East Barrel

Dijet Production in Polarized
Proton-Proton Collisions at
STAR
200 GeV at STAR
Matthew Walker
for the STAR Collaboration
April 12, 2011

✦ Brief theoretical motivation
✦ Experimental Overview
✦ Cross Section Analysis
✦ Asymmetry Analysis
✦ Status of ongoing analysis
Outline
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
2

x!u
0.02
–
to ∆χ = 1. In order to account for unexpected
stomary to consider instead of ∆χ2 = 1 between
e of uncertainty.
e first moments of u and d resemble a parabola
ix units relative to those from KRE, due to the
at the overall goodness of KKP fit is poorer than
es for δd computed with the respective best fits
to the ideal situation. However for δu, they only
very good example of how the ∆χ2 uation. However for δu, they only
ple of how the ∆χ
= 1 does not
rences between the available sets of fragmentation
2 = 1 does not
the available sets of fragmentation
Theoretical Motivation
0.04
✦ Polarized 0 DIS tells us that the
spin contribution 0.4 from quark
-0.02 spin is only ~30%.
x!g –
x!s –
DSSV
DNS KRE
-0.04
DNS KKP
DSSV !" 2 =1
DSSV !" 2 0.2
Without RHIC data =2%
With RHIC data
0.04
0.02
0
KRE -0.02 (NLO)
KKP (NLO)
unpolarized
KRE -0.04 " 2
KRE " min +1
KRE " 2
KRE " min +2%
10 -2
x!s –
x
0
-0.2
0.06
0.04
0.02
0
10 -1
-0.02
10 -2
x
KRE (NLO)
KKP (NLO)
unpolarized
KRE " 2
KRE " +1
1
0.4
0.2
0
-0.2
10 -1
D. de Florian et al., Phys. Rev. D71, 094018 (2005). D. de Florian et al., Phys. Rev. Lett. 101 (2008) 072001
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
-0.04
0.06
0.04
x!d –
1
2
x!g
= 1
GRSV maxg
GRSV ming
10 -2
x
10 -1
0.04
0.02
2 ∆Σ + Lq +∆G + Lg
x
0
-0.02
-0.04
1
0.3
0.2
0.1
0
-0.1
-0.2
Substantial
improvement for
0.05 < x < 0.2,
but large
uncertainties at
low x
3

Theoretical Motivation
✦ Extracting gluon polarization
ALL = d∆σ
dσ
= ∆f1 ⊗ ∆f2 ⊗ σh · aLL ⊗ D h f
f1 ⊗ f2 ⊗ σh ⊗ D h f
∆f1
∆f2
σh
long-range short-range long-range
Extract ∆g(x,Q 2 ) using a global fit
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
1
2
aLL
= 1
1
0.75
0.5
0.25
0
-0.25
-0.5
-0.75
-1
2 ∆Σ + Lq +∆G + Lg
qg → qg
qq → qq q¯q → q¯q
gg → q¯q
gg → gg
-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 1
∆G(Q 2 ) =
� 1
0
cosθ*
∆g(x, Q 2 )dx
4

Inclusive jets
✦ Run 6 results: GRSV-MAX/
GRSV-MIN ruled out, a gluon
polarization between GRSV-std
and GRSV-zero favored
See Pibero Djawotho’s talk for more on inclusive jets from STAR
A LL systematics (x 10 -3 )
Reconstruction +
Trigger Bias
Non-longitudinal
Polarization
Relative
Luminosity
Backgrounds
D. de Florian et al. PRL 101 (2008) 072001.
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
[-1,+3]
(p T dep)
~ 0.03
(p T dep)
0.94
1 st bin ~ 0.5
else ~ 0.1
p T systematic ± 6.7%
5

Correlation Measurements
✦ Reconstructing multiple physics
objects (di-jets, photon/jet)
provides information about
initial parton kinematics
✦ STAR well suited for correlation
measurements with its large
acceptance
x1 = 1 √ s (pT 3e η3 + pT 4e η4 )
x2 = 1 √ s (pT 3e −η3 + pT 4e −η4 )
M = √ x1x2s
η3 + η4 = ln x1
x2
STAR Collaboration
PRL 100 (2008) 232003
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
6

✦ RHIC produces
polarized proton
beams up to 250
GeV in energy
✦ Siberian snake
magnets in the
AGS and RHIC
help protect beam
from depolarized
resonances
Experimental Setup
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
7

Blue
East
!=-1
BBC
Tai Sakuma, Thesis, MIT (2010)
STAR Detector
BEMC
TPC
!=0
Not shown:
Zero-degree calorimeters,
time-of-flight, polarimeters
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
!=1
West
Yellow
Tai Sakuma
8

Jet
π +
π 0
g
q
Jet Terminology
parton particle detector
Tracks, Energy Depositions
Detector Effects
Hadrons, Leptons
Parton Branching, Hadronization,
Underlying Event
Partons
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
9

Data
✦ 2006 Data: 5.39 pb -1 taken during RHIC Run 6
✦ 2009 Data: ~10 pb -1 taken during RHIC Run 9
✦ Jet Patch Trigger:
✦ 1x1 in φxη patch
of towers in the
BEMC (400
towers)
✦ Midpoint Cone
Algorithm with Split-
Merge
✦ Cone Radius: 0.7
✦ Seed 0.5 GeV
Tai Sakuma, Thesis, MIT (2010)
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
10

Data/Simulation Run 6
✦ 2006 Simulation:
✦ 11 STAR MC productions
producing 4M events with
partonic pT between 3 GeV
and 65 GeV
✦ PYTHIA 6.410, CDF Tune A
✦ Run 6 data and simulation
agreement is good
Tai Sakuma, Thesis, MIT (2010)
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
11

d 3 !/dMd! 3d! 4 [pb/GeV]
10 5
10 4
10 3
10 2
10
1
d 3 !
dMd! 3d! 4
STAR Run-6
2006 Cross Section
Systematic Uncertainty
Theory
Dijet Cross Section
pp @ 200 GeV
Cone Radius = 0.7
max(p T) > 10 GeV, min(p T) > 7 GeV
-0.8 < ! < 0.8, |!!| < 1.0
|!!| > 2.0
NLO pQCD + CTEQ6M
Had. and UE. Corrections
STAR Preliminary
! !
Ldt = 5.39pb!1
30 40 50 60 70 80 90
Mjj [GeV]
Tai Sakuma, Thesis, MIT (2010)
✦ Unpolarized differential cross
section between 24 and 100
(GeV/c 2 )
✦ NLO theory predictions using
CTEQ6M provided by de
Florian with and without
corrections for hadronization
and underlying event from
PYTHIA
✦ Statistical Uncertainties as
lines, systematics as rectangles
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
12

(Data - Theory) / Theory
-1.0 -0.5 0.0 0.5 1.0
2006 Cross Section
Systematic Uncertainty
Theoretical Uncertainty
! STAR
!
Ldt = 5.39 pb!1
Data-theory Comparison
of Dijet Cross Section
pp @ 200 GeV
Cone Radius = 0.7
max(p T) > 10 GeV, min(p T) > 7 GeV
-0.8 < ! < 0.8, |!!| < 1.0, |!!| > 2.0
Preliminary
30 40 50 60 70 80 90
M jj [GeV]
STAR Run-6
Theory:
CTEQ6M
NLO pQCD
Had. UE. Corrections
Tai Sakuma, Thesis, MIT (2010)
✦ Comparison to theory
(including hadronization
and underlying event
correction) shows good
agreement within
systematic uncertainties
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
13

2006 Asymmetry
ALL = 1
PBPY
✦ Asymmetry formula:
✦ N ++ : like sign yields
✦ N +- : unlike sign yields
✦ R: relative luminosity
✦ P: polarization
N ++ − RN +−
N ++ + RN +−
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
14

✦ Run 6 Longitudinal double
helicity asymmetry
✦ Systematic uncertainties
show effects on trigger
efficiency from different
theory scenarios
✦ Scale uncertainty (8.3%)
from polarization
uncertainty not shown
2006 Asymmetry
A LL
M jj [GeV]
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
0.08
0.06
0.04
0.02
0.00
-0.02
Dijet A LL
pp @ 200 GeV
Cone Radius = 0.7
max(p T) > 10 GeV
min(p T) > 7 GeV
-0.8 < ! < 0.8, |!!| < 1.0
|!!| > 2.0
GRSV STD
DSSV
GRSV !g = 0
GRSV !g = ! g
Data Run-6
Sys. Uncertainty
STAR Preliminary
! !
Ldt = 5.39pb!1
30 40 50 60 70 80
15

2009 Simulation
✦ Different detector, different trigger, updated geometry
✦ 9 STAR MC productions with partonic pT > 2 GeV
✦ PYTHIA 6.4.23, proPt0 (PYTUNE 329)
✦ Virtual Machine prepared with STAR software stack and deployed to over 1000 machines
✦ Run using cloud computing resources at Clemson University in South Carolina (Ranked
#85 best supercomputer)
✦ Over 12 billion events
generated by PYTHIA, filtered
to allow only 36 million to
undergo detector simulation
(GEANT3), and 10 million
through full reconstruction
✦ Took over 400,000 CPU hours
and generated 7 TB of files
transferred to BNL
✦ Largest physics simulation on
cloud, largest STAR simulation
Jul17 Jul24 Jul31
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
N Machines
1400
1200
1000
800
600
400
200
0
Available Machines
Working Machines
Idle Machines
Date
16

✦ Run 9 data
simulation
agreement is
good
Data/Simulation Run 9
Normalized Yields
(Data-Simu)/Simulation
6
10
5
10
4
10
3
10
Data
Simulation
20 30 40 50 60 70 80 90 100
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
20 30 40 50 60 70 80 90 100
2
Invariant Mass (GeV/c
STAR Run 9 Data Preliminary
)
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
5
10
4
10
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
η
34
5
10
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
0 0.1 0.2 0.3 0.4 0.5 0.6
1
Rcone
= 0.7
-0.8 < η < 0.8
| Δη|
< 1.0
| Δφ|
> 2.0
p+p → Jet + Jet + X
s = 200 GeV
STAR Preliminary
-1
0 0.1 0.2 0.3 0.4 0.5 0.6
cos( θ*)
17

LL
A
East Barrel - East Barrel and West Barrel - West Barrel
0.08
0.06
0.04
0.02
0
-0.02
MC GS-C(pdf set NLO)
2009 STAR Data
Systematic Uncertainties
20 30 40 50 60 70 80
Run 9 Asymmetry
2
M [GeV/c ]
LL
A
East Barrel - West Barrel
0.08
0.06
0.04
0.02
0
-0.02
Scale uncertainty
GRSV std
DSSV
20 30 40 50 60 70 80
East West East West
2
M [GeV/c ]
20 30 40 50 60 70 80
2
M [GeV/c ]
STAR Matthew Walker, MIT
March 29, 2011
Jet Meeting
LL
A
0.08
0.06
0.04
0.02
0
-0.02
Full Acceptance
√
s = 200 GeV
p + p → jet + jet + X
STAR
Preliminary
18

Kinematic Sensitivity
5
10
4
10
3
10
2
10
10
1
-1
10
-2
10
10
x
-1
10
-2
East Barrel - East Barrel East Barrel - West Barrel
-1
10 1
1
X X
STAR
X
Preliminary
√
s = 200 GeV
p + p → jet + jet + X
20 30 40 50 60 70 80 90 100
2
Invariant Mass (GeV/c )
5
10
4
10
3
10
2
10
-1
10
10
10
x
STAR Matthew Walker, MIT
March 29, 2011 Jet Meeting 19
10
1
-2
1
-1
10
-2
x1:
20.0 < M < 30.0
x2:
20.0 < M < 30.0
x1:
70.0 < M < 80.0
x2:
70.0 < M < 80.0
-1
10 1
x1
20 30 40 50 60 70 80 90 100
2
Invariant Mass (GeV/c )
x
2
X

Summary
✦ Correlations measurements provide constraints on parton
kinematics, which helps constrain the shape of Δg(x)
✦ 2006 Dijet cross section (5.39 pb -1 ) shows good agreement with
NLO calculations
✦ First Dijet double-spin asymmetry (FOM = 0.59 pb -1 ) from
2006 data suggests preference away from GRSV-std scenario
✦ 2009 Dijet asymmetry analysis underway with FOM = 1.21
pb -1 analyzed to date, and more to come, allows for the first
separation into multiple pseudorapidity acceptances
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
20

Backup
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
21

LL
A
2009 Projections
east barrel - east barrel and west barrel - west barrel
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
MC
GRSV std
GRSV m03
GRSV zero
GS-C(pdf set NLO)
2009 STAR Data
-0.02
20 30 40 50 60 70 80
Wed Sep 22 15:18:55 2010 ]
2
M [GeV/c
-0.02
20 30 40 50 60 70 80
East West East West
2
M [GeV/c ]
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
LL
A
east barrel - west barrel
0.06
0.05
0.04
0.03
0.02
0.01
0
-0.01
Scale uncertainty
GRSV std
DSSV
STAR
Projected Precision
22

ALL,j =
�
�
k
2009 Asymmetry
�
k
αjk(
i PB,iPY,i(N5,i,k + N10,i,k) − PB,iPY,iRi(N6,i,k + N9,i,k))
�
αjk(
i P 2 B,iP 2 Y,i (N5,i,k + N10,i,k)+P 2 B,i,jP 2 Y,i,jRi(N6,i,k + N9,i,k))
✦ The value of ALL in a bin j is given by the above formula
✦ αjk are the matrix elements for the unfolding
✦ Changing the jet energy scale results in different unfolding
matrices
✦ The calculation is repeated for the different matrices to get the
uncertainty on ALL due to the jet energy scale
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
23

Dijet Run 9 Projected
STAR Matthew Walker, MIT
April 12, 2011
SPIN 2011
24