Electromagnetic field produced in high-energy small collision systems within charge density models of nucleons

Recent experiments show that Δy,an observable designed to detect the chiral magnetic effect(CME),in small collision systems(p+A) is similar to that in heavy ion collisions(A+A).This introduces a challenge to the existence of the CME because it is believed that no azimuthal correlation exists between the orientation of the magnetic field(Φ_(B)) and participant plane(Φ_(2)) in small collision systems.In this work,we introduce three charge density models to describe the inner charge distributions of protons and neutrons and calculate the electric and magnetic fields produced in small p+A collisions at both RHIC and LHC energies.Our results show that the contribution of the single projectile proton is the main contributor to the magnetic field after averaging over all participants.The azimuthal correlation between Φ_(B) and Φ_(2) is small but not vanished.Additionally,owing to the large fluctuation in field strength,the magnetic-field contribution to Δγ may be large.

Investigating the elliptic anisotropy of identified particles in p-Pb collisions with a multi-phase transport model

The elliptic azimuthal anisotropy coefficient(v_(2))of the identified particles at midrapidity(|η|<0.8)was investigated in p-Pb collisions at√s_(NN)=5.02 TeV using a multi-phase transport model(AMPT).The calculations of differential v_(2)based on the advanced flow extraction method of light flavor hadrons(pions,kaons,protons,andΛ)in small collision systems were extended to a wider transverse momentum(p_(T))range of up to 8 GeV/c for the first time.The string-melting version of the AMPT model provides a good description of the measured p_(T)-differential v_(2)of the mesons but exhibits a slight deviation from the baryon v_(2).In addition,we observed the features of mass ordering at low p_(T)and the approximate number-of-constituentquark(NCQ)scaling at intermediate p_(T).Moreover,we demonstrate that hadronic rescattering does not have a significant impact on v_(2)in p-Pb collisions for different centrality selections,whereas partonic scattering dominates in generating the elliptic anisotropy of the final particles.This study provides further insight into the origin of collective-like behavior in small collision systems and has referential value for future measurements of azimuthal anisotropy.

Nucleus-Nucleus Effects in Fully Differential Cross Sections for Energetic C6++He Collisions with Small Momentum Transfer

The modified Coulomb-Born approximation with and without the internuclear interaction （MCB-NN and MCB） is used to calculate the fully differential cross sections （FDCS） for the single ionization of helium by lOO MeV/amu C6＋ impact. The effects of the internuclear interaction on the FDCS are examined in geometries. The results are compared with experimental data and theoretical predictions from a three-body distorted-wave （3DW） model and a time-dependent close-coupling model. It is shown that the present MCB-NN results are in good agreement with the experiments in the scattering plane and the MCB results qualitatively reproduce the experimental structure outside the scattering plane. In particular, the MCB theory predicts the ＇double-peak＇ structure in the perpendicular plane.