Babar/CM2 A-to-Z at Manchester

James Werner

Particle identification using Monte Carlo for EMC performance evaluation.

These plots contain all particles detected by EMC, which matches with Monte Carlo simulation. BaBar software identifies all charged particles as pions, which should introduce some problems for analysis programs and event selection. I developed a second test to guarantee that the match is correct, and only particles with norma less than 5% were accepted.

These plots show only pions with norma less than 5%. Detectors have limits for their ability to detect particles. This threshold is function of particle's mass and energy, and how it interacts with the detector material. Below the threshold, particles leave a asmall amount of energy in the detector. It is impossible to know the particle energy beyond the threshold, because the same amount of energy will be deposited in the detector for any particle momentum. Another problem is any that particle with energy bigger than the threshold will deposit the same amount of energy.

These plots show why the EMC is useless to detect kaons. Most of the charged particles are below the threshold and almost all kaons leave the same amount of energy in the detector, independent of its energy, together with all other particles over the threshold. Crystal doping and specification should displace the threshold over the maximum energy kaon peak. This explains why EMC is not useful to discriminate Pions from Kaons.
The surface plot shows a number of peaks over the background. This can represent some structure of the parent particle. Depending on the interval between energy levels, it could be modelled as rotational or vibrational collective modes, or different reaction channels. This will be analysed in the Pi0 project in detail.

How to discriminate Pions from Kaons??????

There is not a visual way to discriminate them. However, I am using only one first order discriminant. Using Artificial Intelligence, I am able to search for high order discriminate functions that evaluate each track and classify it as a Pion or a Kaon, evaluating the accuracy as well. This technique will be used in the Pi0 project later.