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Longitudinal polarization of  and in DIS at COMPASS

Longitudinal polarization of  and in DIS at COMPASS. M.G.Sapozhnikov Joint Institute for Nuclear Research, Dubna On behalf of the COMPASS Collaboration. Physical motivation. Longitudinal polarization of  and  in DIS is sensitive to: s(x), s(x) polarization of strange quarks s

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Longitudinal polarization of  and in DIS at COMPASS

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  1. Longitudinal polarization of  and in DIS at COMPASS M.G.Sapozhnikov Joint Institute for Nuclear Research, Dubna On behalf of the COMPASS Collaboration

  2. Physical motivation Longitudinal polarization of  and  in DIS is sensitive to: • s(x), s(x) • polarization of strange quarks s •  spin structure M.Sapozhnikov, JINR

  3.  production in DIS, quark fragmentation Quark fragmentation  spin structure Spin transfer from polarized muon Spin transfer from polarized quark

  4.  spin structure • SU(6) quark model: s = 1, u = d = 0 100% polarization to u or d quarks is no influence on polarization of  P() - 0 (for u –quarks dominance) • Burkardt-Jaffe: u = d = -0.23 P() – negative • B.Q.Ma et al.: u = d =s P() – positive • Lattice calculations: u = d~0, s=0.68 P() ~ 0 M.Sapozhnikov, JINR

  5. Production  and  is mainly due to fragmentation of target remnant and u,d-quarks • Spin transfer to  and  is mainly due to interaction with strange quark and antiquark M.Sapozhnikov, JINR

  6. COMPASS Detector SAS Muon filter 2 MWPCs ECal2 & HCal2 LAS SM2 Muon filter 1 ECal1 & HCal1 GEM & MWPCs SciFi RICH Drift. Ch. SM1 Silicon SciFi GEM & MWPCs Scintillating fibers GEM & Straws Beam Micromegas Polarized target 160 GeV µ+ beam 2.8. 108 µ/spill (4.8 s) Pb = -0.760.04 - 2003 Pb = -0.800.04 - 2004 M.Sapozhnikov, JINR

  7. Polarized 6LiD target (2002-2004) M.Sapozhnikov, JINR

  8. Production of () No PID used M.Sapozhnikov, JINR

  9. Event selection ’+ V1 p V2 +  q - • Primary vertex: in the target • Secondary vertex: 5 cm downstream the target • pT > 23 MeV/c •  < 0.01 rad • Q2 >1 (GeV/c)2 • 0.2<y<0.9 M.Sapozhnikov, JINR

  10. Comparison with other experiments M.Sapozhnikov, JINR

  11. <xBj> = 0.05 <xF> = 0.23 <y> = 0.46 <Q2>=3.31 GeV2 Good agreement between data and MC M.Sapozhnikov, JINR

  12.  <xBj> = 0.050 <xF> = 0.22 <y> = 0.48 <Q2>=3.27 GeV2

  13. Longitudinal polarization PL =+(-)0.642 ±0.013 - () decay parameter P - polarization vector k - unit vector along the decay proton momentum L-axis - along the momentum of virtual photon M.Sapozhnikov, JINR

  14. Determination of the angular distribution: • sidebands subtraction M.Sapozhnikov, JINR

  15. Angular distributions of  and  • (run 2004) • Acceptance correction – using unpolarized MC • P(K0)=0.011±0.005 M.Sapozhnikov, JINR

  16. Longitudinal spin transfer DLL DLL’ - polarization of the struck quark along the axis L is transferred to the  along the secondary axis L’ In our case: L=L’ PL = DLL Pb D(y) Pb – beam polarization, D(y) – depolarization factor M.Sapozhnikov, JINR

  17. Comparison of  and  : x DLL() DLL() Preliminary DLL() = -0.012 ± 0.047 ± 0.024 DLL() = 0.249 ± 0.056 ± 0.049 The results are averaged over target polarization

  18. Comparison of  and  : xF The results are averaged over target polarization

  19. PL: dependence on the target polarization P= P--P+ =-0.010.04,  = 0.010.05, 

  20. Comparison with other experiments :  Preliminary M.Sapozhnikov, JINR

  21. Comparison with other experiments :  Preliminary M.Sapozhnikov, JINR

  22. Theory predictions for  and Preliminary J.Ellis et al., Eur.Phys.J. C52 (2007) 603   M.Sapozhnikov, JINR

  23. Theory predictions for  and Preliminary   J.Ellis et al., Eur.Phys.J. C52 (2007) 603 M.Sapozhnikov, JINR

  24. Sensitivity to the strange distribution s(x) CTEQ5L GRV98 DLL(s)=0, BJ model DLL(s)=0, SU(6) model M.Sapozhnikov, JINR

  25. Sensitivity to the strange distribution s(x) CTEQ5L GRV98 DLL(s)=0, BJ model DLL(s)=0, SU(6) model

  26. Conclusions • Preliminary results on  and  spin transfer in DIS are obtained on statistics 70000  and 42000  • DLL() DLL() • DLL() ~ 0 • DLL() may be as large as 0.4-0.5 • First measurement of the () polarization for different target polarization. No significant dependence is found. • Comparison with theory: • Spin transfer to  is sensitive to s(x) • Present statistics is only 25% of already accumulated. More interesting things are coming. M.Sapozhnikov, JINR

  27. Backup slides M.Sapozhnikov, JINR

  28. Influence to different PDF’s Q2 = 4 GeV2 CTEQ5L GRV98LO M.Sapozhnikov, JINR

  29. Polarization of  from quark fragmentation Spin transfer from polarized muon Spin transfer from polarized quark M.Sapozhnikov, JINR

  30. Polarization of : PT =0 M.Sapozhnikov, JINR

  31. DLL() > DLL() Even if s(x)=s(x), DLL() > DLL() due to difference of the denominator: Du,d() > Du,d() • Independent quark fragmentation: • DLL() > DLL() • Sensitivity to s(x) • Are these conclusions still valid in a more advanced model? M.Sapozhnikov, JINR

  32. Spin transfer from polarized quark to  Polarized quarks, indeed, transfer the polarization to . M.Sapozhnikov, JINR

  33. Impact of LEP data D. de Florian, M.Stratmann, W.Vogelsang, PRD 57(1998)5811 1- SU(6) 2 – BJ 3 - u = d =s M.Sapozhnikov, JINR

  34. Theory predictions for / • Liang Zuo-tang et al. Phys.Rev.D72 (2005) 033006 -0.6 0 0.6 xF M.Sapozhnikov, JINR

  35. Transverse polarization PY M.Sapozhnikov, JINR

  36.  - between virtual photon and p in  c.m.s. • Kaon background is important at large cos • cut -1 < cos <0.6 M.Sapozhnikov, JINR

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