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Analyzing   photoproduction data on the proton

Analyzing   photoproduction data on the proton. H. Haberzettl (GWU) K. Nakayama (UGA) key references: PRC69, 065212 (’04), nucl-th/0507044. Outline of the talk. Motivation. Description of  N    N (in conjunction with NN → h ′ NN):

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Analyzing   photoproduction data on the proton

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  1. Analyzing  photoproduction data on the proton H. Haberzettl (GWU)K. Nakayama (UGA) key references: PRC69, 065212 (’04), nucl-th/0507044

  2. Outline of the talk • Motivation. • Description of N  N (in conjunction with NN→h′NN): ● model for gN→h′N. ●analysis of the SAPHIR data (PLB444, ’98). ●analysis of the (preliminary) CLAS data (M. Dugger et al.). • Outlook.

  3. Motivation • Extract information on nucleon resonances in the less explored higher N* mass region: • ● high-mass resonances in low partial-wave states. • ● missing resonances. ● excitation mechanism of these resonances. • Constrain the NNh′ coupling constant (0≤ gNNh′ ≤ 7.3): • ● particular interest in connection to the “nucleon-spin crisis” • (EMC collaboration,PLB206, ’88). NNh′ coupling constant is related • to the flavor-singlet axial charge GA through the U(1) • Goldberger-Treiman relation: Shore&Veneziano, NPB381, ’92. GA(0) ≈ 0.16±0.10 (SMC collaboration, PRD56,’97) quark contribution to the proton “spin” gluon contribution to the proton “spin”

  4. Available photoproduction data & models : Theory: ● quark models: Z. Li, JPG23, ’97. Q. Zhao, PRC63, ’01. ● (tree-level) effective Lagrangian: J. Zhang et al., PRC52, ’95. B. Borasoy, EPJA9, ’00. W. Chiang et al., PRC68, ’03. A. Sibirtsev et al., nucl-th/0303044. ● unitary approach: B. Borasoy et al., PRC66, ‘02. (s-wave coupled channel relativistic unitary approach ) Experiment: ● total cross sections: ABBHHM, PR175, ’68. AHHM, NPB108, ’76. SAPHIR, PLB444, ’98. ● angular distributions: SAPHIR, PLB444, ’98. CLAS, (M. Dugger, this meeting) ● expected data: Crystal Barrel - ELSA, (I. Jaegle, this meeting).

  5. Aim of the SAPHIR data analysis : • Shed light on the contradictory conclusions of existing model calculations: origin of the shape of the observed angular distribution:  interference among N* (S11 & P13) resonances.[Zhao,’01]  interference between N* (S11) and t-channel (Regge) currents. [Chiang et al., ‘03]  t-channel current(mec + exponential form factor).[Sibirtsev et al., ‘03]  t-channel current: ●Regge trajectory. [Chiang et al., ’03] ●meson-exchange[others] • Are we able to identify N* resonances from the (differential) cross section data ? • Can we constrain the NN coupling constant, gNN ? • Combined analysis with hadronic induced reactions: NNNN.

  6. N   N (model): GNNh′→ (gNNh′, lNNh′) Gvh′g→ (Lvh′g) cutoff parameter GRNg→ (fRNg) mass (mR) & width ( GR) GRNh′→ (gRNh′ , l RNh′ )

  7. gp→h′p(SAPHIR data, PLB444,’98 ) mec+S11 mec+S11+nuc (a) (b) angular distribution & absolute normalization : due to an interference among different currents. (c) mec+S11+P11

  8. gp→h′p(SAPHIR data, PLB444,’98 ) mec+S11+P11+ nuc (d) gNNh′ cannot be much larger than 3

  9. gp→h′p ( insensitivity of the cross section to the resonance mass ) cross section: rather insensitive to the N* mass.

  10. gp→h′p(mec x Regge trajectory) mec regge Gvh′g Regge trajectory. [Chiang et al., ’03] r,w–exchange + (dip./exp.) form factor at Gvh′g.

  11. Some conclusions with the SAPHIR data : • On the shape of the angular distribution : Interference among different currents (especially, N* & t-channel) is crucial (corroborates the Chiang et al.‘s findings). • r,w–exchange vrs. Regge trajectory: provided one introduces a form factor at the vh′g-vertex (mec), they describe the data equally well. • Cross sections alone are unable to pin down precisely the resonance mass values. • gNNh′< 3. To improve, needs more accurate data at high-energy and large backward angles (more precise CLAS data will change this conclusion).

  12. NN - h′NN(model): DWBA: FSI ISI transition current

  13. pp→h′pp : excitation mechanism of the S11 resonance can be studied total S11(1646) mec P11(1873) (data: SPESIII,’98; COSY11,’98-’04; DISTO,’00)

  14. gp→h′p (preliminary CLAS data, M. Dugger et al. )

  15. pp(M. Dugger et al., latest data set) ● preliminary data ● latest data

  16. gp→h′p( preliminary CLAS data, M. Dugger et al.) : ●resonances required: S11, P11, P13, D13 ●curves correspond to different set of parameters with comparable c2. ●data at more forward and backward angles would constrain more the model parameters.

  17. Resonances : set c2/Ndata gNNh′ resonances included I 3.72 0.01 S11(1913), P11(1994), P13(1909), D13(1900+2084). II 3.85 1.49 S11(1535+1626+2092), P11(1712+2094+2474), P13(1941), D13(1726+2092). III 3.82 0.00 S11(1538+1846), P11(1710+2002), D13(1814+2090). IV * 3.55 1.12 S11(1535+1650+2090), P11(1440+1710+2100), P13(1720+1900), D13(1520+1700+2080). * masses fixed to the PDG values

  18. gp→h′p(dynamical content) : Set I Set II 2/N=3.72 2/N=3.85

  19. 2/N=3.82 gp→h′p(dynamical content) : Set III Set IV 2/N=3.55

  20. gp→h′p( can nuc & mec be fixed ? ) : would require data beyond the resonance region

  21. gp→h′p( prediction for the total cross section ) : ● sharp rise near threshold due to S11 resonance. ● bump around W=2.09 GeV due to D13 (and possibly P11) resonance. [ PDG: D13(2080) **, P11(2100) * ]

  22. gp→h′p( beam and target asymmetries ) : much more sensitive to the model parameters than cross sections

  23. Some conclusions with the CLAS data : • The CLAS data can be reproduced with the inclusion of spin-1/2 and -3/2 resonances, whose (resonance) parameters are consistent with those quoted in the PDG. • The existing cross section data, however, do not impose enough constraints to pin down the resonance parameters. ●data at more forward and backward angles would help constrain more those parameters. ●spin-observables (beam and target asymmetries) will impose much more stringent constraints. • We predict a bump in the total cross section around W=2.09 GeV. If this is confirmed (needs data), D13(2080) and/or P11(2100) resonance is likely to be responsible for this bump. • gNNh′ should not be much larger than 2 (more exclusive data is needed and/or needs to go beyond the resonance region to pin it down).

  24. Outlook : • Experimentally: total cross section. differential cross section for more forward and backward angles. spin-observables: beam and target asymmetries.  nn/dnp (CB at ELSA): shed light on t-channel mesonic current. • Theoretically:  higher spin resonances [D15(1675),F15(1685)]. ●final state interaction (no realistic N FSI is currently available).  coupled channel approach.

  25. The End

  26. Resonance widths , , , R→Np : qiR =qi (W=mR ) R→Npp :

  27. Phenomenological contact current free of any singularities free parameters

  28. Resulting model parameters : R=150 MeV R=150 MeV

  29. Resulting model parameters : 2/N=3.82 2/N=3.85 2/N=3.55 2/N=3.72

  30. gp→h′p( meson-exchange vrs. Regge trajectory ) : High-precision CLAS data: ● Regge trajectory is, at best, comparable to the meson-exchange: c2/N meson-exchange Regge trajectory Set I 3.72 4.19 Set IV 3.55 3.82

  31. Available data & models ( pppp ) : Theory: ● DWBA (meson-exchange models): Sibirtsev & Cassing, EPJA2, ’98. Bernard et al., EPJA4, ’99. Gedalin et al., NPA650, ’99. Baru et al., EPJA6, ’99. Nakayama et al., PRC61, ’99. Experiment: ● total cross sections: SPESIII, PLB438,’98. DISTO, PLB491,’00. COSY11, PRL80,’98; PLB474,’00; PLB482,’03; EPJA20,’04. ● angular distributions: DISTO, PLB491,’00. (Q = 144 MeV) COSY11, EPJA20,’04. (Q = 47 MeV) too many unknown parameters: (need independent reactions to fix some of those parameters)

  32. pp→h′pp (SPESIII,’98; COSY11,’98-’04; DISTO,’00 data) : mec+S11 mec+S11+nucmec+S11+P11mec+S11+P11+nuc

  33. pp→h′pp [ang. distr. at Q=46.6 MeV (COSY11,’04) excluded from the fit] : mec+S11 mec+S11+nucmec+S11+P11mec+S11+P11+nuc

  34. S11 resonace excitation mechanism(s) ? mec+S11 mec+S11+nuc mec+S11+P11 3.62 16.34 11.11 -0.49 -2.25 11.25 0.24 7.75 -1.93

  35. pp-h′pp(some conclusions) : • Dominant reaction mechanism: S11 resonance. • Existing data cannot constrain on the excitation mechanism(s) of the S11 resonance: data on pn→h′pn and/or pn→h′d will impose more stringent constraints (isoscalar vrs isovector meson-exchange).  and also spin-observables (e.g., Ay in -meson production can disentangle pseudoscalar- and vector-meson exchanges; also Axx ). • DISTO vrs. COSY11 data on the angular distribution: needs data for Q > 50 MeV.

  36. pp→h′pp (based on the CLAS data results) :

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