Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich

1. Towards Polarized Antiprotons at FAIR http://www.fz-juelich.de/ikp/pax Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich Kyoto, October 3, 2006

2. Outline • PAX physics program • Accelerator configuration for FAIR • Towards polarized antiprotons Towards Polarized Antiprotons at FAIR

3. QCD Physics at FAIR (CDR): unpolarized Antiprotons in HESR HESR PAX Polarized Antiprotons Central PAX Physics Case: Transversity distribution of the nucleon in Drell-Yan: FAIR as successor of DIS physics • last leading-twist missing piece of the QCD description of the partonic structure of the nucleon • observation 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 () Towards Polarized Antiprotons at FAIR

4. PAX Physics Program • Transversity • Electromagnetic Form Factors • Hard Scattering Effects • SSA in DY, origin of Sivers function • Soft Scattering • Low-t Physics • Total Cross Section • pp interaction Towards Polarized Antiprotons at FAIR

5. Leading Twist Distribution Functions R L L R L R R L quark quark’ 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 proton proton’ R L 1/2 -1/2     -     Probabilistic interpretation in helicity base: + f1(x) q(x) spin averaged (well known) - Dq(x) helicity diff. (known) g1(x) No probabilistic interpretation in the helicity base (off diagonal) h1(x) u = 1/2(uR + uL) u = 1/2(uR - uL) Transversity base dq(x) helicity flip (unknown)

6. Transversity Properties: • Probes relativistic nature of quarks • No gluon analog for spin-1/2 nucleon • Different evolution than • Sensitive to valence quark polarization Chiral-odd: requires another chiral-odd partner epe’hX ppl+l-X Direct Measurement Indirect Measurement: Convolution of with unknown fragment. fct. Impossible in DIS Towards Polarized Antiprotons at FAIR

7. Polarizedantiproton beam → Polarizedproton target (both transverse) l+ q2=M2 l- q qT p p qL M invariant Mass of lepton pair Transversity in Drell-Yan processes Towards Polarized Antiprotons at FAIR

8. Proton Electromagnetic Formfactors • Measurement of relative phases of magnetic and electric FF in the time-like region • Possible only via SSA in the annihilation pp → e+e- • Double-spin asymmetry • independent GE-Gm separation • test of Rosenbluth separation in the time-like region S. Brodsky et al., Phys. Rev. D69 (2004) Towards Polarized Antiprotons at FAIR

9. Facilty for Antiproton and Ion Research (GSI, Darmstadt, Germany) • Proton linac (injector) • 2 synchrotons (30 GeV p) • A number of storage rings •  Parallel beams operation Towards Polarized Antiprotons at FAIR

10. PAX Collider Setup PAX Collider Luminosity> 1031 cm-2s-1 Towards Polarized Antiprotons at FAIR

11. Polarized Antiprotons • Intense beam of polarized antiprotons was never produced: • Conventional methods (ABS) not appliable • Polarized antiprotons from antilambda decay • I < 1.5∙105 s-1 (P ≈ 0.35) • Antiproton scattering off liquid H2 target • I < 2∙103 s-1 (P ≈ 0.2) • Stern-Gerlach spin separation in a beam (never tested) • 5/2006 (Th. Walcher et al.) polarized electron beam See Talk by K. Aulenbacher (9A, Fr) • Spin filteringis the only succesfully tested technique Towards Polarized Antiprotons at FAIR

12. P beam polarization Q target polarization k || beam direction σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k) For initially equally populated spin states:  (m=+½) and  (m=-½) transverse case: longitudinal case: Unpolarized anti-p beam Polarized H target Principle of spin-filtering Towards Polarized Antiprotons at FAIR

13. P beam polarization Q target polarization k || beam direction Polarized anti-p beam σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k) For initially equally populated spin states:  (m=+½) and  (m=-½) transverse case: longitudinal case: Unpolarized anti-p beam Principle of spin-filtering Polarized H target Towards Polarized Antiprotons at FAIR

14. 1992 Filter Test at TSR with protons Experimental Setup Towards Polarized Antiprotons at FAIR

15. 1992 Spin Filter Test at TSR with protons Results Experimental Setup T=23 MeV F. Rathmann. et al., PRL 71, 1379 (1993) Towards Polarized Antiprotons at FAIR

16. 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 prot. into ring acceptance (σS=52 mb) • Spin-transfer from pol. el. of target atoms to stored prot. (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 σ1 = 85.6mb (-> more in next talk by N.N. Nikolaev) Towards Polarized Antiprotons at FAIR

17. Spin Filtering: Present Status • Spin filtering works, but: • Controversial interpretations of FILTEX experiment • Further experimental tests necessary • How does spin filtering work? • Which role do electrons play? •  Tests with protons at COSY • 2. No data to predict polarization from filtering with antiprotons •  Measurements with antiprotons at AD/CERN Towards Polarized Antiprotons at FAIR

18. Spin Filtering studies at COSY • Goal: • Understanding the spin filtering mechanism: • Disentangle electromagnetic and hadronic contributionsto the polarizing cross section Towards Polarized Antiprotons at FAIR

19. Polarizing cross sections from the two models TSR … only hadronic (Budker-Jülich) - electromagnetic + hadronic (Meyer-Horowitz) A measurement of seff to 10% precision requires polarization measurement with DP/P = 10%. Towards Polarized Antiprotons at FAIR

20. How to disentangle hadronic and electromagnetic contributions to seff? Method 1: Polarization build-up experiments • 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) Strong fields can be applied only longitudinally (minimal beam interference) - Snake necessary AD Experiments require both transverse and longitudinal (weak) fields. AD Experiments will be performed also with D target. Target polarimetry requires BRP for pure electron and D polarization. Towards Polarized Antiprotons at FAIR

21. Experimental setup • Low-beta section • Polarized target (former HERMES target) • Detector • Snake • Commissioning of AD setup Towards Polarized Antiprotons at FAIR

22. Low beta section • bx,ynew = 0.3 m -> increase in density with respect to ANKE: factor 30 • Shorter buildup time, higher rates • Larger polarization buildup rate due to larger acceptance • Use of former HERMES target (more details in A. Nass’ 9A, Fr) S.C. quadrupoles necessary for AD experiment Towards Polarized Antiprotons at FAIR

23. 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 Towards Polarized Antiprotons at FAIR

24. Figure of Merit at new IP Calculation based on Budker-Jülich Topt ~ 55 MeV Towards Polarized Antiprotons at FAIR

25. ANKE vs new IP: Polarization New IP ANKE • Expectations based on Budker-Jülich: • T = 40 MeV • Ninj=1.5x1010 protons Polarization [%] Towards Polarized Antiprotons at FAIR

26. Detector concept • Will measure beam polarization by using the polarization observables: • p-p elastic (COSY) • pbar-p 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 at AD • AD experiment will require an openable cell Towards Polarized Antiprotons at FAIR

27. Hans-Otto Meyer’s idea “If polarized electrons polarize an initially unpolarized beam, then, unpolarized electrons should depolarize an initially polarized beam!” Method 2: Depolarization experiments Prediction for ANKE/COSY (4 weeks) • Electrons in 4He storage cell target: • Large analyzing power • Large counting rates • Distinguish electron effect from normal depolarization in COSY • Prerequisites: • Large beam lifetime • Large polarization lifetime 4He empty 4He New Proposal for COSY turned in this week Towards Polarized Antiprotons at FAIR

28. Target Snake E-cooler AD ring at CERN Study of spin filtering in pbar-p (pbar-d) scattering T= 5 - 2.8 GeV Np = 3·107 Measurement of effective polarization cross-section Both transverse and longitudinal Variable acceptance at target Polarized D target First measurement for spin correlations in pbar-p (and pbar-D)

29. 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 Towards Polarized Antiprotons at FAIR

30. yx Fall 2006 Submission of proposal to COSY-PAC Beam depolarization studies (Beam lifetime studies) Spring 2007Submission of FP 7 application Fall 2007Technical proposal to COSY-PAC for spin filtering Technical proposal to SPSC for spin filtering at AD 2006-2007 Design and construction phase 2008-2009 Spin-filtering studies at COSY Commissioning of AD experiment 2009 Installation at AD 2009-2010 Spin-filtering studies at AD Quite a challenge in front of us: Young (and less young) polarization enthusiasts are welcome! Towards Polarized Antiprotons at FAIR