1. 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

2. 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

3. 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

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

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

6. 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

7. 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/0501073, accepted Phys. Lett. B)

8. 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

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

10. 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 > 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

11. 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 2002-2004 data (all Q 2 ) (ΔG/G) = 0.05

12. 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

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

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

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

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

22. 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 < 0.05 0.1 < y < 0.9

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

26. 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 beam … flagship experiment