Towards Polarized Antiprotons at FAIR

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1 Towards Polarized Antiprotons at FAIR Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich Kyoto, October 3, 2006

2 Outline PAX physics program Accelerator configuration for FAIR Towards polarized antiprotons Frank Rathmann Towards Polarized Antiprotons at FAIR 2of 30

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 h 1 q (x,q 2 ) of the proton for valence quarks (A TT in Drell-Yan >0.2) transversely polarized proton beam or target ( ) transversely polarized antiproton beam ( ) Frank Rathmann Towards Polarized Antiprotons at FAIR 3of 30

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 Frank Rathmann Towards Polarized Antiprotons at FAIR 4of 30

Leading Twist Distribution Functions Probabilistic interpretation in helicity base: quark proton quark proton f 1 (x) g 1 (x) h 1 (x) R R + 1/2 1/2 1/2 1/2 R R - L L L L 1/2 1/2 1/2 1/2 R L 1/2-1/2

5 Leading Twist Distribution Functions Probabilistic interpretation in helicity base: quark proton quark proton f 1 (x) g 1 (x) h 1 (x) R R + 1/2 1/2 1/2 1/2 R R - L L L L 1/2 1/2 1/2 1/2 R L 1/2-1/2 q(x) spin averaged (well known) q(x) helicity diff. (known) No probabilistic interpretation in the helicity base (off diagonal) Transversity base u = 1/ 2(u R + u L ) u = 1/ 2(u R -u L ) - δq(x) helicity flip (unknown)

6 Transversity Properties: - Probes relativistic nature of quarks - No gluon analog for spin-1/2 nucleon 2 - Different Q evolution than q - Sensitive to valence quark polarization Chiral-odd: requires another chiral-odd partner p p l + l - X ep e h X Impossible in DIS Direct Measurement Indirect Measurement: Convolution of with unknown fragment. fct. Frank Rathmann Towards Polarized Antiprotons at FAIR 6of 30

7 Transversity in Drell-Yan processes Polarized antiproton beam Polarized proton target (both transverse) l + l - q 2 =M 2 q q T p q L p 2 q 2 q 2 e h (x, M )h (x, M ) q A dσ dσ q TT = â TT 2 2 dσ + dσ e q(x, M )q(x, M 2 ) q q 1 2 q = u, u,d, d,... M invariant Mass of lepton pair Frank Rathmann Towards Polarized Antiprotons at FAIR 7of 30

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 G E -G m separation test of Rosenbluth separation in the time-like region A y τ = q Polarization P y (for θ = 45 ) = E M [( 1+ cos ( θ) ) G + sin ( θ) G / τ] / 4m 2 p S. Brodsky et al., Phys. Rev. D69 (2004) sin(2θ) Im(G M 1/Q fit (log 2 Q 2 )/Q 2 fit impr. (log 2 Q 2 )/Q 2 fit IJL fit * q 2 (GeV 2 ) G ) E τ Frank Rathmann Towards Polarized Antiprotons at FAIR 8of 30

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 Frank Rathmann Towards Polarized Antiprotons at FAIR 9of 30

PAX Collider Setup PAX Collider Luminosity> 10 31 cm -2 s -1

10 PAX Collider Setup PAX Collider Luminosity> cm -2 s -1 Frank Rathmann Towards Polarized Antiprotons at FAIR 10 of 30

11 Polarized Antiprotons Intense beam of polarized antiprotons was never produced: Conventional methods (ABS) not appliable Polarized antiprotons from antilambda decay I < s -1 (P 0.35) Antiproton scattering off liquid H 2 target I < 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 filtering is the only succesfully tested technique Frank Rathmann Towards Polarized Antiprotons at FAIR 11 of 30

12 Principle of spin-filtering σ tot = σ 0 + 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: σ tot± = σ 0 ± σ Q σ tot± = σ 0 ± ( σ + σ ) Q Unpolarized anti-p beam Polarized H target Frank Rathmann Towards Polarized Antiprotons at FAIR 12 of 30

13 Principle of spin-filtering σ tot = σ 0 + 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: σ tot± = σ 0 ± σ Q σ tot± = σ 0 ± ( σ + σ ) Q Unpolarized Polarized anti-p beam Polarized H target Frank Rathmann Towards Polarized Antiprotons at FAIR 13 of 30

14 1992 Filter Test at TSR with protons Experimental Setup Frank Rathmann Towards Polarized Antiprotons at FAIR 14 of 30

15 1992 Spin Filter Test at TSR with protons Experimental Setup Results T=23 MeV F. Rathmann. et al., PRL 71, 1379 (1993) Frank Rathmann Towards Polarized Antiprotons at FAIR 15 of 30

16 Two interpretations of FILTEX result 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? 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 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 σ 1 = 85.6 mb (-> more in next talk by N.N. Nikolaev) Frank Rathmann Towards Polarized Antiprotons at FAIR 16 of 30

17 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 Towards Polarized Antiprotons at FAIR 17 of 30

18 Spin Filtering studies at COSY Goal: Understanding the spin filtering mechanism: Disentangle electromagnetic and hadronic contributions to the polarizing cross section Frank Rathmann Towards Polarized Antiprotons at FAIR 18 of 30

19 Polarizing cross sections from the two models TSR only hadronic (Budker-Jülich) - electromagnetic + hadronic (Meyer-Horowitz) A measurement of σ eff to 10% precision requires polarization measurement with P/P = 10%. Frank Rathmann Towards Polarized Antiprotons at FAIR 19 of 30

20 How to disentangle hadronic and electromagnetic contributions to σ 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 (P z = 0), and Pure nuclear polarized target (P e =0) Inj. states P e P z Interaction Holding field 1> Elm. + had. transv. + longit. weak (20 G) 1> + 4> 1> + 2> only had. only elm. longitudinal strong (3kG) 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. Frank Rathmann Towards Polarized Antiprotons at FAIR 20 of 30

21 Experimental setup Low-beta section Polarized target (former HERMES target) Detector Snake Commissioning of AD setup Frank Rathmann Towards Polarized Antiprotons at FAIR 21 of 30

rates Larger polarization buildup rate due to larger acceptance Use of former HERMES

22 Low beta section β new x,y = 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 Frank Rathmann Towards Polarized Antiprotons at FAIR 22 of 30

23 ANKE vs new IP: Acceptance and Lifetime Cross sections only hadronic - electromagnetic + hadronic Lifetimes ANKE new-ip COSY average ψ acc = 1 mrad.. ψ acc = 2 mrad Frank Rathmann Towards Polarized Antiprotons at FAIR 23 of 30

24 Figure of Merit at new IP Calculation based on Budker-Jülich T opt ~ 55 MeV Frank Rathmann Towards Polarized Antiprotons at FAIR 24 of 30

25 ANKE vs new IP: Polarization Expectations based on Budker-Jülich: T = 40 MeV N inj =1.5x10 10 protons Polarization [%] New IP ANKE PIT Filter. time Polar. Total rate Meas. Time ( P/P=10%) ANKE 2τ = 16 h 1.2 % 7.5x10 2 s min 5τ = 42 h 3.5 % 5x10 s min New IP 2τ = 5 h 16 % 2.2x10 4 s -1 1 s 5τ = 13 h 42 % 1.5x10 3 s -1 < 1 s Frank Rathmann Towards Polarized Antiprotons at FAIR 25 of 30

Silicon telescopes Thin 5µm Teflon cell needed Angular resolution for the forward particle for p-pbar

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 Frank Rathmann Towards Polarized Antiprotons at FAIR 26 of 30

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 Electrons in 4 He storage cell 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 New Proposal for COSY turned in this week 4 He empty 4 He Frank Rathmann Towards Polarized Antiprotons at FAIR 27 of 30

AD ring at CERN Study of spin filtering in pbar-p (pbar-d) scattering Target Snake T= 5-2.

28 AD ring at CERN Study of spin filtering in pbar-p (pbar-d) scattering Target Snake T= GeV N p = E-cooler 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 Antiproton Beam Polarization (Hadronic Interaction: Longitudinal Case) P beam lifetimes Ψ acc =20 mrad P beam lifetimes Ψ acc =10-50 mrad Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) 0.05 Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) T (MeV) T (MeV) Frank Rathmann Towards Polarized Antiprotons at FAIR 29 of 30

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

Spin-physics with Polarized Antiprotons at GSI

http://www.fz-juelich.de/ikp/pax Spin-physics with Polarized Antiprotons at GSI Frank Rathmann Forschungszentrum JülichJ Spin Physics and Beyond, Madison, June 10, 2005 QCD Physics at FAIR (CDR): unpolarized