Hadron Spectra and Yields Experimental Overview Julia Velkovska INT/RHIC Winter Workshop, Dec 13-15, 2002

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 2 Outline l Spectra  Radial flow  Does every particle flow ?  What are the freeze-out conditions ? l Yields and Ratios  Chemical properties of the system  Is T ch > T fo ? l How far in p T do soft processes dominate ? l Conclusions

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 3 Charged hadron spectra at 200 GeV l Exponential at low p T < 2 GeV/c l Power-low at high p T > 2 GeV/c

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 4 Spectral shape evolution with centrality p T < 2 GeV/c l Inverse slope increases with centrality due to radial flow l Relatively little change from 0 – 50 % p T > 2 GeV/c l Suppression of high p T hadrons increasing with centrality

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 5  P spectra from Star l High quality data over 9 centrality selections l Shape described by blast wave fit

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 6 Spectra with broad momentum range from PHENIX 0 – 5 % % % 15 – 20 % 20 – 30 % 30 – 40 % 40 – 50 % 50 – 60 % 60 – 70 % 70 – 80 % 80 – 93 % Au+Au at  s = 200 GeV PHENIX preliminary

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 7 The general features l Peripheral :  ~ equal slopes  Pions dominate over (anti)protons at all p T l Central  low-pt slopes increase with particle mass  proton and anti- proton yields equal the pion yield at high p T

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 8 Comparison for 200 GeV central data from all RHIC experiments l Relatively good agreement on preliminary data l Low p T data from PHOBOS will help constrain extrapolations to p T = 0 GeV/c

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 9 Characterizing the expansion l Strong radial flow:  Spectra are NOT exponential in m T  Inverse slopes depend on fitted (measured) range  Curvature increases with particle mass  At high m T all spectra converge to the same slope  versus mass – better than T eff versus mass, but still depends on fit function – very low p T data helps 1/m T dN/dm T (a.u.) m T -m mass

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 10 versus mass M. Kaneta/N. Xu (STAR) prediction with T th and obtained from blastwave fit (green line) prediction for T ch = 170 MeV and =0 pp no rescattering, no flow no thermal equilibrium STAR preliminary F. Wang of  and  from exponential fits in m T Do they flow ? Or is lower due to different fit function?

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 11 Fits to Omega m T spectra M. van Leeuwen (NA49) At SPS  and  are now found to be consistent with common freeze-out Maybe  and  are consistent with a blastwave fit at RHIC Need to constrain further  more data & much more for v 2 of  C. Suire (STAR) SPS/NA49 RHIC STAR preliminary  T is not well constrained !

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 12 systematics: centrality and beam energy open symbol : 130 GeV data Systematic error on 200 GeV data  (10 %), K (15 %),  p (14 %) [GeV/c] Increase of as a function of N part and tends to saturate  < K < proton (pbar) Consistent with radial flow increasing with beam energy and centrality But also can come from initial state multiple scattering or gluon saturation.

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 13 Kinetic freeze out parameters l From hydrodynamics fit Au+Au at sqrt(s NN ) =200GeV Top 5% centrality : STAR: T fo ~ 100 MeV  T  ~ 0.55c (130) & 0.6c (200) PHENIX: T fo ~ 121MeV(130) &110 MeV(200)  T  ~ 0.47c (200) Full model calculations give similar results

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 14 BRAHMS, submitted to PRL 12/07/02 nucl-ex/ Becattini: T=170,  s =1 PBM (PhysLettB518 (2000)41) predicts y=0 ratios almost exactly K - /K + = exp(2  s/T)(pbar/p) 1/3 K - /K + =(pbar/p) 1/4 is a fit to the data points Thermal parameters from K - /K and pbar/p ratios

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 15 The chemistry of the collisions Thermal models work well in describing particle ratios, even for the multi-strange particles : T ch = 177 MeV – close to critical temperature

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 16 Short-lived resonances : a measure for rescattering timescale Chemical freeze- out Kinetic freeze- out K * lost K * measured   K K*K* K K*K* K*K*  K   K*K* K K Consistent with sudden freeze-out

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 17 Is T ch > T fo ? l Single freeze-out model: Broniowski,Florkowski hep-ph/ l 2 thermal and 2 geometric (flow) parameters describe all central data including K *0 (892)  How good is the agreement really ?  Plots of theory/experiment on a linear scale ?  Comparison to other observables?

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 18 When does the flow start ? P.Kolb and R. Rapp hep-ph/ l Including pre-equilibrium transverse flow field improves agreement with the data centrality 0-5% 20-30% 40-50%

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 19 And how far in p T does flow dominate? Fit the soft part of , K,p spectra using hydrodynamics expression h + + h - =  , K, p l Compare to measured non- identified charged data l Significant soft component up to 2.5 – 3 GeV/c 130 GeV PHENIX

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 20 Another approach: look for jet fragmentation ratios as seen in pp data Experimentally observed: above pt=2 GeV/c particles are fragments of jets Characteristic particle composition determined by fragmentation function Soft to hard transition in p/  ratio

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 21 (anti)proton/pion ratio: Can we determine soft to hard transition? l Ratios steeply rising to p T ~ 2 GeV/c l Above p T = 2 GeV/c – flat  ~ 1 for central Au+Au  ~ 0.3 – 0.4 for peripheral Au+Au l Is there a peak ? At what p T do we get to the pQCD ratios ?

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 22 If protons are soft up to 4 Gev/c u R < 1 in regime of soft physics u R = 1 at high-p T where hard scattering dominates u R< 1 at high-p T suppression R= pions protons T slope ~ sqrt [ (1+<    <    For m T > 2 m 0 central peripheral

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 23 Scaling the proton+anti-proton spectra Radial flow Collision scaling ? N bin

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 24 How does the ratio Central/peripheral look ? …. and more details l See PHENIX talk by Jiangyoung Jia l And overview talk by David d’Enterria

INT/RHIC Winter Workshop 2002 Julia Velkovska (BNL) 25 Conclusions l A wealth of spectra, yields, ratios measurements from the first 2 years of RHIC l Spectral shapes consistent with strong radial expansion l Success of thermal chemical models  Almost net baryon free system with T ch close to critical temperature l Resonance studies show time-scale for emission is short, T ch close to T fo l Abundant protons+anti-protons at intermediate/high p T. How do they get there ?