p and polarized antiprotons

Transcription

1 Spokespersons: F. Rathmann and P.L. Spin-physics p and polarized antiprotons Paolo Lenisa Università di Ferrara and INFN - ITALY PAX PANDA Stokholm, P.Lenisa

2 Polarized antiprotons: why? Study of the proton spin P.Lenisa Physics with Polarized Antiprotons

3 Where is the proton spin? the proton is an object we thought we knew so well, but which reveals another face when it spins. J. Ellis QPM: Δu Δd Δ v v Σ s EMC 988 =0.3 ±... gluons are important! SLAC, CERN, DESY: Σ G ΔΣ L don t forget the orbital angular momentum! G L g P.Lenisa Physics with Polarized Antiprotons 3

4 How to study the nucleon structure? deep-inelastic scattering DIS Q lab EE'- cos =/ph. wavel. resolution lab Q Mν P P Proton momentum fraction carried by the struck uark Q M deep high h resolution: inelastic M M proton has structure X P.Lenisa Physics with Polarized Antiprotons 4

5 Polarized deep inelastic scattering ΔΣ L G L L g J J J g inclusive dis polarised beam and/or polarised target semi-inclusive i i DIS flavour separation eclusive dis inclusive hadrons P.Lenisa Physics with Polarized Antiprotons 5

6 Eperimental e.g. HERMES Polarized e + /e - beam Polarized internal target Detector 7.5 GeV e + /e - <P b >~ 53±.5 self-polarised % electrons: e b <P b >~ 53±.5 % P.Lenisa Physics with Polarized Antiprotons 6

7 Polarized semi-inclusiveinclusive DIS flavour tagging + ud - ud K - us distribution function fragmentation function d h f z d D z f f h f, z=e h / P.Lenisa Physics with Polarized Antiprotons 7

8 Quark/anti-uark helicity distributions u uarks large positive polarisation d uarks negative polarisation sea uarks u, d, s compatible with 0 in measured -range: P.Lenisa Physics with Polarized Antiprotons 8

9 Where do we stand? the spin structure of the nucleon H, ZEUS,++ HERMES COMPASS CERN RHIC SLAC HERMES, ++ P.Lenisa Physics with Polarized Antiprotons 9

10 Where do we stand? the spin structure of the nucleon H, ZEUS,++ HERMES, ++ Transversity h, HERMES COMPASS CERNE N RHIC SLAC HERMES JLab b P.Lenisa Physics with Polarized Antiprotons 0

11 Study of the proton spin Quark structure of the nucleon Tw Corr S L γ 5 γ 5 γ S T n h = unpolarised uarks and nucleons longitudinally polarised uarks and nucleons transversely polarised uarks and nucleons Well known Known Less known P.Lenisa

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

13 Transversity with SIDIS HERMES & COMPASS Collins FF Transversity H Sivers Collins FF rans ers ty Sivers moment h h h, N, N, N, N, A S h S h S h S h T S h UT S S h S h P.Lenisa 3 Physics with Polarized Antiprotons

14 Collins HERMES ep X δ H z first time: transversity & Collins FF are non-zero! P.Lenisa Physics with Polarized Antiprotons 4

15 Transversity with SIDIS A sin S δ H z A UT e + e - ep e' πx ed e' hx e e jet jet X P.Lenisa Physics with Polarized Antiprotons 5

16 First etraction of transversity 007 Common fit of HERMES, COMPASS, BELLE Transversity Collins function d d u Anselmino et al. PRD75007 P.Lenisa Physics with Polarized Antiprotons 6

17 First etraction 007: transversity lower than models A. Bacchetta, Trento 007 P.Lenisa Physics with Polarized Antiprotons 7

18 New etraction 008: close to most models Prokudin et al. at Ferrara Prokudin et al. at Ferrara A. Prokudin, Ferrara 008 P.Lenisa Physics with Polarized Antiprotons 8

19 Can we claim to have measured transversity? Well Collins Etraction of Transversity model dependence for Transverse Momentum Dependences! d h sin sin,,, p z D d k k d d d e p z H dy d k k d d d e A h h S h S h S Collins UT,, p z D dy k k d d d e h S Anselmino, Boglione, D Alesio, Kotzinian, Murgia, Prokudin, Turk Phys Rev D75: k transverse uark momentum in nucleon p transverse hadron momentum in fragmentation Phys. Rev. D75:0503,007 p g The transverse momentum dependencies are unknown and difficult to obtain eperimentally P.Lenisa 9 obtain eperimentally Physics with Polarized Antiprotons

20 k evolution SIDIS and BELLE at different scales: <Q > =.4 GeV vs Q = 0 GeV Both azimuthal asymmtries involve TMDs beyond tree level Anselmino et al. use: H z,k = D zfz,k Evolution is taken to be the one of D z Modification of the k dependence is also important Etraction from SIDIS remains a hard theoretical challenge: new possibly direct measurements needed! P.Lenisa Physics with Polarized Antiprotons 0

21 Measurement of Transversity D. Boer, Ferrara 008 Double polarized DY is a uniue process Self-sufficient No TMD P.Lenisa Physics with Polarized Antiprotons

22 h from p-p Drell-Yan The dream: l l * h from p p Drell Yan S Drell-Yan d,... d, u, u, M invariant Mass 9 4 e s M d dm d F s M M invariant Mass of lepton pair / / s Q s M L F F TT TT e h h h h e a A ˆ d d d d P.Lenisa Physics with Polarized Antiprotons

23 Hadron Physics Dream Machine Asymmetric double-polarized proton 5 GeV/c antiproton 3.5 GeV/c collider Luminosity: >0 3 cm - s - p p P.Lenisa Physics with Polarized Antiprotons 3

24 h u from p-p Drell-Yan at PAX TT TT e h h h h e a A ˆ d d d d d i u-dominance h u > h d ˆ u u h h a A u u TT TT PAX : u u PAX : s= ~ valence uarks A TT large ~ P.Lenisa 4 Physics with Polarized Antiprotons

25 Events for Drell-Yan processes CERN NA5 450 GeV/c Fermilab E GeV/c M M J / Usually taken as "safe region" M J / s Q >4 GeV P.Lenisa Physics with Polarized Antiprotons 5

26 PAX Detector Concept Physics: h distribution sin EMFF sin pbar-p p elastic high t Azimuthally Symmetric: BARREL GEOMETRY LARGE ANGLES Eperiment: Fleible Facility e + e - Detector: Etremely rare DY signal 0-7 p-pbar Maimum m Bjorken- coverage M interval Ecellent PID hadron/e rejection ~ 0 4 High mass resolution % Moderate lepton energies GeV Magnet: Keeps beam polarization vertical Compatible with Cerenkov Compatible with pol. target TOROID NO FRINGE FIELD P.Lenisa Physics with Polarized Antiprotons 6

27 PAX Detector Concept GEANT simulation Cerenkov 00 m 0 m Designed for Collider but compatible with fied target P.Lenisa Physics with Polarized Antiprotons 7

28 Background to Drell-Yan e + e - 0 min. eperiment: 0 8 p-pbar pbar interactions several DY events & -- combinatorial +charm bckg Background : 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 verte decay P.Lenisa Physics with Polarized Antiprotons 8

29 Precision in h measurement year of data taking at GeV collider L = cm - s - p=0.8 pbar=0.5 p-p p 0 % precision on the h u in the valence region P.Lenisa Physics with Polarized Antiprotons 9

30 Measurement of Transversity: what about PANDA? There is only a single self-sufficient process with a single polarized beam Single spin-asymmetry in pp or pp Drell-Yan P.Lenisa Physics with Polarized Antiprotons 30

31 A window to transversity: pbar - p l + l - X Only self-sufficient single spin-asymmetry involves TMDs Unpolarized DY production cross-section analogue of BELLE cos asymmetry Single-polarized DY production cross-section analogue of SIDIS Collins asymmetry P.Lenisa Physics with Polarized Antiprotons 3

32 Kinematics and cross section: fied target vs collider e,m, M,M, d 4 M dm d 9M s F M = s F =Q L / s = - d dσ/dm nb 0 - k events/day collider GeV 5 GeV GeV fied target 5 GeV coll M M GeV/c GeV P.Lenisa Physics with Polarized Antiprotons 3

33 MC Simulations I A. Bianconi NIM A593, Unpolarized case: p p + - X 50 5 events < T < GeV/c < T < 3 GeV/c 5.5 < M ll<.5 +- GeV T > GeV/c 60 o < CS +<0 o Luminosity = 0 3 cm - s - = 0.8 nb Rate = s - M. Maggiora Univ. Torino and INFN I Cos asymmetry related to h not negligble and measurable Study of the dependence from T possible P.Lenisa Physics with Polarized Antiprotons 33

34 MC Simulations II A. Bianconi, M. Radici Phys. Rev. D7, Single-spin asymmetry: p p + - X related to h T 50 5 events < T < GeV/c < T < 3 GeV/c related to f T Sin s asymmetry y related to h T not negligble g and measurable Study of the dependence from T possible Sin s asymmetry related to f T very small Weak T dependenced P.Lenisa Physics with Polarized Antiprotons 34

35 A polarized target in PANDA? A very difficult task! ask F. Maas Positioning: Keep good PID for EM physics No N parasitic run possible Technical issues: Transport of polarized gas Compensation of solenoidal field Pumping p g of polarized gas Possible options: new detector with thoroidal field? additional IP in HESR? P.Lenisa Physics with Polarized Antiprotons 35

36 Polarized antiprotons: why? Proton electromagnetic tic form-factors factors P.Lenisa Physics with Polarized Antiprotons 36

37 Electromagnetic Form Factors TIMELINE: - Describe int. structure of the nucleon -Information about proton ground state -Test for models of nucleon structure - Wavelength tunable with Q : < 0 0. GeV integral uantities i 0.-0 GeV internal structure > 0 GeV pqcd scaling 93 Stern: anomalus magnetic moment of the proton 950 Hofstadter first measurement of the proton s radius through elastic electron scattering Nobel Prize in Polarization transfer measurementm P.Lenisa Physics with Polarized Antiprotons 37

38 Electromagnetic Form Factors p p =k -k J F MM F i k k One-photon-echange approimation: Pauli-Dirac F and F or Sachs G E and G M G M M = F + F G E = F + F = /4M In the Breit reference system, Sachs FFs are the Fourier transform of the charge and magnetization distributions P.Lenisa Physics with Polarized Antiprotons 38

39 Space-like and Time-like regions FFs are analytical functions. One photon echange: functions of t = = -Q. t= <0 spacelike real function Scattering e - + h => e - + h t= >0 timelike comple function Annihilation _ e + + e - => h + h _ lim SL TL F lim F Different from pqcd predictions P.Lenisa Physics with Polarized Antiprotons 39

40 Measurement of SL-FF: Rosenbluth separation Rosenbluth separation SL FFs scaling: G Mp p p G E charge and magnetization have the same distribution - FFs described 0% by dipole formula G D 0. 8 GeV Q P.Lenisa Physics with Polarized Antiprotons 40

41 Measurement of SL-FF: Polarization Transfer Polarization transfer 958 Akhiezer et al., Sov. Phys. Jept. 6, e e p P T P L G G E M Pt P l Ee E e ' tan M -P t and P l of the scattered proton measured simultaneously using C P.Lenisa Physics with Polarized Antiprotons 4

42 SL-Form Factors: proton data All Rosenbluth data from SLAC and Jlab in agreement Dramatic discrepancy between Rosenbluth and recoil polarization techniue Q dependence suggests different charge and magnetization spatial distributions inside the nucleon Is the proton round? Dramatic discrepancy! P.Lenisa Physics with Polarized Antiprotons 4

43 Eplanation?: two photon echange Interference of one- and two-photon amplitudes Elastic electron-proton to positron-proton ratio P. Blunden P.Lenisa Physics with Polarized Antiprotons 43

44 Eperiments to Verify Echange VEPP3 CLAS Eperiment proposals to verify hypothesis: e+/e- ratio: CLAS/PR04-6 secondary e+/e- beam Novosibirsk/VEPP-3 storage ring / internal target BLAST@DORIS/DESY storage ring / internal target SSA: PR Hall A e-dependence: PR04-9 polarized, PR05-07 unpolarized P.Lenisa Physics with Polarized Antiprotons 44

45 Projected results for OLYMPUS DESY 500 hours each 000 for hours e+ and each e - for Lumi=0 e+ and e - 33 cm - s - Lumi=0 33 cm - s - R. Milner, DESY, 009 P.Lenisa Physics with Polarized Antiprotons 45

46 Measurement of TL-FF d C G M cos G E sin d 4s d = s/ 4M G M dominates the cross section for s >> 4M G M = G E at the physical threshold s = 4M No independent etraction of both TL FFs performed nb G E remains unmeasured E P.Lenisa Physics with Polarized Antiprotons 46

47 Time-Like FFs: proton data The dashed line is a fit to the PQCD prediction G M p s ln C s The epected Q behaviour is reached uite early, however... P.Lenisa Physics with Polarized Antiprotons 47

48 Time-Like FFs: proton data The dashed line is a fit to the pqcd prediction G M p s ln C s The epected Q behaviour is reached uite early, however there is still a factor of between timelike and spacelike. P.Lenisa Physics with Polarized Antiprotons 48

49 Time-like form factor PANDA P.Lenisa Physics with Polarized Antiprotons 49

50 Pion-rejection = 8. Gev/c F. Maas Univ. of Mainz GSI D P.Lenisa 50

51 Epected count-rates and statistical projection G E =G M fb cm - s - F. Maas P.Lenisa Physics with Polarized Antiprotons 5

52 Measurement of G E and G M PANDA - Use of different angular dependence for G E and G M -Generated events: F. Maas fb cm - s - P.Lenisa Physics with Polarized Antiprotons 5

53 Back to the dream Double polarized pbar-p annihilation: E. Tomasi, F. Lacroi, C. Duterte, G.I. Gakh, EPJA 4, Most contain moduli G E, G M Independent d 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 net transparencies P.Lenisa Physics with Polarized Antiprotons 53

54 A possible facility: pbar on polarized p target EXPERIMENT: Fied target eperiment: polarized antiprotons protons in CSR p>00 MeV/c fied polarized protons target P. Lenisa Physics with polarized antiprotons 54

55 Theoretical models pro oton ne eutron a μp*g GEp/GMp c GEn Spacelike Timelike Electric Magnetic Electric Magnetic Q GeV Q GeV b GMp p/gd/μp Q GeV d GMn/μn/GD Q GeV QCD inspired Bosted PRC 5, Etended d VDM VDM : IJL Hohler E.L.Lomon PRC 66, F. Iachello..PLB 43, NPB 4, E. Tomasi, F. Lacroi, C. Duterte, G.I. Gakh, EPJA 4, P.Lenisa Physics with Polarized Antiprotons 55

56 Polarization and Models in T.L. Region A A y A yy VDM : IJL Et. VDM QCD inspired A z R A zz E. Tomasi, F. Lacroi, C. Duterte, G.I. Gakh, EPJA 4, P.Lenisa Physics with Polarized Antiprotons 56

57 Single Spin Observables A. Z. Dubnickova, S. Dubnicka, M.P. Rekalo Nuovo Cimento A09, Polarization P y for θ = /Q fit log Q /Q fit impr. log Q /Q fit IJL fit Contains imaginary part Access relative phase Very sensitive to different dff models GeV S.J. Brodsky, C.E. Carlson, J.R. Hiller, D.S. Hwang PRD 69, P.Lenisa Physics with Polarized Antiprotons 57

58 Polarized antiprotons: why? Polarized pbar-p hard-scattering P.Lenisa Physics with Polarized Antiprotons 58

59 Hard polarized scattering Unpolarized p-p p elastic cross section Beam P Target d/dt Dividing idi d/dt at 90 o c.m by 4 made all p-p elastic data fit on a single curve scaled p P.Lenisa Physics with Polarized Antiprotons 59

60 Hard p-p polarized scattering T=0.85 GeV The graeatest asymmetries ti in hadron physics ever seen by a human being Brodsky D.G. Crabb et al., PRL 4, The results challenge the prevailing theory that describes the proton s structure and forces Krish, 987 One of the unsolved mysteries of hadron physics Brodsky Brodsky, 005 the thorn in the side of QCD Glashow It would be very interesting to performe this measurements with polarized antiprotons. P.Lenisa Physics with Polarized Antiprotons 60

61 Polarized antiprotons a missing tool for hadron physics! * Proton-spin structure: Complete map of transversity Flavour separation * Electromagnetic Form Factors Independent etraction 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 * *Wealth of single-spin asymmetries Let s polarize them! net talk by H. Ströher P.Lenisa Physics with Polarized Antiprotons 6

62 P.Lenisa 6

63 Cross-section s=45 GeV s=0 GeV Asymmetry s=45 GeV s=0 GeV P.Lenisa 63

64 Higher energy p-p machine s 00GeV V. Barone, T. Calarco and A. Drago Phys. Rev. D s Asymmetry A LL >A TT s JPARC ideal P.Lenisa 64

65 Radiative corrections Cross-section section s=45 GeV s=0 GeV Asymmetry Shimizu et al. PRD s=45 GeV s=0 GeV P.Lenisa DY at FAIR 65

66 Resolution Better than % mass resol * dependence of h * resonance vs continuum Mandatory to study M below J/ψ mass Verte resolution high enough to study charm background P.Lenisa DY at FAIR 66

67 Background in pbar-p e + e - P.Lenisa 67

68 Reconstructed events = 5.4 GeV/c F. Maas P.Lenisa 68

69 Eperimental Development of polarized proton beams ZGS T= GeV AGS T= GeV 9 dep. resonances s P B >70% 45 dep. resonances Polarized target P.Lenisa Physics with Polarized Antiprotons 69

70 A DY TT What about p-p Drell-Yan? PAX, JPARC, NICA e h h h h a TT e i Asymmetries evoluted under the assumption: s 0GeV h, Q 0, Q 0 ~CQSM A. Drago 006 Asymmetry at RHIC very low ~0.0 Aymmetry is large >0. for p p at PAX, JPARC, NICA energies Complementary measurement to p -p P.Lenisa Physics with Polarized Antiprotons 70

71 DY events distribution pp, pp and pd p-p p-p, p, p-d At = A ~ h TT u Direct measurement of h u for 0.05<<0.5 M /s = ~ Etraction of h d, h for <0. p p p p p d : complete mapping of transversity P.Lenisa Physics with Polarized Antiprotons 7

72 Sivers function from pp or pp PAX Test of Universality f,p T, p T SIDIS f T T DY SIDIS : ep ex PAX : p p e e X E704 : p p X A.V. Efremov et al., Phys. Lett. B 6, / M / s e y M. Anselmino et al., Phys. Rev. D7, P.Lenisa Physics with Polarized Antiprotons 7