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Analyzing   photoproduction data on the proton

This presentation focuses on analyzing photoproduction data, specifically the reaction γN → η'N, to extract crucial information regarding nucleon resonances in the higher mass region. The analysis includes examination of existing SAPHIR and CLAS data, discussing model interpretations and constraints on the NNη' coupling constant. Key topics include the shape of angular distributions, interference effects among resonances, and implications for the "nucleon-spin crisis." The ultimate aim is to improve our understanding of nucleon dynamics and the excitation mechanisms of high-mass resonances.

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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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