Ultraviolet laser calibration of drift chambers

Abstract

We demonstrate the use of a focused ultraviolet laser as a track calibration source in drift chambers, and specifically in a small time projection chamber (TPC). Drift chambers such as TPCs reconstruct the trajectories of charged particles by amplifying and collecting electrons produced by ionization of gas atoms with which the target particle collides. The ultraviolet laser induces a two-photon ionization of gaseous organic compounds along the beam, providing an artificially produced track which may then be used as a calibration source, particularly because it behaves as a particle of infinite momentum whose trajectory is straight in a magnetic field. To this end, we present measurements of the ionization profile of the laser for various gasses and model this ionization in terms of photon flux.