High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT...
Transcript of High pT angular correlations from STAR · Olga Evdokimov University of Illinois at Chicago INT...
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High pT angular correlations from STAR
Olga Evdokimov for the STAR collaboration
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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
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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?
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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
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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
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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
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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
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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
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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
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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)
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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
0º
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
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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
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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
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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%
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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
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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”
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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
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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
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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
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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
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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)
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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
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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…
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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
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Back-Up
7-11 May 2012 Olga Evdokimov
University of Illinois at Chicago INT Ridge Workshop
STAR
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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
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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
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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
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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