79 research outputs found
Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV
We search for the standard model Higgs boson produced in association with an
electroweak vector boson in events with no identified charged leptons, large
imbalance in transverse momentum, and two jets where at least one contains a
secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1
integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV
recorded by the CDF II experiment at the Tevatron. We find 268 (16) single
(double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are
expected from standard model background processes. We place 95% confidence
level upper limits on the Higgs boson production cross section for several
Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115
GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model
prediction.Comment: 8 pages, 2 figures, submitted to Phys. Rev. Let
Measurement of Ratios of Fragmentation Fractions for Bottom Hadrons in p-pbar Collisions at sqrt{s}=1.96 TeV
This paper describes the first measurement of b-quark fragmentation fractions
into bottom hadrons in Run II of the Tevatron Collider at Fermilab. The result
is based on a 360 pb-1 sample of data collected with the CDF II detector in
p-pbar collisions at sqrt{s}=1.96 TeV. Semileptonic decays of B0, B+, and B_s
mesons, as well as Lambda_b baryons, are reconstructed. For an effective bottom
hadron p_T threshold of 7 GeV/c, the fragmentation fractions are measured to be
f_u/f_d=1.054 +/- 0.018 (stat) +0.025-0.045(sys) +/- 0.058 (Br),
f_s/(f_u+f_d)=0.160 +/- 0.005 (stat) +0.011-0.010 (sys) +0.057-0.034 (Br), and
f_{Lambda_b}/(f_u+f_d)=0.281\pm0.012 (stat) +0.058-0.056 (sys) +0.128-0.086
(Br), where the uncertainty (Br) is due to uncertainties on measured branching
ratios. The value of f_s/(f_u+f_d) agrees within one standard deviation with
previous CDF measurements and the world average of this quantity, which is
dominated by LEP measurements. However, the ratio f_{Lambda_b}/(f_u+f_d) is
approximately twice the value previously measured at LEP. The approximately 2
sigma discrepancy is examined in terms of kinematic differences between the two
production environments.Comment: Submitted to PRD, 54 pages, 53 plot
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
Search for Third Generation Vector Leptoquarks in p anti-p Collisions at sqrt(s) = 1.96 TeV
We describe a search for a third generation vector leptoquark (VLQ3) that
decays to a b quark and tau lepton using the CDF II detector and 322 pb^(-1) of
integrated luminosity from the Fermilab Tevatron. Vector leptoquarks have been
proposed in many extensions of the standard model (SM). Observing a number of
events in agreement with SM expectations, assuming Yang-Mills (minimal)
couplings, we obtain the most stringent upper limit on the VLQ3 pair production
cross section of 344 fb (493 fb) and lower limit on the VLQ3 mass of 317
GeV/c^2 (251 GeV/c^2) at 95% C.L.Comment: 7 pages, 2 figures, submitted to PR
Searches for Direct Pair Production of Supersymmetric Top and Supersymmetric Bottom Quarks in p-pbar Collisions at sqrt(s)=1.96 TeV
We search for direct pair production of supersymmetric top quarks and
supersymmetric bottom quarks in proton-antiproton collisions at sqrt(s)=1.96
TeV, using 295 pb^-1 of data recorded by the Collider Detector at Fermilab (CDF
II) experiment. The supersymmetric top (supersymmetric bottom) quarks are
selected by reconstructing their decay into a charm (bottom) quark and a
neutralino, which is assumed to be the lightest supersymmetric particle. The
signature of such processes is two energetic heavy-flavor jets and missing
transverse energy. The number of events that pass our selection for each search
process is consistent with the expected standard model background. By comparing
our results to the theoretical production cross sections of the supersymmetric
top and supersymmetric bottom quarks in the minimal supersymmetric standard
model, we exclude, at a 95% confidence level in the frame of that model, a
supersymmetric top quark mass up to 132 GeV/c^2 for a neutralino mass of 48
GeV/c^2, and a supersymmetric bottom quark mass up to 193 GeV/c^2 for a
neutralino mass of 40 GeV/c^2.Comment: 12 pages, 5 figures, submitted to Phys. Rev.
Two-Particle Momentum Correlations in Jets Produced in ppbar Collisions at s**(1/2) = 1.96-TeV
We present the first measurement of two-particle momentum correlations in
jets produced in collisions at TeV. Results are
obtained for charged particles within a restricted cone with an opening angle
of 0.5 radians around the jet axis and for events with dijet masses between 66
and 563 GeV/c. A comparison of the experimental data to theoretical
predictions obtained for partons within the framework of resummed perturbative
QCD in the next-to-leading log approximation (NLLA) shows that the parton
momentum correlations survive the hadronization stage of jet fragmentation,
giving further support to the hypothesis of local parton-hadron duality. The
extracted value of the NLLA parton shower cutoff scale set
equal to is found to be
MeV.Comment: Submitted to Phys.Rev.
Measurement of the top-quark mass using missing +jets events with secondary vertex -tagging at CDF II
We present a measurement of the top-quark mass in collisions at
\hbox{} TeV which uses events with an inclusive signature of
missing transverse energy and jets. % The event selection is sensitive to
independent of the
lepton flavor, and results in a large acceptance for decays. %
All-hadronic decays and events with identified electrons or muons are
vetoed to provide a statistically independent sample with respect to all
previous measurements. % The top-quark mass is inferred from the distribution
of the scalar sum of all jet transverse energies and the missing transverse
energy. Using 311 pb of integrated luminosity recorded by the Collider
Detector at Fermilab, we measure a top-quark mass (stat.)(syst.) GeV/. While the uncertainty on
is larger than that of other measurements, the result is statistically
uncorrelated with those of other methods, and thus can help to reduce the
overall uncertainty when combined with other existing measurements.Comment: 8 pages, 4 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
First Flavor-Tagged Determination of Bounds on Mixing-Induced CP Violation in Bs -> J/psi phi Decays
This Letter describes the first determination of bounds on the CP-violation
parameter 2*beta_s using Bs decays in which the flavor of the bottom meson at
production is identified. The result is based on approximately 2,000 Bs ->
J/psi phi decays reconstructed in a 1.35 fb-1 data sample collected with the
CDF II detector using p-bar p collisions produced at the Fermilab Tevatron. We
report confidence regions in the two-dimensional space of 2*beta_s and the
decay-width difference Delta-Gamma. Assuming the standard model predictions of
2*beta_s and Delta-Gamma, the probability of a deviation as large as the level
of the observed data is 15%, corresponding to 1.5 Gaussian standard deviations.
Dedicated to the memory of our dear friend and colleague, Michael P. Schmidt.Comment: 7 pages, 2 figures, submitted to PR
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