1. Study of spin structure of nucleon in COMPASS - measurement of G/G
Kaori Kondo
University of Bochum
On behalf of the COMPASS collaboration

2. Structure of Nucleon Nucleon Spin :
quark
gluon
orbital angular momentum
A small fraction of nucleon spin is carried by quarks!!
Where does the rest of the nucleon spin come from?
naïve parton model : Σ=1
CERN, SLAC, DESY, JLAB:
Σ ~ 0.30
large G = G(x) ?
g(x): Probability to detect spin+ (spin-) gluon
in spin+ proton as a function of Bjorken x.
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

3. PGF probes gluons Direct measurement of G is provided by
Photon Gluon Fusion (PGF) in polarized DIS
Double spin asymmetry
Experiment measure
Pb : beam polarization
Pt : target polarization
f : dilution factor
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

4. COMPASS collaboration
COmmon Muon and Proton Apparatus for Structure and Spectroscopy
Bielefeld, Bochum, Bonn (ISKP), Bonn (PI), Burdwan and Calcutta,
CERN, Chubu, Dubna (LPP and LNP), Erlangen, Freiburg, (Heidelberg),
(Helsinki), KEK, Lisbon, Mainz, Miyazaki, Moscow (INR), Moscow (LPI),
München (LMU), München (Technische Universität),
(Nagoya), Prague, Protvino, Saclay, Tel Aviv,
Torino (University and INFN), Trieste (University and INFN),
Warsaw (SINS), Warsaw (TU), Yamagata
To study hadron structure and hadron spectroscopy
~240 physicists from over 28 Institutes
start taking data in 2002
DG/G, DS, Transversity, Pentaquark, Exclusive ρ0, Λ physics
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

5.
LHC
COMPASS
SPS

6. COMPASS Spectrometer 2 stages spectrometer with 2 magnets (SM1, SM2)
Tracking (SciFi, Silicon, MicroMega, GEM, MWPC, DC, Straw)
PID (RICH, ECAL, HCAL, muon filter)
Trigger Hodoscopes
m filter
0.003 < x < 0.5
10-3 < Q2 < 10 (GeV/c)2
MWPC
ECal&HCal1/2
Straws
SM2
Drift chamber
RICH
Target
SM1
SciFi, Silicon
m beam
MicroMegas
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

7. Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

8. Polarized beam and target
simultaneous measurement
160 GeV µ+ beam
* µ/spill (4.8 s / 16.2 s)
* Pb ~ 76 % longitudinally naturally polarised
* luminosity: ~ cm-2 s-1
Spin orientation is reversed to cancel out the systematic error from detector acceptance difference between the cells
by magnetic field rotation (3 times /day)
by DNP microwave frequency change
deuteron target (6LiD)
* Pt ~ 50 % longitudinally polarised by DNP
* cell size: f30mm x 600mm long
* 2 or 3 cells oppositely polarized at the same time
* spin orientation can be reversed
target
µ+ beam
target
µ+ beam
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

9. Accessing G/G There are 2 ways to tag PGF process… q = c “OPEN CHARM”
charmed meson production event
 no background asymmetry, less MC dependent.
 small statistics
q = u,d,s “HIGH pT HADRON PAIRS” events with 2 hadrons with high pT
 Large statistics
 physical background: „model” (MC) dependent,
Leading order analysis in the moment..
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

10. Open Charm Kaon identification with RICH up to 50 GeV/c
PGF is the main reaction
for charmed pair production in DIS,
Most frequently, D mesons are produced in the independent fragmentation of c pair.
(BR 4%)
Kaon identification with RICH
up to 50 GeV/c
Kinematical cut to suppress combinatorial background
z(D0)> z=ED/n
|cosqK*|<0.5
(BR 68%)
~30% D0 comes from D* decays
combinatorial background highly suppressed
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

11. MKpp - (MKp + Mp) [MeV/c2]
D* tagging
MKpp - (MKp + Mp) [MeV/c2]
MKp - MD0(PDG) [MeV/c2]
MKpp - (MKp + Mp) (MeV) D*
(2002)
MKpp - (MKp + Mp) [MeV/c2] D0
(2002)
MKp - MD0(PDG) [MeV/c2]
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

12. Reconstructed D mesons
Effective signal:
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

13. Extracting G/G f : dilution factor ~0.4 Pb : beam polarization ~0.8
Pt : target polarization ~0.5
S/(S+B): determined from fit
Parameterization to calculate aLL from kinematics with one reconstructed meson
Neural network trained with AROMA Monte Carlo
Strong correlation between NN aLL and AROMA aLL
correlation factor: 82 %
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

14. G/G result from open charm
D0 + D* result 2002 – 2004:
(prelim.)
systematic error under investigation: no clear systematic effect seen
NLO analysis, resolved photon contribution study planed.
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

15. High pT Hadron Pairs High Q2 analysis Q2>1 (GeV/c)2
PGF in the other method..
High Q2 analysis
Q2>1 (GeV/c)2
low statistics (10%)
LEPTO-MC
Low Q2 analysis
Q2<1 (GeV/c)2
additional resolved photon background events
high statistics
PYTHIA-MC
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

16. High pT Hadron Pairs: Q2 >1(GeV/c)2
PGF
LO DIS
QCD compton
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

17. High pT Hadron Pairs: Q2 >1(GeV/c)2
pT1, pT2 > 0.7 GeV/c, ΣpT2 > 2.5 (GeV/c)2
0.1 < y < 0.9
small x region: A1d is small, LODIS and QCDC neglected
Monte Carlo generator LEPTO:
data result:
(prelim.)
systematic error: false asymmetry mainly contributes
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

18. High pT Hadron Pairs: Q2 <1(GeV/c)2
Direct
Resolved
photon
PGF
QCDC
neglect
LO DIS
neglect
MC event generator PYTHIA is used for low Q² analysis
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

19. High pT Hadron Pairs: Q2 <1(GeV/c)2
Contribution from resolved photons
unknown: polarised PDFs of the photon
known: unpolarised PDFs of the photon
 use unpolarised PDFs to constrain polarised PDFs
Adds a limited uncertainty
to the estimation of (G/G)(xg)
G/G:
0.010 (minimum), (maximum)
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

20. High pT Hadron Pairs: Q2 <1(GeV/c)2
Systematic error mostly comes from PYTHIA tuning
data result:
published:PLB 633 (2006) 25-32
data result:
(prelim.)
systematic error: exp. syst. (0.014), MC syst. (0.052), photon contribution (0.013)
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

21. G/G Summary GRSV200: Glück et al., Phys. Rev. D63 (2001) 094005
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

22. P.Liebing, RBRC Spin 2006, Kyoto
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

23. Summary
COMPASS presents new results of ΔG/G using 2002 – 2004 data in three different methods
open charm channel
High pT hadron pairs Q2>1 (GeV/c)2
High pT hadron pairs Q2<1 (GeV/c)2
Small G is preferred
Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006