RevModPhys.84.1307

Momentum band in principle a wider band is accessible

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Unformatted text preview: empirical evaluation of the Fermi and GamowTeller strengths for a given nucleus. This is particularly relevant for ðp; nÞ reactions at high incident energies and forward angles, where the direct reaction mechanism dominates. The use of ðp; nÞ reactions is particularly favorable for studying weak interaction matrix elements for a number of reasons. The reaction is naturally spin selective and spin sensitive over a wide range of beam energies. Furthermore, small angle scattering is relatively easy to prove experimentally. This approach was first explored empirically by Goodman and others (Goodman et al., 1980; Watson 6 Examples of known sum rules to this effect include the Ikeda sum rule for the Gamow-Teller strength (Ikeda, 1964) X 2 2 MGT ðZ ! Z þ 1Þi À MGT ðZ ! Z À 1Þi ¼ 3ðN À ZÞ: i . Rev. Mod. Phys., Vol. 84, No. 3, July–September 2012 et al., 1985) and later expanded in a seminal paper by Taddeucci et al. (1987). Provided that ðp; nÞ forward scattering data on a particular nucleus are available, one can reduce the uncertainties on the corresponding neutrino cross section considerably. Data on ðp; nÞ scattering have been taken for a variety of nuclear targets, with particular focus on isotopes relevant for solar neutrino physics and stellar astrophysics. An example of the latter would be the treatment of the neutrino cross section at low energies for 71 Ga (Haxton, 1998). F. Experimental tests of low-energy cross sections on nuclei Low-energy neutrino cross sections feature prominently in a variety of model-building scenarios. Precise knowledge of the inclusive and differential cross section feeds into reactor neutrino analysis, supernova modeling, neutrino oscillation tests, and countless others. Yet, the number of direct experimental tests of these cross sections is remarkably few. We describe some examples next. 1. Hydrogen Inverse beta decay holds a special place for experimental neutrino physics, as it is via this channel that neutrinos were first detected (Cowan et al., 1956; Navarro, 2006). Currently, the technique of tagging inverse beta decay is prevalently used in the field for the identification and study of neutrino interactions. Inverse beta decay and neutrino absorption are still, after 60 years, the main reaction channels used for detecting reactor and solar neutrinos. Within the context of studying neutrino cross sections, however, the experimental data are somewhat limited. Most studies of neutrino interactions on protons (hydrogen) come from reactor experiments, whereby neutrinos are produced from the fission of 235 U, 239 Pu, 241 Pu, and 238 U. These experiments include Institut Laue-Langevin (ILL)-Grenoble (Kwon et al., 1981; ¨ Hoummada et al., 1995),7 Gosgen (Zacek et al., 1986), ROVNO (Kuvshinnikov et al., 1991), Krasnoyarsk (Vidyakin et al., 1987), and Bugey (Declais et al., 1994; Achkar et al., 1995), the latter of which had the most precise determination of the cross section. In almost all cases, t...
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