1. 1 STAR Results High-p T, Electro-Magnetic and Heavy Flavor Probes Manuel Calderón de la Barca UC Davis for the STAR Collaboration

2. 2 Outline  Di-hadron correlations: Interaction of jet with bulk   -  Correlations: charged and identified  Systematics of h-h correlations vs p T trig, assoc, mid- forward .  Hard Probes: Comparison to calculable processes  Photons : Direct  in d+Au collisions  Heavy Flavor Production  Charm cross section  e-h correlations: b contribution to non-photonic electrons  Midrapidity  (1s+2s+3s) production in p+p   -h correlations in p+p

3. 3  -  Correlations: Background  Near-side long range correlation in   STAR, nucl-ex/0509030  near side “ridge”  How do structures, yields, evolve…  Centrality, kinematics (wide pt ranges), particle identification?  Little guidance from theory: data driven approach Phys. Rev. C73 (2006) 064907 mid-central AuAu p t < 2 GeV d+Au, 40-100%Au+Au, 0-5% 3 < p T (trig) < 6 GeV 2 < p T (assoc) < p T (trig) 0.8< p t < 4 GeV nucl-ex/0607003 See Poster by Ron Longacre  / √  ref

4. 4 Study near-side yields Study away-side correlated yields and shapes Components  near-side jet peak  near-side ridge  v2 modulated background  -  Component Picture Strategy: Subtract  from  projection: isolate ridge-like correlation Definition of “ridge yield”: ridge yield := Jet+Ridge(   )  Jet(  ) Can also subtract large .     3<p t,trigger <4 GeV p t,assoc. >2 GeV Au+Au 0-10% preliminary

5. 5 The  “Ridge” + “Jet” yield vs Centrality 3<p t,trigger <4 GeV p t,assoc. >2 GeV Au+Au 0-10% preliminary Jet+Ridge (  ) Jet (  ) Jet  ) yield ,  ) N part “Jet” yield constant with N part See Talk by Jörn Putschke Reminder from p T <2 GeV:  elongated structure already in minbias AuAu  elongation in p-p  to  elongation in AuAu. PRC 73, 064907 (2006) p+p. low p T Number corr. Au+Au. low p T pT corr.  / √  ref

6. 6 Jet + Ridge Charged hadrons: ridge yield increased vs. Npart ,K 0 s both have increase of near-side yield with centrality in Au+Au , K 0 s : ratio of yields in central Au+Au/d+Au ~ 4-5 ridge yield of K 0 S < ridge yield of  -> “ridge” yield increases with centrality -> “jet” yield is constant vs Npart same yield as in d+Au ,K 0 s Near-side associated yield vs centrality, Au+Au See Talk by Jana Bielcikova Jet

7. 7 STAR preliminary Central AuAu: Ridge, Jet Yield vs p T, trig p T, assoc p t,assoc. > 2 GeV Ridge yield ~ constant (slightly decreasing) vs. p T trig Ridge Jet “Jet spectrum” much harder than inclusive gets harder w/ increasing p t,trigger “Ridge spectrum” close to inclusive ~ independent of p t,trigger Central Ridge Persists up to highest p T trig See Talk by Jörn Putschke STAR preliminary

8. 8  Measure hadron triggered fragmentation functions:  D h1,h2 (z T )  z T =p T assoc /p T trig  Similarity between AuAu and dAu after ridge subtraction Are the AuAu results with the ridge subtracted the same as dAu, EVEN at low p T ? Near-side z T Distributions: “Jet” Preliminary See Talk by Mark Horner

9. 9 Near-side z T distributions similar to dAu no 50% dilution from thermal coalescence triggers? Phys.Rev. C70 (2004) 024905  Measure hadron triggered fragmentation functions:  D h1,h2 (z T )  z T =p T assoc /p T trig  Ratio AuAu/dAu  Similarity between AuAu and dAu after ridge subtraction See Talk by Mark Horner Near-side z T Distributions: “Jet” Preliminary 8<p T trig <15 GeV/c STAR PRL 97 162301

10. 10 Away-Side: p T trig Dependence 0-12% 1.3 < p T assoc < 1.8 GeV/c 4.0 < p T trig < 6.0 GeV/c 6.0 < p T trig < 10.0 GeV/c Away-side:  Structures depend on range of p T.  becomes flatter with increasing p T trig  yield increases 3.0 < p T trig < 4.0 GeV/c AuAu 0-12% Central contribution to away-side becomes more significant with harder p T trig => fills dip Preliminary Away side See Talk by Mark Horner

11. 11  High z T for hard triggers shows “standard” suppression (~0.2)  Larger yields seen at low z T or low p T trig  bulk response  Deviation from suppression depends on p T trig Away-side: z T Distributions Preliminary 2.5 8 GeV/c (STAR PRL 97, 162301) See Talk by Mark Horner

12. 12 Correlation from FTPC to MTPC Trigger: 3<p T trig <4 GeV/c, A.FTPC: 0.2<p T assoc < 2 GeV/c, A.TPC: 0.2<p T assoc < 3 GeV/c Near-side correlation: consistent with zero Away-side correlations are very similar! Energy loss picture is the same for mid- and forward  ? Need quantitative calculations for correlations analyses! AuAu 0-10% AuAu 0-5% AuAu 60-80% STAR Preliminary 2.7<| η assoc |<3.9 See Talk by Levente Molnar STAR Preliminary

13. 13 Hard Probes:  0 ’s and  in STAR  EMCal  0 s in p+p  preliminary result from subset of year 5 data  good agreement with pQCD + KKP fragmentation  disfavors Kretzer FFs d+Au  direct photons and d+Au  double ratio:  (  incl /  0) / (  decay /  0) = 1 +  dir /  decay  direct  signal consistent with NLO pQCD  baseline results for Au+Au analysis  No discrepancy between STAR & PHENIX. See Talk by Martijn Russcher

14. 14 d  NN cc /dy from p+p to A+A  D 0, e ±, and μ ± combined fit  Advantage: Covers ~95% of cross section  Mid-rapidity d  NN cc /dy vs Nbin   NN cc follows binary scaling  Charm production from initial state (as expected)  Higher than FONLL prediction in pp collisions. See Talk by Chen Zhong

15. 15 Checking STAR electrons  Discrepancy between STAR and PHENIX  Investigated method to estimate Photonic background. No issues found.  Reanalyzed from scratch  pp results change by ~25%  dAu results change by ~10%  AuAu results do not change  Within systematics  Still difference btw. STAR & PHENIX  R AA still slightly below most c+b calculations.  Future: low material run  Improve uncertainty on background  Issue remains: no information on contribution from beauty. PHENIX hep-ex/0609010 STAR, submitted to PRL STAR Au+Au 0-5%

16. 16 Can we tell how much beauty?  Use e-h Correlation  Large B mass compared to D  Semileptonic decay: e gets larger kick from B.  Broadened e-h correlation on near-side.  Extract B contribution  Use PYTHIA shapes  Con: Model dependent  Pro: Depends on decay kinematics  well described  Fit ratio B/(B+D) See Talk by Xiaoyan Lin e-h from B e-h from D Fit

17. 17 p+p 200 GeV B contribution to NP electrons vs. p T  Fit e-h correlation with PYTHIA Ds and Bs  Non-zero B contribution  Contribution consistent with FONLL  Model dependent (PYTHIA)  Depends mainly on kinematics of D/B decay (not on Fragmentation).  Dominant systematic uncertainty:  photonic background rejection efficiency  Additional uncertainties under study See Talk by Xiaoyan Lin Beauty !

18. 18 More Beauty:  signal in p+p  Large dataset sampled in Run VI  Luminosity limited trigger  Analyzed 5.6 pb -1, with corrections.  Measure  (1s+2s+3s) d  /dy at y=0 STAR Preliminary p+p 200 GeV e+e- M inv Background Subtracted See Talk by Pibero Djawotho e+e- M inv Unlike-Sign Pairs — Like-Sign Pairs STAR Preliminary p+p 200 GeV

19. 19 Mid-rapidity  (1s+2s+3s) Cross section  Integrate yield at mid-rapidity: |y|<0.5   (1s+2s+3s) BR * d  /dy  91 ± 28 stat ± 22 syst pb -1 (Preliminary)  Consistent with NLO pQCD calculations at midrapidity.  Trigger ready for next run and RHIC II: luminosity limited STAR Preliminary p+p 200 GeV See Talk by Pibero Djawotho y d  /dy (nb) Counts

20. 20 p+p Towards  -jet: ( ,  0)-h  Correlation analysis See Talk by Subhasis Chattopadhyay Use “shower-shapes” in EMC: Create two samples Enriched photon sample (mix ,  0 ) Enriched  0 sample (almost pure  0 ) Reduction in near angle peak in Photon sample Away-side yields only slightly reduced Effect more prominent for larger Et trigger  0 Mixed Photon

21. 21 Promising for future  -jet studies: RHIC II Spectra for  -tagged Events Use  -enriched sample: plot away-side p T -spectra for photon-tagged events Matches charged hadron spectra in direct photon events from HIJING. See Talk by Subhasis Chattopadhyay

22. 22 Conclusions and Outlook  Near Side : Broadening along . (“Jet”+”  Ridge”)  “ridge” yield: steep increase with centrality,  “jet” yield: constant with centrality, increasing with p T trig  After subtraction of long range , D(z T ) similar to dAu.  Unmodified “jet” after subtraction?  Away side:  Central: contribution to  =  increases with harder p T trig, fills dip  Away side jet shapes at forward rapidities : similar to midrapidity in d+Au and Au+Au  Energy loss picture is similar at forward and mid-rapidity?  Direct  Signal in d+Au matches pQCD  Charm   Larger than NLO by ~4, Still difference with PHENIX.  Beauty:  Non-zero beauty contribution to non-photonic electrons   (1s+2s+3s) in p+p: Consistent with pQCD at y=0.   -h correlations : First  -jet measurement.   -h : First steps towards RHIC II.

23. 23 Backup

24. 24 correlation functions before elliptic flow subtraction correlation functions after elliptic flow subtraction syst. error due to v 2 uncertainty ~ 25%  Correlation, strange particle triggers, Au+Au 200 GeV Selection criteria: 3.0 GeV/c < p T trigger < 3.5 GeV/c 1 GeV/c < p T associated < 2 GeV/c |  | < 1 STAR preliminary trigger: baryon/meson baryon/antibaryon See Talk by J. Bielcikova

25. 25 Direct photons for correlation analysis Standard methods used for extraction of photons: Statistical method by Reconstruction of inclusive photons Subtract photons from decay of    etc. Cannot be used for correlation. Method: Enhance  using difference in shower shapes.. Compare correlation functions between  -enriched (narrow EM showers)  0-enriched (broader EM showers) mixed PHOTON 00

26. 26 Associated p T Dependence  Centrality : 0 - 12%  Associated p T (rows):  0.3 – 0.8 GeV/c  0.8 – 1.3 GeV/c  1.3 – 1.8 GeV/c  2.0 – 4.0 GeV/c  Triggers (columns):  2.5 – 4.0 GeV/c  3.0 – 4.0 GeV/c  4.0 – 6.0 GeV/c  6.0 – 10.0 GeV/c  Detailed cases:  3 rd row  right column 7 p T trig p T assoc Preliminary see talk by M. Horner

27. 27 Heavy Flavor Production  e-h Correlations  Understanding features in heavy quark measurements requires experimental measurement of B and D contributions.  First try: use non- photonic electron correlations.  See talk from Xiaoyan Lin