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Particle Physics

Particle Physics. Overview. We do Particle Physics to understand the fundamental nature of the universe! Many Open questions What do we want to explore/understand in the future? We smash particles together at the Large Hadron Collider (LHC) and analyse the fragments in detectors

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Particle Physics

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  1. Particle Physics

  2. Overview • We do Particle Physics to understand the fundamental nature of the universe! • Many Open questions • What do we want to explore/understand in the future? • We smash particles together at the Large Hadron Collider (LHC) and analyse the fragments in detectors • Some basics on how a detector works • Look in more detail at one of them: ATLAS

  3. Mont Blanc Lake airport CERN LHC ring 27 Km long ~100 m under ground

  4. ATLAS CMS 2 general-purpose detectors The LHC World of CERN One specialised for B-physics One specialised for heavy ions collisions e.g. lead-lead collisions CMS 2300 Physicists 176 Institutions 38 countries 550 MCHF LHCb 650 Physicists 48 Institutions 14 countries 75 MCHF ATLAS 2100 Physicists 167 Institutions 37 countries 550 MCHF ALICE 1000 Physicists 97 Institutions 30 countries 140 MCHF 4

  5. The detector Forcom- parison Length: ~40m Radius: ~10m Weight: ~ 7000 t ~100 empty Boeing 747 Each detector consists of many different components Each component specialised in measuring one aspect of the event

  6. 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 (can look similar to W or Z events!) 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mmm, or Heem • If you have time, you can search for this event yourself To do the exercise we use the Atlantis visualisation program As we don’t have real data yet, we will use simulations

  7. How to detect particles in a detector • Tracking detector component • 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

  8. 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

  9. 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

  10. 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) • Example: We • Characteristics: • Electron with high “side-ways” or transverse energy • Neutrino measured indirectly via large missing “side-ways” 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-ways” component • typically “interesting” collisions contain particles with big “side-ways” energies

  11. Example: We • Electron track in tracking detector has high “side-ways” or transverse momentum (pT>10GeV) • To see this yourself, • click on ‘pick’ • Example: We • Electron track in tracking detector has high “side-ways” or transverse momentum (pT>10GeV) • To see this yourself, • click on ‘pick’ • move the pointer to the track and click on it • Example: We • Electron track in tracking detector has high “side-ways” or transverse momentum (pT>10GeV) • To see this yourself,

  12. Example: We • Electron track in tracking detector has high “side-ways” or 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: We • Electron track in tracking detector has high “side-ways” or 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

  13. Example: We • Electron deposits large “side-ways” energy (ET) in electro-magnetic calorimeter (ET>10GeV) • To see this yourself • move the pointer to the ‘purple square’ and click on it • Example: We • Electron deposits large “side-ways” energy (ET) in electro-magnetic calorimeter (ET>10GeV) • To see this yourself,

  14. Example: We • Electron deposits large “side-ways” energy (ET) in electro-magnetic calorimeter (ET>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 (ET) in electro-magnetic calorimeter (ET>10GeV) • To see this yourself • move the pointer to the ‘purple square’ and click on it • Selected ‘square’ becomes grey • ET is shown here

  15. 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 (ETmiss > 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 (ETmiss > 10GeV) • -Red dashed line in end-on view • Value shown here • Example: We • Characteristics: • Electron with high “side-ways” energy • -We now know how to identify them! • Neutrino measured indirectly via large missing “side-ways” or transverse energy (ETmiss > 10GeV) • -Red dashed line in end-on view • Value shown here • Typically electron and ETmiss are ‘back-to-back’ • 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 (ETmiss > 10GeV)

  16. Next event • Click on ‘Next’ 

  17. Example: W • Characteristics: • Large missing “side-way” energy (ETmiss > 10GeV) • Example: W • Characteristics: • Large missing “side-way” energy (ETmiss > 10 GeV) • 1 muon with high track “side-way” momentum (pT>10GeV) Example: W Characteristics:

  18. Muon identification • Track in muon detector • Muon identification • Track in muon detector • Track in tracking detector Muon identification

  19. Example: W • Characteristics: • Large missing “side-way” energy (ETmiss > 10 GeV) • 1 muon with high track “side-way” momentum (pT>10GeV) • here also some other low momentum tracks around from collision fragments  • Example: W • Characteristics: • Large missing “side-ways” energy (ETmiss > 10 GeV) • 1 muon with high track “side-way” momentum (pT>10GeV) 

  20. Example: Zee Characteristics: 2 electrons in the event

  21. 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 

  22. 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 • 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

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

  24. 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 • 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! • We’ll try to check all the results if there’s time • look at the detector displays or continue and 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mmm, Heeee or Heem) in the whole sample…. • 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

  25. One last thing... • In the directory on the Desktop you will find: • Atlantis Instructions – how to load the software • Summary Sheet – typical event signatures • Overview Sheet – how to identify specific particles • Look at the poster boards for extra info! • Remember: Types of Events (“particles produced in one collision”) • W e ( Electron + neutrino ) • W  ( Muon + neutrino ) • Z ee ( Electron + Electron ) • Z  ( Muon + Muon ) • Background from jet production (can look similar to W or Z events!)

  26. EXTRAS

  27. 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 is not fully reconstructed and is shortened • Example: Zee • Here’s 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 • Example: Zee • Here’s another one

  28. 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)

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