| Hadronic matter is a fundamental platform to understand the strong interaction in nature.The best known hadronic matter are proton and neutron,which are nonelementary particles composed of three light quarks.The reason why protons and neutrons can be tightly bound inside the nucleus is the existence of nuclear force,and the nuclear force in nuclear physics is actually a performance of long-range strong interaction among quarks and gluons.Hence,the understanding of the strong interaction is extremely important for further learning how the world and the universe constitute,which is a big scientific proposition.In the past ten years,with the continuous accumulation of high-energy collision experimental data,some new hadronic states have been successively discovered in several major high-energy physics experiments,which are named by XYZ,whose nature is one of the hot topics in particle physics in recent years.The discovery of these XYZ particles provides a rich research object for the study of hadron physics phenomenology and non-perturbative problems of strong interactions.In this thesis,we first review the research background and related experimental progress of the charmoniumlike XYZ states,and here we focus on the five kinds of charmoniumlike XYZ structures observed in different production processes.Then we introduce the main phenomenological models used in this thesis,including the effective Lagrangian approach based on chiral symmetry and heavy quark symmetry and the unquenched relativized quark potential model.Later,we study the first topic of this thesis,i.e.,the solution for the charmoniumlike Y problem.Y particles mean a series of charmoniumlike Y states directly observed in electron-positron collision experiments,which include Y(4220),Y(4320),Y(4360),Y(4390),Y(4630),Y(4660).Due to the obvious inconsistency between properties of these Y states and the conventional charmonia,the Y problem composed of these Y particles has attracted extensive attention from theorists in the past ten years.Based on the updated data of charmoniumlike state Y(4220)reported in the hidden-charm channels of the e+e-annihilation,we propose a 4S-3D mixing scheme to categorize Y(4220)into the J/ψ family.We find that the present experimental data can support this charmonium assignment to Y(4220).Thus,Y(4220)plays a role of a scaling point in constructing higher charmonia above 4 GeV.To further test this scenario,we predict its charmonium partner ψ(4380),whose evidence is found by analyzing the e+e-→ψ(3686)π+π-data from BESIII.Later,we present the mass spectrum of higher charmonia around and above 4.6 GeV by adopting the unquenched potential model.We perform a combined fit to the updated experimental data of e+e-→ψ(2S)π+π-and e+e-→ΛcΛc.To understand the"platform" structure observed in the range of 4.57～4.60 GeV existing in the invariant mass spectrum of e+e-→ΛcΛc of BESIII,we introduce a new resonance structure with mY1=4585±2 MeV andΓY1=29.8±8.0 MeV.Combining another charmoniumlike Y2 state Y(4630)or Y(4660),which has been proved to be a same structure in our scheme,we indicate that the two Y states are mixtures of 6S and 5D cc states.This is first study to understand the mystery of Y particle in a unified theoretical framework.Additionally,our studies provide new insights to establish the higher charmonium spectrum.In order to better understand the nature of Y(4220)state,we studied the Y(4220)production in the process of pp→Y(4220)π0 within the effective Lagrangian approach.We first study the e+e-→ Y(4220)→ppπ0 reaction at center-of-mass energy 4.258 GeV.We show that the inclusion of nucleon and nucleon resonance leads to a quite good description of the experimental data of π0p and π0p invariant mass distributions.Then,the total and angular distributions of the pp→Y(4220)π0 reaction are investigated.It is shown that the nucleon pole is dominant but the contributions from excited nucleon resonances are non-Legligible.The pp→Y(4220)π0 reaction is a peculiar platform for studying the property of Y(4220)and our calculated results may be tested at the forthcoming PANDA experiments.Next,we find a Critical Energy induced Enhancement(CEE)mechanism for the general three-body open-charm process at the e+e-collisions,which utilizes the peculiar kinematic behavior of the e+e-annihilation process involving three-body final states.We present a general analysis of a three-body process e+e-→BC→ B(C→DE).When the center-of-mass(CM)energy of the e+e-collision satisfies a critical relation(?)=mB+mC,there clearly exists the reflection peak of an intermediate C state near the threshold of the invariant mass distribution of mBE or mBD,whose formation is very sensitive to the CM energy.The reflection enhancement phenomenon induced at the critical energy means that a new cluster of charmoniumlike structures can be experimentally mapped.What is more important is that a series of optimal CM energy points to search for new charmoniumlike structures in three-body open-charm processes from e+e-annihilation are suggested,which can be accessible at BESⅢ and further Belle Ⅱ as a new research topic.As the applications of CEE mechanism,we first propose a universal non-resonant explanation to decode two charged charmoniumlike structures Zc(3885)and Zc(4025),which are only the reflection from the P-wave charmed meson D1(2420)involved in e+e-→D(*)D*π.This opinion is different from the usual tetraquark assignment.Additionally,the BESⅢ collaboration recently reported a charged hidden-charm structure with strangeness in the recoil mass of K+ of a process e+e-→DS*-d0k+ or Ds-d*0k+,which is named as Zcs(3985)-.The newly observed charged structure can be treated as a partner structure with strangeness of well-known Zc(3885)-reported in a process e+e-→D*-D0π+.By applying CEE mechanism,we find that the Zcs(3985)can be explained as a reflection structure of charmed-strange meson Ds2*(2573),which is produced from the open-charm decay of Y(4660)with a Ds*meson.Furthermore,we predicted the angular distribution of final state Ds*-in process e+e-→Ds*-D0K+ based on our proposed reaction mechanism,which may be an essential criterion to test the non-resonant nature of Zcs(3985)further.The third topic of this thesis is the fully-heavy enhancement structure in di-charmonium invariant mass spectrum.Very recently,the LHCb Collaboration reported the observation of several enhancements in the invariant mass spectrum of a J/ψ pair between 6.2 and 7.4 GeV.We propose the dynamical mechanism to mimic the experimental data of a di-J/ψmass spectrum given by LHCb,which is based on the reactions,where all the possible combinations of a double charmonium directly produced by a proton-proton collision are transferred into a final state J/ψJ/ψ.We find that the LHCb experimental data can be well reproduced.We further extend our framework to predict the line shape of more potential fully-heavy structures in the invariant mass spectrum of J/ψψ(3686),J/ψψ(3770),ψ(3686)ψ(3686),and J/ψγ(1S)at high energy proton-proton collisions,whose verification in experiments should be helpful to further clarify the nature of X(6900).Furthermore,the corresponding peak mass positions of each of predicted fully-heavy structures are also given.These predictions can be tested in LHCb and CMS,which can be as a potential research issue in near future.Finally,we study how to construct highly exciting light vector strangeonium states above 2.0 GeV.Here,we propose a new perspective to construct the light vector meson family,which utilizes the cross section data from electron-positron collision within the support of spectroscopy of light vector meson.As an application,we perform a combined analysis to the measured data of the cross section of open-strange processes e+e-→K+K-,e+e-→KK*+c.c.,e+e-→K*+K*-,e+e-→K1(1270)+K-,e+e-→K1(1400)+K-,e+e-→K2*(1430)K+c.c.and e+e-→K(1460)+K with the support of study of hadron spectroscopy.We reveal the contribution of the possible light vector mesons around 2 GeV to reproduce the cross section data of the reported open-strange processes from e+e-annihilation which may provide a new perspective to construct the light vector meson family and understand the Y(2175). |
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