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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!

• 
• There is exactly one particle that can be seen in this event display. It moves to the bottom right in side view. The event is displayed in both end and side view. Which particle is it?
• The same event as before in side view but enlarged.
• Additional information (reconstructed information) about the particle that flew to the bottom right is shown in the top right corner of the picture. What do you call this particle?

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

• 
• Again, there is only one particle shown in this event display. It moves again to the bottom right (in side view). The event is displayed in both end and side view. Which particle is it?
• An enlarged picture of the same event in side view.
• Additional information of the particle that moves to the bottom right is shown inside the information box that is put to the top right corner of this picture? What do you call this particle?

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

• 
• In this event you have to identify two particles. Which ones are they?
• Enlarged end view of the same event.
• Information about the particle the moves to the top right in side view.

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

Alternative 1 (Electron) is correct. Alternative 2 (Positron) ist 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 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.

• 
• Which particles and/or objects are seen in this event?
• An enlarged view of the same event in end view. The data in the top left corner refer back to the particle that moves to the bottom in this view and whose track is coloured red in the tracking detector.
• Information about the particle that moves to the lft in forward direction is shown in the information box. What do you call the shown objects?

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) does not.

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.

• 
• Which particles and/or objects are seen in this event? There are two objects in the "Physics Object"" tab. Note also that a pT cut of > 5GeV is applied.
• Here is an enlarged view of the same event in end view. Only one track is left after the pT cut of > 5 GeV.
• Here is the same event in the forward direction.

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