The COMPASS spin physics program Stefano Panebianco CEASaclay

The COMPASS spin physics program Stefano Panebianco (CEA/Saclay) on behalf of the COMPASS Collaboration XXXXth Rencontres de Moriond QCD and High Energy Hadronic Interactions La Thuile, March 12 th -19 th 2005 The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Overview • Spin structure of the nucleon • Polarized quark PDF • Gluon polarization – High pt hadron pair leptoproduction – Open charm leptoproduction • Transversity • Conclusions The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Nucleon parton distributions μ • Unpolarized DIS : q(x, Q 2) and g(x, Q 2) P • Here Polarized DIS : Dq = q - q , DG = g - g The COMPASS spin physics program Rencontres de Moriond S. Panebianco

The spin of the nucleon The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Deep inelastic scattering The COMPASS spin physics program Rencontres de Moriond S. Panebianco

The COMPASS spectrometer SM 2 RICH • Two stage spectrometer (SM 1: 1 Tm, SM 2: 5. 2 Tm) Sci-Fibers GEM & MWPC • Track reconstruction (new technologies: Sci-Fibers, GEMs, Micromegas, straws) Sci-Fibers Silicon The COMPASS spin physics program • Particle identification (RICH, ECAL, HCALs, m. Filters) Rencontres de Moriond S. Panebianco

Dq The inclusive asymmetry A 1 • g-nucleon asymmetry: • COMPASS has: – high energy – high luminosity – high dilution factor for a solid state target • • Unique result in the low x region important to test QCD sum rules (hep-ex/0501073, accepted Phys. Lett. B) The COMPASS spin physics program Rencontres de Moriond S. Panebianco

How to measure DG/G Photon-Gluon Fusion (PGF) m’ m g* g N X Two tagging methods: -High pt hadron pairs -Open charm The COMPASS spin physics program Rencontres de Moriond S. Panebianco

High pt hadron pair production @ Q 2>1 Ge. V 2 to reduce LODIS The COMPASS spin physics program From Monte-Carlo Rencontres de Moriond S. Panebianco

DG/G from high pt hadron pair, Q 2 > 1 2002/2003 data: A||/D = - 0. 015 ± 0. 080 (stat. ) ± 0. 013 (syst. ) ΔG/G = 0. 06 ± 0. 31 stat. ± 0. 06 syst. BUT. . . 10% of statistics The COMPASS spin physics program Rencontres de Moriond S. Panebianco

DG/G from high pt hadron pair, all Q 2 At Q 2 < 1 additional background Resolved photon processes High statistics Projection for 2002 -2004 data (all Q 2) The COMPASS spin physics program Rencontres de Moriond d(ΔG/G) = 0. 05 S. Panebianco

ΔG/G from open charm c c The COMPASS spin physics program D 0 D* + Rencontres de Moriond K- π+ (BR 4%) D 0 π+ + c. c. S. Panebianco

Open charm raw asymmetry The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Measurement of the quark transversity The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Collins and Sivers asymmetries The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Conclusions The COMPASS spin physics program Rencontres de Moriond S. Panebianco

The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Pairs of hadrons with high p. T h 1 h 2 N Photon Gluon Fusion • current fragmentation: x. F > 0. 1 z > 0. 1 • event cuts: 2 2 Q > 1 (Ge. V/c) , x. Bj < 0. 05 0. 1 < y < 0. 9 The COMPASS spin physics program • 2 high pt hadrons: pt > 0. 7 Ge. V/c pt 12+pt 22 > 2. 5 (Ge. V/c)2 2 m(h h ) > 1. 5 Ge. V/c 1 2 Rencontres de Moriond S. Panebianco

The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Future Fixed Target Programme at CERN Villars meeting, 22 -28 Sept. CERN seminar Villars by John DAINTON “ FT hadron program remains very competitive …………. COMPASS complete in medium term - ΔG/G, transversity, polarisability, spectroscopy - SPSC p. o. t. concern prioritise COMPASS longer term - GPD measurements would be unique” Conclusions (personal) by Michelangelo MANGANO “ COMPASS m beam … flagship experiment ” The COMPASS spin physics program Rencontres de Moriond S. Panebianco