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Register a new userMeasurement of the pionium lifetime
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M. Zhabitsky
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We report the progress in the measurement of the pionium lifetime by the DIRAC Collaboration at CERN (PS212). Based on data collected in 2001-2003 on Ni targets we have achieved the precision of 11% in the measurement of the pionium lifetime, which corresponds to the measurement of S-wave pion-pion scattering lengths difference |a0-a2| with the accuracy of 6%.
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The FOCUS experiment(FNAL-E831) has used two channels, $Omega^- pi^+$ and $Xi^-K^- pi^+ pi^+$,to measure the lifetime of the $Omega_c^0$ charmed baryon. From a sample of $64 pm 14$ signal events at a mass of 2.698 GeV/$c^2$, we measure an $Omega_c^0$ lifetime of $72 pm 11$ (stat.) $pm 11$ (sys.) fs, substantially improving upon the current world average.
The ratio of the Lambda b baryon lifetime to that of the B0 meson is measured using 1.0/fb of integrated luminosity in 7 TeV center-of-mass energy pp collisions at the LHC. The Lambda b baryon is observed for the first time in the decay mode Lambda b -> J/psi pK-, while the B0 meson decay used is the well known B0 -> J/psi pi+K- mode, where the pi+ K- mass is consistent with that of the K*0(892) meson. The ratio of lifetimes is measured to be 0.976 +/- 0.012 +/- 0.006, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the B0 meson lifetime, the Lambda b lifetime is found to be 1.482 +/- 0.018 +/- 0.012 ps. In both cases the first uncertainty is statistical and the second systematic.
We report a measurement of the lifetime of the $Omega_c^0$ baryon using proton-proton collision data at center-of-mass energies of 7 and 8~TeV, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The sample consists of about 1000 $Omega_b^-toOmega_c^0mu^-bar{ u}_{mu} X$ signal decays, where the $Omega_c^0$ baryon is detected in the $pK^-K^-pi^+$ final state and $X$ represents possible additional undetected particles in the decay. The $Omega_c^0$ lifetime is measured to be $tau_{Omega_c^0} = 268pm24pm10pm2$ fs, where the uncertainties are statistical, systematic, and from the uncertainty in the $D^+$ lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value.
The lifetime of the $tau$-lepton is measured using the process $e^+e^-rightarrowtau^+tau^-$, where both $tau$-leptons decay to $3pi u_tau$. The result for the mean lifetime, based on $711,mathrm{fb}^{-1}$ of data collected with the Belle detector at the $Upsilon(4S)$ resonance and $60,mathrm{MeV}$ below, is $tau = (290.17 pm 0.53(mathrm{stat.}) pm 0.33(mathrm{syst.}))cdot10^{-15},mathrm{s}$. The first measurement of the lifetime difference between $tau^+$ and $tau^-$ is performed. The upper limit on the relative lifetime difference between positive and negative $tau$-leptons is $|Deltatau| / tau < 7.0 times 10^{-3}$ at 90% CL.
A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at $sqrt{s}=7$ and 8 TeV, is used to reconstruct $63pm9$ $Omega_b^-toOmega_c^0pi^-$, $Omega_c^0to pK^-K^-pi^+$ decays. Using the $Xi_b^-toXi_c^0pi^-$, $Xi_c^0to pK^-K^-pi^+$ decay mode for calibration, the lifetime ratio and absolute lifetime of the $Omega_b^-$ baryon are measured to be begin{align*} frac{tau_{Omega_b^-}}{tau_{Xi_b^-}} &= 1.11pm0.16pm0.03, tau_{Omega_b^-} &= 1.78pm0.26pm0.05pm0.06~{rm ps}, end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for $tau_{Omega_b^-}$ only). A measurement is also made of the mass difference, $m_{Omega_b^-}-m_{Xi_b^-}$, and the corresponding $Omega_b^-$ mass, which yields begin{align*} m_{Omega_b^-}-m_{Xi_b^-} &= 247.4pm3.2pm0.5~{rm MeV}/c^2, m_{Omega_b^-} &= 6045.1pm3.2pm 0.5pm0.6~{rm MeV}/c^2. end{align*} These results are consistent with previous measurements.
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