Cluster counting in helium based gas mixtures

The statistical advantages deriving from counting primary ionization, as opposed to the conventional energy loss measurement, are extensively discussed. A primary ionization counting method is proposed for a ''traditional'', cylindrical, single sense wire cell drift chamber, which makes use of a helium based gas mixture. Its conceptual feasibility is proven by means of a simple Monte Carlo simulation. A counting algorithm is developed and tested on the simulation output. A definition of the parameters of the read-out and of the digitizing electronics is given, assuming the described counting algorithm applied to a general detector design, in order to have a complete and realistic planning of a cluster counting measurement. Finally, some interesting results from a beam test, performed according to the described parameters, on primary ionization measurements and on pi/mu separation are shown.