefly review results from a recent search for the H-dibaryon, and discuss some properties of the newly discovered states -the proton-antiproton state and the so-called XYZ mesons- and compare them with expectations for conventional quark-antiquark mesons and the predicted QCD-exotic states.

Possibility of observation of hidden-bottom pentaquark resonances in bottomonium photoproduction on protons and nuclei near threshold

We study theΥ(1S)meson photoproduction on protons and nuclei at near-threshold center-of-mass energies below 11.4 GeV(or at the corresponding photon laboratory energies Eγbelow 68.8 GeV).We calculate the absolute excitation functions for the nonresonant and resonant photoproduction ofΥ(1S)mesons off protons at incident photon laboratory energies of 63-68 GeV by considering direct(γp→Υ(1S)p)and two-step(γp→P^+b(11080)→Υ(1S)p,γp→P^+b(11125)→Υ(1S)p,γp→P^+b(11130)→Υ(1S)p)Υ(1S)production channels within different scenarios for the nonresonant total cross section of the elementary reactionγp→Υ(1S)p and for branching ratios of the decays P^+b(11080)→Υ(1S)p,P^+b(11125)→Υ(1S)p,and P^+b(11130)→Υ(1S)p.We also calculate an analogous function for the photoproduction ofΥ(1S)mesons on the 12C and 208Pb target nuclei in the near-threshold center-of-mass beam energy region of 9.0-11.4 GeV by considering the respective incoherent direct(γN→Υ(1S)N)and two-step(γp→P^+b(11080)→Υ(1S)p,γp→P^+b(11125)→Υ(1S)p,γp→P^+b(11130)→Υ(1S)p andγn→P^0b(11080)→Υ(1S)n,γn→P^0b(11125)→Υ(1S)n,γn→P^0b(11130)→Υ(1S)n)Υ(1S))production processes using a nuclear spectral function approach.We demonstrate that a detailed scan of theΥ(1S)total photoproduction cross section on proton and nuclear targets in the near-threshold energy region in future high-precision experiments at the proposed high-luminosity electron-ion colliders EIC and EicC in the US and China should provide a definite result for or against the existence of the nonstrange hidden-bottom pentaquark statesP^+bi and P^0bi(i=1,2,3)as well as clarify their decay rates.

Electromagnetic properties of the Pc(4312) pentaquark state

Using the light-cone QCD sum rules,we evaluate the magnetic moment of the P_c(4312) pentaquark state by considering both the \bar D\Sigma_c molecular and diquark-diquark-antiquark state,with quantum numbers J^P=2/1^(-1).In the calculations,we use the diquark-diquark-antiquark and molecular form of the interpolating currents for the P_(c4312) pentaquark and the distribution amplitudes of the photon.The numerical results for the magnetic moment obtained using the two different pictures are quite different from each other,which can be used to pin down the underlying structure of P_(c4312) .Any experimental measurement of the magnetic moment in the near future will provide an understanding of the internal structure of this pentaquark state.

Properties of the P_(c)(4312)pentaquark and its bottom partner

We present an analysis of the newly observed pentaquark P(4312)+to shed light on its quantum num-bers.To do that,the QCD sum rules approach is used.The measured mass of this particle is close to the∑++cD-threshold and has a small width,which supports the possibility of its being a molecular state.We consider an inter-polating current in a molecular form and analyze both the positive and negative parity states with spin-1/2.We also consider the bottom counterpart of the state with similar molecular form.Our mass result for the charm pentaquark state supports that the quantum numbers of the observed state are consistent with J^(P)=1/2^(-).

A novel method to test particle ordering and final state alignment in helicity formalism

In this study,the non-trival effect of the selection of reference particles for decay angle definitions is demonstrated when constructing the partial-wave amplitude of multi-body decays using helicity formalism.This issue is often ignored in the standard use case of helicity formalism.A new technique is proposed to test the selection of the particle ordering,and it can also be used as a generalized method to calculate the rotation operators that are used for the final-state alignment between different decay chains.Moreover,numerical validations are performed to support the arguments and to verify the effectiveness of the proposed technique.

Recent results from LEPS

Photoproduction of baryons with strangeness,such as the Σ（1385）,Λ（1520） and possibly the Θ ＋,are described from measurements at the LEPS/SPring-8 facility in Japan.Linearly polarized photons in the energy range of 1.5–2.4 GeV,along with the forward-angle kinematics at LEPS,provide unique data to learn about these baryons,which are non-perturbative solutions of QCD.