1. Masterclass 20081 Introduction to hands-on Exercise Aim of the exercise Find out what happens in proton-proton collisions at the LHC as seen by the ATLAS detector Categories of Events W e W Z ee Z Background from jet production (which might look like W or Z event) All the above signals are well-known processes in addition we added one event from a yet undiscovered particle we hope to find soon H 4e, H 4, or H ee There will be a prize for the group 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 Principle of collider physics At the LHC you collide protons against protons The collision energy is used to create particles (E=mc 2 ) We see the end products of the reaction not the reaction itself We have to deduce what happened in the reaction from end products Identification of particles in our detector done through their interaction with matter Our detector is build symmetrically around collision point It is composed of several layers of detectors, each detector probes a different aspect of the event (= sum of particles produced in collision)

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 Example: Z ee Lego plot in - projection of energy deposits in the calorimeters Electro-magnetic component in green Hadronic component in red 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 Example: Z ee Lego plot in - projection of energy deposits in the calorimeters Electro-magnetic component in green Hadronic component in red 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

6. Masterclass 20086 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

7. Masterclass 20087 To read our events Click on File Click on Read Event

8. Masterclass 20088 Look on your results page to find out what is the number of your first event to analyse Now find your first event in list Look on your results page to find out what is the number of your first event to analyse Now find your first event in list Click open

9. Masterclass 20089 Example: Z ee Characteristics: 2 electrons in the event Example: Z ee Characteristics: 2 electrons in the event Electron deposit its energy in electro- magnetic calorimeter Example: Z ee Characteristics: 2 electrons in the event Electron deposits its energy in electro- magnetic calorimeter Track in tracking detector in front of shower in calorimeter Example: Z ee Characteristics: 2 electrons in the event Electron deposits its energy in electro- magnetic calorimeter Track in tracking detector in front of shower in calorimeter No trace in other detectors

10. Masterclass 200810 Example: Z ee Track in tracking detector have high transverse momentum (p T ) To see this yourself, click on pick move the pointer to the track and click on it Example: Z ee Track in tracking detector have high transverse momentum (p T >10GeV) To see this yourself, click on pick Example: Z ee Track in tracking detector have high transverse momentum (p T >10GeV)

11. Masterclass 200811 Example: Z ee Track in tracking detector have high 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: Z ee Track in tracking detector have high 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

12. Masterclass 200812 Example: Z ee large transverse energy (E T ) deposits in electromagnetic calorimeter (E T >10GeV) To see this yourself move the pointer to the cluster and click on it Example: Z ee large transverse energy (E T ) deposits in electromagnetic calorimeter (E T >10GeV)

13. Masterclass 200813 Example: Z ee large transverse energy (E T ) deposits in electromagnetic calorimeter (E T >10GeV) To see this yourself move the pointer to the cluster and click on it Selected cluster becomes grey E T is shown here Example: Z ee large transverse energy (E T ) deposits in electromagnetic calorimeter (E T >10GeV) To see this yourself move the pointer to the cluster and click on it Selected cluster becomes grey

14. Masterclass 200814 Next event Click on Next

15. Masterclass 200815 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 are not fully reconstructed and are shortened 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

16. Masterclass 200816 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)

17. Masterclass 200817 Example: Z Characteristics: 2 muons in the event track in tracking detector Example: Z Characteristics: 2 muons in the event track in tracking detector tiny traces in the calorimeters track in the muon detector Example: Z Characteristics: 2 muons in the event track in tracking detector tiny traces in the calorimeters 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: W Characteristics: 1 muon in the event Example: W Characteristics: 1 muon in the event Large missing transverse energy (E T miss > 10GeV) pick-button would work as well Typically muon and E T miss are back-to-back (if is in central region) Example: W Characteristics: Example: W Characteristics: 1 muon in the event Large missing transverse energy (E T miss > 10GeV) pick-button would work as well

19. Masterclass 200819 Example: W e Characteristics: Example: W e Characteristics: 1 electron in the event Example: W e Characteristics: 1 electron in the event large missing transverse energy (E T miss ) as electron in forward region, electron and E T miss not back-to- back Example: W e Characteristics: 1 electron in the event large missing transverse energy (E T miss ) as electron in forward region, electron and E T miss not back-to-back looks like event in side view not well balanced (energy conservation) Example: W e Characteristics: 1 electron in the event large missing transverse energy (E T miss )

20. Masterclass 200820 Example: W e Characteristics: 1 electron in the event large missing transverse energy (E T miss ) as electron in forward region, electron and E T miss not back-to- back looks like event in side view not well balanced (energy conservation) Hint: check p T of tracks if in doubt!

21. Masterclass 200821 Summary so far Zee Two electrons with track P T > 10 GeV Small Missing E T : Missing E T < 10 GeV Z Two muons with track P T > 10 GeV Small Missing E T : Missing E T < 10 GeV W One muon with track P T > 10 GeV Large Missing E T : Missing E T > 10 GeV We One electron with track P T > 10 GeV Large Missing E T : Missing E T > 10 GeV All the above events might have some additional low energy particles

22. Masterclass 200822 Example: background Characteristics: Example: background Characteristics: Bundles of particles (jets) are produced Energy deposited in the electro-magnetic and hadronic calorimeter Example: background Characteristics: 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: Bundles of particles (jets) are produced Energy deposited in the electro-magnetic and hadronic calorimeter Several tracks belonging to a jet are found Hint: how to see same jet in different projections Click on the violet squares colour change in all projections

23. Masterclass 200823 Example: background Characteristics: Example: background Characteristics: Bundles of particles (jets) are produced Energy deposited in the electro-magnetic and hadronic calorimeter Several tracks belonging to a jet are found Hint: how to see same jet in different projections Click on the violet squares colour change in all projections Example: background Characteristics: Bundles of particles (jets) are produced Energy deposited in the electro-magnetic and hadronic calorimeter Several tracks belonging to a jet are found Hint: how to see same jet in different projections Click on the violet squares colour change in all projections Example: background Characteristics: Bundles of particles (jets) are produced Energy deposited in the electro-magnetic and hadronic calorimeter Several tracks belonging to a jet are found Hint: how to see same jet in different projections Click on the violet squares colour change in all projections

24. Masterclass 200824 Remember: Sometimes its not so obvious if its a jet or an electron Electron has ONLY electro-magnetic component Jet has electro-magnetic AND hadronic component

25. Masterclass 200825 Example: background Sometimes you will find electrons in background events (not coming from W e or Z ee) Hint: only one electron not Z ee small missing E T not W e

26. Masterclass 200826 Example: background … or you could find muons in your background events

27. Masterclass 200827 Exercise … enough talking …. Lets start! Click the shortcut to Atlantis on your computer Click on File (upper right) and then Read event Look on your sheet and select the first event indicated on your sheet Study the event and classify it into 5 different categories W e, W, Z ee, Z, background If you decided what type it is, tick the corresponding box (,,, etc) Only one tick per event! Go to the next event using Next classify … tick … next … Once you have analysed 20 events youre done. Not before! look at the detector displays or continue and hunt for the Higgs If you dont manage to classify all events just stop where you are at the end and do the final count Dont forget there is also one H 4, H 4e or H 2e2 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