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Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR. Lake Louise Winter Institute, February 23, 2008 David Staszak (UCLA) STAR Collaboration. The Proton Helicity Distribution. 1/2 = ∆S q + ∆G + L q,g. Gluon Helicity:. - PowerPoint PPT Presentation
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1STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR
Lake Louise Winter Institute, February 23, 2008
David Staszak (UCLA)
STAR Collaboration
2STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
The Proton Helicity Distribution
1/2 = ∆Sq + ∆G + Lq,g
∆Sq: sum of spin contributions from all quarks, anti-quarks
Measured experimentally by DIS in the kinematic range 0.003 < x < 0.8
∆G: contribution from gluons
Gluon Helicity:
G=
We know 20-30% of proton’s total spin
Poorly Constrained from DIS, this is a major goal of the RHIC Spin Group
Lq,g: gluon and quark angular momentum contributions
The future…
3STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Accessing ∆G via ALL
€
ALL =Δσ
σ=
σ ++ −σ +−
σ ++ + σ +−∝
ΔfaΔfb
fa fb
ˆ a LL
Several contributing sub-processes: +
Inclusive Jet Signal: High Cross Section + Avoid fragmentation functions
+ +…
B. Jager et. al, Phys Rev D70 034010
4STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
G Models
• Many different models of ∆G
• GRSV has set up an inclusive jet/hadron framework to translate ∆G ALL at RHIC energies and STAR kinematics
• GRSV represents a good “first guess”
x·∆G(x)
x·∆
G
x
Vogelsang and Stratmann
Full G integral not covered by STAR acceptance
— GRSV— GS— BB— LSS— AAC— DNSI
Q2=100GeV2/c2
5STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
STAR Detector
EM Calorimeter (Pb/Scintillator):• Particle Neutral Energy• Barrel 0<<1 (2003-2005) -1<<1 (2006)• Endcap 1.09<<2.0
Beam-Beam Counter:• MinBias Trigger• Relative Luminosities • 3.4<||<5
Time Projection Chamber:• Charged Tracks PT
• -1.4<<1.4
100 GeV Polarized Proton Beams
All detectors have full azimuthal coverage
EndCapEMC
BBC
EMC Barrel
BBC TPC
6STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Experimentally Measuring ALL
€
€
ALL =1
P1P2
(N ++ + N−−) − R(N +− + N−+)
(N ++ + N−−) + R(N +− + N−+)
€
R =L++ + L−−
L+− + L−+
Relative Luminosity R from BBC Coincidence Rates for different Bunch Patterns
Polarization of Beams from CNI Polarimeters taken at set time intervals
Numbers of Jets Nij Reconstructed for Different Bunch Patterns
7STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
First Results: 2003+2004 Cross Section and ALL
Published: Phys. Rev. Lett. 97 252001 (2006)
• Limited Statistics• Theory curves based on ∆G parameterizations of DIS data• GRSV-STD is best fit to DIS data
• Agreement within systematics with NLO QCD over 7 orders of magnitude• Theory: B. Jager et. al, Phys Rev D70 034010
8STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Final 2005 ALL
0.2 < < 0.8
- Error bars are statistical only- Grey bands are systematic uncertainty
• Gehrmann-Sterling (GS-C) model calculation inserted into GRSV’s inclusive jet framework Phys.Rev.D53:6100-6109(1996)
9STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
ALL Systematics
effect (x 10 -3)
Reconstruction + Trigger Bias
2-5 (pT dependent)
Non-longitudinal Polarization
0.1-0.8 (pT dependent)
Relative Luminosity 0.94
Backgrounds 0.70
pT systematic [-5.4%,+6.7%]
Trigger Bias: The natural interaction mix (gg/qg/qq) can be biased in our sample from our triggers which rely on neutral energy only.
Reconstruction Bias: 25% jet resolution mixed with steeply falling pT spectrum means on average that we over-estimate the jet energy.
Combining PYTHIA partonic information with polarization models of G, we can calculate: ALL(PARTONIC) ALL (GEANT) ALL(GEANT+TRIGGER)
Reconstruction Bias is the difference between ALL(PARTONIC) and ALL (GEANT)
Trigger Bias is the difference between ALL(PARTONIC) and ALL(GEANT+TRIGGER)
10STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
GRSV DIS
2005 ALL - ∆G Constraints
*Theoretical Uncertainties not included
GRSV DIS best fit=0.241 = -0.45 to 0.7
PRD 63, 094005 (2001)
Within GRSV framework, G can’t be much larger than STD
Vogelsang and Stratmann
11STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
2006 Preliminary ALL
- Only Jet Patch Data Shown
• 2 4 pb-1 (more on the way!)
• BEMC fully instrumented, EEMC towers included
• 50 55% Beam Polarization
• Increased trigger thresholds better statistics at high pT
2006 Improvements
-0.7 < < 0.9
12STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
2006 Preliminary ALL
* GRSV-STD excluded with 99% CL
* g < -0.7 excluded with 90% CL
13STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Summary and Outlook
Inclusive jet channel is one way in which the RHIC Spin Group is able to access ∆G
2005 and 2006 inclusive jet results are a significant contribution to global understanding of ∆G
500pp GeV running is on the horizon expanded x-range
From STAR, Di-jet and Gamma-Jet measurements are on the way. Gamma-Jet can measure G(x) as a function of x, whereas Inclusive Jet can only measure an integrated x-range.
A global analysis of worldwide measurements is necessary to come to a definitive answer for ∆G
14STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Backup Slides
15STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Comparison: 2006 - 2005 ALL
16STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Model Dependent ALL Curves
Vogelsang and Stratmann
17STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
STAR Jet Reconstruction and Triggering
part
onpa
rtic
lede
tect
or
etcp
e
,,
,
πγν ,,
gq,
Jet Reconstruction • Midpoint Cone Algorithm• 0.5 GeV seed energy• 0.4 Cone Radius (2005), 0.7 C.R. (2006)
hep-ex/0005012
2005/2006 Trigger Mix• MinBias - BBC Coincidence• HighTower - ∆x = .05x.05 EMC patch above threshold• JetPatch - ∆x = 1x1 EMC patch above threshold
18STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Data/MC Comparison
PRL 97, 252001 (2006)
19STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
2006 Systematic Uncertainties
effect (x 10 -3)
Reconstruction + Trigger Bias
[-1,+3] (pT dependent)
Non-longitudinal Polarization
~0.03(pT dependent)
Relative Luminosity
0.94
Backgrounds 1st bin ~ 0.5Else ~ 0.1
pT systematic 6.7%
20STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Jet Reconstruction and Trigger Bias
Step 1: Use PYTHIA+GEANT to estimate the pT shift from detector jets to particle jets
Step 2: Simulate the difference in ALL between detector and particle jets for various gluon polarization scenarios
Particle jetsShifted detector jetsDetector jets
Step 3: Choose the largest difference for each jet pT bin
21STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Single Spin Asymmetries
22STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Relative Luminosity Systematic
Calculated using the BBC:
Cross-checked using theZero Degree Calorimeter (ZDC),another luminosity monitor
Difference (below) interpreted as a systematic on the relative luminosity
Difference between BBC and ZDC is 0.001
€
R3 =Lparallel
Lantiparallel
ALL(R3 + 0.001) - ALL (R3)
R3(BBC) - R3(ZDC)
ALL(R3 - 0.001) - ALL (R3)
Systematic estimated as the difference betweenALL(R3) and ALL(R3 ± 0.001)
23STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Background Systematic
Background manifests itself as jets with large neutral energy deposit
Difference between High Background and Low
Background Samples 05.0<bgf AbgLL
€
Abg = 0.00837 ± 0.00639
Background
Removed from analysis
( ) ( ) ( ) ( )( )Tbg
TbgLLTbgTLL
Tmeas
pf
pApfpApA
LL +
×+=
1
Background Fraction Background Asym Jet EEMC/ETot
€
ALLEMF>0.8 = 0.00837 ± 0.00639€
fbkg = 0.0014 ± 0.0012
JP2
24STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Non-longitudinal Beam Polarization Systematic
Non-longitudinal beam polarization changes ALL:
To bound this effect,
Calculate A from transverse data: |A |
0.1
Estimate the beam transverse polarization component Local polarimetry (BBC up-down and left-right asymmetries)
€
δA LLAΣ =|tanθB tanθ Y cos φY − φ B( ) A Σ |
€
⇒ |δA LLAΣ | ≤ 0.003