Testing the Recombination Model at RHIC using multi-strange baryon correlations

1. Testing the Recombination Model at RHIC using multi-strange baryon correlations 23rd Winter Workshop on Nuclear Dynamics, Big Sky, MT Betty Abelev UI Chicago for the STAR Collaboration

2. Understanding the medium • Measure probes after Thermal freeze-out • Look for probes that traverse the entire medium • Initial state hard scattering  jets Betty Abelev

3. = ≈ Ethres 2 m 200 MeV s Medium Probes: Strangeness Hamieh et al.: Phys. Lett. B486 (2000) 61 • Partonic system vs. hadron gas • Canonical ensemble vs. grand-canonical • Exact q.n. conservation • Overall q.n. conservation & chemical potentials (sss) Enhancement of strange baryons (dss) (uds) R. Stock on strangeness enhancement: “Fading away of small volume canonical constraints” hep-ph/0312039 Betty Abelev

4. Strangeness at intermediate pT • Strange particle RCP (Central/peripheral) • Mesons suppressed more than baryons at intermediate pT • Mesons suppressed more than baryons • Baryon/meson ratioincreases with centrality L/K0S Betty Abelev

5. 10-1 10-2 10-3 10-4 dN/pTdpTdy 1 2 3 4 5 [GeV/c] Coalescence/Recombination of partons 3 GeV/c hadron can be • Produced via fragmentation • If meson: coalescence of 2 1.5 GeV/c partons • If baryon: 3 1 GeV/c partons (more abundant!) ReCo cartoon • Recombination: • Shower (S) • Thermal (T) • S & T can mix • Particle spectra are a sum of various components • Exponential (thermal) parton spectrum qualitatively explains baryon excess at mid pT R.Hwa et al, Phys.Rev.C70 (024904) 2004. Betty Abelev

6. Prediction from Rec. Model by Hwa et al • Use Azimuthal correlations • measure fragmentation (shower-quark contribution) • ifΩ: sss at intermediate pT come mostly from TTT • noΩcorrelation partners! • Shower s-quarks are suppressed w.r.t u & d quarks -- • Ω: sss at intermediate pT comes mostly fromTTT ! • Differ significantly fromΛ, which includes non-strange quarks R.C Hwa & C.B. Yang nucl-th/0602024 • W(STAR) L(STAR) W: statistically challenging! Betty Abelev

7. q y q x Statistical Jet Measurement • Particles from same jet  closely aligned in f • Use characteristic jet cone shape for a statistical jet study High pT track X Df • Find a trigger particle (pT>2 GeV/c) • Find an associated particle (pTtrg>pTas>1.5 GeV/c) in the same event • Computefat primary vertex for each • ComputeDfat primary vertex Betty Abelev

8. Azimuthal Correlation Function • Results in a double-peaked correlation function • Normalize by Ntriggers • p+p and d+Au: 2 Gaussians + flat background • Au+Au: 2 Gaussians +flat background+ flow same-side away-side If no SSS contribution to W spectrum  same-side W-h would be flatin most central Au+Au Betty Abelev

9. How to get V2 for multi-strange? • Mesons and Baryons seem to have different v2 at same pT. • If flow is collective • Should scale with n, number of valence quarks (partons) • Scaling works! J. Adams et al (STAR), Phys. Rev. Lett. 95 (2005) 122301 • Can use L v2 for X and W Betty Abelev

10. Au+Au azimuthal correlations results • A clear same-side W-h peak is observed for 2.5-4.5 GeV/c W baryon triggers! Betty Abelev

11. Au+Au azimuthal correlation results • The magnitude of the same-side peak is independent of s-quark content! Uncertainty due to v2 determination methods Betty Abelev

12. Comparison to singly-strange (Λ & K0S) • For same-side meson and baryon yields are similar • No dependence on strangeness content • Yields increase as a function of pT Betty Abelev

13. A reference: X Correlations in d+Au What kind of same-side signal to expect with no medium? (not enough statistics in p+p, not enough statistics to measure Ω. Look at Ξ-h in d+Au) X-h correlation is observed in d+Au. Same-side yield: 0.015±0.026 Away-side yield: 0.04±0.016 |h|<0.75 pTtrig>2.0 GeV/c 1.5 GeV/c <pTas<pTtrig STAR Preliminary Betty Abelev

14. 2-dimensional correlations: Df-Dh Dh beam direction • Extend analysis in 2 dimensions • Same procedure as for f, only use h coordinates of trigger and associated • Elongation in Dh under the jet peak: “the ridge” jet+ridge ridge  pTtrigger=3-6 GeV/c, 1.5 GeV/c <pTassociated< pTtrigger   jet ridge    STAR, PRC73, 064907 (2006)\ Betty Abelev

15. Jet and ridge as a function of centrality • L jet-only contribution consistent across Nch • At this pT trig & pT assoc.: 5 x increase of jet+ridge from d+Au to Au+Au  increase is all in the ridge. • Compare Xd+Au result with X result in Au+Au: • The pT-integrated (2-6 GeV/c) yield in Au+Au (0.20±0.05) is 10 x the yield in d+Au (0.015±0.026)! • The ridge? • Measuring jet only: divide the Dh space in jet+ridge (1) and ridge-only (2) regions • Subtract (2) from (1) to obtain jet-only measurement Jana Bielcikova’s talk, this workshop Jet + Ridge Jet only Betty Abelev

16. X-h in Df-Dh: the dip 2.5<pTtrig<4.5 GeV/c 1.5<pTas<pTtrig • The signal is indistinguishable from the ridge (perhaps visually only) • We observe a dip in the signal in the Dh=Df=0 region • This dip (though to be a detector effect) is still under investigation • Expect a significant loss of signal due to the dip STAR Preliminary Betty Abelev

17. 2-D X correlation results • The point-by-point subtraction of the two regions: result consistent with 0 STAR Preliminary STAR Preliminary STAR Preliminary Df Df Df • Subtracting the fits: the result is encouraging, but is qualitative – large errors. We don’t yet have the statistics to subtract the ridge Betty Abelev

18. Conclusions • Multi-strange baryon azimuthal correlations were observed in d+Au and Au+Au data • X baryon same-side azimuthal correlation yield in central Au+Au is ten times that in d+Au data • Omega baryon same-side peak was observed in most central Au+Au, contrary to predictions • The ridge was observed in Dh-Df X baryon correlations in Au+Au, and the excess X Au+Au yield is likely due to the ridge • The statistics are not yet sufficient to separate jet and ridge contributions for multi-strange • Outlook: • Omega spectrum measured to a higher pT to detect onset of fragmentation • Study of the ridge: its composition and dependence on kinematic and geometrical variables • Study of the away-side Betty Abelev