Download or read book Search for Direct Pair Production of Supersymmetric Top Quarks Decaying to All hadronic Final States in Pp Collisions at u221A s written by and published by . This book was released on 2016 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here, results are reported from a search for the pair production of top squarks, the supersymmetric partners of top quarks, in final states with jets and missing transverse momentum. The data sample used in this search was collected by the CMS detector and corresponds to an integrated luminosity of 18.9 fb–1 of proton-proton collisions at a centre-of-mass energy of 8 TeV produced by the LHC. The search features novel background suppression and prediction methods, including a dedicated top quark pair reconstruction algorithm. The data are found to be in agreement with the predicted backgrounds. Exclusion limits are set in simplified supersymmetry models with the top squark decaying to jets and an undetected neutralino, either via a top quark or through a bottom quark and chargino. Models with the top squark decaying via a top quark are excluded for top squark masses up to 755 GeV in the case of neutralino masses below 200 GeV. For decays via a chargino, top squark masses up to 620 GeV are excluded, depending on the masses of the chargino and neutralino.

Download or read book Search for Supersymmetry in Hadronic Final States written by Hannsjörg Artur Weber and published by Springer. This book was released on 2015-06-11 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: The project reported here was a search for new super symmetric particles in proton-proton collisions at the LHC. It has produced some of the world’s best exclusion limits on such new particles. Furthermore, dedicated simulation studies and data analyses have also yielded essential input to the upgrade activities of the CMS collaboration, both for the Phase-1 pixel detector upgrade and for the R&D studies in pursuit of a Phase-2 end cap calorimeter upgrade.

Download or read book Search for Supersymmetry in the All hadronic Final State Using Top Quark Tagging in Pp Collisions at Sqrt s written by and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A search is presented for supersymmetry in all-hadronic events with missing transverse momentum based on tagging of top quarks. The data sample corresponds to an integrated luminosity of 2.3 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC. Search regions are defined using the properties of reconstructed jets, the presence of bottom and top quark candidates, and an imbalance in transverse momentum. With no statistically significant excess of events observed beyond the expected contributions from the standard model, we set exclusion limits at 95% confidence level on the masses of new particles in the context of simplified models of direct and gluino-mediated top squark production. For direct top squark production with decays to a top quark and a neutralino, top squark masses up to 740 GeV and neutralino masses up to 240 GeV are excluded. Gluino masses up to 1550 GeV and neutralino masses up to 900 GeV are excluded for models of gluino pair production where each gluino decays to a top-antitop quark pair and a neutralino.

Download or read book Search for Scalar Top Quarks and Higgsino Like Neutralinos written by Takuya Nobe and published by Springer. This book was released on 2015-11-30 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reports a search for theoretically natural supersymmetry (SUSY) at the Large Hadron Collider (LHC). The data collected with the ATLAS detector in 2012 corresponding to 20 /fb of an integrated luminosity have been analyzed for stop pair production in proton–proton collisions at a center-of-mass energy of 8 TeV at the Large Hadron Collider (LHC) in the scenario of the higgsino-like neutralino. The author focuses on stop decaying into a bottom quark and chargino. In the scenario of the higgsino-like neutralino, the mass difference between charginos and neutralinos (Δm) is expected to be small, and observable final-state particles are likely to have low-momentum (soft). The author develops a dedicated analysis with a soft lepton as a probe of particles from chargino decay, which suppresses the large amount of backgrounds. As a result of the analysis, no significant SUSY signal is observed. The 95% confidence-level exclusion limits are set to masses of stop and neutralino assuming Δm = 20 GeV. The region with ΔM (the mass difference between stop and neutralino) 70 GeV is excluded for the first time at stop mass of less than 210 GeV. The author also excludes the signals with ΔM 120 GeV up to 600 GeV of stop mass with neutralino mass of less than 280 GeV. The author clearly shows very few remaining parameter spaces for light stop (e.g., topology of stop decay is extremely similar to the SM top quark) by combining his results and previous ATLAS analyses. His results provide a strong constraint to searches for new physics in the future.

Download or read book Search for Supersymmetry in Pp Collisions at sqrt s written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A search for supersymmetry in hadronic final states with highly boosted W bosons and b jets is presented, focusing on compressed scenarios. The search is performed using proton-proton collision data at a center-of-mass energy of 8 TeV, collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. Events containing candidates for hadronic decays of boosted W bosons are identified using jet substructure techniques, and are analyzed using the razor variables $M_\mathrm{R}$ and $R^2$, which characterize a possible signal as a peak on a smoothly falling background. The observed event yields in the signal regions are found to be consistent with the expected contributions from standard model processes, which are predicted using control samples in the data. The results are interpreted in terms of gluino pair production followed by their exclusive decay into top squarks and top quarks. The analysis excludes gluino masses up to 1.1 TeV for light top squarks decaying solely to a charm quark and a neutralino, and up to 700 GeV for heavier top squarks decaying solely to a top quark and a neutralino.

Download or read book Beyond Standard Model Collider Phenomenology of Higgs Physics and Supersymmetry written by Marc Christopher Thomas and published by Springer. This book was released on 2016-08-01 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis studies collider phenomenology of physics beyond the Standard Model at the Large Hadron Collider (LHC). It also explores in detail advanced topics related to Higgs boson and supersymmetry – one of the most exciting and well-motivated streams in particle physics. In particular, it finds a very large enhancement of multiple Higgs boson production in vector-boson scattering when Higgs couplings to gauge bosons differ from those predicted by the Standard Model. The thesis demonstrates that due to the loss of unitarity, the very large enhancement for triple Higgs boson production takes place. This is a truly novel finding. The thesis also studies the effects of supersymmetric partners of top and bottom quarks on the Higgs production and decay at the LHC, pointing for the first time to non-universal alterations for two main production processes of the Higgs boson at the LHC–vector boson fusion and gluon–gluon fusion. Continuing the exploration of Higgs boson and supersymmetry at the LHC, the thesis extends existing experimental analysis and shows that for a single decay channel the mass of the top quark superpartner below 175 GeV can be completely excluded, which in turn excludes electroweak baryogenesis in the Minimal Supersymmetric Model. This is a major new finding for the HEP community. This thesis is very clearly written and the introduction and conclusions are accessible to a wide spectrum of readers.

Download or read book Search for Top squark Pairs Decaying Into Higgs Or Z Bosons in Pp Collisions at u221A s written by and published by . This book was released on 2014 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our search for supersymmetry through the direct pair production of top squarks, with Higgs (H) or Z bosons in the decay chain, is performed using a data sample of proton–proton collisions at √s= 8TeV collected in 2012 with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 19.5 fb-1. The search is performed using a selection of events containing leptons and bottom-quark jets. No evidence for a significant excess of events over the standard model background prediction is observed. The results are interpreted in the context of simplified supersymmetric models with pair production of a heavier top-squark mass eigenstate t̃/sup2 source decaying to a lighter top-squark mass eigenstate t̃/sup2 via either t̃/sup2 → Ht̃/sup1 or tsup̃/sup2 →Ztsup̃/sup1, followed in both cases by tsup̃/sup1→ t?sup0̃1, where ?sup0̃1 source is an undetected, stable, lightest supersymmetric particle. The interpretation is performed in the region where the mass difference between the tsup̃/sup1 and ?sup0̃1 states is approximately equal to the top-quark mass (mt1-msup?01≃mt), which is not probed by searches for direct tsup̃/sup1 squark pair production. This analysis excludes top squarks with mass mt1 575 GeVand msubt2

Download or read book Search for Direct Scalar Top Pair Production in Final States with Two Tau Leptons in Pp Collisions at S written by Ewan Chin Hill and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The ATLAS Experiment at the CERN Large Hadron Collider is a particle physics experiment to study fundamental particles and their interactions at very high energies. Supersymmetry is a theory of new physics beyond the Standard Model of particle physics. A search for directly produced pairs of the supersymmetric partner of the top quark was performed using 20 fb^-1 of proton--proton collision data at a centre of mass energy of 8 TeV taken in 2012. The search targeted a model where the supersymmetric partner of the top quark (``scalar top'') decays via the supersymmetric partner of the tau lepton (``scalar tau'') into the supersymmetric partner of the graviton (``gravitino''). Scalar top candidates were searched for in pp collision events with either two hadronically decaying taus, two light leptons (electrons or muons), or one hadronically decaying tau and one light lepton. The numbers of events passing the analysis selection criteria agree with the Standard Model expectations. Exclusion limits at the 95% confidence level were set as a function of the scalar top and scalar tau masses. Depending on the scalar tau mass, ranging from the 87 GeV limit set by the LEP experiments to a few GeV below the scalar top mass, lower limits between 490 GeV and 640 GeV were placed on the scalar top mass within the model considered.

Download or read book Search for Pair Production of Scalar Top Quarks Decaying to A Lepton and a B Quark in 1 96 TeV P bar p Collisions written by and published by . This book was released on 2008 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: I present the results of a search for pair production of scalar top quarks ($ ilde{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. I assume each $ ilde{t}$1 decays into a ? lepton and a b quark, with branching ratio ?, and search for final states containing either an electron or a muon from a leptonic ? decay, a hadronically decaying ? lepton, and two or more jets. Two candidate events pass my final selection criteria, consistent with the expectation from standard model processes. I present upper limits on the cross section times branching ratio squared ?($ ilde{t}$1$ ilde{t}$1) x ?2 as a function of the stop mass m($ ilde{t}$1). Assuming ? = 1, I set a 95% confidence level limit m($ ilde{t}$1) > 153 GeV=c2. These limits are also fully applicable to the case of a pair produced third generation scalar leptoquark that decays into a ? lepton and a b quark.

Download or read book Search for Pair Production of Supersymmetric Top Quarks in Dilepton Events from p bar p Collisions at sqrt s written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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]).

Download or read book 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 published by . This book was released on 2008 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Search for Pair Production of Scalar Top Quarks Decaying to a tau Lepton and a beta Quark in 1 96 tev Pp Collisions written by Vadim Gennadyevich Khotilovich and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: I present the results of a search for pair production of scalar top quarks (t̃1) in an R-parity violating supersymmetric scenario using 322 pb−1 of pp collisions at [square root]s = 1.96 TeV collected by the upgraded Collider Detector at Fermilab. I assume each t̃1 decays into a [tau] lepton and a [beta] quark, with branching ratio [beta], and search for nal states containing either an electron or a muon from a leptonic [tau] decay, a hadronically decaying [tau] lepton, and two or more jets. Two candidate events pass my nal selection criteria, consistent with the expectation from standard model processes. I present upper limits on the cross section times branching ratio squared [sigma](t̃1t̃1) X [beta]2 as a function of the stop mass (mt̃1). Assuming [beta]= 1, I set a 95% condence level limit m(t̃1)> 153 GeV=c2. These limits are also fully applicable to the case of a pair produced third generation scalar leptoquark that decays into a [tau] lepton and a [beta] quark.

Download or read book Search for Massive Supersymmetric Particles Decaying to Many Jets Using the ATLAS Detector in Pp Collisions at Root S written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of a search for decays of massive particles to fully hadronic final states are presented. This search uses 20.3 fb-1 of data collected by the ATLAS detector in [arrow]" TeV proton-proton collisions at the LHC. Signatures based on high jet multiplicities without requirements on the missing transverse momentum are used to search for R-parity-violating supersymmetric gluino pair production with subsequent decays to quarks. Our analysis was performed using a requirement on the number of jets, in combination with separate requirements on the number of b-tagged jets, as well as a topological observable formed from the scalar sum of the mass values of large-radius jets in the event. Results were interpreted in the context of all possible branching ratios of direct gluino decays to various quark flavors. No significant deviation is observed from the expected Standard Model backgrounds estimated using jet counting as well as data-driven templates of the total-jet-mass spectra. Gluino pair decays to ten or more quarks via intermediate neutralinos are excluded for a gluino with mass mg~

Download or read book Search for Direct Pair Production of Scalar Top Quarks in the Single and Dilepton Channels in Proton proton Collisions at sqrt s written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Search for Massive Supersymmetric Particles Decaying to Many Jets Using the ATLAS Detector in Pp Collisions at u221A s written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of a search for decays of massive particles to fully hadronic final states are presented. This search uses 20.3 fb-1 of data collected by the ATLAS detector in √s = 8 TeV proton-proton collisions at the LHC. Signatures based on high jet multiplicities without requirements on the missing transverse momentum are used to search for R-parity-violating supersymmetric gluino pair production with subsequent decays to quarks. The analysis is performed using a requirement on the number of jets, in combination with separate requirements on the number of b-tagged jets, as well as a topological observable formed from the scalar sum of the mass values of large-radius jets in the event. Results are interpreted in the context of all possible branching ratios of direct gluino decays to various quark flavors. No significant deviation is observed from the expected Standard Model backgrounds estimated using jet counting as well as data-driven templates of the total-jet-mass spectra. Gluino pair decays to ten or more quarks via intermediate neutralinos are excluded for a gluino with mass m-g 1TeV for a neutralino mass msubsup-/supX/subsubsup0/sup1/sub = 500 GeV. Direct gluino decays to six quarks are excluded for mgsubsup-/supg

Download or read book Search for Pair Production of Supersymmetric Top Quarks in Dilepton Events at the Tevatron written by William Johnson and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We search for pair production of the supersymmetric partner of the top quark, the stop quark, decaying to a b-quark and a chargino with a subsequent decay into a neutralino, lepton, and neutrino. Using 2.7 fb−1 of [square root]s=1.96 TeV proton on antiproton collision data collected by the CDF II experiment, we reconstruct the mass of candidate stop events and fit the observed mass spectrum to a combination of standard model processes and stop signal. No evidence of stop pair production is found, therefore we set 95% C.L. limits on the masses of the stop and the neutralino for several values of the chargino mass and the branching ratio B(X̃±/1[right arrow]X̃01l±v).

Download or read book The Search for Direct Top squark Production in Hadronic Final States with the ATLAS Detector at square Roots s written by Christian Lüdtke and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Supersymmetry poses one of the best motivated theories for particle physics beyond the Standard Model. It can provide a dark matter candidate and enable grand unification. The supersymmetric partner of the top quark, the top squark, can provide a cancellation of diverging radiative corrections to the Higgs-boson mass and thereby avoid the hierarchy problem of the Standard Model. In this thesis, a search for top squarks in final states with jets and missing transverse momentum is presented. Proton-proton collisions at a centre-of-mass energy of √s = 13 TeV, produced by the Large Hadron Collider, were recorded by the ATLAS detector. The analysed dataset corresponds to an integrated luminosity of 36.1 fb-1. No significant excess above the Standard Model background was observed. The analysis results are interpreted as exclusion limits on the top-squark mass and the neutralino mass in various scenarios that address specific aspects of the supersymmetry