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Experimental Particle Physics PHYS6011 Joel Goldstein, RAL

Introduction to experimental particle physics, covering accelerators and colliders, particle interactions, types of detectors, and data analysis techniques. Focus on collider experiments such as CDF at the Tevatron, identifying particles and physics processes, reconstructing collisions, and extracting maximum information from outgoing particles.

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Experimental Particle Physics PHYS6011 Joel Goldstein, RAL

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  1. Experimental Particle PhysicsPHYS6011Joel Goldstein, RAL Introduction & Accelerators Particle Interactions and Detectors (2) Collider Experiments Data Analysis

  2. So far: Accelerators and colliders Particle interactions Types of detectors Combine them to do physics… Example: CDF at the Tevatron Proton-antiproton collisions Fermilab and the Tevatron CDF and DØ Identifying particles Identifying physics processes top production Collider Experiments

  3. e+ ? e- Z q e+ _ q e- Reconstructing Collisions What happened here? or something more exotic..... • extract maximum information outgoing particles

  4. Hard scatter Proton-Antiproton Collisions • Protons are composite objects: valence & sea quarks; gluons • Really parton-parton collisions • Underlying event: • Most lost at low angles • Some in detector • pz unknown • Extra detector hits • Initial partons unknown • Huge total cross section (10s of mb) Underlying event

  5. 30 miles west of Chicago 10 square miles Started operating in 1972 Major discoveries 1977 Bottom quark 1995 Top quark 1999 Direct CP Violation 2000 Tau Neutrino Fermilab

  6. Fixed target beams Fermilab Accelerators Collider experiments

  7. The Tevatron Run II • Upgraded for 2001 • s = 1.96 TeV • proton-antiproton collisions • 396 ns bunch crossing • L ~ 100×1030 cm-2s-1 • 3 interactions per crossing • 4-8 fb-1 by 2009

  8. CDF - optimised for tracking The Experiments DØ - optimised for calorimetry

  9. 2001Upgrade Higher luminosity Newer technology CDF

  10. Iron/scintillator TIME OF FLIGHT L00 CDF Components Muon detectors (drift and scintillator) Lead/scintillator 1.4 T B Field Very fast scintillator Fast drift chamber 8 layers of silicon

  11. DAQ Data acquisition Processing Storage Trigger and DAQ A million channels at 2.5 MHz Trigger • Event selection 200 kB at 100 Hz

  12. Hard process with final state X and Y X Y Feynman Level

  13. Standard Model Particles Lifetime ~ ps Confined Short lived Non interacting

  14. Particles Signatures • Electron, photons, muons and jets π±, K ±, p • Tau ID depends on decay mode

  15. b,c,τwill travel a few mm then decay c decay vertex b decay vertex e+ primary vertex e- Vertex Tagging • Precise tracking shows “displaced vertices” • Easiest for b hadrons

  16. Tracks and energies below a threshold not shown! Two Electron Event Small hadronic energy Large EM energy High momentum track

  17. Dijet + MET • Two jets • energy in EM and hadron • many tracks Alternate view of calorimeter • pT not balanced • undetected particles

  18. Top quark discovered at CDF and DØ in 1995 Need to identify top pair production Br (t→bW+)  100% Br (W→qq)  70% Br (W→lν)  10% per l Finding Top Quarks • Semileptonic channel • l is electron or muon • easy to identify • only one neutrino NB may be higher order effects

  19. Electron or muon 30% of the time Signature: 2 light quark jets 2 bottom jets One electron or muon Missing transverse momentum Extras: Underlying event Higher order processes Multiple interactions Top Pair Production

  20. Top Event Muon Light quark jets 3 cm Missing pT b tagged jets

  21. Next Time... Doing physics analysis (http://www-cdf.fnal.gov)

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