Abstract
A measurement is presented of the top-quark mass in the all-jets channel using a sample of tt̄ candidate events requiring at least six jets in the final state. The data have been collected by CMS in pp collisions at 7 TeV and correspond to an integrated luminosity of 3.54 fb−1. In this channel, a very tight event selection is needed to reduce the huge amount of multi-jet events. In addition, the signal fraction and mass resolution is improved by the use of a kinematic fit. An ideogram method is used to measure the top-quark mass with the background estimated from data through an event mixing technique. The top-quark mass is measured to be mt = 173.5 ± 0.7 (stat.) ± 1.3 (syst.) GeV.
Highlights
A first top-quark mass measurement in all-jets final states is presented with the CMS detector [1]
The analysis employs a kinematic fit of the tt final state and likelihood functions for each event (“ideograms”) that depend on mt and jet energy scale (JES)
All events after the b-tagging selection are taken as input, mixing the jets between the different events such that in every newly generated event all jets are originating from different events, keeping at least two b-tagged jets in the new event
Summary
A first top-quark mass (mt) measurement in all-jets final states is presented with the CMS detector [1]. This final state yields the largest signal, it is dominated by multijet background. The event selection is very similar to the one from the CMS tt cross section measurement in the same final state [3]. The analysis employs a kinematic fit of the tt final state and likelihood functions for each event (“ideograms”) that depend on mt and jet energy scale (JES). The simulated tt sample and modeled background are normalized to data with an expected signal fraction (fsig) from simulation, which depends on the cross section [9, 10, 11] and the selection efficiency for tt events
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