A.Magnon IWHSS ‘08 – Torino March 31, 2008 1 Gluon Polarisation Overview quark contribution to nucleon spin. Why G ? G from scaling violations G from hadron production - Open charm - COMPASS - High p T hadrons pairs & single - COMPASS/HERMES G from pp collisions - RHIC A. Magnon (CEA-Saclay/IRFU & COMPASS)
Gluon Polarisation Overview. DS, quark contribution to nucleon spin. Why D G ? D G from scaling violations D G from hadron production - Open charm - COMPASS - High p T hadrons pairs & single - COMPASS/HERMES D G from pp collisions - RHIC A. Magnon (CEA-Saclay/IRFU & COMPASS). - PowerPoint PPT Presentation
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A.Magnon IWHSS ‘08 – TorinoMarch 31, 2008
1
Gluon Polarisation Overview
quark contribution to nucleon spin. Why G ? G from scaling violations G from hadron production - Open charm - COMPASS
- High pT hadrons pairs & single - COMPASS/HERMES
G from pp collisions - RHIC A. Magnon (CEA-Saclay/IRFU & COMPASS)
A.Magnon IWHSS ‘08 – TorinoMarch 31, 2008
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Early measurements of (1)
SLAC Polarized electrons
large, “as expected” 1976-1983
g1p
xBj
SLAC
Compatible with =0.6
∫g1p
xBj
xBjg1p
Ellis-Jaffe = 0.6
EMC
EMC @ CERN polarized
Access lower x, = 0.12 ± 0.17
→ ” Spin crisis ’’ 1988
A.Magnon IWHSS ‘08 – TorinoMarch 31, 2008
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Early measurements of (2)
HERMES, SLAC high precision, SMC @ CERN lower x
g1 for proton & neutron (deuteron) …
Bjorken Sum Rule relates proton & neutron g1=∫g1dx003.0181.0)(
6
1 2111 QC
g
g NS
V
Anp
024.0012.011 174.0
np
Theory, Q2=5 GeV2
SMC
= 0.2 - 0.3 confirmed to be small
Bjorken OK + s determination + first flavor separation …
Good agreement between NLO pQCD calculations and data confirmation that theory can be used to extract spin dependent pdf’s from RHIC data
PHENIX data
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Log10(xgluon)NLO pQCD: 0 pT=29 GeV/c xgluon=0.020.3 GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 ) Each pT bin corresponds to a wide range in xgluon, heavily overlapping with other pT bins. These data is not much sensitive to variation of G(xgluon) within our x range. Any quantitative analysis should assume some G(xgluon) shape
From pT to xgluon (PHENIX, 0X)
√s=200 GeV
G.Bunce
Dubna Spin07
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Calc. by W.Vogelsang and M.Stratmann
GRSV “standard”, G(Q2=1GeV2)=0.4, is excluded
by data on >3 sigma level: 2(std)2min>9
Only exp. stat. uncertainties are included (the effect of syst. uncertainties is expected to be small in the final results) Theoretical uncertainties are not included
From ALL to G (PHENIX, 0 with GRSV)
“3 sigma”
G.Bunce
Dubna Spin07
A.Magnon IWHSS ‘08 – TorinoMarch 31, 2008
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From ALL to G (STAR, jetX with GRSV)
2005 STAR preliminary
Systematic error band
Measured Jet PT (GeV)
GRSV DIS
Large gluon polarisation scenario is not consistent with data
J.C.Dunlop
Dubna Spin07
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Different sensitivity of + and - to the sign of G …. e.g. G > 0
πLL
πLL
πLL AAA
ο
STARSTAR
No constraint on G yet …
STAR, inclusive ± production (mid - η)
J.C.Dunlop
Dubna Spin07
Dramatic increase in precision in Run 2006
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G from RHIC
High statistics available to constrain G in xg range (0.02 – 0.3)
G not large (consistent with zero)
“Standard” scenario, G (Q2=1GeV2) = 0.4, is excluded
by data on > 3 sigma level: 2(std)2min > 9
(PHENIX ?)
Theoretical uncertainties might be significant
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RHIC, prospects
Improve exp. (stat.) uncertainties, move to higher pT
- more precise G in probed x range - probe (lower) and higher x and constrain G vs x Different channels - different systematics - different x, - gq -> q (pp -> jet), sensitive to G sign, parton kinematics well constrained, theoretically clean Different √s, 62 GeV, 200 GeV, 500 GeV
Substantial FOM = P4L needed
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Conclusion, possible scenarios
G Lq Lg
½ = 1/2 × 0.3 + 0.35 + 0 + 0
½ = 1/2 × 0.3 + 0.0 + 0.35
½ = 1/2 × 0.3 - 0.35 + 0.70
COMPASS/RHIC JLab/HERMES/COMPASS
From COMPASS & RHIC:
G =|∫G(xG)| ≤ 0.4 ?
≈ a0 = 0.3
a0 =
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Additional slides
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Measurements of G/G
xg binning
High pT
in 2006
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PHENIX, different s
s=62 GeV 0 cross section described by NLO pQCD within theoretical uncertainties
Sensitivity of Run6 s=62 GeV data collected in one week is comparable to Run5 s=200 GeV data collected in two months, for the same xT=2pT/s
s=500 GeV will give access to lower x; starts in 2009
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Method- parameterize polarised parton distributions at Q0
2
e.g. qi ~ xi (1-x)i(1+ix)
- DGLAP evolution to measured Q2 - calculate g1 and fit all existing g1 data together
DGLAP evolution equations rule ∂/∂ lnQ2
dependence of parton distribution functions
and G coupled in the evolution
→ Extract G(x)
G from scaling violations
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AAC – NLO, hep-ph/0603213 including g1 new data from HERMES, COMPASS and JLAB + PHENIX ALL 0