Magnetized liquid Argon detector for electron charge sign discrimination

A liquid Argon time projection chamber (TPC) immersed in magnetic field is proposed for systematic study and parameter optimisation in electron/muon charge sign discrimination and muon momentum determination by magnetic deflection. Design criteria and preliminary calculation are described. A proof of principle experiment is proposed using an electron beam of 1-10 GeV/c momentum incident on a prototype liquid argon TPC approximately 0.8 × 0.8 × 3.2 m that is placed in a 1-T magnetic field. Introduction A liquid Argon TPC appears to be an ideal instrument for detection and reconstruction of neutrino interaction events due to its specific measuring capabilities, such as fine-grain 3d-imaging, dE/dx tracking and hadron/electromagnetic calorimetric response. See for example the event in Figure 1. While extensive experience has been accumulated on the liquid Argon TPC technique, its performance in magnetic field remains to be demonstrated. Figure 1: Nuclear interaction recorded in ICARUS T600 during the first setting-up of the detector. In the case of neutrino beams from neutrino factories based on muon storage rings, the detection of charged current neutrino interactions with leptons (e, μ) with charge sign opposite to that expected from the stored μ sign, is, by itself, a proof of oscillation. Thus, the identification of the charge sign for e’s and μ's through magnetic deflection is the qualifying feature of detectors for such physics. For muons of any energy, their long observable path permits deflections (and hence the sign of their charge) to be rather easily detected against the multiple scattering even at field intensities of ∼0.2 T. For electrons, the useful tracking is reduced to their path before showering (1÷2 Xo) and then the charge sign discrimination, at 3-σ, requires a magnetic field intensity of 0.4 T at 1 GeV/c and 1.2 T at 10 GeV/c (see Figure 3). From simulations, it results that, in many cases, the electromagnetic shower axis follows, along several radiation lengths, the path of the primary electron and then the shower itself appears bent, in the range up to its maximum, accordantly with the sign and the momentum of the primary electron. The electron charge sign identification results then an interesting and intriguing theme to be worked up with a dedicated R&D program. The program is based on a liquid Argon TPC to be tested in a 1÷10 GeV/c electron test beam. The active volume should have good shower containment (∼20 Xo length, ∼6 RM transverse size). The cryostat is outfitted with a solenoid coil able to generate fields up to ∼1 T. With such a device it will be possible also a systematic study of the operating parameters in the muon momentum measurement by magnetic deflection in a liquid Argon TPC. 1 ICARUS detector: for a description and a complete reference list visit the sites http://www.aquila.infn.it:80/icarus/index.html and http://pcnometh4.cern.ch.