Search for a Higgs Boson in the Decay Channel $H$ to ZZ(*) to $q$ Qbar $\ell-̂$ L+ in $pp$ Collisions at $\sqrt{s}

Search for a Higgs Boson in the Decay Channel $H$ to ZZ(*) to $q$ Qbar $\ell-̂$ L+ in $pp$ Collisions at $\sqrt{s}
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Release: 2012
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A search for the standard model Higgs boson decaying into two Z bosons with subsequent decay into a final state containing two quark jets and two leptons, H to ZZ(*) to q q-bar l-l+ is presented. Results are based on data corresponding to an integrated luminosity of 4.6 inverse femtobarns of proton-proton collisions at sqrt(s)=7 TeV, collected with the CMS detector at the LHC. In order to discriminate between signal and background events, kinematic and topological quantities, including the angular spin correlations of the decay products, are employed. Events are further classified according to the probability of the jets to originate from quarks of light or heavy flavor or from gluons. No evidence for the Higgs boson is found, and upper limits on its production cross section are determined for a Higgs boson of mass between 130 and 600 GeV.

Discovery of a Higgs Boson in the H to ZZ to 4 Leptons Channel

Discovery of a Higgs Boson in the H to ZZ to 4 Leptons Channel
Author: Adish Pradeep Vartak
Publisher:
Total Pages: 206
Release: 2014
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ISBN: 9781303948466

A search for the standard model Higgs boson is presented using data collected in pp collisions at the LHC with the CMS detector. Two distinct Higgs boson decay channels are analyzed. The H --> ZZ --> 2l2[Nu] channel, where l = e or [mu], is analyzed with data collected in 2011 at sqrt(s) = 7 TeV corresponding to an integrated luminosity of 4.6 fb−1. No significant excess of events is observed above the background expectation and the presence of a standard model Higgs boson is excluded in the mass range 270-440 GeV at 95% confidence level. The H --> ZZ --> 4l channel is analyzed with data collected in 2011 and 2012 corresponding to integrated luminosities of 5.1 and 19.7 fb−1 at sqrt(s) = 7 and 8 TeV respectively. A new boson is observed with a local significance of 6.7 standard deviations. The mass of this particle is measured to be 125.6±0.4(stat)±0.2(syst) GeV, and it has a signal strength of 1.04+0.29/-0.25(stat) +0.14/-0.08(syst) relative to the standard model Higgs boson expectation. The width of this particle is measured to be less than 3.6 GeV at 95% confidence level. The spin and parity of this particle is found to be consistent with the standard model Higgs boson.

Observation of a Higgs Boson in the H to ZZ to 4L Decay Channel and Using Z to 4L Decays as a Calibration Tool in Studies of the Higgs Boson Properties

Observation of a Higgs Boson in the H to ZZ to 4L Decay Channel and Using Z to 4L Decays as a Calibration Tool in Studies of the Higgs Boson Properties
Author: Matthew Alexander Snowball
Publisher:
Total Pages: 261
Release: 2014
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A search for the Higgs boson in the decay channel H to ZZ to 4 leptons is performed using data from proton-proton collisions corresponding to and integrated luminosity of 5.1 inverse femtobarns at a center-of-mass energy of 7 TeV and 19.7 inverse femtobarns at a center-of-mass energy of 8 TeV data. A new boson is observed as a narrow resonance with a local significance of 6.8 standard deviations, a measured mass of 125.6 +/- 0.4(stat.) +/- 0.2 (syst.) GeV, and a total width less than or equal to 3.4 GeV at a 95% confidence level. The production cross section of the new boson times the branching fraction to four leptons is measured to be 0.93 +0.26 -0.23(stat.) +0.13 -0.09(syst.) times that predicted by the standard model. Its spin-parity properties are found to be consistent with the expectations for the Standard Model Higgs boson. In addition, measurements of the Z to 4 lepton mass and width are presented. The mass of Z boson decaying to 4 leptons is found to be 91.16 +/- 0.23 GeV while the width is found to be 2.98 +0.54 -0.50 GeV. Spin-parity properties of the Z boson are shown to be consistent with expectation from the Standard Model.

Combined Results of Searches for the Standard Model Higgs Boson in Pp Collisions at Sqrt(s)

Combined Results of Searches for the Standard Model Higgs Boson in Pp Collisions at Sqrt(s)
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Release: 2012
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Combined results are reported from searches for the standard model Higgs boson in proton-proton collisions at sqrt(s)=7 TeV in five Higgs boson decay modes: gamma pair, b-quark pair, tau lepton pair, W pair, and Z pair. The explored Higgs boson mass range is 110-600 GeV. The analysed data correspond to an integrated luminosity of 4.6-4.8 inverse femtobarns. The expected excluded mass range in the absence of the standard model Higgs boson is 118-543 GeV at 95% CL. The observed results exclude the standard model Higgs boson in the mass range 127-600 GeV at 95% CL, and in the mass range 129-525 GeV at 99% CL. An excess of events above the expected standard model background is observed at the low end of the explored mass range making the observed limits weaker than expected in the absence of a signal. The largest excess, with a local significance of 3.1 sigma, is observed for a Higgs boson mass hypothesis of 124 GeV. The global significance of observing an excess with a local significance greater than 3.1 sigma anywhere in the search range 110-600 (110-145) GeV is estimated to be 1.5 sigma (2.1 sigma). More data are required to ascertain the origin of this excess.

An Observation of a Higgs Boson in the H to ZZ to Four Leptons Decay Channel and the Studies of Its Spin-Parity Properties

An Observation of a Higgs Boson in the H to ZZ to Four Leptons Decay Channel and the Studies of Its Spin-Parity Properties
Author: Aurelijus Rinkevicius
Publisher:
Total Pages: 134
Release: 2014
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An observation of a new particle and its studies in the ZZ-to-four-lepton mode is done using the 5.1 + 19.7 fb-1 amount of data collected at 7- and 8-TeV center-of-mass collisions, respectively. The particle appeared as a mass resonance of 125.6+-0.4(stat.)+-0.2(syst.) GeV with a local significance of 6.8 standard deviations. With an assumption that it has Higgs boson properties, we measure its width to be less than or equal to 0.022 GeV at a 95% confidence level. The signal strength, a ratio to the predicted number of events, in this decay mode is measured to be 0.93+0.25-0.23 (stat.)-0.09+0.13 (syst.). The particle's spin-parity properties are found to be consistent with the Standard Model Higgs boson with a meaningful statistical power. The specially designed matrix-element-based signal-to-background discrimination techniques, in a wide sense, are proven to be both deterministic and correct. A full-scale verification is presented using the Z-to-four-lepton analysis.

Observation and Examination of a Higgs Boson in the ZZ to Four Lepton Channel

Observation and Examination of a Higgs Boson in the ZZ to Four Lepton Channel
Author: Duncan Kelley Ralph
Publisher:
Total Pages: 123
Release: 2014
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ISBN:

Results are presented on 5.1 fb- 1 of proton-proton collisions at a center of mass energy of 7 TeV and 19.7 fb- 1 at 8 TeV in a search for decays of the Standard Model (SM) Higgs boson to two Z bosons to four charged leptons. We observe a single excess above background expectation with a significance of 7.4 standard deviations at a mass of 125.6 ±0.4(stat) ±0.2(syst) GeV. This excess has a signal strength parameter ... We examine the transverse momentum spectrum of the new particle and find it to be consistent with the SM expectation, and also determine that the Standard Model JPC = 0++ is favored over the plausible alternative hypotheses.

Search for the Standard Model Higgs Boson in the H -] WW -] Lepton+neutrino+q'qbar Decay Channel

Search for the Standard Model Higgs Boson in the H -] WW -] Lepton+neutrino+q'qbar Decay Channel
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Release: 2011
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We present a search for the standard model Higgs boson (H) in ppbar collisions at sqrt{s}=1.96 TeV in events containing a charged lepton (ell), missing transverse energy, and at least two jets, using 5.4 fb-̂1 of integrated luminosity recorded with the D0 detector at the Fermilab Tevatron Collider. This analysis is sensitive primarily to Higgs bosons produced through the fusion of two gluons or two electroweak bosons, with subsequent decay H->WW->ell+nu+q'qbar, where ell is an electron or muon. The search is also sensitive to contributions from other production channels, such as WH->ell+nu+bbbar In the absence of signal, we set limits at the 95% C.L. on the cross section for H production sigma(ppbar->H+X) in these final states. For a mass of MH=160 GeV, the limit is a factor of 3.9 larger than the cross section in the standard model, and consistent with expectation.

Search for a Standard Model Higgs Boson in the $\tau\tau$ Decay Channel Produced in $p\bar{p}$ Collisions at $\sqrt{s}$

Search for a Standard Model Higgs Boson in the $\tau\tau$ Decay Channel Produced in $p\bar{p}$ Collisions at $\sqrt{s}$
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Total Pages: 238
Release: 2011
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This thesis describes the search for the Standard Model Higgs boson decaying to tau lepton pairs, in the Tevatron proton-antiproton collisions at a center of mass energy $\sqrt{s}$ = 1.96 TeV. The search is based on approximately 2.3 fb$^{-1}$ of CDF Run II data and is performed by considering the following signal processes: WH($\rightarrow\tau\tau$), ZH($\rightarrow\tau\tau$), qHq'$\rightarrow$q$\tau\tau$q' and gg$\rightarrow$H$\rightarrow\tau\tau$. Events are selected by requiring an hadronic tau and one isolated electron or muon, coming from the leptonic decay of one of the two taus. In addition, at least one calorimeter jet must be present in the final state. We expect 921.8$\pm$48.9 background events in the 1 jet channel and 159.4$\pm$11.6 in the $\ge$ 2 jets channel, while in data we observe 965 and 166 events, respectively. In order to improve the search sensitivity we employ a multivariate technique, based on a set of Boosted Decision Trees trained to get the best sep aration between signal and the dominant sources of background. We observe no evidence for a Higgs boson signal and therefore we set a 95\% confidence level (C.L.) upper limit on the cross section relative to the SM predictions ($\sigma/\sigma_{\mathrm{SM}}$). Results are presented for the Higgs boson mass varying from M$_\mathrm{H}$ = 100 GeV/$c^2$ to M$_\mathrm{H}$ = 150 GeV/$c^2$. For the mass hypothesis of 120 GeV/c$^2$ the observed limit is 27.2, while the corresponding expected value is 23.4$^{+9.8}_{-6.4}$.