4,043 research outputs found

    Limits on the neutron-antineutron oscillation time from the stability of nuclei

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    We refute a recent claim by Nazaruk that the limits placed on the free--space neutron--antineutron oscillation time τnnˉ\tau_{{n\bar n}} can be improved by many orders of magnitude with respect to the estimate τnnˉ>2(T0/Γ)1/2\tau_{{n\bar n}}>2(T_0/\Gamma)^{1/2}, where T0T_0 is a measured limit on the annihilation lifetime of a nucleus and Γ∌100\Gamma\sim 100 MeV is a typical antineutron-nucleus annihilation width.Comment: 4 pages, Latex, submitted to Physics Letters

    Neutrino scattering as a probe for the strange content of the nucleon

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    We consider different methods and observables which can be obtained by the measurement of neutrino scattering off nucleons and nuclei with the purpose of finding evidence for the strange form factors of the nucleon, which enter into structure of the nucleonic weak neutral current.Comment: 8 pages, 2 figures Contribution to 20th Max Born Symposium, Wroclaw (Poland), December 7-10, 200

    Weak non-mesonic decay of Hypernuclei

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    We review the mechanism of weak decay of hypernuclei, with emphasis on the non-mesonic decay channels. Various theoretical approaches are discussed and the results are compared with the available experimental data.Comment: 15 pages, 3 figures, Talk presented at XXVIII Mazurian Lakes Conference, Krzyze, Poland, August 31-September 7, 2003. To be published in Acta Physica Pol. B 35 (2004

    The Pion in Electromagnetic and Weak Neutral Current Nuclear Response Functions

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    The impact of pionic correlations and meson--exchange currents in determining the (vector) response functions for electroweak quasielastic lepton scattering from nuclei is discussed. The approach taken builds on previous work where the Fermi gas model is used to maintain consistency in treating forces and currents (gauge invariance) and to provide a Lorentz covariant framework. Results obtained in first-order perturbation theory are compared with infinite-order summation schemes (HF and RPA) and found to provide quite successful approximations for the quasielastic response functions. The role of pionic correlations in hardening the responses R_L and R_T is investigated in some detail, including studies of the relative importance of central and tensor pieces of the force and of exchange and self-energy diagrams; in addition, their role in significantly modifying the longitudinal parity-violating response R_{AV}^L is explored. The MEC are shown to provide a small, but non-negligible, contribution in determining the vector responses.Comment: TeX, 21 figures (Postscript, available from the authors), MIT preprint CTP\#219

    Influence of nucleonic motion in Relativistic Fermi Gas inclusive responses

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    Impulsive hadronic descriptions of electroweak processes in nuclei involve two distinctly different elements: one stems from the nuclear many-body physics --- the medium --- which is rather similar for the various inclusive response functions, and the other embodies the responses of the hadrons themselves to the electroweak probe and varies with the channel selected. In this letter we investigate within the context of the relativistic Fermi gas in both the quasi-elastic and N→ΔN\to\Delta regimes the interplay between these two elements. Specifically, we focus on expansions in the one small parameter in the problem, namely, the momentum of a nucleon in the initial wave function compared with the hadronic scale, the nucleon mass. Both parity-conserving and -violating inclusive responses are studied and the interplay between longitudinal (LL) and transverse (TT and Tâ€ČT') contributions is highlighted.Comment: 11 pages, 1 figur

    Weak Decay of Hypernuclei

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    The focus of these Lectures is on the weak decay modes of hypernuclei, with special attention to Lambda-hypernuclei. The subject involves many fields of modern theoretical and experimental physics, from nuclear structure to the fundamental constituents of matter and their interactions. The various weak decay modes of Lambda-hypernuclei are described: the mesonic mode and the non-mesonic ones. The latter are the dominant decay channels of medium--heavy hypernuclei, where, on the contrary, the mesonic decay is disfavoured by Pauli blocking effect on the outgoing nucleon. In particular, one can distinguish between one-body and two-body induced decays. Theoretical models employed to evaluate the (partial and total) decay widths of hypernuclei are illustrated, and their results compared with existing experimental data. Open problems and recent achievements are extensively discussed, in particular the determination of the ratio Gamma_n/Gamma_p, possible tests of the Delta I=1/2 rule in non-mesonic decays and the puzzling asymmetric non-mesonic decay of polarized hypernuclei.Comment: 59 pages, 13 figures Lectures given at the International School of Physics "Enrico Fermi" Course on: HADRON PHYSICS, Varenna (Lake Como), June 22nd - July 2nd, 200