BNL Seminar 10/02

High pt Hadrons in STAR: Past, Present, and Future

Michael L. Miller

Yale University

For the STAR Collaboration

Transverse Dynamics 03/03

Mike 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

RAA at 200 GeV, RCP 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)

Transverse Dynamics 03/03

Mike Miller

The STAR Detector

Time Projection Chamber ||<1.5, 0<||<2

Central Trigger BarrelZero Degree

Calorimeters

Beam Beam CountersScintillating tiles: 3.5<||

<5

Transverse Dynamics 03/03

Mike Miller

How to Measure Minbias p+p?

Mea

n pt

GeV

/c

0 80Multiplicity

0.3

0

.8

0 2 4 6 8 10pt

<pt> scales with mult.

Vertexing efficiency increases with mult. => bias!

Analyze tracks from primary interaction without vertexing.

Jon Gans (Yale) et al.

Transverse Dynamics 03/03

Mike 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

Transverse Dynamics 03/03

Mike Miller

RAA at 200 GeV

New: 6-10 GeV region

Central: RAA does not go to 1

Errors dominated by p+p statistics

“Hints” at flat ratio at pt>6

RAA measured entirely at STAR

Transverse Dynamics 03/03

Mike Miller

RCP at 200 GeV

High statistics measurement in Au+Au

Plateau

Factor 3-5 suppression at pt>6

Below “naïve” Npart scaling

Transverse Dynamics 03/03

Mike Miller

Flavored RCP at 200 GeVR

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

Transverse Dynamics 03/03

Mike 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?

Transverse Dynamics 03/03

Mike 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 StateE-loss? Pt-broadening?More challenging to measure…

Transverse Dynamics 03/03

Mike Miller

Correlation Method: Measurement

Statistical leading particle analysis

Histogram in 2-d• N: vs.

project

py

px

2 GeV

4 GeV

2 ,1 1

trig

d ND d

N d d

2

, ,

,:

trig assoc trig trig

d N

d d

Ntrigger: Total number of trigger particles: (4<pT<6)

Once pt<2, particles disappear

Transverse Dynamics 03/03

Mike Miller

Correlation Method: Ref. Model

Au+Au correlations: Jetsdi-jets elliptic flow Combinatorial

Background

model pp 22 1 2 cos 2D D B v

Compare Au+Au to p+pIncorporate known sources of

signal and dominant background

B*v2Systematic dependence on v2

decreases with higher pt threshold

Transverse Dynamics 03/03

Mike Miller

Correlation Method: Ref. ModelAlgorithm: model pp 2

2 1 2 cos 2D D B v

Au+Au measurement

Background term

pp measurement

0.75 2.25

Fit B in non-jet region

Add p+p to background term

Transverse Dynamics 03/03

Mike Miller

Quantify with Ratio

2

1

22

2

1 2 cos 2 ,

AuAu

AA pp

D B vI d

D

= + AuAu pp background

- = AuAu background pp

- 1

AuAu backgroundI

pp

Au+Au Measurement

p+p Measurement

background

Transverse Dynamics 03/03

Mike Miller

What is IAA telling us?

Why is IAA< 1?

Not an experimental artifact

Interesting physics?

Shadowing?

Initial state multiple scattering?

Final state effects?

Disappearance of away side correlation

Transverse Dynamics 03/03

Mike Miller

Correlation Musings: BroadeningAlgorithm: model pp 2

2 1 2 cos 2D D B v

Au+Au measurement

Background term

pp measurement

0.75 2.25

Fit B in non-jet region

Add p+p to background term

As away side broadens, does it leak into fit region?

Transverse Dynamics 03/03

Mike 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 RAA, RCP flat from 6<pt<11

Transverse Dynamics 03/03

Mike 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 IAA measurement at higher

ptLower combinatoric backgroundReduce 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 RAA, RCP flat from 6<pt<11

Transverse Dynamics 03/03

Mike 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

Transverse Dynamics 03/03

Mike Miller

A Glimpse of What’s Coming

di-jet Vs. from STAR p+p

Back to back and come in pairs!

Raw STAR Preliminary

Transverse Dynamics 03/03

Mike Miller

A Glimpse of What’s Coming

Increase jet pt, tighten di-jet peakMeasure Nuclear kt in d+Au

di-jet vs from STAR p+pjettp

Raw STAR Preliminary

Transverse Dynamics 03/03

Mike Miller

A Glimpse of What’s Coming

2 2 (from jet axis)R

tracks in jet vs. vs. from STAR p+pjett tp R p

chargeMeasure , , in jet and w.r.t. thrust axist tp N p

Raw STAR Preliminary

Transverse Dynamics 03/03

Mike Miller

ConclusionsSTAR has measured p+p

spectrum to 10 GeVRatio 200/130

Well modeled by pQCD calculation plus Cronin

RAA

Suppressed for pt>2, flat from 6<pt<10

RCP

Suppressed for pt>2, flat from 6<pt<12

CorrelationsJet like correlations in near angle region

Provides strong constraint on particle production models

Disappearance of away side jet

Futured+Au inclusives (RAA, RCP)d+Au correlations (stats!, will address saturation/mini-jet prediction)

p+p and d+Au jets

Transverse Dynamics 03/03

Mike Miller

Backup slides

Transverse Dynamics 03/03

Mike 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 Ncharge (at y=0) could bias most peripheral bin to harder fragmenting jets. IAA<1

Why is IAA(Npart=0) < 1?

Transverse Dynamics 03/03

Mike 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?