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Register a new userMeasurement of Orthopositronium Decay Rate Using SiO2 Powder: Integration of Thermalization into Time Spectrum
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The intrinsic decay rate of orthopositronium (o-Ps) formed in SiO_2 powder was measured using a modified method which determined the time dependence of the pick-off annihilation rate using high-energy-resolution germanium detectors. That is, the main systematic error due to thermalization was accounted for and integrated into the time spectrum fitting procedure. The averaged value was found to be lambda_(o-Ps)=7.0399+0.0020-0.0021(stat.) +-0.0015(sys.) mu s^{-1}, which agrees well with the O(alpha^2) QED prediction; varying 2.8-4.2 experimental standard deviations from other measurements.
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Positronium is an ideal system for the research of the bound state QED. New precise measurement of orthopositronium decay rate has been performed with an accuracy of 150 ppm. This result is consistent with the last three results and also the 2nd order correction. The result combined with the last three is 7.0401$pm0.0007mu mathrm{sec}^{-1}$ (100 ppm), which is consistent with the 2nd order correction and differs from the 1st order calculation by 2.6$sigma$ It is the first test to validate the 2nd order correction.
The order - alpha radiative corrections to the differential decay rate of polarized orthopositronium are obtained. Their influences on the three photons coincidence rate as a function of positronium polarization is considered.
We propose an experiment to search for invisible decays of orthopositronium (o-Ps) with a 90% confidence sensitivity in the branching ratio as low as $10^{-8}$. Evidence for this decay mode would unambigously signal new physics: either the existence of extra--dimensions or fractionally charged particles or new light gauge bosons. The experimental approach and the detector components of the proposed experiment are described.
The intrinsic decay rate of orthopositronium formed in ${rm SiO_2}$ powder is measured using the direct $2gamma$ 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 $7.0396pm0.0012 (stat.)pm0.0011 (sys.)mu s^{-1}$, which is consistent with our previous measurements with about twice the accuracy. Results agree well with the $O(alpha^2)$ QED prediction, and also with a result reported very recently using nanoporous film.
A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay $Lambda_b^0toLambda_c^+mu^-overline{ u}$ is reported, using data corresponding to $3 fb^{-1}$ collected with the LHCb detector in proton-proton collisions. The $Lambda_c^+mu^-overline{ u}$(+ anything) final states are reconstructed through the detection of a muon and a $Lambda_c^+$ baryon decaying into $pK^-pi^+$, and the decays $Lambda_b^0toLambda_c^+pi^+pi^-mu^-overline{ u}$ are used to determine contributions from $Lambda_b^0to Lambda_c^{star+}mu ^-bar{ u}$ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, $q^2$, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.
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