Recent measurement of ΔG/G at COMPASS Sébastien Procureur – CEA Saclay on behalf of the COMPASS...

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Transcript of Recent measurement of ΔG/G at COMPASS Sébastien Procureur – CEA Saclay on behalf of the COMPASS...

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Recent measurement of G/G at COMPASS Sbastien Procureur CEA Saclay on behalf of the COMPASS collaboration EPS200523/07/2005 Slide 2 The Nucleon spin = + G + L q + L g Sbastien ProcureurEPS2005 Slide 3 - Quark model: 0.75 - QCD + s = 0 (Ellis-Jaffe): 0.6 - Experimentaly: a 0 (=?) 0.2 The Nucleon spin = + G + L q + L g quarks gluons orb. mom. = a 0 + 3( s /2 ) G Sbastien ProcureurEPS2005 Slide 4 The Nucleon spin = + G + L q + L g quarks gluons orb. mom. Necessary to measure G - Quark model: 0.75 - QCD + s = 0 (Ellis-Jaffe): 0.6 Sbastien ProcureurEPS2005 - Experimentaly: a 0 (=?) 0.2 = a 0 + 3( s /2 ) G Slide 5 G/G measurement main DIS diagrams (up to 1 st order): LO PGFQCDC only PGF is sensitive to G/G Sbastien ProcureurEPS2005 Slide 6 G/G measurement A pgf = G/G * a LL pgf if factorization holds (need a hard scale): we need to select PGF events( S suppressed) with a hard scale hard part soft part Sbastien ProcureurEPS2005 Slide 7 PGF selections Open charm channel J.Pretzs talk 2 high p T hadrons channel: (q,q) (h 1,h 2 ) with high p T large stat, suppress LO, but still physical background scale: p T , Q A LL /D = R pgf G/G a LL pgf + (A LL /D) back ? h1h1 h2h2 Sbastien ProcureurEPS2005 Slide 8 Physical background A LL /D = R pgf G/G a LL pgf + R qcdc q/q a LL qcdc all Q Sbastien ProcureurEPS2005 Slide 9 + R qq q/q a LL qq q/q Physical background A LL /D = R pgf G/G a LL pgf + R qcdc q/q a LL qcdc Q < 1 all Q Sbastien ProcureurEPS2005 Slide 10 + R qg G/G a LL qg q/q Physical background A LL /D = R pgf G/G a LL pgf + R qcdc q/q a LL qcdc + R qq q/q a LL qq q/q all Q Q < 1 Sbastien ProcureurEPS2005 Slide 11 + R gq q/q a LL gq ( G/G) Physical background A LL /D = R pgf G/G a LL pgf + R qcdc q/q a LL qcdc + R qq q/q a LL qq q/q + R qg G/G a LL qg q/q all Q Q < 1 Sbastien ProcureurEPS2005 Slide 12 + R gg G/G a LL gg ( G/G) Physical background A LL /D = R pgf G/G a LL pgf + R qcdc q/q a LL qcdc + R qq q/q a LL qq q/q + R qg G/G a LL qg q/q + R gq q/q a LL gq ( G/G) all Q Q < 1 Sbastien ProcureurEPS2005 Slide 13 Inputs: -generation of Monte Carlo evts -parametrization (world data) -pQCD calculations what about the rest (Q < 1GeV)?? Physical background A LL /D = R pgf G/G a LL pgf + R qcdc q/q a LL qcdc + R qq q/q a LL qq q/q + R qg G/G a LL qg q/q + R gq q/q a LL gq ( G/G) + R gg G/G a LL gg ( G/G) Sbastien ProcureurEPS2005 Slide 14 Resolved photon processes polarised parton distribution functions of (virtual) photon are unknown! BUT: -q (x, ) < q (x, ) < q (x, ) leads to 2 extreme (min&max) scenarios additional (theoretical) uncertainty, but we can continue! measured! Sbastien ProcureurEPS2005 Slide 15 MC/data comparison Q Generator PYTHIA is used for Q Results for high p T low Q Asymmetry for 2002+2003 (p T > 0.7 GeV, p T > 2.5 GeV): G/G: A LL /D = 0.002 0.019(stat) 0.003 (syst) G/G(x g =0.1, =3GeV) = +0.024 0.089(stat.) 0.014(exp.syst) 0.052(MC.syst) 0.018(photon) 0.057 Sbastien ProcureurEPS2005 Slide 20 Comparison with other results G = 2.48 G = 0.62 G = 0.16 (GRSV param.) Sbastien ProcureurEPS2005 Slide 21 Summary Most precise measurement of G/G up to now: G/G(x g =0.1, =3GeV) = +0.024 0.089(stat.) 0.052(syst.) G is small or G(x g ) crosses 0 around x g = 0.1 For the 1 st time, Res. Phot. asym. taken into account Next steps: 2004 data analysis (G/G) 0.05 (also 2006 run) NLO analysis Other channel: single high p T hadron Sbastien ProcureurEPS2005 Slide 22 Spares Sbastien ProcureurEPS2005 Slide 23 COMPASS acceptance Sbastien ProcureurEPS2005 Slide 24 Results from RHIC-PHENIX Sbastien ProcureurEPS2005 Slide 25 Asymmetry versus p T Sbastien ProcureurEPS2005 Slide 26 Experimental systematics Asymmetries calculated with low p T events A exp = A A false according to microwave setting A +A f A - A f 1% of false asymmetries in 2003 data Sbastien ProcureurEPS2005 Slide 27 Polarised 6 LiD Target P D : 50% Dilution factor: 40% Two 60 cm long target cells with opposite polarisation Superconducting Solenoid (2.5 T ) 3 He 4 He dilution refrigerator (T~50mK) Dipole (0.5 T) Reconstructed interaction vertices Sbastien ProcureurEPS2005