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Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich

Road to Polarized Antiprotons: Depolarization Studies and Spin Filtering Experiments at COSY and AD. Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich. FNAL, Jan 25, 2008. Polarized Antiprotons. Intense beam of polarized antiprotons was never produced :

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Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich

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  1. Road to Polarized Antiprotons:Depolarization Studies and Spin Filtering Experiments at COSY and AD Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich FNAL, Jan 25, 2008

  2. 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) • Little polarization from pbarC scattering exp’ts at LEAR • Stern-Gerlach spin separation in a beam (never tested) • 6/2007 Walcher/Arenhoevel: polarized electrons/positrons Spin filteringis the only succesfully tested technique Road to polarized Antiprotons

  3. 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- Road to polarized Antiprotons

  4. 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 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 Only pp elastic scattering contributes No contribution from other two effects σ1 = 85.6mb Road to polarized Antiprotons

  5. Effective Polarizing cross sections TSR … only hadronic (Budker-Jülich) - electromagnetic + hadronic (Meyer-Horowitz) … FILTEX does not provide the answer Road to polarized Antiprotons

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

  7. arXiv:0706.3765v3 [physics.acc-ph] 14Nov 2007 Road to polarized Antiprotons

  8. Detuned Cooler Voltage Tdetuned= 50 s Nominal Cooler Voltage Tnominal = 100 s Principle of the Depolarization Measurementusing co-moving electrons of the e-cooler Eh = 0.001 MeV ΔV = 235 V D2 Target on Ecool on D2 Target off Ecool on/detuned Road to polarized Antiprotons

  9. Machine Test for Depolarization Measurements(Nov. 2007) Switch off ecooler Detuned ecooler ΔU=150 V  Machine-wise, experiment is feasible Road to polarized Antiprotons

  10. New Low Energy Polarimeter for COSY (Nov. 2007) ANKE Target Chamber Two Silicon Tracking Telecopes Road to polarized Antiprotons

  11. Performance of New Low Energy Polarimeter (Nov. 2007) Road to polarized Antiprotons

  12. Polarimetry 45 MeV Road to polarized Antiprotons

  13. First Measurement of Polarization Lifetime at Tp = 45 MeV (Nov. 2007) Experimental determination of the depolarizing ep cross ~ March 2008 Road to polarized Antiprotons

  14. Spin Filtering studies at COSY • Low-beta section • Polarized target (former HERMES target) • Detector (partially former HERMES Silicon recoil) • Commissioning of AD setup • Goal: • Complete understanding of the spin filtering mechanism • Disentangle electromagnetic and hadronic contributionsto the polarizing cross section Road to polarized Antiprotons

  15. Low-β section • bx,ynew = 0.3 m -> large increase in target density • Shorter buildup time, higher rates • Larger polarization buildup rate due to larger acceptance Superconducting quadrupoles necessary Road to polarized Antiprotons

  16. Target Snake E-cooler Spin Filtering at AD of CERN Study of spin filtering in pbar-p (pbar-d) scattering T= 5 - 2.8 GeV Np = 3·107 • Measurement of effective polarization buildup cross-section • Both transverse and longitudinal • Variable acceptance at target • Test also polarized D target • First ever measurement for spin correlations in pbar-p (and pbar-D) Road to polarized Antiprotons

  17. B World-First: 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 Road to polarized Antiprotons

  18. 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 Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering) 3 beam lifetimes Ψacc=20 mrad 2 beam lifetimes Ψacc=10-50 mrad Road to polarized Antiprotons

  19. Outlook until ~2012 Fall 2007 Submission of proposal to COSY-PAC - Beam depolarization studies - Beam and polarization lifetime studies Spring 2008Technical proposal to COSY-PAC for spin filtering Technical proposal to SPSC for spin filtering at AD 2008-2009 Design and construction phase 2009 Spin-filtering studies at COSY Commissioning of AD experiment Then Installation at AD Spin-filtering studies at AD Design of the APR Quite a challenge in front of us: Young (and less young) polarization enthusiasts are welcome! Road to polarized Antiprotons

  20. 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) • Little polarization from pbarC scattering exp’ts at LEAR • Stern-Gerlach spin separation in a beam (never tested) • 6/2007 Walcher/Arenhoevel: polarized electrons/positrons • Spin filteringis the only succesfully tested technique Road to polarized Antiprotons

  21. Topics • Introduction • Depolarization Studies using unpolarized Electrons • Testing the Arenhoevel/Walcher Predictions • Upper Limit of the Depolarizing Cross Section • Spin Filtering Studies at COSY and AD Road to polarized Antiprotons

  22. Experimental Setup at TSR (1992) Road to polarized Antiprotons

  23. 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 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 Only pp elastic scattering contributes No contribution from other two effects σ1 = 85.6mb Road to polarized Antiprotons

  24. 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 Road to polarized Antiprotons

  25. Spin Filtering studies at COSY • Goal: • Understanding the spin filtering mechanism: • Disentangle electromagnetic and hadronic contributionsto the polarizing cross section Road to polarized Antiprotons

  26. Experimental setup • Low-beta section • Polarized target (former HERMES target) • Detector • Snake • Commissioning of AD setup Road to polarized Antiprotons

  27. Low-β 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 and Breit-Rabi Polarimeter Superconducting quadrupoles necessary Road to polarized Antiprotons

  28. 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 Road to polarized Antiprotons

  29. New IP ANKE ANKE vs new IP: Polarization • Expectations based on Budker-Jülich: • T = 40 MeV • Ninj=1.5x1010 protons Polarization [%] Road to polarized Antiprotons

  30. 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 Target polarimetry requires BRP for pure electron and nuclear polarization. Road to polarized Antiprotons

  31. 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 buildup cross-section • Both transverse and longitudinal • Variable acceptance at target • Test also polarized D target • First ever measurement for spin correlations in pbar-p (and pbar-D) Road to polarized Antiprotons

  32. 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 Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering) 3 beam lifetimes Ψacc=20 mrad 2 beam lifetimes Ψacc=10-50 mrad Road to polarized Antiprotons

  33. Depolarization Studies using unpolarized Electrons • Use electrons in ecooler instead of target electrons to observe depolarization Rough extraction for numerical estimates Road to polarized Antiprotons

  34. Ecooler Settings for Tp=45 MeV • Typical parameters of COSY Cooler • Electron Current 240 mA • Cross section 5 cm2 • Length 2 m • Nominal Voltage 24.5 kV • Electron target thickness seen by the protons Road to polarized Antiprotons

  35. Estimated Polarization Lifetime Road to polarized Antiprotons

  36. Energy Resolution of Protons in Electron Rest System to electron rest system Tp = 65, 45, 30 MeV Road to polarized Antiprotons

  37. Polarimetry Road to polarized Antiprotons

  38. Polarimetry Road to polarized Antiprotons

  39. Beam Polarization with detuned cooler D2 Target on Ecool on D2 Target off Ecool on/detuned Eh = 0.001, 0.002, 0.003 MeV Road to polarized Antiprotons

  40. Counting statistics • With • 109 stored protons at T = 45 MeV • Target thickness dt(D2) = 2·1014 cm-2 • Injected Beam Polarization P = 0.8 • Detector system as shown • After 1 cycle (250 s): ΔP = 0.108 15 cycles (~1 h): ΔP = 0.03 150 cycles (~10h): ΔP = 0.009 Road to polarized Antiprotons

  41. Estimated Precision of Polarization Lifetime based on Counting Statistics in Polarimeter Eh = 0.001, 0.01, 0.1 MeV Measuring time per point: ~14 h Road to polarized Antiprotons

  42. Estimated Precision of Polarization Lifetime based on counting statistics Eh = 0.002 MeV Measuring time per point: ~14 h Road to polarized Antiprotons

  43. Outlook beyond 2012 • Phase 0: present -2012 • Physics: buildup measurements @ COSY and CERN • APR design and construction • Phase I: 2015-2019 • APR+CSR @ GSI • Physics: EMFF, p-pbar elastic with fixed target • Phase II: 2020 - … • HESR+CSR asymmetric collider • Physics: h1 Road to polarized Antiprotons

  44. Antiproton Facility spares

  45. The Antiproton Facility HESR (High Energy Storage Ring) • Length 442 m • Bρ = 50 Tm • N = 5 x 1010 antiprotons High luminosity mode • Luminosity = 2 x 1032 cm-2s-1 • Δp/p ~ 10-4 (stochastic-cooling) High resolution mode • Δp/p ~ 10-5 (8 MV HE e-cooling) • Luminosity = 1031 cm-2s-1 SIS100/300 HESR Super FRS CR Gas Target and Pellet Target: cooling power determines thickness NESR Antiproton Production Target Beam Cooling: e- and/or stochastic 2MV prototype e-cooling at COSY • Antiproton production similar to CERN • Production rate107/sec at 30 GeV • T = 1.5 - 15 GeV/c Road to polarized Antiprotons

  46. Spin Filtering spares

  47. B World-First: 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 Road to polarized Antiprotons

  48. I/I0 0.8 Beam Polarization 0.6 0.4 0.2 0 2 6 4 t/τbeam Polarization Buildup: General Features IV statistical error of a double polarization observable (ATT) Measuring time t to achieve a certain error δATT t ~ FOM = P2·I (N ~ I) Optimimum time for Polarization Buildup given by maximum of FOM(t) tfilter = 2·τbeam Road to polarized Antiprotons

  49. Figure of Merit at new IP Calculation based on Budker-Jülich Topt ~ 55 MeV Road to polarized Antiprotons

  50. 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 Road to polarized Antiprotons

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