determination of the gluon polarisation at compass & rhic sébastien procureur (cea - saclay)...
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Determination of the gluon polarisation at
COMPASS & RHICSébastien Procureur (CEA - Saclay)
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
STARSTAR
The nucleon spin structureThe nucleon spin structure
½= ½ΔΣ + ΔG + Lq + Lg
quark spin gluon spin orbital momenta
Prediction 2: (QCD & s=0)ΔΣ ~ 0.6
ΔΣ ~ 0.75Prediction 1: (Naive quark model)
Experiment: a0 = ΔΣ – (3S/2)ΔG ~ 0.2! (EMC, SMC, SLAC)
expect G(Q²) = dxg G(xg,Q²) ~ 1.5 @ Q² ~ 1GeV²
~ 2.5 @ Q² ~ 3GeV²Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
The nucleon spin structureThe nucleon spin structureΔG contributes to scaling violation of g1
ΔG(Q²=1) = 0.53 +/- 1.93 (AAC 2000)
ΔG(Q²=1) = 0.50 +/- 1.27 (AAC 2003)
ΔG(Q²=1) = 0.47 +/- 1.08 (AAC 2006)
Small available Q² range for g1 large uncertainties on G
Direct measurement of G needed
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
hep-ph/0312112
Direct measurement of ΔGDirect measurement of ΔG
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
or
lepton beam
or
nucleon target
heavy flavor, high pT
or
or
proton beam
proton beam
0, (PHENIX),jets (STAR)
STARSTAR
polarized p-p collider (RHIC) polarized semi-inc. DIS
Hard probe
RHIC @ BNLRHIC @ BNL
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
AGSLINACBOOSTER
Polarized Source
Spin RotatorsPartial Snake
Siberian Snakes
200 MeV Polarimeter
AGS Polarimeter
Rf Dipole
RHIC pC Polarimeters Absolute Polarimeter (H jet)
PHENIX
PHOBOS BRAHMS & PP2PP
STAR
Siberian Snakes
Helical Partial Snake
Strong Snake
Spin Flipper
RHIC
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
LLA
P1
P2
RNN
RNN
PP 21
1
(R = L++/L-- : relative luminosity)
Run number Lintegrated P Figure of Merit (P4L )
Run 3 (2003) 350 nb-1 27% 1.86nb-1
Run 4 (2004) 120 nb-1 40% 3.1nb-1
Run 5 (2005) 3.8 pb-1 47% 185nb-1
G/G @ RHICG/G @ RHIC
22
~
q
q
q
q
G
G
G
G
Muon IDPanels
CentralArms
North MuonArm
South MuonArm
Ring ImagingCerenkov
EM Calorimeter
Muon TrackingChambers
Beam-BeamCounter
Multiplicity/VertexDetector
Time ExpansionChamber
Drift Chambers
Pad Chambers
Time of FlightPanels
Four spectrometer arms with excellent trigger and DAQ capabilities.
PHENIX detectorPHENIX detector
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
0 cross section0 cross section
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
Very good agreement with NLO
Xsection calculation!
ResultsResults
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
Theory model C.L.(%)
GRSV-std 17.1-21.7
GRSV-max (g=g) 0.0-0.0
GRSV g=0 16.7-18.4
GRSV g=−g 0.0-0.7
0 reconstruction (with background asym. subtraction)
17.2 pbLdt
Large acceptance TPC and EMC -1<η<2
STAR detectorSTAR detector
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
ResultsResults
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
STARSTAR Inclusive Jet Cross section
STAR Preliminary
14.0 pbLdt
Large G already disfavored
2003-2004 data:
+ results from 2005 soon…
RHIC projectionsRHIC projections
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
STARSTAR
Results of unprecedent precision in the next years:
pQCD analysis
+ PHENIX data on
COMPASS
SPS
LHC
Beam: 2 . 108 µ+/ spill (4.8s / 16.2s) Luminosity ~5 . 1032 cm-2 s-1 Beam polarization: -80%Beam momentum: 160 GeV/c
COMPASS @ CERNCOMPASS @ CERN
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
COMPASSCOMPASS
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
G/G @ COMPASSG/G @ COMPASS
LO Compton Photon gluon fusion (PGF)
Spin asymmetries ALL of the main diagrams in DIS:
Only PGF is sensitive to (G/G)(xg) (but S suppressed)
ALL = LLa )( gxG
G*ALL q
q
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
Open charm channel
q = c, then c D0 or D* K,
c
c
: no physical background
: low statistics
Selections of PGFSelections of PGF
scale: mc
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
ΔG/G with open charmΔG/G with open charm
)( gLL xG
Ga
BS
S
ALL =
D* D0+ S K+ + S
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
)(41.057.0)15.0~( statxG
Gg
D0 K+
Open charm channel
q = c, then c D or D* K,
c
c
: no physical background
: low statistics
High pT hadrons channel
(q,q) (h1,h2) with high transverse momentum wrt * direction
: physical background
: large statistics
Selections of PGFSelections of PGF
scale: mc scale: pT , Q²
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
ALL/D = Rpgf G/G aLLpgf
+ Rqcdc q/q aLL
qcdc
+ Rqq q/q aLLgq (G/G)
+ Rqg G/G aLLqg (q/q)
+ …
Need a Monte Carlo simulation
Theoretical inputs for polarisations of partons in virtual photon…
+ resolved photons!(low Q²)
G/G with high pT hadronsG/G with high pT hadrons
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
high Q²
pT
Monte Carlo simulationMonte Carlo simulationPYTHIA generator for low Q² + GEANT for spectro simul.
Good description of the data by the simulation!
RPGF 30%
RRes.Phot 50%
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
Data/MCData & MC
5.2)( gxG
16.0)( gxG
62.0)( gxG
ResultsResults
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
2002-2004 data
(2002-2003 data:PLB 633 (2006) 25-32)
Favours small values of G
Next stepsNext steps
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
Results from 2004 data for Q² > 1 GeV²
Improved high pT selection with Neural Network
New magnet larger acceptance larger xg
Improved RICH (particle identification)
Extraction of G/G at different xg
very soon!
New run in 2006
NLO analysis (theoretical inputs)
ConclusionConclusion• Efforts on G measurement start to pay!
• Agreement between RHIC and COMPASS data
• Very exciting results are expected in the next few years!
½= ½ΔΣ + ΔG + Lq + Lg
½0.2 + 0.4 + 0.0 + 0.0possible scenarios:½0.2 + 0.0 + 0.4
G not large ΔΣ small ( predictions)
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
… + … + …
SparesSpares
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur
Resolved photon asymmetryResolved photon asymmetry
1st estimation of the resolved photon asymmetry!
• Problem: polarized PDFs of virtual photons not measured!
-q,npert(xp,0²) < q,npert(xp,0²) < q,npert(xp,0²) • Solution:
measured!
Allows us to obtain a range for (q/q) and (G/G) !
Adds a limited uncertainty to the estimation of (G/G)(xg)
q,pert(xp,²) calculable
Determination of G at COMPASS & RHIC PAVI06, Milos S.Procureur