Road to Polarized Antiprotons Depolarization Studies and Spin

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 Frank Rathmann Road to polarized Antiprotons

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 H 2 target • I < 2∙ 103 s-1 (P ≈ 0. 2) Little polarization from pbar. C 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 Frank Rathmann Road to polarized Antiprotons 2

1992 Filter Test at TSR with protons Results Experimental Setup T=23 Me. V F. Rathmann. et al. , PRL 71, 1379 (1993) Low energy pp scattering 1<0 tot+< tot. Frank Rathmann Road to polarized Antiprotons Expectation Target Beam 3

Two interpretations of FILTEX result Observed polarization build-up: d. P/dt = ± (1. 24 ± 0. 06) x 10 -2 h-1 P(t)=tanh(t/τ1), 1/τ1=σ1 Qdtf σ1 = 72. 5 ± 5. 8 mb 1994 1. 2. 3. 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. 6 mb Frank Rathmann Road to polarized Antiprotons 4

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

Spin Filtering: Present Status 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 Frank Rathmann Road to polarized Antiprotons 6

ar. Xiv: 0706. 3765 v 3 [physics. acc-ph] 14 Nov 2007 Frank Rathmann Road to polarized Antiprotons 7

Principle of the Depolarization Measurement using co-moving electrons of the e-cooler Eh = 0. 001 Me. V ΔV = 235 V Detuned Cooler Voltage Tdetuned= 50 s Nominal Cooler Voltage Tnominal = 100 s Frank Rathmann D 2 Target off Ecool on/detuned Road to polarized Antiprotons D 2 Target on Ecool on 8

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

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

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

Polarimetry 45 Me. V Frank Rathmann Road to polarized Antiprotons 12

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

Spin Filtering studies at COSY 1. Low-beta section Goal: 2. Polarized target (former HERMES target) mechanism • Complete understanding of the spin filtering 3. Detectorelectromagnetic (partially former and HERMES Silicon recoil) • Disentangle hadronic contributions to the polarizing cross section 4. Commissioning of AD setup Frank Rathmann Road to polarized Antiprotons 14

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 Frank Rathmann Road to polarized Antiprotons 15

Spin Filtering at AD of CERN Study of spin filtering in pbar-p (pbar-d) scattering Target Snake T= 5 - 2. 8 Ge. V Np = 3· 107 E-cooler 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) Frank Rathmann Road to polarized Antiprotons 16

World-First: Antiproton Polarizer Ring (APR) B Injection Siberian Snake e-Cooler ABS APR 150 m Extraction e-Cooler Internal Experiment Polarizer Target Large Acceptance APR Small Beam Waist at Target High Flux ABS Dense Target beam tube feeding tube Frank Rathmann F. Rathmann et al. , PRL 94, 014801 (2005) β=0. 2 m q=1. 5· 1017 s-1 T=100 K, longitudinal Q (300 m. T) db=ψacc∙β∙ 2 dt=dt(ψacc), lb=40 cm (=2·β) df=1 cm, lf=15 cm Road to polarized Antiprotons 17

Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering) P 3 beam lifetimes Ψacc=20 mrad 0. 20 P 0. 20 0. 15 2 beam lifetimes Ψacc=10 -50 mrad 0. 10 0. 05 Model A: T. Hippchen et al. , Phys. Rev. C 44, 1323 (1991) 50 100 150 200 250 T (Me. V) Frank Rathmann 0. 10 0. 05 Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) 50 Road to polarized Antiprotons 100 150 200 T (Me. V) 18

Outlook until ~2012 Fall 2007 Submission of proposal to COSY-PAC - Beam depolarization studies - Beam and polarization lifetime studies Spring 2008 Technical 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! Frank Rathmann Road to polarized Antiprotons 19

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 H 2 target • I < 2∙ 103 s-1 (P ≈ 0. 2) • Little polarization from pbar. C 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 Frank Rathmann Road to polarized Antiprotons 20

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

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

Two interpretations of FILTEX result Observed polarization build-up: d. P/dt = ± (1. 24 ± 0. 06) x 10 -2 h-1 P(t)=tanh(t/τ1), 1/τ1=σ1 Qdtf σ1 = 72. 5 ± 5. 8 mb 1994 1. 2. 3. 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. 6 mb Frank Rathmann Road to polarized Antiprotons 23

Spin Filtering: Present Status 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 Frank Rathmann Road to polarized Antiprotons 24

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 25

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

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 Frank Rathmann Road to polarized Antiprotons 27

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

ANKE vs new IP: Polarization • T = 40 Me. V • Ninj=1. 5 x 1010 protons Polarization [%] Expectations based on Budker-Jülich: New IP ANKE PIT Filter. time Polar. Total rate Meas. Time (DP/P=10%) ANKE 2 t = 16 h 1. 2 % 7. 5 x 102 s-1 44 min 5 t = 42 h 3. 5 % 5 x 10 s-1 26 min 2 t = 5 h 16 % 2. 2 x 104 s-1 1 s 5 t = 13 h 42 % 1. 5 x 103 s-1 <1 s New IP Frank Rathmann Road to polarized Antiprotons 29

How to disentangle hadronic and electromagnetic contributions to eff ? 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) Inj. states Pe Pz Interaction |1> +1 +1 Elm. + had. |1> + |4> 0 +1 only had. |1> + |2> +1 0 only elm. Holding field transv. + longit. weak (20 G) longitudinal strong (3 k. G) Strong fields can be applied only longitudinally (minimal beam interference) - Snake necessary Target polarimetry requires BRP for pure electron and nuclear polarization. Frank Rathmann Road to polarized Antiprotons 30

AD ring at CERN Study of spin filtering in pbar-p (pbar-d) scattering Target Snake T= 5 - 2. 8 Ge. V Np = 3· 107 E-cooler 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) Frank Rathmann Road to polarized Antiprotons 31

Theoretical estimate of Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Spin Filtering) P 3 beam lifetimes Ψacc=20 mrad 0. 20 P 0. 20 0. 15 2 beam lifetimes Ψacc=10 -50 mrad 0. 10 0. 05 Model A: T. Hippchen et al. , Phys. Rev. C 44, 1323 (1991) 50 100 150 200 250 T (Me. V) Frank Rathmann 0. 10 0. 05 Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) 50 Road to polarized Antiprotons 100 150 200 T (Me. V) 32

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 33

Ecooler Settings for Tp=45 Me. V Typical parameters of COSY Cooler • Electron Current 240 m. A • Cross section 5 cm 2 • Length 2 m • Nominal Voltage 24. 5 k. V Electron target thickness seen by the protons Frank Rathmann Road to polarized Antiprotons 34

Estimated Polarization Lifetime Frank Rathmann Road to polarized Antiprotons 35

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

Polarimetry Frank Rathmann Road to polarized Antiprotons 37

Polarimetry Frank Rathmann Road to polarized Antiprotons 38

Beam Polarization with detuned cooler D 2 Target off Ecool on/detuned D 2 Target on Ecool on Eh = 0. 001, 0. 002, 0. 003 Me. V Frank Rathmann Road to polarized Antiprotons 39

Counting statistics • With – 109 stored protons at – Target thickness – Injected Beam Polarization – Detector system as shown – After 1 cycle (250 s): 15 cycles (~1 h): 150 cycles (~10 h): Frank Rathmann T = 45 Me. V dt(D 2) = 2∙ 1014 cm-2 P = 0. 8 ΔP = 0. 108 ΔP = 0. 03 ΔP = 0. 009 Eh (Me. V) ΔV (V) τp(A-W) (s) P(t=250 s) 0. 001 234 0. 04 0 0. 002 332 25 0. 10 0. 003 407 2000 0. 78 Road to polarized Antiprotons 40

Estimated Precision of Polarization Lifetime based on Counting Statistics in Polarimeter Eh = 0. 001, 0. 1 Me. V Measuring time per point: ~14 h Frank Rathmann Road to polarized Antiprotons 41

Estimated Precision of Polarization Lifetime based on counting statistics Eh = 0. 002 Me. V Measuring time per point: ~14 h Frank Rathmann Road to polarized Antiprotons 42

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: h 1 Frank Rathmann Road to polarized Antiprotons 43

Antiproton Facility spares Frank Rathmann Road to polarized Antiprotons

The Antiproton Facility HESR (High Energy Storage Ring) • Length 442 m • Bρ = 50 Tm • N = 5 x 1010 antiprotons SIS 100/300 High luminosity mode • Luminosity = 2 x 1032 cm-2 s-1 • Δp/p ~ 10 -4 (stochastic-cooling) HESR High resolution mode • Δp/p ~ 10 -5 (8 MV HE e-cooling) • Luminosity = 1031 cm-2 s-1 Super FRS CR Antiproton Gas Target and Pellet Target: cooling power determines thickness NESR Production Target • Antiproton production similar to CERN • Production rate 107/sec at 30 Ge. V • T = 1. 5 - 15 Ge. V/c Frank Rathmann Beam Cooling: e- and/or stochastic 2 MV prototype e-cooling at COSY Road to polarized Antiprotons 45

Spin Filtering spares Frank Rathmann Road to polarized Antiprotons

World-First: Antiproton Polarizer Ring (APR) B Injection Siberian Snake e-Cooler ABS APR 150 m Extraction e-Cooler Internal Experiment Polarizer Target Large Acceptance APR Small Beam Waist at Target High Flux ABS Dense Target beam tube feeding tube Frank Rathmann F. Rathmann et al. , PRL 94, 014801 (2005) β=0. 2 m q=1. 5· 1017 s-1 T=100 K, longitudinal Q (300 m. T) db=ψacc∙β∙ 2 dt=dt(ψacc), lb=40 cm (=2·β) df=1 cm, lf=15 cm Road to polarized Antiprotons 47

Polarization Buildup: General Features IV Measuring time t to achieve a certain error δATT (N ~ I) Beam Polarization t ~ FOM = P 2·I I/I 0 statistical error of a double polarization observable (ATT) Optimimum time for Polarization Buildup given by maximum of FOM(t) tfilter = 2·τbeam 0. 8 0. 6 0. 4 0. 2 0 Frank Rathmann Road to polarized Antiprotons 2 4 6 t/τbeam 48

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

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 Me. V) • 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 Frank Rathmann Road to polarized Antiprotons 50

Beam Polarization in a dedicated Antiproton Polarizer Beam Polarization P(2∙τbeam) Polarisation buildup through spin transfer Horowitz & Meyer, PRL 72, 3981 (1994) H. O. Meyer, PRE 50, 1485 (1994) ψacc(mrad) 0. 4 50 30 10 0. 3 0. 2 0. 1 0 1 10 100 T (Me. V) PAX will exploit spin-transfer to polarize antiprotons and to go after transversity Frank Rathmann Road to polarized Antiprotons 51

Hans-Otto Meyer’s suggestion “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 Prediction for ANKE/COSY (4 weeks) 4 He Approved new Proposal for COSY Frank Rathmann Road to polarized Antiprotons empty 4 He 52

Polarization Buildup: σtot = σ0 + σ ∙P∙Q + σ||∙(P∙k)(Q∙k) P beam polarization Q target polarization k || beam direction For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: Time dependence of P, I, and FOM Frank Rathmann Road to polarized Antiprotons 53

Polarization Buildup: σtot = σ0 + σ ∙P∙Q + σ||∙(P∙k)(Q∙k) P beam polarization Q target polarization k || beam direction Principle of spin-filtering For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: Unpolarized anti-p beam Polarized H target Frank Rathmann Road to polarized Antiprotons 54

Polarization Buildup: σtot = σ0 + σ ∙P∙Q + σ||∙(P∙k)(Q∙k) P beam polarization Q target polarization k || beam direction For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: Polarized Unpolarized anti-p beam Polarized H target Frank Rathmann Road to polarized Antiprotons 55

1992 Filter Test at TSR with protons Results Experimental Setup T=23 Me. V F. Rathmann. et al. , PRL 71, 1379 (1993) Low energy pp scattering 1<0 tot+< tot. Frank Rathmann Road to polarized Antiprotons Expectation Target Beam 56

Rate Estimate Für 1*E 9 Protonen mit einer Polarisation von 0. 8. Target sind 2 E 14/cm 2 d und die Strahlenergie beträgt 45 Me. V. Die Plots findest du angehängt. Weitere Zahlen: Totale Zählraten L: 5. 8/s R: 8. 1/s Error of Polarization after 1 s: 0. 86 (Die 0. 13 waren bei 100 s E 7 Teilchen, aber 30 mal. . ) Integriert man über 100 s (Strahllebensdauer ebenfalls 100 s) dann erhält man (100 -100/e)=63. 2 -fache Statistik also einen Fehler von 0. 86/sqrt(63. 2)=0. 108. Dies ist leider deutlich schlechter als die erhofften 0. 02, aber sicherlich kein Showstopper. Dauer eines Zyklus: 10 s für Injektion 100 s für E-Cooler-Spielerei 100 s für Polarisationsmessung 5 s für Extraktion =============== 215 s = 4 Min(240 s) In einer Stunde hätten wir also 15 Zyklen also einen Fehler von 0. 03. Nach 10 h: 0. 009. 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 57

Depolarization Study at COSY “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 Prediction for ANKE/COSY (4 weeks) • Distinguish electron effect from normal depolarization in COSY • Prerequisites: • Large beam lifetime • Large polarization lifetime 4 He Approved new Proposal for COSY empty 4 He Explore also option with co-moving electrons in cooler Frank Rathmann Road to polarized Antiprotons 58