The Study On The Production Processes Of New Hadron States

With increasing experiment data stimulated by the improvement of experimental facilities and technology in the past decades,a series of new hadron states have been discovered.Some new hadron states can not be accommodated in the conventional quark model,which attracts the physicist great interest.Most of new hadron states lie in the charmonium or bottomonium region,where the non-perturbative effect becomes important.In order to investigate the properties of new hadron states,some effective approaches have been employed to deal with non-perturbative effect.The investigation on new hadron states can deepen our understanding of QCD,especially for non-perturbative QCD effect and color confinement mechanism.Therefore,it is crucial to study new hadron states theoretically.In the introduction,I present a short review of the history of particle physics and the status of new hadron states,the QCD theory and Quark model.In Chapter 2,I introduce the approaches used for studying new hadron states,which include effective Lagrangian approach,nonrelativistic effective field theory and hadron loop model.In Chapter 3,I mainly present our investigation on the production processes of new hadron states,which includes:(1)we study the production mechanism of Zb(’)from γ(5S,6S)decay with the nonrelativistic effective field theory.Our estimations indicate that the loop contributions with all intermediate states being the S-wave ground state bottom mesons are negligible,while the loops with one bottom meson being the broad Bo or B1’ resonance could provide the dominant contributions to the γ(5S)→Zb(’)π.It is found that such a mechanism is not suppressed by the large width of the B0/B1’ resonance.In addition,we also estimate the branching ratios for the γ(6S)→Zb(’)π which could be tested by future precise measurements at Belle-Ⅱ.(2)We study the production mechanism of charmonium-like states Zc(3900)and Zc(4020)from Bc decay with an effective Lagrangian approach.The results indicated Bc+→Zc(3900)+π0 has a large branching ratio,which could provide an important source of the production of Zc(3900)from the semi-exclusive decay of b-flavored hadrons reported by DO Collaboration,which can be tested by the exclusive measurements in LHCb.(3)we study the production of Pc(4312),Pc(4440)and Pc(4457)from Λb decay in a molecular scenario by using an effective Lagrangian approach.The ratios of the branching fractions are estimated,which are almost independent on the model parameters.We also find the ratios of the productions of the branching fractions of Ab→PcK and Pc→J/Ψp can be well interpreted in the molecular scenario,which supports the molecular assumptions of Pc states.Moreover,we obtain the order of magnitude of the branching ratios of Ab→PcK,which could also be tested by the future measurements in LHCb.(4)Recently,the LHCb Collaboration reported a hidden-charm pentaquark state with strangeness named Pcs(4459).We investigate the Pcs(4459)production fromΞb decay in a molecular scenario by using an effective Lagrangian approach.We discussed two possible assignment of the JP quantum numbers and their relevant branching ratios.Different from the Pc states,the form factors of Ξb→Ξchave been estimated theoretically,thus we could calculate the magnitude of the branching ratios of Ξb→Pcs(4459)K.In Chapter 4,I mainly introduce our study on the decay processes of new hadron states,which includes:(1)We investigate the hidden bottom decay process Zb(’)→γj(1D)π(J=1,2,3),and combining with the production process γ(5S)→Zb(’)π we investigate dipion transition of γ(5S)and γj(1D)π(J=1,2,3).The ratios of branching fraction of Zb(’)→γJ(1D)π(J=1,2,3)was predicted,which could be tested by Belle Ⅱ.Further study indicates the dominant source of the anomalous decay widths ofγ(5S)→γ(1D)π+π-should be Zb(’),i.e.,the transition occurs via the cascade decaysγ(5S)→Zb(’)±π(?)→γ(lD)π±π(?).In a reasonable model parameter region,our results are coincide with the experimental measured branching ratios of γ(5S)→γ(1D)π+π-in magnitude,which further prove the dipion transition between γ(5S)and γJ(1D)π(J=1,2,3)is dominated by Zb(’).(2)In a molecular scenario,we investigate the isospinbreaking phenomena in X(3872)decay.We assume that the source of the strong isospin violation comes from the different coupling strengths of X(3872)to its charged components D*+D-and neutral components D*0D0 as well as the interference between the charged meson loops and neutral meson loops.By using the measurement of the ratioΓ[X(3872)→π+π-π0J/Ψ]/Γ[X(3872)→π+π-J/Ψ]and our estimation,the model parameter can be fixed.With the determined parameter range,we find that the estimated ratioΓ[X(3872)→π0xcl/Γ[X(3872)→π+π-J/Ψ]is well consistent with the measurement from the BESIII collaboration.Moreover,the partial width ratio of π0xcJ for J＝0,1,2 is estimated,which could be tested by further precise measurements of BESIII and Belle II.In the last section,we present a short summary and look forward to the research prospect of new hadron states.