3,775 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

    Determination of the branching ratios Γ(KL3π0)/Γ(KLπ+ππ0)\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi^+ \pi^- \pi^0) and Γ(KL3π0)/Γ(KLπeν)\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi e \nu )

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    Improved branching ratios were measured for the KL3π0K_L \to 3 \pi^0 decay in a neutral beam at the CERN SPS with the NA31 detector: Γ(KL3π0)/Γ(KLπ+ππ0)=1.611±0.037\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi^+ \pi^- \pi^0) = 1.611 \pm 0.037 and Γ(KL3π0)/Γ(KLπeν)=0.545±0.010\Gamma (K_L \to 3 \pi^0) / \Gamma (K_L \to \pi e \nu ) = 0.545 \pm 0.010. From the first number an upper limit for ΔI=5/2\Delta I =5/2 and ΔI=7/2\Delta I = 7/2 transitions in neutral kaon decay is derived. Using older results for the Ke3/Kμ\mu 3 fraction, the 3π0\pi^0 branching ratio is found to be Γ(KL3π0)/Γtot=(0.211±0.003)\Gamma (K_L \to 3 \pi^0 )/ \Gamma_{tot} = (0.211 \pm 0.003), about a factor three more precise than from previous experiments

    Irreversible Quantum Mechanics in the Neutral K-System

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    The neutral Kaon system is used to test the quantum theory of resonance scattering and decay phenomena. The two dimensional Lee-Oehme-Yang theory with complex Hamiltonian is obtained by truncating the complex basis vector expansion of the exact theory in Rigged Hilbert space. This can be done for K_1 and K_2 as well as for K_S and K_L, depending upon whether one chooses the (self-adjoint, semi-bounded) Hamiltonian as commuting or non-commuting with CP. As an unexpected curiosity one can show that the exact theory (without truncation) predicts long-time 2 pion decays of the neutral Kaon system even if the Hamiltonian conserves CP.Comment: 36 pages, 1 PostScript figure include

    Quantum Interference: From Kaons to Neutrinos (with Quantum Beats in between)

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    Using the vehicle of resolving an apparent paradox, a discussion of quantum interference is presented. The understanding of a number of different physical phenomena can be unified, in this context. These range from the neutral kaon system to massive neutrinos, not to mention quantum beats, Rydberg wave packets, and neutron gravity.Comment: 12 pages, LaTeX, 3 figure

    First Observation and Measurement of the Decay K+- -> pi+- e+ e- gamma

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    Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e- gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7 estimated background events. With K+- -> pi+- pi0D as normalisation channel, the branching ratio is determined in a model-independent way to be Br(K+- -> pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x 10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass allow a comparison with predictions of Chiral Perturbation Theory.Comment: 13 pages, 3 figures. Accepted for publication in Phys.Lett.
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