955 research outputs found

    Transmission time of wave packets through tunneling barriers

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    The transmission of wave packets through tunneling barriers is studied in detail by the method of quantum molecular dynamics. The distribution function of the times describing the arrival of a tunneling packet in front of and behind a barrier and the momentum distribution function of the packet are calculated. The behavior of the average coordinate of a packet, the average momentum, and their variances is investigated. It is found that under the barrier a part of the packet is reflected and a Gaussian barrier increases the average momentum of the transmitted packet and its variance in momentum space.Comment: 23 pages, 5 figure

    Probability distribution of arrival times in quantum mechanics

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    In a previous paper [V. Delgado and J. G. Muga, Phys. Rev. A 56, 3425 (1997)] we introduced a self-adjoint operator T^(X)\hat {{\cal T}}(X) whose eigenstates can be used to define consistently a probability distribution of the time of arrival at a given spatial point. In the present work we show that the probability distribution previously proposed can be well understood on classical grounds in the sense that it is given by the expectation value of a certain positive definite operator J^(+)(X)\hat J^{(+)}(X) which is nothing but a straightforward quantum version of the modulus of the classical current. For quantum states highly localized in momentum space about a certain momentum p00p_0 \neq 0, the expectation value of J^(+)(X)\hat J^{(+)}(X) becomes indistinguishable from the quantum probability current. This fact may provide a justification for the common practice of using the latter quantity as a probability distribution of arrival times.Comment: 21 pages, LaTeX, no figures; A Note added; To be published in Phys. Rev.

    Quantum probability distribution of arrival times and probability current density

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    This paper compares the proposal made in previous papers for a quantum probability distribution of the time of arrival at a certain point with the corresponding proposal based on the probability current density. Quantitative differences between the two formulations are examined analytically and numerically with the aim of establishing conditions under which the proposals might be tested by experiment. It is found that quantum regime conditions produce the biggest differences between the formulations which are otherwise near indistinguishable. These results indicate that in order to discriminate conclusively among the different alternatives, the corresponding experimental test should be performed in the quantum regime and with sufficiently high resolution so as to resolve small quantum efects.Comment: 21 pages, 7 figures, LaTeX; Revised version to appear in Phys. Rev. A (many small changes

    Near-threshold Photoproduction of Phi Mesons from Deuterium

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    We report the first measurement of the differential cross section on ϕ\phi-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, K+K^+ and KK^- near the theoretical production threshold of 1.57 GeV. The extracted differential cross sections dσdt\frac{d\sigma}{dt} for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. This experiment establishes a baseline for a future experimental search for an exotic ϕ\phi-N bound state from heavier nuclear targets utilizing subthreshold/near-threshold production of ϕ\phi mesons

    Absorption of the ω\omega and ϕ\phi Mesons in Nuclei

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    Due to their long lifetimes, the ω\omega and ϕ\phi mesons are the ideal candidates for the study of possible modifications of the in-medium meson-nucleon interaction through their absorption inside the nucleus. During the E01-112 experiment at the Thomas Jefferson National Accelerator Facility, the mesons were photoproduced from 2^{2}H, C, Ti, Fe, and Pb targets. This paper reports the first measurement of the ratio of nuclear transparencies for the e+ee^{+}e^{-} channel. The ratios indicate larger in-medium widths compared with what have been reported in other reaction channels.Comment: 6 pages, 4 figure

    Induced polarization of {\Lambda}(1116) in kaon electroproduction

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    We have measured the induced polarization of the Λ(1116){\Lambda}(1116) in the reaction epeK+Λep\rightarrow e'K^+{\Lambda}, detecting the scattered ee' and K+K^+ in the final state along with the proton from the decay Λpπ\Lambda\rightarrow p\pi^-.The present study used the CEBAF Large Acceptance Spectrometer (CLAS), which allowed for a large kinematic acceptance in invariant energy WW (1.6W2.71.6\leq W \leq 2.7 GeV) and covered the full range of the kaon production angle at an average momentum transfer Q2=1.90Q^2=1.90 GeV2^2.In this experiment a 5.50 GeV electron beam was incident upon an unpolarized liquid-hydrogen target. We have mapped out the WW and kaon production angle dependencies of the induced polarization and found striking differences from photoproduction data over most of the kinematic range studied. However, we also found that the induced polarization is essentially Q2Q^2 independent in our kinematic domain, suggesting that somewhere below the Q2Q^2 covered here there must be a strong Q2Q^2 dependence. Along with previously published photo- and electroproduction cross sections and polarization observables, these data are needed for the development of models, such as effective field theories, and as input to coupled-channel analyses that can provide evidence of previously unobserved ss-channel resonances.Comment: 13 figure
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