Recent results from high-energy longitudinal polarized proton-proton collisions at 200GeV at RHIC

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Recent results from high-energy longitudinal
polarized proton-proton collisions at 200GeV at
RHIC

• Tai Sakuma
• MIT

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The gluon contribution to the proton spin, ?G, is
poorly constrained.
Polarized DIS found that quarks carry only a
small fraction of the proton spin
?G is only loosely constrained from polarized
DIS data.
??0.2
quarks
gluons
orbital motions
proton spin
polarized pp
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One of the goals of RHIC-Spin is to determine ?G
with polarized pp collisions.
In proton-proton collisions, gluons are in the
initial states at lowest order.
polarized pp
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In polarized pp collisions, ALL is the most
important quantity to measure to determine ?G.
ALL

• the double spin asymmetry in polarized pp
  collisions

- sensitive to ?G
As an example of ALL, this is one of the early
results from STAR.
PRL 97 (2006) 252001
polarized pp
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ALL is sensitive to ?G
The result is compared with theory predictions
from GRSV working group.
As an example of ALL, this is one of the early
results from STAR.
PRL 97 (2006) 252001
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ALL is sensitive to ?G
GRSV x?G(x)
The result is compared with theory predictions
from GRSV working group.
PRL 97 (2006) 252001

• GRSV polarized pdf
• PRD 63 (2001) 094005
• GRSV - std
• GRSV - max
• GRSV - min
• GRSV - zero

Best fit to pDIS Large uncertainty
3 extreme scenarios
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ALL is sensitive to ?G
GRSV x?G(x)
The result is compared with theory predictions
from GRSV working group.
PRL 97 (2006) 252001

• GRSV polarized pdf
• PRD 63 (2001) 094005
• GRSV - std
• GRSV - max
• GRSV - min
• GRSV - zero

Best fit to pDIS Large uncertainty
3 extreme scenarios
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ALL is sensitive to ?G
GRSV x?G(x)
Perturbative QCD
PRL 97 (2006) 252001

• GRSV polarized pdf
• PRD 63 (2001) 094005
• GRSV - std
• GRSV - max
• GRSV - min
• GRSV - zero

Best fit to pDIS Large uncertainty
3 extreme scenarios
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The pQCD framework was confirmed by the cross
section, which justify the use of ALL.
Perturbative QCD
The measured cross sections agree with NLO pQCD
calculations over several orders of magnitude for
various final states.
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This framework needs to be tested to justify the
use of ALL to put constraint on ?G
Perturbative QCD
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The cross section measurement is important to
confirm pQCD framework
Perturbative QCD
PRL 97 (2006) 252001
One of the cross section measurements from
STAR. The results agree with NLO pQCD calculation.
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The cross sections agree with NLO pQCD
calculations over several orders of magnitude for
various final states.
??
??
jet
?
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ALL is predicted for various final states with
different ?G models
GRSV x?G(x)
??
??
jet
?
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ALL is measured for various final states
??
jet
J/?
??
??
??
?
??
??
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STAR inclusive jet ALL

• 2006 RHIC Run
• 4.7 pb-1
• Polarization 60
• Jet Patch Trigger
• Energy in a patch of calorimeter
• towers (???x ?? 1 x 1) gt 8.3 GeV
• Midpoint Cone Algorithm
• Cone Radius 0.7
• PARTICLE jet pT
• Corrected measured jet pT to true jet
  pT
• with Pythia MC sample

systematics
ALL systematics (x 10-3)
Jet Reconstruction Trigger Bias -2, 5 (pT dep)
Non-longitudinal Polarization 0.03 (pT dep)
Relative Luminosity 0.94
Backgrounds 0.5 (1st bin), 0.1(else)
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STAR inclusive jet ALL
The results are compared with the GRSV ALL
predictions.
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STAR inclusive jet ALL
The series of ?G spanning ?G-min and ?G-max
To quantify the impact on ?G
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STAR inclusive jet ALL
ALL predictions based on the series of ?G
The series of ?G spanning ?G-min and ?G-max
To quantify the impact on ?G
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STAR inclusive jet ALL
Comparison of the results with the series of the
ALL predictions
allowed region
GRSV STD
ALL predictions based on the series of ?G
Confidence Levels from the comparison
For example, the C.L. for ?G 0.3 is about 0.1.
This means that if ?G 0.3 is true, the
probability that we observe ALL that is in worse
agreement than the ALL we actually observed is
0.1 percent.
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STAR inclusive jet ALL
allowed region
Impact on ?G

• The 2006 results excluded ?G lt -0.7 and ?G gt 0.2
  with C.L. 90 within the GRSV framework.
• The results are consistent with pDIS data.

GRSV STD
Confidence Levels from the comparison
For example, the C.L. for ?G 0.3 is about 0.1.
This means that if ?G 0.3 is true, the
probability that we observe ALL that is in worse
agreement than the ALL we actually observed is
0.1 percent.
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PHENIX Inclusive p0 ALL

• ?? ? ??
• highly segmented EMCal
• ???x ?? 0.01 x 0.01
• Run 5
• 3.5 pb-1
• Polarization 50
• Run 6
• 7.5 pb-1
• Polarization 60
• Final scaling error will be 10
• Soft physics contribution
• 10 at 2 GeV
• Corrected for the background ALL

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PHENIX Inclusive p0 ALL
ALL predictions based on the series of ?G
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PHENIX Inclusive p0 ALL
Comparison of the results with the series of the
ALL predictions
ALL predictions based on the series of ?G

• Within the GRSV framework,
• ?2min 7/7 NDF
• ?2min 3? ? -0.8 lt ?G lt 0.2

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The constraints on ?G from the STAR and PHENIX
results
inclusive ?0
inclusive jets
The combined results constrain ?G
STAR and PHENIX results are consistent and
complementary
The analysis was done within the GRSV framework
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Beyond GRSV framework
The analysis was done within the GRSV framework
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Beyond GRSV framework
The analysis was done within the GRSV framework
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Beyond GRSV framework
The range of x probed is 0.02 lt x lt 0.3
The analysis was done within the GRSV framework
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Beyond GRSV framework
Gehrmann-Stirling Set C (GS-C) has highly
polarized gluon in low x and ?G 1
The range of x probed is 0.02 lt x lt 0.3
The analysis was done within the GRSV framework
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Beyond GRSV framework
Gehrmann-Stirling Set C (GS-C) has highly
polarized gluon in low x and ?G 1
The range of x probed is 0.02 lt x lt 0.3
ALL for GS-C is consistent with the results from
RHIC Spin
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Beyond GRSV framework
Gehrmann-Stirling Set C (GS-C) has highly
polarized gluon in low x and ?G 1
The range of x probed is 0.02 lt x lt 0.3
?G 1 is ruled out within the GRSV framework but
is still possible for much different shape of
x?G(x)
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The low-x region needs to be measured.
500 GeV Forward ?, ?jet
The range of x probed is 0.02 lt x lt 0.3
Forward Meson Spectrometer (FMS)
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New global analysis is starting at BNL.
?G(x) models
ALL predictions
pDIS data
ALL measurements
constrains on ?G
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New global analysis is starting at BNL.
New global analysis at BNL

• include both pDIS and RHIC Spin data for global
  fits of the polarized pdf.
• started at BNL in the Fall 2007.
• collaborative effort of
• theorists from GRSV, DNS
• and
• experimentalists from
• STAR and PHENIX.

pDIS data
ALL measurements
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Summary

• ALL for various final states in polarized pp
  collisions is measured at 200 GeV at RHIC.
• ALL from RHIC is constraining ?G to -0.8 lt ?G lt
  0.2 with 90 C.L. within the GRSV framework and
  the probed x range of 0.02 lt x lt 0.3.
• Significant measured sensitivity is expected at
  RHIC with ?, ?jet channels and 500 GeV run with
  access to lower x.
• A global analysis of the polarized parton
  distributions with pDIS and RHIC data is starting
  at BNL.