Studies of parton distributions at a neutrino factory

The determination of parton distribution functions in the nucleon and nuclei is important for obtaining precise hadron-reaction cross sections, from which any new exotic signature could be found. We show that a future neutrino factory could provide important information on the parton distributions. First, a recent effort concerning the parametrization of nuclear parton distributions is explained. It suggests that the factory should be important for determining unknown behavior of valence-quark distributions in nuclei at small x. Second, the facility could be used for understanding nucleon spin structure and isospin violation in the parton distributions. 1 Nuclear parton distributions Unpolarized parton distribution functions are now well known from very small x to relatively large x. However, polarized distributions and nuclear parton distributions are not precisely determined at this stage because of the lack of a variety of data. In the recent years, several parametrizations of polarized distributions have been proposed. It was, however, unfortunate that there was no available χ analysis for nuclear distributions until recently. An initial effort of such a nuclear parametrization is discussed in Ref. [1]. The nuclear parton distributions are provided at Q0=1 GeV 2 as f i (x,Q 2 0) = wi(x,A, Z) fi(x,Q 2 0) with i=uv, dv, q̄, or g. Here, fi(x,Q 2 0) is a distribution in the nucleon, and wi(x,A, Z) is a weight function which takes into account nuclear modification. It is defined with parameters ai, bi, ci, di, and βi: wi(x,A, Z) = 1 + ( 1− 1 A1/3 ) ai(A,Z) + bix+ cix 2 + dix 3