2,919 research outputs found

    CP Violation and Arrows of Time Evolution of a Neutral KK or BB Meson from an Incoherent to a Coherent State

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    We study the evolution of a neutral KK meson prepared as an incoherent equal mixture of K0K^0 and K0ˉ\bar{K^0}. Denoting the density matrix by \rho(t) = {1/2} N(t) [\1 + \vec{\zeta}(t) \cdot \vec{\sigma} ] , the norm of the state N(t)N(t) is found to decrease monotonically from one to zero, while the magnitude of the Stokes vector ζ(t)|\vec{\zeta}(t)| increases monotonically from zero to one. This property qualifies these observables as arrows of time. Requiring monotonic behaviour of N(t)N(t) for arbitrary values of γL,γS\gamma_L, \gamma_S and Δm\Delta m yields a bound on the CP-violating overlap δ=KLKS\delta = \braket{K_L}{K_S}, which is similar to, but weaker than, the known unitarity bound. A similar requirement on ζ(t)|\vec{\zeta}(t)| yields a new bound, δ2<1/2(ΔγΔm)sinh(3π4ΔγΔm)\delta^2 < {1/2} (\frac{\Delta \gamma}{\Delta m}) \sinh (\frac{3\pi}{4} \frac{\Delta \gamma}{\Delta m}) which is particularly effective in limiting the CP-violating overlap in the B0B^0-B0ˉ\bar{B^0} system. We obtain the Stokes parameter ζ3(t)\zeta_3(t) which shows how the average strangeness of the beam evolves from zero to δ\delta. The evolution of the Stokes vector from ζ=0|\vec{\zeta}| = 0 to ζ=1|\vec{\zeta}| = 1 has a resemblance to an order parameter of a system undergoing spontaneous symmetry breaking.Comment: 13 pages, 6 figures. Inserted conon "." in title; minor change in text. To appear in Physical review

    Unstable particles as open quantum systems

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    We present the probability preserving description of the decaying particle within the framework of quantum mechanics of open systems taking into account the superselection rule prohibiting the superposition of the particle and vacuum. In our approach the evolution of the system is given by a family of completely positive trace preserving maps forming one-parameter dynamical semigroup. We give the Kraus representation for the general evolution of such systems which allows one to write the evolution for systems with two or more particles. Moreover, we show that the decay of the particle can be regarded as a Markov process by finding explicitly the master equation in the Lindblad form. We also show that there are remarkable restrictions on the possible strength of decoherence.Comment: 11 pp, 2 figs (published version

    Paramaterizations of inclusive cross sections for pion production in proton-proton collisions. II. Comparison to new data

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    A set of new, precise data have recently been made available by the NA49 collaboration for charged pion production in proton-proton and proton-Carbon reactions at 158 GeV. The current paper compares this new data to five currently available arithmetic parameterizations. Although a precise fit is not expected, two of the parameterizations do not work very well but the other three are able to provide a moderately good, but not precise fit to the proton-proton data. The best two of these three parameterizations are scaled to the proton-Carbon data and again provide a moderately good, but not precise fit.Comment: 11 pages, 13 figures, Accepted for publication in Physical Review

    QCD corrections to the decay H+tbˉH^+ \to t \bar{b} in the Minimal Supersymmetric Standard Model

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    We present a complete calculation of the QCD corrections (of the order αs\alpha_s) to the width of the decay H+tbˉH^+ \to t \bar{b} within the Minimal Supersymmetric Standard Model. We find that the QCD corrections are quite important, and that the supersymmetric QCD corrections (due to gluino, stop and sbottom exchange) can be comparable to or even larger than the standard QCD corrections in a large region of the supersymmetric parameter space. This is mainly due to the effect of large left-right mixings of stop and sbottom. This could significantly affect the phenomenology of the H+H^+ search.Comment: 12 pages latex, 5 uuencoded figures, LateX file of text and PS-files of the text and the figures are also available via anonymous ftp at ftp://info.oeaw.ac.at/pub/hephy-pub/631 . Figures have been changed (and fig. 5 added), and accordingly the discussion of thes

    Measurement of the branching ratio of the decay Ξ0Σ+μνˉμ\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}

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    From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 Ξ0Σ+μνˉμ\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu} candidates with a background contamination of 30.8±4.230.8 \pm 4.2 events. From this sample, the BR(Ξ0Σ+μνˉμ\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}) is measured to be (2.17±0.32stat±0.17syst)×106(2.17 \pm 0.32_{\mathrm{stat}}\pm 0.17_{\mathrm{syst}})\times10^{-6}
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