Two-particle Azimuthal Angular Correlation In The Color Glass Condensate Formalism

At high energy collisions,with the nonlinear QCD evolution,the proton can gen-erate an interesting partonic substructure with a large number of partons,and the gluon density tends to be saturation at the small-x region.The Color Glass Condensate(CGC)framework is an effective quantum field theory to describe the nonlinear QCD evolution of dense partons and gluon saturation phenomenon.In small collisional systems,the unexpected collective phenomenon has been dis-covered in high multiplicity events and tends to be one of the most interesting and im-portant topics.In the Color Glass Condensate formalism,based on the multi-scattering between incoming partons in the proton and the dense gluon field in the nucleus,the initial state can generate sizable values of the collective phenomenon.In this thesis,we systematically study the two-particle azimuthal angular correlation in the Color Glass Condensate framework.In the Color Glass Condensate formalism,multi-dipole correlators play an impor-tant role in multi-particle azimuthal angular correlation in proton-nucleus collisions.In term of 1/Nc expansions,we evaluate the 2-dipole correlator and the 3-dipole correlator.Also,we derive a general expression of the n-dipole correlator up to the 1/Ncn order.This work provides an effective technique to explore the collective phenomenon of 4-particle,6-particle,and multi-particle.Moreover,using the dilute-dense limit,we systematically study the anisotropic harmonics of two-particle azimuthal angular correlations in proton-nucleus collisions.We find gluon-gluon,gluon-quark,and quark-gluon channels do not have any contribu-tion to odd harmonics,only the quark-quark channel can generate sizable values of odd harmonics for two-particle correlations.Our results indicate that the initial state can generate sizable values of collectivity in small collisional systems.In addition,using the same formalism,we systematically describe the differential spectra of a heavy meson with a light particle in proton-nucleus collisions and find that the initial state can generate the sizable elliptic flow of J/? and D0 meson that agrees with the experimental data from CMS collaborations in high multiplicity events.Also,we predict the v2 of Y and B meson.Our results indicate that the initial state correlation maybe is the origin of anisotropic flow in small collisional systems.Finally,recently,the collaboration from LHC has observed the sizable value of the long-range correlations for light hadrons in photo-nuclear collisions as well.And similar to a proton,with rare fluctuation,a long-lifetime virtual photon can generate an inter-esting partonic substructure with a large number of partons in high-energy collisions.These indicate we can explain the collective phenomena using the CGC formalism in high multiplicity events in photo-nuclear collisions.Our calculations first reveal that the initial state can generate the sizable elliptic flow of light hadron in the photo-nuclear ultra-peripheral AA collisions,which agrees with the measurement of ATLAS collab-orations.Besides,we predict the two-particle correlations in the low-Q2 region of the upcoming Electron-Ion Collider(EIC).The high luminosity EIC with mutable colli-sional energy has a better ability to explore the structure of proton and nuclei and will shed light on the origin of the collective phenomenon in the ?*A collisions.