103 research outputs found
Search for the Lepton-Number-Violating Decay
A sensitive search for the lepton-number-violating decay has been performed using a sample of hyperons
produced in 800 GeV/ -Cu collisions. We obtain at 90% confidence, improving on the best
previous limit by four orders of magnitude.Comment: 9 pages, 5 figures, to be published in Phys. Rev. Let
Evidence for the Decay Sigma+ -> p mu+ mu-
We report the first evidence for the decay Sigma+ -> p mu+ mu- from data
taken by the HyperCP experiment(E871) at Fermilab. Based on three observed
events, the branching ratio is B(Sigma+ -> p,mu+,mu-) = [8.6 +6.6,-5.4(stat)
+/-5.5(syst)] x 10**-8. The narrow range of dimuon masses may indicate that the
decay proceeds via a neutral intermediate state, Sigma+ -> p P0, P0 -> mu+ mu-,
with a P0 mass of 214.3 +/- 0.5 MeV/c**2 and branching ratio B(Sigma+ -> p P0;
P0 -> mu+ mu-) = [3.1 +2.4,-1.(stat) +/-1.5(syst)] x 10**-8.Comment: As published in PR
Measurement of the Alpha Asymmetry Parameter for the Omega- to Lambda K- Decay
We have measured the alpha parameter of the Omega- to Lambda K- decay using
data collected with the HyperCP spectrometer during the 1997 fixed-target run
at Fermilab. Analyzing a sample of 0.96 million Omega- to Lambda K^-, Lambda to
p pi- decays, we obtain alpha_Omega*alpha_Lambda =
[1.33+/-0.33(stat)+/-0.52(syst)] x 10^{-2}. With the accepted value of
alpha_Lambda, alpha_Omega is found to be [2.07+/-0.51(stat)+/-0.81(syst)] x
10^{-2}.Comment: 5 pages, 4 figures, to be appeared as a Rapid Communication in Phys.
Rev.
Mechanical properties of electrodeposited nanocrystalline and ultrafine-grained Zn-Sn coatings
This study investigates the effects of grain size on the mechanical properties of Zn-Sn alloy coatings. Nanocrystalline (average grain size = 78 ± 18 nm) and ultrafine-grained (average grain size = 423 ± 96 nm) Zn-Sn coatings were electrodeposited on steel substrates from gluconate electrolytes containing organic additives. The microstructure, surface roughness and mechanical properties of electrodeposited coatings were investigated using field emission scanning electron microscopy (FE-SEM), three dimensional (3D) surface profilometry, nano-hardness, nano-scratch and nano-wear tests. The average surface amplitude parameters such as mean surface roughness (Sa) and root mean square roughness (Sq) decreased by at least 80% while, hardness increased from 209 ± 66 MPa to 523 ± 140 MPa, due to grain refinement from ultrafine-grained to nanocrystalline structure. Nano-scratch results indicated that a deeper grove was formed on the surface of ultrafine-grained coatings than nanocrystalline coatings during the sliding process. For both coatings coefficient of friction increased gradually over the entire sliding duration and reached to maximum of 0.24 ± 0.04 and 0.12 ± 0.02 in ultrafine-grained and nanocrystalline coatings respectively. Wear volume of the coatings decreased by 64.5% due to grain refinement from ultrafine-grained to nanocrystalline structure
Observation of Parity Violation in the Omega-minus -> Lambda + K-minus Decay
The alpha decay parameter in the process Omega-minus -> Lambda + K-minus has
been measured from a sample of 4.50 million unpolarized Omega-minus decays
recorded by the HyperCP (E871) experiment at Fermilab and found to be [1.78 +/-
0.19(stat) +/- 0.16(syst)]{\times}10^{-2}. This is the first unambiguous
evidence for a nonzero alpha decay parameter, and hence parity violation, in
the Omega-minus -> Lambda + K-minus decay.Comment: 10 pages, 7 figure
HyperCP: A high-rate spectrometer for the study of charged hyperon and kaon decays
The HyperCP experiment (Fermilab E871) was designed to search for rare
phenomena in the decays of charged strange particles, in particular CP
violation in and hyperon decays with a sensitivity of
. Intense charged secondary beams were produced by 800 GeV/c protons
and momentum-selected by a magnetic channel. Decay products were detected in a
large-acceptance, high-rate magnetic spectrometer using multiwire proportional
chambers, trigger hodoscopes, a hadronic calorimeter, and a muon-detection
system. Nearly identical acceptances and efficiencies for hyperons and
antihyperons decaying within an evacuated volume were achieved by reversing the
polarities of the channel and spectrometer magnets. A high-rate
data-acquisition system enabled 231 billion events to be recorded in twelve
months of data-taking.Comment: 107 pages, 45 Postscript figures, 14 tables, Elsevier LaTeX,
submitted to Nucl. Instrum. Meth.
Hadroproduction of the Chi1 and Chi2 States of Charmonium in 800 GeV/c Proton-Silicon Interactions
The cross sections for the hadroproduction of the Chi1 and Chi2 states of
charmonium in proton-silicon collisions at sqrt{s}=38.8 GeV have been measured
in Fermilab fixed target Experiment 771. The Chi states were observed via their
radiative decay to J/psi+gamma, where the photon converted to e+e- in the
material of the spectrometer. The measured values for the Chi1 and Chi2 cross
sections for x_F>0 are 263+-69(stat)+-32(syst) and 498+-143(stat)+-67(syst) nb
per nucleon respectively. The resulting sigma(Chi1}/sigma(Chi2) ratio of
0.53+-0.20(stat)+-0.07(syst), although somewhat larger than most theoretical
expectations, can be accomodated by the latest theoretical estimates.Comment: 4 pages, 4 figure
High Statistics Search for the Theta+(1.54) Pentaquark State
We have searched for Theta+(1.54) -> K0,p decays using data from the 1999 run
of the HyperCP experiment at Fermilab. We see no evidence for a narrow peak in
the K0,p mass distribution near 1.54 GeV/c among 106,000 K0,p candidates, and
obtain an upper limit for the fraction of Theta+(1.54) to K0,p candidates of
<0.3% at 90% confidence.Comment: 4 pages, 4 figure
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