11 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.
Precision Measurement of the X(3872) Mass in J/psi pi+ pi- Decays
We present an analysis of the mass of the X(3872) reconstructed via its decay to J/psi pi+ pi- using 2.4 fb^-1 of integrated luminosity from ppbar collisions at sqrt(s) = 1.96 TeV, collected with the CDF II detector at the Fermilab Tevatron. The possible existence of two nearby mass states is investigated. Within the limits of our experimental resolution the data are consistent with a single state, and having no evidence for two states we set upper limits on the mass difference between two hypothetical states for different assumed ratios of contributions to the observed peak. For equal contributions, the 95% confidence level upper limit on the mass difference is 3.6 MeV/c^2. Under the single-state model the X(3872) mass is measured to be 3871.61 +- 0.16 (stat) +- 0.19 (syst) MeV/c^2, which is the most precise determination to date.We present an analysis of the mass of the X(3872) reconstructed via its decay to J/ψπ+π- using 2.4 fb-1 of integrated luminosity from pp̅ collisions at √s=1.96 TeV, collected with the CDF II detector at the Fermilab Tevatron. The possible existence of two nearby mass states is investigated. Within the limits of our experimental resolution the data are consistent with a single state, and having no evidence for two states we set upper limits on the mass difference between two hypothetical states for different assumed ratios of contributions to the observed peak. For equal contributions, the 95% confidence level upper limit on the mass difference is 3.6 MeV/c2. Under the single-state model the X(3872) mass is measured to be 3871.61±0.16(stat)±0.19(syst) MeV/c2, which is the most precise determination to date.Peer reviewe
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
Direct Bound on the Total Decay Width of the Top Quark in p(p)over-bar Collisions at root s=1.96 TeV
We present the first direct experimental bound on the total decay width
of the top quark, Gamma(t), using 955 pb(-1) of the Tevatron's p (p)
over bar collisions recorded by the Collider Detector at Fermilab. We
identify 253 top-antitop pair candidate events. The distribution of
reconstructed top quark mass from these events is fitted to templates
representing different values of the top quark width. Using a confidence
interval based on likelihood-ratio ordering, we extract an upper limit
at 95\% C.L. of Gamma(t) < 13.1 GeV for an assumed top quark mass of 175
GeV/c(2)
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
First Measurement of ZZ Production in ppbar Collisions at sqrt(s)=1.96 TeV
7 pages, 1 figure. Submitted to Phys. Rev. LettWe report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the llll channel, we observe three ZZ candidates with an expected background of 0.096^{+0.092}_{-0.063} events. In the llnunu channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of llll and llnunu channels, we observe an excess of events with a probability of to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is sigma(ppbar -> ZZ) = 1.4^{+0.7}_{-0.6} (stat.+syst.) pb, consistent with the standard model expectation
Search for Standard Model Higgs Boson Production in Association with a W Boson at CDF
35 pages, 10 figuresInternational audienceWe present a search for standard model Higgs boson production in association with a W boson in proton-antiproton collisions () at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately 1 fb-1. We select events consistent with a signature of a single lepton (), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a neural network filter technique. The observed number of events and the dijet mass distributions are consistent with the standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching ratio ranging from 3.9 to 1.3 pb for Higgs boson masses from 110 to 150 GeV/c2, respectively
Search for Standard Model Higgs Boson Production in Association with a W Boson at CDF
35 pages, 10 figuresWe present a search for standard model Higgs boson production in association with a W boson in proton-antiproton collisions () at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately 1 fb-1. We select events consistent with a signature of a single lepton (), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a neural network filter technique. The observed number of events and the dijet mass distributions are consistent with the standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching ratio ranging from 3.9 to 1.3 pb for Higgs boson masses from 110 to 150 GeV/c2, respectively
Search for Standard Model Higgs Boson Production in Association with a W Boson at CDF
35 pages, 10 figuresWe present a search for standard model Higgs boson production in association with a W boson in proton-antiproton collisions () at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately 1 fb-1. We select events consistent with a signature of a single lepton (), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a neural network filter technique. The observed number of events and the dijet mass distributions are consistent with the standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching ratio ranging from 3.9 to 1.3 pb for Higgs boson masses from 110 to 150 GeV/c2, respectively