Status of the Experiment Polarizing antiprotons E. Steffens – University of Erlangen-Nürnberg for the PAX Collaboration E. Steffens - DSPIN PAX Experiment

Introduction We have proposed a method to polarize antiprotons by „spin-filtering“ 2 PAX ExperimentE. Steffens - DSPIN2009

Is it possible, and how, to provide polarized antiproton beams in HESR ? High Energy Storage Ring (HESR) for a beam of antiprotons 3 PAX ExperimentE. Steffens - DSPIN2009 Introduction New initiative, driven by the FAIR-project at GSI

Introduction Our knowledge about pp interaction is limited: Lack of polarization data! Restricted to single-spin (A 0n00, A 000n ) data. No spin-correlation data! Attempts at LEAR ( ) to produce polarized stored antiprotons were unsuccessful! Revival of ideas about stored polarized antiprotons: → PAX experiment at FAIR (see PAX TP hep-ex/ ) Polarized antiprotons: A missing tool Nucleon-antinucleon scattering at the parton level Hadron spectroscopy Nucleon-antinucleon scattering at low energy E. Steffens - DSPIN2009PAX Experiment 4

E. Steffens - DSPIN2009PAX Experiment 5 Physics Case: Transversity distribution of the nucleon in Drell-Yan:  Last leading-twist missing piece of the QCD description of the partonic structure of the nucleon  Direct measurement 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 (  )  + many polarization observables in pp scattering PAX → Polarized Antiprotons

Quark Transversity Distribution in Drell-Yan Double transverse spin asymmetry: First direct measurement: No competitive processes 6 PAX ExperimentE. Steffens - DSPIN2009

Plan of talk  Polarizing antiprotons …  Proposals, ideas, calculations, …  Present status of pp interaction models  Experiments FILTEX (TSR) e p spin flip cross section measurement at COSY Spin-filtering at AD/CERN Spin-filtering at COSY  Conclusion Task taken on by the PAX Collaboration: ~100 members 16 institutions Spokespersons: P. Lenisa (Ferrara), F. Rathmann (Jülich) 7 PAX ExperimentE. Steffens - DSPIN2009

Two Methods: Spin-dependent loss versus spin flip For an ensemble of spin ½ particles with projections + (  ) and – (  ) 8 PAX ExperimentE. Steffens - DSPIN2009

Proposed methods: Spin flip → Need for an experimental test of this idea! 9 PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: Idea Use proton beam and co-moving electrons Turn experiment around: p e → p e into p e → p e i.e. observe depolarization of a polarized proton beam COSY electron cooler (detuned) Velocity mismatch 10 PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: Tools p e-cooler ANKE cluster target & STT T p = 49.3 MeV Use (transversely) polarized proton beam circulating in COSY Switch on (detuned) electron cooler to depolarize proton beam Analyze proton polarization with internal D 2 -cluster target of ANKE 11 PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: Feasibility Detuning e-cooler for 5 s only ensures that proton momentum stays fixed. After detuning, proton energy slowly follows electron energy:  U = 245 V   v e = 1.5·10 -3 c  f R = 40 Hz in 5 s:  v p /  v e ~ PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: Polarimetry pd elastic scattering: detection in two (L-R) symmetric Silicon Tracking Telescopes p D2D2 Deuteron identification d p 13 PAX ExperimentE. Steffens - DSPIN2009

ep spin flip cross section at COSY: Result No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than the predicted b. 14 PAX ExperimentE. Steffens - DSPIN  10 7 |Relative velocity of electrons in proton rest frame| (c)  depol (barn) Nominal proton energy in electron rest frame (keV)       10 7 D.Oellers et al., Physics Letters B 674 (2009) 269 Meanwhile, Mainz group discovered numerical problems in the calculation → two errata. Analytical calculation by Novosibirsk group (Strakhovenko et al): Spin flip negligible!

Spin-dependent loss: Spin-filtering Polarization build-up of an initially unpolarized particle beam by repeated passage through a polarized hydrogen target in a storage ring: 15 PAX ExperimentE. Steffens - DSPIN2009

P beam polarization Q target polarization k || beam direction σ tot = σ 0 + σ 1 ·P·Q + σ 2 ·(P·k)(Q·k) transverse case:longitudinal case: For initially equally populated spin states:  (m=+½) and  (m=-½) Unpolarized anti-p beam Polarized target Polarization Buildup E. Steffens - DSPIN200916PAX Experiment

P beam polarization Q target polarization k || beam direction σ tot = σ 0 + σ 1 ·P·Q + σ 2 ·(P·k)(Q·k) transverse case:longitudinal case: For initially equally populated spin states:  (m=+½) and  (m=-½) Unpolarized anti-p beam Polarized target Polarized anti-p beam Polarization Buildup E. Steffens - DSPIN200917PAX Experiment

E. Steffens - DSPIN2009PAX Experiment 18 statistical error of a double polarization observable (A TT ) Measuring time t to achieve a certain error δ ATT t ~ FOM = P 2 ·I Figure of Merit and optimum filtering time (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

Spin-filtering at TSR: „FILTEX“ – proof-of-principle → Spin filtering works for protons F. Rathmann et al., PRL 71, 1379 (1993) 19 PAX ExperimentE. Steffens - DSPIN2009 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 / SPSC-P-337) Polarization build-up process quantitatively understood! TSR spin filtering with protons: σ exp =73 ± 6 mb Average theoretical value: σ theo =86 ± 2 mb Good agreement: ~2 σ discrepancy Brief summary in: D. Oellers et al., Phys. Lett. B 674, 269 (2009).

20 pp interaction models E. Steffens - DSPIN2009PAX Experiment

Spin-dependence of the pbar-p interaction E. Steffens - DSPIN2009 PAX Experiment 21 Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991). Model OBEPF: J. Haidenbauer, K. Holinde, A.W. Thomas, Phys. Rev. C 45, 952 (1992). Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995). Measurement of the polarization buildup equivalent to the determination of σ 1 and σ 2 Once a polarized antiproton beam is available, spin-correlation data can be measured at AD ( MeV)

PAX at the AD (the only place worldwide) E. Steffens - DSPIN2009PAX Experiment 22 PAX target section Electron cooler Siberian snake

E. Steffens - DSPIN2009PAX Experiment 23 Experimental Setup Atomic Beam Source Six additional quadrupoles Breit-Rabi Polarimeter Target chamber: Detector system + storage cell

Polarized Target E. Steffens - DSPIN2009 PAX Experiment 24 Q x Q y Q z : Quantization axis is reoriented by a weak magnetic guide field of 10 G Injected hyperfine states from ABS BRP measures occupation numbers of different HFS + corrections → Target Polarization x y z

ABS Target chamber Breit-Rabi polarimeter Electric power Cooling water Atomic Beam Source and Breit-Rabi Polarimeter E. Steffens - DSPIN2009 PAX Experiment 25 COSY/AD beam axis

Atomic Beam Source and Breit-Rabi Polarimeter E. Steffens - DSPIN2009PAX Experiment26 BRP vacuum HFT QMAs ABS/TC vacuum Bake-out Coils power

Target chamber, cell and detector system E. Steffens - DSPIN2009PAX Experiment27 Storage cell: jet density  100 Silicon strip detectors Atomic beam Stored beam Guide field coils (x, y, z) movable flow limiter

E. Steffens - DSPIN2009PAX Experiment28 12 x 2 HERMES recoil detectors + 12 x 1 PAX STT detectors Full system consisting of 36 Detectors Target cell + Detectors with cooling system and shielding Detectors surrounding the openable storage cell 1 PAX Layer 2 HERMES1 PAX STT Detector System

Openable storage cell E. Steffens - DSPIN2009PAX Experiment29 closedopened AD beam envelope at injection requires openable storage cell P. Belochitsky - CERN

AD optics (P. Belochitsky - CERN) E. Steffens - DSPIN2009PAX Experiment30 At injection“Squeezed” 1.Beam is injected with low-β section moderately powered on. 2.At experiment energy (T<450 MeV), β-functions are „squeezed“ by fully powering on low-β magnets. 3.Then storage cell is closed and gas is injected.

Expected polarizations after filtering for two lifetimes transverse A D 31 PAX ExperimentE. Steffens - DSPIN2009 longitudinal

Expected polarizations after filtering for two lifetimes 32 PAX ExperimentE. Steffens - DSPIN2009 Model A: Production of longitudinal polarization θ acc > 13 mrad → P(2∙τ b ) changes only marginally Limit

Main phases of installation at AD E. Steffens - DSPIN PAX Experiment Phase 1 Phase 2 Phase 3 Installation of six magnets for the low-β insertion Spin-filtering measurements up to 70 MeV with transverse beam polarization Installation of the target chamber: Machine acceptance studies. Stacking studies

Time plan for AD E. Steffens - DSPIN2009PAX Experiment 34 PhaseTimeDescription 1Shutdown 2009/ weeks 3 weeks Installation of six magnets for the low-β insertion. Commissioning of the low-β section: demonstrate compatibilty with AD users PAX optics implementation 2a 2b Shutdown 2010/11 2 weeks in weeks in 2011 Shutdown 2011/12 2 weeks in 2012 Installation of the target chamber. Machine acceptance studies. Stacking studies (split in sessions). Installation of ABS, BRP, and detector system. Measurement of H target polarization with antiproton beam. 36 weeks in 2012Spin-filtering measurements using H and D target up to 70 MeV with transverse beam polarization. 4Shutdown 2012/13 4 weeks in 2013 Shutdown possibly extended up to six months. Implementation and commissioning of electron cooler upgrade to 300 keV. Commissioning of the electron cooler with beam. 56 weeks in 2013Spin-filtering measurements using H and D target up to 430 MeV with transverse beam polarization. 6Shutdown 2013/14Implementation of the Siberian snake. 78 weeks in 2014Spin-filtering measurements with H and D target up to 430 MeV with longitudinal beam polarization. PAX ready to set sequence into motion by installing low-β section into the AD end of this year!

E. Steffens - DSPIN2009PAX Experiment 35 Phase 1: All AD magnets remain in place Installation of six magnets for the low-β insertion. Commissioning of the low-β section Central quad taken out only after commissioning Same performance of machine as before Layout of vacuum system, based on suggestions by the CERN group (→ NEG works) Pumping crosses Turbo pump 200 l/s Ion getter pump 400 l/s 2 x SAES GP500 NEG pump 1900 l/s

Spin-filtering studies at COSY ABS BRP COSY-Quadupoles Low-β quadrupoles Target chamber with storage cell and detector system E. Steffens - DSPIN PAX Experiment Main purpose: 1.Repeat spin-filtering with protons. No surprises expected 2.Commissioning of the experimental setup for AD Proposal to COSY PAC submitted in July 2009 Low-β magnet installation at COSY

Time plan for COSY PhaseTimeBeam timeDescription 1Summer 2009 Fall weeks Installation of four magnets for the low–β insertion. Commissioning of the low–β section and machine acceptance measurement. 2Summer week 2×1 week 4 weeks Installation of the target chamber, ABS, BRP and a detection system for spin–filtering. Measurement of the acceptance angle at the target position. Measurement of the target polarisations in dp and pd. Spin filtering at COSY with transverse beam polarisation. 3Summer weeks Installation of the complete AD detector. Commissioning of the installed equipment. 4Summer week 4 weeks Implementation of the two additional solenoids in the injection beam line, ANKE ABS and detectors. Commissioning of the Siberian snake. Spin filtering at COSY with longitudinal beam polarisation. 5Summer weeks Implementation of the AD Siberian snake. Commissioning of the AD Siberian snake. E. Steffens - DSPIN2009PAX Experiment 37

Conclusions  Polarized antiprotons: a missing tool for spin physics  First measurement of the spin-dependence of pbar-p interaction  AD unique machine!  Commissioning of equipment at COSY  Clear strategy and commitment by PAX Collaboration 38 PAX ExperimentE. Steffens - DSPIN2009 Now and here or never!

Spare transparencies E. Steffens - DSPIN2009PAX Experiment 39

Hadron Physics „Dream Machine“ … an asymmetric (double-polarized) proton (15 GeV/c) – antiproton (3.5 GeV/c) collider using HESR, CSR and APR 40 PAX ExperimentE. Steffens - DSPIN2009 p p

PAX Experiment 41 h 1u from p  -p  Drell-Yan at PAX PAX :    s=x 1 x 2 ~ valence quarks (A TT large ~ ) u-dominance |h 1u |>|h 1d | Similar predictions by Efremov et al., Eur. Phys. J. C35, 207 (2004) Anselmino et al. PLB 594,97 (2004) 1year run: 10 % precision on the h 1u (x) in the valence region P p =10% P p =30%

Proposed methods: Some history … EPAC 1988  Stern-Gerlach splitting never tried (huge effort) 42 PAX ExperimentE. Steffens - DSPIN2009

PAX Experiment 43 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 Figure of Merit and optimum filtering time (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

ep spin flip studies at COSY: Principle (1) p e-cooler ANKE cluster target & STT T p = 49.3 MeV Use (transversely) polarized proton beam circulating in COSY Switch on (detuned) electron cooler to depolarize proton beam Analyze proton polarization with internal D 2 -cluster target of ANKE 44 PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: Feasibility Detuning e-cooler for 5 s only ensures that proton momentum stays fixed. After detuning, proton energy slowly follows electron energy:  U = 245 V   v e = 1.5·10 -3 c  f R = 40 Hz in 5 s:  v p /  v e ~ PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: Cycle setup time (s) Target offTarget on Number of Beam Particles T detuned 49·5 s T nominal 49·5 s   10 8 Ecooler Voltage (V) tuned cycledetuned cycle T nominal 49·5 s T electron-off 49·5 s Compare cycle-by-cycle: No electrons to detuned electrons 46 PAX ExperimentE. Steffens - DSPIN2009

Beam current 0 P tuned P detuned Determine P tuned and P detuned from identical cycles, except for detuned cooler 47 PAX ExperimentE. Steffens - DSPIN2009 ep spin flip studies at COSY: Super Cycle

Depolarization Studies at COSY: Results (1) pd elastic scattering: detection in two (L-R) symmetric silicon tracking telescopes p D2D tuned cooler detuned cooler Proton kinetic energy in electron rest frame (keV) Beam Polarization Tuned and detuned beam polarizations 48 PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: Results (1) pd elastic scattering: detection in two (L-R) symmetric silicon tracking telescopes p D2D2 Measured ratio of polarizations vs Proton Kinetic energy in electron rest frame Nominal proton kinetic energy in electron rest frame (keV) P detuned /P tuned 49 PAX ExperimentE. Steffens - DSPIN2009

ep spin flip studies at COSY: New calc´s ~ 1 mb → No effect expected! 50 PAX ExperimentE. Steffens - DSPIN2009

Atomic Beam Source and Breit-Rabi Polarimeter E. Steffens - DSPIN2009PAX Experiment51 BRP vacuum HFT QMAs ABS/TC vacuum Bake-out Coils power

Development of cryopump for target chamber E. Steffens - DSPIN PAX Experiment Task taken on by Gatchina group TPH 1600 Gate valves Active baffles 8 K Shield 75 K Cryo chamber Cold head

Question 15: Vacuum System for Spin Filtering at AD E. Steffens - DSPIN2009PAX Experiment 53 Intensity of ABS = 6x10 16 H/s (2 HFS) Q = 3x10 16 H 2 /s = 1.24x10 -3 mbarl/s Effusive flow out of one side of the target cell into the acceptance angle of the flow limiter  FL with diameter d FL : Q cell = 1.5x10 16 (1-cos 2  FL ) H 2 /s Direct flow out of the target chamber through the flow limiters Q TC =p TC x C Conductance of the flow limiter: C=302 (134) l/s for d FL =30 (20) mm Pressure in the adjacent beam line p BL = (Q cell +Q TC )/2500 l/s (NEG) Cryopump S=20000 l/s p TC = Q/S = 6.2x10 -8 mbar p TC

Crucial: Vacuum system E. Steffens - DSPIN2009PAX Experiment54

pp and np scattering experiments at LEAR E. Steffens - DSPIN2009PAX Experiment 55

E. Steffens - DSPIN2009PAX Experiment 56 np cross sections

E. Steffens - DSPIN2009PAX Experiment 57 pp integrated cross sections

E. Steffens - DSPIN2009PAX Experiment 58 pp differential cross sections

E. Steffens - DSPIN2009PAX Experiment 59 pp differential cross sections

E. Steffens - DSPIN2009PAX Experiment 60 pp analyzing powers

E. Steffens - DSPIN2009PAX Experiment 61 pp → nn differential cross sections

E. Steffens - DSPIN2009PAX Experiment 62 pp → nn differential cross sections

E. Steffens - DSPIN2009PAX Experiment 63 pp → nn differential cross sections

E. Steffens - DSPIN2009PAX Experiment 64 pp → nn analyzing powers

Depolarization parameter D 0n0n E. Steffens - DSPIN2009PAX Experiment 65

Novosibirsk Model predictions for the antiproton beam polarization after filtering for two beam lifetimes with Hydrogen target E. Steffens - DSPIN2009PAX Experiment66 V.F. Dmitriev et al., NIM B 266, 1122 (2008)

E. Steffens - DSPIN2009PAX Experiment 67 of 19 First Measurement of Polarization Lifetime at T p = 45 MeV (Nov. 2007)

Expected antiproton beam polarization AD machine acceptance: A x =180  m, A y =200  m Cooled 2  beam emittance = 1  m Realistic calculation of  acc (mrad) using AD lattice functions and triangular density distribution in storage cell Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) 68PAX ExperimentE. Steffens - DSPIN2009 Storage cell radius (mm) Acceptance angle (mrad) 8

Beam lifetime E. Steffens - DSPIN2009PAX Experiment Single-Coulomb scattering at the target dominates beam loss

Polarization buildup cross section E. Steffens - DSPIN2009PAX Experiment70

COSY low-  section cell Storage cell at COSY is not required to be openable E. Steffens - DSPIN PAX Experiment

Time plan for COSY PhaseTimeBeam timeDescription 1Summer 2009 Fall weeks Installation of four magnets for the low–β insertion. Commissioning of the low–β section and machine acceptance measurement. 2Summer week 2×1 week 4 weeks Installation of the target chamber, ABS, BRP and a detection system for spin–filtering. Measurement of the acceptance angle at the target position. Measurement of the target polarisations in dp and pd. Spin filtering at COSY with transverse beam polarisation. 3Summer weeks Installation of the complete AD detector. Commissioning of the installed equipment. 4Summer week 4 weeks Implementation of the two additional solenoids in the injection beam line, ANKE ABS and detectors. Commissioning of the Siberian snake. Spin filtering at COSY with longitudinal beam polarisation. 5Summer weeks Implementation of the AD Siberian snake. Commissioning of the AD Siberian snake. E. Steffens - DSPIN2009PAX Experiment 72 No way to measure P z with an unpolarized target → P z ∙ Q z ∙ A zz

Conclusions  Polarized antiprotons: a missing tool for spin physics  First measurement of the spin-dependence of pbar-p interaction  AD unique machine!  Commissioning of equipment at COSY  Clear strategy and commitment by PAX Collaboration Now and here or never! 73 PAX ExperimentE. Steffens - DSPIN2009 Georg Christoph Lichtenberg ( ) If you want to see something new, you have to create something new.