1. BNL Seminar 10/02 High p t Hadrons in STAR: Past, Present, and Future Michael L. Miller Yale University For the STAR Collaboration

2. Transverse Dynamics 03/03Mike Miller Past, Present, Future  High-pt suppression for 2<pt<6. 1  Large and flat v2 for pt>2. 2  Pt>4 particle production in p+p, Au+Au consistent with jet fragmentation (same side correlation). 2  Disappearance of the away side jet. 3 What’s old?  STAR measurements from p+p  Pt spectrum  R AA at 200 GeV, R CP at 200 GeV  Is 6 GeV a special number? What’s new?  What happened to the away side jet?  Musings on correlation method  Teaser: beyond correlations! What’s coming? 1.C. Adler et al. Phys. Rev. Lett. 89, 202301 (2002) 2.C. Adler et al.Phys. Rev. Lett. 90, 032301 (2003) 3.C. Adler et al. Phys. Rev. Lett. 90, 082302 (2003)

3. Transverse Dynamics 03/03Mike Miller The STAR Detector  Time Projection Chamber  |  |<1.5, 0<|  |<2   Central Trigger Barrel  Zero Degree Calorimeters  Beam Beam Counters  Scintillating tiles: 3.5<|  |<5

4. Transverse Dynamics 03/03Mike Miller How to Measure Minbias p+p? Mean pt GeV/c 0 80Multiplicity 0.3 0.8 0 2 4 6 8 10 pt  scales with mult.  Vertexing efficiency increases with mult. => bias! Analyze tracks from primary interaction without vertexing. Jon Gans (Yale) et al.

5. Transverse Dynamics 03/03Mike Miller Charged Pt Spectra at 200 GeV  Au+Au:  7 centralities,  11 GeV  p+p:  From STAR  9 GeV First measured p+p spectrum from STAR

6. Transverse Dynamics 03/03Mike Miller R AA at 200 GeV  New: 6-10 GeV region  Central: R AA does not go to 1  Errors dominated by p+p statistics  “Hints” at flat ratio at pt>6 R AA measured entirely at STAR

7. Transverse Dynamics 03/03Mike Miller R CP at 200 GeV  High statistics measurement in Au+Au  Plateau  Factor 3-5 suppression at pt>6  Below “naïve” N part scaling

8. Transverse Dynamics 03/03Mike Miller Flavored R CP at 200 GeV R CP STAR preliminary  Baryon production longstanding puzzle  Peak value PID dependent  Argue: location of turnover changes?  At pt>6, common suppression  Statement: “more baryons than mesons” is valid only at intermediate pt

9. Transverse Dynamics 03/03Mike Miller Sqrt(s) Ratio: 200/130  Well described by pQCD plus Cronin (X.N. Wang)  Ratio relatively insensitive to e-loss  Ratio relatively insensitive to p.d.f.  Is pQCD+Cronin a unique explanation?

10. Transverse Dynamics 03/03Mike Miller Correlation Functions: Open Questions  Correlation functions producing exciting results  Initial state or final state effects?  Initial State:  Nuclear kt? Shadowing?  Measure these with d+Au on disk!  Final State  E-loss? Pt-broadening?  More challenging to measure…

11. Transverse Dynamics 03/03Mike Miller Correlation Method: Measurement  Statistical leading particle analysis  Histogram in 2-d N:  vs.   project pypy pxpx 2 GeV 4 GeV N trigger : Total number of trigger particles: (4<p T <6) Once pt<2, particles disappear

12. Transverse Dynamics 03/03Mike Miller Correlation Method: Ref. Model  Au+Au correlations:  Jets  di-jets  elliptic flow  Combinatorial Background  Compare Au+Au to p+p  Incorporate known sources of signal and dominant background B*v2 Systematic dependence on v2 decreases with higher pt threshold

13. Transverse Dynamics 03/03Mike Miller Correlation Method: Ref. Model  Algorithm: Au+Au measurement Background term pp measurement Fit B in non-jet region Add p+p to background term

14. Transverse Dynamics 03/03Mike Miller Quantify with Ratio Au+Au Measurement p+p Measurement background

15. Transverse Dynamics 03/03Mike Miller What is I AA telling us?  Why is I AA < 1? Not an experimental artifact  Interesting physics?  Shadowing?  Initial state multiple scattering?  Final state effects? Disappearance of away side correlation

16. Transverse Dynamics 03/03Mike Miller Correlation Musings: Broadening  Algorithm: Au+Au measurement Background term pp measurement Fit B in non-jet region Add p+p to background term As away side broadens, does it leak into fit region?

17. Transverse Dynamics 03/03Mike Miller Correlations: What are they good for?   Away side correlation does disappear!  Intra-jet Correlations (Fragmentation):  Shapes, widths, charge dependent yields  At what pt does the away side reappear?  Measure of e-loss  R AA, R CP flat from 6<pt<11

18. Transverse Dynamics 03/03Mike Miller Correlations: What’s Coming?  Correlations using PID tagged triggers  Lambda, k0  Correlations w.r.t. the reaction plane  d+Au correlations  Test Saturation model predictions  Much higher statistical reach than current p+p  Allow I AA measurement at higher pt  Lower combinatoric background  Reduce systematic error from v2 What’s beyond correlations?  Away side correlation does disappear!  Intra-jet Correlations (Fragmentation):  Shapes, widths, charge dependent yields  At what pt does the away side reappear?  Measure of e-loss  R AA, R CP flat from 6<pt<11

19. Transverse Dynamics 03/03Mike Miller Full Jet Reconstruction  Measure Fragmentation functions in p+p, d+Au  Measure pt where fragmentation functions no longer scale with jet pt  Compare “minbias” jets with “correlation” jets  Are they at high z?  Measure nuclear kt in d+Au  Challenges:  Jet definition  Jet finding in high-density  Jet energy calibration  Corrected data vs. experimentally filtered predictions?  STAR Capabilities  Multiple algorithms implemented (UA1, seedless-cone, midpoint-cone, kt-cluster, etc.)  Use p+p data sample as reference

20. Transverse Dynamics 03/03Mike Miller A Glimpse of What’s Coming Back to back and come in pairs! Raw STAR Preliminary

21. Transverse Dynamics 03/03Mike Miller A Glimpse of What’s Coming  Increase jet pt, tighten di-jet peak  Measure Nuclear kt in d+Au Raw STAR Preliminary

22. Transverse Dynamics 03/03Mike Miller A Glimpse of What’s Coming Raw STAR Preliminary

23. Transverse Dynamics 03/03Mike Miller Conclusions  STAR has measured p+p spectrum to 10 GeV  Ratio 200/130  Well modeled by pQCD calculation plus Cronin  R AA  Suppressed for pt>2, flat from 6<pt<10  R CP  Suppressed for pt>2, flat from 6<pt<12  Correlations  Jet like correlations in near angle region  Provides strong constraint on particle production models  Disappearance of away side jet  Future  d+Au inclusives (R AA, R CP )  d+Au correlations (stats!, will address saturation/mini-jet prediction)  p+p and d+Au jets

24. Transverse Dynamics 03/03Mike Miller Backup slides

25. Transverse Dynamics 03/03Mike Miller Correlation Musings: trigger bias Two fragmentation scenarios, pt conserved 2 GeV 4 GeV Soft: Nch=7 2 GeV 4 GeV Hard: Nch=4 Centrality from N charge (at y=0) could bias most peripheral bin to harder fragmenting jets. I AA <1 Why is I AA (N part =0) < 1?

26. Transverse Dynamics 03/03Mike Miller An Exercise for the Student  Utilize all symmetries of the problem  Minimize threshold effect  Maximize signal to noise  Well defined near/away ratio? Minimize v2 dependence Look at all pt’s Allow comparisons of Au-Au to p+p, centrality dependences, etc. Reaction Plane Thrust Axis Is there an easy, robust way to measure fragmentation changes in Au+Au?