3,805 research outputs found
The ARGUS Vertex Trigger
A fast second level trigger has been developed for the ARGUS experiment which
recognizes tracks originating from the interaction region. The processor
compares the hits in the ARGUS Micro Vertex Drift Chamber to 245760 masks
stored in random access memories. The masks which are fully defined in three
dimensions are able to reject tracks originating in the wall of the narrow
beampipe of 10.5\,mm radius.Comment: gzipped Postscript, 27 page
Application of Al-Cu-W-Ta graded density impactors in dynamic ramp compression experiments
Graded density impactors (GDIs) are used to dynamically compress materials to extreme conditions. Two modifications to a previously developed Mg-Cu-W GDI are made in this work before using it in a dynamic compression experiment: Mg is replaced with Al and a Ta disk is glued to the back. The Mg phase is replaced by Al because FCC Al remains solid to higher pressure along its Hugoniot compared to Mg. The addition of the Ta disk creates a constant particle velocity regime and facilitates a definition of peak pressure states. Microstructure analysis, profilometry, and ultrasonic C-scans of the Al-Cu-W GDI all confirm excellent uniformity. We evaluated signal variation in the radial direction of a dynamically compressed Al-LiF bilayer target to evaluate the contribution of spatial nonuniformity to errors. Velocity traces from five photon Doppler velocimetry (PDV) probes located at different radial distances from the center of the target varied at most by 1.1% with a root mean square of 0.3% during the compression ramp, demonstrating low PDV measurement error over a relatively large experimental area. The experimental PDV data also agrees well with 1D simulations that use inputs from predictive characterization models developed for the material properties resulting from tape casting, laminating, and powder consolidation processes. Low measurement error during quasi-isentropic compression, leading to better precision, ensures a robust platform to reach extreme compression and low-temperature recovery states and facilitates discovery via synthesis, quenching, and preservation of new high-pressure phases
Application of Al-Cu-W-Ta graded density impactors in dynamic ramp compression experiments
Graded density impactors (GDIs) are used to dynamically compress materials to extreme conditions. Two modifications to a previously developed Mg-Cu-W GDI are made in this work before using it in a dynamic compression experiment: Mg is replaced with Al and a Ta disk is glued to the back. The Mg phase is replaced by Al because FCC Al remains solid to higher pressure along its Hugoniot compared to Mg. The addition of the Ta disk creates a constant particle velocity regime and facilitates a definition of peak pressure states. Microstructure analysis, profilometry, and ultrasonic C-scans of the Al-Cu-W GDI all confirm excellent uniformity. We evaluated signal variation in the radial direction of a dynamically compressed Al-LiF bilayer target to evaluate the contribution of spatial nonuniformity to errors. Velocity traces from five photon Doppler velocimetry (PDV) probes located at different radial distances from the center of the target varied at most by 1.1% with a root mean square of 0.3% during the compression ramp, demonstrating low PDV measurement error over a relatively large experimental area. The experimental PDV data also agrees well with 1D simulations that use inputs from predictive characterization models developed for the material properties resulting from tape casting, laminating, and powder consolidation processes. Low measurement error during quasi-isentropic compression, leading to better precision, ensures a robust platform to reach extreme compression and low-temperature recovery states and facilitates discovery via synthesis, quenching, and preservation of new high-pressure phases
Measurement of Branching Fractions and Rate Asymmetries in the Rare Decays B -> K(*) l+ l-
In a sample of 471 million BB events collected with the BABAR detector at the
PEP-II e+e- collider we study the rare decays B -> K(*) l+ l-, where l+ l- is
either e+e- or mu+mu-. We report results on partial branching fractions and
isospin asymmetries in seven bins of di-lepton mass-squared. We further present
CP and lepton-flavor asymmetries for di-lepton masses below and above the J/psi
resonance. We find no evidence for CP or lepton-flavor violation. The partial
branching fractions and isospin asymmetries are consistent with the Standard
Model predictions and with results from other experiments.Comment: 16 pages, 14 figures, accepted by Phys. Rev.
Improved Limits on decays to invisible final states
We establish improved upper limits on branching fractions for B0 decays to
final States 10 where the decay products are purely invisible (i.e., no
observable final state particles) and for final states where the only visible
product is a photon. Within the Standard Model, these decays have branching
fractions that are below the current experimental sensitivity, but various
models of physics beyond the Standard Model predict significant contributions
for these channels. Using 471 million BB pairs collected at the Y(4S) resonance
by the BABAR experiment at the PEP-II e+e- storage ring at the SLAC National
Accelerator Laboratory, we establish upper limits at the 90% confidence level
of 2.4x10^-5 for the branching fraction of B0-->Invisible and 1.7x10^-5 for the
branching fraction of B0-->Invisible+gammaComment: 8 pages, 3 postscript figures, submitted to Phys. Rev. D (Rapid
Communications
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Measurement of B(B-->X_s {\gamma}), the B-->X_s {\gamma} photon energy spectrum, and the direct CP asymmetry in B-->X_{s+d} {\gamma} decays
The photon spectrum in B --> X_s {\gamma} decay, where X_s is any strange
hadronic state, is studied using a data sample of (382.8\pm 4.2) \times 10^6
e^+ e^- --> \Upsilon(4S) --> BBbar events collected by the BABAR experiment at
the PEP-II collider. The spectrum is used to measure the branching fraction B(B
--> X_s \gamma) = (3.21 \pm 0.15 \pm 0.29 \pm 0.08)\times 10^{-4} and the
first, second, and third moments = 2.267 \pm 0.019 \pm 0.032 \pm
0.003 GeV,, )^2> = 0.0484 \pm 0.0053 \pm 0.0077 \pm
0.0005 GeV^2, and )^3> = -0.0048 \pm 0.0011 \pm 0.0011
\pm 0.0004 GeV^3, for the range E_\gamma > 1.8 GeV, where E_{\gamma} is the
photon energy in the B-meson rest frame. Results are also presented for
narrower E_{\gamma} ranges. In addition, the direct CP asymmetry A_{CP}(B -->
X_{s+d} \gamma) is measured to be 0.057 \pm 0.063. The spectrum itself is also
unfolded to the B-meson rest frame; that is the frame in which theoretical
predictions for its shape are made.Comment: 37 pages, 19 postscript figures, submitted to Phys. Rev. D. No
analysis or results have changed from previous version. Some changes to
improve clarity based on interactions with Phys. Rev. D referees, including
one new Figure (Fig. 13), and some minor wording/punctuation/spelling
mistakes fixe
Search for lepton-number violating processes in B+ -> h- l+ l+ decays
We have searched for the lepton-number violating processes B+ -> h- l+ l+
with h- = K-/pi- and l+ = e+/mu+, using a sample of 471+/-3 million BBbar
events collected with the BaBar detector at the PEP-II e+e- collider at the
SLAC National Accelerator Laboratory. We find no evidence for these decays and
place 90% confidence level upper limits on their branching fractions Br(B+ ->
pi- e+ e+) K- e+ e+) pi-
mu+ mu+) K- mu+ mu+) < 6.7 x 10^{-8}.Comment: 8 pages, 4 postscript figures, submitted to Phys. Rev. D. R
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Precise Measurement of the e+ e- --> pi+ pi- (gamma) Cross Section with the Initial-State Radiation Method at BABAR
A precise measurement of the cross section of the process
from threshold to an energy of 3GeV is obtained
with the initial-state radiation (ISR) method using 232fb of data
collected with the BaBar detector at center-of-mass energies near
10.6GeV. The ISR luminosity is determined from a study of the leptonic process
, which is found to agree with the
next-to-leading-order QED prediction to within 1.1%. The cross section for the
process is obtained with a systematic uncertainty
of 0.5% in the dominant resonance region. The leading-order hadronic
contribution to the muon magnetic anomaly calculated using the measured
cross section from threshold to 1.8GeV is .Comment: 58 pages, 56 figures, to be submitted to Phys. Rev.
Cross Sections for the Reactions e+e- --> K+ K- pi+pi-, K+ K- pi0pi0, and K+ K- K+ K- Measured Using Initial-State Radiation Events
We study the processes e+e- --> K+ K- pi+pi-gamma, K+ K- pi0pi0gamma, and K+
K- K+ K-gamma, where the photon is radiated from the initial state. About
84000, 8000, and 4200 fully reconstructed events, respectively, are selected
from 454 fb-1 of BaBar data. The invariant mass of the hadronic final state
defines the \epem center-of-mass energy, so that the K+ K- pi+pi- data can be
compared with direct measurements of the e+e- --> K+ K- pi+pi- reaction. No
direct measurements exist for the e+e- --> K+ K-pi0pi0 or e+e- --> K+ K-K+ K-
reactions, and we present an update of our previous result with doubled
statistics. Studying the structure of these events, we find contributions from
a number of intermediate states, and extract their cross sections. In
particular, we perform a more detailed study of the e+e- --> phi(1020)pipigamma
reaction, and confirm the presence of the Y(2175) resonance in the phi(1020)
f0(980) and K+K-f0(980) modes. In the charmonium region, we observe the J/psi
in all three final states and in several intermediate states, as well as the
psi(2S) in some modes, and measure the corresponding product of branching
fraction and electron width.Comment: 35 pages, 42 figure
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