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

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

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

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

5. P.Lenisa Polarized Antiprotons Experiments 5 M invariant Mass of lepton pair Inclusive DIS Semi-inclusive DIS Drell-Yan h 1 from p-p Drell-Yan

6. P.Lenisa Polarized Antiprotons Experiments 6 EXPERIMENT: Asymmetric collider: polarized protons in HESR (p=15 GeV/c) polarized antiprotons in CSR (p=3.5 GeV/c) s=200 GeV 2 The PAX proposal at FAIR (phase II) (Same “s” as Main Injector beam on fixed target)

7. P.Lenisa Polarized Antiprotons Experiments 7 h 1 from p-p Drell-Yan PAX :    s=x 1 x 2 ~0.02-0.3 valence quarks (A TT large ~ 0.2-0.3 ) u-dominance |h 1u |>|h 1d | First direct measurement of h 1 for valenc quarks No competitive processes RHIC: τ=x 1 x 2 =M 2 /s~10 -3 → Exploration of the sea quark content (polarizations small!) A TT very small (~ 1 %)

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

9. P.Lenisa 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 Q 2: < 0.1 GeV 2 integral quantities 0.1-10 GeV 2 internal structure > 20 GeV 2 pQCD scaling k’ k p p’ q=k’-k      qiqF M qFJ 2 2 2 1 2  One-photon-exchange approximation: Pauli-Dirac (F 1 and F 2 ) or Sachs (G E and G M ) G M (q 2 ) = F 1 (q 2 ) + F 2 (q 2 ) G E (q 2 ) = F 1 (q 2 ) +  F 2 (q 2 )  =q 2 /4M 2 In the Breit reference system, Sachs FFs are the Fourier transform of the charge and magnetization distributions

10. P.Lenisa Polarized Antiprotons Experiments 10 Space-like and Time-like regions FFs are analytical functions. of t = q 2 = -Q 2. e - + h => e - + h Scattering t=q 2 <0 (spacelike) real function Annihilation e + + e - => h + h _ _ t=q 2 >0 (timelike) complex function

11. P.Lenisa Polarized Antiprotons Experiments 11 Polarization Rosenbluth Space-Like FFs: proton data Proton Electromagnetic Form-Factors: data JLab results dramatically changed picture of the Nucleon: - G E p /G M p decreases with Q 2 Time-Like FFs: proton data - Q 2 dependence suggests different charge and magnetization spatial distributions inside the nucleon Is the proton round?

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

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

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

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

16. P.Lenisa 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

17. P.Lenisa Polarized Antiprotons Experiments 17 Polarizedpbar-phard-scattering Physics with Polarized Antiprotons Polarized Antiprotons

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

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

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

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

22. P.Lenisa Polarized Antiprotons Experiments 22 More single-spin asymmetries

23. P.Lenisa Polarized Antiprotons Experiments 23 pqpq PqPq π k┴k┴ Collins effect = fragmentation of polarized quark depends on P q · (p q x k ┴ ) Sivers effect = number of partons in polarized proton depends on P · (p x k ┴ ) P p k┴k┴ q k┴k┴ q PqPq p Boer-Mulders effect = polarization of partons in unpolarized proton depends on P q · (p x k ┴ ) These effects may generate SSA pqpq PP  k┴k┴ Polarizing FF = polarization of hadrons from unpolarized partons depends on P L · (p q x k ┴ ) PDFs FFs Single-spin asymmetries Correlation functions

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

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

26. P.Lenisa Polarized Antiprotons Experiments 26 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 Summary 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