Mainz: Drechsel, Tiator Taipei: Guan Yeu Chen, SNY P11 resonances with DMT dynamical model for πN scattering and pion e.m. production Shin Nan Yang National Taiwan University Dubna: Kamalov Mainz: Drechsel, Tiator Taipei: Guan Yeu Chen, SNY The 8th International Workshop on the Physics of Excited Nucleons, Jlab, May 17-20, 2011
Motivation for DMT model To construct a meson-exchange model forπN scattering and e.m. production of pion so that a consistent extraction of the resonance properties like, mass, width, and form factors, from both reactions can be achieved. Comparison with LQCD results requires reliable extraction. consistent extractions → minimize model dependence? The resonances we study are always of the type which results from dressing of the quark core by meson cloud. → understand the underlying structure and dynamics 2
Taipei-Argonne πN model: meson-exchange N model below 400 MeV Three-dimensional reduction : Cooper-Jennings reduction scheme which satisfies soft-pion theorem and unitarity 3
Choose to be given by 4
Hung, Yang, and Lee, Phys. Rev. C64, 034309 (2001) renormalization of nucleon mass and pion-nucleon coupling constant done for P11 channel Hung, Yang, and Lee, Phys. Rev. C64, 034309 (2001) 5
DMT πN model: extension of Taipei-Argonne model to energies ≦ 2 GeV Inclusion of ηN channel in S11 Introduce higher resonances as indicated by the data G.Y. Chen et al., Phys. Rev. C 76 (2007) 035206. 6
Extraction of Breit-Wigner parameters With only one resonance, Note that both tB and tR have the same phase of 7
We only have elastic πN cut included !! 9
Self-energy ΣR(E) Breit-Wigner mass MR and width ΓR 10
Dynamical model for N → N To order e, the t-matrix for N → N is written as two ingredients vk , tkN Both on- & off-shell 11
Dubna-Mainz-Taipei (DMT) 12
Test of the backgrounds Near threshold,
Results of DMT model near threshold, 14
M. Weis et al., Eur. Phys. J. A 38 (2008) 27 15
Photon Beam Asymmetry near Threshold Data: A. Schmidt et al., PRL 87 (2001) @ MAMI DMT: S. Kamalov et al., PLB 522 (2001) 16
D. Hornidge (CB@MAMI) private communication PRELIMINARY
The blue dashed lines correspond to the nonresonant background
Bare and physical resonance masses as well as total widths , all in units of MeV, single pion branching ratios , and background phases for resonances. Upper lines: our results, lower lines: results of the PDG. (deg) **** (PDG) 1612 1418 1445±25 436 325±125 44 65±10 32 *** (PDG) 1798 1803 1710±30 508 180±100 15±5 40 * (PDG) 2196 2247 2125±75 1020 260±100 42 12±2 2100
Pole positions and residues for resonances. (deg) SP RM(5) **** (PDG) 1371 1366 1365±15 95 90 95±15 50 48 46±10 -79 -87 -78 -100±35 RM(6) *** (PDG) 1746 1721 1756 1720±50 184 92 150 115±75 11 5 10±4 -54 -164 -49 -175±35 RM * (PDG) 1868 2120±240 238 240±80 7 14±7 -216 35±35
Proton helicity element for fits obtained from LE and HE. MAID 2001 MAID DMT PDG 2000 HE fit -71 -81 -77 -65±4 LE fit -93
black line, full DMT model Blue dashed line, background only red dashed line, no 2nd and 3rd P11 resonances in DMT model
black line, full DMT model red dashed line, removing second P11 resonance from DMT model
with only P11(1710) red MAID 2007 black DMT 2001 green SAID (FA06K)
red MAID 2007 black DMT 2001 green SAID (FA06K)
with addition of a narrow P11 resonance of mass = 1700 MeV, width = 47 MeV with MAID2007
with addition of a narrow P11 resonance of mass = 1700 MeV, width = 47 MeV with MAID2007
SUMMARY Within DMT model for pion-nucleon scattering and pion photoproduction, parameters for the three P11 resonances have been extracted. The extracted values agree well, in general, with the PDG values. ‧only one pole is found corresponding to the Roper. ‧2nd and 3rd P11 resonances are definitely needed in DMT model. ‧indication for a narrow P11 resonance at around 1700 MeV with a width ～ 50 MeV both πN and γπ reactions. The choice of background potentials lead to excellent agreement with low energy neutral pion production data production data from MAMI. → reliable separation of background and resonance contributions ?