Search For The Standard Model Higgs Boson In The H To Ww To Ell Nu Ell Nu Decay Mode With 4 7 Fb Of Atlas Data At Sqrt S
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Search For The Standard Model Higgs Boson In The H To Ww To Ell Nu Ell Nu Decay Mode With 4 7 Fb Of Atlas Data At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2014
Search For The Standard Model Higgs Boson In The H To Ww To Ell Nu Ell Nu Decay Mode With 4 7 Fb Of Atlas Data 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.
Discovery Of The Higgs Boson Measurements Of Higgs Boson Properties And Search For High Mass Beyond The Standard Model Scalar Particle In The Diphoton Final State With The Atlas Detector At The Large Hadron Collider
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Author : Hongtao Yang
language : en
Publisher:
Release Date : 2016
Discovery Of The Higgs Boson Measurements Of Higgs Boson Properties And Search For High Mass Beyond The Standard Model Scalar Particle In The Diphoton Final State With The Atlas Detector At The Large Hadron Collider written by Hongtao Yang 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.
With 4.8~$\rm{fb}^{-1}$ of proton-proton collision data collected at $\sqrt{s}=7~\rm{TeV}$ in 2011, and 5.9~$\rm{fb}^{-1}$ collected at $\sqrt{s}=8~\rm{TeV}$ in 2012 by the ATLAS detector at the Large Hadron Collider, an excess of 4.5 standard deviations from the background-only hypothesis is observed near 126.5~GeV in the diphoton invariant mass spectra. Along with the excesses observed in the $H \rightarrow ZZ^{(*)}\rightarrow \ell\ell\ell\ell$ and $H \rightarrow WW^{(*)}\rightarrow \ell\nu\ell\nu$ channels, the observation of a Higgs-like particle is established at 6.0 standard deviations level. With more data accumulated during LHC Run~1, the measurements of Higgs boson couplings and mass in the $H\to\gamma\gamma$ channel are conducted by the ATLAS experiment based on 4.5~$\rm{fb}^{-1}$ of proton-proton collisions at $\sqrt{s}=7~\rm{TeV}$ collected in 2011, and 20.3~$\rm{fb}^{-1}$ at $\sqrt{s}=8~\rm{TeV}$ collected in 2012. The combined signal strength, defined as number of observed Higgs boson decays to diphoton divided by the corresponding Standard Model prediction, is measured to be $1.17 \ ^{+0.28}_{-0.26}$ assuming the Higgs boson mass being 125.4~$\rm{GeV}$. The signal strengths for individual Higgs boson production processes are also measured, and are found to be in good consistency with the Standard Model. The mass of the Higgs boson is measured in $H\to\gamma\gamma$ channel by the ATLAS experiment to be $125.98 \pm 0.50$~\GeV. This measurement is combined with the ones from ATLAS $H \rightarrow ZZ^{(*)}\rightarrow \ell\ell\ell\ell$ as well as CMS $H\to\gamma\gamma$ and $H \rightarrow ZZ^{(*)}\rightarrow \ell\ell\ell\ell$. The Higgs boson mass measured from the combination is $125.09\pm0.24~\rm{GeV}$. With LHC center-of-mass energy increased to 13~TeV, a search for high mass Beyond the Standard Model scalar resonance is performed in the diphoton decay channel based on 15.4~$\rm{fb}^{-1}$ of proton-proton collision data collected by the ATLAS detector during 2015 and 2016. While a notable wide excess was first observed in the diphoton invariant mass spectrum from the 2015 data (3.2~$\rm{fb}^{-1}$) with mass near 750~GeV, it is not confirmed by the 2016 data with much higher statistics (12.4~$\rm{fb}^{-1}$). Limits on the production cross section times branching ratio of such resonances are set.
Search For The Standard Model Higgs Boson In The H Ww Lepton Neutrino Q Qbar Decay Channel
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Author :
language : en
Publisher:
Release Date : 2011
Search For The Standard Model Higgs Boson In The H Ww Lepton Neutrino Q Qbar Decay Channel written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
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 The Standard Model Higgs Boson In The Decay Mode H Ww Lnulnu
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Author :
language : en
Publisher:
Release Date : 2009
Search For The Standard Model Higgs Boson In The Decay Mode H Ww Lnulnu 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.
The question of the nature and principles of the universe and our place in it is the driving force of science since Mesopotamian astronomers glanced for the first time at the starry sky and Greek atomism has been formulated. During the last hundred years modern science was able to extend its knowledge tremendously, answering many questions, opening entirely new fields but as well raising many new questions. Particularly Astronomy, Astroparticle Physics and Particle Physics lead the race to answer these fundamental and ancient questions experimentally. Today it is known that matter consists of fermions, the quarks and leptons. Four fundamental forces are acting between these particles, the electromagnetic, the strong, the weak and the gravitational force. These forces are mediated by particles called bosons. Our confirmed knowledge of particle physics is based on these particles and the theory describing their dynamics, the Standard Model of Particles. Many experimental measurements show an excellent agreement between observation and theory but the origin of the particle masses and therefore the electroweak symmetry breaking remains unexplained. The mechanism proposed to solve this issue involves the introduction of a complex doublet of scalar fields which generates the masses of elementary particles via their mutual interactions. This Higgs mechanism also gives rise to a single neutral scalar boson with an unpredicted mass, the Higgs boson. During the last twenty years several experiments have searched for the Higgs boson but so far it escaped direct observation. Nevertheless these studies allow to further constrain its mass range. The last experimental limits on the Higgs mass have been set in 2001 at the LEP collider, an electron positron machine close to Geneva, Switzerland. The lower limit set on the Higgs boson mass is m{sub H}> 114.4 GeV/c2 and remained for many years the last experimental constraint on the Standard Model Higgs Boson due to the shutdown of the LEP collider and the experimental challenges at hadron machines as the Tevatron. This thesis was performed using data from the D0 detector located at the Fermi National Accelerator Laboratory in Batavia, IL. Final states containing two electrons or a muon and a tau in combination with missing transverse energy were studied to search for the Standard Model Higgs boson, utilizing up to 4.2 fb−1 of integrated luminosity. In 2008 the CDF and D0 experiments in a combined effort were able to reach for the first time at a hadron collider the sensitivity to further constrain the possible Standard Model Higgs boson mass range. The research conducted for this thesis played a pivotal role in this effort. Improved methods for lepton identification, background separation, assessment of systematic uncertainties and new decay channels have been studied, developed and utilized. Along with similar efforts at the CDF experiment these improvements led finally the important result of excluding the presence of a Standard Model Higgs boson in a mass range of m{sub H} = 160-170 GeV/c2 at 95% Confidence Level. Many of the challenges and methods found in the present analysis will probably in a similar way be ingredients of a Higgs boson evidence or discovery in the near future, either at the Tevatron or more likely at the soon starting Large Hadron Collider (LHC). Continuing to pursue the Higgs boson we are looking forward to many exciting results at the Tevatron and soon at the LHC. In Chapter 2 an introduction to the Standard Model of particle physics and the Higgs mechanism is given, followed by a brief outline of existing theoretical and experimental constraints on the Higgs boson mass before summarizing the Higgs boson production modes. Chapter 3 gives an overview of the experimental setup. This is followed by a description of the reconstruction of the objects produced in proton-antiproton collisions in Chapter 4 and the necessary calorimeter calibrations in Chapter 5. Chapter 6 follows with an explanation of the phenomenology of the proton-antiproton collisions and the data samples used. In Chapter 7 the search for the Standard Model Higgs boson using a di-electron final state is discussed, followed by the analysis of the final states using muons and hadronic decaying taus in Chapter 8. Finally a short outlook for the prospects of Higgs boson searches is given in Chapter 9.
Search For The Standard Model Higgs Boson Produced In Association With A Standard W Or A Z Boson And Decaying To Bottom Quarks
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Author :
language : en
Publisher:
Release Date : 2014
Search For The Standard Model Higgs Boson Produced In Association With A Standard W Or A Z Boson And Decaying To Bottom Quarks 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 the standard model Higgs boson (H) decaying to b b-bar when produced in association with a weak vector boson (V) is reported for the following channels: W(mu nu)H, W(e nu)H, W(tau nu)H, Z(mu mu)H, Z(e e)H, and Z(nu nu)H. The search is performed in data samples corresponding to integrated luminosities of up to 5.1 inverse femtobarns at sqrt(s) = 7 TeV and up to 18.9 inverse femtobarns at sqrt(s) = 8 TeV, recorded by the CMS experiment at the LHC. An excess of events is observed above the expected background with a local significance of 2.1 standard deviations for a Higgs boson mass of 125 GeV, consistent with the expectation from the production of the standard model Higgs boson. The signal strength corresponding to this excess, relative to that of the standard model Higgs boson, is 1.0 +/- 0.5./abstract
Search For The Higgs Boson In H To Ww To Ell Nu Ell Nu Decays
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Author :
language : en
Publisher:
Release Date : 2010
Search For The Higgs Boson In H To Ww To Ell Nu Ell Nu Decays 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.
We present a search for the standard model (SM) Higgs boson decaying to a pair of W bosons that in turn decay leptonically, H → WW* → l?l?. We consider events produced in p{bar p} collisions at √s = 1.96 TeV, with two oppositely charged lepton candidates (ee−, e{sup {+-}}?{sup {+-}}, or?+?−), and missing transverse energy. The data were collected with the D0 detector at the Fermilab Tevatron collider, and correspond to an integrated luminosity of 5.4 fb−1. No excess of events over background is observed, and limits on SM Higgs boson production are determined.
Search For The Standard Model Higgs Boson In H To Ww To Ell Nu J J Channel In 1 96 Tev Proton Antiproton Collisions
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Author :
language : en
Publisher:
Release Date : 2011
Search For The Standard Model Higgs Boson In H To Ww To Ell Nu J J Channel In 1 96 Tev Proton Antiproton Collisions written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
We searched for Standard Model Higgs boson decaying into WW(*), where one of the W bosons decays leptonically and the other hadronically. We used 4.6 $fb^{-1}$ of data collected with the CDF detector in Tevatron Run II. We composed a likelihood discriminant using kinematic variables in order to maximize the signal/background separation. We set upper limits on Higgs boson production cross section for Higgs boson masses between 150 and 200 GeV/$c^2$. The results range from 5.69 ($m_H$ = 170 GeV/$c^2$) to 52.5 ($m_H$ = 150 GeV/$c^2$) times the Standard Model values at 95 % confidence level.
Measurement Of Top Quark Properties And Search For The Standard Model Higgs Boson In Proton Anti Proton Collisions At Sqrt S
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Author :
language : en
Publisher:
Release Date : 2011
Measurement Of Top Quark Properties And Search For The Standard Model Higgs Boson In Proton Anti 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 2011 with categories.
We present a measurement of the top quark mass and of the top-antitop (tf) pair production cross section and a search for the Standard Model Higgs boson with CDF II Detector in pp collisions at $\sqrt{s}$ = 1.96 TeV. The integrated luminosity of 2.9 $fb^{-1}$ is used for top-antitop pair production cross section and top quark mass measurement. We adopt a neural-network algorithm to select candidate events from six or more jets. At least one of these jets should be required to be b jet, as identified by the reconstruction of a secondary vertex inside the jet. The mass measurement is based on a likelihood fit incorporating reconstructed mass distributions representative of signal and background, where the absolute jet energy scale (JES) is measured simultaneously with the top quark mass. The measurement yields a value of 174.8 ± 2.4 (stat + JES) $^{+1.2}_{-1.0}$ (syst) GeV/$c^2$, where the uncertainty from the absolute jet energy scale is evaluated together with the statistical uncertainty. The procedure also measures the amount of signal from which we derive a cross section, $\sigma_{t\bar{t}}$ = 7.2 ± 0.5 (stat) ±1.0 (syst) ± 0.4 (lum) $pb$, for the measured values of top quark mass and JES. Top quark mass and W boson mass constrain the mass of the Standard Model Higgs boson, indirectly. This prediction implies MH = 89 $^{+35}_{-26}$GeV/$c^2$ (68% confidence level) as of July 2010. Therefore, we concentrate on the Standard Model Higgs mass search region with $\le$ 135 GeV / $c^2$ . Then, we search for the Standard Model Higgs boson associated with vector boson using the decay modes consisting of leptons only: Signal processes are $WH \to \ell \nu + \tau\tau$ and $ZH \to l l + \tau \tau$. We simply select 3 or 4 lepton including hadronic T to pick candidate events out. To improve search sensitivity, we adopt Support Vector Machine to discriminate signals from backgrounds. Using about 6.2 $fb^{-1}$ data, there was no clear discrepancy between data and our background estimation. Therefore, we extract cross section upper limit of the Standard Model Higgs production at 95 % confidence level. The observed upper limit on assumption of $M_H$ = 115 GeV/$c^2$ is 25.1 x $\sigma^{SM}$ at 95% confidence level while the expectation is 17.3 x $\sigma ^{SM}$ at 95%.
First Search For The Standard Model Higgs Boson Using The Semileptonic Decay Channel
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Author :
language : en
Publisher:
Release Date : 2010
First Search For The Standard Model Higgs Boson Using The Semileptonic Decay Channel 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.
This dissertation presents the first search for the standard model Higgs boson (H) in decay topologies containing a muon, an imbalance in transverse momentum (E{sub T}) and jets, using p{bar p} collisions at √s = 1.96 TeV with an integrated luminosity of 4.3 fb−1 recorded with the D0 detector at the Fermilab Tevatron Collider. This analysis is sensitive primary to contributions from Higgs bosons produced through gluon fusion, with subsequent decay H → WW → [mu][nu]jj where W represents a real or virtual W boson. In the absence of signal, limits are set at 95% confidence on the production and decay of the standard model Higgs boson for M{sub H} in the range of 115-200 GeV. For M{sub H} = 165 GeV, the observed and expected limits are factors of 11.2 larger than the standard model value. Combining this channel with e[nu]jj final states and including earlier data to increase the integrated luminosity to 5.4 fb−1 produces observed(expected) limits of 5.5(3.8) times the standard model value.
Search For The Standard Model Higgs Boson In The Decay Mode H W W L L L Nu L Nu At The D Experiment
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Author : Björn Penning
language : en
Publisher:
Release Date : 2009
Search For The Standard Model Higgs Boson In The Decay Mode H W W L L L Nu L Nu At The D Experiment written by Björn Penning 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.