High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT...

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1 High p T angular correlations from STAR Olga Evdokimov for the STAR collaboration

Transcript of High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT...

Page 1: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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High pT angular correlations from STAR

Olga Evdokimov for the STAR collaboration

Page 2: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Outline

Ridge – from discovery to systematic studies:

Systematic studies in pT space System-size & path-length effects 3-particle ∆η-∆η-correlations Hadro-chemistry

Summary and a few fitting exercises to discuss

“Triggered Scheme”: preferred direction

ZYAM v2-subtracted

Page 3: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

The “famous plot” contenders of the jet-quenching era:

Disappearance of the away

side jet in central Au+Au, not d+Au

Near-side long-range ∆η correlation, central Au+Au: jet+ridge?

PRL 91 (2003)

072304

4<pT trig<6 GeV/c 2<pT assoc<pT trig

Ridge – the discovery

PLB 704 (2011)

467

jet+ridge?

Page 4: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Ridge -101 PLB 704 (2011)

467

Discovered first in Au+Au collisions at RHIC No ridge signal in d+Au Extends to acceptance boundary Persists to the highest trigger pT measured

Presenter
Presentation Notes
Y_slice fits with s=0.3 Solid and dashed lines – pol0 and pol1 fits to 1<dEta<1.8
Page 5: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Ridge behaves like the “bulk”

In more ways than one: Jet ~ pp, d+Au , Ridge ~ Bulk; no sensitivity to charge ordering

Production mechanisms for jet and ridge differ

C Suarez,QM08 PRL 105 (2010)

22301

pTT>3GeV/c, pT

A >1GeV/c

Presenter
Presentation Notes
Lines – exponential fits to the data b) dPhi<0.7; pTtrig> 3GeV, pTassoc>1, lines – gaussian fits
Page 6: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Ridge hadro-chemistry Jet + Ridge Jet

Steep but smooth increase of same-side yield vs. centrality Associated yields ratio of ~5 for Au+Au/d+Au No changes (?) to “Jet” part

Page 7: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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New PID for Triggers

7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

0-10% Au+Au, 4 < pT,trigger < 6 GeV/c, pt,assoc. > 1.5 GeV/c

Unidentified

nσπ > Cπ, 95%

pure pion sample

π K P

nσπ < Cπ,

pion-depleted sample

a. u

.

K Kauder,QM11

nσπ

Page 8: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Large jet-like cone, small ridge from pion triggers

Smaller cone, large ridge from P+K triggers

(p±+K±) trigger

π± trigger

More correlations with PID

0-10% Au+Au, 4 < pT,trigger < 6 GeV/c, pt,assoc. > 1.5 GeV/c

Page 9: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Trigger: π± (P±+K±) Charged h

d+Au MB

…with d+Au reference:

Near-side ∆η−projection |∆φ|<0.73

Higher jet-like amplitude for pions, d+Au ~ Au+Au Ridge most significantly contributed by non-pion-triggers

Au+Au, top 10%

4 < pT,trigger < 6 GeV/c, pt,assoc. > 1.5 GeV/c

Page 10: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Centrality and energy dependence 3 < pT,trigger < 6 GeV/c, pt,assoc. > 1.5 GeV/c

PRC 85 (2012) 14903

Ridge is a common feature of various AA collisions at RHIC Continuous growth with centrality; smaller ridge for lower energy

(same for jet yield) Ratio is independent of collision energy (within errors)

Presenter
Presentation Notes
For the same kinematic selections, the data at √sNN = 62.4 GeV correspond to a lower jet energy which may imply the decrease of the ridge yield with the parton energy, as observed for the jet-like yield.
Page 11: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

in-plane φS=0 out-of-plane φS=90o

90º

STAR Preliminary

arXiv:1010.0690

Same-side yield Jet: d+Au ~ Au+Au

Ridge decreases from in-plane to out-of-plane

Flow effects?

Path-length effects

200 GeV Au+Au 20-60% 3< pT,trigger < 4GeV/c, 1 <pt,assoc. < 3 GeV/c

V2{EP} V2{4} d+Au

Page 12: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Near-side: ∆η-∆η correlations

No apparent substructure – no gluon fragments/flow coupling?

No cross-like term – ridge and cone

decoupled?

PRL 105 (2010) 22301

3< pT,trigger < 10GeV/c, 1<pt,assoc. < 3 GeV/c

Page 13: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Substructures in Ridge?

Excess of correlated yields at large R in central Au+Au data No significant substructures for ridge

3< pT,trigger < 10GeV/c, 1<pt,assoc. < 3 GeV/c

Presenter
Presentation Notes
Average correlated hadron pair density per trigger particle as function of R for jet and ridge components
Page 14: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

2+1 to study di-jets “pin” the jet axis selecting back-to-back triggers

Does every jet have it?

Raw, uncorrected signal

∆φ -1 -2 0 1 2 3 4 5

a.u.

0.6

0.4

0.2

π ± 0.2

Central Au+Au ~ d+Au. No away-side suppression! Shapes of near- and away-sides are similar

∆φ projection: no significant shape/yield modifications ∆η projection: no apparent ridge

8< pT,t1 < 10GeV/c, pT,t1 >4GeV/c, pt,assoc. >1.5GeV/c

H. Pei, DPF2011

Residuals: Au+Au – d+Au

200 GeV Au+Au, 10%

Page 15: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

pT>2.1GeV/c pT>1.7GeV/c pT>1.1GeV/c

Au-Au: 80-100% Au-Au: 00-10% Au-Au: 70-80% Au-Au: 50-60%

ref

ρρ∆

proton-proton

Δϕ Δη

Centrality evolution

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STAR preliminary

Au-Au: 00-10% Au-Au 0-10%: √sNN = 200GeV

3<pt,trigger<4 GeV

pt,assoc.>2 GeV

pT>0.15GeV/c

ref

ρρ∆

Δϕ Δη

Un-triggered correlations at high pT

Momentum evolution C. De Silva, WWND2012

Page 16: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Evaluating the contributions

Requirements for modeling (IMHO) Occam’s razor Centrality, pT evolution Consistent physics assumptions Orthogonality (mis)conceptions

longitudinal fragmentation 1D gaussian

η Δ

φ Δ η Δ

φ Δ

dipole quadrupole cos(2 φ Δ )

Same side Minijet Peak, 2D gaussian

Away - side - cos( φ )

Fit “Triggered” Fit “Un-triggered”

Page 17: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

arXi

v: 1

011.

5249

v2

v2

v3

Δϕ Δη

Au+Au 0-1%

Motivation for “vn fit” STAR preliminary Cross-talk between data and theory:

Extra-central collisions Transport model predictions

Page 18: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Modification assessment

Alver and Roland, PRC 81, 054905 (2010)

STAR preliminary

Comparison with flow: STAR preliminary

C. De Silva, WWND2012

PLB 704 (2011)

467

SS peak modifications: In pp the peak becomes symmetric at ~1GeV/c The peak is broader in Au+Au for all momenta studied Remains asymmetric (Δη vs. Δφ) for pT<4GeV/c

Presenter
Presentation Notes
Page 19: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

To be or not to be… That is, to separate or not

Jet v Ridge

1) Separating – shape fitting or how to “make” a ridge in d+Au fit prefers pedestal that could fake significant “ridge”

Data + Fit Residuals

Integrated yield difference under

jet peak Gauss-Exp: ~0.03 (or 10% of ridge in central Au+Au)

pTT=4-6 GeV/c, pT

A >1.5GeV/c, d+Au

Presenter
Presentation Notes
AuAu as described in the other powerpoint I don’t know Hua’s details for 2008 d+Au, but the pT cuts are identical to mine No zyam 2D Fit with SS Gaus + pedestal Projections were done on |Dh|<1.5 and |Df|<1.0 2D fits in the same range for d+Au; for Au+Au 2D fit was over all Df
Page 20: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Other fitting exercises… 2) What is the jet-shape?

Generalized Gaussian trigger pT

Low High

2 n 1

Generalized Gaussian pT

T=4-6 GeV/c, pTA >1.5GeV/c, d+Au

Forcing n=2 may add non-negligible

contribution to ridge (~25% )

pTT=8-10 GeV/c, pT

A >1.5GeV/c, d+Au

Presenter
Presentation Notes
2D fit : pedestal = 0.080 Yield = 0.272 Gaussian fit : pedestal = 0.088 Yield = 0.299 ± 0.002 Exponential fit : pedestal = 0.079 Yield = 0.268 ± 0.003 Gen. Gaussian fit : pedestal = 0.084 Yield = 0.286 ± 0.003 (b = 1.37 ± 0.05)
Page 21: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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For harder jets: • excess at large ∆η over

Gauss expectations • cos(3∆φ)-type modulation

χ2/ndf = 1.8

V22= 0.0051

7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Data Fit

SS Gaus

Residuals

cos(∆φ)

Other fitting exercises… 3) Do data demand the ridge?

“Up-to-quadruple” fit

cos(2∆φ)

Presenter
Presentation Notes
“Up-to-quadruple” fit
Page 22: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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χ2/ndf = 1.67

7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Data Fit Residuals

Does Ridge == v3?

“Consistent” < “proven”

For harder jets: • No statistically significant

structures in residuals with v3-like term

V22= 0.0069

cos(∆φ) cos(2∆φ) cos(3∆φ) SS Gaus

Page 23: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Data Fit Residuals

For harder jets: • Assuming ridge is a same-side

feature (for ex. ), e.g. same-side Gauss leaves no significant structures in residuals

So it is v3! Or is it?

χ2/ndf = 1.64

V22= -0.0014 !

SS Gaus cos(∆φ) cos(2∆φ) SS 1D Gaus

Which one is right? Need to think of [away-side] jet shape first…

Page 24: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Summary Ridge – a complicated structure, with features of

Jets modified by the medium Broadened same-side peak Yjet/Yridge energy dependence

Medium interplaying with the jets Charge combination effects Reaction plane dependence No apparent substructures

Features not well-placed yet: No apparent pT

trig dependence Ridge PID-dependence Ridge in di-jet

Presenter
Presentation Notes
3 particle - – no substructure in ridge 2+1 correlations – unmodified di-jet observation
Page 25: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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Back-Up

7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

STAR

Presenter
Presentation Notes
MATT LUZUM (IPHT) FLOW EXPLAINS LONG-RANGE CORRELATIONS Quantitative evidence of flow hypothesis: 1 Centrality dependence, size, of v3 and v2 (Alver & Roland, Phys.Rev. C81 (2010) 054905) (Alver, Gombeaud, Luzum, Ollitrault, Phys.Rev. C82 (2010) 034913) 2 pt-dependence and orientation with respect to event plane (Luzum, Phys.Lett. B696 (2011) 499-504) *(Luzum & Ollitrault, Phys.Rev.Lett. 106 (2011) 102301) 3 Centrality dependence of “ridge amplitude” (Sorensen, Bolliet, Mocsy, Pandit, Pruthi, arXiv:1102.1403) 4 Factorization, mass dependence, . . . (See plenary/parallel talks from ALICE, ATLAS, CMS, . . . ) Current long-range 2-particle data can be explained by flow alone*.
Page 26: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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Away-side shape from d+Au

7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Fit SS Gaus cos(∆φ)

χ2/ndf = 1.9

= +

χ2/ndf = 1.5

SS Gaus AS Gaus

= +

Residuals pTT=4-6 GeV/c, pT

A >1.5GeV/c, d+Au

Page 27: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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Width modifications for PID

7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

Trigger PID

Pure cone yield

Pure cone yield σ σ

π±

trigger 0.22 ± 0.01 0.19 ± 0.01 0.34 ± 0.03 0.28 ± 0.03

(P±+K±) trigger 0.12 ± 0.01 0.14 ± 0.02 0.27 ± 0.01 0.22 ± 0.01

Charged hadron 0.173 ± 0.005 0.168 ± 0.007 0.30 ± 0.01 0.23 ± 0.01

d+Au Au+Au

All errors statistical only!

d+Au Au+Au

“Pure Cone”: Au+Au d+Au

Similar associated hadron yields between d+Au and Au+Au for each type of trigger

Larger pure cone yield for pion than P+K triggers

Page 28: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

d+Au, ETT=8-10 GeV, 2D fit

Residual peak is very pronounced: 2D Gaussian is a bad fit function. 1D indicates that a pure exponential would work well.

Data Data + Fit Residuals

Page 29: High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT Ridge Workshop Centrality and energy dependence 3 < p T,trigger < 6 GeV/c, p t,assoc.

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Fitting exercise details

7-11 May 2012 Olga Evdokimov

University of Illinois at Chicago INT Ridge Workshop

2010 data, MB trigger, 0-10% pT

T=4-6 GeV, pTA>1.5 GeV

NFit>=20 and |dca|<3cm for triggers and associates 1.2M triggered events that satisfy quality cuts

Only did single-particle and pair acceptance correction Histo is identical to the one shown at QM11 on slide 5. 2D Fit with

SS Gaus + V1 (Dipole) + V2 (Quadrupole) (+ V3 ) Bins with track splitting excluded from fit and set to zero in residuals, but not

in rebinned histo (very minor effect). χ2 / ndf is better for fit with v3, but right now numbers not usable (issues with

excluded bins) For reference:

v2T*v2

A from ½(v2{EP}+v2{4}) = 0.0054 BG level from zyam fit with this v2 is 3.63