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Research 2: P Allfrey

Research 2: P Allfrey

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  • 1. Heavy-Ion Physics with the CMS experiment at the Large Hadron Collider Philip Allfrey University of Auckland, for the CMS Collaboration
  • 2. Outline• Large Hadron Collider and Compact Muon Solenoid Experiment• Quark-Gluon Plasma• Jet Quenching• Upsilon suppression• Grid computing
  • 3. Large Hadron Collider
  • 4. CMS DetectorEM Calorimeter (ECAL) Hadron Calorimeter (HCAL) Beam Scintillator Counters (BSC) Forward Calorimeter (HF) TRACKER(Pixels and Strips) MUON MUON (Barrel) (Endcaps) 4
  • 5. Quarks and Gluons• Protons and neutrons made up of quarks and gluons• Quarks and gluons normally bound within a nucleon, can’t exist in isolation• If enough matter with enough energy compressed into small enough volume, get a ‘soup’ of unbound quarks and gluons• This is known as a quark-gluon plasma (QGP) 5
  • 6. Heavy Ion Physics• Goal of high-energy heavy-ion physics to produce and study a quark-gluon plasma• Allows experimental study of QCD in extreme temperature/energy density• Various probes/signatures – jet quenching, heavy quark production, elliptic flow, correlations… 6
  • 7. Heavy Ion CollisionsLorentz- Nuclei collide. Quarks and Plasmacontracted Binary collisions gluons freed, expands andnuclei between quarks plasma formed cools, quarksapproach and gluons can and gluons produce jets or form bound heavy quarks states (particles)
  • 8. Jet quenching• Pair of jets must be formed back-to-back to conserve momentum• Jets not necessarily formed in centre of colliding nuclei, so have different path lengths in the medium• Therefore back-to-back jets with different energies imply energy loss• Signature of QGP
  • 9. Examples of Jets in CMSBalanced Unbalanced Energy Energy
  • 10. Dijet energy imbalance Pb Pb PbPb Pb Pb Semi-Peripheral Semi-Central Central E E j1 j2Jet energy AJ  T T Phys Rev C 84asymmetry E E T j1 T j2 (2011) 024906
  • 11. Quarkonia• Bound state of quark-antiquark pair is called quarkonium• Quarks and gluons carry colour charge, can move around in QGP => screening• If screening radius drops below binding radius, quarkonia should melt• Screening radius decreases with increasing temperature, therefore suppression of quarkonia acts as thermometer of QGP• Look for suppression of Upsilon (ϒ, b anti-b pair) in both heavy-ion and proton-proton collisions 11
  • 12. ϒ→μ+μ- mass spectrum proton-proton Pb-Pbϒ(1S) ϒ(3S) ϒ(2S) 12 Phys. Rev. Lett., 107 (2011) 052302
  • 13. Double Ratio• Compare ratios of ϒ(2S+3S) relative to ϒ(1S) in PbPb & pp• Benefits from cancellation of possible acceptance and efficiency differences PbPb (2S + 3S) (1S) PbPb  0.24 0.12 (stat) ± 0.02 (sys) +0.13 pp (2S + 3S) (1S) pp  0.78 +0.16 (stat) ± 0.02 (sys) 0.14 (2S + 3S) (1S) PbPb  0.31+0.19 (stat) ± 0.03 (sys) 0.15 (2S + 3S) (1S) pp First observation of suppression of excited ϒ states 13
  • 14. Grid Overview• Computing and data storage requirements of LHC experiments too large for single site to handle• Distributed among computing centres worldwide• Classed as Tier-0,1,2 or 3 depending on resources and responsibilities• Based on OSG or gLite middleware 14
  • 15. CMS Grid Sites by TierTier 0 Tier 1 Tier 2 Tier 3 15
  • 16. ArchitectureNon-trivial to set up, even if documented! 16
  • 17. ArchitectureComputing Interface CMS- SpecificStorage Monitoring 17
  • 18. Performance• Certified by Asia-Pacific ROC• 50k CPU-hours over past 12 months• Users from 15 different countries 18
  • 19. Summary• Jet quenching and suppression of excited upsilon states observed at CMS• Made possible by greater energy at LHC• Interpreted as signatures of QGP formation• NZ contributing to analysis of LHC data with Tier-3 Grid site