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Results from STAR experiment at RHIC

Results from STAR experiment at RHIC. Bedanga Mohanty,VECC, Kolkata. Outline. Motivation STAR experiment Results from p+p collisions Results from d+Au collisions Results from Au+Au collisions Summary. Motivation : What QCD tells us……. V(r). r. Lattice Q C D prediction:.

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Results from STAR experiment at RHIC

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  1. Results from STAR experiment at RHIC Bedanga Mohanty,VECC, Kolkata Outline • Motivation • STAR experiment • Results from p+p collisions • Results from d+Au collisions • Results from Au+Au collisions • Summary WHEPP-9, IOP, Bubhaneswar January 4th 2006

  2. Motivation : What QCD tells us…… V(r) r WHEPP-9, IOP, Bubhaneswar January 4th 2006

  3. LatticeQCDprediction: F. Karsch, Prog. Theor. Phys. Suppl. 153, 106 (2004) TC≈1708 MeV, eC≈1 GeV/fm3 Motivation : phase transition At high temperature/density we expect a phase transition from a state where quarks are confined to a state where they are de-confined WHEPP-9, IOP, Bubhaneswar January 4th 2006

  4. Quark Gluon Plasma Shuryak publishes first “review” of thermal QCD and coins a phrase. “Because of the apparent analogy with similar phenomena in atomic physics, we may call this phase of matter the QCD (or quark-gluon) plasma.”(QGP) Plasma ≡ ionized gas which is macroscopically neutral & exhibits collective effects Usually plasmas are e.m., here color forces QGP  a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes. WHEPP-9, IOP, Bubhaneswar January 4th 2006

  5. Why study this phase transition • Properties of QCD • Big Bang was long back • Neutron stars are far away • Nucleon synthesis • Color superconductivity • Thermodynamics of matter under extreme conditions • Phase transition,tri-critical point • Dark Matter ?? Chiral symmetry restored Tri-critical point?? WHEPP-9, IOP, Bubhaneswar January 4th 2006

  6. The Early Universe, Kolb and Turner 8 gluons, 2 spins;  2 quark flavors, anti-quarks, 2 spins, 3 colors g : Effective number of degrees-of-freedom per relativistic particle Can this phase transition be created in laboratory ? Current attempts hadron  QGP QGP  hadrons First attempt at QGP formation was successful WHEPP-9, IOP, Bubhaneswar January 4th 2006

  7. Is it experimentally possible ? Lattice gauge theory – critical temperature for phase transition is around 170 MeV  corresponds to energy density of 1-2 GeV/fm3 Estimated that energy density achieved in central region of nucleus-nucleus collision can be as high as 10 GeV/fm3 QGP and a chiral symmetry restored matter can be created in Laboratory WHEPP-9, IOP, Bubhaneswar January 4th 2006

  8. STAR experiment at RHIC Run Year Species sNN[GeV ] Ldt 01 2000 Au+Au 130 1 b-1 02 2001/2 Au+Au 200 24 b-1 p+p 200 0.15 pb-1 03 2002/3 d+Au 200 2.74 nb-1 p+p 200 0.35 pb-1 04 2003/4 Au+Au 200 241 b-1 Au+Au 62 9 b-1 05 2004/5 Cu+Cu 200 3 nb-1 Cu+Cu 62 0.19 nb-1 Cu+Cu 22.5 2.7 b-1 p+p 200 3.8 pb-1 The STAR Collaboration: 50 Institutions, ~ 500 People USA, Brazil, China, Croatia, Czech Republic, England, France, Germany, India, Netherlands, Poland, Russia and Switzerland WHEPP-9, IOP, Bubhaneswar January 4th 2006

  9. Highlight of the first paper from STAR PMD • First time in Heavy-Ion collisions we showed that photons and pions follow energy independent limiting fragmentation. • We have resolved the contradictory results (from two contemporary experiments at RHIC) on the impact parameter dependence of limiting fragmentation of charged particles. The STAR Detector Large acceptance: 2p coverage at mid-rapidity Detectors : K. H. Ackerman et al., Nucl. Instrum. Methods Phys. Res., Sect. A 499 (2003) 624 Magnet Coils Central Trigger Barrel (CTB) ZCal Time Projection Chamber (TPC) Year 2000 Barrel EM Cal (BEMC) Silicon Vertex Tracker (SVT)Silicon Strip Detector (SSD) FTPCEndcap EM CalFPD TOFp, TOFr FPD PMD WHEPP-9, IOP, Bubhaneswar January 4th 2006

  10. Observable in STAR Energy, momentum, spatial position and multiplicity WHEPP-9, IOP, Bubhaneswar January 4th 2006

  11. V0 decayvertices Ks p + + p - L  p + p - L  p + p + X-  L + p - X+L + p + W  L + K- Log10(dE/dx) “Kinks”: K  +  Resonances in invariant mass spectra dE/dx in TPC STAR Preliminary Au+Au 40% to 80% 0 f0K0S  K*0 Electron ID via p/E in EMC Log10(p) 0.2  pT  0.9 GeV/c Time of Flight (ToF) Particles identified in STAR WHEPP-9, IOP, Bubhaneswar January 4th 2006

  12. Nucleon-Nucleon and Nucleon-Nucleus collisions We will start from simpler systems p+p and d+Au collisions then present results from Au+Au collisions • Test predictions from pQCD • Transition point of dominance of hard over soft process • Unique data on particle ratios at high pT • Reference system for understanding nuclear effects WHEPP-9, IOP, Bubhaneswar January 4th 2006

  13. Quark Distribution Functions determined from deep-inelastic lepton-hadron collisions How quarks are distributed in hadrons we collide Theory of particle production in p+p collisions How quarks and gluons fragment into hadrons What is the probability that 2 quarks will interact collide Hadron # 1 Quarks – fragment into hadrons Hadron # 2 Quark-Quark Cross-Section Determined from hadron-hadron collisions. Quark Fragmentation Functions determined from e+e- annihilations WHEPP-9, IOP, Bubhaneswar January 4th 2006

  14. STAR data and NLO pQCD First time in p+p and d+Au collisions baryon (proton+anti proton) production reasonably well understood within the framework of NLO pQCD WHEPP-9, IOP, Bubhaneswar January 4th 2006

  15. STAR preliminary STAR preliminary Transition from soft to hard process domination occurs at pT ~ 2 GeV/c in p+p and d+Au collision systems Transition from soft to hard process WHEPP-9, IOP, Bubhaneswar January 4th 2006

  16. STAR preliminary n is sensitive to structure function and fragmentation function What more from Scaling of particle production e+ and e- does not have a parton distribution function. There is a (sNN )2 factor multiplied to cross section TPC Collaboration, H. Aihara, et al., Phys. Rev. Lett. 61 (1988) 1263 ARGUS Collaboration, H. Albrecht, et al., Z. Phys. C 44 (1989) 547 ALEPH Collaboration, D. Buskulic, et al., Z. Phys. C 66 (1995) 355 WHEPP-9, IOP, Bubhaneswar January 4th 2006

  17. STAR preliminary STAR preliminary Nuclear Modification Factor : d+Au collisions Phys. Rev. Lett. 91 (2003) 072304 • RdAu for p > 1, Cronin effect • Absence of high pT suppression in particle production • RdAu (p + pbar) > RdAu (p) Similar dependence has been observed at lower energies. Phys. Rev D 19 (1979) 764 WHEPP-9, IOP, Bubhaneswar January 4th 2006

  18. Summary from p+p and d+Au collisions • NLO pQCD calculations consistent with pion and proton production in p+p and d+Au collisions at high pT at RHIC • For p+p collisions this is independently verified by the observed xT scaling. • xT and mT scaling of pions and protons in p+p and d+Au collisions shows the transition from dominance of soft to hard process occurs ~ pT = 2 GeV/c • Significant Cronin effect observed in d+Au collisions and NO suppression in high pT particle production • The nuclear modification factor for baryons is higher than mesons in intermediate region of pT • The pbar/p is around 0.8 for p+p collisions.It seems to decrease with pT for d+Au collisions WHEPP-9, IOP, Bubhaneswar January 4th 2006

  19. Time What happens when 2 heavy ions collide Courtesy of S. Bass Now we will address : Is QGP formed at RHIC ? When is the particle composition (which change via inelastic collisions) decided ? What is the freeze-out (after elastic collisions among hadrons have ceased) conditions at RHIC ? WHEPP-9, IOP, Bubhaneswar January 4th 2006

  20. STAR data : Freeze-out conditions at RHIC Distance > mean free path elastic collisions ceases The particle spectra are fitted to hydrodynamics motivated functional forms to extract the freeze-out temperature (random aspect) and radial flow velocity (collective aspect) WHEPP-9, IOP, Bubhaneswar January 4th 2006

  21. Hydro pQCD Hydrodynamics and spectra Au+Au central , √s = 200 GeV • RHIC: Tfo~ 100 MeV •  bT  ~ 0.55 c Good agreement with hydrodynamic prediction for soft EOS (QGP+HG) WHEPP-9, IOP, Bubhaneswar January 4th 2006

  22. Freeze-out conditions at RHIC Tcritical p,K,p: Tkin decreases, b increases with centrality X, W (low hadronic x sections): higher Tkin and significant radial flow. peripheral central WHEPP-9, IOP, Bubhaneswar January 4th 2006

  23. Chemical Freeze-out conditions at RHIC Tch gs Chemical freeze-out temperature ~ 165 MeV Rare particles chemical and kinetic freeze-out at same temperature Strangeness is chemically equilibrated WHEPP-9, IOP, Bubhaneswar January 4th 2006

  24. Discovery of quark structure of proton Penetrating probes Discovery of the atomic nucleus Penetrating probe :a particle Medium:Au - nucleus Penetrating probe :electron Medium :proton Can we do a similar thing to discover QGP ? WHEPP-9, IOP, Bubhaneswar January 4th 2006

  25. Jets hadrons q q hadrons Penetrating probes needs to be created here What are the probes Heavy particles (charm and bottom) WHEPP-9, IOP, Bubhaneswar January 4th 2006

  26. It measures the deviation of the AB collision at a given centrality from a superposition of pp collision. If at high pT: RAB = 1 → no nuclear effects RAB > 1 → enhanced hadron production in AuAu RAB < 1 → suppressed hadron production in AuAu X Nbin Leading particle spectra Au+Au p+p WHEPP-9, IOP, Bubhaneswar January 4th 2006

  27. High pT particle production is suppressed pQCD + Shadowing + Cronin pQCD + Shadowing + Cronin + Energy Loss • Deduced initial gluon density at t0 = 0.2 fm/c dNglue/dy ≈ 800-1200 • e≈ 15 GeV/fm3(e.g. X.N. Wang nucl-th/0307036) 100 times ordinary nuclear matter Factor of 5 suppression High pT particle production suppressed – dense matter formed WHEPP-9, IOP, Bubhaneswar January 4th 2006

  28. What about heavy particles ? Coupling of heavy quarks to medium is less due to mass p If energy loss is due to radiative process then RAA for electrons from heavy flavour > RAA for light hadrons Medium so dense – even heavy particles are stopped ! Results indicate energy loss mechanism still to be understood WHEPP-9, IOP, Bubhaneswar January 4th 2006

  29. Particle species dependence Rcp for baryons and mesons different at intermediate pT and then becomes similar at higher pT Medium allows for recombination at partonic level Recombination + Fragmentation: R. J. Fries, S. A. Bass, et. al. nucl-th/0306027 WHEPP-9, IOP, Bubhaneswar January 4th 2006

  30. Trigger particle Near side jet Dj Away side jet ?? Di-hadron correlations Adler et al., PRL90:082302 (2003) Adams et al., Phys. Rev. Let. 91 (2003) Back to back suppression is a final state effect, consistent with expectations of parton energy loss in a dense medium Associated particles Correlation of trigger particles 4<pT<6.5 GeV withassociated particles 2<pT<pT,trig p+p, peripheral Au+Au: 2 jets Central Au+Au: no away-side jet Suppression of associated particles on away side d+Au control: 2 jets No ‘jet’-suppression WHEPP-9, IOP, Bubhaneswar January 4th 2006

  31. Out-of-plane in-plane Suppression depends on distance traveled The back to back correlation depends on the average distance traveled through the medium! Au+Au centrality: 20-60% WHEPP-9, IOP, Bubhaneswar January 4th 2006

  32. Almond shape overlap region in coordinate space Interactions/ Rescattering Anisotropy in momentum space Azimuthal Anisotropy of Emission: Elliptic Flow dN/df ~ 1+2 v2(pT)cos(2f) + …. f = atan(py/px) v2= cos2f v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane Elliptic flow observable sensitive to early evolution of system Mechanism is self-quenching Large v2 is an indication of early thermalization WHEPP-9, IOP, Bubhaneswar January 4th 2006

  33. Large v2 observed at RHIC Hydrodynamical models with soft Equation-of-State (EOS) describe data well for pT (< 2.5 GeV/c) v2(p) > v2(K) > v2 (p) ~ v2(L)  compatible with early equilibration ... Contrast to lower collision energies where hydro overpredicts elliptical flow WHEPP-9, IOP, Bubhaneswar January 4th 2006

  34. Hydro Limits: Like a Perfect Liquid ? U. Heinz, nucl-th/0407067 Hydro Limit (RHIC) First time hydrodynamics without any viscosity describes heavy ion reactions: Thermalization time t = 0.6 fm/c, Energy Density: e=20 GeV/fm3 e =spatial eccentricity = y2-x2/y2+x2 S =overlap area WHEPP-9, IOP, Bubhaneswar January 4th 2006

  35. Semileptonic D decays Partonic collectivity at RHIC large v2 (even f, X, W): strong interactions at early stage large v2 of f, X, W(low hadronic x-sections): partonic collectivity at RHIC. Collective flow is generated during the partonic stage already. WHEPP-9, IOP, Bubhaneswar January 4th 2006

  36. Baryon meson splitting observed in flow 200 GeV Au+Au Medium allows for recombination at partonic level WHEPP-9, IOP, Bubhaneswar January 4th 2006

  37. Constituent quark scaling of v2 scaled meson and baryon v2 agrees at intermediate pT Flow for non-photonic electrons consistent with those of light mesons Favors scenario in which charm quark flows as light quarks Strong coupling of charm quark to the medium WHEPP-9, IOP, Bubhaneswar January 4th 2006

  38. Summary There is compelling experimental evidence that heavy-ion collisions at RHIC has produced a state of matter characterized by • Very high initial energy density (> 15 GeV/fm3) • Very high initial temperature (> 400 MeV >> 1012 K) • Density of unscreened color charges 10 times that of nucleon • A matter so strongly coupled that even heavy quarks flow • A matter so dense that heavy quarks and 10 GeV hadrons are stopped • A matter allows for partonic recombination WHEPP-9, IOP, Bubhaneswar January 4th 2006

  39. Summary This state of matter is not describable in terms of ordinary color-neutral hadrons, because there is no known self-consistent theory of matter composed of ordinary hadrons at the measured densities The most economical description of this matter is in terms of the underlying quark and gluon degrees of freedom References : BRAHMS Collaboration, I Arsene et al., Nucl. Phys. A 757: 1, 2005 PHOBOS Collaboration, B.B. Back et al., Nucl. Phys. A 757: 28, 2005 STAR Collaboration, J. Adams et al., Nucl. Phys. A 757: 102, 2005 PHENIX Collaboration, K. Adcox et al., Nucl. Phys. A 757: 184, 2005 WHEPP-9, IOP, Bubhaneswar January 4th 2006

  40. Late Breaking News • November, 2005 issue of Scientific American • “The Illusion of Gravity” • J. Maldacena • A test of this prediction comes from the Relativistic Heavy Ion Collider (RHIC) at BrookhavenNational Laboratory, which has been colliding gold nuclei at very high energies. A preliminary analysis of these experiments indicates the collisions are creating a fluid with very low viscosity. Even though Son and his co-workers studied a simplified version of chromodynamics, they seem to have come up with a property that is shared by the real world. Does this mean that RHIC is creating small five-dimensional black holes? It is really too early to tell, both experimentally and theoretically. (Even if so, there is nothing to fear from these tiny black holes-they evaporate almost as fast as they are formed, and they "live" in five dimensions, not in our own four-dimensional world.) WHEPP-9, IOP, Bubhaneswar January 4th 2006

  41. Gluon to p fragmentation more in KKP than Kretzer STAR data and NLO pQCD Baryon (proton+anti proton) production not consistent with KKP FF At higher rapidity data prefers Kretzer FF than KKP FF PDF : CTEQ6 WHEPP-9, IOP, Bubhaneswar January 4th 2006

  42. Particle Ratios – in p+p and p+A collisions Same-charge particle ratios for high pT hadrons p/p+ Vs. pT reflects FF ratio Dpu /Dp+ u A rapid drop of p/p+ with pT followed by a high pT flattening – scattered point-like diquarks as a source of high pT protons (Phys.Lett.B149:509,1984) pbar/p- : pbar must be produced by scattering of sea-quarks or gluons or rank ordering Decrease in pbar/p-  decreasing importance of these processes Opposite-charge particle ratios for high pT hadrons p-/p+ Vs. pT or x may reflect the d/u structure function ratio in protons pbar/p Vs. pT : p has valence quarks common with nucleons, so it may reflect the fraction of protons of gluonic origin (assuming that gluons fragment equally into p and pbar). WHEPP-9, IOP, Bubhaneswar January 4th 2006

  43. p-/p+ ~ 1- independent of pT • pbar/p decreases with pT • p/p+ and pbar/p- increases with pT up to 2 GeV/c and then decreases. Particle ratio • p-/p+ ~ 1andpbar/p ~ 0.8 • pQCD predicts a more prominent pT dependence, Phys.Rev.C 58 (1998) 2321 • p/p+ and pbar/p- increases with pT ~ 2 GeV/c and then decreases to ~ 0.2 • p/p+ agrees with lower energy results. • pbar/p- shows a distinct energy dependence WHEPP-9, IOP, Bubhaneswar January 4th 2006

  44. STAR data and phenomenological model Model based on parton ladder splitting does a reasonable job. Parton ladder : dynamical process of parton-parton scattering with successive emission of partons WHEPP-9, IOP, Bubhaneswar January 4th 2006

  45. FPD PMD dNch/dh/0.5Npart FTPC STAR preliminary dNp/dh/0.5Npart dNg/dh/0.5Npart STAR preliminary Nucl-ex/0502008 (To appear in PRL) h - ybeam h - ybeam h - ybeam forward physics Forward rapidity at RHIC probes CGC. CGC will be even more important at LHC (and at mid-rapidity). See talk, B. Mohanty (section 1b) • Consistent with the CGC framework. • RdAu-p0 lower than h-: p+ph-is isospin suppressed at large h. • Photons: centrality independent limiting fragmentation. • Charged particles: centrality dependent limiting fragmentation. • Pions follow limiting fragmentation in heavy-ion collisions. WHEPP-9, IOP, Bubhaneswar January 4th 2006

  46. Au+Au 0-10% Au+Au 0-10% p+p p+p Baryon enhancement • Large enhancement in baryon/meson ratios in central Au+Au collisions • Maximum at pT~3 GeV/c, after which approach towards p+p • Indication of dominant non-fragmentation contribution • At what pT is this contribution no longer dominant? L/K0s Au+Au 0-5% p+p WHEPP-9, IOP, Bubhaneswar January 4th 2006 See talk, Barannikova(1a) and Salur(5a)

  47. Analogy in Atomic System • Same phenomena observed in gases of strongly interacting atom (Gehm et al. Science 298 (2002) 2179) • Gas of trapped 6Li atoms: excite Feshbach resonance via magnetic field (38th vibrational Li2 state)  0 energy, huge cross-section  explodes hydrodynamically, shows elliptic flow The RHIC fluid behaves like this, that is, a strongly coupled fluid. WHEPP-9, IOP, Bubhaneswar January 4th 2006

  48. Gluon to p fragmentation more in KKP than Kretzer STAR data and NLO pQCD Baryon (proton+anti proton) production not consistent with KKP FF PDF : CTEQ WHEPP-9, IOP, Bubhaneswar January 4th 2006

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