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Ultra-relativistic Heavy Ion Reactions

Explore nuclear modifications in heavy-ion collisions, QCD studies, and high-pt particle production. Discuss key measurements, expectations, jet focus, software development, and future plans at RHIC and LHC.

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Ultra-relativistic Heavy Ion Reactions

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  1. Ultra-relativistic Heavy Ion Reactions Birmingham group activities in STAR and ALICE Lee Barnby

  2. Outline • Physics Motivation • Introduction and key measurements at RHIC • Expectations at LHC • Focus on jets • Activities in STAR at Brookhaven • Physics analysis contribution • Software development • Status and near future • Future plans in ALICE at CERN • Outlook Lee Barnby

  3. Introduction • Heavy-ion collisions allow the study of QCD in the non-perturbative regime. • Coloured objects (self-) interacting in the strong coupling (large S) regime. • Phase transition is predicted from Lattice QCD. Lee Barnby

  4. Key RHIC measurements • Particle multiplicity + Bjorken estimate  Energy density ≈ 4.6 GeV fm-3 • Hadron spectra + thermal models  TCH≈ 176 MeV B ≈ 41 MeV • Observed collective flow + ideal hydrodynamics  early thermalisation, low viscosity Strongly coupled QGP - ‘Perfect Liquid’ Lee Barnby

  5. The experimental status early universe 250 200 RHIC quark-gluon plasma Chemical Temperature Tch [MeV] SPS Lattice QCD 150 AGS 100 deconfinement chiral restoration SIS hadron gas 50 chemical freeze-out curve neutron stars atomic nuclei 0 0 200 400 600 800 1000 1200 Net Baryon density B [MeV] Lee Barnby

  6. Lattice QCD  vs T LHC ? RHIC SPS Hotter, longer-lived, larger system Lee Barnby

  7. Jets in heavy ion collisionsNuclear Modification of high-pt particle production X.-N. Wang and M. Gyulassy, Phys. Rev. Lett. 68 (1992) 1480 key prediction: jets are quenched Leading hadron Fragmentation radiated gluons pTOT pT pL heavy nucleus partons proton Partons are quarks and gluons proton • Dominant process in p+p • theoretically well-understood • provides connection to QCD theory • calculational framework to extract density, cS … Lee Barnby

  8. RHIC - high pT suppression • Charged particle spectra from d+Au and Au+Au compared • Scaled to take account of system size • Central Au+Au show factor 5 suppression at high pT Ratio to p+p Lee Barnby

  9. RHIC - disappearance of back-to-back jets • Di-jets create distinctive back-to-back correlation in particle pairs. • Opposite side to trigger is absent only in central Au+Au collisions. Trigger particle Associated (near-side) Df Associated (away-side) Lee Barnby

  10. Towards jet tomography away side same side d+Au Au+Au Dh Dh Df Df • Exploring • quark flavour dependence, flavour-tagged jets • energy, pT,and centrality dependencies Hot topic for experiment and theory Lee Barnby

  11. Promising directions - rare probes • Heavy flavour (c, b quarks) • Access to mass-dependence of energy loss • Calibrated probe ( -jet) • Measure energy of  know energy deposited • These measurements available with further running at RHIC and are even better prospects for LHC. Lee Barnby

  12. LHC Expectations- Growth of hard cross section • p+p data for s 23-1800 GeV • Soft particle production (pT < 1GeV/c) rising but with same order of magnitude • At large pT rise of several orders of magnitude • Heavy-ions at LHC have sNN = 5500 GeV Increasing energy Lee Barnby

  13. Birmingham group- Current activities and responsibilities • Collaboration roles • Analysis group co-ordinator (LB) • Strangeness group is one of 9 in STAR • Chaired paper editorial committees (PJ, JN), chair of talks committee (PJ) • Physics Analysis - two strands • High-pt probes to study medium response • Local modifications to; multiplicity, T, particle ratios • Strangeness production • Hadron phase thermodynamics, hadronisation mechanisms, scaling of particle production with volume Lee Barnby

  14. Birmingham group - Current activities and responsibilities cont. • Software • A major STAR enterprise • several 100k lines of code due to complexity of events • Developing and testing important components of reconstruction software • Contributions to maintaining and making more realistic simulation software • Pilot project developing GRID capabilities • Joined Open Science Grid Intention now is to move to ALICE Lee Barnby

  15. Future in ALICE • Physics case for move to LHC • Hotter, long-lived, larger, with increased cross-section for rare processes • Possible New Physics • Gluon saturation • A new energy frontier for hadron collisions • ALICE already has the upgrades STAR is planning • Particle ID (TOF), higher DAQ rate, inner Si Lee Barnby

  16. Future in ALICE cont • Activities and plans • Pb+Pb running should start in 2009 • Can envisage initial 5 year programme (2009-2013) • We will initially start work applying STAR particle correlation analysis • Contact with ALICE physics analysis group already • Our experience working with a similar detector at a collider facility will be a considerable advantage in physics exploitation. Lee Barnby

  17. Future in ALICE cont • Combined Nuclear and Particle Groups effort • NP group Bridging Funding secured to help with transition and synchronise funding schedule • Bring expertise from working with real data • Particle group delivered and commissioning ALICE trigger • Potential importance for rare probe physics • Personnel: • 2 PIs Peter Jones and David Evans • 1 Senior RF O. Villalobos-Baillie • 1 RS Fellow C. Lazzeroni  3 RFs • Currently 7 students (!) • A significant presence in a field with a large international interest (~2000 people) Lee Barnby

  18. RHIC II high luminosity Continued LHC running Search for critical point Compressed Baryonic Matter experiment at FAIR 2013/4 onwards RHIC as a decelerator 2010 run Electron Ion Collider eA collisions to probe nuclear PDFs BNL and J-Lab proposals Outlook for Heavy-ion PhysicsLonger term plans and proposals 250 200 150 100 50 0 qgp Tch [MeV] RHIC critical point? SPS AGS hadron gas SIS 0 200 400 600 800 1000 1200 B [MeV] Lee Barnby

  19. Backup slides Lee Barnby

  20. Gluon saturation • At smaller momentum fraction (x) number of gluons appears to increase • Should saturate at some point • Not easily accessible at RHIC • Can be seen at mid-rapidity at LHC • Saturation scale has A1/3 dependence Lee Barnby

  21. Measuring jets by two-particle correlations Trigger particle Associated (near-side) Df Associated (away-side) Phys Rev Lett90, 082302 4 < pT (trigger) < 6 GeV/c 2 < pT (associated) < pT (trigger) * Flow background subtracted Lee Barnby

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