dr. Paolo Lenisa Università di Ferrara and INFN – ITALY on behalf of the PAX-Collaboration

1. Perspectives for Polarized Antiprotons dr. Paolo Lenisa Università di Ferrara and INFN – ITALY on behalf of the PAX-Collaboration XIV International Workshop on Polarized Sources, Targets and Polarimetry St. Petersburg, 13.09.2011 Polarized Antiprotons

2. Polarized Antiprotons Motivation: Missing tool for Hadron Physics Polarized Antiprotons

3. Quark structure of the nucleon longitudinally polarised quarks and nucleons transversely polarised quarks and nucleons unpolarised quarks and nucleons Known Well known Less known Polarized Antiprotons

4. Quark structure of the nucleon longitudinally polarised quarks and nucleons transversely polarised quarks and nucleons unpolarised quarks and nucleons Inclusive DIS Semi-inclusive DIS Drell-Yan HERMES,COMPASS,JLab Polarized Antiprotons

5. Accesso totransversitythroughDrell-Yan Polarized Antiprotons

6. A double polarized pbar-p collider for FAIR Asymmetric (double-polarized) proton (15 GeV/c) – antiproton (3.5 GeV/c) collider p p Polarized Antiprotons

7. h1u from p-p Drell-Yan at PAX Pp=30% • u-dominance • |h1u|>|h1d| Pp=10% 1 year run -> 10 % precision on the h1u (x) in the valence region Polarized Antiprotons

8. Rosenbluth Polarization Study of the Proton Electromagnetic Form-Factors Space-Like FFs: proton data Time-Like FFs: proton data • JLab results dramatically changed picture of the Nucleon: • GEp/GMp decreases with Q2 • data suggest GEpcrosses 0 at Q28 GeV2 Expected Q2 behaviour reached quite early, however ... ... there is still a factor of 2 between timelike and spacelike. Additional and more precise measurements needed Polarized Antiprotons

9. Double polarized pbar-p annihilation: E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005) • Most contain moduli GE, GM • Independent GE-GM separation • Test of Rosenbluth separation in the time-like region • Access to GE-GM phase • Very sensitive to different models Polarized Antiprotons

10. Axx Ayy Ay VDM : IJL Ext. VDM ‘QCD inspired’ Axz Azz R Polarization and Models in T.L. Region E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005) Polarized Antiprotons

11. Polarized Antiprotons Method: The mechanism of spin-filtering Polarized Antiprotons

12. Polarized antiprotons • Intense beam of polarized pbarnever produced: • Synchr. radiation ~ m(g4/R) -> tpol~107 y in 20 TeV pbar ring • Conventional methods (ABS) not applicable • Polarized pbar from antilambda decay • I< 1.5∙105 s-1 (P ≈ 0.35) • Pbar scattering off liquid H2 target • I< 2∙103 s-1 (P ≈ 0.2) PAX Status Report

13. Productionofpolarization in a stored beamTwoMethods: Loss versus spinflip For an ensembleofspin ½ particleswithprojections+() and– () Polarized Antiprotons

14. Spin-filtering Polarization build-up of a circulating particle beam by interaction with a polarized gas target Polarized Antiprotons

15. Polarization Buildup Unpolarized anti-p beam Polarized target S beam-particlespin Q targetpolarization k || beam direction Polarized Antiprotons

16. Polarized anti-p beam Unpolarized anti-p beam Polarization Buildup S beam-particlespin Q targetpolarization k || beam direction Optimum (blackcurve) after 2 lifetimesfiltering Polarized target Polarized Antiprotons

17. Spin-filteringat TSR: „FILTEX“ – proof-of-principle F. Rathmann et al., PRL 71, 1379 (1993) Spin filteringworksforprotons PAX submitted new proposal to find out how well does spin filtering work for antiprotonsMeasurement ofthe Spin-Dependenceofthe pp Interaction atthe AD Ring (CERN-SPSC-2009-012 / SPSC-P-337) Polarized Antiprotons

18. PAX@COSY :Proton polarization Polarized Antiprotons Experimental program: Measurements with pbar at AD-Ring PAX@AD/CERN:Antiproton polarization PAX@FAIR:Eexperimentswith pol. pbar Polarized Antiprotons

19. Measurements at AD (CERN) • Aim: 1st measurement of the spin-dependence of the pbar-p cross section • Method: measurement of polarization build-up by spin-filtering PAX target section Polarized Antiprotons

20. Spin-dependence of the pbar-p interaction Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991). Model OBEPF:J. Haidenbauer, K. Holinde, A.W. Thomas, Phys. Rev. C 45, 952 (1992). Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995). Polarized Antiprotons

21. Expected polarizations after filtering for two lifetimes • Measurement of the polarization buildup allows determination of σ1andσ2 • Oncepbarpolarizationavailable, spin-correlationcoefficientsaccessible transverse longitudinal A D Polarized Antiprotons

22. More recentcalculations… PLB 690 (2010) Cross sections Projected polarizations Polarized Antiprotons

23. Polarized Antiprotons Experimental program Measurements with p at COSY-Ring (Germany) PAX@AD/CERN:Antiproton polarization PAX@COSY :Proton polarization PAX@FAIR:Experiments withpol. pbar Polarized Antiprotons

24. Spin-filtering at COSY Main purpose: 1. Commissioning of the experimental setup for CERN/AD 2. Quantitative understanding of the machine parameters WASA e-cooler ANKE PAX Polarized Antiprotons

25. Installation of low-β section (2009) • Beamhastofitthroughstoragecell target (dt=5x1013atoms/cm2) • Increase acceptance angle at target position Polarized Antiprotons

26. Commissioningofthe experimental setup (2010) I. Machinestudies: Low-bsection • Nonegative impact on the COSY operation • Model in goodagreement • withmeasurement: β~ 0.3m • -> beam fitsthroughthecell! Polarized Antiprotons

27. Commissioningofthe experimental setup (2010) I. Machinestudies: Studies of beam-lifetimelimitations In case intra-beam scattering poses a limitation, increase of beam emittance should increase lifetime! (Touschek) • Increaseofbeam emittancebytiltingofelectron cooler beam • Beam emittancemeasuredwithionisationproflemonitor Polarized Antiprotons

28. Commissioningofthe experimental setup (2010) II. Polarized Target ABS Breit-Rabi polarimeter • Spin filtering requires >1013 atoms/cm2 → • ABS + openable storage cell • Analysis of target polarization by Breit-Rabi polarimeter(BRP) and a target gas analyzer (TGA) Polarized Antiprotons

29. BRP: Continousmonitoringofthetargetpolarization Polarized Antiprotons

30. Commissioningofthe experimental setup (2010) III. Beam Polarimeter p D2 pdelasticscattering:detection in two (L-R) symmetricSilicon Tracking Telescopes Deuteron identification d p Polarized Antiprotons

31. Commissioningofthe experimental setup (Aug. 2011) IV. Installation of NEG pump (12000 l/s) Polarized Antiprotons

32. September 2011 ongoingbeamtime: I Measurement of ring acceptance In an ideal machine Single-Coulomb scattering at the target dominates beam loss cooled beam ring acceptance target lost movableframesystem COSY beam Polarized Antiprotons

33. September 2011 ongoingbeamtime: II Ring polarizationstudies • Measurement of polarization lifetime: tP>105s • Measurement of spin-flip efficiency: e=0.987 Polarized Antiprotons

34. Spin-filtering cycle Polarization dP/dt0.18%/h Cycle COSY measurement Polarized Antiprotons

35. To be continued …. Ferrara - Castello Estense Sebastiano Filippi: “The spinning top game" – XVI cent. Polarized Antiprotons

36. Additional slides Polarized Antiprotons

37. pp interaction models Polarized Antiprotons

38. 0penable storagecell • Atomic beam source provides polarized hydrogen target • Storage cell target to reach dt=5x1013atoms/cm2 open closed Nuclear polarization of the hydrogen target determined with the Breit-Rabi polarimeter after opening and closing of the storage cell a few times Polarized Antiprotons

39. Polarisation buildup cross sections Folie 34

40. Polarizedantiprotons on fixed target (PAX-PhaseI) EXPERIMENT: Fixed target experiment: polarized antiprotons protons in CSR (p>200 MeV/c) fixed polarized protons target Polarized Antiprotons