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STAR Results

High-pT, Electro-Magnetic and Heavy Flavor Probes

Manuel Calderón de la Barca

UC Davisfor the STAR

Collaboration

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Outline

Di-hadron correlations: Interaction of jet with bulk - Correlations: charged and identified Systematics of h-h correlations vs pT 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

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- 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 AuAupt < 2 GeV

d+Au, 40-100% Au+Au, 0-5%

3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

0.8< pt < 4 GeVnucl-ex/0607003See Poster by Ron Longacre

/√

ref

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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<pt,trigger<4 GeV

pt,assoc.>2 GeVAu+Au 0-10%

preliminary

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The “Ridge” + “Jet” yield vs Centrality

3<pt,trigger<4 GeV

pt,assoc.>2 GeV

Au+Au 0-10%

preliminary preliminaryJet+Ridge ()Jet ()Jet)

yie

ld

,

)

Npart“Jet” yield constantwith Npart

See Talk by Jörn Putschke

Reminder from pT<2 GeV:

elongated structure already in minbias AuAu elongation in p-p to elongation in AuAu.

PRC 73, 064907 (2006)

p+p. low pT

Number corr. Au+Au. low pT

pT corr.

/√

ref

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Jet + Ridge

Charged hadrons: ridge yield increased vs. Npart,K0

s both have increase of near-side yield with centrality in Au+Au, K0

s: ratio of yields in central Au+Au/d+Au ~ 4-5ridge yield of K0

S < ridge yield of -> “ridge” yield increases with centrality -> “jet” yield is constant vs Npart

same yield as in d+Au

,K0s Near-side associated yield vs

centrality, Au+Au

See Talk by Jana Bielcikova

Jet

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STAR preliminary

Central AuAu: Ridge, Jet Yield vs pT, trig pT, assoc

pt,assoc. > 2 GeV

Ridge yield ~ constant

(slightly decreasing) vs. pT

trig

RidgeJet

“Jet spectrum” much harder than

inclusive

gets harder w/ increasing

pt,trigger

“Ridge spectrum” close to

inclusive

~ independent of pt,trigger

Central

Ridge Persists up to highest pT trig

See Talk by Jörn Putschke

STAR preliminary

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Measure hadron triggered fragmentation functions: Dh1,h2(zT) zT=pT

assoc/pT

trig

Similarity between AuAu and dAu after ridge subtraction

Are the AuAu results with the ridge subtracted the same as dAu, EVEN at low pT?

Near-side zT Distributions: “Jet”

Preliminary

See Talk by Mark Horner

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Near-side zT distributions similar to dAu

no 50% dilution from thermal coalescence triggers?

Phys.Rev. C70 (2004) 024905

Measure hadron triggered fragmentation functions: Dh1,h2(zT) zT=pT

assoc/pT

trig

Ratio AuAu/dAu

Similarity between AuAu and dAu after ridge subtraction

See Talk by Mark Horner

Near-side zT Distributions: “Jet”

Preliminary

• 8<pTtrig<15 GeV/c

STAR PRL 97 162301

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Away-Side: pTtrig Dependence

0-12%

1.3 < pTassoc < 1.8

GeV/c

4.0 < pTtrig < 6.0 GeV/c 6.0 < pT

trig < 10.0 GeV/c

Away-side: Structures depend on range of

pT.

becomes flatter with increasing pT

trig

yield increases

3.0 < pTtrig < 4.0 GeV/c

AuAu 0-12%

Central contribution to away-side

becomes more significant with

harder pTtrig => fills dip

PreliminaryAway side

See Talk by Mark Horner

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High zT for hard triggers shows “standard” suppression (~0.2)

Larger yields seen at low zT or low pT

trig bulk response

Deviation from suppression depends on pT

trig

Away-side: zT Distributions

Preliminary

2.5 < pTtrig < 4.0 GeV/c never reaches the 0.250.06 IAA

away-side suppression for pTtrig>8 GeV/c (STAR PRL 97,

162301)See Talk by Mark Horner

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Correlation from FTPC to MTPC

Trigger: 3<pTtrig<4 GeV/c, A.FTPC: 0.2<pT

assoc< 2 GeV/c, A.TPC: 0.2<pTassoc< 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<|ηassoc|<3.9

See Talk by Levente Molnar

STAR Preliminary

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Hard Probes: 0’s and in STAR EMCal 0s 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

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dNNcc/dy from p+p to A+A

D0, e±, and μ± combined fit Advantage: Covers ~95% of cross

section Mid-rapidity dNN

cc/dy vs Nbin NN

ccfollows binary scaling Charm production from initial state

(as expected) Higher than FONLL prediction in pp

collisions.

See Talk by Chen Zhong

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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 RAA 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%

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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 Be-h from DFit

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p+p 200 GeV

B contribution to NP electrons vs. pT 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 studySee Talk by Xiaoyan Lin

Beauty !

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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 Preliminaryp+p 200 GeVe+e- Minv

Background Subtracted

See Talk by Pibero Djawotho

e+e- Minv • Unlike-Sign Pairs— Like-Sign Pairs

STAR Preliminaryp+p 200 GeV

19dt pb L

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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 Preliminaryp+p 200 GeV

See Talk by Pibero Djawotho

y

d/

dy

(nb

)

Cou

nts

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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 sampleAway-side yields only slightly reduced

Effect more prominent for larger Ettrigger

0

MixedPhoton

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Promising for future -jet studies: RHIC II

Spectra for -tagged Events

Use -enriched sample:plot away-side pT-spectra for photon-tagged events

Matches charged hadron spectra in direct photon events from HIJING.

See Talk by Subhasis Chattopadhyay

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Conclusions and Outlook Near Side: Broadening along . (“Jet”+” Ridge”)

“ridge” yield: steep increase with centrality, “jet” yield: constant with centrality, increasing with pT

trig

After subtraction of long range , D(zT) similar to dAu. Unmodified “jet” after subtraction?

Away side: Central: contribution to = increases with harder pT

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.

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Backup

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correlation functions before elliptic flow subtraction

correlation functions after elliptic flow subtraction syst. error due to v2 uncertainty ~ 25%

Correlation, strange particle triggers, Au+Au 200 GeV

Selection criteria: 3.0 GeV/c < pT

trigger < 3.5 GeV/c 1 GeV/c < pT

associated < 2 GeV/c || < 1

STAR STAR preliminarypreliminary

STAR STAR preliminarypreliminary

STAR STAR preliminarypreliminary

STAR STAR preliminarypreliminary

trigger: baryon/meson baryon/antibaryontrigger: baryon/meson baryon/antibaryon

See Talk by J. Bielcikova

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Direct photons for correlation analysisStandard 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

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Associated pT Dependence Centrality : 0 -

12% Associated pT

(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:

3rd row right column

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pTtrig

pTassoc

Preliminary

see talk by M. Horner

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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