Search For New Physics In The Exclusive Delayed E T Final State In Pp Collisions At U221a S

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Search For New Physics In The Exclusive Delayed E T Final State In Pp Collisions At U221a S

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Author :
language : en
Publisher:
Release Date : 2012

Search For New Physics In The Exclusive Delayed E T Final State In Pp Collisions At U221a S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.

This dissertation presents a search for heavy, long-lived, neutral particles that decay to photons in proton anti-proton collisions with a center of mass energy of 1.96 TeV at the Collider Detector at Fermilab (CDF) experiment. Such particles are typical of models of Gauge Mediated Supersymmetry Breaking (GMSB). We select events with a single photon, missing transverse energy, and little other activity in the detector. We model the photon arrival time for Standard Model and non-collision sources using a data-driven method and consider photons which have a time of arrival at the detector which is significantly delayed relative to predictions. Using 6.3 fb-1 of data collected from December 2004 to June 2010, we observe 322 events in the signal region compared to a background prediction of 287 ± 24 events. While the data are consistently above predictions, we report a model excess with a significance of 1.2 standard deviations from the null hypothesis.

Model Independent Search For New Phenomena In Pp Collisions At U221a S

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Author :
language : en
Publisher:
Release Date : 2012

Model Independent Search For New Phenomena In Pp Collisions At U221a S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.

We describe a model independent search for physics beyond the standard model in lepton final states. We examine 117 final states using 1.1 fb-1 of pp collisions data at √s = 1.96 TeV collected with the D0 detector. We conclude that all observed discrepancies between data and model can be attributed to uncertainties in the standard model background modeling, and hence we do not see any evidence for physics beyond the standard model.

A Search For New Phenomena In Pp Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2016

A Search For New Phenomena In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.

A search for new phenomena is performed in final states containing one or more jets and an imbalance in transverse momentum in pp collisions at a centre-of-mass energy of 13 TeV. The analysed data sample, recorded with the CMS detector at the CERN LHC, corresponds to an integrated luminosity of 2.3 inverse femtobarns. Several kinematic variables are employed to suppress the dominant background, multijet production, as well as to discriminate between other standard model and new physics processes. The search provides sensitivity to a broad range of new-physics models that yield a stable weakly interacting massive particle. The number of observed candidate events is found to agree with the expected contributions from standard model processes, and the result is interpreted in the mass parameter space of fourteen simplified supersymmetric models that assume the pair production of gluinos or squarks and a range of decay modes. For models that assume gluino pair production, masses up to 1575 and 975 GeV are excluded for gluinos and neutralinos, respectively. For models involving the pair production of top squarks and compressed mass spectra, top squark masses up to 400 GeV are excluded.

Search For New Physics In Final States With Low Transverse Energy Photon And Missing Transverse Energy In Proton Proton Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2015

Search For New Physics In Final States With Low Transverse Energy Photon And Missing Transverse Energy In Proton Proton Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.

A search for new physics in the [gamma]+ET nal state is performed using pp collision data corresponding to an integrated luminosity of 7.3 fb-1 collected at √s = 8 TeV using low threshold triggers in a phase space region de ned by ET > 45 GeV and ET > 40 GeV.

Search For New Physics In Final States With Two Opposite Sign Same Flavor Leptons Jets And Missing Transverse Momentum In Pp Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2016

Search For New Physics In Final States With Two Opposite Sign Same Flavor Leptons Jets And Missing Transverse Momentum In Pp Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.

A search is presented for physics beyond the standard model in final states with two opposite-sign, same-flavor leptons, jets, and missing transverse momentum. The data sample corresponds to an integrated luminosity of 2.3 inverse femtobarns of proton-proton collisions at sqrt(s)=13 TeV collected with the CMS detector at the LHC in 2015. The analysis uses the invariant mass of the lepton pair, searching for a kinematic edge or a resonant-like excess compatible with the Z boson mass. Both search modes use several event categories in order to increase the sensitivity to new physics. These categories are based on the rapidity of the leptons, the multiplicity of jets and b jets, the scalar sum of jet transverse momenta, and missing transverse momentum. In addition, phase space regions are included for which excesses were reported using the sqrt(s)=8 TeV data. A local significance of 2.6 sigma for a kinematic edge search was observed by the CMS Collaboration, and of 3.0 sigma for events compatible with the Z boson mass by the ATLAS Collaboration. The observations in all signal regions are consistent with the expectations from the standard model, and the results are interpreted in the context of simplified models of supersymmetry.

Search For New Physics In The Multijet And Missing Transverse Momentum Final State In Proton Proton Collisions At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2014

Search For New Physics In The Multijet And Missing Transverse Momentum Final State In Proton Proton Collisions At Sqrt S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with categories.

A search for new physics is performed in multijet events with large missing transverse momentum produced in proton-proton collisions at $\sqrt{s}$ = 8 TeV using a data sample corresponding to an integrated luminosity of 19.5 fb−1collected with the CMS detector at the LHC. The data sample is divided into three jet multiplicity categories (3-5, 6-7, and ≥8 jets), and studied further in bins of two variables: the scalar sum of jet transverse momenta and the missing transverse momentum. The observed numbers of events in various categories are consistent with backgrounds expected from standard model processes. Exclusion limits are presented for several simplified supersymmetric models of squark or gluino pair production.

Search For New Physics In The Dijet Mass Spectrum And Dijet Ratio In P P Collisions At S 1 2

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Author :
language : en
Publisher:
Release Date : 2010

Search For New Physics In The Dijet Mass Spectrum And Dijet Ratio In P P Collisions At S 1 2 written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.

A search for new Physics is performed with inclusive dijet final states in pp collisions, using data corresponding to an integrated luminosity of 120 ± 13 nb−1 collected by the CMS experiment at LHC. Generic upper limits at the 95% confidence level (CL) are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, or gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% CL: string resonances, with mass less than 1.67 TeV, excited quarks, with mass less than 0.59 TeV and axigluons and colorons with mass less than 0.52 TeV. A search for quark compositeness in the form of quark contact interactions is conducted using the dijet centrality ratio, which quantifies the angular distribution of the dijets. The measurement is found to agree with the predictions of the Standard Model and the statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions of 1.9 TeV at the 95% confidence level. The above results extend previously published limits on these models.

Search For New Physics In The Dijet Mass Spectrum And Dijet Ratio In P P Collisions At S

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Author :
language : en
Publisher:
Release Date : 2010

Search For New Physics In The Dijet Mass Spectrum And Dijet Ratio In P P Collisions At S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.

A search for new Physics is performed with inclusive dijet final states in pp collisions, using data corresponding to an integrated luminosity of 120 ± 13 nb−1 collected by the CMS experiment at LHC. Generic upper limits at the 95% confidence level (CL) are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, or gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% CL: string resonances, with mass less than 1.67 TeV, excited quarks, with mass less than 0.59 TeV and axigluons and colorons with mass less than 0.52 TeV. A search for quark compositeness in the form of quark contact interactions is conducted using the dijet centrality ratio, which quantifies the angular distribution of the dijets. The measurement is found to agree with the predictions of the Standard Model and the statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions of 1.9 TeV at the 95% confidence level. The above results extend previously published limits on these models.

Search For New Phenomena In Monophoton Final States In Proton U2013 Proton Collisions At

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Author :
language : en
Publisher:
Release Date : 2016

Search For New Phenomena In Monophoton Final States In Proton U2013 Proton Collisions At written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.

In this paper, results are presented from a search for new physics in final states containing a photon and missing transverse momentum. The data correspond to an integrated luminosity of 19.6 fb-1 collected in proton–proton collisions at √s = 8 TeV with the CMS experiment at the LHC. No deviation from the standard model predictions is observed for these final states. New, improved limits are set on dark matter production and on parameters of models with large extra dimensions. In particular, the first limits from the LHC on branon production are found and significantly extend previous limits from LEP and the Tevatron. Finally, an upper limit of 14.0 fb on the cross section is set at the 95% confidence level for events with a monophoton final state with photon transverse momentum greater than 145 GeV and missing transverse momentum greater than 140 GeV.

Search For New Physics In Electron Tau Final States In Proton Antiproton Collisions At 1 96 Tev

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Author : Carsten Noeding
language : en
Publisher:
Release Date : 2006

Search For New Physics In Electron Tau Final States In Proton Antiproton Collisions At 1 96 Tev written by Carsten Noeding and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.

During the last decades, particle physicists have studied the tiniest building blocks of matter--the quarks and the leptons--and the forces between them in great detail. From these experiments, a theoretical framework has been built that describes the observed results with high precision. The achievement of this theory, which is referred to as the Standard Model of elementary particle physics, was the elaboration of a unified description of the strong, weak and electromagnetic forces in the framework of quantum gauge-field theories. Moreover, the Standard Model combines the weak and electromagnetic forces in a single electroweak gauge theory. The fourth force which is realized in nature, gravity, is too weak to be observable in laboratory experiments carried out in high-energy particle physics and is not part of the Standard Model. Although the Standard Model has proven highly successful in correlating a huge amount of experimental results, a key ingredient is as yet untested: the origin of electroweak symmetry breaking. Currently, the only viable ansatz that is compatible with observation is the Higgs mechanism. It predicts the existence of a scalar particle, called the Higgs boson, and the couplings to the fundamental Standard Model particles, however not its mass. An upper limit on the mass of the Higgs boson of {approx} 1 TeV can be inferred from unitarity arguments. One of the key tasks of particle physics in the next years will be to verify the existence of this particle. The introduction of an elementary scalar particle in a quantum field theory is highly problematic. The Higgs boson mass is subject to large quantum corrections, which makes it difficult to understand how its mass can be less than a TeV as required by theory. In addition, the Standard Model does not provide an answer to fundamental questions like the values of free parameters of the model, the pending integration of gravity or the evolution of the coupling constants of the fundamental forces at large energy regimes. Hence there are strong reasons to believe that the Standard Model is only a low-energy approximation to a more fundamental theory. One of the best studied candidates for an extension of the Standard Model is supersymmetry, which predicts the existence of a supersymmetric partner for each fundamental particle that differs only in spin. To allow different masses for Standard Model particles and their corresponding supersymmetric partners, supersymmetry must be broken. The mechanism behind supersymmetry breaking is currently unknown, however, various hypotheses exist. Supersymmetric models do not only solve the problem of the large quantum corrections to the Higgs boson mass, but they also allow the unification of the coupling constants at a common scale. In addition, certain supersymmetric models provide a suitable candidate for cold dark matter, which represents a large fraction of mass in our universe. Searches for supersymmetric particles have been performed by the four LEP experiments (ALEPH, DELPHI, L3, OPAL) up to the kinematic limit. Since no evidence for supersymmetric particles has been found, lower limits on their masses have been derived. The search for supersymmetry is now continuing at the Tevatron collider, located at the Fermi National Accelerator Laboratory in Batavia, Illinois. Two dedicated detector systems, CDF and D0, are installed at the Tevatron to analyze proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. A particular promising discovery channel for supersymmetry within the Tevatron energy range is the trilepton channel. In this channel, the lighter supersymmetric partners of the Higgs and gauge bosons, the charginos and neutralinos, decay into final states with leptons or hadrons and missing energy. Using the leptonic final states, the signal can be separated from the large Standard Model background. Supersymmetry requires an extension of the Standard Model Higgs sector, leading to more than one neutral Higgs boson. Enhanced couplings result in sizable cross sections for Higgs boson production, and the decay into a tau pair becomes an important Higgs boson discovery channel. Within the present thesis, a search for new physics predicted by constrained supersymmetric models is performed in final states consisting of an electron and a tau using data collected with the D0 detector from April 2002 to July 2004. The first analysis searches for the associated production of the lightest chargino and the second lightest neutralino in final states with an electron, a hadronically decaying tau, an additional lepton and missing transverse energy: e + {tau}{sub h} + {ell} + E{sub T}. The second analysis searches for neutral supersymmetric Higgs bosons in the decay mode {phi} {yields} {tau}{tau} {yields} e + {tau}{sub h} + E{sub T}. To improve the sensitivity, the results are interpreted in combination with other channels.