1. GLUON POLARISATION EINN 2005 introduction
Fulvio Tessarotto
INFN – Trieste
introduction
ΔG from inclusive data analysis
direct measurements of ΔG/G
1) method and previous measurements
2) recent results from COMPASS
3) measurements at RHIC
outlook
EINN 2005

2. measuring Q2 variations of g1 we can try to get DG
In inclusive polarised DIS one can measure an asymmetry in the differential cross-section:
and extract the struture function g1.
In the QPM g1 has a simple interpretation:
In QCD at NLO g1 may depend explicitely on DG:
measuring Q2 variations of g1 we can try to get DG
Fulvio Tessarotto EINN 2005
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3. ½= ½ΔΣ + ΔG + Lq + Lg The nucleon spin quarks gluons orb. mom.
Ellis-Jaffe: ΔΣ = a0 ≈ 0.6
experimentally: a0 ≈ 0.25
ΔΣ = a0 + 3(s/2) ΔG
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4. 1/2 = ½ 0.32 + 0.80 + Lz = 0.96 + Lz Two years ago …
SLAC (E142, E143, E154, E155)
CERN (EMC, SMC)
DESY (HERMES)
185 exp. points
DG not well constrained
not extracted
N.B. DS in JET scheme does NOT depend on Q2.
n=1 moments of PD, JET scheme, Q2=1 GeV2
Spin-dependent PDFs
1/2 = ½ Lz = Lz
E. Leader, A. Sidorov, D. Stamenov
Phys. Rev. D67 (2003)
 Lz is negative
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5. ... Dg and Dq were largely unconstrained
Direct Dg measurement
Is this still true?
The pure polarized species, the frequent polarization reverse, the beam and apparatus stabilities make possible to measure for the first time the inclusive asymmetries on the level of Compare to the fixed target experiment.
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6. final g1 data - Very good statistics - Smearing (resolution and
radiative corr.) →
correlation between x bins
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7. g1n(x) at high x from JLAB
PRL 92, (2004)
pQCD + no Lz →
A1=Du/u= Dd/d=1 at high x
Very accurate A1n at high x
A1n > 0 at x > 0.5
+ world A1p → Dd/d < 0
so Lz not negligible ?
Du/u
Dd/d
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8. g1d(x) at low x
PLB 612 (2005) 154
g1/F1
new data : DS =0.202 ( ) → ( )
COMPASS systematically > SMC at low x
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9. NLO QCD fits with new data + new unpolarised PDFs
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10. to know DG we still need to measure it
possible trend toward smaller DG but the results are scattered:
to know DG we still need to measure it
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11. polarised p p collision: RHIC
Direct Measurements:
polarised p p collision: RHIC
semi-inclusive deep inelastic scattering: DESY, CERN
(Photon Gluon Fusion)
History:
Idea proposed by R.D.Carlitz, J.C.Collins and A.H.Mueller,
Phys.Lett.B 214, 229 (1988)
……..and many more
revisited by A.Bravar,D.von Harrach and A.Kotzinian,
Phys.Lett.B 421, 349 (1998)
Method used in HERMES for photoproduction
HERMES, A.Airapetian et al., Phys.Rev.Lett.84, 2584 (2000)
Applied for DIS region by SMC (data with Q2 >1GeV2)
SMC, B.Adeva et al.., Phys. Rev. D 70, (2004).

12. ΔG/G from Photon-Gluon Fusion
Strategies to suppress background:
1) Open charm production:
q = c unique, no background
charm fragmentation, 1.2 D0 per event
D0 -> K- π+ (BR 4%), D*+(~20%) -> D0 π+
2) High-PT hadron pair production: q=u,d,s
skT(intr) = 450 MeV/c
spT(frag) = 350 MeV/c
pQCD scale set by:
1) ŝ > 4mc2 or
2) ŝ > (pt1+pt2)2
Photon-Gluon Fusion
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13. HERMES & DESY 27.5 GeV e Pure atomic H or D targets
Spectrometer with complete
hadron identification
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14. HERMES ALL from high pT hadron pairs
photoproduction
Proton target
<xg> = 0.17
<Q2> = 0.06 (GeV/c)2
Promising channel, but …
theoretical uncertainties
may be large
Statistics decreases with pT
Fulvio Tessarotto EINN 2005
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15. ∆G/G = -0.200.290.11 ΔG/G from SMC DIS events
Q2 > 1 GeV2, 0.4<y<0.9
xF > 0.1, S pT2 > 2.5 (GeV/c)2
1% of inclusive sample
µ+ 190 GeV Pµ= -0.78±0.03
∆G/G = -0.200.290.11
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16. LHC SPS COMPASS COMPASS EXPERIMENT
Beam: µ+/ spill (4.8s / 16.2s)
Luminosity: ~ cm-2 s-1
Beam polarisation: 76%
Beam momentum: GeV/c
LHC
SPS
COMPASS
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17. Spectrometer 2002 -> 2004 trigger-hodoscopes SPS 160 GeV
DW45
straws
SM2 dipole
Muon-filter2,MW2
RICH_1
HCAL1
Gem_11
SM1 dipole
ECAL2,HCAL2
Polarised Target
MWPC Gems Scifi
SPS 160 GeV
2.108m/spill
Muon-filter1,MW1
Veto
straws,MWPC,Gems,SciFi
Gems,SciFi,DCs,straws
Silicon
SciFi
Micromegas,DC,SciFi
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18. New detector technologies

19. ΔG/G from open charm c D0 K- π+ (BR 4%) D*+ D0 π+ + c.c.
charm contribution to the nucleon wave function is small
Special trigger: quasi real
photoproduction
DsPGF at NLO:
Bojak, Stratmann NPB 540 (1999) 345; A.P. Contogouris and G. Grispos, Phys. Rev. D 62 (2000).
ŝ = m2cc
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20. D* tagging: D* D0 π (Kπ)π MKpps-MKp -Mp (MeV/c2) Cuts: D* D0 π
zD > 0.2
|cos q*| < 0.85 (Background)
10 < pK < 35 GeV/c (RICH PID)
D* D0 π
no vertex
detector
(solid target!)
MKp -MD0 (MeV/c2)
D K π
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21. ΔG/G = -1.08 ± 0.73 ΔG/G from open charm <xg> ~0.15
D0 (untagged, 2003) eventi
D*+→D0π+ (2003)
1100 eventi
D0 → K π π0
ΔG/G = ± 0.73
<xg> ~0.15
0.73  0.43 with 2004 data
MC: Aroma + PolDis
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22. Pairs of hadrons with high pt and Q2 > 1 GeV/c
Photon Gluon Fusion
current fragmentation:
event cuts:
xF > 0.1
z > 0.1
Q2 > 1 (GeV/c)2
xBj < 0.05
0.1 < y < 0.9
2 high pt hadrons:
pt > GeV/c
pt12+pt22 > 2.5 (GeV/c)2
m(h1h2) > GeV/c2
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23. Result for high pt asymmetry
Asymmetry for high-pt hadron pairs at Q2 > 1 (GeV/c)2:
Aγ*d = ± (stat.) ± (syst.)
2002/03 data
Systematic uncertainty contains contributions from:
target and beam polarisation measurement (5% resp. 3%)
upper limit on false asymmetries (0.013)
determination of D and f (5% each)
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24. determination of ΔG/G
Leading Order
Photon Gluon Fusion
QCD-Compton
cut on xBj < 0.05:
Relative Fractions determined by Monte Carlo (LEPTO)
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25. Data Monte Carlo comparision
Use LEPTO Monte Carlo for Q2>1 (GeV/c)2 including RADGEN
Determination of the
fraction of PGF events
in LEPTO:
σPGF/σtot = 0.34 ± 0.07 (syst.)
Variation of the cut on pt2
Standard and modified* set of
fragmentation parameters
* SMC, B. Adeva et al., Phys. Rev. D70:012002, 2004
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26. COMPASS result for ΔG/G
2002/03 data
Q2 > 1 (GeV/c)2
ΔG/G = ± 0.31stat. ± 0.06syst.
at <xg> = 0.13 ± 0.08
10% of
statistics
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GSA,B,C: T. Gehrmann and W. Sterling, Z. Phys. C65 (1994) 461.

27. Pairs of hadrons with high pt and Q2 < 1 GeV/c
ALL/D = Rpgf G/G aLLpgf
all Q²
+ Rqcdc q/q aLLqcdc
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28. Physical background ALL/D = Rpgf G/G aLLpgf all Q²
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q 
Q² < 1
Fulvio Tessarotto EINN 2005
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29. Physical background ALL/D = Rpgf G/G aLLpgf all Q²
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q 
Q² < 1
+ Rqg G/G aLLqg q/q 
Fulvio Tessarotto EINN 2005
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30. Physical background ALL/D = Rpgf G/G aLLpgf all Q²
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q 
+ Rqg G/G aLLqg q/q 
Q² < 1
+ Rgq q/q aLLgq (G/G) 
Fulvio Tessarotto EINN 2005
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31. Physical background ALL/D = Rpgf G/G aLLpgf all Q²
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q 
+ Rqg G/G aLLqg q/q 
Q² < 1
+ Rgq q/q aLLgq (G/G) 
+ Rgg G/G aLLgg (G/G) 
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32. Physical background ALL/D = Rpgf G/G aLLpgf + Rqcdc q/q aLLqcdc
Inputs:
generation of Monte Carlo evts
parametrization (world data)
pQCD calculations
+ Rqq q/q aLLqq q/q 
+ Rqg G/G aLLqg q/q 
+ Rgq q/q aLLgq (G/G) 
+ Rgg G/G aLLgg (G/G) 
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33. Resolved photon processes
polarised parton distribution functions of (virtual…) photon are
unknown!
BUT:
-q(x,²) < q(x,²) < q(x,²)
measured
leads to 2 extreme (min&max) scenarios
 additional (theoretical) uncertainty
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34. .data Q² MC/data comparison PYTHIA generator is used for Q²<1GeV²
GEANT is used for spectrometer simulation Q²
.data
- MC
data/MC
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35. .data .data pT MC/data comparison - MC - MC data/MC data/MC
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36. Results from MC The Monte Carlo describes our data quite well!
Rpgf ≈ 31%
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37. Gluon polarisation, high pT pairs
Q2>1GeV2 :
data
Q2<1GeV2:
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38. Gluon polarisation results:
GRSV2000
NLO fits to g1
m2 = 3 Gev2
ΔG/G (xg ≈ 0.1) is small
DG>1 disfavoured
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39. Fulvio Tessarotto EINN 2005
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40. ΔG/G from two jet events
Leading hadron used as jet tag
Hard Scattering Process
qg+gq qq gg
Pt [GeV/c]
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41. Prompt photon production asymmetry
Gluon Compton Dominates
At LO no fragmentation function
Small contamination from annihilation A1
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42. 2 superconducting rings 3.8 km circumference
NSRL
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43. RHIC – first polarized hadron collider
Absolute Polarimeter (H jet)
pC Polarimeters
PHOBOS
BRAHMS
Siberian Snakes
Siberian Snakes
PHENIX
STAR
Spin Rotators
(longitudinal polarization)
Spin flipper
Spin Rotators
(longitudinal polarization)
Solenoid Partial Siberian Snake
Pol. H- Source
LINAC
BOOSTER
5% Helical Partial Siberian Snake
AGS
200 MeV Polarimeter
Internal Polarimeter
pC Polarimeter
Rf Dipole
25% Helical Partial Siberian Snake
Achieved ~ 50% beam polarization at 100 GeV
Achieved ~ 30% beam polarization at 205 GeV on first try!
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44. New AGS helical snakes 2.6 m 2.6 m
6 % helical snake build at Tokana Industries funded by RIKEN.
2.6 m
Warm snake avoids polarization mismatch at AGS injection and extraction.
Cold strong snake eliminates all depolarizing resonances in AGS.
2.6 m
25% s.c. helical snake build at BNL
Fulvio Tessarotto EINN 2005
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45. STAR spin physics program: ∆G, ∆q/∆q, δq
Large acceptance TPC
and EMC -1<η<2
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46. ΔG – Star: ALL for jets (2005)
0.2
0.4
0.6
0.8
1.0
0.0 gg qq qg
Inclusive Jets :LO
W. Vogelsang
2005
pT (GeV)
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47. Philosophy: PHENIX Detector Central Arms: Muon Arm: Global Detectors
High rate capability & granularity
Good mass resolution and particle ID
Sacrifice acceptance
Central Arms:
||<0.35, =2900
Charged particle ID and tracking;
photon ID
Muon Arm:
1.2<||<2.4
Muon ID and tracking
Global Detectors
Collision trigger
Collision vertex characterization
Relative luminosity
Local Polarimetry
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48. π0 prompt γ pp -> π0/prompt g + X
Excellent agreement with NLO & NLL
calculation with collider data !
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49. pp -> p0 + X 2003/4 Outlook 2005/7 Run 5 (April –June 2005):
absolute polarimeter: ∆Pb/Pb~7%
∫Ldt ~ 3pb-1, <Pb>~0.45
 reduces statistical error by factor 7
2003/4
PHENIX ALL for Inclusive p0 production at √s=200 GeV, data with about ∫Ldt~0.3pb-1 and <Pb>~0.3
Outlook 2005/7
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50. B. Jaeger et al. Phys. Rev. D67, 054005 (2003)
Y. Fukao, spin2004
B. Jaeger et al. Phys. Rev. D67, (2003)
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51. ΔG at RHIC – summary & outlook
Various channels, large coverage in xg
- Jet/leading hadron production :
First results of ALL pp p0 +X from PHENIX
Very good perspective for p+- at PHENIX and jets at STAR
- Direct photon production:
hard scale 100 GeV 2, xg reconstructed in STAR
- Heavy flavours, ...
RHIC Spin program on track, major effort to reach performance
Run s1/2(GeV) Pbeam L(pb-1)
>
>
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52. Physics vs Luminosity and Polarization at RHIC
Outlook
Physics vs Luminosity and Polarization at RHIC
see Spin report to DOE
L= 1x1031cm-2s x1031cm-2s x1032cm-2s-1
P= ……………………………………
√s= ……………………… GeV ………………… GeV|
eRHIC
… (RHIC II)
10 pb-1 …………………………………… 275pb …… pb-1
@ 200GeV
@ 500GeV
ELIC
Inclusive hadrons + Jets
~ 25% Transverse Physics
Charm Physics
direct photons
bottom physics
W-physics
ALL(hadrons, Jets)
ALL(charm)
ALL(γ)
AL(W)
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53. PHENIX Forward Upgrade: W-physics and jet+photon
Muon Trigger Upgrade
 RPC + FPGA based
trigger logic
Nose cone calorimeter
 W-Si calorimeter
Trigger RPC Locations
June 2005: $1.99M NSF
MRI grant approved +
$280k institutional support
UC Riverside, Abilene Christian, Iowa State, U. Illinois, U. Colorado, Columbia, Georgia Tech., RBRC, Kyoto, Peking U.,
RPC2
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54. ∆G Measurements by 2012
see Spin report to DOE
s=200 GeV incl. 0 prod’n
s=500 GeV incl. jet prod’n
Final results on ∆G will come from combined NLO analysis of RHIC and DIS
RHIC measurements will span broad range in x with good precision. Multiple channels with independent theo. and exp. uncertainties.
Uncertainty through extrapolation to small x
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55. COMPASS
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56. COMPASS upgrade in 2006 3 m 6 m 5 m Photon Detectors: CsI MWPC vessel
mirror
wall
vessel
radiator:
C4F10
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57. 2006 will be a very important year
Figure of Merit for open charm
FoM
2002 – > 2006
FoM(DG/G)
s(DG/G)=1/FoM1/2
hard work to increase FoM
2006 will be a very important year
Fulvio Tessarotto EINN 2005
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58. Fulvio Tessarotto EINN 2005
Milos,

59. Additional equipment to the COMPASS setupμ’ p’ μ
DVCS μp  μ’p’
At these energies (for μ, μ’, and )
the missing mass technique is not adapted
M2required = (mp+mπ)2-mp2
= 0.25 GeV2
M2observed > 1 GeV2
 ECal 1 or 2
  12°
Recoil detector
to insure exclusivity
to be designed and built
+ additional calorimeter
at larger angle
Nμ=2.108/SPS cycle
(duration 5.2s, each 16.8s)
2.5m liquid H2 target
to be designed and built
L = cm-2 s-1
Fulvio Tessarotto EINN 2005
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60. COMPASS far future: GPD’s, transversity, DG/G and hadron program will benefit from a possible upgrade of the SPS:
a Superconducting SPS (1 TeV) is better suited to LHC needs;
A bright future for DG both at short and long term
Fulvio Tessarotto EINN 2005
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