Study of sequential semileptonic decays of b hadrons produced at the Tevatron

We present a study of rates and kinematical properties of lepton pairs contained in central jets with transverse energy E_T > 15 GeV that are produced at the Fermilab Tevatron collider. We compare the data to a QCD prediction based on the HERWIG and QQ Monte Carlo generator programs.We find that the data are poorly described by the simulation, in which sequential semileptonic decays of single b quarks (b --> l c X with c --> l s X) are the major source of such lepton pairs.Comment: 25 pages, 8 figures. Some typos were fixed in the text and bibliography. Submitted to Phys. Rev.

Phenomenological study of the atypical heavy flavor production observed at the Fermilab Tevatron

We address known discrepancies between the heavy flavor properties of jets produced at the Tevatron collider and the prediction of conventional-QCD simulations. In this study, we entertain the possibility that these effects are real and due to new physics. We show that all anomalies can be simultaneously fitted by postulating the additional pair production of light bottom squarks with a 100% semileptonic branching fraction.Comment: 30 pages, 13 figures, 3 tables. Submitted to Phys. Rev.

Search for narrow resonances below the Upsilon mesons

We have investigated the invariant mass spectrum of dimuons collected by the CDF experiment during the 1992-1995 run of the Fermilab Tevatron collider to improve the limit on the existence of narrow resonances set by the experiments at the SPEAR e+e- collider. In the mass range 6.3-9.0 GeV/c^2, we derive 90% upper credible limits to the ratio of the production cross section times muonic branching fraction of possible narrow resonances to that of the Y(1S) meson. In this mass range, the average limit varies from 1.7 to 0.5%. This limit is much worse at the mass of 7.2 GeV/c^2 due to an excess of 250+-61 events with a width consistent with the detector resolution.Comment: 20 pages, 9 figures. This version has some typos fixed in the text and bibliography. A reference was added in bibliography. Submitted to Phys. Rev. D With this last submission we provide the version accepted for publication in Phys.Rev.

Heavy Flavours in Collider Experiments

Current issues in the studies of Heavy Flavours in colliders are described with particular emphasis on experiments in which the UK is involved. Results on charm production at HERA are examined and compared to those at the Tevatron. B production rates at the Tevatron as well as the status of B lifetimes and mixing in the LEP collaborations and at the Tevatron are highlighted. The measurement of sin2beta from CDF is described as well as the most recent results on top physics at the Tevatron

Determination of the Jet Energy Scale at the Collider Detector at Fermilab

A precise determination of the energy scale of jets at the Collider Detector at Fermilab at the Tevatron $p\bar{p}$ collider is described. Jets are used in many analyses to estimate the energies of partons resulting from the underlying physics process. Several correction factors are developed to estimate the original parton energy from the observed jet energy in the calorimeter. The jet energy response is compared between data and Monte Carlo simulation for various physics processes, and systematic uncertainties on the jet energy scale are determined. For jets with transverse momenta above 50 GeV the jet energy scale is determined with a 3% systematic uncertainty

Measurement of J/Psi and Psi(2S) Polarization in ppbar Collisions at sqrt(s) = 1.8 TeV

We have measured the polarization of J/Psi and Psi(2S) mesons produced in p\bar{p} collisions at \sqrt{s} = 1.8 TeV, using data collected at CDF during 1992-95. The polarization of promptly produced J/Psi [Psi(2S)] mesons is isolated from those produced in B-hadron decay, and measured over the kinematic range 4[5.5] < P_T < 20 GeV/c and |y| < 0.6. For P_T \gessim 12 GeV/c we do not observe significant polarization in the prompt component.Comment: Revised version, accepted for publication in Physical Review Letter

Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV

We present results of searches for diphoton resonances produced both inclusively and also in association with a vector boson (W or Z) using 100 pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on the product of cross section times branching ratio for both p\bar p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive production to the expectations from heavy sgoldstinos we derive limits on the supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the sgoldstino mass and the choice of other parameters. Also, using a NLO prediction for the associated production of a Higgs boson with a W or Z boson, we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82 GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure

Search for the Supersymmetric Partner of the Top-Quark in ppˉp \bar{p} Collisions at s=1.8TeV\sqrt{s} = 1.8 {\rm TeV}

We report on a search for the supersymmetric partner of the top quark (stop) produced in $t \bar{t}$ events using $110 {\rm pb}^{-1}$ of $p \bar{p}$ collisions at $\sqrt{s} = 1.8 {\rm TeV}$ recorded with the Collider Detector at Fermilab. In the case of a light stop squark, the decay of the top quark into stop plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with Standard Model $t \bar{t}$ production and decay. Hence, we set limits on the branching ratio of the top quark decaying into stop plus LSP, excluding branching ratios above 45% for a LSP mass up to 40 {\rm GeV/c}$^{2}$.Comment: 11 pages, 4 figure

Measurement of the Strong Coupling Constant from Inclusive Jet Production at the Tevatron pˉp\bar pp Collider

We report a measurement of the strong coupling constant, $\alpha_s(M_Z)$, extracted from inclusive jet production in $p\bar{p}$ collisions at $\sqrt{s}=$1800 GeV. The QCD prediction for the evolution of $\alpha_s$ with jet transverse energy $E_T$ is tested over the range 40<$E_T$<450 GeV using $E_T$ for the renormalization scale. The data show good agreement with QCD in the region below 250 GeV. In the text we discuss the data-theory comparison in the region from 250 to 450 GeV. The value of $\alpha_s$ at the mass of the $Z^0$ boson averaged over the range 40<$E_T$<250 GeV is found to be $\alpha_s(M_{Z})= 0.1178 \pm 0.0001{(\rm stat)}^{+0.0081}_{-0.0095}{\rm (exp. syst)}$. The associated theoretical uncertainties are mainly due to the choice of renormalization scale (^{+6%}_{-4%}) and input parton distribution functions (5%).Comment: 7 pages, 3 figures, using RevTeX. Submitted to Physical Review Letter