Study On Propertiesof Pentaquark States With QCD Sum Rules

In 2003,Belle collaboration reported X(3872)in the decays of B?X(3872)K,X(3872)?J/??+?,thereafter more and more exotic hadron states have been observed experimentally.These new particles cannot be accommodated in the traditional quark models,and no new model can perfectly and uniformly explain the productions,decays,masses and structures of these new particles.In 2005,LHCb discovered Pc(4380)and Pc(4450)in the J/? pinvariant mass spectrum which beyond the traditional baryon models.They are the best candidates for compact pentaquark states or loose meson-baryon molecular states,which attract a lot of research works.The discovery presents a new challenge to theoretical physicists,and the exploration of the structures and properties of those new hadron states has become a new research hotspot.Quantum chromodynamics(QCD)is a successful theory in describing the high energy strong interaction.However,in the low energy region,the strong coupling constant leads to the failure of perturbation theory.Theoretical physicists have to apply various phenomenological models to study these new hadron states.The QCD sum rules is based on the first principle,the quark currents are constructed according to the quantum numbers of hadrons,and the operator product expansion of two-point or three-point vacuum correlation functions are performed.The perturbative contributions are reflected in the Wilson's coefficients,and the nonperturbative contributions are characterized by gluon condensates and quark condensates.Based on the hypothesis of hadron quark duality,the basic hadron parameters are determined.The QCD sum rules approach overcomes model dependence to a great extent.At present time,it has been widely applied to study the mass spectra and decay properties of hadrons.The calculated results based on QCD sum rules are generally in good agreements with the experimental data,so it is a reliable threoretical method.Using QCD sum rules,we can construct a large number of different types of currents to study the inter structures and properties of new hadron states.The study of these new hadron states can deepen our understanding of QCD low energy dynamics and hadron spectroscopy,and provide a strong support and guidance for high-energy physics experiments.In this paper.we apply QCD rum rules to study properties of pentaquark states.we assign the heavy baryon as diquark-diquark-antiquark type pentaquark states or meson-baryon type pentaquark molecular states to calculate the masses.hadronic coupling constants and decay widths of hadrons with QCD rum rules.By comparing with the experimental data,the structures and properties of heavy baryon states are studied.We try to explain multiquark states using hadronic dressing mechanism.The main works of this paper are presented as follow:1.we assign ?b(6227)as the pentaquark molecular state with Jp=1/2± to study its inner structure.We construct meson-baryon type currents to calculate the masses and pole residues of the pentaquark molecular states using QCD sum rules.By comparing with the experimental data,we dicuss the possibility to assign ?b(6227)as the 1/2±pentaquark molecular states.2.We construct ? type baryon currents JA(x)and J?(x)to interpolate the flavor antitriplet heavy baryon states ?Q,?Q(2S),?Q and ?Q(2S).We study the ground states and the first radial excited states of the flavor antitriplet heavy baryon states with JP=1/2+ using QCD sum rules.For the first time,we obtain very stable QCD sum rules for the heavy baryon states.Finally,we use the Regge trajectories to obtain the masses of the second radial excited states.The influence of truncation of vacuum condesates on calculation results is discussed.3.we construct the scalar-diquark-scalar-diquark-antiquark type and axialvector-diquark-axialvector-diquark-antiquark type interpolating currents to study the charmed pentaquark states suscu with JP=1/2± using the QCD sum rules.We employ three types of energy scale parameters to investigate the masses and pole residues of the charmed pentaquark states.By comparing these results with experiment data,we find that if we take pole contributions in the scope of 40%-60%,we can get more reasonable prediction using the energy scale formula(?)than the other two types of energy scale parameters.The energy scale formula(?)can improve the pole contributions dramatically and enhance the operator product expansion convergence remarkably,especially for the negative parity states.The calculation results support assigning the new excited ?c states to be the scalar-diquark-scalar-diquark-antiquark type and axialvector-diquark-axialvector-diquark-antiquark type charmed pentaquark states suscu with JP=1/2-.4.Based on rigorous quark-hadron quality,we study the hadronic coupling constants of the lowest diquark-diquark-antiquark type hidden-charm pentaquark state with JP=1/2-using the QCD sum rules,and calculate the partial decay widths.We explore the possible inner strctures and quantum numbers of Pc(4312).The total width?(Pc)=14.32±3.31MeV is compatible with the experimental value?Pc(4312)=9.8±2.7-4.5+3.7 MeV from the LHCb collaboration,and favors assigning the Pc(4312)to be[ud][uc]c pentaquark state with JP=1/2-.The hadronic coupling constants have the relation(?),and favor the hadronic dressing mechanism.The Pc(4312)may have a diquark-diquark-antiquark type pentaquark core with the typical size of the qqq type baryon states,and the strong couplings to the meson-baryon pairs D0?c+ and D-?c++ lead to some pentaquark molecule components,and the Pc(4312)may spend a rather large time as the D0?c+ and D-?c++ molecular state.