21 research outputs found
Measurement of the fraction of t-tbar production via gluon-gluon fusion in p-pbar collisions at sqrt(s)=1.96 TeV
We present a measurement of the ratio of t-tbar production cross section via
gluon-gluon fusion to the total t-tbar production cross section in p-pbar
collisions at sqrt{s}=1.96 TeV at the Tevatron. Using a data sample with an
integrated luminosity of 955/pb recorded by the CDF II detector at Fermilab, we
select events based on the t-tbar decay to lepton+jets. Using an artificial
neural network technique we discriminate between t-tbar events produced via
q-qbar annihilation and gluon-gluon fusion, and find
Cf=(gg->ttbar)/(pp->ttbar)<0.33 at the 68% confidence level. This result is
combined with a previous measurement to obtain the most precise measurement of
this quantity, Cf=0.07+0.15-0.07.Comment: submitted to Phys. Rev.
Measurement of Resonance Parameters of Orbitally Excited Narrow B^0 Mesons
We report a measurement of resonance parameters of the orbitally excited
(L=1) narrow B^0 mesons in decays to B^{(*)+}\pi^- using 1.7/fb of data
collected by the CDF II detector at the Fermilab Tevatron. The mass and width
of the B^{*0}_2 state are measured to be m(B^{*0}_2) =
5740.2^{+1.7}_{-1.8}(stat.) ^{+0.9}_{-0.8}(syst.) MeV/c^2 and \Gamma(B^{*0}_2)
= 22.7^{+3.8}_{-3.2}(stat.) ^{+3.2}_{-10.2}(syst.) MeV/c^2. The mass difference
between the B^{*0}_2 and B^0_1 states is measured to be
14.9^{+2.2}_{-2.5}(stat.) ^{+1.2}_{-1.4}(syst.) MeV/c^2, resulting in a B^0_1
mass of 5725.3^{+1.6}_{-2.2}(stat.) ^{+1.4}_{-1.5}(syst.) MeV/c^2. This is
currently the most precise measurement of the masses of these states and the
first measurement of the B^{*0}_2 width.Comment: 7 pages, 1 figure, 1 table. Submitted to Phys.Rev.Let
Search for a Higgs Boson Decaying to Two W Bosons at CDF
We present a search for a Higgs boson decaying to two W bosons in ppbar collisions at sqrt(s)=1.96 TeV center-of-mass energy. The data sample corresponds to an integrated luminosity of 3.0 fb-1 collected with the CDF II detector. We find no evidence for production of a Higgs boson with mass between 110 and 200 GeV/c^2, and determine upper limits on the production cross section. For the mass of 160 GeV/c^2, where the analysis is most sensitive, the observed (expected) limit is 0.7 pb (0.9 pb) at 95% Bayesian credibility level which is 1.7 (2.2) times the standard model cross section
Inclusive Search for Squark and Gluino Production in ppbar Collisions at sqrt{s} = 1.96 TeV
We report on a search for inclusive production of squarks and gluinos in
ppbar collisions at sqrt{s}=1.96 TeV, in events with large missing transverse
energy and multiple jets of hadrons in the final state. The study uses a CDF
Run II data sample corresponding to 2 fb-1 of integrated luminosity. The data
are in good agreement with the standard model predictions, giving no evidence
for any squark or gluino component. In an R-parity conserving minimal
supergravity scenario with A_0 = 0, mu < 0 and tanbeta = 5, 95% C.L. upper
limits on the production cross sections in the range between 0.1 pb and 1 pb
are obtained, depending on the squark and gluino masses considered. For gluino
masses below 280 GeV/c2, arbitrarily large squark masses are excluded at the
95%C.L., while for mass degenerate gluinos and squarks, masses below 392 GeV/c2
are excluded at the 95% C.L.Comment: Paper submitted to Phys. Rev. Letter
Polarizations of J/psi and psi(2S) Mesons Produced in ppbar Collisions at 1.96 TeV
We have measured the polarizations of \jpsi and \psiprime mesons as
functions of their transverse momentum \pt when they are produced promptly in
the rapidity range with \pt \geq 5 \pgev. The analysis is performed
using a data sample with an integrated luminosity of about 800 \ipb collected
by the CDF II detector. For both vector mesons, we find that the polarizations
become increasingly longitudinal as \pt increases from 5 to 30 \pgev. These
results are compared to the predictions of nonrelativistic quantum
chromodynamics and other contemporary models. The effective polarizations of
\jpsi and \psiprime mesons from -hadron decays are also reported.Comment: 8 pages, 7 figures, published in Physical Review Letter
Measurement of the top quark mass with dilepton events selected using neuroevolution at CDF
Revised version as published in Phys. Rev. LettWe report a measurement of the top quark mass in the dilepton decay channel . Events are selected with a neural network which has been directly optimized for statistical precision in top quark mass using neuroevolution, a technique modeled on biological evolution. The top quark mass is extracted from per-event probability densities that are formed by the convolution of leading order matrix elements and detector resolution functions. The joint probability is the product of the probability densities from 344 candidate events in 2.0 fb of collisions collected with the CDF II detector, yielding a measurement of .We report a measurement of the top-quark mass Mt in the dilepton decay channel tt̅ →bl′+νl′b̅ l-ν̅ l. Events are selected with a neural network which has been directly optimized for statistical precision in top-quark mass using neuroevolution, a technique modeled on biological evolution. The top-quark mass is extracted from per-event probability densities that are formed by the convolution of leading order matrix elements and detector resolution functions. The joint probability is the product of the probability densities from 344 candidate events in 2.0 fb-1 of pp̅ collisions collected with the CDF II detector, yielding a measurement of Mt=171.2±2.7(stat)±2.9(syst) GeV/c2.Peer reviewe
Measurement of the t(t)over-bar production cross section in the all-jet final state in pp collisions at √s=7 TeV
This article is the pre-print version of the final published paper that is available from the link below.A measurement is presented of the tt production cross section (σtt) in protonproton collisions at a centre-of-mass energy of 7TeV, in the all-jet final state that contains at least six jets, two of which are tagged as originating from b quarks. The data correspond to an integrated luminosity of 3.54 fb-1, collected with the CMS detector at the LHC. The cross section is determined through an unbinned maximum likelihood fit of background and tt signal to the reconstructed mass spectrum of tt candidates in the data, in which events are subjected to a kinematic fit assuming a tt → W+bW-b → 6 jets hypothesis. The measurement yields σtt = 139±10 (stat.) ±26 (syst.) ±3 (lum.) pb, a result consistent with those obtained in other tt decay channels, as well as with predictions of the standard model
Search for High-Mass \boldmath Resonances in \boldmath Collisions at \boldmath1.96 TeV
A search for high-mass resonances in the final state is presented based on 2.5 fb of 1.96 TeV collision data from the CDF II detector at the Fermilab Tevatron. The largest excess over the standard model prediction is at an invariant mass of 240 GeV/. The probability of observing such an excess arising from fluctuations in the standard model anywhere in the mass range of 150--1,000 GeV/ is 0.6% (equivalent to 2.5 ). We exclude the standard model coupling and the Randall-Sundrum graviton for with masses below 963 and 848 GeV/ at the 95% credibility level, respectively.A search for high-mass resonances in the e+e- final state is presented based on 2.5 fb-1 of √s=1.96 TeV pp̅ collision data from the CDF II detector at the Fermilab Tevatron. The largest excess over the standard model prediction is at an e+e- invariant mass of 240 GeV/c2. The probability of observing such an excess arising from fluctuations in the standard model anywhere in the mass range of 150–1000 GeV/c2 is 0.6% (equivalent to 2.5σ). We exclude the standard model coupling Z′ and the Randall-Sundrum graviton for k/M̅ Pl=0.1 with masses below 963 and 848 GeV/c2 at the 95% credibility level, respectively.Peer reviewe
Search for Supersymmetry in p (p)over-bar Collisions at root s=1.96 TeV Using the Trilepton Signature for Chargino-Neutralino Production
We use the three lepton and missing energy trilepton signature to search
for chargino-neutralino production with 2.0 fb(-1) of integrated
luminosity collected by the CDF II experiment at the Tevatron p (p) over
bar collider. We expect an excess of approximately 11 supersymmetric
events for a choice of parameters of the mSUGRA model, but our
observation of 7 events is consistent with the standard model
expectation of 6.4 events. We constrain the mSUGRA model of
supersymmetry and rule out chargino masses up to 145 GeV/c(2) for a
specific choice of parameters