The quest for the QGP: 20 years of heavy ion physics

1. The quest for the QGP:20 years of heavy ion physics J. Schukraft

2. world map, late 15th century QCD map, late 20th century Explorations Search for the QGP* Search for a sea passage to India* A Mid-Fifteenth-Century European World Map (1466) The Mediterranean basin, known to Ptolemy and later Europeans, is fairly accurately depicted, but the Eastern portions of the map are very incomplete since they were based on often-fictitious travelers’ accounts rather than observation. *Original idea from H. Satz and D. Karzheev, Hard probes WS, Portugal, 2004 https://webh04.cern.ch/event-hardprobes04/

3. Headline Barcelona News April 1493 Explorers Columbus: visionary, enthusiastic adventurer Not afraid to venture far into the unknown with little guidance and marginal preparation. As befits the brave (and lucky), he made a BIG discovery. ‘In 1493, Columbus wrote a brief report concerning his discoveries of "Islands of India beyond the Ganges." It was intended as a public notice to announce his discoveries and to garner support for another voyage. The first edition of this letter was printed in Spanish in Barcelona in April 1493.’ Quote from US library of Congress

4. 1434 1455 1460 1482 1485 1488 Thomas Kostecki, Vasco da Gama (1998) Explorers Vasco da Gama: methodical explorer Building on years of systematic ‘experimental’ discoveries, one step at a time.. As befits the diligent, he reached his goal in due time For the last leg, VdG was guided by an Indian pilot, arranged for by Ahmed ibn Majid in Malindi.

5. 20th Century Explorers Bikash, the Indian pilot Hans, the visionary adventurer Louis, the systematic explorer • Lessons from the 15th century: • - there are different approaches to make a discovery • you don’t always find what you set out to discover • - when venturing into the unknown, have the Indians ‘on board’ • India: Strong and recognized partner in quest for QGP • > 60 physicists, > 8 Institutes • - participation in SPS, RHIC and LHC programs • 5th largest nation in ALICE • strong Theory community

6. What are we looking for ? 15th century explorers: direct trade route to the ‘Origin of Spices’ 20th century explorers: understanding the ‘Origins of Matter’ Da Gama arriving in India, 1498 NA35 streamer chamber picture, ca 1990

7. QGP: The ‘Original’ State of Matter • QGP = true ground state of QCD • melting matter => deconfinementstudy phase diagram of matter • melting vaccum(gluon condensate) =>chiral symmetry restoration dynamical origin of constituent mass • Phase transitions involving elementary quantum fields • phase transitions and spontaneous symmetry breakingcentral to HEP • QCD transition is the only one accessible dynamically • Cosmology & Astrophysics • early Universe at ~ 1 ms • interior of neutron stars • new domain of hot & dense QCD • surprises ?

8. Melting Matter

9. QCD chiral symmetry breaking SM Higgs mechanism The Dark Mystery of Matter What stuff is the Universe made of ?? • Elementary Particles 0.1% • 12 matter particles(quarks, leptons) • only 4 relevant today (u, d, e, n) • 13 force particles (3 massive, 10 massless) • Composite Particles (hadrons) 4% • hundreds… • only 2 are relevant (p,n), making nuclei • Dark Matter 23% • made of unknown particles • Dark Energy 73% • vacuum energy • of completely unknown origin • should be infinite or exactly 0 We don’t know how and why for ~ 5% We don’t even know what for the other 95%

10. Recent Lattice QCD ‘Maps’ • recent progress • improved actions • improved symmetries • larger lattices • crit. temperature • energy density • EOS Tc ~ 175 ± 8 ± 8 MeV • ec ~ (6±2) Tc4 • (e-3P) ¹ 0

11. Heavy Ion Collision t = 0 t = 5 fm/c t = 1 fm/c t = - 3 fm/c t = 10 fm/c t = 40 fm/c QGP pre-equilibrium hard collisions hadron gas freeze-out

12. ?

13. X 5 X 10 X 30 Experimental Facilities • AGS (1986 - 1998) • Beam: Elab < 15 GeV/N, Ös ~ 4 GeV/N • Users: 400 Experiments: 4 big, several small • SPS (1986 - 2003) • Beam: Elab < 200 GeV/N, Ös < 20 GeV/N • Users: 600 Experiments: 6-7 big, several small • RHIC (>2000) • Beam: Ös < 200 GeV/N • Users: 1000 • Experiments: 2 big, 2 small • LHC (>2007) • Beam: Ös < 5500 GeV/N • Users: 1000 • Experiments: 1 dedicated HI, 3 pp expts

14. 1434 1455 1460 1482 1485 1488 Roadmap, 3rd ICPA-QGP Jaipur, March 1997 Very complex reactions can be measured and analyzed • large systems • thousand of particles • Volume > 4000 fm3 • energy density up to 3 GeV/fm3 • strongly interacting system • hadronic rescattering • collective phenomena (flow) • thermal particle ratios f(T, m) • signs of ‘new state of matter’ • e+e- pairs (chiral symmetry rest. ?) • J/y suppression (deconfinement ?)

15. Dpx > Dpy Soft Probes: Elliptic Flow • Flow: Correlation between coordinate and momentum space • close particles move at similar velocity and direction • flow builds up in an interacting medium with pressure gradients • for given boundary conditions, flow profile depends on • Equation of State EoS and viscosityh of ‘fluid’ • Hydrodynamics of perfect fluid: h = 0, l = 0 (‘strongly interacting’) Elliptic Flow reduces spatial anisotropy -> acts at early times

16. First Flow Measurement at SPS • Remember Columbus: • Elliptic Flow not expected at SPS • PMD meant to look for photon/hadron fluctuations (Centauro like events), discovered flow instead WA93/98 PMD detectors measures azimuthal anisotropy of photons Presented by Indian group (Y. Viyogi) at QM’95 • Implications: • strongly interacting ‘matter’ • collective expansion • ~1/2 ideal hydrodynamics Particle emission is correlated !

17. Correlation method: The lowest yield (Ro=0) Most probable yield (Ro=6 fm) Subtraction method Subtraction method, upper limit Predictions hadronic gas QGP pQCD sum WA98 QM 2004 Photons: Thermal Radiation ? • Thermal photons • ‘heat’ radiation from initial hot phase • ‘El Dorado’ of QGP physics • rate ~ T4 => sensitive to early phase • rate ~ lifetime => contribution from hadronic phase • very challenging measurement • high pt: direct QCD hard scattering • medium pt: p0 decay photons • finally sighted at very low pt ??? CERN Press release in 2000 on ‘Evidence for new state of matter’ ‘It is expected that the present "proof by circumstantial evidence" for the existence of a quark-gluon plasma in high energy heavy ion collisions will be further substantiated by more direct measurements (e.g. electromagnetic signals which are emitted directly from the quarks in the QGP) ...’

18. c beams of hard probes: jets, J/y …. c c c c c Onset of Deconfinement ? Ca 1986 normal matter QGP Hard Probes: J/Psi suppression

19. NA44 NA49 Radial expansion, ‘Hubble Flow’ Thermal particle ratios f(m,T)’ NA49/Ceres mass generation Deconfinement NA50 SPS Experiments

20. Current hunting ground for Quark Gluon Plasma The Relativistic Heavy Ion Collider

21. STAR parton energy loss PHENIX PHOBOS BRAHMS Elliptic Flow small angle particles Particle Production RHIC Experiments

22. STAR PRL 86, (2001) 402 || < 1.3 0.1 < pt < 2.0 Momentum space py px Flow at RHIC • matter at RHIC: ~ perfect fluid with ~ zero mean free path ! • huge effect (almost 2:1 at high pt) • almost perfect agreement with hydro f(impact parameter, pt, particle mass)

23. leading particle NOT suppressed hadrons beams of hard probes: jets, J/y …. q q hadrons leading particle NOT suppressed peripheral Vacuum central QGP Hard Probes : Jet Quenching jet quenching measures ‘radiation ‘ length of QGP dE ~ mD2 x L2 mD = Debye screening mass • high pt partons: • Vacuum: fragment into hadrons =>JETS • Matter: additional scattering => more gluon radiation • normal ‘cold’ matter:small effect • QGP: strong effect (up to several 10 GeV) • observables of ‘jet quenching’ • leading parton looses energy • energy shows up in soft partons around jet axis

24. India or America ? • SPS/AGS: ‘new state of matter’ • solid evidence for collective,thermal hadronic matter • new effects: quarkonia suppression & low mass lepton pair spectrum • RHIC: dense (thermalized ?) partonic matter • elliptic flow compatible with hydrodynamical limit • Hydro = limit of zero mean-free-path => strongly interacting fluid,¹ gas ! • almost ideal fluid, h/s ~ 0.1 (much better than water !) • jet quenching compatible with complete absorption from interior • strength of interaction seems mysteriously high

25. QCD map, late 20th century QCD, early 21st century RHIC QG-Plasma or QG-Molasses ? • QGP: weakly interacting ‘gas’ of quarks and gluons • deconfined, chiral symmetry restored • sQGP: strongly interacting partonic fluid Columbus:‘Having now accomplished the undertaking upon which I set out,… I advanced forward, thinking that I could find some town - but at length, perceiving that nothing new was likely to appear - I determined to make no further search.’ The journey must go on !

26. Future place for studying the Quark Gluon Plasma The Large Hadron Collider

27. ALICE Set-up TOF TRD HMPID TPC PMD ITS Muon Arm PHOS Size: 16 x 26 m Weight: 10,000 tons

28. ALICE Collaboration ~ 1000 Members (63% from CERN MS) ~30 Countries ~80 Institutes

29. The ALICE Magnet: ready for the experiment to move in!

30. Inside the ALICE TPC

31. PMD prototype Manas electronics chip Muon Chamber India in Alice

32. 1434 1455 1460 1482 1485 1488 RHIC Past-Present-Future • AGS/SPS: 1986 – 1994 • existence & properties of hadronic phase • chemical & thermal freeze-out, collective flow,… • SPS: 1994 – 2003 • ‘compelling evidence for new state of matterwith many properties predicted for QGP’ • J/Y suppression (deconfinement ?) • low mass lepton pairs (chiral restoration ?) • RHIC: 2000 - ? • compelling evidence -> establishing the (s)QGP ? • parton flow, parton energy loss • LHC: 2007 - ?? • ‘go west’ or find the ‘Island of India beyond the Ganges’ • precision spectroscopy of ‘ideal plasma ‘QGP • heavy quarks (c,b), Jets, Y, thermal photons We are on an exciting and wondrous exploration, not taking any chances: We have the Indian pilot and his crew ‘on board’