Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR
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Transcript of Inclusive Jet Longitudinal Spin Asymmetry Measurements with Polarized p+p Collisions at STAR
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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
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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…
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3STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Accessing ∆G via ALL
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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
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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
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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
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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
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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
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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)
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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)
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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
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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
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12STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
2006 Preliminary ALL
* GRSV-STD excluded with 99% CL
* g < -0.7 excluded with 90% CL
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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
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14STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Backup Slides
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15STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Comparison: 2006 - 2005 ALL
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16STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Model Dependent ALL Curves
Vogelsang and Stratmann
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17STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
STAR Jet Reconstruction and Triggering
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,,
,
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
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18STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Data/MC Comparison
PRL 97, 252001 (2006)
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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%
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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
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21STARSTAR LLWI, Feb 23, 2008 David Staszak UCLA
Single Spin Asymmetries
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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
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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)
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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
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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
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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