238 research outputs found
Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at sqrt(s_nn) = 130 GeV
The minimum bias multiplicity distribution and the transverse momentum and
pseudorapidity distributions for central collisions have been measured for
negative hadrons (h-) in Au+Au interactions at sqrt(s_nn) = 130 GeV. The
multiplicity density at midrapidity for the 5% most central interactions is
dNh-/deta|_{eta = 0} = 280 +- 1(stat)+- 20(syst), an increase per participant
of 38% relative to ppbar collisions at the same energy. The mean transverse
momentum is 0.508 +- 0.012 GeV/c and is larger than in central Pb+Pb collisions
at lower energies. The scaling of the h- yield per participant is a strong
function of pt. The pseudorapidity distribution is almost constant within
|eta|<1.Comment: 6 pages, 3 figure
Measurement of the Lifetime Difference Between B_s Mass Eigenstates
We present measurements of the lifetimes and polarization amplitudes for B_s
--> J/psi phi and B_d --> J/psi K*0 decays. Lifetimes of the heavy (H) and
light (L) mass eigenstates in the B_s system are separately measured for the
first time by determining the relative contributions of amplitudes with
definite CP as a function of the decay time. Using 203 +/- 15 B_s decays, we
obtain tau_L = (1.05 +{0.16}/-{0.13} +/- 0.02) ps and tau_H = (2.07
+{0.58}/-{0.46} +/- 0.03) ps. Expressed in terms of the difference DeltaGamma_s
and average Gamma_s, of the decay rates of the two eigenstates, the results are
DeltaGamma_s/Gamma_s = (65 +{25}/-{33} +/- 1)%, and DeltaGamma_s = (0.47
+{0.19}/-{0.24} +/- 0.01) inverse ps.Comment: 8 pages, 3 figures, 2 tables; as published in Physical Review Letters
on 16 March 2005; revisions are for length and typesetting only, no changes
in results or conclusion
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
Measurement of and Production in Collisions at = 1.96 TeV
The Standard Model predictions for and production are
tested using an integrated luminosity of 200 pb of \ppbar collision data
collected at the Collider Detector at Fermilab. The cross sections are measured
selecting leptonic decays of the and bosons, and photons with
transverse energy GeV that are well separated from leptons. The
production cross sections and kinematic distributions for the and
are compared to SM predictions.Comment: 7 pages, 4 figures, submitted to PR
Measurement of B(t->Wb)/B(t->Wq) at the Collider Detector at Fermilab
We present a measurement of the ratio of top-quark branching fractions R= B(t
-> Wb)/B(t -> Wq), where q can be a b, s or a d quark, using lepton-plus-jets
and dilepton data sets with integrated luminosity of ~162 pb^{-1} collected
with the Collider Detector at Fermilab during Run II of the Tevatron. The
measurement is derived from the relative numbers of t-tbar events with
different multiplicity of identified secondary vertices. We set a lower limit
of R > 0.61 at 95% confidence level.Comment: 7 pages, 2 figures, published in Physical Review Letters; changes
made to be consistent with published versio
Search for ZZ and ZW Production in ppbar Collisions at sqrt(s) = 1.96 TeV
We present a search for ZZ and ZW vector boson pair production in ppbar
collisions at sqrt(s) = 1.96 TeV using the leptonic decay channels ZZ --> ll nu
nu, ZZ --> l l l' l' and ZW --> l l l' nu. In a data sample corresponding to an
integrated luminosity of 194 pb-1 collected with the Collider Detector at
Fermilab, 3 candidate events are found with an expected background of 1.0 +/-
0.2 events. We set a 95% confidence level upper limit of 15.2 pb on the cross
section for ZZ plus ZW production, compared to the standard model prediction of
5.0 +/- 0.4 pb.Comment: 7 pages, 2 figures. This version is accepted for publication by Phys.
Rev. D Rapid Communication
Measurement of the Cross Section for Prompt Diphoton Production in p-pbar Collisions at sqrt(s) = 1.96 TeV
We report a measurement of the rate of prompt diphoton production in
collisions at using a data sample of 207
pb collected with the upgraded Collider Detector at Fermilab (CDF II).
The background from non-prompt sources is determined using a statistical method
based on differences in the electromagnetic showers. The cross section is
measured as a function of the diphoton mass, the transverse momentum of the
diphoton system, and the azimuthal angle between the two photons and is found
to be consistent with perturbative QCD predictions.Comment: 7 pages, 3 figures,revtex4. Version accepted by PRL, but with cross
section tables i
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s}=1.96 TeV using Lepton + Jets Events with Secondary Vertex b-tagging
We present a measurement of the ttbar production cross section using events
with one charged lepton and jets from ppbar collisions at a center-of-mass
energy of 1.96 TeV. In these events, heavy flavor quarks from top quark decay
are identified with a secondary vertex tagging algorithm. From 162 pb-1 of data
collected by the Collider Detector at Fermilab, a total of 48 candidate events
are selected, where 13.5 +- 1.8 events are expected from background
contributions. We measure a ttbar production cross section of 5.6^{+1.2}_{-1.1}
(stat.) ^{+0.9}_{0.6} (syst.) pb.Comment: 28 pages, 20 figures. Published in Physical Review
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
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