3,625 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

    Resolution studies of cosmic-ray tracks in a TPC with GEM readout

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    A large volume TPC is a leading candidate for the central tracking detector at a future high energy linear collider. To improve the resolution a new readout based on micro-pattern gas detectors is being developed. Measurements of the spatial resolution of cosmic-ray tracks in a GEM TPC are presented. We find that the resolution suffers if the readout pads are too wide with respect to the charge distribution at the readout plane due to insufficient charge sharing. For narrow pads of 2 x 6 mm**2 we measure a resolution of 100 micometer at short drift distances in the absence of an axial magnetic field. The dependence of the spatial resolution as a function of drift distance allows the determination of the underlying electron statistics. Our results show that the present technique uses about half the statistical power available from the number of primary electrons. The track angle effect is observed as expected.Comment: 18 pages, 8 figures, version as published in Nucl. Inst. Met

    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

    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

    Parametrizations of Inclusive Cross Sections for Pion Production in Proton-Proton Collisions

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    Accurate knowledge of cross sections for pion production in proton-proton collisions finds wide application in particle physics, astrophysics, cosmic ray physics and space radiation problems, especially in situations where an incident proton is transported through some medium, and one requires knowledge of the output particle spectrum given the input spectrum. In such cases accurate parametrizations of the cross sections are desired. In this paper we review much of the experimental data and compare to a wide variety of different cross section parametrizations. In so doing, we provide parametrizations of neutral and charged pion cross sections which provide a very accurate description of the experimental data. Lorentz invariant differential cross sections, spectral distributions and total cross section parametrizations are presented.Comment: 32 pages with 15 figures. Published in Physical Review D62, 094030. File includes 6 tex files. The main file is paper.tex which has include statements refering to the rest. figures are in graphs.di

    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

    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
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