1. Masterclass 20141 Introduction to hands-on Exercise Aim of the exercise  Identify electrons (e), 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  Data from 2010 LHC collisions!  Aim of the exercise: Do W and Z decay equally often in electrons and muons?  In addition we added one event which is a candidate Higgs event, it may appear as:  H  eeee, H , or H  ee  There will be a mystery prize for the first group to identify this event !!! To do the exercise we use the Atlantis visualisation program

2. Masterclass 20142 Principle of collider experiment At the LHC you collide protons against protons The collision energy is used to create particles Identify created particles in our detectors Done through their interaction with matter We can only ‘see’ the end products of the reaction not the reaction itself and then have to deduce what happened from this Our detector is built symmetrically around the collision point It is composed of several layers of detectors, each detector probes a different aspect of the event

3. Masterclass 20143 How it works…

4. Masterclass 20144 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

5. Masterclass 20145 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 20146 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 20147 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 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 Note, what you see here are the energy deposits in space. length gives magnitude, but everything is within this calorimeter! Electron identification Electron deposits its energy in electro-magnetic calorimeter Track in tracking detector in front of shower in calorimeter 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)

8. Masterclass 20148 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 ‘hand’ move the pointer to the track and click on it

9. Masterclass 20149 Example: W  e Electron track in tracking detector has high “side- ways” or transverse momentum (p T >10GeV) To see this yourself, click on ‘hand’ 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 ‘hand’ move the pointer to the track and click on it Selected track becomes white p T is shown here

10. Masterclass 201410 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

11. Masterclass 201411 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

12. Masterclass 201412 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 -Not shown if value very small! -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 -Not shown if value very small! Typically electron and E T miss are ‘back- to-back’ 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 -Not shown if value very small! Value shown here

13. Masterclass 201413 Next event Click on ‘Next’

14. Masterclass 201414 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 201415 Muon identification Track in muon detector Muon identification Track in muon detector Track in tracking detector

16. Masterclass 201416 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 201417 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 201418 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 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 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 201419 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 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

20. Masterclass 201420 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 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 Also note: sometimes jets might be produced in addition to the W and Z bosons  In this case this is not a background event! 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 Missing “side-ways” energy can be also present in background events but typically it’s small

21. Masterclass 201421 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 Many more W’s are produced compared to Z events Note: in reality there many more background events than here 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! Once you have analysed 20 events you’re done! Just add up the totals. 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 If you finish your 20 events you can hunt for the Higgs by looking at other set(s) of events – ask a demonstrator There is only 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

22. Masterclass 201422 “Candidate” Higgs Hopefully many of you found the candidate Higgs event. On an event-by-event basis we can’t say for sure “this was a Higgs” Discovery is made in a statistical manner: