Measurement of the Jet Mass in Highly Boosted T-tbar Events from Pp Collisions at $\sqrt{s}$
Measurement of the Jet Mass in Highly Boosted T-tbar Events from Pp Collisions at $\sqrt{s}$

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Published: 2017

Total Pages:

ISBN-13:

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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.

Measurement of the Top Quark Mass with in Situ Jet Energy Scale Calibration Using Hadronic W Boson Decays at CDF-II.
Measurement of the Top Quark Mass with in Situ Jet Energy Scale Calibration Using Hadronic W Boson Decays at CDF-II.

Author: Jean-François Arguin

Publisher:

Published: 2006

Total Pages: 0

ISBN-13: 9780494159187

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We report a measurement of the top quark mass with the upgraded Collider Detector at Fermilab (CDF-II). The top quarks are produced in pairs (tt−) in proton-antiproton collisions with a center-of-mass energy of 1.96 TeV. Each top quark decays to a W boson and a bottom quark. We select candidate events in which one W boson decays hadronically and the other decays to an electron or a muon and its associated neutrino. The data sample, which corresponds to an integrated luminosity of 318 pb-1, contains 138 tt− candidates. A top quark mass is reconstructed for each event by placing energy and momentum constraints on the top quark pair decay products. We also employ the reconstructed mass of the hadronic W boson decays W & rarr; jj to constrain in situ the largest systematic uncertainty of the top quark mass measurement, the jet energy scale. Monte Carlo templates of the reconstructed top quark and W boson mass are produced as a function of the top quark mass and the jet energy scale. The distribution of reconstructed top quark and W boson mass in the data are compared to the Monte Carlo templates using a likelihood fit to obtain Mtop = 173.5+3.9-3.8 GeV/c2. This constitutes the most precise measurement of the top quark mass to date. This measurement can be used to constrain the mass of the Higgs boson, a central particle in the Standard Model of particle physics that has yet to be observed. We also demonstrate that this new technique reduces naturally the jet, energy scale uncertainty as more data is accumulated and thus provides the capability to measure Mtop with an uncertainty of 2 GeV/c2 or better by the end of the CDF-II experiment.