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First Hints for Jet Quenching at RHIC

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Presentation on theme: "First Hints for Jet Quenching at RHIC"— Presentation transcript:

1 First Hints for Jet Quenching at RHIC
Axel Drees, SUNY Stony Brook QM2001, Stony Brook, January 20, 2001 An Experimental Summary Introduction Knowledge from p-p and p-A collisions Mini-review of CERN results First data from RHIC Summary

2 Hard Probes In Heavy Ion Collisions
a) formation phase parton scattering b) hot and dense phase Quark Gluon Plasma Hadron Gas c) freeze-out emission of hadrons “hard” probes cc, bb and jets during formation phase parton scattering processes with large Q2 create high mass or high momentum objects penetrate hot and dense matter sensitive to state of hot and dense matter color screening in partonic phase  J/y suppression dE/dx by strong interaction  jet quenching matter box vacuum QGP beams of hard probes: jets, J/y …. ???? Axel Drees 29-Apr-19

3 Jet in Heavy Ion Collisions
jets and mini-jets contribute ~30% of particle production at RHIC energies observable in A-A collisions by high pt leading particles azimuthal correlation scattered quarks radiate energy (~ GeV/fm) in colored medium suppression of high pt particles “jet quenching” suppression of angular correlation hadrons q leading particle leading particle schematic view of jet production Axel Drees 29-Apr-19

4 Inclusive pt-Distribution in p-p
Data available over wide range of s, but not for 130 GeV power law: pp = d2N/dpt2 = A (p0+pt)-n interpolate A, p0, n to 130 GeV Axel Drees 29-Apr-19

5 Extrapolating from pp to AA
5% central min. bias pp hard scattering processes scale with binary collisions: scale to min. bias Au-Au: scaling to central collisions: systematic errors ~20-30% at 5 GeV Axel Drees 29-Apr-19

6 The Cronin Effect modification of pt spectrum in p-A collisions:
ratio analysis: for p-Au collisions: increases above 1 at ~2 GeV saturates at ~2 GeV eventually decreases to 1 at high pt Axel Drees 29-Apr-19

7 Results from the SPS data well described by pQCD
data equally well described by hydrodynamic fit Axel Drees 29-Apr-19

8 Comparing CERN-SPS Pb-Pb to p-p
X.N.Wang soft/hard transition? RAA exhibits typical “Cronin effect” behavior at SPS energy high pt spectra evolve systematically from pp  pA  AA no need to invoke energy loss Axel Drees 29-Apr-19

9 Evidence for hard scattering at SPS?
J.Rak, CERES H.Büsching, WA98 back-to-back azimuthal angular correlation for pions with pt >1.2 GeV (or photons not shown) angular correlation at 180o width of drops with pt: correlation stronger than expected from elliptic flow: measure v2 from dN/d: p sensitive to jet like correlation and elliptic flow Df (i) p (ii) p mostly sensitive to elliptic flow Df reaction plane Axel Drees 29-Apr-19

10 First Hints from dN/d at RHIC
X.N. Wang with quenching No jet quenching STAR PHENIX BRAHMS hard scattering soft physics scales like number of participating nucleons scales like number of binary collisions Axel Drees 29-Apr-19

11 Inclusive pt Spectra of charged Particles
J.C. Dunlop, STAR F. Messer, PHENIX first high pt data from RHIC: pt range to 6 GeV, covering >6 orders of magnitude well above what was reached at the SPS reasonable agreement: small differences in shape and yield centrality selection … Axel Drees 29-Apr-19

12 Inclusive pt Spectra of Pions
0 from 1 to 4 GeV good agreement with h- below 2 GeV agreement in shape with  from 0.3 to 2.2 GeV G. David, PHENIX F. Messer, PHENIX J.Velkovska, PHENIX Axel Drees 29-Apr-19

13 Remarks on charged particle spectra
F. Messer, PHENIX J.Velkovska, PHENIX h - = p + p - + K - p yield = p - yield at GeV p/p ~ 0.6 at all pt p yield = p + yield at ~ 2 GeV H.Ohnishi, PHENIX Axel Drees 29-Apr-19

14 Comparison to central Au-Au to p-p
Use identical p-p parameterization for all data sets normalize data to number of binary collisions divide by p-p parameterization UA1(130)/42 mb Ratio exhibits characteristic features: increases up to ~ 2 GeV saturates at RAA < 1 decrease at high pt Issues: large systematic error ~ 30% data: normalization, differences in shape, centrality selection, p/p contribution .. systematic uncertainty of p-p parameterization Axel Drees 29-Apr-19

15 Comparison to Central Au-Au to p-p
systematic check: use different p-p parameterization divide by p-p parameterization UA1(130) scaled to TAA within systematic errors: RAA < 1 RAA very different form expectation: increase at low pt exceeds 1 at ~2 GeV “Cronin effect” approaches 1 at high pt very different from SPS: follows expectation Axel Drees 29-Apr-19

16 Centrality Dependence of pt Spectra
F. Messer, PHENIX G.David, PHENIX Centrality dependence: complete systematic for charged central and peripheral for p0 Comparison to p-p central below p-p extrapolation peripheral agree reasonably with p-p extrapolation (note systematic uncertainty ~60% due to Ncoll) Axel Drees 29-Apr-19

17 Ratio Central/Peripheral
normalize central and peripheral to number of collisions different systematic errors: many experimental errors cancel systematic uncertainty ~60% on Ncoll Ratio exhibits characteristic features: increases up to ~ 2 GeV saturates at RAA < 1 decrease at high pt within systematic errors: RAA < 1 Axel Drees 29-Apr-19

18 Comparison with QCD calculations I
thanks to X.N. Wang for providing calculations Peripheral Au-Au collisions excellent agreement with ‘simple’ pQCD calculation for charged particles and for identified p0 Axel Drees 29-Apr-19

19 Comparison with QCD Calculations II
central Au-Au collisions p-QCD over estimates the cross-section for p0 at least a factor of 5 for charged factor of 2 (calculation does not describe p &p contribution) shadowing and pt-broadening seem insufficient calculation including constant energy loss consistent with p0 for charged magnitude & shape different in detail Axel Drees 29-Apr-19

20 Double-Differential Yields
F. Messer, PHENIX as function of pt and Ncoll Ncoll soft physics does not scale with Ncoll low pt <1 GeV hard physics in per. collisions decrease for central collisions high pt 4 -5 GeV double differential yields exhibit interesting structure Axel Drees 29-Apr-19

21 Azimuthal Anisotropy f  X.Y. Wang Anisotropy in geometry: path lenght
Anisotropy in jet quenching: hydro valid up to some pt without dE/dx v2  0 with finite dE/dx anisotropy in geometry  v2 > 0 f path lenght nucl-th/ Axel Drees 29-Apr-19

22 Charged particle anisotropy 0 < pt < 4.5 GeV/c
STAR data: only statistical errors plotted. Systematic error 10% - 20% for pt = 2 – 4.5 GeV/c Hydro+GLV: M. Gyulassy, I. Vitev and X.N. Wang, nucl-th/ Raimond Snellings, STAR azimuthal angular correlation measured by v2: hydrodynamic behavior up to ~1.5 GeV followed by saturation comparison to a recent theoretical calculation compatible with jet quenching scenario sensitivity to initial conditions Axel Drees 29-Apr-19

23 Comparison with pt distribution
Hydro+GLV: M. Gyulassy, I. Vitev and X.N. Wang, nucl-th/ calculation compatible with anisotropy measurement and pt - spectra Axel Drees 29-Apr-19

24 Summary amount an variety of RHIC data exceeds all expectations
only 4 months after the first run at RHIC we saw very interesting high-pt data from PHENIX and STAR charged and identified particles pt spectra to GeV azimuthal angular correlation out to 4.5 GeV pt spectra from peripheral collisions seem well reproduced by extrapolations from p-p pt spectra from central collisions show clear deviation from p-p extrapolation premature to draw definite or quantitative conclusions high pt-physics has proven to be a useful new penetrating probe complementary to charmoniuum production RHIC run 2001: more complete experimental setups higher statistics  higher pt accurate p-p reference data amount an variety of RHIC data exceeds all expectations high-pt data are consistent with “jet quenching” scenarios Axel Drees 29-Apr-19

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