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Investigating Time-like Form Factors in Particle Physics: A Comprehensive Overview

This presentation delves into the significance of measuring time-like form factors (TLFF) in particle physics, particularly in relation to space-like form factors (SLFF). It discusses the need for TLFF measurements, the insights they can provide, and the current state of available data and calculations. The presentation highlights the challenges posed by sparse data in the SL region and advocates for better constraints on theoretical models. The goal is to elucidate the underlying physics and foster advancements in experimental techniques necessary for these measurements.

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Investigating Time-like Form Factors in Particle Physics: A Comprehensive Overview

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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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