Search for Supersymmetry Using Diphoton Events in Proton-antiproton Collisions at a Center of Mass Energy of 1.96 TeV
Search for Supersymmetry Using Diphoton Events in Proton-antiproton Collisions at a Center of Mass Energy of 1.96 TeV

Author: Eun Sin Lee

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Published: 2010

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This dissertation presents the results of a search for supersymmetry in protonantiproton collisions with a center of mass energy of 1.96 TeV studied with the Collider Detector at Fermilab. Our strategy is to select collisions with two photons in the final state that have the properties of being the decays of very massive supersymmetric particles. This includes looking for large total energy from the decayed particles as well as for the presence of particles that leave the detector without interacting. We find no events using 2.6 fb−1 of data collected during the 2004-2008 collider run of the Fermilab Tevatron which is consistent with the background estimate of 1.4 " 0.4 events. Since there is no evidence of new particles we set cross section limits in a gaugemediated supersymmetry model with X01 ---> [gamma]G, where the X01 and G are the lightest neutralino and the gravitino (the lightest supersymmetric particle), respectively. We set limits on models as a function of the X01 mass and lifetime, producing the world's most sensitive search for X01 by excluding masses up to 149 GeV/c2 for X01 lifetimes much less than 1 ns.

Search for Supersymmetry Using Diphoton Events in P Anti-p Collisions at a Center of Mass Energy of 1.96-TeV.
Search for Supersymmetry Using Diphoton Events in P Anti-p Collisions at a Center of Mass Energy of 1.96-TeV.

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Published: 2010

Total Pages: 234

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This dissertation presents the results of a search for supersymmetry in proton-antiproton collisions with a center of mass energy of 1.96 TeV studied with the Collider Detector at Fermilab. Our strategy is to select collisions with two photons in the final state that have the properties of being the decays of very massive supersymmetric particles. This includes looking for large total energy from the decayed particles as well as for the presence of particles that leave the detector without interacting. We find no events using 2.6 fb−1 of data collected during the 2004-2008 collider run of the Fermilab Tevatron which is consistent with the background estimate of 1.4 ± 0.4 events. Since there is no evidence of new particles we set cross section limits in a gauge-mediated supersymmetry model with {tilde {chi}}1° → [gamma]{tilde G}, where the {tilde {chi}}1° and {tilde G} are the lightest neutralino and the gravitino (the lightest supersymmetric particle), respectively. We set limits on models as a function of the {tilde {chi}}1° mass and lifetime, producing the world's most sensitive search for {tilde {chi}}1° by excluding masses up to 149 GeV/c2 for {tilde {chi}}1° lifetimes much less than 1 ns.

Search for Supersymmetry in Proton-proton Collisions at 7 TeV in Events with a Single Lepton, B-tagged Jets and Missing Transverse Momentum at the LHC Using Data Collected from the CMS Detector
Search for Supersymmetry in Proton-proton Collisions at 7 TeV in Events with a Single Lepton, B-tagged Jets and Missing Transverse Momentum at the LHC Using Data Collected from the CMS Detector

Author: Wing Howard To

Publisher:

Published: 2013

Total Pages: 145

ISBN-13: 9781303052842

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This thesis describes a search for supersymmetry (SUSY) at the Large Hadron Collider using data collected in Run 2011 at center of mass energy of 7 TeV by the Compact Muon Solenoid detector with an integrated luminosity of 4.98 $fb{-1}$. First, the Large Hadron Collider is briefly described along with the Compact Muon Solenoid detector. Second, the Standard Model of particle physics is described which leads to the motivations for supersymmetry and its description. Finally, a search for supersymmetry in events with a single lepton, 2 b-tagged jets and missing transverse energy is documented in detail. The results are used to predict the yields from the standard model in bins missing transverse energy (\met) and total transverse hadronic energy (HT). Limits are set using these results using a minimal supergravity SUSY model and simplified model spectra SUSY model.

Search for Supersymmetry in Events with One Lepton and Multiple Jets in Proton-proton Collisions at Sqrt(s)
Search for Supersymmetry in Events with One Lepton and Multiple Jets in Proton-proton Collisions at Sqrt(s)

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Published: 2016

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A search for supersymmetry is performed in events with a single electron or muon in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 2.3 inverse femtobarns. Several exclusive search regions are defined based on the number of jets and b-tagged jets, the scalar sum of the jet transverse momenta, and the scalar sum of the missing transverse momentum and the transverse momentum of the lepton. The observed event yields in data are consistent with the expected backgrounds from standard model processes. The results are interpreted using two simplified models of supersymmetric particle spectra, both of which describe gluino pair production. In the first model, each gluino decays via a three-body process to top quarks and a neutralino, which is associated with the observed missing transverse momentum in the event. Gluinos with masses up to 1.6 TeV are excluded for neutralino masses below 600 GeV. In the second model, each gluino decays via a three-body process to two light quarks and a chargino, which subsequently decays to a W boson and a neutralino. The mass of the chargino is taken to be midway between the gluino and neutralino masses. In this model, gluinos with masses below 1.4 TeV are excluded for neutralino masses below 700 GeV.

Search for Gauge Mediated SUSY Breaking in Diphoton Events in Proton Anti-proton Collisions at S**(1/2)
Search for Gauge Mediated SUSY Breaking in Diphoton Events in Proton Anti-proton Collisions at S**(1/2)

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Published: 2005

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The authors present the results of a search for anomalous production of diphoton events with large missing transverse energy using the Collider Detector at Fermilab. In 202 pb[sup -1] of p[bar p] collisions at [radical]s = 1.96 TeV they observe no candidate events, with an expected standard model background of 0.27 [+-] 0.07(stat) [+-] 0.10(syst) events. The results exclude a lightest chargino of mass less than 167 GeV/c[sup 2], and lightest neutralino of 93 GeV/c[sup 2] at 95% confidence level in a gauge-mediated supersymmetry-breaking model with a light gravitino.

Search for Supersymmetry in Proton-proton Collisions at 8 TeV in Events with a Single Lepton, Large Jet Multiplicity, and Multiple B Jets
Search for Supersymmetry in Proton-proton Collisions at 8 TeV in Events with a Single Lepton, Large Jet Multiplicity, and Multiple B Jets

Author: Paul B. Geffert

Publisher:

Published: 2014

Total Pages: 257

ISBN-13: 9781321349412

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This thesis describes a search for supersymmetry in events with a single lepton, large jet multiplicity, multiple b jets, and significant transverse momentum imbalance in 19.3 fb-1 of pp collisions at center of mass energy of 8 TeV recorded in 2012 by the Compact Muon Solenoid experiment at the Large Hadron Collider. This signature targets strongly produced massive gluinos which decay through top squarks. The observed yields in the signal regions, spanning a broad range of event kinematics, agree with the Standard Model background predictions, which are obtained with a heavy reliance on data control samples. The results of this search are interpreted as cross section limits in the context of simplified supersymmetric scenarios in which gluinos are pair produced and cascade decay to a four top quark, two lightest neutralino final state. By comparing these limits with gluino pair production cross sections, gluinos with mass less than 1 TeV are excluded for low lightest neutralino masses, largely independent of top squark mass.

Search for Supersymmetry in the Monophoton Final State at CMS at a Center of Mass Energy of 13 TeV
Search for Supersymmetry in the Monophoton Final State at CMS at a Center of Mass Energy of 13 TeV

Author: De-Lin Xiong

Publisher:

Published: 2022

Total Pages: 0

ISBN-13:

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The mission of the CMS experiment at the LHC is to investigate and discover unknown physics in proton-proton collision events. This thesis presents a search for new physics in final states containing a photon and missing transverse momentum in proton-proton collisions at $\\\\sqrt{s}$ = 13 TeV, using the data collected in Run II (2016, 2017 and 2018) by the CMS experiment at the LHC, corresponding to an integrated luminosity of 137 $\\\\text{fb}^{-1}$. The standard model (SM) background in monophoton events can be a problem for sensitivity to new physics. The sensitivity to new physics scenarios can potentially be enhanced by other event properties. A new strategy that can potentially enhance the new physics sensitivity is the track multiplicity from the small mass splitting supersymmetry (SUSY). SUSY with small mass splittings indicates the masses difference between the SUSY particles is small ($\\\\tilde{q}, squark \\\\approx \\\\tilde{\\\\chi}$, dark matter particle). The track multiplicity in monophoton dataset with different bins of track $p_T$ will be studied, and compared with expectation.

Search for Supersymmetry in Events with Photons and Missing Transverse Energy in Pp Collisions at 13 TeV.
Search for Supersymmetry in Events with Photons and Missing Transverse Energy in Pp Collisions at 13 TeV.

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Published: 2016

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The results of a search for new physics in final states with photons and missing transverse energy are reported. The study is based on a sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 inverse femtobarns. Final states with two photons and significant missing transverse energy are used to search for supersymmetric particles in models of supersymmetry (SUSY) with general gauge-mediated (GGM) supersymmetry breaking. No excess is observed with respect to the standard model expectation, and the results are used to set limits on gluino pair production and squark pair production in the GGM SUSY framework. Gluino masses below 1.65 TeV and squark masses below 1.37 TeV are excluded at a 95% confidence level.

Search for Supersymmetry in pp Collisions at √s = 8 TeV with a Photon, Lepton, and Missing Transverse Energy
Search for Supersymmetry in pp Collisions at √s = 8 TeV with a Photon, Lepton, and Missing Transverse Energy

Author: Yutaro Iiyama

Publisher: Springer

Published: 2017-06-14

Total Pages: 182

ISBN-13: 3319586610

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This Ph.D. thesis is a search for physics beyond the standard model (SM) of particle physics, which successfully describes the interactions and properties of all known elementary particles. However, no particle exists in the SM that can account for the dark matter, which makes up about one quarter of the energy-mass content of the universe. Understanding the nature of dark matter is one goal of the CERN Large Hadron Collider (LHC). The extension of the SM with supersymmetry (SUSY) is considered a promising possibilities to explain dark matter. The nominated thesis describes a search for SUSY using data collected by the CMS experiment at the LHC. It utilizes a final state consisting of a photon, a lepton, and a large momentum imbalance probing a class of SUSY models that has not yet been studied extensively. The thesis stands out not only due to its content that is explained with clarity but also because the author performed more or less all aspects of the thesis analysis by himself, from data skimming to limit calculations, which is extremely rare, especially nowadays in the large LHC collaborations.