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Ultra-relativistic Heavy Ion Reactions

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

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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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