Σ+ production in pp collisions at s=13 TeV

Abstract

The measurement of Σ+ production in pp collisions at s=13 TeV is presented. The measurement is performed at midrapidity in both minimum-bias and high-multiplicity pp collisions at s=13 TeV. The Σ+ is reconstructed via its weak-decay topology in the decay channel Σ+→p+π0 with π0→γ+γ. In a novel approach, the neutral pion is reconstructed by combining photons that convert in the detector material with photons measured in the calorimeters. The transverse-momentum (pT) distributions of the Σ+ and its rapidity densities dN/dy in both event classes are reported. The pT spectrum in minimum-bias collisions is compared to QCD-inspired event generators. The ratio of Σ+ to previously measured Λ baryons is in good agreement with calculations from the Statistical Hadronization Model. The high efficiency and purity of the novel reconstruction method for Σ+ presented here will enable future studies of the interaction of Σ+ with protons in the context of femtoscopic measurements, which could be crucial for understanding the equation of state of neutron stars. © CERN for the benefit of the ALICE Collaboration 2026.