The COMPASS spin physics program Rencontres de Moriond S. Panebianco The COMPASS spin physics program Stefano Panebianco (CEA/Saclay) on behalf of the COMPASS Collaboration XXXX th 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 p t hadron pair leptoproduction –Open charm leptoproduction Transversity Conclusions

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

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 RICH Sci-Fibers GEM & MWPC Sci-Fibers Silicon Two stage spectrometer (SM1: 1Tm, SM2: 5.2 Tm) Track reconstruction (new technologies: Sci-Fibers, GEMs, Micromegas, straws) Particle identification (RICH, ECAL, HCALs, Filters) SM2

The COMPASS spin physics program Rencontres de Moriond S. Panebianco -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 The inclusive asymmetry A 1 q (hep-ex/ , accepted Phys. Lett. B)

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

The COMPASS spin physics program Rencontres de Moriond S. Panebianco High p t hadron pair Q 2 >1 From Monte-Carlo GeV 2 to reduce LODIS

The COMPASS spin physics program Rencontres de Moriond S. Panebianco G/G from high p t hadron pair, Q 2 > 1 G/G from high p t hadron pair, Q 2 > /2003 data: A || /D = ± (stat.) ± (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 G/G from high p t hadron pair, all Q 2 G/G from high p t hadron pair, all Q 2 At Q 2 < 1additional background Resolved photon processes High statistics Projection for data (all Q 2 ) (ΔG/G) = 0.05

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

The COMPASS spin physics program Rencontres de Moriond 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

Pairs of hadrons with high p T Photon Gluon Fusion h1h1 h2h2 current fragmentation: event cuts: x F > 0.1 z > 0.1 p t > 0.7 GeV/c p t1 2 +p t2 2 > 2.5 (GeV/c) 2 m(h 1 h 2 ) > 1.5 GeV/c 2 2 high p t hadrons: N Q 2 > 1 (GeV/c) 2, x Bj < < y < 0.9

The COMPASS spin physics program Rencontres de Moriond S. Panebianco

Future Fixed Target Programme at CERN Villars meeting, 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 beam … flagship experiment