ABSTRACT
We report on a search for the standard model Higgs boson decaying into pairs of τ leptons in pp collisions produced by the Tevatron at sqrt[s]=1.96 TeV. The analyzed data sample was recorded by the CDFII detector and corresponds to an integrated luminosity of 6.0 fb(-1). The search is performed in the final state with one τ decaying leptonically and the second one identified through its semihadronic decay. Since no significant excess is observed, a 95% credibility level upper limit on the production cross section times branching ratio to the ττ final state is set for hypothetical Higgs boson masses between 100 and 150 GeV/c2. For a Higgs boson of 120 GeV/c2 the observed (expected) limit is 14.6 (15.3) the predicted value.
ABSTRACT
We report an indirect search for nonstandard model physics using the flavor-changing neutral current decays BâK(*)µ(+)µ(-). We reconstruct the decays and measure their angular distributions, as a function of q(2)=M(µµ)(2)c(2), where M(µµ) is the dimuon mass, in pp¯ collisions at âs=1.96 TeV using a data sample corresponding to an integrated luminosity of 6.8 fb(-1). The transverse polarization asymmetry A(T)(2) and the time-reversal-odd charge-and-parity asymmetry A(im) are measured for the first time, together with the K* longitudinal polarization fraction F(L) and the muon forward-backward asymmetry A(FB) for the decays B(0)âK(*0)µ(+)µ(-) and B(+)âK(*+)µ(+)µ(-). The BâK*µ(+)µ(-) forward-backward asymmetry in the most sensitive kinematic regime, 1≤q(2)<6 GeV(2)/c(2), is measured to be A(FB)=0.29(-0.23)(+0.20)(stat)±0.07(syst), the most precise result to date. No deviations from the standard model predictions are observed.
ABSTRACT
A search for a narrow Higgs boson resonance in the diphoton mass spectrum is presented based on data corresponding to 7.0 fb{-1} of integrated luminosity from pp collisions at sqrt[s]=1.96 TeV collected by the CDF experiment. No evidence of such a resonance is observed, and upper limits are set on the cross section times branching ratio of the resonant state as a function of Higgs boson mass. The limits are interpreted in the context of the standard model and one fermiophobic benchmark model where the data exclude fermiophobic Higgs bosons with masses below 114 GeV/c{2} at a 95% Bayesian credibility level.
ABSTRACT
A search has been performed for B(s)(0) â µ+ µ- and B(0) â µ+ µ- decays using 7 fb(-1) of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. The observed number of B(0) candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of B(B(0) â µ+ µ-) < 6.0 × 10(-9) at 95% confidence level. We observe an excess of B(s)(0) candidates. The probability that the background processes alone could produce such an excess or larger is 0.27%. The probability that the combination of background and the expected standard model rate of B(s)(0) â µ+ µ- could produce such an excess or larger is 1.9%. These data are used to determine B(B(s)(0)â µ+ µ-) = (1.8(-0.9) (+1.1)) × 10(-8) and provide an upper limit of B(B(s)(0) â µ+ µ-) < 4.0 × 10(-8) at 95% confidence level.
ABSTRACT
We present a search for a new particle T' decaying to a top quark via T' â t + X, where X goes undetected. We use a data sample corresponding to 5.7 fb(-1) of integrated luminosity of p p collisions with sqrt[s] = 1.96 TeV, collected at Fermilab Tevatron by the CDF II detector. Our search for pair production of T' is focused on the hadronic decay channel, pp â T'T' â tt + XX â bqq b qq + XX. We interpret our results in terms of a model where T' is an exotic fourth generation quark and X is a dark matter particle. The data are consistent with standard model expectations. We set a limit on the generic production of T'T' â tt + XX, excluding the fourth generation exotic quarks T' at 95% confidence level up to m(T') = 400 GeV/c(2) for m(X) ≤ 70 GeV/c(2).
ABSTRACT
We report the first observation of the baryonic flavor-changing neutral current decay Λ(b)(0)âΛµ(+)µ(-) with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses a pp collisions data sample corresponding to 6.8 fb(-1) at âs = 1.96 TeV collected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for Λ(b)(0)âΛµ(+)µ(-) are measured. We find B(Λ(b)(0)âΛµ(+)µ(-))=[1.73 ± 0.42(stat) ± (syst)] × 10(-6). We also report the first measurement of the differential branching ratio of B(s)(0)âϵ(+)µ(-), using 49 signal events. In addition, we report branching ratios for B(+)âK(+)µ(+)µ(-), B(0)âK(0)µ(+)µ(-), and BâK(*)(892)µ(+)µ(-) decays.
ABSTRACT
We present a measurement of the top-quark mass using a sample of t Ìt events in 5.7 fb(-1) of integrated luminosity from p Ìp collisions at the Fermilab Tevatron with âs=1.96 TeV and collected by the CDF II Detector. We select events having large missing transverse energy, and four, five, or six jets with at least one jet tagged as coming from a b quark, and reject events with identified charged leptons. This analysis considers events from the semileptonic t Ìt decay channel, including events that contain tau leptons. The measurement is based on a multidimensional template method. We fit the data to signal templates of varying top-quark masses and background templates, and measure a top-quark mass of M(top)=172.32±2.4(stat)±1.0(syst) GeV/c(2).
ABSTRACT
We present a search for new physics in events with two high pT leptons of the same electric charge, using data with an integrated luminosity of 6.1 fb(-1). The observed data are consistent with standard model predictions. We set 95% C.L. lower limits on the mass of doubly charged scalars decaying to like-sign dileptons, m(H±±) > 190-245 GeV/c(2), assuming 100% BR to ee, µµ or eµ.
Subject(s)
Elementary Particles , Physics/instrumentation , Models, Theoretical , UncertaintyABSTRACT
The observation of the bottom, strange baryon Ξ(b)(0) through the decay chain Ξ(b)(0)âΞ(c)(+)π-, where ΞΞ(c)(+)âΞ- π+ π+, Ξ-âΛπ-, and Λâpπ-, is reported by using data corresponding to an integrated luminosity of 4.2 fb(-1) from pp collisions at square root(s)=1.96 TeV recorded with the Collider Detector at Fermilab. A signal of 25.3(-5.4)(+5.6) candidates is observed whose probability of arising from a background fluctuation is 3.6×10(-12), corresponding to 6.8 gaussian standard deviations. The Ξ(b)(0) mass is measured to be 5787.8±5.0(stat)±1.3(syst) MeV/c2. In addition, the Ξ(b)- baryon is observed through the process Ξ(b)-âΞ(c)(0)π-, where Ξ(c)(0)âΞ- π+, Ξ-âΛπ-, and Λâpπ-.
ABSTRACT
This Letter reports a measurement of the cross section of prompt isolated photon pair production in pp collisions at a total energy square root(s)=1.96 TeV using data of 5.36 fb(-1) integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. The measured cross section, differential in basic kinematic variables, is compared with three perturbative QCD predictions, a leading order parton shower calculation and two next-to-leading order calculations. The next-to-leading order calculations reproduce most aspects of the data. By including photon radiation from quarks before and after hard scattering, the parton shower prediction becomes competitive with the next-to-leading order predictions.
ABSTRACT
We present the results of a search for a very light CP-odd Higgs boson a(1)(0) originating from top quark decays t â H(±)b â W(±(*)) a(1)(0)b, and subsequently decaying into τ+ τ-. Using a data sample corresponding to an integrated luminosity of 2.7 fb(-1) collected by the CDF II detector in pp collisions at 1.96 TeV, we perform a search for events containing a lepton, three or more jets, and an additional isolated track with transverse momentum in the range 3 to 20 GeV/c. Observed events are consistent with background sources, and 95% C.L. limits are set on the branching ratio of t â H(±)b for various masses of H(±) and a(1)(0).
ABSTRACT
We present the first model independent search for three-jet hadronic resonances within multijet events in sqrt(s) = 1.96 TeV pp collisions at the Fermilab Tevatron using the CDF II detector. Pair production of supersymmetric gluinos and squarks with hadronic R-parity violating decays is employed as an example of a new physics benchmark for this signature. Selection criteria based on the kinematic properties of an ensemble of jet combinations within each event help to extract signal from copious QCD background. No significant excess outside the top quark mass window is observed in data with an integrated luminosity of 3.2 fb(-1). We place 95% confidence level limits on the production cross section σ(pp â XX')×BR(gg â 3 jet + 3 jet) where X, X' = g, q, or q, with q, q â g + jet, as a function of gluino mass, in the range of 77 GeV/c2 to 240 GeV/c2.
ABSTRACT
Using Zγ candidate events collected by the CDF detector at the Tevatron Collider, we search for potential anomalous (non-standard-model) couplings between the Z boson and the photon. Zγ couplings vanish at tree level and are heavily suppressed at higher orders; hence any evidence of couplings indicates new physics. Measurements are performed using data corresponding to an integrated luminosity of 4.9 fb(-1) in the Zâνν¯ decay channel and 5.1 fb(-1) in the Zâl(+)l(-) (l=µ, e) decay channels. The combination of these measurements provides the most stringent limits to date on Zγ trilinear gauge couplings. Using an energy scale of Λ=1.5 TeV to allow for a direct comparison with previous measurements, we find limits on the CP-conserving parameters that describe Zγ couplings to be |h(3)(γ,Z)|<0.022 and |h(4)(γ,Z)|<0.0009. These results are consistent with standard model predictions.
ABSTRACT
A search for new dielectron-mass resonances using data recorded by the CDF II detector and corresponding to an integrated luminosity of 5.7 fb(-1) is presented. No significant excess over the expected standard model prediction is observed. In this data set, an event with the highest dielectron mass ever observed (960 GeV/c(2)) was recorded. The results are interpreted in the Randall-Sundrum (RS) model. Combined with the 5.4 fb(-1) diphoton analysis, the RS-graviton lower-mass limit for the coupling k/M¯(Pl)=0.1 is 1058 GeV/c(2), making it the strongest limit to date.
ABSTRACT
We report on the first measurement of the angular distributions of final state electrons in pp¯ â γ*/Z â e(+)e(-) + X events produced in the Z boson mass region at âs1.96 TeV. The data sample collected by the CDF II detector for this result corresponds to 2.1 fb(-1) of integrated luminosity. The angular distributions are studied as a function of the transverse momentum of the electron-positron pair and show good agreement with the Lam-Tung relation, consistent with a spin-1 description of the gluon, and demonstrate that, at high values of the transverse momentum, Z bosons are produced via quark-antiquark annihilation and quark-gluon Compton processes.
ABSTRACT
We report a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb(-1). The observed distribution has an excess in the 120-160 GeV/c(2) mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In this Letter, we report studies of the properties of this excess.
ABSTRACT
We report measurements of direct CP-violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using a data sample corresponding to 1 fb(-1) of integrated luminosity, we obtain the first measurements of direct CP violation in bottom strange mesons, A(CP)(B(s)(0)âK(-)π(+))=+0.39±0.15(stat)±0.08(syst), and bottom baryons, A(CP)(Λ(b)(0)âpπ(-))=+0.03±0.17(stat)±0.05(syst) and A(CP)(Λ(b)(0)âpK(-))=+0.37±0.17(stat)±0.03(syst). In addition, we measure CP violation in B(0)âK(+)π(-) decays with 3.5σ significance, A(CP)(B(0)âK(+)π(-))=-0.086±0.023(stat)±0.009(syst), in agreement with the current world average. Measurements of branching fractions of B(s)(0)âK(+)K(-) and B(0)âπ(+)π(-) decays are also updated.
ABSTRACT
We present a search for a new particle T' decaying to top quark via T' â t + X, where X is an invisible particle. In a data sample with 4.8 fb(-1) of integrated luminosity collected by the CDF II detector at Fermilab in pp collisions with âs = 1.96 TeV, we search for pair production of T' in the lepton + jets channel, pp â tt + X + X â âνbqq'b + X + X. We interpret our results primarily in terms of a model where T' are exotic fourth generation quarks and X are dark matter particles. Current direct and indirect bounds on such exotic quarks restrict their masses to be between 300 and 600 GeV/c2, the dark matter particle mass being anywhere below m(T'). The data are consistent with standard model expectations, and we set 95% confidence level limits on the generic production of T'T' â tt + X + X. For the dark matter model we exclude T' at 95% confidence level up to m(T') = 360 GeV/c2 for m(X) ≤ 100 GeV/c2.
ABSTRACT
We reconstruct the rare decays B(+)âK(+)µ(+0µ(-0, B90)âK*(892)(0)µ(+)µ(-), and B(s)(0)âÏ(1020)µ(+)µ(-) in a data sample corresponding to 4.4 fb(-1) collected in pp collisions at â[s]=1.96 TeV by the CDF II detector at the Tevatron Collider. Using 121±16 B(+)âK(+)µ(+)µ(-) and 101±12 B(0)âK(*0)µ(+)µ(-) decays we report the branching ratios. In addition, we report the differential branching ratio and the muon forward-backward asymmetry in the B(+) and B(0) decay modes, and the K(*0) longitudinal polarization fraction in the B(0) decay mode with respect to the squared dimuon mass. These are consistent with the predictions, and most recent determinations from other experiments and of comparable accuracy. We also report the first observation of the B(s)(0)âϵ(+)µ(-) decay and measure its branching ratio BR(B(s)(0)âϵ(+)µ(-))=[1.44±0.33±0.46]×10(-6) using 27±6 signal events. This is currently the most rare B(s)(0) decay observed.
ABSTRACT
We present a direct measurement of the mass difference between t and t quarks using tt candidate events in the lepton+jets channel, collected with the CDF II detector at Fermilab's 1.96 TeV Tevatron pp Collider. We make an event by event estimate of the mass difference to construct templates for top quark pair signal events and background events. The resulting mass difference distribution of data is compared to templates of signals and background using a maximum likelihood fit. From a sample corresponding to an integrated luminosity of 5.6 fb(-1), we measure a mass difference, ΔM(top) = M(t) - M(t) = -3.3 ± 1.4(stat) ± 1.0(syst) GeV/c2, approximately 2 standard deviations away from the CPT hypothesis of zero mass difference.