3,233 research outputs found
Precision Measurement of Orthopositronium Decay Rate Using SiO_2 Powder
The intrinsic decay rate of orthopositronium formed in powder
is measured using the direct correction method such that the time
dependence of the pick-off annihilation rate is precisely determined using high
energy-resolution germanium detectors. As a systematic test, two different
types of powder are used with consistent findings. The intrinsic
decay rate of orthopositronium is found to be , which is consistent with previous measurements using powder with about twice the accuracy. Results agree well with a recent
QED prediction, varying experimental standard
deviations from other measurements.Comment: 16 pages, 7 figures included. To be published in Physics Letters
Solution of Orthopositronium lifetime Puzzle
The intrinsic decay rate of orthopositronium formed in powder
is measured using the direct correction method such that the time
dependence of the pick-off annihilation rate is precisely determined. The decay
rate of orthopositronium is found to be , which is consistent with our previous measurements with
about twice the accuracy. Results agree well with the QED
prediction, and also with a result reported very recently using nanoporous
film
SUSY physics with early data Understanding ATLAS detector and backgrounds
With the imminent start of the ATLAS data taking in 2007, the well considered strategy is necessary for the good understanding of the detector performance from in situ calibration and the realistic estimation of the Standard Model background. These are urgent issue for the new physics discovery channels especially for the SUSY searches in the early data taking of LHC run. The talk starts with the breif overview of the ATLAS detector and the calibration commissioning, then the realistic background estimation using real data and the matrix element calculation continues. Finally the newly obtained SUSY discovery potential with newly estimated backgrounds is presented
Longitudinal spin transfer of Lambda and anti-Lambda in polarized pp collisions at \sqrt s=200 GeV at STAR
We report our measurement on longitudinal spin transfer, D_LL, from high
energy polarized protons to and hyperons in
proton-proton collisions at with the STAR detector at
RHIC. The current measurements cover , pseudorapidity
and transverse momenta up to using the data taken
in 2005. The longitudinal spin transfer is found to be D_LL= -0.03\pm 0.13
(stat) \pm 0.04(syst)\LambdaD_{LL} = -0.12 \pm
0.08(stat) \pm 0.03(syst)\bar{\Lambda} =
0.5 = 3.7 GeV/c$. The prospects with 2009 data and the future
measurements are also given.Comment: 6 pages, 3 figures, presentation at the SPIN2010 International
Symposium, Juelich (Germany), Sep. 27-Oct. 2, 201
Measurement of the analyzing power of proton-carbon elastic scattering in the CNI region at RHIC
The single transverse spin asymmetry, A_N, of the p-carbon elastic scattering
process in the Coulomb Nuclear Interference (CNI) region was measured using an
ultra thin carbon target and polarized proton beam in the Relativistic Heavy
Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were
collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100
GeV). A_N was obtained as a function of momentum transfer -t. The results were
fit with theoretical models which allow us to assess the contribution from a
hadronic spin flip amplitude.Comment: Contribution to the proceedings of the 16th International Spin
Physics Symposium, spin2004 (Trieste
Measurement of the analyzing power in pp elastic scattering in the peak CNI region at RHIC
We report the first measurements of the A_N absolute value and shape in the
-t range from 0.0015 to 0.010GeV/c^2 with a precision better than 0.005 for
each A_N data point using a polarized atomic hydrogen gas jet target and the
100 GeV RHIC proton beam.Comment: 4 pages, 5 figure
Precise measurement of positronium hyperfine splitting using the Zeeman effect
Positronium is an ideal system for the research of the quantum
electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of
positronium, , gives a good test of the bound state
calculations and probes new physics beyond the Standard Model. A new method of
QED calculations has revealed the discrepancy by 15\,ppm (3.9) of
between the QED prediction and the experimental
average. There would be possibility of new physics or common systematic
uncertainties in the previous all experiments. We describe a new experiment to
reduce possible systematic uncertainties and will provide an independent check
of the discrepancy. We are now taking data and the current result of
has been obtained so far. A measurement with a precision of (ppm) is
expected within a year.Comment: 8 pages, 8 figures, 2 tables, proceeding of LEAP2011, accepted by
Hyperfine Interaction
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