RevModPhys.84.1307

Coupling strengths for the known fermion elds is

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Unformatted text preview: trengths for the known fermion fields is shown in Table I. A more in-depth discussion of these topics can be found in a variety of introductory textbooks. We highlight the work of Giunti and Kim (2007) as an excellent in-depth resource for the interested reader. As such, neutrino-electron scattering is a powerful probe of the nature of the weak interaction, both in terms of the total cross section as well as its energy dependence (Marciano and Parsa, 2003). We will briefly examine the experimental tests of these reactions in the next section. Before leaving neutrino-lepton interactions completely, we turn our attention to the last possible reaction archetype, where the charged current and neutral-current amplitudes interfere with one another. Such a combined exchange is realized in e þ e ! e þ e scattering (see Fig. 3). The interference term comes into play by shifting gf ! gf þ 1 V V 2 and gf ! gf þ 1 . A A 2 One remarkable feature of neutrino-electron scattering is that it is highly directional in nature. The outgoing electron is emitted at very small angles with respect to the incoming neutrino direction. A simple kinematic argument shows that indeed Ee 2 e 2m e : 1311 and the standard model as a whole. Consider as an example " the first observation of the reaction  þ eÀ !  þ eÀ " made with the CERN bubble chamber neutrino experiment, Gargamelle (Hasert et al., 1973); see Fig. 4. This observation, in conjunction with the observation of neutral-current deep inelastic scattering (Hasert et al., 1973; Benvenuti et al., 1974), confirmed the existence of weak neutral currents and helped solidify the SUL ð2Þ Â Uð1ÞY structure of the standard model (Weinberg, 1967; ’t Hooft, 1971). The very observation of the phenomena made a profound impact on the field of particle physics. Subsequent experiments further utilized the information from the observed rates of neutral-current reactions as a gauge for measuring sin2 W directly. Neutrino-lepton scattering is a particularly sensitive probe in this regard because to first order (and even to further orders of , see Sec. II.D), the cross sections depend only on one parameter, sin2 W . Various experimental methods have been employed to measure neutrino-lepton scattering. Among the first included " the observation of e þ eÀ ! eÀ þ e scattering by Reines, " Gurr, and Sobel (1976) at the Savannah River Plant reactor complex. Making use of the intense e flux produced in " reactors, a Æ20% measurement of the weak mixing angle was extracted. A more recent result from the Taiwan EXperiment On Neu-trinO (TEXANO) experiment (Deniz and Wong, 2008; Deniz et al., 2010) also utilizes reactor antineutrinos as their source. There exists an inherent difficulty in extracting these events, as they are often masked by large low-energy backgrounds, particularly those derived from uranium and thorium decays. The majority of the recent precision tests have been carried...
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