3,018 research outputs found

    Precision Measurement of Orthopositronium Decay Rate Using SiO_2 Powder

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    The intrinsic decay rate of orthopositronium formed in SiO2{\rm SiO_2} powder is measured using the direct 2γ2\gamma 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 SiO2{\rm SiO_2} powder are used with consistent findings. The intrinsic decay rate of orthopositronium is found to be 7.0396±0.0012(stat.)±0.0011(sys.)μs17.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}, which is consistent with previous measurements using SiO2{\rm SiO_2} powder with about twice the accuracy. Results agree well with a recent O(α2)O(\alpha^2) QED prediction, varying 3.85.63.8-5.6 experimental standard deviations from other measurements.Comment: 16 pages, 7 figures included. To be published in Physics Letters

    Solution of Orthopositronium lifetime Puzzle

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    The intrinsic decay rate of orthopositronium formed in SiO2{\rm SiO_2} powder is measured using the direct 2γ2\gamma 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 7.0396±0.0012(stat.)±0.0011(sys.)μs17.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}, which is consistent with our previous measurements with about twice the accuracy. Results agree well with the O(α2)O(\alpha^2) QED prediction, and also with a result reported very recently using nanoporous film

    SUSY physics with early data Understanding ATLAS detector and backgrounds

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    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

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    We report our measurement on longitudinal spin transfer, D_LL, from high energy polarized protons to Λ\Lambda and Λˉ\bar{\Lambda} hyperons in proton-proton collisions at s=200GeV\sqrt{s} = 200 GeV with the STAR detector at RHIC. The current measurements cover Λ\Lambda, Λˉ\bar\Lambda pseudorapidity η<1.2|\eta| < 1.2 and transverse momenta pTp_T up to 4GeV/c4GeV/c 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)forinclusive for inclusive \Lambdaand and D_{LL} = -0.12 \pm 0.08(stat) \pm 0.03(syst)forinclusive for inclusive \bar{\Lambda}hyperonswith hyperons with = 0.5and and = 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

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    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

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    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

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    Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, ΔHFS\Delta_{\mathrm{HFS}}, 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 (3.9σ\sigma) of ΔHFS\Delta_{\mathrm{HFS}} 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 ΔHFS=203.3951±0.0024(stat.,12ppm)±0.0019(sys.,9.5ppm)GHz\Delta_{\mathrm{HFS}} = 203.395\,1 \pm 0.002\,4 (\mathrm{stat.}, 12\,\mathrm{ppm}) \pm 0.001\,9 (\mathrm{sys.}, 9.5\,\mathrm{ppm})\,\mathrm{GHz} has been obtained so far. A measurement with a precision of OO(ppm) is expected within a year.Comment: 8 pages, 8 figures, 2 tables, proceeding of LEAP2011, accepted by Hyperfine Interaction
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