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Towards Polarized Antiprotons

Towards Polarized Antiprotons. Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich Workshop on „Observables in Antiproton-Proton Interactions“ Trento, July 3-7, 2006. Polarized Antiprotons. Intense beams of polarized pbar never produced

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Towards Polarized Antiprotons

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  1. Towards Polarized Antiprotons Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich Workshop on „Observables in Antiproton-Proton Interactions“ Trento, July 3-7, 2006

  2. Polarized Antiprotons • Intense beams of polarized pbar never produced • Conventional methods (ABS) not appliable • 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) • Stern-Gerlach spin separation of a stored beam • untested • 15.05.2006 (Walcher et al.): Use polarized electron beam Spin-filteringis the only succesfully tested technique Observables in Antiproton-Proton Interactions

  3. For initially equally populated spin states:  (m=+½) and  (m=-½) transverse case: longitudinal case: Spin Filter Method P beam polarization Q target polarization k || beam direction σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k) Time dependence of P and I (removal only) Observables in Antiproton-Proton Interactions

  4. I/I0 0.8 Beam Polarization 0.6 0.4 0.2 0 2 6 4 t/τbeam Optimum Interaction Time statistical error of a double polarization observable (ATT) Measuring time t to achieve a certain error δATT ~ FOM = P2·I (N ~ I) Optimimum time for Polarization Buildup given by maximum of FOM(t) tfilter = 2·τbeam Observables in Antiproton-Proton Interactions

  5. 1992 Filter Test at TSR with protons Experimental Setup Observables in Antiproton-Proton Interactions

  6. |1> e- p mj = +1/2 mi=+1/2 mi=-1/2 mi=-1/2 mj = -1/2 mi=+1/2 Polarized Atomic Beam Source 1 |1> Atoms with mj=+½ focused in sextupole magnets |2> |3> RF transitions select HFS |4> Observables in Antiproton-Proton Interactions

  7. 1992 Filter Test at TSR with protons Results Experimental Setup T=23 MeV F. Rathmann. et al., PRL 71, 1379 (1993) Low energy pp scattering 1<0  tot+<tot- Observables in Antiproton-Proton Interactions

  8. Two interpretations of FILTEX result Observedpolarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1 P(t)=tanh(t/τ1), 1/τ1=σ1Qdtf σ1 = 72.5 ± 5.8 mb Spin-filtering works! But how? 1994: Meyer and Horowitz: three distinct effects • Selective removal through scattering beyond θacc=4.4 mrad (σR=83 mb) • Small angle scattering of target protons into ring acceptance (σS=52 mb) • Spin-transfer from polarized e- of H atoms to stored protons(σE=-70 mb) σ1= σR+ σS + σE = 65 mb 2005: Milstein & Strakhovenko + Nikolaev & Pavlov: only one effect • Selective removal through scattering beyond θacc=4.4 mrad (σR=85.6 mb)No contribution from other two effects (cancellation of scattering and transmission) σ1 = 85.6mb Details in Nikolaevs Talk Observables in Antiproton-Proton Interactions

  9. Spin-Filtering: Present Situation • Spin Filtering works, but: • controversial interpretations of TSR result • no experimental data base for antiprotons • experimental tests needed with • Protons at COSY • Antiprotons at AD of CERN Observables in Antiproton-Proton Interactions

  10. Spin-filtering studies at COSY • Objective: • Understanding of spin-filtering mechanism: • Disentangle electromagnetic and hadronic contributionsto the polarizing cross section Observables in Antiproton-Proton Interactions

  11. Polarizing cross sections from the two models TSR … only hadronic - electromagnetic + hadronic A measurement of seff to 10% precision requires polarization measurement with DP/P = 10%. Observables in Antiproton-Proton Interactions

  12. Strong fields can be applied only longitudinally (minimal beam interference) - Snake necessary Target polarimetry requires BRP for pure electron polarization. AD Experiments require both transverse and longitudinal (weak)fields. How to disentangle hadronic and electromagnetic contributions to seff? • Injection of different combinations of hyperfine states • Different electron and nuclear polarizations • Null experiments possible: • Pure electron polarized target (Pz = 0), and • Pure nuclear polarized target (Pe=0) Observables in Antiproton-Proton Interactions

  13. Experimental setup • Low-beta section • Polarized target (former HERMES target) • Detector • Snake • Commissioning of AD setup Observables in Antiproton-Proton Interactions

  14. Low beta section • bx,ynew = 0.3 -> increase in density with respect to ANKE: factor 30 • Lower buildup time, higher rates • Larger polarization buildup rate due to higher acceptance • Use of HERMES target (already in Jülich) S.C. quadrupole development applicable to AD experiment Observables in Antiproton-Proton Interactions

  15. Acceptance @ ANKE Acceptance @ new-IP ANKE vs new IP: Acceptance and Lifetime Cross sections Lifetimes … only hadronic - electromagnetic + hadronic __ COSY average ψacc = 1 mrad ….. ψacc = 2 mrad Observables in Antiproton-Proton Interactions

  16. Figure of Merit at new IP Calculation based on Budker-Jülich Topt ~ 55 MeV Observables in Antiproton-Proton Interactions

  17. New IP ANKE ANKE vs new IP: Polarization • Expectations based on Budker-Jülich for: • T = 40 MeV • Ninj=1.5x1010 protons Polarization [%] Observables in Antiproton-Proton Interactions

  18. Present Status • Low-beta section • to be designed and constructed (with AD in mind) • Polarized target • being setup at IKP/FZJ (from HERMES) • Detector • Use of ANKE STT development • Additional forward detector needed for AD • Siberian snake for longitudinal running needed Observables in Antiproton-Proton Interactions

  19. Timeline Fall 2006 Submission of full proposal to COSY 2006-2007 Design and construction phase 2008 Spin-filtering studies at COSY Commissioning of AD experiment 2009 Installation at AD 2009-2010 Spin-filtering studies at AD Observables in Antiproton-Proton Interactions

  20. B Antiproton Polarizer Ring (APR) Injection Siberian Snake APR e-Cooler e-Cooler Internal Experiment Extraction 150 m ABS Polarizer Target F. Rathmann et al., PRL 94, 014801 (2005) Large Acceptance APR Small Beam Waist at Targetβ=0.2 m High Flux ABSq=1.5·1017 s-1  Dense TargetT=100 K, longitudinal Q (300 mT) beam tube db=ψacc·β·2dt=dt(ψacc), lb=40 cm (=2·β) feeding tube df=1 cm, lf=15 cm

  21. Beam Lifetime Coulomb Loss Total Hadronic ψacc(mrad) 40 10 8 beam lilfetime τbeam (h) 6 30 25 4 20 2 10 10 100 1000 T (MeV) Beam lifetimes in the APR Observables in Antiproton-Proton Interactions

  22. P P 0.20 0.20 0.15 0.15 0.10 0.10 0.05 0.05 Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) T (MeV) 100 200 50 150 T (MeV) 100 250 200 50 150 Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Case) 3 beam lifetimes Ψacc=20 mrad 2 beam lifetimes Ψacc=10-50 mrad • Experimental Study required: • Repetition of Filtex with protons at COSY • Final Design of APR: Filter studies with p at AD of CERN Observables in Antiproton-Proton Interactions

  23. σEM|| (mb) Atomic Electrons 600 500 Pure Electrons 400 300 200 100 T (MeV) 1 10 100 A Pure Polarized Electron Target? Maxiumum σEM|| for electrons at rest: (675 mb ,Topt = 6.2 MeV): Gainfactor ~15 over atomic e- in a PIT • Density of an Electron-Cooler fed by 1 mA DC polarized electrons: • Ie=6.2·1015 e/s • A=1 cm2 • l=5 m • dt = Ie·l·(β·c·A)-1 = 5.2·108 cm-2 New calculations for smaller relative energies  Talk by Walcher • Electron target density by factor ~106 smaller, • no match for a PIT (>1014 cm-2) Observables in Antiproton-Proton Interactions

  24. Conclusions • Outstanding physics potential of polarized antiprotons • Different proposals for polarizing antiprotons, but only one successfull experimental method (spin-filtering) • Understanding of spin-filtering process still incomplete • COSY will play a fundamental role in understanding the spin filtering process and in commissioning for the decisive experiment with antiprotons at AD • Once hadronic buildup mechanism is verified Filtering Studies at AD to determine σ1 and σ2 of pbarp scattering to optimize APR design Observables in Antiproton-Proton Interactions

  25. Spares Observables in Antiproton-Proton Interactions

  26. Detector concept • Reactions: • p-p elastic (COSY) • p-pbar elastic (AD) • Good azimuthal resolution (up/down asymmetries) • Low energy recoil (<8 MeV) • Silicon telescopes • Thin 5μm Teflon cell needed • Angular resolution for the forward particle for p-pbar • AD experiment will require an openable cell Observables in Antiproton-Proton Interactions

  27. Models A and D Calculations by Johann Haidenbauer Observables in Antiproton-Proton Interactions

  28. Observables in Antiproton-Proton Interactions

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