Possibility of observing nu p elastic scattering in a hydrogen bubble chamber at LAMPF II

There is great interest in accurately measuring nu/sub μ/p elastic scattering (and anti nu/sub μ/p elastic scattering). These reactions proceed through the weak neutral current (WNC). An accurate measurement of the cross sections would provide a detailed test of the Weinberg-Salam model. The present world's supply of events totals approx. 300 nu/sub μ/p and approx. 150 anti nu/sub μ/p events with q2 greater than or equal to 0.3 (GeV/c)2. Existing and proposed measurements are plagued by large backgrounds and systematic uncertainties. Extending the measurements to lower q2 would be the most accurate determination of the space-time structure of the WNC. The experimental difficulty in achieving an accurate measurement of the elastic scattering cross secction is primarily the poor event signature. All one can detect is the low energy recoil proton. The kinematic energy of the proton is related to q2 by q2 = 2m/sub p/T/sub p/. Thus measuring at lower q2 implies measuring lower energy recoil protons. The problem is compounded for protons bound in nuclei. The Fermi momentum of the initial state proton and the nuclear binding energies distort the observed q2 spectrum. A detector which completely avoids these problems is a hydrogen bubble chamber as all of the protons are free. In addition, the correction due to nu n → nu n events where the neutron charge exchanges is not present. In past experiments this has been a large correction (20 to 30%). Finally, a hydrogen bubble chamber is an ideal detector for neutrino-proton elastic scattering as it is, in essence, the ultimate fine-grained instrument to observe low energy recoil protons