skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: A precise measurement of the top quark mass

Abstract

We present a measurement of the mass of the top quark using data from proton-antiproton collisions recorded at the CDF experiment in Run II of the Fermilab Tevatron. Events are selected from the single lepton plus jets final state (t$$\bar{t}$$ → W +bW -$$\bar{b}$$ → ℓvbq$$\bar{q}$$'$$\bar{b}$$). The top quark mass is extracted using a calculation of the probability density for a t$$\bar{t}$$ final state to resemble a data event. This probability density is a function of both top quark mass and energy scale of calorimeter jets, constrained in situ with the hadronic W boson mass. Using 167 events observed in 955 pb -1 integrated luminosity, we achieve the single most precise measurement of top quark mass to date of 170.8 ± 2.2 (stat.) ± 1.4 (syst.) GeV/c 2, where the quoted statistical uncertainty includes uncertainty from the determination of the jet energy scale.

Authors:
 [1]
  1. Univ. of California, Los Angeles, CA (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
902873
Report Number(s):
FERMILAB-THESIS-2007-05
TRN: US200721%%376
DOE Contract Number:
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CALORIMETERS; FERMILAB COLLIDER DETECTOR; FERMILAB TEVATRON; INTERMEDIATE BOSONS; LEPTONS; LUMINOSITY; PROBABILITY; T QUARKS; Experiment-HEP

Citation Formats

Mohr, Brian N. A precise measurement of the top quark mass. United States: N. p., 2007. Web. doi:10.2172/902873.
Mohr, Brian N. A precise measurement of the top quark mass. United States. doi:10.2172/902873.
Mohr, Brian N. Sun . "A precise measurement of the top quark mass". United States. doi:10.2172/902873. https://www.osti.gov/servlets/purl/902873.
@article{osti_902873,
title = {A precise measurement of the top quark mass},
author = {Mohr, Brian N.},
abstractNote = {We present a measurement of the mass of the top quark using data from proton-antiproton collisions recorded at the CDF experiment in Run II of the Fermilab Tevatron. Events are selected from the single lepton plus jets final state (t$\bar{t}$ → W+bW-$\bar{b}$ → ℓvbq$\bar{q}$'$\bar{b}$). The top quark mass is extracted using a calculation of the probability density for a t$\bar{t}$ final state to resemble a data event. This probability density is a function of both top quark mass and energy scale of calorimeter jets, constrained in situ with the hadronic W boson mass. Using 167 events observed in 955 pb-1 integrated luminosity, we achieve the single most precise measurement of top quark mass to date of 170.8 ± 2.2 (stat.) ± 1.4 (syst.) GeV/c2, where the quoted statistical uncertainty includes uncertainty from the determination of the jet energy scale.},
doi = {10.2172/902873},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}

Thesis/Dissertation:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this thesis or dissertation.

Save / Share:
  • The top quark is a very special fundamental particle in the Standard Model (SM) mainly due to its heavy mass. The top quark has extremely short lifetime and decays before hadronization. This reduces the complexity for the measurement of its mass. The top quark couples very strongly to the Higgs boson since the fermion-Higgs Yukawa coupling linearly depends on the fermion’s mass. Therefore, the top quark is also heavily involved in Higgs production and related study. A precise measurement of the top quark mass is very important, as it allows for self-consistency check of the SM, and also gives a insight about the stability of our universe in the SM context. This dissertation presents my work on the measurement of the top quark mass in dilepton final states of tmore » $$\bar{t}$$ events in p$$\bar{p}$$ collisions at √s = 1.96 TeV, using the full DØ Run II data corresponding to an integrated luminosity of 9.7 fb -1 at the Fermilab Tevatron. I extracted the top quark mass by reconstructing event kinematics, and integrating over expected neutrino rapidity distributions to obtain solutions over a scanned range of top quark mass hypotheses. The analysis features a comprehensive optimization that I made to minimize the expected statistical uncertainty. I also improve the calibration of jets in dilepton events by using the calibration determined in t$$\bar{t}$$ → lepton+jets events, which reduces the otherwise limiting systematic uncertainty from the jet energy scale. The measured mass is 173.11 ± 1.34(stat) +0.83 -0.72(sys) GeV .« less
  • The top quark has been discovered by CDF and D0 experiments in 1995 at the proton-antiproton collider Tevatron. The amount of data recorded by both experiments makes it possible to accurately study the properties of this quark: its mass is now known to better than 1% accuracy. This thesis describes the measurement of the top pair cross section in the electron muon channel with 4, 3 fb -1 recorded data between 2006 and 2009 by the D0 experiment. Since the final state included a muon, improvements of some aspects of its identification have been performed : a study ofmore » the contamination of the cosmic muons and a study of the quality of the muon tracks. The cross section measurement is in good agreement with the theoretical calculations and the other experimental measurements. This measurement has been used to extract a value for the top quark mass. This method allows for the extraction of a better defined top mass than direct measurements as it depends less on Monte Carlo simulations. The uncertainty on this extracted mass, dominated by the experimental one, is however larger than for direct measurements. In order to decrease this uncertainty, the ratio of the Z boson and the top pair production cross sections has been studied to look for some possible theoretical correlations. At the Tevatron, the two cross sections are not theoretically correlated: no decrease of the uncertainty on the extracted top mass is therefore possible.« less
  • The top quark is the heaviest standard model quark. Discovered in 1995 by the two Tevatron experiments it has atypical properties. In particular its time life is so short that it decays before hadronizing, so the top quark mass could be measured with a high precision. Data collected by the DØ experiment between 2002 and 2009, which represent an integrated luminosity of 5.4 fb⁻¹, are used to measure the top quark mass by using the matrix element method in the three dilepton channels: dielectron, electron--muon and dimuon. The measured mass, 174.0 ± 1.8 (stat.) ± 2.4 (syst.) GeV, is inmore » a good agreement with other measurements and limited by the systematic uncertainties for the first time in these channels. In this thesis different approaches have been studied to improve the accuracy of this measurement: the use of b-quark jet identification in order to optimize the selection of top--anti-top events and a better determination of the main systematic uncertainties. A special attention has been paid to the Monte-Carlo simulation of muons in D0: the improved smearing procedure for the simulated muons, discussed in this thesis, will be used to increase the accuracy of the top properties measurements as well as the precision of many other D0 measurements.« less
  • Of the six quarks in the standard model the top quark is by far the heaviest: 35 times more massive than its partner the bottom quark and more than 130 times heavier than the average of the other five quarks. Its correspondingly small decay width means it tends to decay before forming a bound state. Of all quarks, therefore, the top is the least affected by quark confinement, behaving almost as a free quark. Its large mass also makes the top quark a key player in the realm of the postulated Higgs boson, whose coupling strengths to particles are proportional to their masses. Precision measurements of particle masses for e.g. the top quark and the W boson can hereby provide indirect constraints on the Higgs boson mass. Since in the standard model top quarks couple almost exclusively to bottom quarks (t → Wb), top quark decays provide a window on the standard model through the direct measurement of the Cabibbo-Kobayashi-Maskawa quark mixing matrix element V tb. In the same way any lack of top quark decays into W bosons could imply the existence of decay channels beyond the standard model, for example charged Higgs bosons as expected in two-doublet Higgs models: t → H +b. Within the standard model top quark decays can be classified by the (lepton or quark) W boson decay products. Depending on the decay of each of the W bosons, tmore » $$\bar{t}$$ pair decays can involve either no leptons at all, or one or two isolated leptons from direct W → e$$\bar{v}$${sub e} and W → μ$$\bar{v}$$ μ decays. Cascade decays like b → Wc → e$$\bar{v}$$ ec can lead to additional non-isolated leptons. The fully hadronic decay channel, in which both Ws decay into a quark-antiquark pair, has the largest branching fraction of all t$$\bar{t}$$ decay channels and is the only kinematically complete (i.e. neutrino-less) channel. It lacks, however, the clear isolated lepton signature and is therefore hard to distinguish from the multi-jet QCD background. It is important to measure the cross section (or branching fraction) in each channel independently to fully verify the standard model. Top quark pair production proceeds through the strong interaction, placing the scene for top quark physics at hadron colliders. This adds an additional challenge: the huge background from multi-jet QCD processes. At the Tevatron, for example, t$$\bar{t}$$ production is completely hidden in light q$$\bar{q}$$ pair production. The light (i.e. not bottom or top) quark pair production cross section is six orders of magnitude larger than that for t$$\bar{t}$$ production. Even including the full signature of hadronic t$$\bar{t}$$ decays, two b-jets and four additional jets, the QCD cross section for processes with similar signature is more than five times larger than for t$$\bar{t}$$ production. The presence of isolated leptons in the (semi)leptonic t$$\bar{t}$$ decay channels provides a clear characteristic to distinguish the t$$\bar{t}$$ signal from QCD background but introduces a multitude of W- and Z-related backgrounds.« less
  • A measurement of the top anti-top quark pair production cross section in pmore » $$\bar{p}$$ collisions at a center-of-mass energy of 1.96 TeV is presented. The measurement is made using data with integrated luminosity of 109.4 pb -1, obtained at the Collider Detector at Fermilab between August 2002 and May 2003. A search is made for the dilepton decay channel of top anti-top production, t$$\bar{t}$$→l+νbl-νl$$\bar{b}$$. The Standard Model dilepton decay channel of the top anti-top quark pair production involves two high transverse momentum leptons, a large missing energy from the undetected neutrinos, two jets from the b and b¯ quark fragmentations. Various Standard Model processes can mimic t$$\bar{t}$$ production in this decay channel. These backgrounds are estimated to be 0.65 ± 0.13 events in an integrated luminosity of 109.4 pb -1. In the data, one ee, three μμ, and two eμ dilepton candidates were observed. From these data, the t$$\bar{t}$$ production cross section of σ t$$\bar{t}$$ =11.4 $$+6.2\atop{-4.6}$$ pb has been measured. This measurement is consistent with the theoretical prediction of the Standard Model, σ t$$\bar{t}$$ =6.70 $$+71\atop{0.88}$$ pb assuming a top quark mass of 175 GeV/c 2.« less