45 research outputs found
Search for a Fourth-Generation Quark More Massive than the Z0 Boson in ppbar Collisions at sqrt(s) = 1.8 TeV
We present the results of a search for pair production of a fourth-generation
charge -1/3 quark (b') in sqrt(s)=1.8 TeV ppbar collisions using 88 pb^(-1) of
data obtained with the Collider Detector at Fermilab. We assume that both
quarks decay via the flavor-changing neutral current process b' -> bZ and that
the b' mass is greater than m_Z + m_b. We studied the decay mode b'b'bar -> ZZ
b bbar where one Z0 decays into e^+e^- or mu^+ mu^- and the other decays
hadronically, giving a signature of two leptons plus jets. An upper limit on
the cross section of ppbar -> b'b'bar times [BR (b' -> bZ)]^2 is established as
a function of the b' mass. We exclude at 95% confidence level a b' quark with
mass between 100 and 199 GeV/c^2 for BR(b' -> bZ) = 100%.Comment: 12 pages, 2 figures, submitted to Phys. Rev. Letters on 9/12/9
Measurement of the Helicity of W Bosons in Top Quark Decays
We use the transverse momentum spectrum of leptons in the decay chain t-->bW
with W-->l nu to measure the helicity of the W bosons in the top quark rest
frame. Our measurement uses a ttbar sample isolated in 106 +/- 4 inverse
picobarns of data collected in ppbar collisions at sqrt(s)=1.8 TeV with the CDF
detector at the Fermilab Tevatron. Assuming a standard V--A weak decay, we find
that the fraction of W's with zero helicity in the top rest frame is F_0 = 0.91
+/- 0.37 (stat) +/- 0.13 (syst), consistent with the standard model prediction
of F_0=0.70 for a top mass of 175 GeV/c**2.Comment: Submitted to PRL. 8 pages, 2 figure
Production of Y(1S) Mesons from chib Decays in pp(bar) Collisions at sqrt(s)=1.8 TeV
We have reconstructed the radiative decays and in collisions
at TeV, and measured the fraction of mesons
that originate from these decays. For mesons with
GeV/, the fractions that come from and
decays are and
, respectively. We have derived the fraction of
directly produced mesons to be .Comment: 13 Pages, 2 figure
Measurement of the B0 anti-B0 oscillation frequency using l- D*+ pairs and lepton flavor tags
The oscillation frequency Delta-md of B0 anti-B0 mixing is measured using the
partially reconstructed semileptonic decay anti-B0 -> l- nubar D*+ X. The data
sample was collected with the CDF detector at the Fermilab Tevatron collider
during 1992 - 1995 by triggering on the existence of two lepton candidates in
an event, and corresponds to about 110 pb-1 of pbar p collisions at sqrt(s) =
1.8 TeV. We estimate the proper decay time of the anti-B0 meson from the
measured decay length and reconstructed momentum of the l- D*+ system. The
charge of the lepton in the final state identifies the flavor of the anti-B0
meson at its decay. The second lepton in the event is used to infer the flavor
of the anti-B0 meson at production. We measure the oscillation frequency to be
Delta-md = 0.516 +/- 0.099 +0.029 -0.035 ps-1, where the first uncertainty is
statistical and the second is systematic.Comment: 30 pages, 7 figures. Submitted to Physical Review
Measurement of the Associated Production Cross Section in Collisions at TeV
We present the first measurement of associated direct photon + muon
production in hadronic collisions, from a sample of 1.8 TeV
collisions recorded with the Collider Detector at Fermilab. Quantum
chromodynamics (QCD) predicts that these events are primarily from the Compton
scattering process , with the final state charm quark producing
a muon. Hence this measurement is sensitive to the charm quark content of the
proton. The measured cross section of is compared to a
leading-order QCD parton shower model as well as a next-to-leading-order QCD
calculation.Comment: 12 pages, 4 figures Added more detailed description of muon
background estimat
Measurement of b Quark Fragmentation Fractions in p-pbar Collisions at sqrt(s)=1.8 TeV
We have studied the production of B hadrons in 1.8-TeV p-pbar collisions. We
present measurements of the fragmentation fractions, f_u, f_d, f_s and
f_baryon, of produced b quarks that yield B^+, B^0, B^0_s and Lambda_b hadrons.
Reconstruction of several electron-charm final states yields
f_s/(f_u+f_d)=0.213+/-0.068 and f_baryon/(f_u+f_d)=0.118+/-0.042, assuming
f_u=f_d. If all B hadrons produced in p-pbar collisions cascade to one of these
four hadrons, we determine f_u=f_d=0.375+/-0.023, f_s=0.160+/-0.044 and
f_baryon=0.090+/-0.029. If we do not assume f_u=f_d, we find
f_d/f_u=0.84+/-0.16.Comment: 16 pages, 1 figure. Submitted to Physical Review Letter
Search for the Flavor-Changing Neutral Current Decays B^+ -> mu^+ mu^- K^+ and B^0 -> mu^+ mu^-K^{*0}
We report on a search for the flavor-changing neutral current decays B^+ ->
mu^+ mu^- K^+ and B^0 -> mu^+ mu^- K^{*0} using 88 pb^{-1} of data from p-pbar
collisions at \sqrt{s}=1.8 TeV, collected with the Collider Detector at
Fermilab. Finding no evidence for these decays, we set upper limits on the
branching fractions B(B^+ -> mu^+ mu^- K^+) mu^+
mu^-K^{*0}) < 4.0x10^{-6} at the 90% confidence level.Comment: 11 pages, 2 figures, submitted to Phys.Rev.Let
The Transverse Momentum and Total Cross Section of E+ E- Pairs in the Z-Boson Region from P Anti-P Collisions at s**(1/2) = 1.8-Tev
The transverse momentum and total cross section of e^+e^- pairs in the
Z-boson region of 66<M_{ee}<116 GeV from collisions at
TeV are measured using 110 pb^{-1} of collisions taken by the
Collider Detector at Fermilab during 1992-1995. The total cross section is
measured to be pb. The differential transverse momentum cross
section is compared with calculations that match quantum chromodynamics
perturbation theory at high transverse momentum with the gluon resummation
formalism at low transverse momentum.Comment: Accepted for Publication in Phys. Rev. Letters, 7 page
Search for Scalar Top and Scalar Bottom Quarks in collisions at TeV
We have searched for direct pair production of scalar top and scalar bottom
quarks in 88 pb of collisions at TeV with the
CDF detector. We looked for events with a pair of heavy flavor jets and missing
energy, consistent with scalar top quark decays to a charm quark and a
neutralino, or scalar bottom quark decays to a bottom quark and a neutralino.
The numbers of events that pass our selection for each process show no
deviation from Standard Model expectations. We compare our results to
next-to-leading order calculations for the scalar quark production cross
sections to exclude regions in scalar quark-neutralino parameter space.Comment: 10 pages, 3 figures. Submitted to Physical Review Letter
Search for a W' Boson via the Decay Mode W' -> mu nu in 1.8 TeV p-pbar Collisions
We report the results of a search for a W' boson produced in p-pbar
collisions at a center-of-mass energy of 1.8 TeV using a 107 pb-1 data sample
recorded by the Collider Detector at Fermilab. We consider the decay channel W'
-> mu nu and search for anomalous production of high transverse mass mu-nu
lepton pairs. We observe no excess of events above background and set limits on
the rate of W' boson production and decay relative to Standard Model W boson
production and decay using a fit of the transverse mass distribution observed.
If we assume Standard Model strength couplings of the W' boson to quark and
lepton pairs, we exclude a W' boson with invariant mass less than 660 GeV/c**2
at 95% confidence level.Comment: 19 pages, 2 figure