High p T results from PHENIX Carla M Vale Brookhaven National Laboratory for the PHENIX Collaboration June

Hard Probes '08Carla M Vale2 Outline Introduction –Current status Single particle spectra & Energy loss –Results, quantitative analysis Azimuthal anisotropy –v 2, path length “Puzzles” : new open questions Di-hadron correlations & the medium response Summary Future developments

Hard Probes '08Carla M Vale3 Where are we? We have learned a lot about the medium that is created in A+A collisions at RHIC… Fit to pp NLO pQCD (W. Vogelsang) T = 221 ± 23 ± 18 MeV (central) T = 224 ± 16 ± 19 MeV (MB) exp + TAA scaled pp direct  …and it’s hot!

Hard Probes '08Carla M Vale4 Where do we want to be going? High-statistics, high- precision data + theory  Develop new methods to extract physical parameters that characterize the medium and its response to hard probes Fit to pp NLO pQCD (W. Vogelsang) T = 221 ± 23 ± 18 MeV (central) T = 224 ± 16 ± 19 MeV (MB) exp + TAA scaled pp direct 

Hard Probes '08Carla M Vale5 How do we get there? “Turn the knobs” –Centrality, RP-dependence, energy dependence, particle species, … Higher luminosity –At various energies and collision species Developments in theory –Knowing the uncertainties Future: detector upgrades –Access to more “knobs”

Hard Probes '08Carla M Vale6 Single particle spectra & Energy loss

Hard Probes '08Carla M Vale7 Hard Scattering in p+p √s = 200 GeV √s = 62.4 GeV p+p: the calibrated reference W. Vogelsang arxiv:

Hard Probes '08Carla M Vale8  0 R AA vs p T : Au+Au, Cu+Cu PHENIX, Cu+Cu 0-10% PHENIX, Cu+Cu 60-94%

Hard Probes '08Carla M Vale9 Centrality Dependence Fit R AA (N part ) with: and extract  fit range  p T > 5 GeV 0.58 ± 0.07 p T > 10 GeV 0.56 ± 0.10 arXiv:

Hard Probes '08Carla M Vale10 Energy Dependence At 200GeV and 62.4GeV suppression is similar and consistent with energy loss effects At 22.4GeV Cronin enhancement dominates It appears that energy loss turns on between 22.4GeV and 62.4GeV, but it’s hard to tell where… PHENIX, arXiv:

Hard Probes '08Carla M Vale11 Measuring p+p cross-sections is important at all energies Until we have p+p collisions at all the same energies as Au+Au, the best we can do is rely on fits from existing data for the R AA The systematic errors have to be taken very seriously when interpreting such results

Quantitative analysis of R AA and models

Hard Probes '08Carla M Vale13 Constraining the models Fit the data by varying the model parameters, and determine the most likely range of values (at 1  level) Key point: take different types of experimental uncertainties into account correctly “A type”: point-to-point, uncorrelated “B type”: correlated “C type”: constant normalization factors To improve: model uncertainties are not yet included in the fits

Hard Probes '08Carla M Vale14 Results Model Name Opacity Parameter PQM = 13.2 ( ) GeV 2 /fm GLVdN g /dy = 1400 ( ) WHDGdN g /dy = 1400 ( ) ZOWW  0 = 1.9 ( ) GeV/fm 3 AMY  s = 0.28 ( ) Linear fitb=0.168 ( ) m= ( )(c/GeV) PHENIX arxiv

Hard Probes '08Carla M Vale15 Measure q-hat through  -jet? J. Frantz, later today We’re just getting started

Azimuthal Anisotropy at high p T

Hard Probes '08Carla M Vale17 v 2 at high p T PHENIX Preliminary Neutral + charged pionFinite v 2 even at high p T

Hard Probes '08Carla M Vale18 Energy loss and path length At high p T, the measured v 2 is not likely to result from the hydrodynamical anisotropy, but from the dependence of the energy loss of hard partons on the medium they have to traverse :  neither R AA nor v 2 describe the complete picture Measure reaction plane dependent R AA

Hard Probes '08Carla M Vale19 Reaction Plane Angular suppressio n pattern is p T dependent, at least up to high p T

Hard Probes '08Carla M Vale20 R AA vs path length % Centrality % Centrality % Centrality % Centrality % Centrality energy loss color charge density average over starting points

Puzzles

Hard Probes '08Carla M Vale22 Direct Photon R AA What is happening at p T ~ 18GeV? K. Okada, Fri

Hard Probes '08Carla M Vale23 R AA for hadrons  0 and  consistent across entire p T range R AA for  is higher, at least for intermediate p T : is it something strange? M. Naglis, Thu

Hard Probes '08Carla M Vale24 J/  Same suppression as at lower energies More suppression at forward rapidity What are the mechanisms at play? New results on v 2 (J/  ) coming up: E. Atomssa & C. Silvestre (Thu)

Hard Probes '08Carla M Vale25 Di-hadron correlations & Medium response

Hard Probes '08Carla M Vale26 Defining the terminology Near sideRidge Away sideShoulder (& Head)

Hard Probes '08Carla M Vale27 Away-side: head vs shoulder PHENIX arXiv: Trends in p T : 1.Away-side yield decreases 2.Shoulder region gradually disappears as the head region starts to dominate

Hard Probes '08Carla M Vale28 RP-dependence: the steady shoulder In-Plane Out-of-Plane Vary the direction of the trigger wrt RP Away side changes, as we go from in to out-of-plane, but shoulder position is constant

Hard Probes '08Carla M Vale29 Near and away: ridge vs shoulder Spectra and yields for ridge and shoulder are similar, and show same trend with centrality What is the connection? J. C.-H. Chen, Tue

Hard Probes '08Carla M Vale30 Summary Energy loss via single hadrons –R AA measurements established, now starting to get quantitative in constraining models –More differential probes (e.g. RP dependence) Open questions –Direct , , J/ , Di-hadron correlations –Even more open questions Look to the future –  -jet –Detector upgrades

Future developments

Hard Probes '08Carla M Vale32 NCC MPC VTX & FVTX rapidity  coverage 2  HBD EMCAL (i) p 0 and direct  with combination of all electromagnetic calorimeters (ii) heavy flavor with precision vertex tracking with silicon detectors combine (i)&(ii) for jet tomography with  -jet (iii) low mass dilepton measurements with HBD + PHENIX central arms Future PHENIX Acceptance for Hard Probes

Extras

Hard Probes '08Carla M Vale34 PHENIX Status Run 7: 200GeV: 650 TB, 5B events New detectors: Run 8: 200GeV: 437 TB, 160B events (sampled) 200GeV: 118 TB, 115B events (sampled) 9GeV: few collisions?

Hard Probes '08Carla M Vale35 62GeV p+p reference from fit Large discrepancies between different data sets contribute to large systematic error for this reference: better to measure it!