The MAID Legacy and Future

Transcription

1 The MAID Legacy and Future Verdun, France, 11 August 1999 Side, Turkey, 29 March 2006 Lothar Tiator, Johannes Gutenberg Universität, Mainz NSTAR Workshop, Columbia, SC, USA, August 20-23, 23, 2017

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3 MAID collaboration ( ) Dubna: Mainz: GWU: Depok: Taipei: Tomsk: Mainz: Sabit Kamalov Dieter Drechsel, Olaf Hanstein, L.T. Cornelius Bennhold ( K) Terry Mart ( ) Shin Nan Yang, Wen Tai Chiang ( Regge models) Alexander Fix ( ) Marc Vanderhaeghen (e, e Regge models) Stefan Scherer, Marius Hilt ( in PT) Viktor Kashevarov ( Regge models)

4 how we looked in 1998 Dieter Drechsel Sabit Kamalov Olaf Hanstein Lothar Tiator

5 short history MAID98: in Mainz we started the MAID project in 1998 with pion photo- and electroproduction and the analysis of space-like transition formfactors MAID2007: latest update on (e,e ) with some extensions in 2009 KaonMAID 2000: isobar model for e, e K and e, e K DMT 2001: dynamical model for e, e, very successfull in the threshold region EtaMAID 2001 and EtaMAID 2003: isobar model for e, e and Two-Pion MAID 2007: isobar model for Chiral MAID 2012: (e, e ) for threshold region in relativistic PT

6 MAID has been used for: - comparison with exp. data - comparison with theoretical models - comparison with partial wave analys - predictions for new measurements - proposals for new experiments - event generators - input for dispersion relations for Compton and virtual Compton scattering - input for nucleon polarizabilities - input for Finite Energy Sum Rules - input for GDH and related Sum Rules - and more up to now: MAID web pages have been called more than 7.7 Million times

7 Dispersion Relations in RCS, VCS and DVCS Barbara Pasquini, Input from pion photo- and electro-production amplitudes of MAID

8 some selected applications: D. Drechsel, B. Pasquini, M. Vanderhaeghen: Dispersion Relations in real and virtual Compton Scattering Phys. Rept. 378 (2003) D. Drechsel, LT: The Gerasimov-Drell-Hearn rum rule and the spin structure of the nucleon Ann. Rev. Nucl. Part. Sci. 54 (2004) M. Gorchtein, C. Lorce, B. Pasquini, M. Vanderhaeghen: Light-front interpetation of proton generalized polarizabilities Phys. Rev. Lett. 104 (2010) O. Tomalak, B. Pasquini, M. Vanderhaeghen: Two-photon exchange corrections to elastic e-p scattering Phys. Rev. D 95 (2017) J. Gasser, M. Hoferichter, H. Leutwyler and A. Rusetsky: Cottingham formula and nucleon polarisabilities Eur. Phys. J. C 75 (2015) proton-neutron difference:

9 space-like and time-like N* excitations space-like region, Q the time-like region is experimentally accessible up to the pseudo-threshold Q 2 = (M N* M N ) 2 = GeV 2 for (1232) = GeV 2 for *(1440) and for very large negative Q 2 Q 2 < (M N* M N ) 2 time-like region, Q

10 The MAID ansatz is basically simple unitary isobar model MAID (in the spirit of dynamical models) unitarized background amplitude unitarized resonance amplitude background amplitude : Born terms, t-channel vector meson exchanges and Regge models resonance amplitude : Nucleon and Delta resonance excitations in Breit-Wigner forms

11 Born terms Born terms play a very different role in pseudoscalar photoproduction: very important for with well-known coupling constant negligible for and with coupling constants < 0.1 important for with practically unknown coupling constants

12 t-channel exchanges (single poles, Regge poles and Regge cuts) Regge trajectories for single poles Regge poles Regge cuts going from the pole model to the Regge model only the propagators must be exchanged: alternatively, if s/s 0 is replaced by fixed-t dispersion relations hold for the Regge amplitudes Regge cuts effectively describe the exchange of 2 trajectories as +f 2 or +P etc. and can contribute to all 4 inv. amplitudes Donnachie, Kalashnikova, 2016

13 The MAID ansatz is basically simple unitary isobar model MAID (in spirit of dynamical models) unitarized background amplitude unitarized resonance amplitude resonance amplitude (Breit-Wigner form) phenomenological parametrization of transition form factors:

14 Resonance excitations isospin conservation: in and N* and can be excited in and only N* are possible in s channel: N*, can be excited on shell in u channel: N*, are off-shell excluded in the isobar model therefore, crossing symmetry is violated in any case the u channel acts more like a background and can be absorbed by other bg contributions crossing symmetry can be restored with fixed-t dispersion relations further details (model dependence) of the MAID Breit-Wigner ansatz:

15 energy-dependent width (very important for pole positions) The width of a Breit-Wigner resonance must be energy dependent. Without the energy dependence, it is just a pole Ansatz and works only in a narrow region around an isolated resonance, very bad for baryons. The following Ansatz provides a correct threshold behavior. At the resonance position W = M R it is normalized to the full width. At high energy the Ansatz is more flexible and model dependent. BW mass M R e.g. for S 11 (1535) pole position in first approximation:

16 MAID2007 with only 4-star4 resonances in PDG 2016 N* resonance table 7 N**** in MAID2007

17 MAID2007 with only 4-star4 resonances in PDG 2016 N* resonance table 6 **** in MAID2007

18 comparing MAID to other models or analyses and to data MAID is not the best model, when it is compared to data: 1) MAID is not so young anymore 2) MAID was not made up to fit everything 3) MAID was constructed by following a minimalistic principle, which means as few parameters as possible these are practically only the real- and virtual photon amplitudes: A 1/2 (Q 2 ), A 3/2 (Q 2 ), S 1/2 (Q 2 ) also called transition form factors other parameters are taken from the literature or PDG in the past, MAID has often proven to exhibit predictive power

19 MAID, SAID and BnGa - comparison for total cross section S+P S+P+D S+P+D+F S+P+D+F+G P. Adlarson et al. (A2 Collaboration at MAMI), Phys. Rev. C92 (2015) Legendre analysis of the differential cross section with statistical errors green and systematical errors cyan MAID2007 SAID CM2012 BG2014 a very detailed comparison is made in Anisovich et al., EPJ A 52 (2016) for new polarization data

20 the main motivation for the development of MAID were the NN* transition form factors and the JLab N* program

21 First NN* N* transition form factor measurement for (1232) Anderson et al, 1952: discovery of the (1232) resonance Roper, 1964: discovery of the Roper resonance N(1440) Ash et al, 1967: inclusive cross section at the peak of the (1232) resonance: Physics Letters 24B (1967)

22 Inelastic Electron Scattering in the Delta Region negligible Ash et al., PL 24B (1967) they also cite Fischer 1966 with a remarkable result from photoproduction analysis: * G M (0)

23 Our analysis with unitary isobar model MAID 98 * G M (0) mainly from a decisive experiment with d d and for and in the region by R. Beck et al. in Mainz

24 Inclusive Cross Section for Real and Virtual Photo Absorption

25 other N and NN* * transition form factors even for the second largest peak of N(1520) the form factors cannot be reliably obtained from inclusive cross sections in general: transition form factors can only be obtained by partial wave analysis, e.g. MAID, JLab separate S 11, P 11, P 33, D 13, F 15, etc from angular distributions and background / resonance separation separate bg and res parts in each partial wave

26 empirical parametrizations for electroproduction the magnetic form factors has a very simple form Q² max 10 GeV² for all other resonances we use the general form: numerical examples for a few resonances: (complete results with 10 resonances: in our Review EPJ ST 198 (2011) 141) 5 GeV² ?? 4?? 4 4 4

27 transition form factors magnetic (M1), electric (E2) & Coulomb (C2) from MAID analysis helicity A 1/2, A 3/2, S 1/2 form factors Sachs E2, M1, C2 form factors

28 N N(1440)1/2 1/2 and N N(1535)1/2 1/2 excitation from MAID ( ) and JLab ( ) analyses P 11 (1440) P 11 (1440) S 11 (1535) S 11 (1535)

29 longitudinal transition form factor of N Roper result of beam-recoil polarization measurement of MAMI/A1 collaboration obtained with beam-recoil double polarization at Q GeV S. Stajner et al. (A1 Collaboration at MAMI), PRL 119, (2017)

30 N N(1520)3/2 and N N(1680)5/2 excitation data : practically all cross sections that went into the fits are from CLAS analysis : MAID MAID JLab JLab

31 currently we are working on an EtaMAID update (this work started about 2 years ago and preliminary results are available, we hope to finish it by the end of the year)

32 Regge + Resonance contributions for photoproduction total cross section Regge + Resonance background from Regge contribution

33 Eta-MAID update with new resonances PDG 2016 N* resonance table 8 N* in 2001/ new N* investigated in 2015/ N* with no evidence for in latest analysis 2017

34 Eta-MAID update: total cross sections for and V. Kashevarov et al. (A2 collaboration at MAMI), PRL 118 (2017) p p p p background bg best fit Regge bg + 3 S 11 res GW/SAID GE09 EtaMAID 2003 best fit S 11 (1895) P 13 (1900) D 13 (2120) Huang 2013 EtaMAID 2003

35 Results for N½ S 11 resonances Results for N½ S 11 V. Kashevarov et al. (A2 collaboration at MAMI), PRL 118 (2017) PDG 2016 PDG 2016 no PDG averages Sokoyan, 2015 for N(1895): effective N = (38 ± 20) % interesting question about N(1895): Is the pole below or above threshold? This is not yet settled!

36 Summary and Outlook work recently finished V. Kashevarov, M. Ostrick, L.T. EtaMAID ( and ') with Regge phenomenology and search for and ' couplings for all N* resonances Mainz-Tuzla-Zagreb Collaboration model-independent single-energy PWA with fixed-t analyticity for A. Svarc, R. Workman, L.T. transition form factors at the pole for MAID and SAID solutions with L+P expansion method in Q 2 region: 0 < Q 2 < 5 GeV 2 future plans V. Kashevarov, L.T. MAID (e,e' ) update with 2- and 3-star N and resonances KaonMAID update