44 research outputs found
Evidence for t\bar{t}\gamma Production and Measurement of \sigma_t\bar{t}\gamma / \sigma_t\bar{t}
Using data corresponding to 6.0/fb of ppbar collisions at sqrt(s) = 1.96 TeV
collected by the CDF II detector, we present a cross section measurement of
top-quark pair production with an additional radiated photon. The events are
selected by looking for a lepton, a photon, significant transverse momentum
imbalance, large total transverse energy, and three or more jets, with at least
one identified as containing a b quark. The ttbar+photon sample requires the
photon to have 10 GeV or more of transverse energy, and to be in the central
region. Using an event selection optimized for the ttbar+photon candidate
sample we measure the production cross section of, and the ratio of cross
sections of the two samples. Control samples in the dilepton+photon and
lepton+photon+\met, channels are constructed to aid in decay product
identification and background measurements. We observe 30 ttbar+photon
candidate events compared to the standard model expectation of 26.9 +/- 3.4
events. We measure the ttbar+photon cross section to be 0.18+0.08 pb, and the
ratio of the cross section of ttbar+photon to ttbar to be 0.024 +/- 0.009.
Assuming no ttbar+photon production, we observe a probability of 0.0015 of the
background events alone producing 30 events or more, corresponding to 3.0
standard deviations.Comment: 9 pages, 3 figure
The first measurement of the top quark mass at CDF II in the lepton+jets and dilepton channels simultaneously
submitted to Phys. Rev. DWe present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of 1.9fb^-1 of ppbar collisions collected at sqrt{s}=1.96 TeV with the CDF II detector at Fermilab's Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the lepton + jets and dilepton decay channels simultaneously. We reconstruct two observables in each channel and use a non-parametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the W decay in the lepton + jets channel, and the top quark mass and the scalar sum of transverse energy of the event in the dilepton channel. We perform a simultaneous fit for the top quark mass and the jet energy scale, which is constrained in situ by the hadronic W boson mass. Using 332 lepton + jets candidate events and 144 dilepton candidate events, we measure the top quark mass to be mtop=171.9 +/- 1.7 (stat. + JES) +/- 1.1 (syst.) GeV/c^2 = 171.9 +/- 2.0 GeV/c^2.We present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of 1.9 fb-1 of pp̅ collisions collected at √s=1.96 TeV with the CDF II detector at Fermilab’s Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the lepton+jets and dilepton decay channels simultaneously. We reconstruct two observables in each channel and use a nonparametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the W decay in the lepton+jets channel, and the top quark mass and the scalar sum of transverse energy of the event in the dilepton channel. We perform a simultaneous fit for the top quark mass and the jet energy scale, which is constrained in situ by the hadronic W boson mass. Using 332 lepton+jets candidate events and 144 dilepton candidate events, we measure the top quark mass to be Mtop=171.9±1.7(stat+JES)±1.1(other syst) GeV/c2=171.9±2.0 GeV/c2.Peer reviewe
Search for the supersymmetric partner of the top quark in pp̅ collisions at √s=1.96 TeV
17 pages, 11 figures. Published in Phys.Rev.D82:092001,2010.We present a search for the lightest supersymmetric partner of the top quark in proton-antiproton collisions at a center-of-mass energy √s=1.96 TeV. This search was conducted within the framework of the R parity conserving minimal supersymmetric extension of the standard model, assuming the stop decays dominantly to a lepton, a sneutrino, and a bottom quark. We searched for events with two oppositely-charged leptons, at least one jet, and missing transverse energy in a data sample corresponding to an integrated luminosity of 1 fb-1 collected by the Collider Detector at Fermilab experiment. No significant evidence of a stop quark signal was found. Exclusion limits at 95% confidence level in the stop quark versus sneutrino mass plane are set. Stop quark masses up to 180 GeV/c2 are excluded for sneutrino masses around 45 GeV/c2, and sneutrino masses up to 116 GeV/c2 are excluded for stop quark masses around 150 GeV/c2.Peer reviewe
Search for the Rare Radiative Decay: in \ppbar\ Collisions at TeV
We present a search for the rare radiative decay \wpigamma\ using data
corresponding to an integrated luminosity of 4.3 \invfb\ of proton-antiproton
collisions at a center of mass energy of 1.96 TeV collected by the CDF
experiment at Fermilab. As no statistically significant signal is observed, we
set a 95% confidence level upper limit on the relative branching fraction
\bratio\ at , a factor of 10 improvement over the previous
limit
Search for New Particles in Final States with Large Jet Multiplicities and Missing Transverse Energy in ppbar Collisions at sqrt(s) = 1.96 TeV
We present a search for a new particle T' decaying to a top quark via T' -> t
+ X, where X goes undetected. We use a data sample corresponding to 5.7 fb-1 of
integrated luminosity of ppbar collisions with sqrt{s} = 1.96 TeV, collected at
Fermilab by the CDF II detector. Our search for pair production of T' is
focused on the hadronic decay channel, ppbar -> T'T' -> tt +XX -> bbqqqq + XX.
We interpret our results in terms of a model where T' is an exotic fourth
generation quark and X is a dark matter candidate. The data are consistent with
standard model expectations. We set a limit on the generic production of
T'T'->tt+XX, excluding the fourth generation exotic quarks T' at 95% confidence
level up to m_T' = 400 GeV/c2 for m_X < 70 GeV/c2
Observation of B0_s -> J/psi K*(892)0 and B0_s -> J/psi K0_S Decays
We report the first observation of two Cabibbo-suppressed decay modes of the
B0_s meson. Using a sample of p-pbar collisions at sqrt{s}=1.96 TeV
corresponding to 5.9 fb-1 of integrated luminosity collected with the CDFII
detector at the Fermilab Tevatron, we search for new B0_s decay modes in a
sample of events containing J/psi to mu+ mu- decays. We reconstruct a B0_s to
J/psi K*(892)0 signal with K^*(892)0 to K+ pi-, observing a yield of 151 +/- 25
events with a statistical significance of 8.0 sigma. We also reconstruct a B0_s
to J/psi K0_S signal with K0_S to pi+ pi-, observing a yield of 64 +/- 14
events with a statistical significance of 7.2 sigma. From these yields, we
extract the branching ratios B(B0_s -> J/psi K*(892)0)= (8.3 +/- 3.8) x 10{-5}
and B(B0_s -> J/psi K0)= (3.5 +/- 0.8) x 10{-5}, where statistical, systematic
and fragmentation fraction uncertainties are included in the combined
uncertainty.Comment: Submitted to Phys. Rev.
Search for New Bottomlike Quark Pair Decays Q(Q)over-bar -\u3e (tW +/-)((t)over-barW +/- in Same-Charge Dileption Events
We 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 \u3e 338 GeV= c2 and mT5= 3 \u3e 365 GeV= c2 at 95% confidence level
Search for Gluino-Mediated Sbottom Production in p-pbar Collisions at sqrt(s)=1.96 TeV
Final version publish in PRLWe report on a search for the supersymmetric partner of the bottom quark produced from gluino decays in data from 2.5 fb-1 of integrated luminosity collected by the Collider Detector at Fermilab at sqrt(s)=1.96 TeV. Candidate events are selected requiring two or more jets and large missing transverse energy. At least two of the jets are required to be tagged as originating from a b quark to enhance the sensitivity. The results are in good agreement with the prediction of the standard model processes, giving no evidence for gluino decay to sbottom quarks. This result constrains the gluino-pair-production cross section to be less than 40fb at 95% credibility level for a gluino mass of 350 GeV.We report on a search for the supersymmetric partner of the bottom quark produced from gluino decays in data from 2.5 fb-1 of integrated luminosity collected by the Collider Detector at Fermilab at √s=1.96 TeV. Candidate events are selected requiring two or more jets and large missing transverse energy. At least two of the jets are required to be tagged as originating from a b quark to enhance the sensitivity. The results are in good agreement with the prediction of the standard model processes, giving no evidence for gluino decay to bottom squarks. This result constrains the gluino-pair-production cross section to be less than 40 fb at 95% credibility level for a gluino mass of 350 GeV/c2.Peer reviewe
Search for Pair Production of Supersymmetric Top Quarks in Dilepton Events from Collisions at = 1.96 TeV
Accepted to Phys. Rev. LettWe present the results of a search for pair production of the supersymmetric partner of the top quark (the stop quark ) decaying to a -quark and a chargino \chargino with a subsequent \chargino decay into a neutralino \neutralino, lepton , and neutrino . Using a data sample corresponding to 2.7 fb of integrated luminosity of collisions at TeV collected by the CDF II detector, we reconstruct the mass of candidate stop events and fit the observed mass spectrum to a combination of standard model processes and stop quark signal. We find no evidence for \pairstop production and set 95% C.L. limits on the masses of the stop quark and the neutralino for several values of the chargino mass and the branching ratio {\cal B}(\chargino\to\neutralino\ell^{\pm}\nu).We present the results of a search for pair production of the supersymmetric partner of the top quark (the top squark t˜1) decaying to a b quark and a chargino χ˜1± with a subsequent χ˜1± decay into a neutralino χ˜10, lepton ℓ, and neutrino ν. Using a data sample corresponding to 2.7 fb-1 of integrated luminosity of pp̅ collisions at √s=1.96 TeV collected by the CDF II detector, we reconstruct the mass of top squark candidate events and fit the observed mass spectrum to a combination of standard model processes and t˜1t˜̅ 1 signal. We find no evidence for t˜1t˜̅ 1 production and set 95% C.L. limits on the masses of the top squark and the neutralino for several values of the chargino mass and the branching ratio B(χ˜1±→χ˜10ℓ±ν).Peer reviewe
Search for exclusive Z boson production and observation of high mass ppbar->gammagamma->p+ll+pbar events in ppbar collisions at sqrt(s) = 1.96 TeV
submitted to Phys. Rev. LettWe present a search for exclusive Z boson production in proton-antiproton collisions at sqrt(s) = 1.96 TeV, using the CDF II detector at Fermilab. We observe no exclusive Z->ll candidates and place the first upper limit on the exclusive Z cross section in hadron collisions, sigma(exclu) gammagamma->p+ll+pbar, and measure the cross section for M(ll) > 40 GeV/c2 and |eta(l)|This Letter presents a search for exclusive Z boson production in proton-antiproton collisions at √s=1.96 TeV, using the CDF II detector. No exclusive Z→l+l- candidates are observed and the first upper limit on the exclusive Z cross section in hadron collisions is found to be σexcl(Z)40 GeV/c2 and |ηl|<4 is found to be σ=0.24-0.10+0.13 pb, which is consistent with the standard model prediction.Peer reviewe