Perspectives for Polarized Antiprotons (PAX: a brief history) Paolo Lenisa Università di Ferrara and INFN – Ferrara - ITALY P.Lenisa PAX story 1 ANKE-PAX Workshop Gatchina, June

We have proposed a method to polarize antiprotons by „spin-filtering“ 2 PAX story The beginning (2005) P.Lenisa

High Energy Storage Ring (HESR) for a beam of antiprotons 3 PAX story P.Lenisa PAX Proposal to FAIR (2005) 178 Collaborators 36 institutions (15 EU, 21 NON-EU)

P.Lenisa PAX story 4 Polarized antiprotons will pave the way to novel double (and single) spin observables: * Proton-spin structure: Complete map of transversity Flavour separation * Electromagnetic Form Factors Independent extraction of moduli of G E -G M in Time-Like region Test of the Rosenbluth separation in TL Measurement of the phase * Hard p-pbar scattering Additional measurement in one of the most intriguing puzzles of HF * Hadron spectroscopy * Low-t pbar-p scattering Spin and isospin dependence of nucleon-antinucleon interaction at low energy Physics with Polarized Antiprotons

P.Lenisa PAX story 5 M invariant Mass of lepton pair Inclusive DIS Semi-inclusive DIS Drell-Yan h 1 from Drell-Yan

P.Lenisa PAX story 6 Phase I: Fixed target experiments in CSR direction of antiprotons Physics: EMFF pbar-p elastic Independent from HESR running pol./unpol. Antiprotons in CSR 0.2 Gev/c<p<2.5 GeV/c polarized internal proton target (antiprotons)

P.Lenisa PAX story 7 Phase II: Asymmetric Proton-Antiproton Collider direction of protons direction of antiprotons Physics: Transversity EMFF pbar-p elastic polarized antiprotons in HESR (p=15 GeV/c) polarized protons in CSR (p=3.5 GeV/c)

P.Lenisa PAX story 8 Antiproton Polarizer Ring (APR) Ring Parameter Beam energy250 MeV Number of antip Ring acceptance250 mm mrad Betatron ampl. at IP< 0.3m Ring circumference86,5 m Snake strength2.4 Tm Injection/Extraction Target Electron Cooler Snake Ion-optics at IP Atomic Beam Source (ABS) parameter ABS flow in feeding tube1,5·10 17 /s Storage cell length40 cm Feeding tube diameter length 1 cm 15 cm Long. holding field300 mT Electron polarization0.9 Cell temperature100 K Final configuration after spin-filtering studies

P.Lenisa PAX story 9 … the PAC would like to stress again the uniqueness of the program with polarized anti-protons and polarized protons that could become available at GSI. Evaluation by QCD-PAC (March 2005) The STI requests R&D work to be continued on the proposed asymmetric collider experiment with both polarized anti-protons and protons: -to demonstrate that the required luminosity for decisive measurements can be reached (->accomplished) - to demonstrate that a high degree of anti-proton polarisation can be reached The STI believes that PAX should become part of the FAIR core research program based on its strong scientific merit once the open problems are convincingly solved. Recommendation of the STI of FAIR (Sept. 2005)

P.Lenisa PAX story 10 Luminosity Considerations for Collider Mode Particle species Momentum / GeV/c Number of bunches Total number of particles Beam lifetime / h Peak luminosity / cm -2 s -1 CSRHESR protonsantiproton · ~ 45~ · CSRHESR antiprotonsproton ~ 1500~ · “old” “new” Antiprotons in HESR -> protons Bunched beams -> coasting L>10 31 s -1 cm : I milestone for PAX

P.Lenisa PAX story 11 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) Spin filtering is the only succesfully tested technique Polarized Antiprotons

How to produce polarized antiprotons? Spin-filtering P.Lenisa Polarization build-up of a circulating particle beam by interaction with a polarized gas target Polarization build-up of a circulating particle beam by interaction with a polarized gas target 12

P.Lenisa PAX story 13 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

P.Lenisa PAX story 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 (2006)

P.Lenisa PAX story 15 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: Status in 2006

P.Lenisa PAX story 16 Eur. Phys. J. A 34, 447 (2007) A new idea (2007)

ep spin flip studies at COSY (2008) 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 17 PAX story P.Lenisa

PAX story 18 Principle of the Depolarization Measurement using co-moving electrons of the e-cooler (COSY-2008) 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

ep spin flip cross section at COSY No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than predicted b 19 PAX story 0 4  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. P.Lenisa 2008: II milestone for PAX

PAX at the AD (2009) PAX story 20 PAX target section Electron cooler Siberian snake Status in 2009: No contribution from EM interaction to polarization buildup. Spin-filtering only viable option Spin-dependence of pbar-p interaction unknown “Warm” solution for AD lattice P.Lenisa

Spin-dependence of the pbar-p interaction 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) P.Lenisa PAX story

22 Additional calculations… PLB 690 (2010) P.Lenisa Cross sections Projected polarizations

PAX story Stages of installation at AD P.Lenisa 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

P.Lenisa PAX story 24 The CERN Saga: PAX requests Oct. 2009PAX request to start phase I of installation not interfering with other experiments. Jan. 2010PAX informs SPSC of acknowledgement of ERC grant. Jan Meeting with Heuer Apr. 2011: PAX sends a draft to SPSC Committee with the successful result of commissioning of single elements of experimental apparatus and request to start installation of phase I in Winter 2011 shutdown, to initiate machine studies in 2012 and to avoid conflicts with ELENA installation during 2013 shutdown. Mar. 2012PAX sends to SPSC Committee a draft with the results of spin-filtering studies.

P.Lenisa PAX story 25 The CERN Saga: SPSC answer Oct. 2009unofficial response from the SPS Committee: … Taking into account the timeline and constraints of the various projects concerned, the SPSC encourages the PAX Collaboration to first perform their spin filtering measurements at COSY, and to report these to the Committee, following which the SPSC will further review the proposal. Jan. 2010Valle’s comment to ERC grant communication Congratulation for getting approval of an ERC advanced grant… The comments by many of the referees on the risk and schedule issues of your project confort me in the prudent attitude of the SPSC in respect with the necessary related AD modification … Looking forward to the PAX filtering measurements at COSY to proceed further with your review! Jan Meeting with Heuer Apr. 2011: SPSC 101 recommendation: The SPSC received a report by the PAX collaboration describing the progress of their program at COSY The SPSC remains concerned by the impact of PAX on the AD antihydrogen programme, the risk factors and manpower requirements for implementing the PAX apparatus at the AD. The Committee considers any installation before the long shutdown to be premature. The Committee is looking forward to the results of the spin filtering measurements. Mar. 2012Draft sent to SPSC with final results of August-October 2011 beamtime Apr. 2012mail from Vallee. We were pleased to see that you finally succeeded to perform a spin filtering measurement at COSY, showing good control of your apparatus as well as theoretical understanding of spin filtering for protons. However inbetween many positive developments have occured at the AD, leading to an updated program for the coming years which is very constrained on both the scientific and logistic points of view. We consider that PAX is now incompatible with this program.

P.Lenisa PAX story 26 PAX gets acknowledgment in the community: EU – grants – I3HP2 WP25 (PolAntiP) Depolarization studies Transverse spin-filtering at COSY – I3HP3 WP25 (PolAntiP) Longitudinal spin-filtering at COSY – Advanced Resarch Grant POLPBAR

P.Lenisa PAX story 27 The CERN Saga: PAX requests Oct. 2009PAX request to start phase I of installation not interfering with other experiments. Jan. 2010PAX informs SPSC of acknowledgement of ERC grant. Jan Meeting with Heuer Apr. 2011: PAX sends a draft to SPSC Committee with the successful result of commissioning of single elements of experimental apparatus and request to start installation of phase I in Winter 2011 shutdown, to initiate machine studies in 2012 and to avoid conflicts with ELENA installation during 2013 shutdown. Mar. 2012PAX sends to SPSC Committee a draft with the results of spin-filtering studies.

P.Lenisa PAX story 28 The CERN Saga Oct. 2009unofficial response from the SPS Committee: … Taking into account the timeline and constraints of the various projects concerned, the SPSC encourages the PAX Collaboration to first perform their spin filtering measurements at COSY, and to report these to the Committee, following which the SPSC will further review the proposal. Jan. 2010Valle’s comment to ERC grant communication Congratulation for getting approval of an ERC advanced grant… The comments by many of the referees on the risk and schedule issues of your project confort me in the prudent attitude of the SPSC in respect with the necessary related AD modification … Looking forward to the PAX filtering measurements at COSY to proceed further with your review! Jan Meeting with Heuer Apr. 2011: SPSC 101 recommendation: The SPSC received a report by the PAX collaboration describing the progress of their program at COSY The SPSC remains concerned by the impact of PAX on the AD antihydrogen programme, the risk factors and manpower requirements for implementing the PAX apparatus at the AD. The Committee considers any installation before the long shutdown to be premature. The Committee is looking forward to the results of the spin filtering measurements. Mar. 2012Draft sent to SPSC with final results of August-October 2011 beamtime Apr. 2012mail from Vallee. We were pleased to see that you finally succeeded to perform a spin filtering measurement at COSY, showing good control of your apparatus as well as theoretical understanding of spin filtering for protons. However inbetween many positive developments have occured at the AD, leading to an updated program for the coming years which is very constrained on both the scientific and logistic points of view. We consider that PAX is now incompatible with this program.

WASA e-cooler ANKE PAX Spin-filtering at COSY ( ) Main purpose: 1. Commissioning of the experimental setup for CERN/AD 2. Quantitative understanding of the machine parameters Main purpose: 1. Commissioning of the experimental setup for CERN/AD 2. Quantitative understanding of the machine parameters P.Lenisa 29 PAX story

ABS Breit-Rabi polarimet er Breit-Rabi polarimet er P.Lenisa 30 PAX story Commissioning ( ): : Installation and commissioning of the HERMES pol. target p D2D : Installation and commissioning of the ANKE beam polarimeter

Commissioning ( ): P.Lenisa 31 PAX story : Installation and commissioning of the low-β section : Studies of beam-lifetime limitations (  : 300 s  8000 s)

P.Lenisa PAX story 32 The CERN Saga: PAX requests Oct. 2009PAX request to start phase I of installation not interfering with other experiments. Jan. 2010PAX informs SPSC of acknowledgement of ERC grant. Jan Meeting with Heuer Apr. 2011: PAX sends a draft to SPSC Committee with the successful result of commissioning of single elements of experimental apparatus and request to start installation of phase I in Winter 2011 shutdown, to initiate machine studies in 2012 and to avoid conflicts with ELENA installation during 2013 shutdown. Mar. 2012PAX sends to SPSC Committee a draft with the results of spin-filtering studies.

P.Lenisa PAX story 33 The CERN Saga Oct. 2009unofficial response from the SPS Committee: … Taking into account the timeline and constraints of the various projects concerned, the SPSC encourages the PAX Collaboration to first perform their spin filtering measurements at COSY, and to report these to the Committee, following which the SPSC will further review the proposal. Jan. 2010Valle’s comment to ERC grant communication Congratulation for getting approval of an ERC advanced grant… The comments by many of the referees on the risk and schedule issues of your project confort me in the prudent attitude of the SPSC in respect with the necessary related AD modification … Looking forward to the PAX filtering measurements at COSY to proceed further with your review! Jan Meeting with Heuer Apr. 2011: SPSC 101 recommendation: The SPSC received a report by the PAX collaboration describing the progress of their program at COSY The SPSC remains concerned by the impact of PAX on the AD antihydrogen programme, the risk factors and manpower requirements for implementing the PAX apparatus at the AD. The Committee considers any installation before the long shutdown to be premature. The Committee is looking forward to the results of the spin filtering measurements. Mar. 2012Draft sent to SPSC with final results of August-October 2011 beamtime Apr. 2012mail from Vallee. We were pleased to see that you finally succeeded to perform a spin filtering measurement at COSY, showing good control of your apparatus as well as theoretical understanding of spin filtering for protons. However inbetween many positive developments have occured at the AD, leading to an updated program for the coming years which is very constrained on both the scientific and logistic points of view. We consider that PAX is now incompatible with this program.

PAX story p cluster targ. + STT (beam polarimetry) polarized target COSY ring Spin-flipper Spin-filtering at COSY (2011) P.Lenisa : III milestone for PAX (more about in Dieter’s talk)

P.Lenisa PAX story 35 The CERN Saga: PAX requests Oct. 2009PAX request to start phase I of installation not interfering with other experiments. Jan. 2010PAX informs SPSC of acknowledgement of ERC grant. Jan Meeting with Heuer Apr. 2011: PAX sends a draft to SPSC Committee with the successful result of commissioning of single elements of experimental apparatus and request to start installation of phase I in Winter 2011 shutdown, to initiate machine studies in 2012 and to avoid conflicts with ELENA installation during 2013 shutdown. Mar. 2012PAX sends to SPSC Committee a draft with the results of spin-filtering studies.

P.Lenisa PAX story 36 The CERN Saga Oct. 2009unofficial response from the SPS Committee: … Taking into account the timeline and constraints of the various projects concerned, the SPSC encourages the PAX Collaboration to first perform their spin filtering measurements at COSY, and to report these to the Committee, following which the SPSC will further review the proposal. Jan. 2010Valle’s comment to ERC grant communication Congratulation for getting approval of an ERC advanced grant… The comments by many of the referees on the risk and schedule issues of your project confort me in the prudent attitude of the SPSC in respect with the necessary related AD modification … Looking forward to the PAX filtering measurements at COSY to proceed further with your review! Jan Meeting with Heuer Apr. 2011: SPSC 101 recommendation: The SPSC received a report by the PAX collaboration describing the progress of their program at COSY The SPSC remains concerned by the impact of PAX on the AD antihydrogen programme, the risk factors and manpower requirements for implementing the PAX apparatus at the AD. The Committee considers any installation before the long shutdown to be premature. The Committee is looking forward to the results of the spin filtering measurements. Mar. 2012Draft sent to SPSC with final results of August-October 2011 beamtime Apr. 2012mail from Vallee. We were pleased to see that you finally succeeded to perform a spin filtering measurement at COSY, showing good control of your apparatus as well as theoretical understanding of spin filtering for protons. However inbetween many positive developments have occured at the AD, leading to an updated program for the coming years which is very constrained on both the scientific and logistic points of view. We consider that PAX is now incompatible with this program.

P.Lenisa PAX story 37 Spin-filtering: status in 2012 No contribution from EM interaction to polarization buildup. Only viable solution for “in-situ” polarization is spin-filtering Complete understanding of the physics spin-filtering mechanism Spin-dependence of proton antiproton interaction still unkown New prediction existing What about the physics case for polarized antiprotons?

38 L.L. Pappalardo - QNP2012 – Palaiseau – April Status in 2005: The nucleon collinear structure P.LenisaPAX story38

39 L.L. Pappalardo - QNP2012 – Palaiseau – April FF Status in 2005: Transversity totally unkown! P.LenisaPAX story39

40 L.L. Pappalardo - QNP2012 – Palaiseau – April Anselmino et al. Phys. Rev. D 75 (2007) Soffer bound xh 1 (x) d u xh 1 (x, k ) T u T d FF + Tensor charge 1: Quark-diquark model 2: Chiral quark soliton model 3: Lattice QCD 4: QCD sum rules M. Anselmino et al hep-ph: milestone in hadron physics: Transversity first extraction P.LenisaPAX story40

41 L.L. Pappalardo - QNP2012 – Palaiseau – April FF 2h Semi-Inclusive DIS 2011: II independent extraction! FF + -Survives integration over transverse momentum -Collinear factorization (simple product) -DGLAP evolution P.LenisaPAX story41

42 L.L. Pappalardo - QNP2012 – Palaiseau – April Phys.Rev.Lett.107:072004,2011 Bacchetta et al., PRL 107 (11) COMPASS 2010 HERMES 2011: II independent extraction! P.LenisaPAX story42

43 L.L. Pappalardo - QNP2012 – Palaiseau – April Sivers worm-gears Boer-Mulders pretzelosity helicity transversity momentum P.LenisaPAX story : A new field has born: The non-collinear structure of the nucleon

P.Lenisa PAX story 44 Physics case for pol.-pbar: status in 2012 A TT in DY production remains the unique direct way to access h 1 Pbar-p, pbar-d, p-p, p-d collider remains a unique machine to perform the flavour decomposition of transversity Interest in Transverse Momentum dependent effect has increased PAX physics case should be updated with the novel TMDs Interest in proton EMFF has developed: Different SL experiment addressing two-photon contribution Still no individual determination yet of FF in the TL region Necessity of a complete space-time description

P.Lenisa PAX story 45 PAX between past and future… Pol.-pbar remain a missing and unique tool for hadron physics Antiproton polarization: Spin-filtering only viable mechanism Complete understanding of spin-filtering Data on spin-dependence of pbar-p interaction needed Keep the option open… … but additional horizon in perspective: besides polarization technology for hadron physics … also polarization technology for fundamental physics The bridge to the new hera is the new PAX detector: Longitudinal spin-filtering Deuteron-breakup Time Reversal Invariance … (EDM) (More about in the talks of Alex, Christian and Yuri…)