https://doi.org/10.1140/epjp/s13360-026-07586-9
Regular Article
Event-by-event fluctuations of mean transverse momentum in proton–proton collisions at 
= 13 TeV with PYTHIA8 and HERWIG7 models
Indian Institute of Technology Bombay, 400076, Mumbai, India
a
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Received:
5
September
2025
Accepted:
17
March
2026
Published online:
6
April
2026
Abstract
Event-by-event fluctuations of the mean transverse momentum(
) are investigated in pp collisions at 
TeV using the Monte Carlo event generators PYTHIA8 and HERWIG7 . Charged particles within 
GeV/c and 
are considered. Dynamical fluctuations, quantified via the normalized two-particle correlator, decrease with multiplicity in line with the independent superposition of multiple parton interactions. The magnitude, however, differs between the two models, reflecting their distinct hadronization mechanisms. The skewness of the 
distribution shows a finite positive value at low multiplicity that vanishes beyond average charge particle multiplicity, 
, indicating a transition toward Gaussian-like fluctuations. Transverse spherocity analysis reveals that jet-dominated events enhance correlation strength and suppress skewness at lower multiplicity, while isotropic events remain more sensitive to model-dependent soft-QCD dynamics. These results demonstrate that fluctuation observables offer valuable constraints on jets, multiparton interactions, and hadronization models in Monte Carlo event generators.
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© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2026
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
