Search for Pair Production of Scalar Top Quarks in Jets and Missing Transverse Energy Channel with the D0 Detector
Search for Pair Production of Scalar Top Quarks in Jets and Missing Transverse Energy Channel with the D0 Detector

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Published: 2008

Total Pages: 156

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This dissertation describes a search for the pair production of scalar top quarks, {tilde t}1, using a luminosity of 995 pb−1 of data collected in p{bar p} collisions with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy (square root)s = 1.96 TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino, {tilde {chi}}1°, where {tilde {chi}}1° is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. The yield of such events in data is found to be consistent with the expectations from known standard model processes. Sets of {tilde t}1 and {tilde {chi}}1° masses are excluded at the 95% confidence level that substantially extend the domain excluded by previous searches. With the theoretical uncertainty on the {tilde t}1 pair production cross section taken into account, the largest limit for m{sub {tilde t}1} is m{sub {tilde t}1}> 150 GeV, for m{sub {tilde {chi}}1°} = 65 GeV.

Search for Pair Production of Scalar Top Quarks in Jets and Missing Transverse Energy Channel with the D0 Detector
Search for Pair Production of Scalar Top Quarks in Jets and Missing Transverse Energy Channel with the D0 Detector

Author: Mansoora Shamim

Publisher:

Published: 2008

Total Pages:

ISBN-13:

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This dissertation describes a search for the pair production of scalar top quarks, tilde[subscript] 1, using a luminosity of 995 pb[superscript-1] of data collected in p[bar over]p collisions with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy sqrt[s] = 1.96 TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino, [tilde chi superscript 0 subscript 1] where [(tilde chi superscript 0 subscript 1)] is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. The yield of such events in data is found to be consistent with the expectations from known standard model processes. Sets of tilde [subscript 1] and tilde chi [superscript 0 subscript 1] masses are excluded at the 95% confidence level that substantially extend the domain excluded by previous searches. With the theoretical uncertainty on the pair production cross section taken into account, the largest limit for m[subscript tilde subscript 1] is m[subscript tilde chi subscript 1> 150 GeV, for m [subscript tilde chi negative 0 subscript 1]= 65 GeV.

Search for Direct Pair Production of Scalar Top Quarks in the Single- and Dilepton Channels in Proton-proton Collisions at $\sqrt{s}$
Search for Direct Pair Production of Scalar Top Quarks in the Single- and Dilepton Channels in Proton-proton Collisions at $\sqrt{s}$

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Published: 2016

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Results are reported from a search for the top squark $ \tilde{t}_1 $, the lighter of the two supersymmetric partners of the top quark. The data sample corresponds to 19.7 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 8 TeV collected with the CMS detector at the LHC. The search targets $ \tilde{t}_1 \to \mathrm{b} \tilde{\chi}^{\pm}_1$ and $ \tilde{t}_1 \to \mathrm{t}^{(*)} \tilde{\chi}^0_1$ decay modes, where $\tilde{\chi}^{\pm}_1$ and $\tilde{\chi}^0_1$ are the lightest chargino and neutralino, respectively. The reconstructed final state consists of jets, b jets, missing transverse energy, and either one or two leptons. Leading backgrounds are determined from data. No significant excess in data is observed above the expectation from standard model processes. The results exclude a region of the two-dimensional plane of possible $ \tilde{t}_1 $ and $\tilde{\chi}^0_1 $ masses. The highest excluded $ \tilde{t}_1 $ and $ \tilde{\chi}^0_1$ masses are about 700 GeV and 250 GeV, respectively.

Search for the Pair Production of Scalar Top Quarks in the Acoplanar Charm Jet Final State in P Anti-p Collisions at S**ư
Search for the Pair Production of Scalar Top Quarks in the Acoplanar Charm Jet Final State in P Anti-p Collisions at S**ư

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Published: 2006

Total Pages: 9

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A search for the pair production of scalar top quarks, {bar t}, has been performed in 360 pb−1 of data from p{bar p} collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron collider. The {bar t} decay mode considered is {bar t} → c{bar {chi}}1°, where {bar {chi}}1° is the lightest supersymmetric particle. The topology analyzed therefore consists of a pair of acoplanar heavy-flavor jets with missing transverse energy. The data show good agreement with the standard model expectation, and a 95% C.L. exclusion domain in the (m{sub {tilde t}}, m{sub {tilde {chi}}1°}) plane has been determined, extending the domain excluded by previous experiments.

Search for the Pair Production of Scalar Top Quarks in the Acoplanar Charm Jet Final State in P Anti-p Collisions at S**1/2
Search for the Pair Production of Scalar Top Quarks in the Acoplanar Charm Jet Final State in P Anti-p Collisions at S**1/2

Author:

Publisher:

Published: 2006

Total Pages: 9

ISBN-13:

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A search for the pair production of scalar top quarks, {bar t}, has been performed in 360 pb−1 of data from p{bar p} collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron collider. The {bar t} decay mode considered is {bar t} → c{bar {chi}}1°, where {bar {chi}}1° is the lightest supersymmetric particle. The topology analyzed therefore consists of a pair of acoplanar heavy-flavor jets with missing transverse energy. The data show good agreement with the standard model expectation, and a 95% C.L. exclusion domain in the (m{sub {tilde t}}, m{sub {tilde {chi}}1°}) plane has been determined, extending the domain excluded by previous experiments.

Measurement of the Top Quark Pair Production Cross-section in the Dilepton Channel Using Lepton Plus Track Selection and Identified B-jets
Measurement of the Top Quark Pair Production Cross-section in the Dilepton Channel Using Lepton Plus Track Selection and Identified B-jets

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Published: 2004

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Using 1.0 fb^{-1} of data collected by the Collider Detector at Fermilab (CDF) from Run II of the Fermilab Tevatron, we measure the top-antitop production cross-section in events with two leptons, significant missing transverse energy, and at least jets, at least one of which is identified as a b-jet. As the Run II dataset grows, more stringent tests of Standard Model predictions for the top quark sector are becoming possible. The dilepton channel, where both top quarks decay t-> W b ->l nu b, is of particular interest due to its high purity. Use of an isolated track as the second lepton significantly increases the dilepton acceptance, at the price of some increase in background, particularly from W + jets events where one of the jets is identified as a lepton. To control the increase in background we add to the event selection the requirement that at least one of the jets be identified as a b-jet, reducing the background contribution from all sources. Assuming a branching ratio of BR(W->l nu) = 10.8% and a top mass of m_top = 175 GeV/c^{2} the measured cross-section is sigma = (10.5 +/- 1.8 stat. +/- 0.8 syst. +/- 0.6 lumi.) pb.