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

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

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

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

COMPASS@CERN LHC COMPASS SPS

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

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

Polarized beam and target simultaneous measurement 160 GeV µ+ beam * 2 108 µ/spill (4.8 s / 16.2 s) * Pb ~ 76 % longitudinally naturally polarised * luminosity: ~ 5 1032 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

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

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)>0.25 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

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

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

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

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

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

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

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: 2002-2003 data result: (prelim.) systematic error: false asymmetry mainly contributes Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

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

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), 0.023 (maximum) Kaori KONDO, PDF2006+JPS2006, Honolulu, 31 Oct. 2006

High pT Hadron Pairs: Q2 <1(GeV/c)2 Systematic error mostly comes from PYTHIA tuning 2002-2003 data result: published:PLB 633 (2006) 25-32 2002-2004 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

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

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

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