Reviving Old Ideas: Polarised Antiproton Beams for Particle Collider Experiments

1. Many exciting old ideas with antiprotons, pre LEAR 1977 - 1984Revival for FAIR / FLAIRTrap experiments active at AD/CERN • pp →YY with S = ±1, ±2, ±3 (possibly YY atomic effects) • CP violation test:αΛ – αΛ = 0 Compare decay asymmetry of Λ and Λ • ELENA: cooled p beams down to 100keV (best stop experim.) Walter Oelert 10.6.10 • S=-2 hadronic states (B=1, 2, 3,…) via p stop. Recoilless! Highest precision • p stop and coincident channeling (dynamic unit cell tomography) • Annihilat. dynamics p+9Be→{αα}380keV • Breeding of cooledd beams in double ring collider. Max. rate, max. quality • Production of polarised p with filter method in cooler ring • …and more • Ideas get lost after a scientific lifetime

2. Ways to make polarised antiproton beams Dieter Grzonka, Kurt Kilian, Walter Oelert, IKP FZ-Jülich Production of antiprotons Spin filter method Antihyperon decay Polarised production Comparison MESON2010 10.–17. 6. 2010 Krakow Monday 14.6.2010

3. Production of antiprotons Convert collision energy into particle-antiparticle pairs energy→ p + p (in 3S1-?) Quasifree production p + p → p + (3p)0<ε<max Symmetric in cm system At 26 GeV/c beam 0 < ε <3360 MeV 2914 MeV/c > pcm > 0 If pcm< 150 MeV/c then S wave production 26 GeV/c beam D. Dekkers CERN PS 1968 K. Kilian et al.1977 pre LEAR memo to PSCC

4. pp→p+(3p) Assumption of quasifree nucleon-nucleon interaction is reasonable. Simple kinematical situation At maximum (3.65 GeV/c) antiprotons are collected, cooled and piled up in storage synchrotrons. From there extremely dense beams are delivered. At CERN (26 GeV) one gets one useful antiproton from 106 beam protons Average p flux I0 = 107 s-1 p lab. Momentum MC simulation

5. Spin filter method Suggested for the future ISR: P.L.Csonka, Nucl. Instr. Meth. 63 (1968) 247 If singlet and triplet cross sections are different, then an internal polarised target depletes one of the stored spin components faster than the other. Polarisation rises on the expense of intensity. Filtering below 1 GeV/c → Important ΔσCb σ = σH + ΔσCb Spin filtering for polarised antiprotons works only with cooling avoids beam blow up and losses by multiple scattering K.Kilian 1980, Pol. Conf. Lausanne, K.Kilian & D.Moehl 1982, Erice LEAR workshop

6. Spin-filtering at TSR: „FILTEX“ – proof-of-principle F. Rathmann et al., PRL 71, 1379 (1993) →Spin filtering works for protons PAX submitted new proposal to find out how well spin filtering works for antiprotons: Measurement of the Spin-Dependence of the pp Interaction at the AD Ring(CERN-SPSC-2009-012 / SPSC-P-337) Frank Rathmann Spin-filtering studies at COSY and AD 6

7. Polarization Buildup: Figure of Merit I/I0 0.8 Beam Polarization 0.6 0.4 0.2 0 2 6 4 t/τbeam statistical error of a double polarization observable (ATT) Measuring time t to achieve a certain error δATT t ~ FOM = P2·I (N ~ I) Other spin dependent processes? E.g. B. Schoch: scatter polarised photons Optimum time for Polarization Buildup given by maximum of FOM(t) tfilter = 2·τbeam P2Τ ? Ask F.R. Frank Rathmann Spin-filtering studies at COSY and AD 7 of 19

8. Λ → p + π+ plab(p) p π+ plab(π+) pcm Antihyperon decay Decay momentum in cm syst. is 101 MeV/c Decay makes p with helicity h = - 0.64. Lorentz boost creates transverse vector polarisation. First and so far only experiment with polarised 200 GeV p at Fermilab. Λ production with primary proton beam. At the end an average of 104 polarised p s-1 A. Bravar et al. Phys. Rev. Lett. 77, 2626 (1996)

9. FNAL experiment: A. Bravar et al. P.R.L.77,2626,(1996) NB: decay polarisation tagging below 0.5 mrad ! Experiment ~ km long

10. Useful antihyperon source in the GeV range (FAIR)pp → ΛΛ → pπ+ pπ- Decay direction of the hyperon defines the polarisation direction of the baryon. The two decay V are tags and spectrometers for each other Most important is geometrical reconstruction of all tracks Will not work with internal target (miserable multi track reconstruction, miserable trigger condition) Branching ratio σΛΛ /σtot = 10-3 cτΛ = 7.89 cm

11. Active sandwich target, tracker, baryon number identifier pp target efficiency ~ 10-2 Insert a flat target for p secondary scattering (done for Λ and Λ scattering)

12. CP violation test A= (αΛ + αΛ ) / (αΛ - αΛ ) = 0 P. D. Barnes et al., PR C54 1877 (1996) 105 pair events (at 1.642 and 1.918 GeV/c) [ A ] = 0.013 ± 0.022 (most precise so far) 100 times smaller error allows relevant CP test Needs 109 pair events or 2x1014 beam p (200 days) As byproduct: “beam” of 109 polarised decay p ΛΛproduction >95% triplet

13. Polarised production • Use the antiproton factory (nearly) as usual. • Cut out kinematical regions in the antiproton production spectrum which would dilute vector polarisation • Avoid pure s wave antiprotons • Cut one side in the horizontal angular distribution • Cut up and down angles • In addition avoid depolarisation in the cooler synchrotron

14. y x

15. S wave region Red lines: angular and momentum acceptance of AD

16. y x

17. Clean cuts may need a “pointlike” source, means a shorter production target Reduction 1/5 Cuts in kinematics Reduction 1/5 I/I0~ 1/25

18. p production and transport to AD - Necessary cuts in p distribution easily made in the existing beam line

19. Existing AD for p stop experiments Acceptance H, V (π mm mrad) 200/180 Acceptance Δp/p (%) ±3.2% Number of p injected 5 107 per cycle

20. AD tune diagram and Limit of spin stability (red lines)

21. CNI polarimeter reaction (coulomb-nuclear interference) allows to check if polarised p come out A = 4.5% maximum at t = - 0.0037 (GeV/c)2 corresponds to 38 mrad for p+p scattering at 3.5 GeV/c Polarisation test at CERN PS Cu (lH2 ) target on external beam 1.5 Tm dipole, 10 cm gap Straw tracker stacks before and after an lH2 analyser target on the p exit side. Adapted to 3.3 to 3.7 GeV/c p Trigger szintillators All in vacuum (Target and detectors exist at COSY TOF) A 2mbpolarim. react.

22. 38 mrad Measurement of antiproton polarisation detector components in vacuum Cerenkov detector n=1.03 scintillator hodoscope straw tubes ( track resolution ~ 100 μm ) antiproton production target 1 cm W PT< 700 MeV/c AD acceptance P= 3.4 – 3.6 GeV/c 1 m beam dump 24 GeV/c proton beam liquid hydrogen analyser target dipole magnet 1.6 T PT< 150 MeV/c ( s-wave ) 2% precision in p polarisation with 4 10^16 primary protons on 8mm W target

23. Comparison

24. Comparison

25. Thank you for your attention

26. polarisation dependent interactions • Spin filter idea with cooling (K. Kilian & D. Moehl1980Lausanne Pol. Conf., 1982 Erice LEAR workshop) Stimulated activities. • Most successful: E. Steffens and the FILTEX collaboration at the TSR in MPI Heidelberg. Proof that it works with protons. F. Rathmann PRL 71 1379 (1993) • Idea of spin transfer at very low energy e↑ + p → e + p↑ in beam – beaminteraction. PAX collaboration at COSY showed that there is no effect • D. Oellers et al. Phys. Lett. B674 (2009) 269 • Certainly polarisation dependent is interaction of circularly polarised photons with p • γ + p → n + πB. Schoch, EPJ 2010

27. Intensity loss - polarisation gain - FOM With a storage cell target (3 1013 pol. prot. cm-2 ) T0~ 2 days (hadronic) K.K. & D.M. Erice 1982

28. Geometry spectrometer (PS185 at LEAR) A stack of 23 wire chambers Decay spectrometer and polarimeter with full acceptance and very high precision