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 Measurement of the Top Quark Pair Production Cross Section in Pp Collisions at Sqrt s written by and published by . This book was released on 2012 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: The top quark pair production cross section is measured in dilepton events with one electron or muon, and one hadronically decaying tau lepton from the decay t anti-t to (l nu(l)) (tau nu(tau)) b anti-b, where l can be either an electron or a muon. The data sample corresponds to an integrated luminosity of 2.0 inverse femtobarns for the electron channel and 2.2 inverse femtobarns for the muon channel, collected by the CMS detector at the LHC. This is the first measurement of the t anti-t cross section explicitly including tau leptons in proton-proton collisions at sqrt(s)=7 TeV. The measured value sigma(t anti-t) = 143 +/- 14 (stat.) +/- 22 (syst.) +/- 3 (lumi.) pb is consistent with the standard model predictions.
Download or read book Search for S Channel Single Top Quark Production 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 is presented for single top quark production in the s channel in proton-proton collisions with the CMS detector at the CERN LHC in decay modes of the top quark containing a muon or an electron in the final state. The signal is extracted through a maximum-likelihood fit to the distribution of a multivariate discriminant defined using boosted decision trees to separate the expected signal contribution from background processes. Data collected at centre-of-mass energies of 7 and 8 TeV yield cross sections of 7.1 +/- 8.1 pb and 13.4 +/- 7.3 pb, respectively, and a best fit value of 2.0 +/- 0.9 for the combined ratio of the measured and expected values. The signal significance is 2.5 standard deviations, and the upper limit on the rate relative to the standard model expectation is 4.7 at 95% confidence level.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 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 Search for Third Generation Scalar Leptoquarks in the T tau Channel in Proton Proton Collisions at sqrt s written by and published by . This book was released on 2015 with total page 41 pages. Available in PDF, EPUB and Kindle. Book excerpt: A search for pair production of third-generation scalar leptoquarks decaying to top quark and $\tau$ lepton pairs is presented using proton-proton collision data at a center-of-mass energy of $\sqrt{s}$ = 8 TeV collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 19.7 fb-1. The search is performed using events that contain an electron or a muon, a hadronically decaying $\tau$ lepton, and two or more jets. The observations are found to be consistent with the standard model predictions. Assuming that all leptoquarks decay to a top quark and a $\tau$ lepton, the existence of pair produced, charge -1/3, third-generation leptoquarks up to a mass of 685 GeV is excluded at 95% confidence level. This result constitutes the first direct limit for leptoquarks decaying into a top quark and a $\tau$ lepton, and may also be applied directly to the pair production of bottom squarks decaying predominantly via the R-parity violating coupling [lambda]' 333.
Download or read book Search for Scalar Charm Quark Pair Production in Pp Collisions at S written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The results of a dedicated search for pair production of scalar partners of charm quarks are reported. The search is based on an integrated luminosity of 20.3 fb–1 of pp collisions at √s=8 TeV recorded with the ATLAS detector at the LHC. The search is performed using events with large missing transverse momentum and at least two jets, where the two leading jets are each tagged as originating from c quarks. The events containing isolated electrons or muons are vetoed. In an R-parity-conserving minimal supersymmetric scenario in which a single scalar-charm state is kinematically accessible, and where it decays exclusively into a charm quark and a neutralino, 95% confidence-level upper limits are obtained in the scalar-charm–neutralino mass plane such that, neutralino masses below 200 GeV, scalar-charm masses up to 490 GeV are excluded.
Download or read book Physics at the Large Hadron Collider written by Amitava Datta and published by Springer Science & Business Media. This book was released on 2010-05-30 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: In an epoch when particle physics is awaiting a major step forward, the Large Hydron Collider (LHC) at CERN, Geneva will soon be operational. It will collide a beam of high energy protons with another similar beam circulation in the same 27 km tunnel but in the opposite direction, resulting in the production of many elementary particles some never created in the laboratory before. It is widely expected that the LHC will discover the Higgs boson, the particle which supposedly lends masses to all other fundamental particles. In addition, the question as to whether there is some new law of physics at such high energy is likely to be answered through this experiment. The present volume contains a collection of articles written by international experts, both theoreticians and experimentalists, from India and abroad, which aims to acquaint a non-specialist with some basic issues related to the LHC. At the same time, it is expected to be a useful, rudimentary companion of introductory exposition and technical expertise alike, and it is hoped to become unique in its kind. The fact that there is substantial Indian involvement in the entire LHC endeavour, at all levels including fabrication, physics analysis procedures as well as theoretical studies, is also amply brought out in the collection.
Download or read book Search for Direct Production of Top Quark Pairs at Sqrt s written by Juan Pablo Gómez Cardona and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The data analyzed correspond to an integrated luminosity of 19.5 fb-1 of proton-proton collisions at sqrt(s) = 8 TeV, collected by the CMS experiment. The topology of the event is defined as the most likely permutation of the objects in the final state corresponding of the Feynman diagram studied. This is accomplished by maximizing likelihood function. An additional discriminant is obtained by finding the matrix elements weight of the most probable permutation by using MADWEIGHT. We define event selection criteria based on correlations of topological and kinematic variables. We show that this technique, based on the topology of the event, competes with the exclusion limits already obtained by previous analyses and has the potential to become a powerful tool for future searches. The document is organized in the following way: First, a brief introduction to the LHC and some of its operation details is given, this is followed by a description of the CMS detector and its sub-detectors. Then the Standard Model is reviewed as well as the reasons why new physics is expected. After this, a brief introduction to SUSY is given, showing the main implications that it has, and some of the solutions given by this theory to the SM limitations. Second, the last, the current status of some SUSY searches is described, their actual limits are shown, and certain strategies used by the CMS experiment to search to SUSY are described. Finally, the analysis performed by us, the results, the conclusions and the future developments are presented.
Download or read book Search for the Production of Four Top Quarks in the Single lepton and Opposite sign Dilepton Final States in Proton proton Collisions at s written by Albert M. Sirunyan and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 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 the Production of Scalar Bottom Quarks in p bar p Collisions at sqrt s written by and published by . This book was released on 2010 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report on a search for direct scalar bottom quark (sbottom) pair production in p{bar p} collisions at (square root)s = 1.96 TeV, in events with large missing transverse energy and two jets of hadrons in the final state, where at least one of the jets is required to be identified as originating from a b quark. The study uses a CDF Run II data sample corresponding to 2.65 fb−1 of integrated luminosity. The data are in agreement with the standard model. In an R-parity conserving minimal supersymmetric scenario, and assuming that the sbottom decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits on the sbottom pair production cross section of 0.1 pb are obtained. For neutralino masses below 70 GeV/c2, sbottom masses up to 230 GeV/c2 are excluded at 95% confidence level.
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 Standard Model Production of Four Top Quarks in Proton proton 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 for events containing four top quarks (ttbar-ttbar) is reported from proton-proton collisions recorded by the CMS experiment at sqrt(s) = 13 TeV and corresponding to an integrated luminosity of 2.6 inverse femtobarns The analysis considers the single-lepton (e or mu)+jets and the opposite-sign dilepton (mu+mu-, mu+/- e-/+, or e+e- )+jets channels. It uses boosted decision trees to combine information on the global event and jet properties to distinguish between ttbar-ttbar and ttbar production. The number of events observed after all selection requirements is consistent with expectations from background and standard model signal predictions, and an upper limit is set on the cross section for ttbar-ttbar production in the standard model of 94 fb at 95% confidence level (10.2 times the prediction), with an expected limit of 118 fb. This is combined with the results from the published CMS search in the same-sign dilepton channel, resulting in an improved limit of 69 fb at 95% confidence level (7.4 times the prediction), with an expected limit of 71 fb. These are the strongest constraints on the rate of ttbar-ttbar production to date.
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.
