Jet Physics with identified particles at RHIC and the LHC

1. Jet Physics with identified particles at RHIC and the LHC R. Bellwied (Wayne State University) Is hadron production in medium different than in vacuum ? 22nd Winter Workshop on Nuclear Dynamics La Jolla, March 11-19, 2006

2. The main topics Hadron production through fragmentation in pp Flavor separated fragmentation functions Baryon – meson effects in pp Canonical strangeness suppression at high pT in pp/AA Tests of recombination through particle identified two-particle correlations in AA

3. Parton distribution functions at RHIC energies are well established through DESY measurements (hep-ex/0305109) RHIC

4. Non-Abelian energy loss XNW, nucl-th/0410049 DEg=DEq DEg=2DEq RHIC & LHC is gluon jet dominated Is energy loss non-abelian ?

5. pQCD @ 130 GeV • Soft+Quench @ 130 GeV Effects due to softer g-PDF and color factor

6. Quark jet tagging through direct g-jets Alternative: Heavy Quark Tag, but g is ‘standard candle’

7. Life is easier at the LHC

8. Thermally-shaped Soft Production Hard Scattering p0 in pp: well described by standard NLO p+p->p0 + X • Ingredients (via KKP or Kretzer) • pQCD • Parton distribution functions • Fragmentation functions hep-ex/0305013 S.S. Adler et al.

9. pp at RHIC: Hadron formation in QCDNLO for heavy masses requires quark separation in fragmentation function FF depend on Q, Einc, and flavor z z Non-valence quark contribution to parton fragmentation into octet baryons at low fractional momentum in pp

10. Success of quark separated fragmentation functions at RHIC

11. ..but, this effect might be collision energy dependent. STAR K0 spectra LHC KKP better at 630 GeV AKK better at 200 GeV The higher the collision energy, the more reliable LO pQCD

12. Why is understanding pp so important ? Is the hadronization process modified from pp to AA ? (Hadronization in medium (universe) vs. hadronization in vacuum) Is baryon production special ? Are recombination effects unique to AA ? The 400 pound gorilla: baryon/meson differences A clue to constituent quark scaling ? Is chiral symmetry restored ? Is the sQGP degree of freedom ‘massive’ ?

13. Breakdown of mT scaling in pp – a signal of gluon jet dominance ? A baryon – meson effect, due to baryon production requirement in string models (di-quark mechanism, di-quarks have lower p). Distinctly different from recombination.

14. Baryon production mechanism through strange particles correlations … • Test phenomenological fragmentation models OPAL ALEPH and DELPHI measurements: Yields and cosQ distribution between correlated pairs distinguishes between isotropic cluster (HERWIG) and non-isotropic string decay (JETSET) for production mechanism. Clustering favors baryon production JETSET is clearly favored by the data. Correlated L-Lbar pairs are produced predominantly in the same jet, i.e. short range compensation of quantum numbers.

15. 630 GeV Collision energy dependence of baryon vs. meson production in pp Baryon / meson differences already in pp collisions How does the ratio look at the LHC ?

16. Life is easier at the LHC !LHC vs. RHIC – leading particle range Cross sections for p+p 14 TeV total : s = 55 mb quark : s= 15 mb gluon: s = 38 mb ALICE pp: Event Recording Rate: 100 Hz Event Recording Bandwidth: 20 MB/s Running Time Per Year: 107 s Events Per Year: 109

17. Are extensions of string models applicable in AA collisions @ RHIC and LHC ? e.g. EPOS++(K.Werner’s talk) Alternative to recombination and fragmentation models Soft-Intermediate particle production through parton cascade in corona

18. Identified Particle RCP • intermediate pt not dominated by fragmentation ? • no flavor dependence in fragmentation region ? • need to establish good high ptPID @ LHC (V0, rdE/dx, RICH ?)

19. RAA of strange baryons A remarkable difference between RAA and RCP that seems unique to strange baryons. Ordering with strangeness content. Is ‘Canonical suppression’ unique to strange hadrons ? This effect must occur ‘between’ pp and peripheral AA collisions

20. Flavor independence of meson RAA ? u,d dominated c,b dominated no flavor dependence in energy loss ??

21. Strange enhancement vs. charm suppression ? Why is canonical suppression (CS) a baryon effect ? CS > energy loss effect @ high pt Is c more suppressed than s ? Is there still CS at LHC energies ? But is it a flavor effect ? Kaon behaves like D-meson, we need to measure Lc at LHC

22. RAA - A mocked upstring picture does well(see V.Topor-Pop talk) Topor Pop et al. hep-ph/0505210 HIJING/BBar + KT ~ 1 GeV Strong Color Field qualitatively describes RAA. SCF - long range coherent fields SCF behavior mimicked by doubling the effective string tension SCF only produced in nucleus-nucleus collisions RAA≠ RCP Apparently EPOS++ can describe data as well

23. Correlation functions for strange particle triggers in Au+Au at 200 GeV trigger: baryon/meson particle/antiparticle STAR preliminary STAR preliminary • Selection criteria: • 3.0 GeV/c<pTtrigger<3.5 GeV/c • 1 GeV/c<pTassociated<2 GeV/c • |h|<1 • Corrections applied: • reconstruction efficiency • of charged particles • TPC sector boundaries STAR preliminary STAR preliminary correlation functions before elliptic flow subtraction correlation functions after elliptic flow subtraction

24. STAR preliminary Near side yield dependence on system size Large AA/pp ratio of near side associated yield Although within statistical errors all trigger particle species behave similarly, yield for “meson” triggered correlations appears to be systematically lower than for “baryon” triggers Why is yield increasing with Npart ? statistical errors only

25. R. Hwa, Z.Tan: nucl-th/0503060 Au+Au d+Au STAR preliminary What does a parton recombination model predict? Au+Au @ 200 GeV 3GeV/c<pTtrigger<6GeV/c • the ratio of near-side associated yield in central/peripheral Au+Au collisions is ~ 3 at pTassociated = 1 GeV/c and decreases slowly with increasing pTassociated • data are in a good agreement with predictions from a parton recombination model: In Au+Au the thermal-shower recombination dominates for Kaon and Lambda triggered jets (no flavor sensitivity)

26. Recombination contribution is quark content dependent (R.Hwa, nucl-th/0602024) mesons baryons Shower contribution significantly suppressed for sss and s-sbar states No W or f trigger two particle correlations in AA. Tests underway

27. Is the near-side associated yield(ridge or jet) flavor dependent ? • - need higher stats • rdE/dx for p and p • easy at LHC

28. Baryon production in pp requires multiple scattering (EPOS or NLO pQCD) No strong flavor effects in high pt two particle correlations. Surprising absence of pQCD effects (gluon vs. quark contributions) in pp and AA. Does the energy loss show the color factor (non-Abelian energy loss ?). Summary High pt strange baryon production in AA enhanced instead of suppressed compared to pp . Is this due to simple canonical suppression in pp ? Any predictions for charmed baryons ? Large associated particle yield in AA compared to pp. Long range Dh correlations might be due to recombination. There might be a baryon/meson trend in agreement with recombination, but it is a small effect. Predictions for f and W need to be tested. The universe consists of baryonic matter. We need to understand basic baryon production in pp (string fragmentation vs. recombination, di-quark formation ? Then we need to determine whether the baryon production mechanism in AA collisions in modified. High pt identified baryon spectra at LHC are crucial (pT > 10 GeV/c). Baryon production in medium might solve ‘universal’ issues.