﻿ International Physics Masterclasses

## Practice Identifying Particles

One can often see tracks of several different particles in each event.

You will do some detective work in this first exercise. Make use of the event display features to find all electrons, muons, photons, neutrinos, and jets in each displayed event.

Use the checkboxes below each exercise to record the type of particles you have just observed by clicking on 'Check'. The 'Hint' button helps you along the way! The 'Correct' button shows the right answer.

Good luck!

particle 1 electron positron muon anti-muon photon neutrino-antineutrino jet

particle 2 electron positron muon anti-muon photon neutrino-antineutrino jet

particle 3 electron positron muon anti-muon photon neutrino-antineutrino jet

Alternative 1 (Electron) is correct. Alternative 2 (Positron) is wrong. The decision whether it is an electron or a positron is to be done by looking at the sign of the PT value. The sign of the PT value of the particle with the red coloured track and only entries in the electromagnetic calorimeter in this event is negative. That's why it is an electric negatively charged lepton, that is stoped inside the electromagnetic calorimeter and from there an electron.

Alternatives 3 and 4 (muon resp. anti-muon) are not true because there isn't a 'visible' particle, that was created from proton-proton-collisions and made it to the muon chambers. Alternative 5 (photon) is wrong since there is no energy deposit in the electromagnetic calorimeter which does not correspond to a track.

Alternative 6 (neutrino) is correct, because a neutrino was emitted in addition to the electron. The neutrino carries a fraction of momentum and leaves the detector undetected. That is why it can only be seen with the help of an energy imbalance measurement. This shows a missing transverse momentum (MET) in direction of the leaving neutrino. As its value of 42 GeV is big enough one can really trace the MET back to neutrino creation.

Alternative 7 (Jets) is wrong because no bundle of particles can be seen.

particle 4 electron positron muon anti-muon photon neutrino-antineutrino jet

Alternative 1 (Electron) is wrong because the particle that travels to the bottom is a positron. The sign of the PT value point to an electric positively charged particle.

Alternative 2 (Positron) is correct.

Alternative 3 (Muon) is true whereas alternative 4 (Anti-muon) is not. Alternative 5 (photon) is wrong since there is no energy deposit in the electromagnetic calorimeter which does not correspond to a track.

Alternatives 6 (Neutrino) and 7 (Jets) are true because on the one hand the missing transverse momentum (MET) is big enough and on the other hand a bundle of particles can be seen inside the event, which especially leave big entries inside the hadronic calorimeters.

particle 5 electron positron muon anti-muon photon neutrino-antineutrino jet