Departmental Oral Examination (Thesis Title: Cluster Counting in Drift Chambers for Particle Identification and Tracking)

Event Date and Time: 
Tue, 2015-09-22 11:00 - 13:00
Room 309, Hennings Building
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 

Drift chambers are a type of gaseous ionization detector used in high-energy physics experiments. They can identify detect charged particles and measure their momentum. When a high-energy charged particle crosses the drift chamber, it ionizes the gas. The liberated electrons drift towards positive-high-voltage wires where an ionization avalanche amplifies the signal. Traditional drift chambers use only the arrival time of the cluster of charge from the closest ionization for tracking, and use only the integral of the whole signal for particle identification.

We constructed prototype drift chambers with the ability to resolve the charge cluster signals from individual ionization events. Different algorithms were studied and optimized to best detect the clusters. The improvements to particle identification were studied using a single-cell prototype, while the improvements to particle tracking were studied using a multiple-layer prototype. The prototypes were built in the context of initial work for the now-cancelled SuperB project, but the results apply to any drift chambers used in flavour-factory experiments.

The results show that the choice of algorithm is not as critical as properly optimizing the algorithm parameters for the dataset. We find that a smoothing time of a few nanoseconds is optimal. This corresponds to a Nyquist frequency of a few hundred megahertz, indicating that gigahertz-bandwidth electronics are not required to make use of this technique.

Particle identification performance is quantified by the fraction of real pions correctly identified as pions when it is required that at most 10% of real pions are mis-identified as muons. In our single-cell prototype, the performance increases from 50% to 60% of pions correctly identified when cluster counting is combined with a traditional truncated-mean charge measurement, compared to the charge measurement alone.

Tracking performance is quantified by the single-cell resolution: the un- certainty in measuring the distance of charged particle track from a given sense wire. In our multiple-layer prototype, the single-cell tracking resolution using traditional methods is measured to be ∼ 150μm. With cluster counting implemented, the resolution is unchanged, indicating that the additional cluster information is not useful.

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