Heavy Ion Physics with CMS

1. Heavy Ion Physics with CMS Bolek Wyslouch MIT

2. Holy Grail of High Energy Nuclear Physics: Quark Gluon Plasma • quarks and gluons, the fundamental constituents of matter, are no longer confined within the dimensions of the nucleon, but free to move around over a volume in which a high enough temperature and/or density prevails • plasma also exhibits the so-called "chiral symmetry" which in normal nuclear matter is spontaneously broken, resulting in effective quark masses which are much larger than the actual masses. • Basically: physics of condensed nuclear matter: phase changes due to multiple interactions of energetic quarks and gluons Bolek Wyslouch

3. m m t n p k p freeze-out hadronization chiral symmetry thermal equilibrium chemical equilibrium deconfinement hadrons mixed plasma partons thermalisation z Particle production in Heavy Ion collisionThe “probes” • mass and width of resonances (r, w) • thermal photons or dileptons (e+e-,m+m-) • strangeness enhancement (K,f, L, X, W) • energy loss of initial partons (jet quenching) • suppression of heavy-quark bound states (J/y , ¡’s  m+m-) Bolek Wyslouch

4. Vacuum QGP ????? Hard probes: cc, bb, jets • High mass or high momentum objects created during formation phase via high Q2 parton scattering • Penetrate hot and dense matter • Sensitive to state of hot and dense matter • Color screening • dE/dx by strong interactions Quarkonia, Jets High pt particles J/Y suppressed ? ’/ ratio ? Bolek Wyslouch

5. Today’s Experiments • Relativistic Heavy Ion Collider on Long Island, a dedicated facility: • Collisions of Au-Au with up to 100 AGeV in each beam • Four Experiments: • Brahms, Phenix, Phobos, Star • So far about 1-2 weeks of data • This year ~9 months • Running 6-9 months per year • Building on CERN/SPS results Bolek Wyslouch

6. Recent results from RHIC • Global features: charged multiplicity, particle production asymmetry (flow) indicate significant increase of energy density compared to pp • Indication of importance of “hard probes” • Jet production may be suppressed (quenched), production of high pt particles is smaller than expected from pp • Looking forward to see J/psi production at RHIC, suppression observed at SPS… Bolek Wyslouch

7. Charged multiplicity at mid-rapidity Bolek Wyslouch

8. Missing high pt particles at RHIC ? Effect seems to be stronger than “Cronin effect” observed in pA Bolek Wyslouch

9. What to expect from RHIC within the next few years • A very detailed study of most if not all “QGP signatures” at RHIC • Many beam energies, ion species, very high luminosity • But: maximum energy at RHIC is limited by ring radius and magnets • Some measurements, especially high pt probes may require higher energies: LHC Bolek Wyslouch

10. What To Expect from LHC • LHC (Large Heavy ion Collider) is expected to provide pA and AA collisions. • Energy: 5.5 GeV per nucleon pair in PbPb • 6 weeks/year • First heavy ion run in March 2007 Bolek Wyslouch

11. Main emphasis: Identified particles at low pt Add-ons for high pt physics Bolek Wyslouch

12. CMS: High pt edge of HI physics Bolek Wyslouch

13. Some CMS Assets of interest to HI • CMS has excellent muon detection capabilities: • |h|<1.3 for barrel and |h|<2.4 with endcaps. • Good mass resolution: 46 MeV for the Upsilon. • Efficient suppression of background from p/K decays: • Electromagnetic calorimeter at 1.3 m from beam axis. • PT threshold at 3.5 GeV/c for a single muon to reach the m-chambers. • Large calorimeter coverage with good jet reconstruction capabilities. Bolek Wyslouch

14. Selected Physics Topicsfirst physics studies by CMS Studies conducted by existing HI group in CMS Pablo Yepes will present the details • Event Characterization (centrality) • Quarkonium Production: Upsilon and J/Y in the barrel • Z detection • Jet Production: • Single/Double jet ratios, jet quenching • Z and g tagged jets • Ultra-Peripheral Collisions: gg and g-Pomeron Muon detector Calorimetry Bolek Wyslouch

15. Stretching CMS Pb-Pb mm Detector designed for pp. However due to flexible design offers unique capabilities for AA Bolek Wyslouch

16. Centrality: Participants vs. Spectators The collision geometry (i.e. the impact parameter) determines the number of nucleons that participate in the collision “Spectators” Only ZDCs measure Npart Zero-degreeCalorimeter “Spectators” • Many things scale with Npart: • Transverse Energy • Particle Multiplicity • Particle Spectra “Participants” Detectors at 90o Bolek Wyslouch

17. Event Characterization In spite of very strong magnetic field (4 Tesla) there is a good correlation between centrality and transverse energy. Bolek Wyslouch

18. Alternative “centrality trigger” • “Zero degree calorimeter” • Small fast calorimeters sensitive to forward neutrons • Very forward region, between two vacuum beam lines • Working at RHIC • Same design can be adopted for LHC • Could be essential for some measurements Bolek Wyslouch

19. Will the DAQ cope with the HI ? • Pb-Pb at L=1027cm-2s-1 (2 experiments running at the time) • LHC HI is relatively low luminosity but the occupancy can be huge, O(100,000) particles • Expected event size ~1.5 M Bytes (or larger, needs study) • With mass storage of 100 MBytes/s one can write ~70 events/s Bolek Wyslouch

20. Needs dedicated, continuing studies • DAQ and trigger: configuration, length of DAQ buffers, trigger thresholds • Most likely need to be reconfigured for the HI run • Lower magnetic field ? • Better jet acceptance • Lower pt threshold for J/psi (?) • functioning of trigger etc Bolek Wyslouch

21. Software for Heavy Ion CollisionsA real challenge ! Example: Small MC PRODUCTION in 2001 PbPb min bias Multiplicity: dNch/dh=1500 time: 6 hours/ev space: 500Mb/ev For 3000 events (0.5 sec LHC) ~3 years for PII 400 MHz ~2Tb disk space. -> minimum 36 computers (for 1 month run). The most interesting events are central dNch/dy=8000 (dNch/dh=6000). The time and the space will be ~24h/ev and ~2Gb/ev. Bolek Wyslouch

22. US Politics • CMS has a great potential to do good physics during Heavy Ion runs at LHC • US Nuclear physics community endorsed US participation in LHC heavy ion program (NSAC Long Range Plan) • Positive signs from DoE/Nuclear • But no miracles: RHIC is big and very hungry • Some of our colleagues prefer Alice CMS Heavy ion group: Lyon, Moscow, St. Petersburg, Dubna From the US: Rice, UC Davis Several US groups are considering participation (MIT, UIC, your colleagues) Schedule and level of participation are driven by RHIC commitments Bolek Wyslouch

23. Schedule and Resources • First HI run will be in 2007 • Needed to get good HI physics in 2007: • Physics studies • DAQ, Trigger and software preparation • Zero-degree calorimeter construction • There will be solid physics base learned at RHIC Bolek Wyslouch

24. Possible plan • Involvement in direct simulation and physics preparation work, ramping up in 2003-2004 • Involvement in US CMS computing together with HEP groups • DoE Nuclear funding for Tier-2(+) size computing resources Bolek Wyslouch

25. Summary • LHC will be a natural continuation of the series of Heavy Ion accelerators • CMS will have unique capabilities at the high transverse momentum frontier • , Z0, g, high pt jets • CMS can provide a natural place to do these measurements in the late-RHIC and post-RHIC era • Complementary to RHIC Bolek Wyslouch