Resonance Searches With The T Bar T Invariant Mass Distribution Measured With The D Experiment At U221a S

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Resonance Searches With The T Bar T Invariant Mass Distribution Measured With The D Experiment At U221a S

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Author :
language : en
Publisher:
Release Date : 2010

Resonance Searches With The T Bar T Invariant Mass Distribution Measured With The D Experiment 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 2010 with categories.

Understanding the universe, its birth and its future is one of the biggest motivations in physics. In order to understand the cosmos, the fundamental particles forming the universe, the components our matter is built of need to be known and understood. Over time physicists have built a theory which describes the physics of the known fundamental particles very well: the Standard Model (SM) of particle physics. The SM describes the particles, their interactions and phenomena with high precision. So far no proven deviations from the SM have been found, though recently evidence for possible physics beyond the SM has been observed. The SM is not describing the mass of the elementary particles however and even with the addition of the Higgs mechanism giving mass to the particles, we have no full theory for all four fundamental forces. We know the model needs to be extended or replaced by another one, as gravitation is not included in the SM. Having a theory which describes all fundamental particles found so far and all but one fundamental interaction is a great success. However, all this describes about 4% of the universe we live inches 23% is dark matter and 73% is dark energy. Dark matter is believed to interact only through gravity and maybe the weak force, which makes it hardly observable. Dark energy is even more elusive. Among other theories the cosmologic constant and scalar fields are discussed to describe it. One should also note that other models exist which for example modify the Newtonian law of gravity. The Higgs mechanism has become the most popular model for mass generation. Alternative theories like Super Symmetry (SUSY), large Extra Dimensions, Technicolor, String Theory, to name just a few, have spread to describe the necessary mass generation or new particles. As proof for new physics beyond the SM has not been found yet, one assumes that new physics will manifest itself at a larger energy scale and therefore a higher particle mass. Particles with high masses are therefore presumed to be a window to test the SM for deviations caused by new physics. The heaviest fundamental particle which is in our reach is the top quark. Its mass is almost as large as that of a complete tungsten atom. It is so heavy, that it decays faster than it can hadronize. It seems the perfect probe to study new physics at the moment. In this analysis the top quark is used as a probe to search for a new resonance, whose properties are similar to a SM Z boson but is much more massive. This analysis will study t{bar t} decays to search for an excess in the invariant mass distribution of the t$\bar{t}$ pairs. Resonant states are suggested for massive Z-like bosons in extended gauge theories, Kaluza Klein states of the gluon or Z, axigluons, topcolor, and other beyond the Standard Model theories. Independent of the exact model a resonant production mechanism should be visible in the t$\bar{t}$ invariant mass distribution. In this thesis a model-independent search for a narrow-width heavy resonance X decaying into t$\bar{t}$ is performed. In the SM, the top quark decays into a W boson and a b quark nearly 100% of the time, which has been proven experimentally, too. The t$\bar{t}$ event signature is fully determined by the W boson decay modes. In this analysis, only the lepton+jets final state, which results from the leptonic decay of one of the W bosons and the hadronic decay of the other, is considered. The event signature is an isolated electron or muon with high transverse momentum, large transverse energy imbalance due to the undetected neutrino, and at least three jets, two of which result from the hadronization of b quarks.

Resonance Searches With The T Overline T Invariant Mass Distribution Measured With The D O Experiment At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2010

Resonance Searches With The T Overline T Invariant Mass Distribution Measured With The D O Experiment 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 2010 with categories.

Understanding the universe, its birth and its future is one of the biggest motivations in physics. In order to understand the cosmos, the fundamental particles forming the universe, the components our matter is built of need to be known and understood. Over time physicists have built a theory which describes the physics of the known fundamental particles very well: the Standard Model (SM) of particle physics. The SM describes the particles, their interactions and phenomena with high precision. So far no proven deviations from the SM have been found, though recently evidence for possible physics beyond the SM has been observed. The SM is not describing the mass of the elementary particles however and even with the addition of the Higgs mechanism giving mass to the particles, we have no full theory for all four fundamental forces. We know the model needs to be extended or replaced by another one, as gravitation is not included in the SM. Having a theory which describes all fundamental particles found so far and all but one fundamental interaction is a great success. However, all this describes about 4% of the universe we live in. 23% is dark matter and 73% is dark energy. Dark matter is believed to interact only through gravity and maybe the weak force, which makes it hardly observable. Dark energy is even more elusive. Among other theories the cosmologic constant and scalar fields are discussed to describe it. One should also note that other models exist which for example modify the Newtonian law of gravity. The Higgs mechanism has become the most popular model for mass generation. Alternative theories like Super Symmetry (SUSY), large Extra Dimensions, Technicolor, String Theory, to name just a few, have spread to describe the necessary mass generation or new particles. As proof for new physics beyond the SM has not been found yet, one assumes that new physics will manifest itself at a larger energy scale and therefore a higher particle mass. Particles with high masses are therefore presumed to be a window to test the SM for deviations caused by new physics. The heaviest fundamental particle which is in our reach is the top quark. Its mass is almost as large as that of a complete tungsten atom. It is so heavy, that it decays faster than it can hadronize. It seems the perfect probe to study new physics at the moment. In this analysis the top quark is used as a probe to search for a new resonance, whose properties are similar to a SM Z boson but is much more massive. This analysis will study t{bar t} decays to search for an excess in the invariant mass distribution of the t{bar t} pairs. Resonant states are suggested for massive Z-like bosons in extended gauge theories, Kaluza Klein states of the gluon or Z, axigluons, topcolor, and other beyond the Standard Model theories. Independent of the exact model a resonant production mechanism should be visible in the t{bar t} invariant mass distribution. In this thesis a model-independent search for a narrow-width heavy resonance X decaying into t{bar t} is performed. In the SM, the top quark decays into a W boson and a b quark nearly 100% of the time, which has been proven experimentally, too. The t{bar t} event signature is fully determined by the W boson decay modes. In this analysis, only the lepton+jets final state, which results from the leptonic decay of one of the W bosons and the hadronic decay of the other, is considered. The event signature is an isolated electron or muon with high transverse momentum, large transverse energy imbalance due to the undetected neutrino, and at least three jets, two of which result from the hadronization of b quarks.

Resonance Searches With The Tt Invariant Mass Distribution Measured With The D Experiment At S

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Author : Thorsten D. Schliephake
language : en
Publisher:
Release Date : 2010

Resonance Searches With The Tt Invariant Mass Distribution Measured With The D Experiment At S written by Thorsten D. Schliephake 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.

Resonance Searches With The Tt Invariant Mass Distribution Measured With The D Experiment At S

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Author : Thorsten D. Schliephake
language : en
Publisher:
Release Date : 2010

Resonance Searches With The Tt Invariant Mass Distribution Measured With The D Experiment At S written by Thorsten D. Schliephake 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.

Resonances From Two Universal Extra Dimensions

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Author :
language : en
Publisher:
Release Date : 2006

Resonances From Two Universal Extra Dimensions written by 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.

Standard model gauge bosons propagating in two universal extra dimensions give rise to heavy spin-1 and spin-0 particles. The lightest of these, carrying Kaluza-Klein numbers (1,0), may be produced only in pairs at colliders, whereas the (1,1) modes, which are heavier by a factor of (square root)2, may be singly produced. We show that the cascade decays of (1,1) particles generate a series of closely-spaced narrow resonances in the t{bar t} invariant mass distribution. At the Tevatron, s-channel production of (1,1) gluons and electroweak bosons will be sensitive to t{bar t} resonances up to masses in the 0.5-0.7 TeV range. Searches at the LHC for resonances originating from several higher-level modes will further test the existence of two universal extra dimensions.

Search For A New Resonance Decaying Into Top Antitop At Tevatron

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Author : Christian Schwanenberger
language : en
Publisher:
Release Date : 2006

Search For A New Resonance Decaying Into Top Antitop At Tevatron written by Christian Schwanenberger 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.

In this report a new search for a narrow-width heavy resonance decaying into top quark pairs (X {yields} t{bar t}) in p{bar p} collisions at {radical}s = 1.96 TeV has been performed using data collected by the D0 detector at the Fermilab Tevatron collider. The analysis considers t{bar t} candidate events in the lepton+jets channel using a lifetime tag to identify b-jets and the t{bar t} invariant mass distribution to search for evidence of resonant production. The analyzed dataset corresponds to an integrated luminosity of approximately 370 pb{sup -1}. Since no evidence for a t{bar t} resonance X is found, upper limits on {sigma}{sub x} x B(X {yields} t{bar t}) for different hypothesized resonance masses using a Bayesian approach are set. Within a topcolor-assisted technicolor model, the existence of a leptophobic Z' boson with M{sub Z'}

Search For Resonances In Diphoton Events At Sqrt S

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Author :
language : en
Publisher:
Release Date : 2016

Search For Resonances In Diphoton Events 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.

Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described. The analysis is based on proton-proton collision data corresponding to an integrated luminosity of 3.2 fb-1 at √s = 13 TeV recorded in 2015. Two searches are performed, one targeted at a spin-2 particle of mass larger than 500 GeV, using Randall-Sundrum graviton states as a benchmark model, and one optimized for a spin-0 particle of mass larger than 200 GeV. Varying both the mass and the decay width, the most significant deviation from the background-only hypothesis is observed at a diphoton invariant mass around 750 GeV with local significances of 3.8 and 3.9 standard deviations in the searches optimized for a spin-2 and spin-0 particle, respectively. The global significances are estimated to be 2.1 standard deviations for both analyses. As a result, the consistency between the data collected at 13 TeV and 8 TeV is also evaluated. Limits on the production cross section times branching ratio to two photons for the two resonance types are reported.

Stochastic Mass Reconstruction

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Author :
language : en
Publisher:
Release Date : 2015

Stochastic Mass Reconstruction 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.

The invariant mass of tau lepton pairs turns out to be smaller than the resonant mass of their mother particle and the invariant mass distribution is stretched wider than the width of the resonant mass as significant fraction of tau lepton momenta are carried away by neutrinos escaping undetected at collider experiments. This paper describes a new approach to reconstruct resonant masses of heavy particles decaying to tau leptons at such experiments. A typical example is a Z or Higgs boson decaying to a tau pair. Although the new technique can be used for each tau lepton separately, I combine two tau leptons to improve mass resolution by requiring the two tau leptons are lined up in a transverse plane. The method is simple to implement and complementary to the collinear approximation technique that works well when tau leptons are not lined up in a transverse plane. The reconstructed mass can be used as another variable in analyses that already use a visible tau pair mass and missing transverse momentum as these variables are not explicitly used in the stochastic mass-reconstruction to select signal-like events.

Search For New Particles Decaying To Dijets B Bar B And T Bar T At Cdf

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Author :
language : en
Publisher:
Release Date : 2001

Search For New Particles Decaying To Dijets B Bar B And T Bar T At Cdf written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.

We present three searches for new particles at CDF. First, using 70 pb[sup[minus]1] of data we search the dijet mass spectrum for resonances. There is an upward fluctuation near 550 GeV/c[sup 2] (2.6[sigma]) with an angular distribution that is adequately described by either QCD alone or QCD plus 5% signal. There is insufficient evidence to claim a signal, but we set the most stringent mass limits on the hadronic decays of axigluons, excited quarks, technirhos, W[prime], Z[prime], and E6 diquarks. Second, using 19 pb[sup[minus]1] of data we search the b-tagged dijet mass spectrum for b[bar b] resonances. Again, an upward fluctuation near 600 GeV/c[sup 2] (2[sigma]) is not significant enough to claim a signal, so we set the first mass limits on topcolor bosons. Finally, using 67 pb[sup[minus]1] of data we search the top quark sample for t[bar t] resonances like a topcolor Z[prime]. Other than an insignificant shoulder of 6 events on a background of 2.4 in the mass region 475--550 GeV/c[sup 2], there is no evidence for new particle production. Mass limits, currently in progress, should be sensitive to a topcolor Z[prime] near 600 GeV/c[sup 2]. In all three searches there is insufficient evidence to claim new particle production, yet there is an exciting possibility that the upward fluctuations are the first signs of new physics beyond the standard model.

Search For Narrow Resonances Lighter Than Upsilon Mesons

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Author :
language : en
Publisher:
Release Date : 2009

Search For Narrow Resonances Lighter Than Upsilon Mesons written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.

We report a search for narrow resonances, produced in p{bar p} collisions at √s = 1.96 TeV, that decay into muon pairs with invariant mass between 6.3 and 9.0 GeV/c2. The data, collected with the CDF II detector at the Fermilab Tevatron collider, correspond to an integrated luminosity of 630 pb−1. We use the dimuon invariant mass distribution to set 90% upper credible limits of about 1% to the ratio of the production cross section times muonic branching fraction of possible narrow resonances to that of the [Upsilon](1S) meson.