Particle production as a function of charged-particle flattenicity in p p collisions at s = 13 TeV

This paper reports the first measurement of the transverse momentum ( p T ) spectra of primary charged pions, kaons, (anti)protons, and unidentified particles as a function of the charged-particle flattenicity in pp collisions at s = 13 TeV . Flattenicity is a novel event shape observable that is measured in the pseudorapidity intervals covered by the V0 detector, 2.8 < η < 5.1 and − 3.7 < η < − 1.7 . According to QCD-inspired phenomenological models, it shows sensitivity to multiparton interactions and is less affected by biases toward larger p T due to local multiplicity fluctuations in the V0 acceptance than multiplicity. The analysis is performed in minimum-bias (MB) as well as in high-multiplicity events up to p T = 20 GeV / c . The event selection requires at least one charged particle produced in the pseudorapidity interval | η | < 1 . The measured p T distributions, average p T , kaon-to-pion and proton-to-pion particle ratios, presented in this paper, are compared to model calculations using 8 based on color strings and EPOS LHC. The modification of the p T -spectral shapes in low-flattenicity events that have large event activity with respect to those measured in MB events develops a pronounced peak at intermediate p T ( 2 < p T < 8 GeV / c ), and approaches the vicinity of unity at higher p T . The results are qualitatively described by , and they show different behavior than those measured as a function of charged-particle multiplicity based on the V0M estimator.