# Measurement of the jet mass in highly boosted t t-bar events from pp collisions at sqrt(s) = 8 TeV

## TL;DR

This paper reports the first measurement of jet mass in highly boosted top quark events from proton-proton collisions at 8 TeV, using CMS data to test top quark production models and extract the top quark mass.

## Contribution

It provides the first measurement of jet mass in boosted top quark events at 8 TeV and assesses its sensitivity to the top quark mass.

## Key findings

- Jet mass distribution measured for highly boosted top quarks.
- The distribution's peak position is sensitive to the top quark mass.
- Results are used to test and validate modeling of boosted top quark production.

## Abstract

The first measurement of the jet mass m[jet] of top quark jets produced in t t-bar events from pp collisions at sqrt(s) = 8 TeV is reported for the jet with the largest transverse momentum pt in highly boosted hadronic top quark decays. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.7 inverse femtobarns. The measurement is performed in the lepton+jets channel in which the products of the semileptonic decay t to bW with W to l nu where l is an electron or muon, are used to select t t-bar events with large Lorentz boosts. The products of the fully hadronic decay t to bW with W to q q'-bar are reconstructed using a single Cambridge-Aachen jet with distance parameter R = 1.2, and pt > 400 GeV. The t t-bar cross section as a function of m[jet] is unfolded at the particle level and is used to test the modelling of highly boosted top quark production. The peak position of the m[jet] distribution is sensitive to the top quark mass m[t], and the data are used to extract a value of m[t] to assess this sensitivity.