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Working group e + e - @ Frascati

Working group e + e - @ Frascati. Milano 4 Nov. 2005. Time - like form factors. Marco Radici INFN - Pavia. Outline. Why should we measure time-like (TL) form factors (FF) ?. What should we learn from TL FF with respect to SL FF ?.

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Working group e + e - @ Frascati

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  1. Working group e+e-@ Frascati Milano 4 Nov. 2005 Time - like form factors Marco Radici INFN - Pavia M. Radici - Time-like form factors

  2. Outline • Why should we measure time-like (TL) • form factors (FF) ? • What should we learn from TL FF • with respect to SL FF ? 3. Which measurements are needed ? 4. Available data and calculations ? M. Radici - Time-like form factors

  3. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? elastic scattering cross section Rosenbluth separation fixed Q2, vary GE slope , GM intercept large errors in GE M. Radici - Time-like form factors

  4. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? polarization transfer M. Radici - Time-like form factors

  5. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? JLab – Hall A Qattan et al. P.R.L. 94 (05) 142301 Blunden et al. nucl-th/0506039 2 ? M. Radici - Time-like form factors

  6. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? pQCD JLab polar. transfer data where is onset of pQCD scaling ? M. Radici - Time-like form factors

  7. GEp GEn GMp GMn Miller, P.R. C66 (02) 032201(R) : LFCBM Ma, Qing, Schmidt, P.R. C65 (02) 035205 : LF diquark Lomon, P.R.C66 (02) 045501 : VMD from H. Gao Int. J. Mod. Phys. E12 (03) 1 erratum E12 (03) 567 Holzwarth, hep-ph/0201138 M. Radici - Time-like form factors

  8. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? SpaceLike TimeLike analytic continuation by Dispersion Relations (DR) But fit to pQCD TimeLike fit to pQCD SpaceLike M. Radici - Time-like form factors

  9. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? pQCD + analyticity But fit to |GMp| M. Radici - Time-like form factors

  10. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? poor statistic integrate d over wide angular range all data assume it’s true only at where steep rise is observed M. Radici - Time-like form factors

  11. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? only 1 measurement for neutron (ADONE-1998) again with scarce angular distributions and with low statistics no polarization of protons and/or electrons M. Radici - Time-like form factors

  12. Questions in SL region • Surprise in SL $ TL • Few and poor TL data • Better constrain models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? IJL CQM pQCD “improved” Brodsky et al. P.R. D69 (04) 054022 Dispersive approach on BaBarand Lear Pacetti talk at Nucleon ’05 - Frascati M. Radici - Time-like form factors

  13. Form factors are complex • |FF| from unpol. cross section • Phases from polarization • Unphysical region • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? F(t) analytic function in t 2C with cut [t0 = 4m2, 1) Dispersion Relation (DR) R Im F(t’)  0 only in [t0=4m2, 1 ) C vector-meson poles and multi-hadron continuum dipole fit to F2 (q2e-i) / F1 (q2 e-i ) !R ! M. Radici - Time-like form factors

  14. Form factors are complex • |FF| from unpol. cross section • Phases from polarization • Unphysical region • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? unpolarized cross section for Rangular asymmetry q2>0 measure 2  at fixed q2 ) get R cos2 typical of Born diagram measure 3  ) explore 2 mechanisms q2<0 Rosenbluth plot change E, e at fixed q2 ) linear plot in  M. Radici - Time-like form factors

  15. Form factors are complex • |FF| from unpol. cross section • Phases from polarization • Unphysical region • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? polarized cross section for Ax, Az require polarization of the electron beam: Pe 0 M. Radici - Time-like form factors

  16. Form factors are complex • |FF| from unpol. cross section • Phases from polarization • Unphysical region • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? phases of FF from Final-State Interactions (FSI) of final baryon system : interference of channels with different phases ( Im (GE*GM) ) pQCD : FSI ! 0 for Q2!1 ) test transition to scaling and Color Transparency (CT) FSI ! T-odd mechanisms are allowed : generates GE = F1 +  F2 = |GE| ei E GM = F1 + F2 = |GM| ei M not possible in elastic scattering Im (GE*GM) = ( -1) Im F2*F1 threshold t1=4M2! Im( )=0 consistent with |GE|=|GM| from GT=1(t1)=0 ambiguity $ -  solved by M. Radici - Time-like form factors

  17. Form factors are complex • |FF| from unpol. cross section • Phases from polarization • Unphysical region • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? discriminate among models that are close in SL region IJL CQM pQCD “improved” M. Radici - Time-like form factors

  18. Form factors are complex • |FF| from unpol. cross section • Phases from polarization • Unphysical region • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? steep rise at threshold tail of narrow resonance at t ≤ 4M2 (baryonium) ? should show up as a dip in some hadronic cross section E687 diffractive photoproduction of 6 Upcoming results from BaBar also W » 1.9 GeV M. Radici - Time-like form factors

  19. Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? measure angular dependence of unpol. cross section ) angular asymmetry R and test 2 mechanisms measure Ay/ sin (E - M) measure Ay / Ax/ tan (E - M) utopia : measure Ai j M. Radici - Time-like form factors

  20. data : proton • models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? ADONE Q2 = 4.4 GeV (1973) CERN Q2 ~ 3.6 (1977) Orsay-DM1 Q2 ~ 3.75-4.56 (1979) Orsay-DM2 Q2 =4-5 (1983) LEAR Q2 ~3.5-4.2 (1994) E760 Q2 ~8.9-13 (1993) FENICE Q2 ~3.7-6 (1994) E835 Q2 ~8.8-18.4 (1999) 11.6-18.2 (2003) CLEO Q2 ~11-12 (2005) BES Q2 ~4-9 (2005) BaBar Q2 ~2-20 (2005) M. Radici - Time-like form factors

  21. data : proton • models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? M. Radici - Time-like form factors

  22. data : neutron • models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? FENICE Q2 ~3.7-6 (1994) but always assumed |GEN| = |GMN| N=p,n M. Radici - Time-like form factors

  23. data • models • Why TL FF ? • What do we learn ? • Which measurements ? • Available data and models ? • Dispersion Relations (DR): • analyticity+unitarity+Vector Mesons (VM) (Drechsel, Meissner, • Hammer, Hoehler,..) • “ “ + input exp. data (Baldini, Pacetti, …) • VM Dominance (VMD) based models (Iachello, Bijker, Lomon, …) • Soliton (Holzwarth) • CQM : Light Front Form (Pace, Salmè, Simula, …) • “ “ “ + \pi cloud (Miller, Jennings, .. ) • Point Form (Pavia + Graz collaboration) • Diquark (Ma, …) • pQCD “inspired” (Brodsky, Ji, Belitski, Yuan, ..) • reviews: Brodsky et al. P.R. D69 (04) 054022 • Tomasi-Gustafsson et al. E.P.J. A24 (05) 419 M. Radici - Time-like form factors

  24. Possible logo ? (from Pacetti talk at Nucleon’05) M. Radici - Time-like form factors

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