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

Frank Rathmann Road to polarized Antiprotons 2 of 19 Intense beam of polarized antiprotons was never produced: Conventional methods (ABS) not appliable Polarized antiprotons from antilambda decay I < 1.5∙10 5 s -1 (P ≈ 0.35) Antiproton scattering off liquid H 2 target I < 2∙10 3 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 filtering is the only succesfully tested technique Polarized Antiprotons

Frank Rathmann Road to polarized Antiprotons 3 of 19 Experimental Setup Results F. Rathmann. et al., PRL 71, 1379 (1993) T=23 MeV Low energy pp scattering  1 <0   tot+ <  tot- Expectation TargetBeam   1992 Filter Test at TSR with protons

Frank Rathmann Road to polarized Antiprotons 4 of 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 prot. into ring acceptance (σ S  =52 mb) 3.Spin-transfer from pol. el. of target atoms to stored prot. (σ E  =-70 mb) σ 1 = σ R  + σ S  + σ E  = 65 mb 2005 Milstein & Strakhovenko + Nikolaev & Pavlov: only one effect Only pp elastic scattering contributes No contribution from other two effectsσ 1 = 85.6 mb Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x h -1 P(t)=tanh(t/τ 1 ), 1/τ 1 =σ 1 Qd t f σ 1 = 72.5 ± 5.8 mb Two interpretations of FILTEX result

Frank Rathmann Road to polarized Antiprotons 5 of 19 … only hadronic (Budker-Jülich) - electromagnetic + hadronic (Meyer-Horowitz) TSR … FILTEX does not provide the answer Effective Polarizing cross sections

Frank Rathmann Road to polarized Antiprotons 6 of 19 Spin Filtering works, but: 1.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 Spin Filtering: Present Status

Frank Rathmann Road to polarized Antiprotons 7 of 19 arXiv: v3 [physics.acc-ph] 14Nov 2007

Frank Rathmann Road to polarized Antiprotons 8 of 19 Principle of the Depolarization Measurement using co-moving electrons of the e-cooler Nominal Cooler Voltage T nominal = 100 s Detuned Cooler Voltage T detuned = 50 s D 2 Target on Ecool on D 2 Target off Ecool on/detuned E h = MeV ΔV = 235 V

Frank Rathmann Road to polarized Antiprotons 9 of 19 Switch off ecooler Machine Test for Depolarization Measurements (Nov. 2007) Detuned ecooler ΔU=150 V  Machine-wise, experiment is feasible

Frank Rathmann Road to polarized Antiprotons 10 of 19 New Low Energy Polarimeter for COSY (Nov. 2007) ANKE Target Chamber Two Silicon Tracking Telecopes

Frank Rathmann Road to polarized Antiprotons 11 of 19 Performance of New Low Energy Polarimeter (Nov. 2007)

Frank Rathmann Road to polarized Antiprotons 12 of 19 Polarimetry 45 MeV

Frank Rathmann Road to polarized Antiprotons 13 of 19 First Measurement of Polarization Lifetime at T p = 45 MeV (Nov. 2007) Experimental determination of the depolarizing ep cross ~ March 2008

Frank Rathmann Road to polarized Antiprotons 14 of 19 Goal: Complete understanding of the spin filtering mechanism Disentangle electromagnetic and hadronic contributions to the polarizing cross section 1.Low-beta section 2.Polarized target (former HERMES target) 3.Detector (partially former HERMES Silicon recoil) Commissioning of AD setup Spin Filtering studies at COSY

Frank Rathmann Road to polarized Antiprotons 15 of 19  x,y new = 0.3 m -> large increase in target density Shorter buildup time, higher rates Larger polarization buildup rate due to larger acceptance Superconducting quadrupoles necessary Low-β section

Frank Rathmann Road to polarized Antiprotons 16 of 19 Target Snake E-cooler T= GeV N p = 3·10 7 Study of spin filtering in pbar-p (pbar-d) scattering 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) Spin Filtering at AD of CERN

Frank Rathmann Road to polarized Antiprotons 17 of 19 e-Cooler APR ABS Polarizer Target Internal Experiment Siberian Snake B Injection 150 m F. Rathmann et al., PRL 94, (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 World-First: Antiproton Polarizer Ring (APR)

Frank Rathmann Road to polarized Antiprotons 18 of 19 Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) T (MeV) T (MeV) P P 2 beam lifetimes Ψ acc =10-50 mrad 3 beam lifetimes Ψ acc =20 mrad Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering)

Frank Rathmann Road to polarized Antiprotons 19 of 19 Fall 2007Submission 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 Design and construction phase 2009Spin-filtering studies at COSY Commissioning of AD experiment ThenInstallation at AD Spin-filtering studies at AD Quite a challenge in front of us: Young (and less young) polarization enthusiasts are welcome! Outlook until ~2012 Design of the APR

Frank Rathmann Road to polarized Antiprotons 20 of 19 Intense beam of polarized antiprotons was never produced: Conventional methods (ABS) not appliable Polarized antiprotons from antilambda decay I < 1.5∙10 5 s -1 (P ≈ 0.35) Antiproton scattering off liquid H 2 target I < 2∙10 3 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 filtering is the only succesfully tested technique Polarized Antiprotons

Frank Rathmann Road to polarized Antiprotons 21 of 19 Topics IntroductionIntroduction Depolarization Studies using unpolarized ElectronsDepolarization Studies using unpolarized Electrons Testing the Arenhoevel/Walcher PredictionsTesting the Arenhoevel/Walcher Predictions Upper Limit of the Depolarizing Cross SectionUpper Limit of the Depolarizing Cross Section Spin Filtering Studies at COSY and ADSpin Filtering Studies at COSY and AD

Frank Rathmann Road to polarized Antiprotons 22 of 19 Experimental Setup at TSR (1992)

Frank Rathmann Road to polarized Antiprotons 23 of 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 prot. into ring acceptance (σ S  =52 mb) 3.Spin-transfer from pol. el. of target atoms to stored prot. (σ E  =-70 mb) σ 1 = σ R  + σ S  + σ E  = 65 mb 2005 Milstein & Strakhovenko + Nikolaev & Pavlov: only one effect Only pp elastic scattering contributes No contribution from other two effectsσ 1 = 85.6 mb Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x h -1 P(t)=tanh(t/τ 1 ), 1/τ 1 =σ 1 Qd t f σ 1 = 72.5 ± 5.8 mb Two interpretations of FILTEX result

Frank Rathmann Road to polarized Antiprotons 24 of 19 Spin filtering works, but: 1.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 Spin Filtering: Present Status

Frank Rathmann Road to polarized Antiprotons 25 of 19 Spin Filtering studies at COSY Goal: Understanding the spin filtering mechanism: Disentangle electromagnetic and hadronic contributions to the polarizing cross section

Frank Rathmann Road to polarized Antiprotons 26 of 19 Experimental setup Low-beta section Polarized target (former HERMES target) Detector Snake Commissioning of AD setup

Frank Rathmann Road to polarized Antiprotons 27 of 19  x,y new = 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 Low-β section

Frank Rathmann Road to polarized Antiprotons 28 of 19 ANKE Cross sections new-IP Lifetimes … only hadronic - electromagnetic + hadronic __ COSY average ψ acc = 1 mrad ….. ψ acc = 2 mrad ANKE vs new IP: Acceptance and Lifetime

Frank Rathmann Road to polarized Antiprotons 29 of 19 PITFilter. timePolar.Total rateMeas. Time (  P/P=10%) ANKE2  = 16 h1.2 %7.5x10 2 s min 5  = 42 h3.5 %5x10 s min New IP2  = 5 h16 %2.2x10 4 s -1 1 s 5  = 13 h42 %1.5x10 3 s -1 < 1 s New IP ANKE Polarization [%] Expectations based on Budker-Jülich: T = 40 MeV N inj =1.5x10 10 protons ANKE vs new IP: Polarization

Frank Rathmann Road to polarized Antiprotons 30 of 19 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. Strong fields can be applied only longitudinally (minimal beam interference) - Snake necessary Target polarimetry requires BRP for pure electron and nuclear polarization. Method 1: Polarization build-up experiments How to disentangle hadronic and electromagnetic contributions to  eff ?

Frank Rathmann Road to polarized Antiprotons 31 of 19 Target Snake E-cooler T= GeV N p = 3·10 7 Study of spin filtering in pbar-p (pbar-d) scattering 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) AD ring at CERN

Frank Rathmann Road to polarized Antiprotons 32 of 19 Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) T (MeV) T (MeV) P P 2 beam lifetimes Ψ acc =10-50 mrad 3 beam lifetimes Ψ acc =20 mrad Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering)

Frank Rathmann Road to polarized Antiprotons 33 of 19 Depolarization Studies using unpolarized Electrons Use electrons in ecooler instead of target electrons to observe depolarization Rough extraction for numerical estimates

Frank Rathmann Road to polarized Antiprotons 34 of 19 Ecooler Settings for T p =45 MeV Typical parameters of COSY Cooler Electron Current 240 mA Cross section 5 cm 2 Length 2 m Nominal Voltage 24.5 kV Electron target thickness seen by the protons

Frank Rathmann Road to polarized Antiprotons 35 of 19 Estimated Polarization Lifetime

Frank Rathmann Road to polarized Antiprotons 36 of 19 Energy Resolution of Protons in Electron Rest System to electron rest system Tp = 65, 45, 30 MeV

Frank Rathmann Road to polarized Antiprotons 37 of 19 Polarimetry

Frank Rathmann Road to polarized Antiprotons 38 of 19 Polarimetry

Frank Rathmann Road to polarized Antiprotons 39 of 19 Beam Polarization with detuned cooler E h = 0.001, 0.002, MeV D 2 Target on Ecool on D 2 Target off Ecool on/detuned

Frank Rathmann Road to polarized Antiprotons 40 of 19 Counting statistics With –10 9 stored protons atT = 45 MeV –Target thickness d t (D 2 ) = 2·10 14 cm -2 –Injected Beam Polarization P = 0.8 –Detector system as shown –After 1 cycle (250 s): ΔP = cycles (~1 h):ΔP = cycles (~10h):ΔP = E h (MeV)ΔV (V)τ p(A-W) (s)P(t=250 s)

Frank Rathmann Road to polarized Antiprotons 41 of 19 Estimated Precision of Polarization Lifetime based on Counting Statistics in Polarimeter E h = 0.001, 0.01, 0.1 MeV Measuring time per point: ~14 h

Frank Rathmann Road to polarized Antiprotons 42 of 19 Measuring time per point: ~14 h E h = MeV Estimated Precision of Polarization Lifetime based on counting statistics

Frank Rathmann Road to polarized Antiprotons 43 of 19 Phase 0: present Physics: buildup COSY and CERN APR design and construction Phase I: GSI Physics: EMFF, p-pbar elastic with fixed target Phase II: … HESR+CSR asymmetric collider Physics: h1 Outlook beyond 2012

Antiproton Facility spares

Frank Rathmann Road to polarized Antiprotons 45 of 19 HESR Antiproton Production Target HESR (High Energy Storage Ring) Length 442 m Bρ = 50 Tm N = 5 x antiprotons High luminosity mode Luminosity = 2 x cm -2 s -1 Δp/p ~ (stochastic-cooling) High resolution mode Δp/p ~ (8 MV HE e-cooling) Luminosity = cm -2 s -1 Antiproton production similar to CERN Production rate 10 7 /sec at 30 GeV T = GeV/c Gas Target and Pellet Target: cooling power determines thickness Super FRS NESR CR Beam Cooling: e - and/or stochastic 2MV prototype e-cooling at COSY SIS100/300 The Antiproton Facility

Spin Filtering spares

Frank Rathmann Road to polarized Antiprotons 47 of 19 e-Cooler APR ABS Polarizer Target Internal Experiment Siberian Snake B Injection 150 m F. Rathmann et al., PRL 94, (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 World-First: Antiproton Polarizer Ring (APR)

Frank Rathmann Road to polarized Antiprotons 48 of 19 statistical error of a double polarization observable (A TT ) Measuring time t to achieve a certain error δ ATT t ~ FOM = P 2 ·I Polarization Buildup: General Features IV (N ~ I) Optimimum time for Polarization Buildup given by maximum of FOM(t) t filter = 2·τ beam t/τ beam I/I Beam Polarization

Frank Rathmann Road to polarized Antiprotons 49 of 19 Figure of Merit at new IP T opt ~ 55 MeV Calculation based on Budker-Jülich

Frank Rathmann Road to polarized Antiprotons 50 of 19 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 Detector concept

Frank Rathmann Road to polarized Antiprotons 51 of 19 Beam Polarization in a dedicated Antiproton Polarizer Beam Polarization P(2·τ beam ) T (MeV)100 Polarisation buildup through spin transfer ψ acc (mrad) 10 Horowitz & Meyer, PRL 72, 3981 (1994) H.O. Meyer, PRE 50, 1485 (1994) PAX will exploit spin-transfer to polarize antiprotons and to go after transversity

Frank Rathmann Road to polarized Antiprotons 52 of 19 “If polarized electrons polarize an initially unpolarized beam, then, unpolarized electrons should depolarize an initially polarized beam!” Method 2: Depolarization experiments Electrons in 4 He storage cell or D cluster-jet target: Large analyzing power Large counting rates Distinguish electron effect from normal depolarization in COSY Prerequisites: Large beam lifetime Large polarization lifetime 4 He empty Prediction for ANKE/COSY (4 weeks) Approved new Proposal for COSY 4 He Hans-Otto Meyer’s suggestion

Frank Rathmann Road to polarized Antiprotons 53 of 19 Polarization Buildup: 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, I, and FOM

Frank Rathmann Road to polarized Antiprotons 54 of 19 Principle of spin-filtering 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) Unpolarized anti-p beam Polarized H target Polarization Buildup:

Frank Rathmann Road to polarized Antiprotons 55 of 19 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) Unpolarized anti-p beam Polarized H target Polarized anti-p beam Polarization Buildup:

Frank Rathmann Road to polarized Antiprotons 56 of 19 Experimental Setup Results F. Rathmann. et al., PRL 71, 1379 (1993) T=23 MeV Low energy pp scattering  1 <0   tot+ <  tot- Expectation TargetBeam   1992 Filter Test at TSR with protons

Frank Rathmann Road to polarized Antiprotons 57 of 19 Rate Estimate Für 1*E9 Protonen mit einer Polarisation von 0.8. Target sind 2E14/cm2 d und die Strahlenergie beträgt 45MeV. Die Plots findest du angehängt. Weitere Zahlen: Totale Zählraten L:5.8/s R:8.1/s Error of Polarization after 1s: 0.86 (Die 0.13 waren bei 100s E7 Teilchen, aber 30mal....) Integriert man über 100s (Strahllebensdauer ebenfalls 100s) dann erhält man ( /e)=63.2 -fache Statistik also einen Fehler von 0.86/sqrt(63.2)= Dies ist leider deutlich schlechter als die erhofften 0.02, aber sicherlich kein Showstopper. Dauer eines Zyklus: 10s für Injektion 100s für E-Cooler-Spielerei 100s für Polarisationsmessung 5s für Extraktion ============================== 215s = 4Min(240s) In einer Stunde hätten wir also 15 Zyklen also einen Fehler von Nach 10h: Wir sollten also ohne Probleme an einem Tag sowohl die Injektionspolarisation, sowie die Polarisation nach E-Cooler-Spielerei messen können.

Frank Rathmann Road to polarized Antiprotons 58 of 19 “If polarized electrons polarize an initially unpolarized beam, then, unpolarized electrons should depolarize an initially polarized beam!” Electrons in 4 He storage cell or D cluster-jet target: Large analyzing power Large counting rates Distinguish electron effect from normal depolarization in COSY Prerequisites: Large beam lifetime Large polarization lifetime 4 He empty Prediction for ANKE/COSY (4 weeks) Approved new Proposal for COSY 4 He Depolarization Study at COSY Explore also option with co-moving electrons in cooler