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dr. Paolo Lenisa Università di Ferrara and INFN - ITALY

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  1. Polarized Antiprotons Experiments • The PAX Collaboration • 178 Collaborators • 36 institutions (15 EU, 21 NON-EU) dr. Paolo Lenisa Università di Ferrara and INFN - ITALY Project X Workshop FNAL, 01/26/08 Polarized Antiprotons Experiments

  2. Physics with Polarized Antiprotons Study of the proton spin Polarized Antiprotons Experiments

  3. Study of the proton spin h1= Quark structure of the nucleon unpolarised quarks and nucleons longitudinally polarised quarks and nucleons transversely polarised quarks and nucleons Only glimpse Well known Known Polarized Antiprotons Experiments

  4. transversely polarised quarks and nucleons Transversity • Probes relativistic nature of quarks • No gluon analog for spin-1/2 nucleon • Different evolution than • Sensitive to valence quark polarization h1 is chirally odd -> it needs a chirally odd partner Inclusive DIS Semi-inclusive DIS Drell-Yan HERMES,COMPASS,JLab Polarized Antiprotons Experiments

  5. M invariant Mass of lepton pair Inclusive DIS Semi-inclusive DIS Drell-Yan h1 from p-p Drell-Yan Polarized Antiprotons Experiments

  6. The PAX proposal at FAIR (phase II) s=200 GeV2 EXPERIMENT: Asymmetric collider: polarized protons in HESR (p=15 GeV/c) polarized antiprotons in CSR (p=3.5 GeV/c) (Same “s” as Main Injector beam on fixed target) Polarized Antiprotons Experiments

  7. h1 from p-p Drell-Yan • u-dominance • |h1u|>|h1d| PAX : M2/s=x1x2~0.02-0.3 valence quarks (ATTlarge ~ 0.2-0.3) RHIC: τ=x1x2=M2/s~10-3 → Exploration of the sea quark content(polarizations small!) ATT very small (~ 1 %) First direct measurement of h1 for valenc quarks No competitive processes Polarized Antiprotons Experiments

  8. Physics with Polarized Antiprotons Proton electromagnetic form-factors Polarized Antiprotons Experiments

  9. Electromagnetic Form Factors - Describe int. structure of the nucleon • Information about proton ground state • Test for models of nucleon structure - Wavelength tunable with Q2: < 0.1 GeV2 integral quantities 0.1-10 GeV2 internal structure > 20 GeV2 pQCD scaling p p’ q=k’-k k’ k • One-photon-exchange approximation: • Pauli-Dirac (F1 and F2) or Sachs (GE and GM) • GM(q2) = F1(q2) + F2(q2) • GE(q2) = F1(q2) + t F2(q2)t=q2/4M2 • In the Breit reference system, Sachs FFs are the Fourier transform of the charge and magnetization distributions k ( ) ( ) m m mn = g + s 2 2 J F q F q i q n 1 2 2 M Polarized Antiprotons Experiments

  10. t=q2>0 (timelike) t=q2<0 (spacelike) real function complex function Annihilation Scattering _ e+ + e- => h+ h e- + h => e- + h _ Space-like and Time-like regions • FFs are analytical functions. of t = q2 = -Q2. Polarized Antiprotons Experiments

  11. Rosenbluth Polarization Proton Electromagnetic Form-Factors: data Space-Like FFs: proton data Time-Like FFs: proton data • JLab results dramatically changed picture of the Nucleon: • GEp/GMp decreases with Q2 Is the proton round? - Q2 dependence suggests different charge and magnetization spatial distributions inside the nucleon Polarized Antiprotons Experiments

  12. Rosenbluth Polarization Proton Electromagnetic Form-Factors: data Space-Like FFs: proton data Time-Like FFs: proton data Is the proton round? Expected Q2 behaviour reached quite early, however ... ... there is still a factor of 2 between timelike and spacelike. Additional direct measurement needed Polarized Antiprotons Experiments

  13. The PAX proposal - Phase I EXPERIMENT: Fixed target experiment: polarized antiprotons protons in CSR (Ek<2.5 GVe) fixed polarized protons target “s” range covered by both Main Injector and Antiproton Accumulator beams on fixed target Polarized Antiprotons Experiments

  14. Double polarized pbar-p annihilation E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005) • Most contain mduli GE, GM • Independent GE-GM separation • Test of Rosenbluth separation in the time-like region • Access to GE-GM phase • Very sensitive to different models Polarized Antiprotons Experiments

  15. Magnetic Electric Magnetic Electric proton neutron VDM : IJL F. Iachello..PLB 43, 191 (1973) QCD inspired Bosted PRC 51, 409 (1995) Extended VDM E.L.Lomon PRC 66, 045501 2002) Hohler NPB 114, 505 (1976) Theoretical models Spacelike Timelike E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005) Polarized Antiprotons Experiments

  16. (Single Spin Asymmetry) A. Z. Dubnickova et al. Nuovo Cimento A109, 241 (1996) S.J. Brodsky et al. PRD 69, 054022 (2004) • Single-spin asymmetry in pp → e+e- • Measurement of relative phases of magnetic and electric FF in the time-like region - Also sensitive to different models Polarized Antiprotons Experiments

  17. Physics with Polarized Antiprotons Polarized pbar-p hard-scattering Polarized Antiprotons Experiments

  18. P Beam Target Hard p-p polarized scattering T=10.85 GeV “The greatest asymmetries in hadron physics ever seen by a human being” (Brodsky) D.G. Crabb et al., PRL 41, 1257 (1978) “One of the unsolved mysteries of hadron physics”(Brodsky, 2005) It would be very interesting to perform these measurements with polarized antiprotons. Polarized Antiprotons Experiments

  19. Physics with Polarized Antiprotons Further perspectives … • Spectroscopy of hadrons • Use of polarization degrees of freedom to decrease number of contributing amplitudes Polarized Antiprotons Experiments

  20. J/y,y production NRQCD Able to reproduce the unpolarized xsec Fixed target exp Fails in predicting polarization vs pT at CDF F. Maltoni et al., hep-ph/0601203 Polarized Antiprotons Experiments

  21. Physics with Polarized Antiprotons Further perspectives … • Spectroscopy of hadrons • Use of polarization degrees of freedom to decrease number of contributing amplitudes • Low-t proton-antiproton scattering • Investigation of spin and isospin dependence of nucleon-antinucleon interaction at low energy Polarized Antiprotons Experiments

  22. More single-spin asymmetries Polarized Antiprotons Experiments

  23. π Pq k┴ pq q P k┴ pp q Pq k┴ pp PL L k┴ pq Single-spin asymmetries Correlation functions Sivers effect = number of partons in polarized proton depends onP· (p x k┴) PDFs Boer-Mulders effect = polarization of partons in unpolarized proton depends onPq· (p x k┴) Collins effect = fragmentation of polarized quark depends onPq· (pqx k┴) FFs Polarizing FF = polarization of hadrons from unpolarized partons depends onPL· (pqx k┴) These effects may generate SSA Polarized Antiprotons Experiments

  24. Sivers from hadron scattering pp→pX BNL-AGS √s = 6.6 GeV 0.6 < pT < 1.2p↑p E704 √s = 20 GeV 0.7 < pT < 2.0p↑p ep→hX Sivers from SIDIS Polarized Antiprotons Experiments

  25. Test of Universality A.V. Efremov et al., Phys. Lett. B 612, 233 (2005) M. Anselmino et al., Phys. Rev. D72, 094007 (2005) The Sivers function Polarized Antiprotons Experiments

  26. Summary • The physics case for polarization expeiments with antiprotons is outstanding • Two options to perform polarization experiments with pbar at FNAL • Single spin-asymmetries • Fixed target in AA or MI • Double spin-asymmetries • Polarizer ring (F. Rathmann -> next talk) + experimental ring • The FNAL pbar-source is a pretious treasure for the world hadron-physics community • Factor 10 higher “real” intensity than the FAIR source “on the paper” in ten years • Future of CERN pbar-source unclear • AD ring low energy, no stacking capability Polarized Antiprotons Experiments