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

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Presentation on theme: "BNL Seminar 10/02 High p t Hadrons in STAR: Past, Present, and Future Michael L. Miller Yale University For the STAR Collaboration."— Presentation transcript:

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 22. 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, (2002) 2.C. Adler et al.Phys. Rev. Lett. 90, (2003) 3.C. Adler et al. Phys. Rev. Lett. 90, (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 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


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

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

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 62, flat from 6

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?


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