Momentum determination via multiple scattering in AQUA-RICH

We present a new technique to measure the momentum of charged particles in a large ring imaging water-Cherenkov-detector (AQUA-RICH). Since Cherenkov photons are emitted with respect to the momentum vector of the particle, they are used to determine the particle direction with an angular resolution of a few mrad, making the deflections due to multiple scattering accessible. Considering the momentum dependence of multiple scattering, the distribution of scattering angles of a single particle can be used to determine its momentum. rformance of this method is tested in Monte Carlo simulation runs with muons in the range 4–24 GeV/c and pathlengths of 10 m. Including all known error sources, resolutions of 11% (4 GeV/c) to 21% (24 GeV/c) are achievable. Longer tracks improve the accuracy significantly up to 4% (18 GeV/c, 80 m).