11 research outputs found
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
The On-orbit Calibrations for the Fermi Large Area Telescope
The Large Area Telescope (LAT) on--board the Fermi Gamma ray Space Telescope
began its on--orbit operations on June 23, 2008. Calibrations, defined in a
generic sense, correspond to synchronization of trigger signals, optimization
of delays for latching data, determination of detector thresholds, gains and
responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA),
measurements of live time, of absolute time, and internal and spacecraft
boresight alignments. Here we describe on orbit calibration results obtained
using known astrophysical sources, galactic cosmic rays, and charge injection
into the front-end electronics of each detector. Instrument response functions
will be described in a separate publication. This paper demonstrates the
stability of calibrations and describes minor changes observed since launch.
These results have been used to calibrate the LAT datasets to be publicly
released in August 2009.Comment: 60 pages, 34 figures, submitted to Astroparticle Physic
First measurement of the double inclusive B / anti-B hadron energy distribution in e+ e- annihilations, and of angle dependent moments of the B and anti-B energies
We have made the first measurement of the double-inclusive B/Bbar energy
distribution in e+e- annihilations, using a sample of 400,000 hadronic Z0 decay
events recorded in the SLD experiment at SLAC between 1996 and 1998. The small
and stable SLC beam spot and the CCD-based vertex detector were used to
reconstruct B/Bbar decay vertices with high efficiency and purity, and to
provide measurements of the kinematic quantities used to calculate the B
energies in this novel technique. We measured the B/Bbar energies with good
efficiency and resolution over the full kinematic range. We measured moments of
the scaled energies of the B and Bbar hadrons vs. the opening angle between
them. By comparing these results with perturbative QCD predictions we tested
the ansatz of factorisation in heavy-quark production. A recent next-to-leading
order calculation reproduces the data.Comment: 17 pages, 6 figures; submitted to Physics Letters
Factorial and cumulant moments in e+ e- ---> hadrons at the Z0 resonance
We present the first experimental study of the ratio of cumulant to factorial
moments of the charged-particle multiplicity distribution in high-energy
particle interactions, using hadronic Z decays collected by the SLD
experiment at SLAC. We find that this ratio, as a function of the moment-rank
, decreases sharply to a negative minimum at , which is followed by
quasi-oscillations. These features are insensitive to experimental systematic
effects and are in qualitative agreement with expectations from
next-to-next-to-leading-order perturbative QCD.Comment: 13 pages, latex file, uuencoded eps figure
Measurement of B0 ---> D(*)+ D*- branching fractions and B0 ---> D*+(s) D*- polarization with a partial reconstruction technique
We present a study of the decays B0->D_s(*)+D*-, using 20.8 fb-1 of e+e-
annihilation data recorded with the BABAR detector. The analysis is conducted
with a partial reconstruction technique, in which only the D_s(*)+ and the soft
pion from the D*- decay are reconstructed. We measure the branching fractions
BR(B0->D_s+D*-) = (1.03 +/- 0.14 +/- 0.13 +/- 0.26)% and BR(B0->D_s*+D*-) =
(1.97 +/- 0.15 +/- 0.30 +/- 0.49)%, where the first error is statistical, the
second is systematic, and the third is the error due to the D_s+->phi pi+
branching fraction uncertainty. From the B0->D_s*+D*- angular distributions, we
measure the fraction of longitudinal polarization Gamma_L/Gamma = (51.9 +/- 5.0
+/- 2.8)%, which is consistent with theoretical predictions based on
factorization.Comment: 9 pages, 4 postscript figues, submitted to Physical Review D (Rapid
Communications
Measurement of the CKM matrix element |V(ub)| with B ---> rho e nu decays
We present a measurement of the branching fraction for the rare decays B->rho
e nu and extract a value for the magnitude of Vub, one of the smallest elements
of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. The results are given for
five different calculations of form factors used to parametrize the hadronic
current in semileptonic decays. Using a sample of 55 million BBbar meson pairs
recorded with the BABAR detector at the PEP-II e+e- storage ring, we obtain
Br(B0->rho- e+ nu)=(3.29 +-0.42 +-0.47 +-0.60) x 10^-4 and |Vub|=(3.64 +-0.22
+-0.25 +0.39-0.56)x10^-3, where the uncertainties are statistical, systematic,
and theoretical, respectively.Comment: Submitted to Phys. Rev. Let
Measurement of the branching fraction and CP violating asymmetries in neutral B decays to D*+- D-+
We present measurements of the branching fraction and CP-violating
asymmetries for neutral B decays to D*+-D-+. The measurement uses a data sample
of approximately 88 million Y(4S) --> B Bbar decays collected with the BABAR
detector at the SLAC PEP-II asymmetric-energy B factory. We measure the
branching fraction to be (8.8 +- 1.0 +- 1.3) x 10^-4 and the time-integrated
CP-violating asymmetry between the rates to D*+D- and D*-D+ to be A = -0.03 +-
0.11 +- 0.05. We also measure the time-dependent CP-violating asymmetry
parameters to be S-+ = -0.24 +- 0.69 +- 0.12, C-+ = -0.22 +- 0.37 +- 0.10 for B
--> D*-D+ and S+- = -0.82 +- 0.75 +- 0.14$, C+- = -0.47 +- 0.40 +- 0.12 for B
--> D*+D-. In each case the first error is statistical and the second error is
systematic.Comment: 7 pages, 3 figures, published as Phys. Rev. Lett 90 (2003) 22180
Measurement of the branching fraction for inclusive semileptonic B meson decays
A largely model-independent measurement of the inclusive electron momentum
spectrum and branching fraction for semileptonic decays of B mesons is
presented based on data recorded at the Upsilon(4S) resonance with the BABAR
detector. Backgrounds from secondary charm decays are separated from prompt B
decays using charge and angular correlations between the electron from one B
meson and a high momentum electron tag from the second B meson. The resulting
branching fraction is BR(B -> X e nu) = (10.87 +-0.18(stat)+-0.30(syst))%.
Based on this measurement we determine the CKM matrix element |V_cb|