Measurement of event shapes in minimum-bias events from proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper measures event-shape variables in proton-proton collisions at 13 TeV, revealing discrepancies between data and simulations, especially in isotropy, and providing detailed unfolded distributions.

Contribution

It presents the first detailed measurement of event-shape variables in minimum-bias proton-proton collisions at 13 TeV, highlighting limitations of current models.

Findings

Data is more isotropic than simulations.

None of the models fully describe the data.

Unfolded distributions and correlations are provided.

Abstract

A measurement of event-shape variables is presented, using a data sample produced in a special run with approximately one inelastic proton-proton collision per bunch crossing. The data were collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 64 $\mu$b$^{-1}$. A number of observables related to the overall distribution of charged particles in the collisions are corrected for detector effects and compared with simulations. Inclusive event-shape distributions, as well as differential distributions of event shapes as functions of charged-particle multiplicity, are studied. None of the models investigated is able to satisfactorily describe the data. Moreover, there are significant features common amongst all generator setups studied, particularly showing data being more isotropic than any of the simulations. Multidimensional unfolded distributions are provided, along with their correlations.