1. Masterclass 20081 Introduction to hands-on Exercise Aim of the exercise Identify electrons, muons, neutrinos in the ATLAS detector Types of Events (particles produced in one collision) W e W Z ee Z Background from jet production (which might look like W or Z event) All the above events are well-known processes in addition we added one event from a yet undiscovered particle, Higgs, we hope to find soon H eeee, H, or H ee There will be a surprise prize for those who identifies this event !!! To do the exercise we use the Atlantis visualisation program As we dont have data yet, we will use simulations

2. Masterclass 20082 How does a collider work?

3. Masterclass 20083 How to detect particles in a detector Tracking detector Measure charge and momentum of charged particles in magnetic field Electro-magnetic calorimeter Measure energy of electrons, positrons and photons Hadronic calorimeter Measure energy of hadrons (particles containing quarks), such as protons, neutrons, pions, etc. Muon detector Measure charge and momentum of muons Neutrinos are only detected indirectly via missing energy not recorded in the calorimeters

4. Masterclass 20084 End-on view of the detector (x-y projection) Warning: Only particles reconstructed in central region shown here (otherwise the particles in the forward would cover the view)! Side view of the detector (R-z projection) Particles in central and forward region are shown

5. Masterclass 20085 Tracking detector (several sub-systems) Electro-magnetic calorimeter Tracking detector (several sub-systems) Electro-magnetic calorimeter Hadronic calorimeter Tracking detector (several sub-systems) Electro-magnetic calorimeter Hadronic calorimeter Muon detector

6. Masterclass 20086 Example: W e Characteristics: - Electron with high side- way or transverse energy - Neutrino measured indirectly via large missing side-way or transverse energy Electron identification Electron deposits its energy in electro-magnetic calorimeter Electron identification Electron deposits its energy in electro-magnetic calorimeter Track in tracking detector in front of shower in calorimeter Detail we cannot measure the whole event energy because energy is lost in very forward region (beam-pipe) better measurement: side-way component typically interesting collisions contain particles with big side-ways energies Electron identification Electron deposits its energy in electro-magnetic calorimeter Track in tracking detector in front of shower in calorimeter No trace in other detectors (electron stops in electro- magnetic calorimeter)

7. Masterclass 20087 Example: W e Electron track in tracking detector has high side- ways or transverse momentum (p T >10GeV) To see this yourself, Example: W e Electron track in tracking detector has high side- ways or transverse momentum (p T >10GeV) To see this yourself, click on pick Example: W e Electron track in tracking detector has high side- ways or transverse momentum (p T >10GeV) To see this yourself, click on pick move the pointer to the track and click on it

8. Masterclass 20088 Example: W e Electron track in tracking detector has high side- ways or transverse momentum (p T >10GeV) To see this yourself, click on pick move the pointer to the track and click on it Selected track becomes grey Example: W e Electron track in tracking detector has high side- ways or transverse momentum (p T >10GeV) To see this yourself, click on pick move the pointer to the track and click on it Selected track becomes white p T is shown here

9. Masterclass 20089 Example: W e Electron deposits large side-ways energy (E T ) in electro-magnetic calorimeter (E T >10GeV) To see this yourself, Example: W e Electron deposits large side-ways energy (E T ) in electro-magnetic calorimeter (E T >10GeV) To see this yourself move the pointer to the purple square and click on it

10. Masterclass 200810 Example: W e Electron deposits large side-ways energy (E T ) in electro-magnetic calorimeter (E T >10GeV) To see this yourself move the pointer to the purple square and click on it Selected square becomes grey Example: W e Electron deposits large side-ways energy (E T ) in electro-magnetic calorimeter (E T >10GeV) To see this yourself move the pointer to the purple square and click on it Selected square becomes grey E T is shown here

11. Masterclass 200811 Example: W e Characteristics: Electron with high side-way energy - We now know how to identify them! Example: W e Characteristics: Electron with high side-way energy - We now know how to identify them! Neutrino measured indirectly via large missing side-way or transverse energy (E T miss > 10GeV) Example: W e Characteristics: Electron with high side-way energy - We now know how to identify them! Neutrino measured indirectly via large missing side-way or transverse energy (E T miss > 10GeV) - Red dashed line in end-on view Example: W e Characteristics: Electron with high side-way energy - We now know how to identify them! Neutrino measured indirectly via large missing side-way or transverse energy (E T miss > 10GeV) - Red dashed line in end-on view - Value shown here Example: W e Characteristics: Electron with high side-way energy - We now know how to identify them! Neutrino measured indirectly via large missing side-way or transverse energy (E T miss > 10GeV) - Red dashed line in end-on view - Value shown here Typically electron and E T miss are back- to-back

12. Masterclass 200812 Next event Click on Next

13. Masterclass 200813 Example: W Characteristics: Example: W Characteristics: Large missing side-way energy (E T miss > 10GeV) Example: W Characteristics: Large missing side-way energy (E T miss > 10 GeV) 1 muon with high track side-way momentum (p T >10GeV)

14. Masterclass 200814 Muon identification Track in muon detector Muon identification Track in muon detector Track in tracking detector

15. Masterclass 200815 Example: W Characteristics: Large missing side- ways energy (E T miss > 10 GeV) 1 muon with high track side-way momentum (p T >10GeV) Example: W Characteristics: Large missing side-way energy (E T miss > 10 GeV) 1 muon with high track side-way momentum (p T >10GeV) here also some other low momentum tracks around from collision fragments

16. Masterclass 200816 Example: Z ee Characteristics: 2 electrons in the event

17. Masterclass 200817 Example: Z Characteristics: 2 muons in the event Here: one in central region Example: Z Characteristics: 2 muons in the event Here: one in central region one in forward region Particles in forward region are not seen in end-on projection! Only in side projection Example: Z Characteristics: 2 muons in the event

18. Masterclass 200818 Example: background Characteristics: Does not contain W e, W, Z ee, Z Example: background Characteristics: Does not contain W e, W, Z ee, Z Typically bundles of particles (jets) are produced Example: background Characteristics: Does not contain W e, W, Z ee, Z Typically bundles of particles (jets) are produced Energy deposited in the electro-magnetic and hadronic calorimeter Several tracks belonging to a jet are found Example: background Characteristics: Does not contain W e, W, Z ee, Z Typically bundles of particles (jets) are produced Energy deposited in the electro-magnetic and hadronic calorimeter

19. Masterclass 200819 Remember: Sometimes its not so obvious if its a jet or an electron Electron stops in electro-magnetic calorimeter, so has ONLY electro-magnetic component Jet goes also in hadronic calorimeter, so has electro-magnetic AND hadronic component

20. Masterclass 200820 Exercise: lets start! The first event you have to analyse is already displayed Study each event and classify it into 5 different categories W e, W, Z ee, Z, background There are some additional sheets to help you next to your computer When you decide what type it is, tick the corresponding box (,, ) Only one tick per event! Go to the next event using Next classify … tick … next … Once you have analysed 20 events youre done! Tell me your results look at the detector displays or continue and hunt for the Higgs If you dont manage to classify all events do not worry! just stop where you are at the end and do the final count Dont forget there is also one Higgs event (H, H eeee or H ee ) in the whole sample and theres a prize waiting…. At the end we will do the final summary and look at the ratio W e /W, Z ee/Z and the ratio W/Z production together

21. Masterclass 200821 EXTRAS

22. Masterclass 200822 Example: Z ee Heres another one Example: Z ee Heres another one In this example electrons do not look so nice Example: Z ee Heres another one In this example electrons do not look so nice Sometimes it happens that the track is not fully reconstructed and is shortened Example: Z ee Heres another one In this example electrons do not look so nice Sometimes it happens that the track is not fully reconstructed and is shortened Sometimes there might be a track near- by from other collision fragments

23. Masterclass 200823 Example: Z ee Heres another one In this example electrons do not look so nice Sometimes it happens that the track are not fully reconstructed and are shortened Sometimes there might be a track near- by from other collision fragments Those are typically low momentum (few GeV)