Abstract
The transverse momentum ($p_\mathrm{T}$) distributions of $\Lambda$, $\Xi^-$, and $\Omega^-$ baryons, their antiparticles, and K$^0_\mathrm{S}$ mesons are measured in proton-proton (pp) and proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV over a broad rapidity range. The data, corresponding to integrated luminosities of 40.2 nb$^{-1}$ and 15.6 $\mu$b$^{-1}$ for pp and pPb collisions, respectively, were collected by the CMS experiment. The nuclear modification factor $R_\mathrm{pPb}$, defined as the ratio of the particle yield in pPb collisions and a scaled pp reference, is measured for each particle. A strong dependence on particle species is observed in the $p_\mathrm{T}$ range from 2 to 7 GeV, where $R_\mathrm{pPb}$ for K$^0_\mathrm{S}$ is consistent with unity, while an enhancement ordered by strangeness content and/or particle mass is observed for the three baryons. In pPb collisions, the strange hadron production is asymmetric about the nucleon-nucleon center-of-mass rapidity. Enhancements, which depend on the particle type, are observed in the direction of the Pb beam. The results are compared to predictions from EPOS LHC, which includes parametrized radial flow. The model is in qualitative agreement with the $R_\mathrm{pPb}$ data, but fails to describe the dependence on particle species in the yield asymmetries measured away from mid-rapidity in pPb collisions.
Highlights
The transverse momentum distributions of the particles produced in high-energy nuclear collisions can provide insights into the nature of the produced hot and dense matter, known as the quark-gluon plasma (QGP), and its dynamical evolution
The many physical processes that contribute to hadron production involve distinct energy scales and dominate different ranges in the pT distributions in various collision systems
Recent measurements from the BNL Relativistic Heavy Ion Collider (RHIC) use high-multiplicity pAu [23], dAu [24], and 3HeAu collisions [25] to study the effects of the initial geometry on the final-state particle correlations
Summary
The transverse momentum (pT) distributions of the particles produced in high-energy nuclear collisions can provide insights into the nature of the produced hot and dense matter, known as the quark-gluon plasma (QGP), and its dynamical evolution. Recent measurements from the BNL Relativistic Heavy Ion Collider (RHIC) use high-multiplicity pAu [23], dAu [24], and 3HeAu collisions [25] to study the effects of the initial geometry on the final-state particle correlations They find that hydrodynamic models that include short-lived QGP droplets provide simultaneous quantitative description of the measurements [26]. The effect of parton multiple scattering is not completely understood and has been shown to depend on multiple factors, e.g., whether the scatterings are elastic, inelastic, coherent or incoherent [12,39] These predictions can be tested with measurements of RpPb in the p- and Pb-going directions separately, and of the particle yield rapidity asymmetry Yasym in pPb collisions, where. The results are compared with predictions from the EPOS LHC model, which includes collective flow in pp and pPb collisions
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