Exotic Hadron Production In Quark Combination Model

The basic quanta of Quantum ChromoDynamics(QCD),quarks and gluons,as well as their colour charges,are observed confined in their bound states,hadrons.Correspondingly, hadrons are colour-singlet(CS),i.e.,the invariant/trivial(totally antisymmetric) representation of the SU_C(3) group.The least number of quarks and/or antiquarks required for constructing such a representation is one quark and one antiquark,or three (anti)quarks.These are just the valence(or constituent) quark numbers for mesons and baryons,respectively.However,naively from the group theory,more(anti)quarks can also construct the trivial representation,hence possibly to form a CS "hadron",e.g.,two quark-antiquark pairs,a quark-antiquark pair with 3(anti)quarks,six(anti)quarks,etc., which are to be called exotic hadrons in this paperWe believe that it is meaningful to consider the exotic hadrons in the combination model.By such investigation we would like to address the common problems for various combination models when open for exotic hadrons,especially unitarity to seek a practical and self-consistent framework to calculate the production of exotic hadrons(if existing). The following two questions about exotic hadrons are very crucial to understand its production mechanism and in constructing its production model.First is the uncertainty of the colour state and the process.The second is the definition of the quark number.One of the famous candidates is f₀(980).It is considered as a general meson as(s(?)),others argue it could be a four-quark state(s(?)(?)q ).We calculate and compare the two situations.In this paper,we investigate the production of exotic hadrons in a quark combination model proposed by the Shandong Group and successfully applied in various high energy collisions.Recently,this model is applied to the central Gold-Gold interactions at relativistic heavy ion collider(RHIC),successfully describes various properties of the production of mesons and baryons.We will consider f₀(980) into a meson state for the s(?) and the four quark state for s(?)(?)q.As for the four quark state,because the model itself does not include such a state,so we want to generate such a state.Then we can consider f₀(980) being the meson molecule. At this time we find out all the meson state who can be composed of such meson molecule, then in accordance with the quark component,the total angular momentum,parity and isospin with the f₀(980).We must give a parameter x to control of the impact of other hadrons,and give four quark state generated by an upper limit.