Improved Λp Elastic Scattering Cross Sections between 0.9 and 2.0 GeV/c as a Main Ingredient of the Neutron Star Equation of State
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Nuclear medium effects on meson production are studied using the binary-collision scaled cross section ratio between events of different charged-particle multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of , corresponding to an integrated luminosity of , were used. The scaling factors in the ratio are determined using a novel approach based on the cross sections measured in the same events. The scaled ratio for is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor. © 2025 CERN, for the CMS Collaboration2025CERNmore » « less
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The polarization of the and hyperons along the beam direction has been measured in proton-lead ( ) collisions at a center-of-mass energy per nucleon pair of 8.16 TeV. The data were obtained with the CMS detector at the LHC and correspond to an integrated luminosity of . A significant azimuthal dependence of the hyperon polarization, characterized by the second-order Fourier sine coefficient , is observed. The values decrease as a function of charged particle multiplicity, but increase with transverse momentum. A hydrodynamic model that describes the observed values in nucleus-nucleus collisions by introducing vorticity effects does not reproduce either the sign or the magnitude of the results. These observations pose a challenge to the current theoretical implementation of spin polarization in heavy ion collisions and offer new insights into the origin of spin polarization in hadronic collisions at LHC energies.more » « less
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