Study On The Production Of The Axial-Vector Meson A₁（1260） In πp Scattering

Mesons and strong interactions have been closely connected since Hideki Yakawa first introduced meson exchange model to explain the internuclear force in 1935.Since then,our understandings of mesons and strong interactions had been developing over time.Now,non-Abelian gauge field theory quantum chromodynamics（QCD）,is the formal theory to describe strong interactions,quarks and gluons are bounded within hadrons via strong interactions.However,because of color confinement,we cannot detect individual quark or gluon in nature.Hadrons,including mesons and baryons,is the smallest element that we can extract from experiments at present.Hadron physics is our most important tool to investigate the microcosm,it can lead us to better understand quantum chromodynamics which dominate strong interaction.Hitherto,most hadrons observed in experiments can be described by conventional quark model.In conventional quark model,mesons are constitute of quark-antiquark pairs q （?）,baryons are constitute of three-quarks qqq.But conventional quark model is not without defect,there are some hadrons observed in experiments inconsistent with the conventional quark model,we call them new hadron states.In principle,quantum chromodynamics describes the formation of hadrons.But,to derive hadron properties directly from quantum chromodynamics is a very difficult task.Lattice calculating method is one way,but it costs too much time and computer resources.Thus,introducing some phenomenological models within the QCD frame is reasonable and necessary,such new phenomenological models include multi-quark states,molecular states,glueballs,and hybrids.They are not fundamental and rigorous approach,but have proven to be quite useful and successful in explaining the so-called new hadron states.Studying of new phenomenological models and new hadron states have attracted more and more physicists’ interest.Based on an effective Lagrangian approach and the unitary chiral perturbation theory,the a₁（1260）axial-vector meson is studied in this paper.It is regarded as a dynamically generated resonance,and further investigated in the πp scattering.First,we have a brief review to the history of elementary particle physics and the Standard Model.Then,we studied the dynamical generate process of a₁（1260）from ρπ and R*K coupled channel interactions in details.and calculated the coupling constants of a₁（1260）to different channels.Next,we studied the a₁（1260）production mechanism in the πp scattering within an effective Lagrangian approach,the total cross section of the π-p → a₁（1260）-p reaction is evaluated.It is found that with a reasonable cut-off parameter,the experimental data can be well reproduced.Furthermore,we predicted the total and differential cross sections of the π-p → a₁（1260）-p reaction,more experiments are expected to test our model and calculation.Finally,we have an outlook of the a₁（1260）production in the photoproduction process.