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May 12, 2009 Paolo Lenisa and Frank Rathmann PAX collaboration

Measurement of the Spin- Dependence of the pp Interaction at the AD Ring Polarizing antiprotons. May 12, 2009 Paolo Lenisa and Frank Rathmann PAX collaboration New Opportunities in the Physics Landscape at CERN. Introduction.

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May 12, 2009 Paolo Lenisa and Frank Rathmann PAX collaboration

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  1. Measurement ofthe Spin-Dependenceofthe pp Interaction atthe AD RingPolarizing antiprotons May 12, 2009 Paolo Lenisaand Frank Rathmann PAX collaboration New Opportunities in the Physics Landscape at CERN

  2. Introduction Wehaveproposeda methodtopolarizeantiprotonsby „spin-filtering“ Polarizing antiprotons

  3. Introduction New initiative, drivenbythe FAIR-projectat GSI (How) isitpossibletoprovidepolarizedantiprotonbeamsin HESR ? High Energy Storage Ring (HESR) for a beam of antiprotons Polarizing antiprotons

  4. QCD Physics at FAIR employs unpolarized Antiprotons PAX→ Polarized Antiprotons HESR Physics Case: Transversity distribution of the nucleon in Drell-Yan: • Last leading-twist missing piece of the QCD description of the partonic structure of the nucleon • Direct measurement of h1q(x,Q2) of the proton for valence quarks(ATT in Drell-Yan >0.2) • transversely polarized proton beam or target () • transversely polarized antiproton beam () • + other polarization observables in pp Polarizing antiprotons

  5. Plan of talk • Polarizingantiprotons … • Proposals, ideas, calculations, … • Experiments • FILTEX (TSR) • epspinflipcrosssectionmeasurementat COSY • Spin-filteringat AD/CERN • Conclusion • Task taken on bythe PAX-collaboration:~100 members, 16 institutions Spokespersons: P. Lenisa (Ferrara), F. Rathmann (Jülich) Polarizing antiprotons

  6. TwoMethods: Loss versus spinflip For an ensembleofspin ½ particleswithprojections+() and– () Polarizing antiprotons

  7. Proposedmethods: Spin flip →Need for an experimental testofthisidea! Polarizing antiprotons

  8. epspinflipcrosssectionmeasurementat COSY Nominal proton energy in electron rest frame (keV) 0 1 2 3 4107 D.Oellers et al., Physics Letters B 674 (2009) 269 2107 depol (barn) 0 -2107 -4107 0 110-3 210-3 310-3 |Relative velocity of electrons in proton rest frame| (c) No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than predicted 1013 b. Meanwhile, Mainz group discovered numerical problems in the calculation → two errata. Polarizing antiprotons

  9. Spin-filtering Polarizationbuild-upof an initiallyunpolarizedparticle beam byrepeatedpassagethrough a polarizedhydrogen target in a storage ring: Polarizing antiprotons

  10. 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 spin filtering works for antiprotons: Measurement ofthe Spin-Dependenceofthe pp Interaction atthe AD Ring(CERN-SPSC-2009-012 / SPSC-P-337) Polarizing antiprotons

  11. PAX at the AD (the only place worldwide) Siberian snake Electron cooler PAX target section Polarizing antiprotons

  12. Experimental Setup Atomic Beam Source Target chamber: Detector system + storage cell Breit-Rabi Polarimeter Six additional quadrupoles Polarizing antiprotons

  13. ExpectedPolarizations after filteringfortwolifetimes transverse longitudinal A • Measurement of the buildup equivalent to the determination of σ1andσ2 • Once a polarized antiproton beam is available, differential double-spin observables can be measured (50-500 MeV) → pp potential. • Protonium gave already first information about pp potential at rest. D Polarizing antiprotons

  14. Time plan (once approved) Proof of compatibility with the other AD users. • PAX ready to set sequence into motion by installing low-β section into the AD end of this year! Polarizing antiprotons

  15. Conclusions • Clear task • Technicallyfeasible • Expertise andcommitmentbyPAX-collaboration • First measurements/achievements • High discovery potential Nowandhereornever! → Polarizing antiprotons

  16. Spare transparencies Polarizing antiprotons

  17. Polarizing antiprotons

  18. Expectedantiproton beam polarization(in an ideal machine) • AD machineacceptance: • Ax=180 m, Ay=200 m • Cooled2 beam emittance = 1 m • Realisticcalculationof acc(mrad) using AD latticefunctionsandtriangulardensitydistribution in storagecell • Model A: T. Hippchenet al., Phys. Rev. C 44, 1323 (1991) • Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) 8 Acceptance angle (mrad) Polarizing antiprotons Storage cell radius (mm)

  19. Beam lifetime Polarizing antiprotons

  20. Target chamber, cell and detector system Atomic beam Stored beam Storage cell Silicon strip detectors Polarizing antiprotons

  21. Phase 1 • Central quadrupole magnet (QDN15) remains in place until compatibility of the AD operation with other users is shown. Polarizing antiprotons

  22. Hadron Physics „Dream Machine“ for FAIR: … an asymmetric (double-polarized) proton (15 GeV/c) – antiproton (3.5 GeV/c) collider using HESR, CSR and APR Polarizing antiprotons

  23. Quark Transversity Distribution in Drell-Yan: Double transverse spin asymmetry: First direct measurement: No competitive processes Polarizing antiprotons

  24. Proposed methods (1): Some history … EPAC 1988 • Stern-Gerlach splitting never tried (huge effort) Polarizing antiprotons

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