Search For The Supersymmetric Partner Of The Top Quark With The Atlas Detector Via Tildet 1 Rightarrow T Widetilde Chi 0 1 And Tildet 1 Rightarrow B Widetilde Chi Pm 1 Decays
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Search For The Supersymmetric Partner Of The Top Quark With The Atlas Detector Via Tildet 1 Rightarrow T Widetilde Chi 0 1 And Tildet 1 Rightarrow B Widetilde Chi Pm 1 Decays
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Author : Francesca Consiglia Ungaro
language : en
Publisher:
Release Date : 2015
Search For The Supersymmetric Partner Of The Top Quark With The Atlas Detector Via Tildet 1 Rightarrow T Widetilde Chi 0 1 And Tildet 1 Rightarrow B Widetilde Chi Pm 1 Decays written by Francesca Consiglia Ungaro and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
Zusammenfassung: The elementary particles composing matter and their interactions are described by the Standard Model of particle physics. The Standard Model of particle physics enabled predictions that were experimentally verified and has been confirmed throughout the past decades by data. Nevertheless, there are several theoretical reasons not to consider it as the ultimate theory.The strongest motivation to expect Physics beyond the Standard Model is the hierarchy problem. The radiative corrections to the mass of the Higgs boson grow quadratically with the square of the energy scale at which the Standard Model is considered to be valid. As a result, the parameters of the Standard Model need to be fine-tuned in order for the mass of the Higgs boson to acquire the value experimentally measured, despite the possibly large corrections.Supersymmetry is a promising theory extending the Standard Model which solves many of its shortcomings, including the hierarchy problem. Supersymmetry postulates a new fermion-boson symmetry resulting in the introduction of new particles, called superpartners, with the same quantum numbers and masses as the Standard Model particles, except for the spin, differing by half a unit. This new symmetry enables a cancellation of the radiative corrections due to the Standard Model particles with the corrections due to the newly introduced superpartners, contributing with opposite sign. Since no superpartners with the same mass as the Standard Model particles have been observed, Supersymmetry must be broken to allow the superpartners to have a mass different from the mass of the corresponding Standard Model particles.In the minimal version of Supersymmetry in terms of new particles, the Minimal Supersymmetric Standard Model, the hierarchy problem can still be solved with a moderate amount of fine-tuning if the masses of at least some of the superpartners are at the TeV energy scale. The conservation of a new multiplicative quantum number, the R-parity, can be assumed to prevent phenomena in contrast with experimental evidences, as the proton decay. Superpartners have R-parity -1, and Standard Model particles R-parity +1. If the conservation of R-parity is assumed, in collider experiments supersymmetric particles can only be produced in even numbers (usually two), and the lightest supersymmetric particles (LSP, usually taken to be the neutralino), is stable.The LHC (Large Hadron Collider), is a hadron collider able to accelerate protons to unprecedented energies. Between 2010 and 2012 it operated at a centre-of-mass energy of the proton-proton collisions of 7 and 8 TeV.Its general-purpose experiments, ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Spectrometer) collected data corresponding to about 5 $fb^{-1}$ at $\sqrt{s}$ = 7 TeV and 20 $fb^{-1}$ at $\sqrt{s}$ = 8 TeV. The LHC and its experiments have been built with the main motivations of searching for the Higgs boson, discovered by the ATLAS and CMS experiments in 2012, and searching for signals of Supersymmetry.There are strong theoretical reasons to expect the supersymmetric particles to lie at the TeV energy scale, which would make them accessible at the LHC.In the Minimal Supersymmetric Standard Model, the lightest superpartner of the top quark, light stop is very likely to be lighter than the superpartners of the other quarks. This thesis focuses on the search for direct stop pair production with the data collected by the ATLAS experiment. Two analyses have been performed, addressing different final states and decay modes.The first analysis targets stop masses close to the mass of the top quark, ideal to solve the hierarchy problem.The mass spectrum assumed is such that m(stop)
Search For Pair Production Of Supersymmetric Top Quarks In Dilepton Events From P Bar P Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2009
Search For Pair Production Of Supersymmetric Top Quarks In Dilepton Events From P Bar P Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
We present the results of a search for pair production of the supersymmetric partner of the top quark (the stop quark ≈1) decaying to a b-quark and a chargino {tilde {chi}}1{sup {+-}} with a subsequent {tilde {chi}}1{sup {+-}} decay into a neutralino {tilde {chi}}1°, lepton l, and neutrino [nu]. Using a data sample corresponding to 2.7 fb−1 of integrated luminosity of p{bar p} collisions at √s = 1.96 TeV collected by the CDF II detector, we reconstruct the mass of candidate stop events and fit the observed mass spectrum to a combination of standard model processes and stop quark signal. We find no evidence for {tilde t}1{bar {tilde t}}1 production and set 95% C.L. limits on the masses of the stop quark and the neutralino for several values of the chargino mass and the branching ratio [Beta]({tilde {chi}}1{sup {+-}} → {tilde {chi}}1°l{sup {+-}}[nu]).
Searches For Scalar Top And Bottom Quarks At The Tevatron
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Author : Thomas Nunnemann
language : en
Publisher:
Release Date : 2006
Searches For Scalar Top And Bottom Quarks At The Tevatron written by Thomas Nunnemann and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
Searches for the supersymmetric partners of top and bottom quarks using data up to 340 pb{sup -1} taken at the Tevatron p{bar p} collider are described. We report on searches for scalar top quarks {tilde t} in the decays {tilde t} {yields} c{tilde {chi}}{sub 1}{sup 0} and {tilde t} {yields} bl{tilde v} and for scalar bottom quarks in the decay {tilde b} {yields} b{tilde {chi}}{sub 1}{sup 0}. No evidence for a signal has been found, but improved exclusion regions have been derived in the framework of a generic minimal supersymmetric extension of the standard model.
A Search For The Lightest Supersymmetric Partner Of The Top Quark At
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Author :
language : en
Publisher:
Release Date : 2010
A Search For The Lightest Supersymmetric Partner Of The Top Quark At written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ({tilde t}1) in 5.4 ± 0.3 fb−1 of data from the D0 detector at a p{bar p} center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino ({tilde {nu}}), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected and new exclusion limits at the 95% C.L. are set for a portion of the (m{sub {tilde t}1}, m{sub {tilde {nu}}}) mass plane.
Search For Pair Production Of The Supersymmetric Partner Of The Top Quark In The T Tilde Anti T Tilde B Anti B E Mu Sneutrino Anti Sneutrino Decay Channel At
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Author :
language : en
Publisher:
Release Date : 2010
Search For Pair Production Of The Supersymmetric Partner Of The Top Quark In The T Tilde Anti T Tilde B Anti B E Mu Sneutrino Anti Sneutrino Decay Channel At written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
We report the result of a search for the pair production of the light top squark decaying to two bottom quarks, an electron, a muon, and two sneutrinos in 3.1 ±0.19 fb−1 of data from the DO detector at the Tevatron, Fermilab's (square root)s = 1.96 TeV p {bar p} collider. No significant excess of events above the standard model prediction was detected and new exclusion limits at the 95% confidence level have been set for a portion of the stop mass-sneutrino mass plane.
Search For Admixture Of Scalar Top Quarks In The T Anti T Lepton Jets Final State At S
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Author :
language : en
Publisher:
Release Date : 2009
Search For Admixture Of Scalar Top Quarks In The T Anti T Lepton Jets Final State At S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
A search for pair production of the lightest supersymmetric partner of the top quark, {tilde t}1, is performed in the lepton+jets channel using 0.9 fb−1 of data collected by the D0 experiment. Kinematic differences between {tilde t}1{bar {tilde t}}1 and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark ({tilde t}1 → {tilde {chi}}1 b) are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.
Search For Admixture Of Scalar Top Quarks In The T Anti T Lepton Jets Final State At S 1 2
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Author :
language : en
Publisher:
Release Date : 2009
Search For Admixture Of Scalar Top Quarks In The T Anti T Lepton Jets Final State At S 1 2 written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
A search for pair production of the lightest supersymmetric partner of the top quark, {tilde t}1, is performed in the lepton+jets channel using 0.9 fb−1 of data collected by the D0 experiment. Kinematic differences between {tilde t}1{bar {tilde t}}1 and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark ({tilde t}1 2!{tilde {chi}}1 b) are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.
Search For Pair Production Of Scalar Top Quarks Decaying To A Tau Lepton And A B Quark In Ppbar Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2008
Search For Pair Production Of Scalar Top Quarks Decaying To A Tau Lepton And A B Quark In Ppbar Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
We present the results of a search for pair production of scalar top quarks ({tilde t}1) in an R-parity violating supersymmetric scenario using 322 pb−1 of p{bar p} collisions at √s = 1.96 TeV collected by the upgraded Collider Detector at Fermilab. We assume each {tilde t}1 decays into a? lepton and a b quark with a branching ratio?, and that the final state contains either an electron or a muon from a leptonic? decay, a hadronically decaying? lepton, and two or more jets. Two candidate events pass our final selection criteria, consistent with the expectation from standard model processes. We present upper limits on the cross section times branching ratio squared?({tilde t}1{bar {tilde t}}1) x?2 as a function of the stop mass m({tilde t}1). Assuming? = 1, we set a 95% confidence level limit m({tilde t}1)> 153 GeV=c2 obtained using a next-to-leading order cross section. These limits are also fully applicable to the case of a pair produced third generation scalar leptoquark decaying into a? lepton and a b quark.
Search For Pair Production Of Scalar Top Quarks In Jets And Missing Transverse Energy Channel With The D0 Detector
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Author :
language : en
Publisher:
Release Date : 2008
Search For Pair Production Of Scalar Top Quarks In Jets And Missing Transverse Energy Channel With The D0 Detector written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
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 New Phenomena With Top Quark Pairs In Final States With One Lepton Jets And Missing Transverse Momentum In Pp Collisions At Square Root S
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Author : ATLAS Collaboration CERN
language : en
Publisher:
Release Date : 2021
Search For New Phenomena With Top Quark Pairs In Final States With One Lepton Jets And Missing Transverse Momentum In Pp Collisions At Square Root S written by ATLAS Collaboration CERN and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
Abstract: A search for new phenomena with top quark pairs in final states with one isolated electron or muon, multiple jets, and large missing transverse momentum is performed. Signal regions are designed to search for two-, three-, and four-body decays of the directly pair-produced supersymmetric partner of the top quark (stop). Additional signal regions are designed specifically to search for spin-0 mediators that are produced in association with a pair of top quarks and decay into a pair of dark-matter particles. The search is performed using the Large Hadron Collider proton-proton collision dataset at a centre-of-mass energy of s√ = 13 TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb−1. No significant excess above the Standard Model background is observed, and limits at 95% confidence level are set in the stop-neutralino mass plane and as a function of the mediator mass or the dark-matter particle mass. Stops are excluded up to 1200 GeV (710 GeV) in the two-body (three-body) decay scenario. In the four-body scenario stops up to 640 GeV are excluded for a stop-neutralino mass difference of 60 GeV. Scalar and pseudoscalar dark-matter mediators are excluded up to 200 GeV when the coupling strengths of the mediator to Standard Model and dark-matter particles are both equal to one and when the mass of the dark-matter particle is 1 GeV