Diagnosing energy loss: PHENIX results on high-p T hadron spectra Baldo Sahlmüller, University of Münster for the PHENIX collaboration

Baldo SahlmüllerQuark Matter Physics Motivation: Why high-p T ? At high energy: hard scattering cross section large Measuring high p T particle yields: –Initial yields and p T distributions can be predicted from p+p measurements + pQCD + cold nuclear effects –Deviations can be attributed to the medium formed in A+A collisions High p T particles (leading particles of jets) as ,  0 can be measured in large BGs (dN ch /d  ~ 700) Quantification with nuclear modification factor: A+A p+p

Baldo SahlmüllerQuark Matter What we already know System size dependence at 200 GeV –Suppression up to high p T –Consistent with dN g /dy = 1200 (Au+Au) and dN g /dy = 370 (Cu+Cu) Questions: What happens at lower energies? Connection towards SPS energies? Similar suppression for similar N part - Consistent with pure density and path length dependence - also: taking into account shape of nuclei

Baldo SahlmüllerQuark Matter The PHENIX Experiment Measurement of ,  0 via  decay Decay  ’s are measured in EMCal –2 sectors PbGl, 6 sectors PbSc in 2 arms –Covers |  |<0.35,  =180° –Granularity fine enough to measure  0 ’s up to p T ~ 25 GeV/c ,  0

Baldo SahlmüllerQuark Matter Diagnosing Heavy Ion Collisions So far: status of investigating energy loss with high p T particle production; dependence on: CentralityOK p T OK System size (OK) => Next step: energy dependence

Baldo SahlmüllerQuark Matter GeV

Baldo SahlmüllerQuark Matter T The p+p Reference Measurement at 200 GeV nucl-ex/ 00  => See poster by A. Bazilevsky!

Baldo SahlmüllerQuark Matter nucl-ex/ Initial State Effects? New PHENIX paper on centrality dependence of  0 +  in d+Au at 200 GeV d+Au as collision system to look for initial state effects => no strong initial state effects nucl-ex/

Baldo SahlmüllerQuark Matter Au+Au at 200 GeV  data from RHIC run 2004 => See poster by M.L. Purschke!

Baldo SahlmüllerQuark Matter R AA at 200 GeV  in Au+Au => Suppression by a factor of 5 in central events

Baldo SahlmüllerQuark Matter R AA at 200 GeV Direct ,  0 and  in Au+Au –Direct  R AA with measured p+p reference! => R AA of  and  0 consistent, both show suppression => R AA of  is smaller than 1 at very high p T 0-10% central events

Baldo SahlmüllerQuark Matter GeV

Baldo SahlmüllerQuark Matter The p+p Reference p+p parameterization at 62.4 GeV: Fit to existing (ISR) data at similar energies (D.d'Enterria. J.Phys.G31, S491 (2005))

Baldo SahlmüllerQuark Matter The p+p Reference Problem: data sets inconsistent => large error  new important RHIC measurement in 2006  Analysis still ongoing

Baldo SahlmüllerQuark Matter Au+Au at 62.4 GeV Au+Au  0 : –Suppression in central events –Important: influence of error in p+p reference! –Theoretical curve: Vitev nucl-th/ dN g /dy =

Baldo SahlmüllerQuark Matter Spectra in Cu+Cu at 62.4 GeV 00  => See poster by T. Sakaguchi!

Baldo SahlmüllerQuark Matter R AA in Cu+Cu at 62.4 GeV Cu+Cu  0 : centrality dependent Important: Influence of error in p+p reference! Centrality dependent behavior Enhancement in peripheral events R AA smaller in central events

Baldo SahlmüllerQuark Matter R AA vs. N part at 62.4 GeV R AA integrated at high p T Again: Large normalization uncertainty from p+p reference R AA smaller towards higher N part Same theoretical model as for 200 GeV data consistent within errors

Baldo SahlmüllerQuark Matter GeV

Baldo SahlmüllerQuark Matter The p+p Reference p+p parameterization at 22.4 GeV: Fit to existing data at similar energies (D.d'Enterria. J.Phys.G31, S491 (2005))

Baldo SahlmüllerQuark Matter  0 at 22.4 GeV Towards SPS energies: Cu+Cu at 22.4 GeV Little centrality dependence

Baldo SahlmüllerQuark Matter SPS and RHIC Same behavior for similar N part (63 at WA98, 67.8 at PHENIX) Blattnig parameterization used for WA98 data (S. Blattnig et. al., Phys.Rev. D62 (2000) / D. D’Enterria, Phys. Lett. B 596 (2004) 32))

Baldo SahlmüllerQuark Matter R AA at Different Energies Comparison of  0 in Cu+Cu at 200, 62.4, and 22.4 GeV –Measured the same collision species over a broad energy range Suppression gets larger with higher energies

Baldo SahlmüllerQuark Matter Particle Ratio

Baldo SahlmüllerQuark Matter Ratio in Au+Au Ratio  /  0 for different centralities in comparison with PYTHIA prediction PYTHIA works very well in describing the ratio in heavy-ion collisions Possible conclusion (for high p T ): Suppression at partonic level, fragmentation outside medium

Baldo SahlmüllerQuark Matter Ratio in p+p and Cu+Cu Ratio  0 Approximately 0.5 at high p T First PHENIX  measurement at 62.4 GeV p+p Cu+Cu nucl-ex/

Baldo SahlmüllerQuark Matter “World” data  All PHENIX data consistent with world data  Ratio shows no obvious energy dependence

Baldo SahlmüllerQuark Matter Data vs. Theory?

Baldo SahlmüllerQuark Matter Comparing to Theories How probable is a certain parameter in theory? Theory: Loizides, hep-ph/ v2 Taking into account errors of measurement (for a certain theory parameter): 1. vary points within 4 RMS of correlated errors, find most probable point 2. calculate probability for large number of randomly picked sets of correlated and uncorrelated errors 3. see how many of these are worse than point from step 1

Baldo SahlmüllerQuark Matter Comparing to Theories another compilation… Theory: I. Vitev, Phys.Lett.B639:38-45,2006

Baldo SahlmüllerQuark Matter Comparing to Theories and another compilation… Theory: William Horowitz

Baldo SahlmüllerQuark Matter Summary Au+Au at 200 GeV –New  measurement up to p T = 15 GeV/c –Similar suppression patterns of  and  0 Cu+Cu at 62.4 GeV –Strong  0 enhancement in peripheral events –R AA gets smaller in central events Cu+Cu at 22 GeV –No significant centrality dependence in  0 production –Consistent with SPS results at 17.3 GeV Ratio  0 –Ratio  0 similar for different collision systems and energies Results in Cu+Cu and Au+Au consistent with partonic energy loss in the medium, fragmentation in the vacuum

Baldo SahlmüllerQuark Matter Finally: Back to the List So far:status of investigating energy loss with high p T particle production; dependence on: –CentralityOK –p T OK –System size (OK)

Baldo SahlmüllerQuark Matter Finally: Back to the List Now:status of investigating energy loss with high p T particle production; dependence on: –CentralityOK –p T OK –System size OK –EnergyOK

13 Countries; 62 Institutions; 550 Participants* *as of March 2005

Baldo SahlmüllerQuark Matter Related Talks and Posters Talks –2.2.5 V. S. Pantuev PHENIX measurements of reaction plane dependence of high-p T photons and pions in Au+Au collisions –3.1.2 Yu. Riabov Measurement of leptonic and hadronic decays of  and  mesons at RHIC by PHENIX –3.2.2 M. Konno High-p T Identified Hadron Production in Au+Au and Cu+Cu Collisions at RHIC- PHENIX –3.3.1 T. Isobe Systematic Study of High-p T Direct Photon Production with the PHENIX Experiment at RHIC Posters –1.14 M. L. Purschke Measurement of  p T distributions in S NN =200 GeV Au-Au collisions at RHIC-PHENIX –1.18 V. Ryabov Measurements of the multi-hadron decays of  and  mesons in heavy ion collisions at S NN = 200 GeV in the PHENIX experiment at RHIC –2.38 M. Shimomura Measurement of Azimuthal Anisotropy for High-p T Charged Hadron at RHIC- PHENIX –2.50 T. Sakaguchi System size and energy dependence of high-p T hadron production measured with the PHENIX experiment at RHIC –2.51 D. Winter High-pT π 0 production with respect to the reaction plane in S NN = 200 GeV Au+Au collisions at PHENIX