ar X iv : h ep - p h / 07 03 25 1 v 1 2 3 M ar 2 00 7 Tests of the Standard Model with Low – Energy Neutrino Beams

We discuss the possibility of using future high–intensity low–energy neutrino beams for precision tests of the Standard Model. In particular we consider the determination of the electroweak mixing angle from elastic and quasi–elastic neutrino–nucleon scattering at a superbeam or β–beam. 1. The High–Intensity Frontier and Neu-trino Beams The search for new physics beyond the standard model in the future will follow two main paths: higher energy and high–intensity [1]. Neu-trino facilities will play an important role in this program: neutrino masses take us beyond the standard model, and a full determination of the pattern of ν masses and mixing will require dedicated high–intensity neutrino beams [2]. However , a high–intensity ν beam can be used not only to study neutrino properties, but also as a sensitive probe of the electroweak interaction. Indeed , it has been shown that a wide spectrum of otherwise very difficult or impossible measurements of strong and electroweak processes would become possible at a high–energy neutrino factory [3]. Here we start addressing the issue whether equally interesting measurements might also be possible with a low energy but sufficiently intense ν beam. Indeed, the main role so far of low– energy tests of the standard model [4] has been in the study of rare processes. Here we will investigate whether with sufficiently high–intensity they may lead to competitive measurements of standard model parameters, specifically the elec-troweak mixing angle. 2. Future Perspectives of Neutrino Physics The development of future neutrino facilities is driven by the study of neutrino masses and mix-ings, and will happen in three stages. In the first phase various facilities will produce conventional ν beams from the decay of a secondary meson beam (producing typically ∼ 10 18 ν/year). Examples of such facilities (now under construction or just commissioned) are MINOS and NOνA, the CERN/Gran Sasso beam, and T2K. In the second stage, planned for the beginning of the next decade, " superbeams " , i.e. conventional beams but with intensities about hundred times higher, should be constructed, exploiting very high–intensity, and relatively low energy primary proton beams. Examples of such facilities are the second phase of T2K, exploiting a 50 GeV and 7 MW proton synchrotron at JParc, and a possible high–energy superbeam at CERN exploiting a 3.5 GeV, 4–5 MW superconducting proton linac (SPL). In the third phase, starting perhaps towards the end of the next decade, neutrinos from decays of a primary …