1. Gluon Polarisation Overview
DS, quark contribution to nucleon spin. Why DG ?
DG from scaling violations
DG from hadron production
- Open charm - COMPASS
- High pT hadrons pairs & single - COMPASS/HERMES
DG from pp collisions - RHIC
A. Magnon (CEA-Saclay/IRFU & COMPASS)
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

2. Early measurements of DS (1)
g1p
xBj
SLAC
Compatible with DS=0.6
SLAC Polarized electrons
DS large, “as expected”
∫g1p
xBj
xBjg1p
Ellis-Jaffe DS = 0.6
EMC
CERN polarized m
Access lower x, DS = 0.12 ± 0.17
→ ” Spin crisis ’’
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

3. Early measurements of DS (2)
HERMES, SLAC high precision, CERN lower x
g1 for proton & neutron (deuteron) …
Bjorken Sum Rule relates proton & neutron g1=∫g1dx
DS = confirmed to be small
Theory, Q2=5 GeV2
SMC
1998
Bjorken OK + as determination + first flavor separation …
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

4. Recent measurements of DS
CERN, m 160 GeV
COMPASS fit to g1 p, n, d world data, MS scheme, Q2 = 3 (GeV/c)2
PLB 647 (2007) 8
DS = 0.30 ± 0.01 (stat) ± 0.02 (evol)
Ds + Ds = ± 0.01 (stat) ± 0.02 (syst)
COMPASS data alone
DESY, e- 27 GeV
HERMES from g1d data, MS scheme, Q2=5 (GeV/c)2,
neglecting x < 0.02 contrib., PRD75 (2007)
DS =0.33 ± (stat) ± (theo) ± (evol)
Ds + Ds = ± (th) ± (exp) ± 0.009(evol)
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

5. ½ = ½ΔΣ + ΔG + <Lq> + <Lg>
Why measure DG ?
½ = ½ΔΣ + ΔG + <Lq> + <Lg>
Measurement of DG important :
1 – How are gluons polarized ?
2- Low value of a0 could be due to axial
anomaly if DG is large.
(A. Efremov O.Teryaev, G. Altarelli – G. Ross)
3 – How large is parton orbital angular
momentum
a0 =
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

6. How to measure DG ? DG from scaling violations
DG from hadron production
- Open charm
- High pT hadrons (pairs, single)
DG from pp collision
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

7. COMPASS NLO QCD fit Q2 = 3 GeV2
Comparison of fits - disagreement of data
with previous QCD fits (LSS05, GRSV, BB)
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

8. COMPASS NLO QCD fit New COMPASS g1d 2006 DG = 0.34 Q2 = 3 GeV2
 G > 0 or  G < 0, |G| ~ 0.3
a0 = ± 0.03 ± 0.05
s = ± 0.01 ± 0.02
2006
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

9. How to measure DG ? DG from scaling violations
DG from hadron production (PGF)
- Open charm
- High pT hadrons (pairs, single)
DG from pp collision
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

10. Photon-gluon fusion (PGF)
Gluon polarisation is measurable in PGF
measure
calculate and
using Monte Carlo N
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

11. DG/G from open charm Open charm, single D meson
c -> (D*) -> (ps) D0 -> Kp(ps) c
cleanest process wrt physical bkgr
combinatorial bkgr, limited statistics
so far LO analysis, NLO in progress c N
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

12. DG/G from open charm COMPASS Data: 2002,2003,2004 & 2006
160 GeV m beam & 6LiD target
nD* = 8675
nD0 = 37398
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

13. DG/G from open charm Analysis uses both aLL and S/(S+B) weighting
aLL obtained from Neural Network trained on MC (AROMA):
input variables : Q2, xbj, y, pT, zD
S/(S+B) given by a parameterization: input variables : target cell,
fPμaLL, pK, θK, zD, cosθ*, pT, RICH Likelihoods
Weighting brings significant improvement in statistics due
to large variations of aLL and S/(S+B) in phase-space
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

14. DG/G from open charm 5 bins in S = S/(S+B) D0 -untagged D* -tagged
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008
5 bins in S = S/(S+B)

15. DG/G from open charm 2006 aLL parameterization aLL generated
aLL reconstructed
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

16. DG/G from open charm 2002 – 2006 data D0 + D* “ New ”
DG/G = ± 0.27 (stat) ± 0.11 (syst)
@ <xg> ~ 0.11, <m2> ~ 13 (GeV/c)2
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

17. How to measure DG ? DG from scaling violations
DG from hadron production (PGF)
- Open charm
- High pT hadrons pairs, Q2 > 1 GeV/c2
DG from pp collision
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

18. ΔG/G from high pT hadron pairs
Q2 > 1 (GeV/c)2 +
Resolved g ~50%
Q2 < 1 (GeV/c)2
q,g
qg,gg g q q
Photon Gluon Fusion ~ 30%
Leading Order
QCD Compton
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

19. ΔG/G from high pT hadron pairs
Analysis uses parameterization of RPGF, RQCDC, RLO, aLLPGF,
aLLQCDC, aLLincl, xg, xC, … etc based on Neural Network
trained on MC (LEPTO for Q2 > 1).
No cut on NN which assigns to each evt. a probability to
originate from LO, PGF or COMPTON.
Dependence on PDFs studied
Parton shower (NLO process) added
Detailed studies of systematics
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

20. ΔG/G from high pT hadron pairs
Two parameters:
O1 & O2 to express
fractions R (PGF, LO
or QCDC) for each
high pT event
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

21. ΔG/G from high pT hadron pairs
Leading hadron
Sub-leading hadron
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

22. ΔG/G from high pT hadron pairs
Probabilities (fractions) of LO, QCDC, PGF : Monte Carlo vs Neural Network
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

23. ΔG/G from high pT hadron pairs
“ New ”
2002 – 2004 data: High pT, Q2 > 1 GeV/c2
DG/G = 0.08 ± 0.10 (stat) ± 0.05(syst)
@ <xg> = 0.082, (range: – 0.123) m2 ~ 3 (GeV/c)2
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

24. ΔG/G from high pT hadron pairs
(Released 2 Oct. 2006, SPIN2006)
2002 – 2004 data: High pT, Q2 < 1 GeV/c2
DG/G = ± (stat) ± (syst)
@ <xg> = 0.085, m2 = 3 (GeV/c)2
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

25.  G/G, direct measurements
GRSV, DG
max, 2.5
std, 0.6
New high pT
min, 0.2
QCD Fits
|DG| ~ 0.3
New open charm
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

26.  G/G, direct measurements
Accurate DG/G from COMPASS data (2002 – 2004) from
high pT hadron pairs, Q2 < 1 GeV/c2 and Q2 > 1 GeV/c2 (new)
DG/G small (~ <xg> = 0.08
Significant improvement for DG/G from open charm
(2002 – ) and aLL + S/B weighting.
Also DG/G (~ <xg> = 0.11
Similar conclusion from new HERMES analysis
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

27. How to measure DG ? DG from scaling violations
DG from hadron production
- Open charm
- high pT hadrons (pairs, single)
DG from pp collision
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

28. RHIC: polarized pp collider
Year P L(pb-1) P4L(*) % % %
(*) G.Bunce Dubna Spin07
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

29. pp collisions @ PHENIX & STAR
Reactions pp -> pX, jet X, gX, cc X, probe gluon
Measure always product of 2 observables
MC required to determine fraction of process
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

30. pp collisions @ PHENIX & STAR
Considerable progress in pQCD NLO calculations
Jäger,Schäfer,
Stratmann,Vogelsang;
de Florian
Jäger,Schäfer,
Stratmann,Vogelsang;
Signer et al.
Gordon,Vogelsang;
Contogouriset al.;
Gordon, Coriano
Bojak, Stratmann;
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

31. Unpol. Cross Section in pp
Good agreement between NLO pQCD
calculations and data  confirmation
that theory can be used to extract
spin dependent pdf’s from RHIC data
pp0 X : hep-ex
PHENIX data
pp X: PRL 98,
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

32. From pT to xgluon (PHENIX, p0X)
√s=200 GeV
NLO pQCD: 0 pT=29 GeV/c  xgluon=0.020.3
GRSV model: G(xgluon=0.020.3) ~ 0.6G(xgluon =01 )
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
Log10(xgluon)
G.Bunce
Dubna Spin07
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

33. Calc. by W.Vogelsang and M.Stratmann
From ALL to DG (PHENIX, p0 with GRSV)
Calc. by W.Vogelsang and M.Stratmann 
“3 sigma”
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
G.Bunce
Dubna Spin07
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

34. From ALL to DG (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
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

35. STAR, inclusive p± production (mid - η)
Different sensitivity of p+ and p-
to the sign of G …. e.g. G > 0 
STAR
No constraint on DG yet …
Dramatic increase in precision in Run 2006
J.C.Dunlop
Dubna Spin07
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

36. DG from RHIC High statistics available to constrain DG in xg range
(0.02 – 0.3)
DG 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
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

37. RHIC, prospects Improve exp. (stat.) uncertainties, move to higher pT
- more precise DG in probed x range
- probe (lower) and higher x and constrain DG vs x
Different channels
- different systematics
- different x,
- gq -> qg (pp -> g jet), sensitive to DG sign, parton
kinematics well constrained, theoretically clean
Different √s, 62 GeV, 200 GeV, 500 GeV
Substantial
FOM = P4L
needed
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

38. Conclusion, possible scenarios
From COMPASS & RHIC:
DG =|∫DG(xG)| ≤ 0.4 ?
DS ≈ a0 = 0.3
a0 =
DS DG Lq Lg
½ = 1/2 ×
½ = 1/2 ×
½ = 1/2 ×
COMPASS/RHIC JLab/HERMES/COMPASS
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

39. Additional slides
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

40. Measurements of DG/G xg binning High pT in 2006 A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

41. 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
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

42. DG from scaling violations
DGLAP evolution equations rule ∂/∂ lnQ2 dependence of parton distribution functions
Method
- parameterize polarised parton distributions at Q02
e.g. Dqi ~ xai (1-x)bi(1+gix)
- DGLAP evolution to measured Q2
- calculate g1 and fit all existing g1 data together
DS and DG coupled in the evolution
→ Extract DG(x)
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

43. Global QCD analysis: AAC - NLO
xDuv
xDG
DG = 0.31 ± 0.32
at Q2=1 GeV2
xDdv
xDq
Dq = ± 0.32
AAC – NLO, hep-ph/
including g1 new data from HERMES, COMPASS and JLAB + PHENIX ALL p0
A.Magnon
IWHSS ‘08 – Torino
March 31, 2008

44. New COMPASS A1d data PLB647 (2007) 8 A.Magnon IWHSS ‘08 – Torino
March 31, 2008