46 research outputs found
Measurement of the top quark mass in the dilepton channel using mT2 at CDF
No full textWe present measurements of the top quark mass using m[subscript T2], a variable related to the transverse mass in events with two missing particles. We use the template method applied to tt̅ dilepton events produced in pp̅ collisions at Fermilab’s Tevatron Collider and collected by the CDF detector. From a data sample corresponding to an integrated luminosity of 3.4 fb[superscript -1], we select 236 tt̅ candidate events. Using the m[subscript T2] distribution, we measure the top quark mass to be M[subscript top]=168.0[subscript -4.0][superscript +4.8](stat)±2.9(syst) GeV/c[superscript 2]. By combining m[subscript T2] with the reconstructed top quark mass distributions based on a neutrino weighting method, we measure M[subscript top]=169.3±2.7(stat)±3.2(syst) GeV/c[superscript 2]. This is the first application of the m[subscript T2] variable in a mass measurement at a hadron collider.United States. Dept. of EnergyNational Science FoundationIstituto Nazionale di Fisica Nucleare of ItalyMinistry of Education, Culture, Sports, Science and Technology of JapanNatural Sciences and Engineering Research Council of CanadaNational Science Council of the Republic of ChinaSwiss National Science FoundationAlfred P. Sloan FoundationBundesministerium für Bildung und Forschung, GermanyKorean Science and Engineering FoundationKorean Research FoundationScience and Technology Facilities Council, United KingdomRoyal Society, United KingdomInstitut National de Physique Nucleaire et Physique des Particules/CNRSRussian Foundation for Basic ResearchMEC (Spain)Slovak R&D AgencyAcademy of Finlan
Inclusive Search for Standard Model Higgs Boson Production in the WW Decay Channel Using the CDF II Detector
No full textWe present a search for standard model (SM) Higgs boson production using pp̅ collision data at √s=1.96 TeV, collected with the CDF II detector and corresponding to an integrated luminosity of 4.8 fb[superscript -1]. We search for Higgs bosons produced in all processes with a significant production rate and decaying to two W bosons. We find no evidence for SM Higgs boson production and place upper limits at the 95% confidence level on the SM production cross section (σ[subscript H]) for values of the Higgs boson mass (m[subscript H]) in the range from 110 to 200 GeV. These limits are the most stringent for m[subscript H]>130 GeV and are 1.29 above the predicted value of σ[subscript H] for m[subscript H]=165 GeV.Academy of FinlandSlovak R&D AgencyPrograma Consolider-Ingenio 2010, SpainMinisterio de Ciencia e Innovación, SpainRussian Foundation for Basic ResearchInstitut National de Physique Nucleaire et Physique des Particules/CNRSScience and Technology Facilities Council and the Royal Society, UKNational Research Foundation of KoreaWorld Class University ProgramBundesministerium für Bildung und Forschung, GermanyAlfred P. Sloan FoundationSwiss National Science FoundationNational Science Council of the Republic of ChinaNatural Sciences and Engineering Research Council of CanadaMinistry of Education, Culture, Sports, Science and Technology of JapanItalian Istituto Nazionale di Fisica NucleareNational Science FoundationUnited States. Dept. of Energ
Search for Technicolor Particles Produced in Association with a W Boson at CDF
No full textWe present a search for the technicolor particles ρT and πT in the process pp̅ →ρT→WπT at a center of mass energy of √s=1.96 TeV. The search uses a data sample corresponding to approximately 1.9 fb-1 of integrated luminosity accumulated by the CDF II detector at the Fermilab Tevatron. The event signature we consider is W→ℓν and πT→bb̅ , bc̅ or bu̅ depending on the πT charge. We select events with a single high-pT electron or muon, large missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with multiple b-tagging algorithms. The observed number of events and the invariant mass distributions are consistent with the standard model background expectations, and we exclude a region at 95% confidence level in the ρT-πT mass plane. As a result, a large fraction of the region m(ρT)=180–250 GeV/c2 and m(πT)=95–145 GeV/c2 is excluded
Top Quark Mass Measurement in the lepton plus jets Channel Using a Matrix Element Method and in situ Jet Energy Calibration
No full textA precision measurement of the top quark mass m(t) is obtained using a sample of t (t) over bar events from p (p) over bar collisions at the Fermilab Tevatron with the CDF II detector. Selected events require an electron or muon, large missing transverse energy, and exactly four high-energy jets, at least one of which is tagged as coming from a b quark. A likelihood is calculated using a matrix element method with quasi-Monte Carlo integration taking into account finite detector resolution and jet mass effects. The event likelihood is a function of mt and a parameter Delta(JES) used to calibrate the jet energy scale in situ. Using a total of 1087 events in 5.6 fb(-1) of integrated luminosity, a value of m(t) 173.0 +/- 1.2 GeV/c(2) is measured
Measurement of the Lambda(0)(b) Lifetime in Lambda(0)(b) -> Lambda(+)(c)pi(-) Decays in p(p)over-bar Collisions at root s=1.96 TeV
No full textWe report a measurement of the lifetime of the Lambda(0)(b) baryon in decays to the Lambda(+)(c)pi(-) final state in a sample corresponding to 1.1 fb(-1) collected in p (p) over bar collisions at root s = 1.96 TeV by the CDF II detector at the Tevatron collider. Using a sample of about 3000 fully reconstructed Lambda(0)(b) events we measure tau(Lambda(0)(b) ) = 1.401 +/- 0.046(stat) +/- 0.035(syst) ps (corresponding to c tau(Lambda(0)(b)) = 420.1 +/- 13.7(stat) +/- 10.6(syst) mu m, where c is the speed of light). The ratio of this result and the world average B-0 lifetime yields tau(Lambda(0)(b))/tau(B-0) = 0.918 +/- 0.038 (stat) and (syst), in good agreement with recent theoretical predictions
Studying the underlying event in Drell-Yan and high transverse momentum jet production at the Tevatron
No full textWe study the underlying event in proton-antiproton collisions by examining the behavior of charged particles produced in association with a large transverse momentum jet (similar to 2: 2 fb(-1)) or with a Drell-Yan lepton pair (similar to 2.7 fb(-1)) in the Z-boson mass region [70 \u3c M(pair) \u3c 110 GeV/c(2)] as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton pair or the leading jet in each event to define regions of eta-phi space that are sensitive to the modeling of the underlying event. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte Carlo models
Observation of single top quark production and measurement of |V subscript tb| with CDF
No full textWe report the observation of electroweak single top quark production in 3.2 fb-1 [fb superscript -1] of pp̅ collision data collected by the Collider Detector at Fermilab at √s=1.96 TeV [square root of s=1.96 TeV]. Candidate events in the W+jets topology with a leptonically decaying W boson are classified as signal-like by four parallel analyses based on likelihood functions, matrix elements, neural networks, and boosted decision trees. These results are combined using a super discriminant analysis based on genetically evolved neural networks in order to improve the sensitivity. This combined result is further combined with that of a search for a single top quark signal in an orthogonal sample of events with missing transverse energy plus jets and no charged lepton. We observe a signal consistent with the standard model prediction but inconsistent with the background-only model by 5.0 standard deviations, with a median expected sensitivity in excess of 5.9 standard deviations. We measure a production cross section of 2.3-0.5+0.6(stat+sys) [2.3 subscript -0.5 superscript +0.6 (stat + sys)] pb, extract the value of the Cabibbo-Kobayashi-Maskawa matrix element |Vtb|=0.91-0.11+0.11(stat+sys)±0.07 [|V subscript tb|=0.91 subscript -0.11 superscript +0.11 (stat + sys)±0.07] (theory), and set a lower limit |Vtb|>0.71 [|V subscript tb|>0.71] at the 95% C.L., assuming mt=175 [m subscript t =175] GeV/c2 [GeV / c superscript 2].United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio
Diffractive W and Z production at the Fermilab Tevatron
No full textWe report on a measurement of the fraction of events with a W or Z boson which are produced diffractively in p̅ p collisions at √s=1.96 [square root of s = 1.96] TeV, using data from 0.6 fb-1 [fb superscript -1] of integrated luminosity collected with the CDF II detector equipped with a Roman-pot spectrometer that detects the p̅ from p̅ +p→p̅ +[X+W/Z]. We find that (1.00±0.11)% of Ws and (0.88±0.22)% of Zs are produced diffractively in a region of antiproton or proton fractional momentum loss ξ [xi] of 0.03<ξ<0.10 [0.03 < xi <0.10] and 4-momentum transferred squared t of -1<t<0 (GeV/c)2 [(GeV/c) superscript 2], where we account for the events in which the proton scatters diffractively while the antiproton dissociates, p̅ +p→[X+W/Z]+p, by doubling the measured proton dissociation fraction. We also report on searches for W and Z production in double Pomeron exchange, p+p̅ →p+[X+W/Z]+p̅ , and on exclusive Z production, p̅ +p→p̅ +Z+p. No signal is seen above background for these processes, and comparisons are made with expectations.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio
Exclusion of an Exotic Top Quark with-4/3 Electric Charge Using Soft Lepton Tagging
No full textWe present a measurement of the electric charge of the top quark using p (p) over bar collisions corresponding to an integrated luminosity of 2: 7 fb(-1) at the CDF II detector. We reconstruct t (t) over bar events in the lepton + jets final state. We use soft lepton taggers to determine the flavor of the b jets, which we use to reconstruct the top quark's electric charge and exclude an exotic top quark with -4/3 charge at 95% confidence level. This is the strongest exclusion of the exotic charge scenario and the first to use soft leptons for this purpose
Search for New Bottomlike Quark Pair Decays Q(Q)over-bar -> (tW +/-)((t)over-barW +/- in Same-Charge Dileption Events
No full textWe report the most restrictive direct limits on masses of fourth- generation down- type quarks b0, and quarklike composite fermions (B or T5= 3), decaying promptly to tW -/+. We search for a significant excess of events with two same- charge leptons (e, mu), several hadronic jets, and missing transverse energy. An analysis of data from pp collisions with an integrated luminosity of 2: 7 fb = 1 collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits mb0, mB > 338 GeV= c2 and mT5= 3 > 365 GeV= c2 at 95% confidence level
