307 research outputs found
Inclusive J/psi and psi(2S) Production from B Decay in p p-bar Collisions
Using information on B-meson fragmentation functions from CERN LEP 1 and
adopting the nonrelativistic QCD factorization formalism proposed by Bodwin,
Braaten, and Lepage, we predict the transverse-momentum distribution of J/psi
mesons originating from the inclusive decays of b hadrons produced in p p-bar
collisions at the Fermilab Tevatron. We determine the relevant colour-octet
charmonium matrix elements from fits to CDF data on prompt charmonium
hadroproduction and to CLEO data on charmonium production from B-meson decay.
Our predictions are found to agree well with recent CDF and D0 data.Comment: 27 pages (Latex), 9 figures (Postscript
Momentum Distribution in the Decay B-->J/psi+X
We combine the NRQCD formalism for the inclusive color singlet and octet
production of charmonium states with the parton and the ACCMM model,
respectively, and calculate the momentum distribution in the decay B-->J/psi+X.
Neglecting the kinematics of soft gluon radiation, we find that the motion of
the b quark in the bound state can account, to a large extent, for the observed
spectrum. The parton model gives a satisfactory presentation of the data,
provided that the heavy quark momentum distribution is taken to be soft. To be
explicit, we obtain epsilon_p=O(0.008-0.012) for the parameter of the Peterson
et al. distribution function. The ACCMM model can account for the data more
accurately. The preferred Fermi momentum p_F=O(0.57 GeV) is in good agreement
with recent studies of the heavy quark's kinetic energy.Comment: revised version to be published in Phys. Rev. D; 27 pages, LaTeX, 7
eps figures, uses a4wide.sty, epsfig.sty and amssymb.st
Do the quark masses run? Extracting from LEP data
We present the first results of next-to-leading order QCD corrections to
three jet heavy quark production at LEP including mass effects. Among other
applications, this calculation can be used to extract the bottom quark mass
from LEP data, and therefore to test the running of masses as predicted by QCD.Comment: 6 pages + 2 figures, LaTeX, uses ReVTe
The STAR Time Projection Chamber: A Unique Tool for Studying High Multiplicity Events at RHIC
The STAR Time Projection Chamber (TPC) is used to record collisions at the
Relativistic Heavy Ion Collider (RHIC). The TPC is the central element in a
suite of detectors that surrounds the interaction vertex. The TPC provides
complete coverage around the beam-line, and provides complete tracking for
charged particles within +- 1.8 units of pseudo-rapidity of the center-of-mass
frame. Charged particles with momenta greater than 100 MeV/c are recorded.
Multiplicities in excess of 3,000 tracks per event are routinely reconstructed
in the software. The TPC measures 4 m in diameter by 4.2 m long, making it the
largest TPC in the world.Comment: 28 pages, 11 figure
Chiral Structure of the Charged Current and the Semileptonic Decay
Using the heavy quark effective theory, chiral structure of the charged current can be determined by the semileptonic decay with
satisfactory theoretical accuracy. We define an asymmetry which is sensitive to
the chirality of the charged current. We show that this
asymmetry has no theoretical uncertainty in the heavy quark limit. It is also
shown that correction to this asymmetry is small and disappears at the
kinematical point of zero momentum transfer.Comment: 17 pages + 2 PostScript figures (submitted by 'figures' command
A Measurement of B Meson Production and Lifetime Using D`â Events in Z0 Decays
A study of B meson decays into D l- X final states is presented. In these events, neutral and charged D mesons originate predominantly from B+ and B0 decays, respectively. The dilution of this correlation due to D** production has been taken into account. From 263700 hadronic Z0 decays collected in 1991 with the DELPHI detector at the LEP collider, 92 D0 --> K- pi+, 35 D+ --> K- pi+ pi+ and 61 D*+ --> D0 pi+ followed by D0 --> K- pi+ or D0 --> K- pi+ pi+ pi-, are found with an associated lepton of the same charge as the kaon. From the D0 l- and D*+ l-, the probability f(d) that a b quark hadronizes into a B- (or B0BAR),meson is found to be 0.44 +/-0.08 +/-0.09, corresponding to a total (B(s) + LAMBDA(b)) hadronization fraction of 0.12(-0.12)+0.24 .By reconstructing the energy of each B meson, the b quark fragmentation is directly measured for the first time. The mean value of the B meson energy fraction is: [X(E)(B)] = 0.695+/-0.015(stat.)+/-0.029(syst.) Reconstructing D-lepton vertices, the following B life-times are measured: tau(B) = 1.27(-0.18)+0.22(stat.)+/-0.15(syst.) ps, where bBAR --> D0 l- X, tau(B) = 1.18(-0.27)+0.39(stat.)+/-0.15(syst.) ps, where BBAR --> D+ l- X, T(B) = 1.19(-0.19)+0.25(stat.)+/-0.15(syst.) ps where BBAR --> D*+ l- X, and an average tau(B) = 1.23(-0.13)+0.14(stat.)+/-0.15(syst.) ps is found. Allowing for decays into D** l- vBAR, the B+ and B0 lifetimes are: tau(B+)= 1.30(0.29)+0.33(stat.)+/-0.15(syst. exp.) +/-0.05(syst. D**) ps, tau(B0)= 1.17(-0.23)+0.29(stat.)+/-0.15(syst. exp.) +/-0.05 (syst. D**) ps, tau(B+)/tau(B0) = 1.11(0.39)+0.51(stat.)+/-0.05(syst. exp.) +/-0.10(syst. D**) ps
Measurement of the triple-gluon vertex from 4-JET events at LEP
From the combined data of 1990 and 1991 of the DELPHI experiment at LEP, 13057 4-jet events are obtained and used for determining the contribution of the triple-gluon vertex. The relevant variables are the generalized Nachtmann Reiter angle theta(NR)* and the opening angle of the two least energetic jets. A fit to their two-dimensional distribution yields C(A)/C(F)=2.12+/-0.35 and N(C)/N(A)=0.46+/-0.19, where C(A)/C(F) is the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung from quarks, and N(C)/N(A), the ratio of the number of quark colours to the number of gluons. This constitutes a convincing model-independent proof of the existence of the triple-gluon vertex, since its contribution is directly proportional to C(A)/C(F). The results are in agreement with the values expected from QCD: C(A)/C(F)=2.25, and N(C)/N(A)=3/8
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
Observation of B_c Mesons in p-bar p Collisions at sqrt{s} = 1.8 TeV
We report the observation of bottom-charmed mesons B_c in 1.8 TeV p-bar p
collisions using the CDF detector at the Fermilab Tevatron. The B_c mesons were
found through their semileptonic decays, B_c -> J/psi lepton X. A fit to the
J/psi lepton mass distribution yielded 20.4 +6.2 -5.5 events from B_c mesons. A
test of the null hypothesis, i.e. an attempt to fit the data with background
alone, was rejected at the level of 4.8 standard deviations. By studying the
quality of the fit as a function of the assumed B_c mass, we determined M(B_c)
= 6.40 +- 0.39 +- 0.13 GeV/c^2. From the distribution of trilepton intersection
points in the plane transverse to the beam direction we measured the B_c
lifetime to be tau(B_c) = 0.46 +0.18 -0.16 +- 0.03 ps. We also measured the
ratio of production cross section times branching fraction for B_c -> J/psi
lepton neutrino relative to that for B+ -> J/psi K to be: 0.132 +0.041 -0.037
(stat) +- 0.031 (syst) +0.032 -0.020 (lifetime)Comment: 79 pages, 28 figures, available at
http://www-cdf.fnal.gov/physics/pub98/cdf4438_Bc_prd_V52.ps . Submitted to
Physical Review
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