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

2. Frank RathmannObservables in Antiproton-Proton Interactions2 Polarized Antiprotons Intense beams of polarized pbar never produced Conventional methods (ABS) not appliable Polarized pbar from antilambda decay -I< 1.5∙10 5 s -1 (P ≈ 0.35) Pbar scattering off liquid H 2 target -I< 2∙10 3 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-filtering is the only succesfully tested technique

3. Frank RathmannObservables in Antiproton-Proton Interactions3 P beam polarization Q target polarization k || beam direction σ tot = σ 0 + σ  ·P·Q + σ || ·(P·k)(Q·k) transverse case:longitudinal case: For initially equally populated spin states:  (m=+½) and  (m=-½) Time dependence of P and I (removal only) Spin Filter Method

4. Frank RathmannObservables in Antiproton-Proton Interactions4 statistical error of a double polarization observable (A TT ) Measuring time t to achieve a certain error δ ATT ~ FOM = P 2 ·I Optimum Interaction Time (N ~ I) Optimimum time for Polarization Buildup given by maximum of FOM(t) t filter = 2·τ beam 02 4 6 t/τ beam I/I 0 0.2 0.4 0.6 0.8 Beam Polarization

5. Frank RathmannObservables in Antiproton-Proton Interactions5 1992 Filter Test at TSR with protons Experimental Setup

6. Frank RathmannObservables in Antiproton-Proton Interactions6 Polarized Atomic Beam Source m j = +1/2 m j = -1/2 m i =-1/2 m i =+1/2 1 |1> |2> |3> |4> ee-ee-p |1> Atoms with m j =+½ focused in sextupole magnets RF transitions select HFS

7. Frank RathmannObservables in Antiproton-Proton Interactions7 1992 Filter Test at TSR with protons Experimental Setup Results F. Rathmann. et al., PRL 71, 1379 (1993) T=23 MeV Low energy pp scattering  1 <0   tot+ <  tot- Expectation TargetBeam  

8. Frank RathmannObservables in Antiproton-Proton Interactions8 Two interpretations of FILTEX result 1994: Meyer and Horowitz: three distinct effects 1.Selective removal through scattering beyond θ acc =4.4 mrad (σ R  =83 mb) 2.Small angle scattering of target protons into ring acceptance (σ S  =52 mb) 3.Spin-transfer from polarized e - of H atoms to stored protons (σ E  =-70 mb) σ 1 = σ R  + σ S  + σ E  = 65 mb 2005: Milstein & Strakhovenko + Nikolaev & Pavlov: only one effect 1.Selective removal through scattering beyond θ acc =4.4 mrad (σ R  =85.6 mb) No contribution from other two effects (cancellation of scattering and transmission) σ 1 = 85.6 mb Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10 -2 h -1 P(t)=tanh(t/τ 1 ), 1/τ 1 =σ 1 Qd t f σ 1 = 72.5 ± 5.8 mb Spin-filtering works! But how? Details in Nikolaevs Talk

9. Frank RathmannObservables in Antiproton-Proton Interactions9 Spin-Filtering: Present Situation Spin Filtering works, but: 1.controversial interpretations of TSR result 2.no experimental data base for antiprotons  experimental tests needed with 1.Protons at COSY 2.Antiprotons at AD of CERN

10. Frank RathmannObservables in Antiproton-Proton Interactions10 Spin-filtering studies at COSY Objective: Understanding of spin-filtering mechanism: Disentangle electromagnetic and hadronic contributions to the polarizing cross section

11. Frank RathmannObservables in Antiproton-Proton Interactions11 Polarizing cross sections from the two models … only hadronic - electromagnetic + hadronic TSR A measurement of  eff to 10% precision requires polarization measurement with  P/P = 10%.

12. Frank RathmannObservables in Antiproton-Proton Interactions12 How to disentangle hadronic and electromagnetic contributions to  eff ? Injection of different combinations of hyperfine states Different electron and nuclear polarizations Null experiments possible: Pure electron polarized target (P z = 0), and Pure nuclear polarized target (P e =0) Inj. statesPePe PzPz InteractionHolding field |1>+1 Elm. + had.transv. + longit.weak (20 G) |1> + |4>0+1only had. longitudinalstrong (3kG) |1> + |2>+10only elm. AD Experiments require both transverse and longitudinal (weak)fields. Strong fields can be applied only longitudinally (minimal beam interference) - Snake necessary Target polarimetry requires BRP for pure electron polarization.

13. Frank RathmannObservables in Antiproton-Proton Interactions13 Experimental setup Low-beta section Polarized target (former HERMES target) Detector Snake Commissioning of AD setup

14. Frank RathmannObservables in Antiproton-Proton Interactions14  x,y new = 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) Low beta section S.C. quadrupole development applicable to AD experiment

15. Frank RathmannObservables in Antiproton-Proton Interactions15 ANKE vs new IP: Acceptance and Lifetime Acceptance @ ANKE Cross sections Acceptance @ new-IP Lifetimes … only hadronic - electromagnetic + hadronic __ COSY average ψ acc = 1 mrad ….. ψ acc = 2 mrad

16. Frank RathmannObservables in Antiproton-Proton Interactions16 Figure of Merit at new IP T opt ~ 55 MeV Calculation based on Budker-Jülich

17. Frank RathmannObservables in Antiproton-Proton Interactions17 PITFilter. timePolar.Total rateMeas. Time (  P/P=10%) ANKE2  = 16 h1.2 %7.5x10 2 s -1 44 min 5  = 42 h3.5 %5x10 s -1 26 min New IP2  = 5 h16 %2.2x10 4 s -1 1 s 5  = 13 h42 %1.5x10 3 s -1 < 1 s ANKE vs new IP: Polarization New IP ANKE Polarization [%] Expectations based on Budker- Jülich for: T = 40 MeV N inj =1.5x10 10 protons

18. Frank RathmannObservables in Antiproton-Proton Interactions18 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

19. Frank RathmannObservables in Antiproton-Proton Interactions19 Timeline Fall 2006Submission of full proposal to COSY 2006-2007Design and construction phase 2008Spin-filtering studies at COSY Commissioning of AD experiment 2009Installation at AD 2009-2010Spin-filtering studies at AD

20. Antiproton Polarizer Ring (APR) e-Cooler APR ABS Polarizer Target Internal Experiment Siberian Snake B Injection 150 m F. Rathmann et al., PRL 94, 014801 (2005) Extraction e-Cooler Small Beam Waist at Target β=0.2 m High Flux ABS q=1.5·10 17 s -1  Dense TargetT=100 K, longitudinal Q (300 mT) beam tubed b =ψ acc ·β·2  d t =d t (ψ acc ), l b =40 cm (=2·β) feeding tube d f =1 cm, l f =15 cm Large Acceptance APR

21. Frank RathmannObservables in Antiproton-Proton Interactions21 Beam lifetimes in the APR 101001000T (MeV) 40 30 25 ψ acc (mrad) 20 10 2 4 6 8 beam lilfetime τ beam (h) 10 Beam Lifetime Coulomb Loss Total Hadronic

22. Frank RathmannObservables in Antiproton-Proton Interactions22 Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Case) Experimental Study required: Repetition of Filtex with protons at COSY Final Design of APR: Filter studies with p at AD of CERN Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) 50 100 150 200 250 T (MeV) 50 100 150 200 T (MeV) 0.05 0.10 0.15 0.20 P 0.05 0.10 0.15 0.20 P 2 beam lifetimes Ψ acc =10-50 mrad 3 beam lifetimes Ψ acc =20 mrad

23. Frank RathmannObservables in Antiproton-Proton Interactions23 A Pure Polarized Electron Target? 1 10 100 T (MeV) σ EM|| (mb) 100 200 300 400 500 600 Pure Electrons Atomic Electrons Maxiumum σ EM|| for electrons at rest: (675 mb,T opt = 6.2 MeV): Gainfactor ~15 over atomic e - in a PIT Density of an Electron-Cooler fed by 1 mA DC polarized electrons: I e =6.2·10 15 e/s A=1 cm 2 l=5 m d t = I e ·l·(β·c·A) -1 = 5.2·10 8 cm -2 Electron target density by factor ~10 6 smaller,  no match for a PIT (>10 14 cm -2 ) New calculations for smaller relative energies  Talk by Walcher

24. Frank RathmannObservables in Antiproton-Proton Interactions24 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 σ 1 and σ 2 of pbarp scattering to optimize APR design

25. Frank RathmannObservables in Antiproton-Proton Interactions25 Spares

26. Frank RathmannObservables in Antiproton-Proton Interactions26 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

27. Frank RathmannObservables in Antiproton-Proton Interactions27 Models A and D Calculations by Johann Haidenbauer

28. Frank RathmannObservables in Antiproton-Proton Interactions28