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 don’t 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 white p T is shown here 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

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 E T is shown here 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

11. Masterclass 200811 Example: W  e Electron deposits large “side-ways” energy (E T ) in electro-magnetic calorimeter (E T >10GeV) Calorimeter E T also visible in ‘lego’ plot where you see the E T distribution in space in the calorimeter

12. Masterclass 200812 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 -Note the thickness corresponds to the magnitude of E T miss 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 -Note the thickness corresponds to the magnitude of E T miss -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 -Note the thickness corresponds to the magnitude of E T miss Typically electron and E T miss are ‘back- to-back’

13. Masterclass 200813 Next event Click on ‘Next’

14. Masterclass 200814 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)

15. Masterclass 200815 Muon identification Track in muon detector Track in tracking detector Muon identification Track in muon detector Muon identification Track in muon detector

16. Masterclass 200816 Example: W  Characteristics: Large missing “side- ways” energy (E T miss > 10 GeV) 1 muon with high track “side-way” momentum (p T >10GeV)

17. Masterclass 200817 Example: Z  ee Characteristics: 2 electrons in the event Example: Z  ee Characteristics: 2 electrons in the event here also some other low momentum tracks around from collision fragments

18. Masterclass 200818 Example: Z  Characteristics: 2 muons in the event Example: Z  Characteristics: 2 muons in the event Here: one in central region Example: Z  Characteristics: 2 muons in the event 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 Here: one in central region one in forward region Note: how muons are visualised in forward region compared to central region! Particles in forward region are not seen in “end-on” projection! Only in “side” projection Always look at side view to get the complete picture!

19. Masterclass 200819 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

20. Masterclass 200820 Remember: Sometimes it’s not so obvious if it’s 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

21. Masterclass 200821 Exercise: let’s 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 you’re done! Calculate the totals and tell me your results look at the detector displays or hunt for the Higgs If you don’t manage to classify all events do not worry! just stop where you are at the end and do the final count Don’t forget there is also one Higgs event (H , H  eeee or H  ee  ) 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