The Search For Vh U2192 Vww Standard Model Higgs Production In The Trilepton Signature With 5 9fb 1 Of Data From P Bar P Collisions At U221a S
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The Search For Vh U2192 Vww Standard Model Higgs Production In The Trilepton Signature With 5 9fb 1 Of Data From P Bar P Collisions At U221a S
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Author :
language : en
Publisher:
Release Date : 2010
The Search For Vh U2192 Vww Standard Model Higgs Production In The Trilepton Signature With 5 9fb 1 Of Data From P Bar P 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 2010 with categories.
We present here the search for Standard Model V H → VWW → lll + ET (missing energy due to neutrinos) production, where V is a W or Z weak vector boson, which uses up to 5.9 fb-1 of integrated luminosity. This analysis has recently added to the CDF high-mass Higgs group three new signal topologies characterized by a tri-lepton signature, which are chosen to isolate the V H → VWW associated production signals in the three-lepton signature. As such, we define three new regions for a WH analysis, a ZH 1-jet analysis, and a ZH ≥ 2-jet analysis with which we expect to contribute an additional 5.8% (for mH = 165 GeV) acceptance to the current H → WW dilepton analysis. The ZH trilepton regions are defined by events passing a Z-boson selection: events having at least one lepton pairing (among three possible pairings) with opposite sign, same flavor, and a dilepton invariant mass within [76.0, 106.0] GeV–a ± 15 GeV window around the Z-boson mass. TheWH trilepton region is then defined as the set of trilepton events that are complement to those chosen by the Z-boson selection. These three new event topologies make a substantial contribution to the H → WW group result. As a measure of the sensitivity of this search, we compute the median expected limit on the at 95% confidence level (?C.L.?) on the production cross section (effectively the rate of production) for a StandardModel Higgs boson and report the result as a ratio to the theoretical production cross section. An observed limit ratio of one or less at a given mass would rule out the production of a Standard Model Higgs boson at that mass with 95% confidence. At mH = 165 GeV, the WH analysis expected limits reach 7.2 times the standard model cross section; the ZH 1-jet analysis is set at 29 times the expected standard model cross section; the ZH ≥ 2-jet analysis is set at 9.9 times the expected standard model cross section; and the combined trilepton analysis is set at 4.9 times the expected standard model cross section. We announce that the combination of this trilepton V H → VWW Higgs boson search and the previous CDF dilepton H → WW search achieves an expected median limit of 1.00 at 165 GeV/c2. The expected median limit of 1.00 indicates we anticipate a 50% probability of ruling out the existence of a Standard Model Higgs boson with a mass of 165 GeV/c2. This is the first time a single hadron collider experiment has achieved sensitivity to the production of a Standard Model Higgs boson. We do not see evidence for a significant signal of Higgs bosons in the data and place observed limits on the production of a Standard Model Higgs boson of 165 GeV/c2 at 1.08 times Standard Model production cross section. Matthew.
Search For The Standard Model Higgs Boson In Zh U2192 V Bar V B Bar B Channel In P Bar P Collisions At U221a S
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Author :
language : en
Publisher:
Release Date : 2011
Search For The Standard Model Higgs Boson In Zh U2192 V Bar V B Bar B Channel In P Bar P 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 2011 with categories.
A search for the standard model Higgs boson is performed in 5.2 fb-1 of p$ar{p}$ collisions at p √s = 1.96 TeV, collected with the DØ detector at the Fermilab Tevatron. The final state considered is a pair of b jets with large missing transverse energy, as expected from p$ar{p}$→ ZH → v$ar{v}$b$ar{b}$ production. The search is also sensitive to the WH → lvb$ar{b}$ channel, where the charged lepton is not identified. Boosted decision trees are used to discriminate signal from background. Good agreement is observed between data and expected backgrounds, and, for a Higgs-boson mass of 115 GeV, a limit is set at 95% C.L. on the cross section multiplied by branching fraction of (p$ar{p}$ → (Z/W)H) × (H → b$ar{b}$) that is a factor 4.57 expected and 3.73 observed larger than the value expected from the standard model.
Measurement Of P Bar P U2192 Z Br Z U2192 And Search For Higgs Bosons Decaying To At U221a S
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language : en
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Release Date : 2008
Measurement Of P Bar P U2192 Z Br Z U2192 And Search For Higgs Bosons Decaying To 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 2008 with categories.
The resonant production of tau-lepton pairs is as interesting for the study of Standard Model (SM) physics as the production of lighter leptons pairs. For new phenomena, such as Higgs boson production or in case new particles beyond the SM would arise, the detection of (resonant) pairs of tau leptons becomes much more interesting. This is due to the fact that tau leptons are much heavier than the other leptons, which increases the chance that these new phenomena would be observed first in this channel. Unfortunately their clean detection is far more difficult than that of muons or electrons. The cross section times branching ratio ?. Br for the process p$ar{p}$ → Z → ?+?- was measured at √s = 1.96 GeV using 1.0 fb-1 of data collected by the D0 experiment. This measurement was performed in the channel in which one of the tau leptons decays to a muon and neutrinos, while the other decays either hadronically or to an electron and neutrinos. A set of 1511 events, of which about 20% estimated background, passed all selection criteria. The trigger and muon reconstruction efficiencies, as well as the efficiency for track reconstruction were obtained from data using the 'tag and probe' method on Z → ?+?- events. The multijet background was estimated from the sample of events which passed all selection criteria but in which the muon and the tau candidate had the same charge. The W → ?v + jets background was modeled by Monte Carlo simulations, but normalized to data. All the other backgrounds, as well as the efficiency for Z → ?+?- events were estimated using simulated events normalized to the theoretical calculations of cross sections at next-to-leading order or next-to-next-to-leading order. The energy of the tau candidates was corrected for the estimated response of the charged pions in the calorimeter, which is of the order 50-80%. Since the charged pion response in data was not well reproduced by the default simulation of hadronic interactions (Geisha), a different simulation (gCALOR) was used to obtain an estimated charged pion response consistent with the one measured in data. This tau energy correction method makes use of the superior resolution of the track momentum measurement compared to the resolution of the tau candidate energy as measured by the calorimeter, which leads to a better data--simulation agreement and a decrease of 10% in the resolution of the visible mass peak. The result of this measurement is ?(p$ar{p}$ → Z) • Br(Z → ?+?-) = 240 ± 8(stat) ± 12(syst) ± 15(lumi) pb, in good agreement with the theoretical predictions of 241.6$+3.6top{3.2}$ pb [79] or 251.9$+5.1top{-12}$ pb [93-95], as well as with other measurements performed by the D0 and CDF experiments in all channels in which the Z boson decays leptonically [96-100]. This is the most precise Z boson cross section measurement to date performed in the tau lepton channel at hadron colliders. The analysis demonstrates the ability of the D0 experiment to identify tau leptons decaying hadronically with good efficiency and high purity, a challenging task in p{bar p} collisions where the number of jets resembling tau leptons is very high. This achievement forms a solid basis for other analyses using hadronic tau lepton decays, such as the search for the Higgs boson decaying into tau-lepton pairs, which was performed for the last part of this thesis.
The Search For Vh Bf To Vww Standard Model Higgs Production In The Trilepton Signature With Bf5 9 Fb Of Data From Bf Ppbar Collisions At Bf Sqrt S
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language : en
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Release Date : 2010
The Search For Vh Bf To Vww Standard Model Higgs Production In The Trilepton Signature With Bf5 9 Fb Of Data From Bf Ppbar Collisions At Bf 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.
We present here the search for Standard Model VH → VWW → lll + E{sub T} (missing energy due to neutrinos) production, where V is a W or Z weak vector boson, which uses up to 5.9 fb−1 of integrated luminosity. This analysis has recently added to the CDF high-mass Higgs group three new signal topologies characterized by a tri-lepton signature, which are chosen to isolate the VH → VWW associated production signals in the three-lepton signature. As such, we define three new regions for a WH analysis, a ZH 1-jet analysis, and a ZH ≥ 2-jet analysis with which we expect to contribute an additional ≈ 5.8% (for m{sub H} = 165 GeV) acceptance to the current H → WW dilepton analysis. The ZH trilepton regions are defined by events passing a Z-boson selection: events having at least one lepton pairing (among three possible pairings) with opposite sign, same flavor, and a dilepton invariant mass within [76.0, 106.0] GeV - a ± 15 GeV window around the Z-boson mass. The WH trilepton region is then defined as the set of trilepton events that are complement to those chosen by the Z-boson selection. These three new event topologies make a substantial contribution to the H → WW group result. As a measure of the sensitivity of this search, we compute the median expected limit on the at 95% confidence level ('C.L.') on the production cross section (effectively the rate of production) for a Standard Model Higgs boson and report the result as a ratio to the theoretical production cross section. An observed limit ratio of one or less at a given mass would rule out the production of a Standard Model Higgs boson at that mass with 95% confidence. At m{sub H} = 165 GeV, the WH analysis expected limits reach 7.2 times the standard model cross section; the ZH 1-jet analysis is set at 29 times the expected standard model cross section; the ZH ≥ 2-jet analysis is set at 9.9 times the expected standard model cross section; and the combined trilepton analysis is set at 4.9 times the expected standard model cross section. We announce that the combination of this trilepton VH → VWW Higgs boson search and the previous CDF dilepton H → WW search achieves an expected median limit of 1.00 at 165 GeV/c2. The expected median limit of 1.00 indicates we anticipate a 50% probability of ruling out the existence of a Standard Model Higgs boson with a mass of 165 GeV/c2. This is the first time a single hadron collider experiment has achieved sensitivity to the production of a Standard Model Higgs boson. We do not see evidence for a significant signal of Higgs bosons in the data and place observed limits on the production of a Standard Model Higgs boson of 165 GeV/c2 at 1.08 times Standard Model production cross section.
The Search For Vh Going To Vww Standard Model Higgs Production In The Trilepton Signature With 5 9fb 1 Of Data From Proton Antiproton Collisions At Center Of Mass Energy
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Author : Jason Michael Nett
language : en
Publisher:
Release Date : 2010
The Search For Vh Going To Vww Standard Model Higgs Production In The Trilepton Signature With 5 9fb 1 Of Data From Proton Antiproton Collisions At Center Of Mass Energy written by Jason Michael Nett 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.
Search For Higgs Boson Production In Proton Antiproton Collisions At U221a S
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Author :
language : en
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Release Date : 2006
Search For Higgs Boson Production In Proton Antiproton 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 2006 with categories.
We performed a search for Standard Model Higgs boson production in association with W boson (p$ar{p}$ → W±H → lvb$ar{b}$) in p$ar{p}$ collisions at √s = 1.96 TeV. The search uses the data collected between February 2002 and February 2006 at Collider Detector at Fermilab (CDF), which corresponds to an integrated luminosity of about 1 fb-1. The experimental final state of WH → lvb$ar{b}$ process is lepton (e±/?±), missing transverse energy and two jets. The largest background in lepton+jets events is W+light flavor process, therefore the identification of jets as b-jets reduces this kind of background significantly. We used displaced SECondary VerTeX b-tagging (SECVTX) technique, which utilizes the signature that b-jets have secondary vertex displaced away from primary vertex because of the long life time of B-mesons. However, there is still much contamination in SECVTX b-tagged jets. Finite resolution of secondary vertex tracking measurements results in false tags, and c-jets are also identified as b-jets due to the long life time of D-mesons frequently. For the purpose of increasing the purity of the SECVTX b-tagged jets, we applied Neural Network to SECVTX tagged jets for the first time by using secondary vertex variables and some variables independent of it. Neural Network filter rejects 65% of light flavor jets and 50% of c-jets from the SECVTX tagged jets. We improved the sensitivity of the Higgs boson signal search by 10% with Neural Network b-tagging technique. Events with one high pT electron or muon, large missing transverse energy and either single SECVTX b-tagged jet which passes the Neural Network filter or at least two SECVTX b-tagged jets are selected. The number of selected events and dijet mass distributions are consistent with the Standard Model background expectations. Therefore we set an upper limit on ?(p$ar{p}$ → WH) • Br(H → b$ar{b}$) as 3.9 to 1.3 for Higgs boson mass from 110 to 150 GeV/c2 at 95% confidence level (C.L.). The upper limit obtained from WH → lvb$ar{b}$ process with 1 fb-1 is far away from the Standard Model Higgs boson production expectation by a factor of 20 to 100 as a function of Higgs boson mass. To obtain stronger constraint on the Higgs boson production, we combined the upper limits obtained in processes of ZH → ?$ar{v}$b$ar{b}$, ZH → l$ar{ℓ}$b$ar{b}$ and gg → H → W+W- → l$ar{ℓ}$v$ar{v}$ at CDF. The combination of different channels gives a constraint on the ratio of 95% confidence level upper limit divided by the Standard Model prediction ((? • Br)95/(? • Br)SM), which results in the ratio as 10 to 40 for Higgs boson mass between 110 and 200 GeV/c2. Finally, the combination of Higgs boson searches between CDF and D0 is also performed. The resulting constraint on (? • Br)95/(? • Br)SM is about 4 to 10 for Higgs boson mass between 110 and 200 GeV/c2.
Search For The Standard Model Higgs Boson In The Wh U2192 V B Bar B Channel With The D0 Detector
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Author :
language : en
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Release Date : 2009
Search For The Standard Model Higgs Boson In The Wh U2192 V B Bar B Channel With The D0 Detector 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.
A search for the Standard Model Higgs boson is performed in 4.0 fb-1 of p$ar{p}$ collisions at √s = 1.96 TeV, collected with the DØ detector at the Fermilab Tevatron. The final state considered is a pair of b-jets with large missing transverse energy and one hadronic tau decay as expected from the reaction p$ar{p}$ → WH → ? v b$ar{b}$. Boosted decision trees are used to discriminate the signal from the background. Good agreement is observed between data and expected backgrounds. For a Higgs boson mass of 115 GeV, a limit is set at 95% C.L. on the cross-section times branching fraction of (p$ar{p}$→ (Z/W)H)×(H → b$ar{b}$) which is 14 times larger than the Standard Model value.
A Search For W H U2192 Vb Bar B Production At The Tevatron
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Author :
language : en
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Release Date : 2008
A Search For W H U2192 Vb Bar B Production At The Tevatron written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
All known experimental results on fundamental particles and their interactions can be described to great accuracy by a theory called the Standard Model. In the Standard Model of particle physics, the masses of particles are explained through the Higgs mechanism. The Higgs boson is the only Standard Model particle not discovered yet, and its observation or exclusion is an important test of the Standard Model. While the Standard Model predicts that a Higgs boson should exist, it does not exactly predict its mass. Direct searches have excluded a Higgs with mH 114.4 GeV at 95% confidence level, while indirect measurements indicate that the mass should be less than 144 GeV. This analysis looks for Wsup±/supH → ?vsub?/subb$ar{b}$ in 1 fbsup-1/sup of data collected with the D0 detector in p$ar{p}$ collisions with √s = 1.96 TeV. The analysis strategy relies on the tracking, calorimetry and muon reconstruction of the D0 experiment. The signature is a muon, missing transverse energy (EsubT/sub) to account for the neutrino and two b-jets. The Higgs mass is reconstructed using the invariant mass of the two jets. Backgrounds are Wsup±/supb$ar{b}$, Wsup±/sup c$ar{c}$, Wsup±/sup + light jets (Wsup±
Search For W U2192 T Bar B In P Bar P Collisions At U221a S
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Author :
language : en
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Release Date : 2009
Search For W U2192 T Bar B In P Bar P 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 2009 with categories.
We present a search for a narrow resonance in the t$ar{b}$ mass spectrum using 1.9 fb-1 of p$ar{p}$ collisions at √s = 1.96 TeV recorded with the CDF II detector at the Fermilab Tevatron. We select events with a lepton, neutrino candidate, and two or three jets from which to construct the t$ar{b}$ mass. We quantify the result using the model of a massive Standard Model-like charged-boson (W') decaying to t$ar{b}$, but we are generally sensitive to the presence of any narrow state decaying to the third generation. For a purely right-handed W' with Standard Model couplings, we set a new limit at 95% confidence of ?(p$ar{p}$ → W'R) x BR(W'R → t$ar{b}$) 0.28 pb and MsubW'subR/sub/sub 800 GeV/c2. The limit increases to MW'R > 825 GeV/c2 if decay to right-handed neutrinos is forbidden. These results are shown in Table 7 and plotted in Figure 7.1. The best prior search found MW' Ge 768 GeV/c2 if leptonic decays are forbidden [16]. For a simple W' model with effective coupling gW', the cross-section is proportional to gW'4. Relaxing the assumption of the universal weak coupling (gW' = gW), our cross-section limits can be rewritten as upper limits on gW', as a function of MW'. This is relevant to both the right-handed W' model as well as a left-handed W' model in which the W'L-W interference is negligible. The excluded region of the gW'-MW' plane is shown in Figure 7.2, with gW' in units of gW. At MW' = 300 GeV/c2, we limit (95% C.L.) the effective coupling to be less than 0.40 of the standard weak coupling.
A Search For The Standard Model Higgs Boson In The Process Zh U2192 L L B Bar B In 4 1 Fb 1 Of Cdf Ii Data
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Author :
language : en
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Release Date : 2010
A Search For The Standard Model Higgs Boson In The Process Zh U2192 L L B Bar B In 4 1 Fb 1 Of Cdf Ii Data 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.
The standard model of particle physics provides a detailed description of a universe in which all matter is composed of a small number of fundamental particles, which interact through the exchange of force - carrying gauge bosons (the photon, W ±, Z and gluons). The organization of the matter and energy in this universe is determined by the effects of three forces; the strong, weak, and electromagnetic. The weak and electromagnetic forces are the low energy manifestations of a single electro-weak force, while the strong force binds quarks into protons and neutrons. The standard model does not include gravity, as the effect of this force on fundamental particles is negligible. Four decades of experimental tests, spanning energies from a few electron-volts (eV) up to nearly two TeV, confirm that the universe described by the standard model is a reasonable approximation of our world. For example, experiments have confirmed the existence of the top quark, the W± and the Z bosons, as predicted by the standard model. The latest experimental averages for the masses of the top quark, W± and Z are respectively 173.1 ± 0.6(stat.) ± 1.1(syst.), 80.399 ± 0.023 and 91.1876 ± 0.0021 GeV/c2. The SM is a gauge field theory of zero mass particles. However, the SM is able to accommodate particles with non-zero mass through the introduction of a theoretical Higgs field which permeates all of space. Fermions gain mass through interactions with this field, while the longitudinal components of the massive W± and Z are the physical manifestations of the field itself. Introduction of the Higgs field, directly leads to the predicted existence of an additional particle, the Higgs boson. The Higgs boson is the only particle of the standard model that has not been observed, and is the only unconfirmed prediction of the theory. The standard model describes the properties of the Higgs boson in terms of its mass, which is a free parameter in the theory. Experimental evidence suggests that the Higgs mass has a value between 114.4 and 186 GeV/c2. Particles with a mass in this range can be produced in collisions of less massive particles accelerated to near the speed of light. Currently, one of only a few machines capable of achieving collision energies large enough to potentially produce a standard model Higgs boson is the Tevatron proton-antiproton collider located at Fermi National Accelerator Laboratory in Batavia, Illinois. This dissertation describes the effort to observe the standard model Higgs in Tevatron collisions recorded by the Collider Detector at Fermilab (CDF) II experiment in the ZH →l+l-b$ar{b}$ production and decay channel. In this process, the Higgs is produced along with a Z boson which decays to a pair of electrons or muons (Z →l+l-), while the Higgs decays to a bottom anti-bottom quark pair (H → b$ar{b}$). A brief overview of the standard model and Higgs theory is presented in Chapter 2. Chapter 3 explores previous searches for the standard model Higgs at the Tevatron and elsewhere. The search presented in this dissertation expands upon the techniques and methods developed in previous searches. The fourth chapter contains a description of the Tevatron collider and the CDF II detector. The scope of the discussion in Chapter 4 is limited to the experimental components relevant to the current ZH →l+l-b$ar{b}$ search. Chapter 5 presents the details of object reconstruction; the methods used to convert detector signals into potential electrons, muons or quarks. Chapter six describes the data sample studied for the presence of a ZH →l+l-b$ar{b}$ signal and details the techniques used to model the data. The model accounts for both signal and non-signal processes (backgrounds) which are expected to contribute to the observed event sample. Chapters 7 and 8 summarize the event selectio...