Introduction to hands-on Exercise

1. 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eem • There will be a prize for the group who identifies this event !!! To do the exercise we use the Atlantis visualisation program As we don’t have data yet, we will use simulations

2. At the LHC you collide protons against protons The collision energy is used to create particles (E=mc2) 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) Principle of collider physics

3. 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. Neutrinos are only detected indirectly via ‘missing energy’ not recorded in the calorimeters • Muon detector • Measure charge and momentum of muons

4. Example: Zee • 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 • Lego plot in - projection of energy deposits in the calorimeters • Electro-magnetic component in green • Hadronic component in red

5. Example: Zee • 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 • Lego plot in - projection of energy deposits in the calorimeters • Electro-magnetic component in green • Hadronic component in red

6. Tracking detector (several sub-systems) • 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. To read ‘our’ events • Click on File • Click on ‘Read Event’

8. Look on your results page to find out what is the number of your first event to analyse • 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. 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. Example: Zee • Track in tracking detector have high transverse momentum (pT) • 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 (pT>10GeV) • To see this yourself, • click on ‘pick’ • Example: Zee • Track in tracking detector have high transverse momentum (pT>10GeV)

11. Example: Zee • Track in tracking detector have high transverse momentum (pT>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 (pT>10GeV) • To see this yourself, • click on ‘pick’ • move the pointer to the track and click on it • Selected track becomes white • pT is shown here

12. Example: Zee • large transverse energy (ET) deposits in electromagnetic calorimeter (ET>10GeV) • To see this yourself • move the pointer to the ‘cluster’ and click on it • Example: Zee • large transverse energy (ET) deposits in electromagnetic calorimeter (ET>10GeV)

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

14. Next event • Click on ‘Next’

15. Example: Zee • Here’s another one • In this example electrons do not look so ‘nice’ • Example: Zee • Here’s 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 • Here’s 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 • Example: Zee • Here’s another one

16. Example: Zee • Here’s 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. 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. Example: W • Characteristics: • 1 muon in the event • Example: W • Characteristics: • 1 muon in the event • Large missing transverse energy (ETmiss > 10GeV) • “pick-button” would work as well • Typically muon and ETmiss are ‘back-to-back’ (if  is in central region) • Example: W • Characteristics: • 1 muon in the event • Large missing transverse energy (ETmiss > 10GeV) • “pick-button” would work as well Example: W Characteristics:

19. Example: We • Characteristics: • 1 electron in the event • Example: We • Characteristics: • 1 electron in the event • large missing transverse energy (ETmiss) • as electron in forward region, electron and ETmiss not ‘back-to-back’ • Example: We • Characteristics: • 1 electron in the event • large missing transverse energy (ETmiss) • as electron in forward region, electron and ETmiss 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 (ETmiss) Example: We Characteristics:

20. Example: We • Characteristics: • 1 electron in the event • large missing transverse energy (ETmiss) • as electron in forward region, electron and ETmiss not ‘back-to-back’ • looks like event in side view not well balanced (energy conservation) • Hint: check pT of tracks if in doubt!

21. Summary so far • Z→ee • Two electrons with track PT > 10 GeV • Small Missing ET: Missing ET < 10 GeV • Z→mm • Two muons with track PT> 10 GeV • Small Missing ET: Missing ET < 10 GeV • W→mn • One muon with track PT > 10 GeV • Large Missing ET: Missing ET > 10 GeV • W→en • One electron with track PT > 10 GeV • Large Missing ET: Missing ET > 10 GeV All the above events might have some additional low energy particles

22. 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 Example: background Characteristics:

23. 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: • 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. Remember: • Sometimes it’s not so obvious if it’s a jet or an electron • Electron has ONLYelectro-magnetic component • Jet haselectro-magnetic AND hadronic component

25. 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 ET not We

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

27. Exercise • … enough talking …. Let’s 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 you’re done. Not before! • look at the detector displays or continue and hunt for the Higgs • If you don’t manage to classify all events just stop where you are at the end and do the final count • Don’t forget there is also one H4, H4e or H2e2 in the whole sample and there’s 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