1,591 research outputs found
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
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
Precision Top-Quark Mass Measurements at CDF
We present a precision measurement of the top-quark mass using the full
sample of Tevatron TeV proton-antiproton collisions collected
by the CDF II detector, corresponding to an integrated luminosity of 8.7
. Using a sample of candidate events decaying into the
lepton+jets channel, we obtain distributions of the top-quark masses and the
invariant mass of two jets from the boson decays from data. We then compare
these distributions to templates derived from signal and background samples to
extract the top-quark mass and the energy scale of the calorimeter jets with
{\it in situ} calibration. The likelihood fit of the templates from signal and
background events to the data yields the single most-precise measurement of the
top-quark mass, \mtop = 172.85 \pm\pmComment: submitted to Phys. Rev. Let
Observation of Hadronic W Decays in t-tbar Events with the Collider Detector at Fermilab
We observe hadronic W decays in t-tbar -> W (-> l nu) + >= 4 jet events using
a 109 pb-1 data sample of p-pbar collisions at sqrt{s} = 1.8 TeV collected with
the Collider Detector at Fermilab (CDF). A peak in the dijet invariant mass
distribution is obtained that is consistent with W decay and inconsistent with
the background prediction by 3.3 standard deviations. From this peak we measure
the W mass to be 77.2 +- 4.6 (stat+syst) GeV/c^2. This result demonstrates the
presence of two W bosons in t-tbar candidates in the W (-> l nu) + >= 4 jet
channel.Comment: 20 pages, 4 figures, submitted to PR
Observation of the moon shadow using a new reconstruction technique in the CLUE experiment
The CLUE experiment, located in La Palma island at 2200 m a.s.l., is an array of 3×3 telescope, detecting the UV
(190–230 nm) ˇCerenkov light produced by atmospheric showers. Due to the higher atmospheric absorption in the UV range than in the visible one, CLUE cannot apply existing algorithms normally used in IACT experiments to determine primary cosmic ray direction. In this paper we present a new method developed by CLUE. The algorithm performances were evaluated using simulated showers. CLUE experiment collected data in the last two years pointing to AGN sources and to Moon. The preliminary results obtained using the new technique on Crab Nebula and on Markarian 421 were presented in a previous paper. Here, we present the preliminary observation of Moon Shadow employing the new method. As described in the paper, we expect in a near future improvements on AGN sources and on Moon Shadow measurement
Search for Chargino-Neutralino Associated Production at the Fermilab Tevatron Collider
We have searched in collisions at = 1.8 TeV for events
with three charged leptons and missing transverse energy. In the Minimal
Supersymmetric Standard Model, we expect trilepton events from
chargino-neutralino (\chione \chitwo) pair production, with subsequent decay
into leptons. We observe no candidate , ,
or events in 106 pb integrated
luminosity. We present limits on the sum of the branching ratios times cross
section for the four channels: \sigma_{\chione\chitwo}\cdot
BR(\chione\chitwo\to 3\ell+X) 81.5 \mgev\sp and
M_\chitwo > 82.2 \mgev\sp for , ~\mgev\sp and
M_\squark= M_\gluino.Comment: 9 pages and 3 figure
Measurement of the top quark mass and top-antitop production cross section from dilepton events at the Collider Detector at Fermilab
We present an analysis of dilepton events originating from top-antitop
production in proton-antiproton collisions at sqrt{s}=1.8 TeV at the Fermilab
Tevatron Collider. The sample corresponds to an integrated luminosity of 109+-7
pb^{-1}. We observe 9 candidate events, with an estimated background of
2.4+-0.5 events. We determine the mass of the top quark to be M_top =
161+-17(stat.)+-10(syst.) GeV/c^2. In addition we measure a top-antitop
production cross section of 8.2+4.4-3.4 pb (where M_top = 175 GeV/c^2 has been
assumed for the acceptance estimate).Comment: 6 pages of text, 3 figure
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 branching ratio and Bs0 lifetime in the decay Bs0 -> J/psi f0(980) at CDF
We present a study of Bs0 decays to the CP-odd final state J/psi f0(980) with
J/psi -> mu+ mu- and f0(980) -> pi+ pi-. Using ppbar collision data with an
integrated luminosity of 3.8/fb collected by the CDF II detector at the
Tevatron we measure a Bs0 lifetime of tau(Bs0 -> J/psi f0(980)) = 1.70
-0.11+0.12(stat) +-0.03(syst) ps. This is the first measurement of the Bs0
lifetime in a decay to a CP eigenstate and corresponds in the standard model to
the lifetime of the heavy Bs0 eigenstate. We also measure the product of
branching fractions of Bs0 -> J/psi f0(980) and f0(980) -> pi+ pi- relative to
the product of branching fractions of Bs0 -> J/psi phi and phi -> K+ K- to be
R_f0/phi = 0.257 +_0.020(stat) +-0.014(syst), which is the most precise
determination of this quantity to date.Comment: accepted by Phys. Rev.
- …