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 Searches for Supersymmetric Particles in Final States with Multiple Top and Bottom Quarks with the Atlas Detector written by Chiara Rizzi and published by Springer Nature. This book was released on 2020-09-01 with total page 279 pages. Available in PDF, EPUB and Kindle. Book excerpt: This PhD thesis documents two of the highest-profile searches for supersymmetry performed at the ATLAS experiment using up to 80/fb of proton-proton collision data at a center-of-mass energy of 13 TeV delivered by the Large Hadron Collider (LHC) during its Run 2 (2015-2018). The signals of interest feature a high multiplicity of jets originating from the hadronisation of b-quarks and large missing transverse momentum, which constitutes one of the most promising final state signatures for discovery of new phenomena at the LHC. The first search is focused on the strong production of a pair of gluinos, with each gluino decaying into a neutralino and a top-antitop-quark pair or a bottom-antibottom-quark pair. The second search targets the pair production of higgsinos, with each higgsino decaying into a gravitino and a Higgs boson, which in turn is required to decay into a bottom-antibottom-quark pair. Both searches employ state-of-the-art experimental techniques and analysis strategies at the LHC, resulting in some of the most restrictive bounds available to date on the masses of the gluino,neutralino, and higgsino in the context of the models explored.

Download or read book Search for Scalar Top at CDF written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We report results of three searches for scalar top quark. Two of the searches look for direct production of scalar top quark followed by the decay of the scalar quark to charm quark and neutralino or bottom and chargino. The third search looks for top quark decaying to scalar top and neutralino followed by the decay of scalar top to bottom quark and neutralino. We find no evidence for the presence of scalar top quark in any of the searches. Therefore, depending on the search we set limits on the production cross-section, BR(t --> {tilde t}1 + {tilde {chi}}°1), or m{sub {tilde t}} vs. m{sub {tilde {chi}}°1}.

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 A Search for the Pair Production of Scalar Top Quarks in Hadronic Final States with the CMS Detector written by Nickolas W. McColl and published by . This book was released on 2015 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt: The sensitivity of this search to models with a top squark decaying to jets and a neutralino through a on-shell top quark extends to 775 GeV in top squark mass and to 650 GeV in models with a top squark decaying through an intermediate chargino.

Download or read book Search for Scalar Quarks at square Root of S written by William Orejudos and published by . This book was released on 1998 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Search for Scalar Top Quark Production in p bar p Collisions at sqrt s written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We report on a search for the supersymmetric partner of the top quark (scalar top) decaying into a charm quark and a neutralino in p{bar p} collisions at √s = 1.96 TeV. The data sample, collected by the CDF II detector at the Fermilab Tevatron, corresponds to an integrated luminosity of 2.6 fb−1. Candidate events are selected by requiring two or more jets and a large imbalance in the transverse momentum. To enhance the analysis sensitivity, at least one of the jets is required to be identified as originating from a charm quark using an algorithm specifically designed for this analysis. The selected events are in good agreement with standard model predictions. In the case of large mass splitting between the scalar top quark and the neutralino we exclude a scalar top quark mass below 180 GeV/c2 at 95% confidence level.

Download or read book Search for New Phenomena in Top Antitop Quarks Final States with Additional Heavy Flavour Jets with the ATLAS Detector written by Daiki Yamaguchi and published by Springer Nature. This book was released on 2019-10-30 with total page 279 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reports on the search for a new heavy particle, the Vector-Like Top quark (VLT), in the Large Hadron Collider (LHC) at CERN. The signal process is the pair production of VLT decaying into a Higgs boson and top quark (TT→Ht+X, X=Ht, Wb, Zt). The signal events result in top–antitop quarks final states with additional heavy flavour jets. The book summarises the analysis of the data collected with the ATLAS detector in 2015 and 2016. In order to better differentiate between signals and backgrounds, exclusive taggers of top quark and Higgs boson were developed and optimised for VLT signals. These efforts improved the sensitivity by roughly 30%, compared to the previous analysis. The analysis outcomes yield the strongest constraints on parameter space in various BSM theoretical models. In addition, the book addresses detector operation and the evaluation of tracking performance. These efforts are essential to properly collecting dense events and improving the accuracy of the reconstructed objects that are used for particle identification. As such, they represent a valuable contribution to data analysis in extremely dense environments.

Download or read book Search for Pair Production of the Scalar Top Quark in the Electron muon Final State written by and published by . This book was released on 2010 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ({tilde t}1) in p{bar p} collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb−1. 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 improved exclusion limits at the 95% C.L. are set in the (M{sub {tilde t}1}, M{sub {tilde {nu}}}) mass plane.

Download or read book Stop Into Stau written by Pierfrancesco Butti and published by . This book was released on 2017 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: "This thesis presents a search for Supersymmetry carried out in a particular scenario arising from the Gauge Mediated Supersymmetry breaking mechanism that assumes a massless gravitino as lightest supersymmetric particle, a scalar tau lepton as next-to-lightest supersymmetric particle and the top squark as the lightest among the quark superpartners. The analysis is performed using the data collected by ATLAS at a centre-of-mass energy √s = 8 TeV during 2012 data taking, for a total of 20.3 fb−1 of integrated luminosity of proton-proton collisions. Scalar top quark candidates are searched for in events with either two light leptons, one hadronically decaying tau and one light lepton or two hadronically decaying taus in the final state. No significant excess over the Standard Model expectation is found and the results are interpreted as 95% confidence lower limits not top squark and scalar tau masses. Depending on the scalar tau mass, lower limits between 490 and 650 GeV are placed on the top squark mass within the model considered. This thesis presents also the results of the track-based alignment of the ATLAS Inner Detector during 2015 data taking campaign and the characterisation of the mechanical deformation of the Insertable B-Layer as function of the operating temperature."--Samenvatting auteur.

Download or read book A Search for Scalar Bottom Quarks from Gluino Decays in Anti p P Collisions at S 1 2 written by and published by . This book was released on 2005 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: We searched for scalar bottom quarks in 156 pb−1 of {bar p}p collisions at √s = 1.96 TeV recorded by the CDF II experiment at the Tevatron. Scalar bottom quarks can be produced from gluino decays in R-parity conserving models of supersymmetry when the mass of the gluino exceeds that of the scalar bottom quark. Then, a scalar bottom quark can decay into a bottom quark and a neutralino. To search for this scenario, we investigated events with large missing transverse energy and at least three jets, two or more of which were identified as containing a secondary vertex from the hadronization of b quarks. We found four candidate events, where 2.6 ± 0.7 are expected from standard model processes, and placed 95% confidence level lower limits on gluino and scalar bottom quark masses of up to 280 and 240 GeV/c2 , respectively.

Download or read book Scalar Top Quark as the Next to Lightest Supersymmetric Particle written by and published by . This book was released on 1999 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: We study phenomenologically the scenario in which the scalar top quark is lighter than any other standard supersymmetric partner and also lighter than the top quark, so that it decays to the gravitino via {tilde t} --> Wb{tilde G}. In this case, scalar top quark events would seem to be very difficult to separate from top quark pair production. However, we show that, even at a hadron collider, it is possible to distinguish these two reactions. We show also that the longitudinal polarization of the final W gives insight into the scalar top and wino/Higgsino mixing parameters.

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 A Search for Scalar Bottom Quarks from Gluino Decays in Anti p P Collisions at S written by and published by . This book was released on 2005 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: We searched for scalar bottom quarks in 156 pb−1 of {bar p}p collisions at √s = 1.96 TeV recorded by the CDF II experiment at the Tevatron. Scalar bottom quarks can be produced from gluino decays in R-parity conserving models of supersymmetry when the mass of the gluino exceeds that of the scalar bottom quark. Then, a scalar bottom quark can decay into a bottom quark and a neutralino. To search for this scenario, we investigated events with large missing transverse energy and at least three jets, two or more of which were identified as containing a secondary vertex from the hadronization of b quarks. We found four candidate events, where 2.6 ± 0.7 are expected from standard model processes, and placed 95% confidence level lower limits on gluino and scalar bottom quark masses of up to 280 and 240 GeV/c2, respectively.

Download or read book Search for a Vector like Quark T Decaying Into Top Higgs in Single Production Mode in Full Hadronic Final State Using CMS Data Collected at 8 TeV written by José David Ruiz Alvarez and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: During 2012, the Large Hadron Collider (LHC) has delivered proton-proton collisions at 8 TeV center of mass energy to the ATLAS and CMS experiments. These two experiments have been designed to discover the Higgs boson and to search for new particles predicted by several theoretical models, as supersymmetry. The Higgs boson has been discovered by ATLAS and CMS experiments on July, 4th of 2012, starting a new era of discoveries in particle physics domain. With the confirmation of the existence of the Higgs boson, searches for new physics involving this boson are of major interest. In particular, data can be used to look for new massive particles that decay into the Higgs boson accompanied with other particles of the standard model. One expected signature is a Higgs boson produced with a top quark, the two heaviest particles in the standard model. The standard model predicts a cross section of top-Higgs production, then any enhancement of their associated production will be a clear signature of physics beyond the standard model. In addition, the existence of physics beyond the standard model can also be reflected by resonances that decay into a top-quark and a Higgs boson. In the first part of my work I describe the theoretical and experimental foundations of the standard model, as well as the experimental device. In the same theoretical chapter, I also discuss the formulation of an extension of the standard model. In addition, I describe a feasibility study of a search of one of the particles predicted by such model. The second part contains the realization of the search for a top partner, T_, within the CMS experiment. This top partner is a new particle very similar to the standard model top quark, but much heavier, that can decay into a top quark and a Higgs boson. The analysis looks for this particle in the full hadronic final state, where the Higgs boson decays into two b-quarks and the top quark decays into three standard model quarks, a b and two light quarks. In this channel, I reconstruct its mass from the identification of all its decay products. As a result of the analysis, I show the limits on the T_ production cross section from the number of observed events in the specific signature.

Download or read book Physics Letters written by and published by . This book was released on 1998 with total page 518 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Top Quark Heavy Flavor Physics And Symmetry Breaking The Proceedings Of The Xxiii International Meeting On Fundamental Physics written by Teresa Rodrigo and published by World Scientific. This book was released on 1996-03-31 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: This meeting discussed the experimental results and theoretical aspects in the field of high energy physics, with special reference to the top quark observation, heavy flavor physics and symmetry-breaking mechanisms. The major topics are developed in a series of course lectures.