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Gaseous Detectors in High Energy Physics Shashikant R. Dugad Tata Institute of Fundamental Research Definitions and Units Typical ionization energy loss by heavy charged relativistic particle 2 MeV/gm-cm-2 Cosmic Rays detected at Ooty 1014-1016 Highest Energy of cosmic rays ~1021 eV LHC proton beam energy 7 TeV Ionization in Gases Choice of Gases Quenching gases Polyatomic gases (CH4) absorbs photons over wide energy range due to its copious vibrational and rotational energy levels Energy dissipation by collision or dissociation into smaller molecules Methane absorbs photons in the range of 7.9-14.5 eV 90%Ar + 10%CH4 (P10) is one of the widely gas used in the proportional counter Signal Formation Avalanche formation within few wire radii and in short interval of time (~1 nSec) Operational Mode Multi Wire Proportional Counter Multi Wire Proportional Counter Resistive Plate Chamber (RPC) Drift Chambers Drift and Diffusion in Gases Electrons and ion drifts under electric field (E) Drift Velocity VD = µ E Mobility µ = eĎ„/m Drift velocity ~ 5cm/ µs Typical drift chamber designs Advantages: Spatial Resolution not limited by cell size Smaller number of channels Resolution depends on diffusion, path fluctuations, electronics, and primary inoisation statistics
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