Scalar Top Quark Search With Jets And Missing Momentum In Pp Collisions At 7 Tev PDF Download
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| Author | : Mariarosaria D'Alfonso |
| Publisher | : |
| Total Pages | : 106 |
| Release | : 2012 |
| Genre | : |
| ISBN | : 9781267933775 |
Download Scalar Top Quark Search with Jets and Missing Momentum in Pp Collisions at 7 TeV Book in PDF, ePub and Kindle
The results of CMS searches for Supersymmetry are interpreted in the context of Simplified Models. A limited set of hypothetical particles and decay chains are introduced to produce a given topological signature. The amplitudes describing the production and decays of these particles are parametrized in terms of the particle massesand their branching ratios to daughter particles. Among the new possible particles, the Higgs mechanism of electroweak symmetry breaking gives a special role to the partnerof the third generation SM particles. In this thesis, I will describe how the comparison of different search strategies on multiple simplified models helps to quantify that the LHC has not put any stringent bounds on them yet. The 4.98 /fb of data collected by CMS, was analyzed to search for the scalar stop in the jets plus met final state. In particular, I will focus on the ttbar background; I will describe in detail the handles used to reduce it and the technique adopted to predict this contribution from data. The data is found to be in agreement with the predicted backgrounds. An upper limit on the cross section times branching ratio is set for the decays stop to LSP plus top and stop to LSP plus b W through a chargino final state.
| Author | : ATLAS Collaboration CERN |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2021 |
| Genre | : |
| ISBN | : |
Download 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 Book in PDF, ePub and Kindle
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
| Author | : |
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| Total Pages | : |
| Release | : 2015 |
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Download Search for Scalar Charm Quark Pair Production in Pp Collisions at S Book in PDF, ePub and Kindle
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.
| Author | : Takuya Nobe |
| Publisher | : Springer |
| Total Pages | : 229 |
| Release | : 2015-11-30 |
| Genre | : Science |
| ISBN | : 9811000034 |
Download Search for Scalar Top Quarks and Higgsino-Like Neutralinos Book in PDF, ePub and Kindle
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.
| Author | : |
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| Total Pages | : 46 |
| Release | : 2016 |
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Download Search for Direct Pair Production of Supersymmetric Top Quarks Decaying to All-hadronic Final States in Pp Collisions at {u221A}s Book in PDF, ePub and Kindle
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.
| Author | : Josh McFayden |
| Publisher | : Springer |
| Total Pages | : 190 |
| Release | : 2014-06-06 |
| Genre | : Science |
| ISBN | : 3319071912 |
Download Third generation SUSY and t ̄t +Z production Book in PDF, ePub and Kindle
This thesis describes searches for new particles predicted by the super symmetry (SUSY) theory, a theory extending beyond the current Standard Model of particle physics, using the ATLAS detector at the CERN Large Hadron Collider. The thesis focuses on searches for stop and sbottom squarks, the SUSY partners of the top and bottom quarks, which are expected to be lighter than the partners of the first and second generation quarks and therefore good candidates for the first evidence of SUSY. It describes novel techniques for estimating and rejecting the Standard-Model backgrounds to searches for these particles. It also includes an independent analysis seeking to constrain the Standard Model ttZ background process, which also represents the first ATLAS search for this rare process at the LHC. The stop squark analysis described, with substantial leading contributions from the author, is the first search for these particles at the LHC to use the jets plus missing transverse energy plus 0-lepton signature and provides the world's best limits on the stop mass for light neutralino LSPs. All in all, the thesis describes three different world-leading analyses in both Standard Model and SUSY physics and therefore represents a major contribution to the field.
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| Total Pages | : 10 |
| Release | : 2008 |
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Download Search for Scalar Top Quarks in the Acoplanar Charm Jets and Missing Transverse Energy Final State in P Anti-p Collisions at S**1/2 Book in PDF, ePub and Kindle
| Author | : |
| Publisher | : |
| Total Pages | : 10 |
| Release | : 2008 |
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| ISBN | : |
Download Search for Scalar Top Quarks in the Acoplanar Charm Jets and Missing Transverse Energy Final State in P Anti-p Collisions at S**ư Book in PDF, ePub and Kindle
| Author | : Nicolas Maximilian Köhler |
| Publisher | : Springer Nature |
| Total Pages | : 263 |
| Release | : 2019-09-13 |
| Genre | : Science |
| ISBN | : 3030259889 |
Download Searches for the Supersymmetric Partner of the Top Quark, Dark Matter and Dark Energy at the ATLAS Experiment Book in PDF, ePub and Kindle
Astrophysical observations implying the existence of Dark Matter and Dark Energy, which are not described by the Standard Model (SM) of particle physics, have led to extensions of the SM predicting new particles that could be directly produced at the Large Hadron Collider (LHC) at CERN. Based on 2015 and 2016 ATLAS proton-proton collision data, this thesis presents searches for the supersymmetric partner of the top quark, for Dark Matter, and for DarkEnergy, in signatures with jets and missing transverse energy. Muon detection is key to some of the most important LHC physics results, including the discovery of the Higgs boson and the measurement of its properties. The efficiency with which muons can be detected with the ATLAS detector is measured using Z boson decays. The performance of high-precision Monitored Drift Tube muon chambers under background rates similar to the ones expected for the High Luminosity-LHC is studied.
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| Release | : 2012 |
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Download Search for Scalar Top Quark Production in $p\bar{p}$ Collisions at $\sqrt{s} Book in PDF, ePub and Kindle
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.
