Experimental Results at RHIC T Hallman Brookhaven National

Experimental Results at RHIC T. Hallman Brookhaven National Laboratory ISMD Kromeriz, Czech Republic August 9 -15, 2005 TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 1

The Outline of this Talk • Brief definition of terms • Recent results on hard probes • Some thoughts about what the data are telling us • Conclusions TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 2

Definition of the terms QGP, v 2, and RAA (RCP) 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. Not required: Ø non-interacting quarks and gluons Ø 1 st- or 2 nd-order phase transition Ø evidence of chiral symmetry restoration TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 3

V 2 (Elliptic Flow) py Peripheral Collisions px z y x Anisotropic Flow Comparison with hydro suggests early (local) thermalization of the matter and an EOS with a soft point Hydro 2005, calculations: Kolb, Heinz and Republic Huovinen. TJH: ISMD 8/9 -15 Kromeriz, Czech 4

Experimental Tools: High p. T (Self-Analyzing) Probes of the Matter at RHIC Nuclear Modification Factor: <Nbinary>/sinelp+p nucleon-nucleon cross section AA leading particle suppressed hadrons q q ? If R = 1 here, nothing new going on RCP is the same construct with peripheral AA spectra as a reference TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 5

Partonic radiative energy loss in dense matter as a means to (indirectly) test deconfinement Thick plasma (Baier et al. ): Gluon bremsstrahlung Thin plasma (Gyulassy et al. ): Linear dependence on gluon density glue: • measure DE gluon density at early hot, dense phase High gluon density requires deconfined matter TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: !) (“indirect” QGP signature 6

An old story by now… STAR Phys. Rev. Lett. 91, 072304 (2003). Pedestal&flow subtracted • • In central Au+Au collisions: – Strong suppression of inclusive hadron production – Disappearance of the away-side jet d+Au looks like p+p Jet quenching in the dense medium p. QCD parton energy loss fits to observed central suppression d. Ng/dy ~ 1000 at start of rapid expansion TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 7

What’s New for the Inclusives? Significantly higher PT • Partonic (vs hadronic) energy loss • Matter is surprisingly opaque • Should provide lower bound on d. Ng/dy System Size Systematics RAA for Cu. Cu: same behavior for the same Npart as in Au. Au, but better precision TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 8

Inclusive Suppression: RAA in Cu+Cu √s. NN=200 Ge. V Au+Au A=197 Cu+Cu A=63 From Au+Au to Cu+Cu: change collision geometry in a more precise/ controlled way Result: Cu+Cu suppressed, but less so than Au+Au TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 9

Geometrical Dependence of RAA p+p • RAA scales smoothly from Au+Au through Cu+Cu to p+ • Scaling prefers Npart 1/3, though Npart 2/3 not strongly excluded TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 10

Limitations of RAA ? RAA at 10 Ge. V/c K. J. Eskola et al. , NP A 747, 511 Central RAA Data (~ strength of interaction) • Leading hadrons preferentially arise from the surface • Limited sensitivity to the region of highest energy density • Need more penetrating probes TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 11

Di-jets at much higher p. T 8 < p. T(trig) < 15 Ge. V/c p. T(assoc)>6 Ge. V STAR Preliminary No background subtraction! Clear emergence of the away-side jet TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 12

Di-jets and the interaction mechanism Scaling factors relative to d+Au ~0. 54 8 < p. T(trig) < 15 Ge. V/c ~0. 25 Direct measurement of the medium modification (and lack thereof) of the away-side jet – Away-side width and fragmentation function – Can partonic energy loss models describe these simultaneously? TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 13

Di-jets and the medium X-N Wang, PLB 595, 165 (2004) 8 < p. T(trig) < 15 Ge. V/c = STAR preliminary Yield should provide the first upper limit on the density of the medium – Constrain the number of active degrees of freedom? [Müller, Rajagopal, hep-ph/0502174] TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 14

How does the medium respond? 4. 0 < p. T(trig) < 6. 0 Ge. V/c 2. 5 < p. T(trig) < 4. 0 Ge. V/c 1. 0<p. T(assoc)<2. 5 Ge. V/c 2. 0<p. T(assoc)<p. T(trig) Ge. V/c 0. 15<p. T(assoc)<4. 0 Ge. V/c STAR Preliminary Measure low-p. T associated hadrons – Away-side particles increase in number and soften in p. T – Away-side flat or small dip for intermediate p. T(trig) TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 15

Conical flow? near • Does a shock wave form? • Three-particle correlations Df 2 – Conical flow: associated particles may appear on opposite sides of Δφ = π Medium away Conical flow near Df 1 Df 2 – Deflected jets: associated particles on the same side of Δφ = π Medium away Deflected jets Df 1 Casalderrey-Solana, Shuryak and Teaney, hep-ph/0411315 Stocker, NP A 750, 121 Ruppert and Muller, PL B 618, 123 TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 16

Three-particle correlations in d+Au and Au+Au p. Ttrig=3 -4, p. Tassoc=1 -2 Ge. V/c 2 -particle corr, bg, v 2 subtracted d+Au min-bias φ2=φ2 -φtrig near Difference in Au+Au average signal per radian 2: center – corner = 0. 3 ± 0. 3 (stat) ± 0. 4 (syst) center – cone = 2. 6 ± 0. 3 (stat) ± 0. 8 (syst) Medium away Au+Au 10% d. N 2/dΔφ1 dΔφ2/Ntrig near φ2=φ2 -φtrig Conical flow Medium away Deflected jets φ1=φ1 -φtrig Elongated along diagonal: k. T effect? deflected jets? Distinctive features of conical flow are not seen in present data with these p. T windows. TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 17

Charm in Au+Au • Important test of radiative picture: reduction in energy loss from heavy quark mass • Non-photonic electrons dominantly from charm decay • Suppression in Au+Au relative to d+Au TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 18

Charm and n. p. electron RAA and v 2 STAR V 2 • Identified D 0 consistent with binary scaling at low p. T • Non-photonic electrons arise primarily from c and b • Large charm suppression and flow at intermediate p. T TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 19

What happens at higher p. T? Heavy quarks Light quarks STAR • • • Rd. Au consistent with binary scaling RAA for central Au+Au shows n. p. electrons are very strongly suppressed at high p. T High-p. T electron suppression is comparable to incl. charged hadron suppression TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 20

(Maybe) not what we expected! Djordjevic et al, nucl-th/0507019 Armesto et al, private comm. See also Armesto et al, Phys. Rev. D 71 (2005) 054027 • b e should be there, too. Theory: RAA > 0. 4 • Data: RAA < 0. 3 – – Is our understanding of c and b production correct? Is our understanding of partonic energy loss correct? How strong are the in-medium interactions? How dense is the medium? TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 21

System-Size Dependence Factor ~3 suppression in central events Suppression roughly at The same level as in NA 50 Pb. Pb even though s is 10 times higher ! (? ) Data show the same trends within errors for all species and even 62 Ge. V TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 22

Comparison to Theory Muon arm Theory Vogt: nucl-th/0507027 Central arm Model of cold nuclear matter effects in agreement with d. Au: Tendency to underpredict suppression in most central Au. Au and events TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech. Cu Republic TJH: 23

System-Size Dependence Models that were successful in describing SPS data (color screeing, co-movers) fail to describe data at RHIC - too much suppression TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic -TJH: 24

System-Size Dependence Implementing regeneration: much better agreement with the data TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 25

J/y Rapidity Dependence Recombination expects narrowing of rapidity distribution which is not observed TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 26

Summarizing this part… PHENIX J/y centrality dependence: 1) Models with only cold nuclear matter effects 2) don’t have enough suppression 2) Models with color screening or comovers and without recombination have too much suppression 3) Models with recombination are in reasonable agreement with the data • Suppression for most central collisions is similar to NA 50 • Energy density and gluon density at RHIC should be much higher (2 -3 times) !? • At RHIC: Recombination compensates stronger QGP screening? TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 27

Some observations • Everything (!!!) flows ( , K, K*, p, , d, , , Ω, D) • The flow (v 2) seems to be built up very quickly (self quenching effect; seen for particles which may decouple early, seen for particles which contain heavy quarks not “born” flowing) – Preponderance of the evidence begs an explanation in which • Flow is developed when the degrees of freedom are those of quarks and gluons • The initial state (and the transition from it) “facilitate” extremely rapid thermalization • The apparent scaling of the v 2 for mesons and baryons with the NCQ suggests the relevant degrees of freedom when the flow is built up is not those of hadrons (BTW, these data 2005, are 8/9 -15 about as good as. Republic they TJH: will get; the ball is in TJH: ISMD Kromeriz, Czech theory’s court) 28

Constituent quark scaling solid: STAR open: PHENIX PRL 91(03) - v 2 appears to scale with number of constituent quarks. - quark coalescence. NCQ scaling “Hydro –like” Constituent quark DOF. Deconfinement? TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 29

Other things we have learned – We know that the matter is extremely dense and it thermalizes very rapidly. First order estimates of the energy density from d. ET/d (a la Bjorken), Hydro, and jet suppression results are consistent and all well in excess of the density needed for a QGP predicted by LQCD (~ 10 -15 Ge. V/fm 3). – The yields of different hadron species up to and including multi-strange hadrons is consistent with a Grand Canonical Statistical distribution which implies a lower limit on the temperature at chemical freezeout of 160 ± 10 Me. V if thermal equilibrium is reached – There is indirect evidence that: • the matter is deconfined • the primary degree of freedom of the matter is that of quarks and gluons • the matter is at high temperature (T > 170 Me. V) – Systematic m-dependence of v 2(p. T) suggests common transverse vel. Field – m. T spectra and v 2 systematics for mid-central collisions at low p. T are well (~20 -30% level) described by hydro expansion of ideal relativistic fluid – Hydro success suggests early thermalization, very short mean free path and high initial energy density (e > 10 Ge. V/fm 3) – Best agreement with v 2 and spectra for therm < 1 fm/c and soft (mixed-phase- dominated) EOS ~ consistent with LQCD expectations for QGP hadron – We need a better understanding of the real sensitivity of Hydro predictions to the EOS, and the freezeout treatment, and to improve consistency in describing spectra, v 2, and HBT. At present we can not draw quantitative conclusions on the properties of the matter such as the equation of state and the presence of a mixed phase. TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 30

Additional thoughts. . The data appear to demand an explanation beyond a purely hadronic scenario: – The lower limit of the energy densities derived from d. ET/dh are ~ 4 -5 Ge. V/fm 3: The hydro-models require early thermalization ( therm< 1 fm/c) and high initial energy density e > 10 Ge. V/fm 3. Their success implies the matter is well described as ideal relativistic fluid – Initial gluon density dng/dy~1000 and initial energy density e~15 Ge. V/fm 3 are obtained from GLV model of jet quenching. A similarly high initial energy density is obtained by other models. All these estimates of energy density are well in excess of ~1 Ge. V/fm 3 obtained in lattice QCD as the energy density needed to form a deconfined phase. The new results on inclusive suppression to ~ 20 Ge. V/c and di-jet tomography TJH: ISMD and 2005, upper 8/9 -15 Kromeriz, Czech TJH: density → should allow lower bounds on Republic the gluon 31

Conclusion central A qualitatively new form of matter is produced in relativistic nucleus-nucleus collisions! Needed: Further work ongoing to establish this is the quark- gluon plasma according to our definition. likely sources of insight on experimental side (in the near term): soft sector: • open charm elliptic flow (inclusive non-photonic electrons) • v 2 systematics (more particles, better statistics) • low mass di-leptons • low p. T direct photons • Fluctuations & multi-particle correlations jets and hard probes: • higher pt; search for away side punch-through • better stats di-hadron correlations wrt reaction plane/ trigger particle • heavy quark suppression (energy loss) (inclusive n-phot electrons) 8/9 -15 Kromeriz, Czech Republic TJH: ISMD 2005, • search forward mono-jets (Run VII) 32

Backup Slides TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 33

Extracting Near-Side Jet Yields • In Au+Au, jetlike correlation sits on top of an additional, ~flat correlation in d+Au, 40 -100% – : cannot differentiate between the two correlations – : additional correlation gets grouped into subtracted background STAR preliminary Au+Au, 0 -5% TJH: ISMD 2005, 8/9 -15 Kromeriz, Czech Republic TJH: 3 < p. T(trig) < 6 Ge. V 2 < p. T(assoc) < p. T(trig) 34

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