| What we have learned and what need to do at RHIC? |
| What we have seen & what we have not seen |
|
| Yasuo MIAKE, Univ. of Tsukuba |
| RHIC and its operation |
| New machine at BNL, operational since 2000. | ||
| Series of measurements; | ||
| Au+Au collisions at ÖsNN = 200 GeV as highest & largest (240 mb-1) | ||
| Au+Au at ÖsNN = 19.6, 130, 200 GeV as energy scan | ||
| p+p at ÖsNN = 200 GeV as comparison data | ||
| d+Au ÖsNN = 200 GeV as controlled comparison | ||
| Npart vs Nbinary |
| Since nucleus is extended object, centrality of collision plays important role. | ||
| For comparison with pp or dAu also for centrality study, we need scaling variables. | ||
| Npart; | ||
| # of participant nucleons | ||
| Particle production in hA is prop. to Npart, (Wounded-Nucleon Model) | ||
| Nbinary; | ||
| # of binary nucleon-nucleon collisions | ||
| Pass through at high energy. | ||
| Evaluation of Npart & Nbinary by Glauber Model. | ||
| Particle production (h distr.) |
| All the data taken at RHIC(Phobos). | ||
| dn/dh ; wider & larger in higher energies. | ||
| Not very flat even at 200 GeV | ||
| Note that it is plotted in h. | ||
| Features of ‘limiting fragmentation’ seen | ||
| Simple application of Lorentz Invariance cannot be done! | ||
| Particle production (total mult.) |
| Total multiplicity per Npart stays constant. | ||
| WNM holds in AA. | ||
| Slight deviation at higher collision energies. | ||
| Deviation from Npart scaling more visible at mid-rapidity. | ||
| Transverse momentum distr. |
| p0 measured in Au+Au up to ~10 GeV/c. | ||
| Second component at high pt region (>4 GeV/c). | ||
| Exponential + Power law | ||
| Importance of hard process at high pt region | ||
| èComparison with pp | ||
| Comparison of Au+Au and pp |
| For comparison, Au+Au & pp spectra scaled by Nbinary. | ||
| In peripheral collisions, Au+Au ~ pp |
||
| In central collisions, Au+Au < pp |
||
| Suppression of yield ? | ||
| Loss of pT ? | ||
| Expected scaling behavior |
| Total mult; Npart scaling | ||
| Low pt region | ||
| Jets; Nbinary scaling | ||
| High pt in high energy collisions | ||
| èExpected behavior; | ||
| From Npart scaling at low pt to Nbinary scaling at high pt region. | ||
| High pt suppression (Jet Quench) |
| Taken as a big surprise! | |
| Clear high pt suppression in Au+Au, while not observed in d+Au. | |
| Since not seen in dAu, effect is not due to initial state, but final state. |
| Disappearance of back-to-back corr. |
| Direct evidence of loss of ‘jet’ | |||
| Azimuthal correlation w.r.t. high pt leading particle (trigger). | |||
| pp ; clean di-jet | |||
| dAu; similar to pp | |||
| Au+Au; Similar on the same side (suggesting jet-like mechanism), but b-to-b disappeared | |||
| Effect is not in initial but in final stage | |||
| Energy loss of partons in dense matter created in Au+Au | |||
| Energy loss of parton |
| Energy loss of charged particle in matter; | |||
| Collisions with atomic electrons, proportional to the electron density | |||
| Radiative energy loss. | |||
| èBether-Heitler Formula | |||
| In QCD, major loss will be radiative | |||
| Energy loss of parton should be proportional to the gluon density | |||
| Empirical analysis of energy loss |
| Empirical analysis of energy loss |
| Sloss from the pT averaged RAA. | |
| 20 % energy loss in central. | |
| Sloss prop. Npart2/3 implies Sloss prop. L2. |
| Next step, |
| Particle identification ! | |
| So far, data shown are charged & p0 | |
| Richer physics from data w. particle identification ! |
| Thermal equilibrium |
| Particle yield ratios well parameterized with Tch, mq,ms. | ||
| Chemical Eq. holds | ||
| Strangeness | ||
| Tch ~ 170 - 180 MeV | ||
| Transverse distr well parameterized with Tth, br. | ||
| Thermal Eq. | ||
| Tth ~ 110 - 120 MeV | ||
| Proton ~ pion at > 2 GeV/c | ||
| Collective expansion in pt ditr |
| Kinematical eq.+Collective expansion velocity | |
| Fit with low pt region |
| Thermal equilibrium |
| Close to the theoretical phase boundary | |
| Similar TRHIC and TSPS implies the existence of the phase boundary. |
| Azimuthal anisotropy v2 |
| In non-central col., participant has almond shape at initial stage. | |||
| Emission of particle in azimuth is influenced by l & R relation. | |||
| l >> R ; isotropic | |||
| l << R ; hydro.èelliptic | |||
| Anisotropy of the coordinate space converted to that of the momentum space. | |||
| As the system expands, effects vanishes | |||
| Sensitive to the initial stage | |||
| スライド19 |
| Large azimuthal anisotropy |
| Getting larger & larger in higher energies. | ||
| Scaling w. h-ybeam !? | ||
| Failure of hadronic scenarios |
| Hadronic scenario underestimates v2 at RHIC. | ||
| V2 ~ 1 - 2 % | ||
| System thermalized early with the mechanism other than hadronic rescatterings. | ||
| From hydro to jet region |
| Low pt region; | |||
| v2(p) > v2(K) > v2(p) | |||
| Good agreement with hydrodynamics | |||
| Very early thermalization (0.6 fm/c) required ! | |||
| Deviations from the hydro at
higher pt ; (> 2 GeV/c) jet region |
|||
| v2(p,K) < v2(p) | |||
| Order Reversed ! | |||
| What is the mechanism to create v2 in the jet region? | |||
| èEnergy loss of parton ! | |||
| Quark recombination model |
| Other possible production mechanism of high pt hadrons than the frag. | ||
| Quarks, anti-quarks combine to form mesons and baryons from universal quark distribution, w. | ||
| Mesons from 2 q with 1/2 of pT, baryons from 3 q with 1/3 of pT. | ||
| Bacause of the steep distr. of w, this process wins at mid-pt. | ||
| Characteristic scaling features expected. | ||
| èQuark number scaling | ||
| Proton dominance by RECO |
| Recombination model explains the proton dominance. |
| Quark number scaling |
| Quark number scaling clearly observed in v2. | |
| Distinct difference between Baryon Meson also seen in RCP |
| Puzzle of baryon dominance |
| In peripheral, p/p ratio similar to those in ee/pp suggesting fragmentaton process. | ||
| Fragmentation process should show np < np as seen in ee/pp. | ||
| In central Au+Au, p/p ratio increases with centrality, suggesting other mechanism like RECO. | ||
| But, RCP~1 (Nbinary scaling) implies hard process. | ||
| Test of ‘jet-like’ property |
| Excess of baryon due to the recombination of thermal ‘quarks’? | |
| Test jet-like properties in protons and mesons | |
| If baryons are all made of thermal quarks w. RECO, there should be no other correlation than the elliptic flow of the thermal quarks. |
| Partner yields of baryon/meson |
| Near side ; | ||
| ~twice of partner yields in Au+Au | ||
| Away side ; | ||
| Baryons at mid-pT originate from the same jet-like mechanism as mesons. | ||
| Open charm production in AA |
| consistent with Ös systematics and binary scaling. | |
| Centrality dependence shows Nbinary scaling. |
| Does charm flow? |
| Data seem to favor flow of the charm. | |
| If so, thermalized & flowing charm supports quark-coalescence & formation of QGP. |
| Summary |
| We have seen partonic matter,ie, a QGP! | |||
| Successful description of the system in terms of statistical thermo-dynamics; | |||
| Particle yield ratios in Tch, m | |||
| Kinematical distribution in Tth and b | |||
| Partonic | |||
| Large azimuthal anisotropy cannot be created with hadronic process. | |||
| High pt suppression and disappearance of back-to-back is at parton level. | |||
| Successful description of quark recombination; | |||
| Phenomenological, but universal quark distribution function! | |||
| Looking for signature of ‘phase transition’ | |||
| Particle production vs. energy |
| Smooth as a function of collision energy | ||
| Total charged mult., dn/deta, shape | ||
| Saturation of v2 !? |
| Previous comparison shows a smooth change with energy. | |
| ‘Sate of the Art’ analysis has revealed the saturation of v2 in ÖsNN = 60 - 200 GeV, which may indicate softening of EOS. |
| What need to be done |
| What we have seen is partonic matter. | ||
| What we have not seen clearly is the phase transition. | ||
| Except for the saturation of v2 !? | ||
| When and how it happens need to be investigated | ||
| Homeworks | ||
| HBT puzzle | ||
| J/y suppression? | ||
| Direct photon | ||
| Energy loss of charm | ||
| HBT puzzle |
| Extended life time of fireball expected if QGP. | ||
| 3D analysis of HBT | ||
| Rout/Rside should reflect life time of fireball. | ||
| Measured Rout/Rside ~ 1 !? | ||
| Failure of theories | ||
| J/y in Au+Au collisions |
| No clear conclusion yet. | ||
| 100 times better statistics recorded on tape. | ||
| Data analysis in progress ! | ||
| Direct photon |
| Direct photon = ‘photon’ excess in experiment. | |
| ‘Photon’ excess = inclusive g - decay g | |
| Consistent with binary scaling | |
| Ratios of particle production |
| Hadro-chemical eq. holds. |
| Energy dependence of v2 (2) |
| RHIC vs SPS |
| One exception? |