# Measurement of the average very forward energy as a function of the track multiplicity at central pseudorapidities in proton-proton collisions at $\sqrt{s} =$ 13 TeV

## TL;DR

This study measures the average energy in the very forward region of proton-proton collisions at 13 TeV, analyzing its dependence on central track multiplicity and comparing results with Monte Carlo predictions.

## Contribution

It provides the first detailed measurement of forward energy as a function of central multiplicity at 13 TeV, testing and challenging current Monte Carlo models.

## Key findings

- All Monte Carlo generators overestimate the hadronic energy fraction.
- The measurement reveals correlations between forward energy and central multiplicity.
- Data constrains models of underlying event structure in high-energy collisions.

## Abstract

The average total energy as well as its hadronic and electromagnetic components are measured with the CMS detector at pseudorapidities $-$6.6 $<$ $\eta$ $<-$5.2 in proton-proton collisions at a centre-of-mass energy $\sqrt{s} =$ 13 TeV. The results are presented as a function of the charged particle multiplicity in the region $|\eta|$ $<$ 2. This measurement is sensitive to correlations induced by the underlying event structure over a very wide pseudorapidity region. The predictions of Monte Carlo event generators commonly used in collider experiments and ultra-high energy cosmic ray physics are compared to the data. All generators considered overestimate the fraction of energy going into hadrons.