43 research outputs found
Top Quark Mass Measurement from Dilepton Events at CDF II with the Matrix-Element Method
We describe a measurement of the top quark mass using events with two charged
leptons collected by the CDF II detector from collisions with TeV at the Fermilab Tevatron. The likelihood in top mass is
calculated for each event by convoluting the leading order matrix element
describing
with detector resolution functions. The presence of background events in the
data sample is modeled using similar calculations involving the matrix elements
for major background processes. In a data sample with integrated luminosity of
340 pb, we observe 33 candidate events and measure This
measurement represents the first application of this method to events with two
charged leptons and is the most precise single measurement of the top quark
mass in this channel.Comment: 21 pages, 14 figure
Search for New Physics in Lepton + Photon + X Events with L=305 pb-1 of ppbar Collisions at roots=1.96 TeV
We present results of a search for anomalous production of events containing
a charged lepton (either electron or muon) and a photon, both with high
transverse momentum, accompanied by additional signatures, X, including missing
transverse energy (MET) and additional leptons and photons. We use the same
kinematic selection criteria as in a previous CDF search, but with a
substantially larger data set, 305 pb-1, a ppbar collision energy of 1.96 TeV,
and the upgraded CDF II detector. We find 42 Lepton+Photon+MET events versus a
standard model expectation of 37.3 +- 5.4 events. The level of excess observed
in Run I, 16 events with an expectation of 7.6 +- 0.7 events (corresponding to
a 2.7 sigma effect), is not supported by the new data. In the signature of
Multi-Lepton+Photon+X we observe 31 events versus an expectation of 23.0 +- 2.7
events. In this sample we find no events with an extra photon or MET and so
find no events like the one ee+gg+MET event observed in Run I.Comment: 7 pages, 3 figures, 1 table. Accepted to PR
Measurement of the Ratio of Branching Fractions B(D0 -> K+ pi-)/B(D0 -> K- pi+) using the CDF II Detector
We present a measurement of R_B, the ratio of the branching fraction for the
rare decay D0 -> K+ pi- to that for the Cabibbo-favored decay D0 -> K- pi+.
Charge conjugate decays are implicitly included. A signal of 2005 +/- 104
events for the decay D0 -> K+ pi- is obtained using the CDF II detector at the
Fermilab Tevatron collider. The data set corresponds to an integrated
luminosity of 0.35 1/fb produced in p-bar/p collisions at sqrt{s}=1.96 TeV.
Assuming no mixing, we find R_B = [ 4.05 +/- 0.21 (stat) +/- 0.11 (syst) ] x
10(-3). This measurement is consistent with the world average, and comparable
in accuracy with the best measurements from other experiments.Comment: 7 pages, 3 figure
Search for Excited and Exotic Muons in the mu+gamma Decay Channel in p-pbar Collisions at sqrt{s} = 1.96 TeV
We present a search for excited and exotic muon states mu*, conducted using
an integrated luminosity of 371 pb^{-1} of data collected in p-pbar collisions
at sqrt{s} = 1.96 TeV at the Tevatron with the CDF II detector. We search for
associated production of mu+mu* followed by the decay mu* -> mu+gamma,
resulting in the mu+mu+gamma final state. We compare the data to model
predictions as a function of the mass of the excited muon M(mu*), the
compositeness energy scale Lambda, and the gauge coupling factor f. No signal
above the standard model expectation is observed in the mu+gamma mass spectrum.
In the contact interaction model, we exclude 107 < M(mu*) < 853 GeV/c^2 for
Lambda = M(mu*); in the gauge-mediated model, we exclude 100 < M(mu) < 410
GeV/c^2 for f/Lambda = 0.01/GeV. These 95% confidence level exclusions extend
previous limits and are the first hadron collider results on mu* production in
the gauge-mediated model.Comment: Submitted to Phys. Rev. Lett., 7 pages, 4 Figure
Measurement of the Top Quark Mass using Template Methods on Dilepton Events in Proton-Antiproton Collisions at sqrt(s)=1.96 TeV
We describe a measurement of the top quark mass from events produced in
proton-antiproton collisions at a center-of-mass energy of 1.96 TeV, using the
Collider Detector at Fermilab. We identify top-antitop candidates where both W
bosons from the top quarks decay into leptons (electron, muon, or tau plus
neutrino) from a data sample of 360 inverse picobarns. The top quark mass is
reconstructed in each event separately by three different methods, which draw
upon simulated distributions of the neutrino pseudorapidity, top-antitop
longitudinal momentum, or neutrino azimuthal angle in order to extract
probability distributions for the top quark mass. For each method,
representative mass distributions, or templates, are constructed from simulated
samples of signal and background events, and parameterized to form continuous
probability density functions. A likelihood fit incorporating these
parameterized templates is then performed on the data sample masses in order to
derive a final top quark mass. Combining the three template methods, taking
into account correlations in their statistical and systematic uncertainties,
results in a top quark mass measurement of 170.1 +/- 6.0 (stat) +/- 4.1 (syst)
GeV/c^2.Comment: 52 pages, 23 figures, 5 tables. Submitted to Physical Review
Search for excited and exotic muons in the mu gamma decay channel in p(p)over-bar collisions root s=1.96 TeV
We search for excited and exotic muon states mu(*) using an integrated luminosity of 371 pb(-1) of p (p) over bar collision data at root s=1.96 TeV. We search for associated production of mu mu(*) followed by the decay mu(*)-\u3emu gamma. We compare the data to model predictions as a function of the mass of the excited muon M-mu(*), the compositeness energy scale Lambda, and the gauge coupling factor f. No signal above the standard model expectation is observed. We exclude 107 \u3c M-mu(*)\u3c 853 GeV/c(2) for Lambda=M-mu(*) in the contact interaction model, and 100 \u3c M-mu(*)\u3c 410 GeV/c(2) for f/Lambda=10(-2) GeV-1 in the gauge-mediated model, both at the 95% confidence level
Observation of Bs to Psi(2S)phi and Measurement of Ratio of Branching Fractions B (Bs --> Psi(2S)phi) / B (Bs --> J/Psi phi)
We report the first observation of Bs to Psi(2S) phi signals using 360 pb^-1
of CDF Run II data sample, where Psi(2S) decays into mu+mu- and J/psi pi+pi-
modes with phi decays to K+K-. We have measured the relative branching ratio of
Br(Bs to Psi(2S)phi)/Br(Bs to J/psi phi) using J/psi, Psi(2S) to mu+mu- decay
mode. We obtain Br(Bs to Psi(2S)phi)/Br(Bs to J/psi phi) = 0.52 +- 0.13 (stat.)
+- 0.04 (syst.) +- 0.06 (BR).Comment: 14 pages, 4 figures, submitted to Phys.Rev.Let
Observation of B-s(0)-\u3e K+K- and measurements of branching fractions of charmless two-body decays of B-0 and B-s(0) mesons in pp collisions at root s=1.96 TeV
We search for decays of the type B-(s)(0)-\u3e h(+)h(\u27-) (where h,h(\u27)=K or pi) in 180 pb(-1) of (p) over barp collisions collected at the Tevatron by the upgraded Collider Detector at Fermilab. We report the first observation of the new mode B-s(0)-\u3e K+K- with a yield of 236 +/- 32 events, corresponding to (f(s)/f(d))xB(B-s(0)-\u3e K+K-)/B(B-0 -\u3e K+pi(-))=0.46 +/- 0.08(stat)+/- 0.07(syst), where f(s)/f(d) is the ratio of production fractions of B-s(0) and B-0. We find results in agreement with world averages for the B-0 modes, and set the following new limits at 90% C.L.: B(B-s(0)-\u3e K-pi(+))\u3c 5.6x10(-6) and B(B-s(0)-\u3epi(+)pi(-))\u3c 1.7x10(-6)
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Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.96 TeV
The production cross-sections of mesons in proton-proton collisions
at a centre-of-mass energy of TeV are measured using a data sample
corresponding to an integrated luminosity of ,
collected by the LHCb experiment. The cross-sections are measured
differentially as a function of transverse momentum, , and
rapidity, , and separately for mesons produced promptly and from
beauty hadron decays (nonprompt). With the assumption of unpolarised
mesons, the production cross-sections integrated over the kinematic range
and are
for prompt mesons and
for nonprompt mesons, where the
first uncertainties are statistical and the second systematic. These
cross-sections are compared with those at TeV and TeV, and
are used to update the measurement of the nuclear modification factor in
proton-lead collisions for mesons at a centre-of-mass energy per
nucleon pair of TeV. The results are compared with
theoretical predictions