PAX project at FAIR http://www.fz-juelich.de/ikp/pax Marco Contalbrigo – INFN and Università di Ferrara - ITALY Tbilisi, 5 September 2006 M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Physics Program M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments Fixed target experiment (√s<2 GeV): pol./unpol. pbar beam (p<4 GeV/c) internal H polarized target Nucleon structure: polarized reactions Cerenkov pbar-p elastic M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Elastic Scattering Low-E pp, pd at AD Polarization build-up studies T=10.85 GeV High-t pp from ZGS, AGS Spin-dependence at large-P (90°cm): Hard scattering takes place only with spins . t=-2Pcm2(1-cos(cm)) Similar studies in pp elastic scattering D.G. Crabb et al., PRL 41, 1257 (1978) M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments Nucleon structure: polarized reactions Cerenkov pbar-p elastic Proton EFFs Fixed target experiment (√s<2 GeV): pol./unpol. pbar beam (p<4 GeV/c) internal H polarized target M. Contalbrigo PAX Polarized Antiproton Experiments

Proton Electromagnetic Formfactors COMPARISON BETWEEN ROSENBLUTH SEPARATION AND POLARIZATION TRANSFER TECNIQUES JLab PT data SLAC RS data TWO DIFFERENTS METHODS TWO DIFFERENTS RESULTS (Phys. Rev.C 68 (2003) 034325) M. Contalbrigo PAX Polarized Antiproton Experiments

Proton Electromagnetic Formfactors Double-spin asymmetry in pp → e+e- independent GE-Gm separation test of Rosenbluth separation in the time-like region Single-spin asymmetry in pp → e+e- Measurement of relative phases of magnetic and electric FF in the time-like region S. Brodsky et al., Phys. Rev. D69 (2004) M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments Nucleon structure: polarized reactions Asymmetric collider (√s=15 GeV): polarized antiprotons in HESR (p=15 GeV/c) polarized protons in CSR (p=3.5 GeV/c) Parton distribution: transversity Cerenkov Drell-Yan pbar-p elastic Proton EFFs Fixed target experiment (√s<2 GeV): pol./unpol. pbar beam (p<4 GeV/c) internal H polarized target M. Contalbrigo PAX Polarized Antiproton Experiments

Leading Twist Distribution Functions proton proton’ quark quark’ Probabilistic interpretation in helicity base: 1/2 R 1/2 L f1(x) + q(x) spin averaged (well known) 1/2 R 1/2 L g1(x) - Dq(x) helicity diff. (known) No probabilistic interpretation in the helicity base (off diagonal) 1/2 -1/2 R L h1(x) Transversity base u = 1/2(uR + uL) u = 1/2(uR - uL) -   dq(x) helicity flip (unknown) M. Contalbrigo PAX Polarized Antiproton Experiments

Transversity Chiral-odd: requires another chiral-odd partner Properties: Probes relativistic nature of quarks No gluon analog for spin-1/2 nucleon Different Q2 evolution than Dq Sensitive to valence quark polarization See talk by M. Anselmino Chiral-odd: requires another chiral-odd partner epe’X epe’hX ppe+e-X Impossible in DIS Direct Measurement Indirect Measurement: convolution with unknown fragment. fct. h1 must couple to another chiral-odd function h1 x h1 h1 x Collins function M. Contalbrigo PAX Polarized Antiproton Experiments

Drell-Yan process Plenty of single and double spin effects Elementary LO interaction: M invariant Mass of lepton pair M. Contalbrigo PAX Polarized Antiproton Experiments Plenty of single and double spin effects

h1q (x, Q2) small and with much Δq(x, Q2) and q(x, Q2) at small x h1 from p-p Drell-Yan 1 2 h1q (x ,Q2) h1q (x, Q2) small and with much slower evolution than Δq(x, Q2) and q(x, Q2) at small x - h1q (x, Q2) ≠ Barone, Calarco, Drago Martin, Schäfer, Stratmann, Vogelsang RHIC: M2/s=x1x2~10-3 → sea quarks (ATT ~ 0.01 ) JPARC/U70: M2/s=x1x2~10-1-10-2 → valence and sea (ATT ~ 0.1 ) PAX: M2/s=x1x2~10-1-10-2 → valence and sea (ATT ~ 0.1 ) M. Contalbrigo PAX Polarized Antiproton Experiments

h1 from pbar-p Drell-Yan M2 > 4 GeV2 Anselmino et al. PLB 594,97 (2004) Similar predictions by Efremov et al., Eur. Phys. J. C35, 207 (2004) PAX : M2/s=x1x2~0.02-0.3 → valence quarks (ATT large ~ 0.2-0.4 ) M. Contalbrigo PAX Polarized Antiproton Experiments

DY events distribution p-pbar p-p M2/s = x1x2 ~ 0.02-0.3 At x1=x2 ATT ~ h1u2 Extraction of h1u for x<0.2 Direct measurement of h1u for 0.05<x<0.5 pbarp+pp complete mapping of transversity M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments Nucleon structure: polarized reactions Asymmetric collider (√s=15 GeV): polarized antiprotons in HESR (p=15 GeV/c) polarized protons in CSR (p=3.5 GeV/c) Parton distribution: transversity Cerenkov Drell-Yan pbar-p elastic SSA Proton EFFs Fixed target experiment (√s<2 GeV): pol./unpol. pbar beam (p<4 GeV/c) internal H polarized target M. Contalbrigo PAX Polarized Antiproton Experiments

Single Spin Asymmetries (and their partonic origin) π Pq k┴ Collins effect = fragmentation of polarized quark depends on Pq· (pq x k┴) pq q P k┴ Sivers effect = number of partons in polarized proton depends on P · (p x k┴) p Pq q Boer-Mulders effect = polarization of partons in unpolarized proton depends on Pq · (p x k┴) k┴ p Collins: chiral-odd Sivers: chiral-even Boer-Mulders: chiral-odd These effects may generate SSA See talk by O. Ivanov, M. Anselmino, O.Shevchenko M. Contalbrigo PAX Polarized Antiproton Experiments

SSA, pp → πX BNL-AGS √s = 6.6 GeV 0.6 < pT < 1.2 p↑p E704 √s = 20 GeV 0.7 < pT < 2.0 p↑p STAR-RHIC √s = 200 GeV 1.1 < pT < 2.5 p↑p E704 √s = 20 GeV 0.7 < pT < 2.0 p↑p SSA, pp → πX M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Collins HERMES Sivers See talk by L. Pappalardo SSA, SIDIS M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments Nucleon structure: polarized reactions Asymmetric collider (√s=15 GeV): polarized antiprotons in HESR (p=15 GeV/c) polarized protons in CSR (p=3.5 GeV/c) Parton distribution: transversity Cerenkov Drell-Yan pbar-p elastic SSA Proton EFFs Charmonium Fixed target experiment (√s<2 GeV): pol./unpol. pbar beam (p<4 GeV/c) internal H polarized target M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Kinematics for Drell-Yan processes Fermilab E866 800 GeV/c CERN NA51 450 GeV/c Q2>4 GeV2 "safe region" Usually taken as QCD corrections might be very large at smaller values of M, for cross-sections, not for ATT: K-factor almost spin-independent H. Shimizu, G. Sterman, W. Vogelsang and H. Yokoya, hep-ph/0503270 V. Barone et al., in preparation M. Contalbrigo PAX Polarized Antiproton Experiments

measure ATT also in J/ψ resonance region q l+ q l+ J/ψ q l– q l– all vector couplings, same spinor structure and, at large x1, x2 measure ATT also in J/ψ resonance region M. A., V. Barone, A. Drago and N. Nikolaev M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments The FAIR project M. Contalbrigo PAX Polarized Antiproton Experiments

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 M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments PAX Accelerator Setup APR: Antiproton Polarizer Ring (Ppbar>0.2) CSR: Cooled Synchrotron Ring ( p<3.5 GeV/c) HESR: High Energy Synchrotron Ring (p<15 GeV/c) M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments PAX Detector Concept GEANT simulation (200 mm) (20 mm) Designed for Collider but compatible with fixed target M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments Phase I: Proton time-like FFs Hard pbar-p elastic scatt. Fixed target experiment (√s<2 GeV): pol./unpol. pbar beam (p<4 GeV/c) internal H polarized target From few hours to few weeks measurements M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments 1 year of run Phase II: Transversity Distribution Asymmetric collider (√s=15 GeV): polarized antiprotons in HESR (p=15 GeV/c) polarized protons in CSR (p=3.5 GeV/c) 10 % precision on the h1u(x) in the valence region M. Contalbrigo PAX Polarized Antiproton Experiments

RINGS SETUP Asymmetric collider Luminosity up to 1031 cm-2s-1 See talk by Y. Shatunov, D. Prasuhn, A. Garishvili, A. Smirnov M. Contalbrigo PAX Polarized Antiproton Experiments

Antiproton Polarization M. Contalbrigo PAX Polarized Antiproton Experiments

1992 Filter Test at TSR with protons Experimental Proof of Principle Results Experimental Setup T=23 MeV F. Rathmann. et al., PRL 71, 1379 (1993) Experimental Proof of Principle M. Contalbrigo PAX Polarized Antiproton Experiments

Spin-filtering: Present situation Spin filtering works, but: controversial interpretations of TSR result no experimental basis for antiprotons Experimental tests: - Protons (COSY at FZJ) - Antiprotons (AD at CERN) See talk by P. Lenisa M. Contalbrigo PAX Polarized Antiproton Experiments

Hadronic Interaction in p-pbar: Longitudinal Case Beam Polarization Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991) 50 100 150 200 250 T (MeV) 0.05 0.10 0.15 0.20 P 3 beam lifetimes Ψacc=20 mrad 2 beam lifetimes Ψacc=10-50 mrad Filter Test: T = 23 MeV Ψacc= 4.4 mrad M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Summary PAX project has an innovative spin physics program * transversity * SSA * EMFF * hard p-pbar scatterings * polarized charmonium production A method to obtain an antiproton beam with high degree of polarization has to be optimized (APR) PAX viable accelerator setup at FAIR provides fexible 2nd IP really matched to the physics items * lots of interesting QCD physics in PAX Phase-I * asymmetric collider ideal to map transversity (Phase-II) M. Contalbrigo PAX Polarized Antiproton Experiments

Timeline Fall 2006 Technical Proposal for COSY-ANKE 2007 Propedeutical studies at COSY-ANKE Technical Proposal for COSY-New IP Technical Proposal for AD 2006-08 Design and construction phase COSY 2008 Spin-filtering studies at COSY Commissioning of AD experiment 2009 Installation at AD 2009-2010 Spin-filtering studies at AD M. Contalbrigo PAX Polarized Antiproton Experiments

Drell-Yan process Plenty of single and double spin effects Elementary LO interaction: M invariant Mass of lepton pair M. Contalbrigo PAX Polarized Antiproton Experiments Plenty of single and double spin effects

PAX Polarized Antiproton Experiments Kinematics for Drell-Yan processes Fermilab E866 800 GeV/c CERN NA51 450 GeV/c Q2>4 GeV2 "safe region" Usually taken as QCD corrections might be very large at smaller values of M, for cross-sections, not for ATT: K-factor almost spin-independent H. Shimizu, G. Sterman, W. Vogelsang and H. Yokoya, hep-ph/0503270 V. Barone et al., in preparation M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Cross-section s=210 GeV2 s=45 GeV2 Asymmetry s=210 GeV2 s=45 GeV2 M. Contalbrigo PAX Polarized Antiproton Experiments

measure ATT also in J/ψ resonance region q l+ q l+ J/ψ q l– q l– all vector couplings, same spinor structure M. A., V. Barone, A. Drago and N. Nikolaev measure ATT also in J/ψ resonance region M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized Antiproton eXperiments Nucleon structure: polarized reactions Asymmetric collider (√s=15 GeV): polarized antiprotons in HESR (p=15 GeV/c) polarized protons in CSR (p=3.5 GeV/c) Parton distribution: transversity Drell-Yan Charmonium Cerenkov pbar-p elastic Proton EFFs Fixed target experiment (√s<2 GeV): pol./unpol. pbar beam (p<4 GeV/c) internal H polarized target M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments COMPASS SSA, SIDIS M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Cross-section s=210 GeV2 s=45 GeV2 Asymmetry s=210 GeV2 s=45 GeV2 M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized antiprotons: present situation Intense beam of polarized pbar never produced: Conventional methods (ABS) not appliable Polarized pbar from antilambda decay I< 1.5∙105 s-1 (P ≈ 0.35) Stern-Gerlach separation of a stored beam (M. Conte and M. Pusterla) Interaction with polarized electron beam (Th. Walcher et al) Spin-filtering is the only succesfully tested technique M. Contalbrigo PAX Polarized Antiproton Experiments

Principle of spin filter method P beam polarization Q target polarization k || beam direction σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k) transverse case: longitudinal case: For initially equally populated spin states:  (m=+½) and  (m=-½) Unpolarized anti-p beam Polarized H target M. Contalbrigo PAX Polarized Antiproton Experiments

Polarized atomic beam source |1> mj = +1/2 mj = -1/2 mi=-1/2 mi=+1/2 1 |1> |2> |3> |4> Atoms with mj=+½ focused in sextupole magnets. RF transitions select HFS. M. Contalbrigo PAX Polarized Antiproton Experiments

Two interpretations of FILTEX result Spin-filtering works! But how? Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1 P(t)=tanh(t/τ1), 1/τ1=σ1Qdtf σ1 = 72.5 ± 5.8 mb Spin-filtering works! But how? 1994. Meyer and Horowitz: three distinct effects Selective removal through scattering beyond θacc=4.4 mrad (σR=83 mb) Small angle scattering off 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 Selective removal through scattering beyond θacc=4.4 mrad (σR=85.6 mb) No contribution from other two effects (cancellation between scattering and transmission) σ1 = 85.6 mb M. Contalbrigo PAX Polarized Antiproton Experiments

How to disentangle had. and elm contributions? 1: Injection of different combination of hyperfine states Different combinations of elm. and hadronic contributions: Pure polarization possible in strong holding field Inj. states Pe Pz Interaction Holding field |1> +1 Elm. + had. Transv. + Long. Weak (20 G) |1>+|4> Only had. Long. Strong. (3kG) |1>+|2> Only elm 2: Longitudinal and transverse target polarization 3: Beam energy variation 4: Beam acceptance variation Different behaviour of elm. and hadronic contribution M. Contalbrigo PAX Polarized Antiproton Experiments

Polarizing cross-section for the two models TSR … only had - elm. + had. A measurement of s with 10 % precision is sufficient. Polarization measurement with DP/P = 10% requested. M. Contalbrigo PAX Polarized Antiproton Experiments

Measurements at COSY at FZJ (2008-2009) Existing ANKE setup Only weak transverse field possible. Goals: Propedeutical studies (beam lifetime) Depolarization studies (e effect) Reproduce TSR set-up M. Contalbrigo PAX Polarized Antiproton Experiments

Measurements at COSY at FZJ (2008-2009) New low-beta IP Strong and weak field polarized target Goals: Disentangle h and e effects Commissioning of AD setup M. Contalbrigo PAX Polarized Antiproton Experiments

Low beta section bx,ynew=0.3 -> increase a factor 30 in density respect ANKE Lower buildup time, higher rates Higher polarization buildup-rate due to higher acceptance Use of HERMES target (in Jülich since March 2006) S.C. quadrupole development applicable to AD experiment M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments Detector concept Reaction: p-p elastic (COSY) p-pbar elastic (AD) Good azimuthal resolution (up/down asymmetries) Low energy recoil (<8 MeV) Teflon cell Silicon tracking telescope Angular resolution on the forward particle for p-pbar M. Contalbrigo PAX Polarized Antiproton Experiments

The ANKE silicon tracking telescope 3 silicon detector layers 69 µm silicon 300/500 µm silicon 128 x 151 segments 51 x 66 mm (≈400 µm pitch) >5 mm Si(Li) 96 x 96 strip 64 x 64 mm (≈666 µm Pitch) cluster beam COSY beam 52 M. Contalbrigo PAX Polarized Antiproton Experiments

ANKE vs new interaction point Cross sections Polarization New IP … elm + had - only had. ANKE PIT Filter. time Polar. Total rate Meas. Time (DP/P=10%) ANKE 2t = 16 h 1.2 % 7.5x102 s-1 44 min 5t = 42 h 3.5 % 5x10 s-1 26 min New IP 2t = 5 h 16 % 2.2x104 s-1 1 s 5t = 13 h 42 % 1.5x103 s-1 < 1 s T=40 MeV Ninj=1.5x1010 M. Contalbrigo PAX Polarized Antiproton Experiments

Measurements at AD at CERN (2009-2010) study of spin-filtering in pp scattering Target Snake Commissioned At COSY For longitudial Polarization T:5 MeV÷2.8 GeV Np = 3·107 E-cooler Measurement of effective polarization cross-section. Both transverse and longitudinal. Variable ring acceptance.and beam energy H and D terget First measurement at all for spin correlations in pp (not pure text experiment!) M. Contalbrigo PAX Polarized Antiproton Experiments

Proton Electromagnetic Formfactors Single-spin asymmetry in pp → e+e- Measurement of relative phases of magnetic and electric FF in the time-like region Double-spin asymmetry in pp → e+e- independent GE-Gm separation test of Rosenbluth separation in the time-like region S. Brodsky et al., Phys. Rev. D69 (2004) M. Contalbrigo PAX Polarized Antiproton Experiments

pp Elastic Scattering from ZGS Spin-dependence at large-P (90°cm): Hard scattering takes place only with spins . T=10.85 GeV Similar studies in pp elastic scattering t=-2Pcm2(1-cos(cm)) D.G. Crabb et al., PRL 41, 1257 (1978) M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments q-p Phase Space acceptance Background peaks at * low energy * forward direction M. Contalbrigo PAX Polarized Antiproton Experiments

Background to Drell-Yan e+e- ½ hour experiment: 2∙108 p-pbar interactions several DY events +- ++ & -- combinatorial +charm bckg Background 1:1 to signal after PID, E>300 MeV, conversion veto, mass cut * the combinatorial component can be subtracted (wrong-sign control sample) * the charm can be reduced (vertex decay) M. Contalbrigo PAX Polarized Antiproton Experiments

PAX Polarized Antiproton Experiments q-p Phase Space Better than 2% mass resol * x dependence of h1 * resonance vs continuum Mandatory to study M below J/ψ mass Vertex resolution high enough to study charm background M. Contalbrigo PAX Polarized Antiproton Experiments

Transversity Chiral-odd: requires another chiral-odd partner Properties: Probes relativistic nature of quarks No gluon analog for spin-1/2 nucleon Different Q2 evolution than Dq Sensitive to valence quark polarization See talk by M. Anselmino Chiral-odd: requires another chiral-odd partner epe’hX ppe+e-X Impossible in DIS Direct Measurement Indirect Measurement: convolution with unknown fragment. fct. h1 must couple to another chiral-odd function h1 x h1 h1 x Collins function M. Contalbrigo PAX Polarized Antiproton Experiments

≠ h1 from p-p Drell-Yan h1q (x, Q2) h1q (x, Q2) small and with much slower evolution than Δq(x, Q2) and q(x, Q2) at small x h1q (x, Q2) - ≠ Barone, Calarco, Drago Martin, Schäfer, Stratmann, Vogelsang RHIC: M2/s=x1x2~10-3 → sea quarks (ATT ~ 0.01 ) JPARC/U70: M2/s=x1x2~10-1-10-2 → valence and sea (ATT ~ 0.1 ) PAX: M2/s=x1x2~10-1-10-2 → valence and sea (ATT ~ 0.1 ) M. Contalbrigo PAX Polarized Antiproton Experiments