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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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Transverse Dynamics 03/03Mike Miller Past, Present, Future High-pt suppression for 2

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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

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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.

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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

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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

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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

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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

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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?

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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

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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

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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

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

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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

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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?

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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

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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

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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

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

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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

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

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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

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Transverse Dynamics 03/03Mike Miller Backup slides

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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?

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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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