[Paper Review] Further evidence for N(1900)P_{13} from photoproduction of hyperons

V. A. Nikonov, A. V. Anisovich+3 more|arXiv (Cornell University)|Jul 24, 2007

Quantum Chromodynamics and Particle Interactions4 citations

TL;DR

This paper presents further evidence for the $N(1900)P_{13}$ resonance using new CLAS data on double polarization observables in photoproduction of hyperons ($\gamma p \to \Lambda K^+, \Sigma^0 K^+$). The analysis of multiple photo- and pion-induced reactions reveals two solution classes, both requiring $N(1900)P_{13}$ with pole positions at $(1915 \pm 50) - i(90 \pm 25)$ MeV, confirming its existence as a 2-star resonance predicted by symmetric three-quark models but not by diquark-quark models.

ABSTRACT

We report further evidence for $N(1900)P_{13}$ from an analysis of a large variety of photo- and pion-induced reactions, in particular from the new CLAS measurements of double polarization observables for photoproduction of hyperons. The data are consistent with two classes of solutions both requiring contributions from $N(1900)P_{13}$ but giving different $N(1900)P_{13}$ pole positions. $(M-iΓ/2) = (1915\pm50)-i(90\pm25)$ MeV covers both solutions. The small elasticity of 10% or less explains why it was difficult to observe the state in $πN$ elastic scattering. $N(1900)P_{13}$ is a 2-star resonance which is predicted by symmetric three-quark models. In diquark-quark models, the existence of the state is not expected.

Motivation & Objective

• To provide independent confirmation of the $N(1900)P_{13}$ resonance, which is predicted by symmetric three-quark models but not by diquark-quark models.
• To resolve the experimental difficulty in observing the state, which has low elasticity (~10%) in $\pi N$ scattering.
• To analyze new CLAS measurements of spin transfer coefficients $C_x$ and $C_z$ in $\gamma p \to \Lambda K^+$ and $\gamma p \to \Sigma^0 K^+$ to constrain resonance properties.
• To improve the description of a broad range of photo- and pion-induced reactions by including an additional $P_{13}$ resonance not accounted for in prior fits.
• To determine the pole positions, branching ratios, and helicity couplings of $N(1900)P_{13}$ using a coupled-channel analysis with multiple reaction channels.

Proposed method

• A coupled-channel analysis is performed using data from photoproduction of hyperons, including differential cross sections and double polarization observables $C_x$ and $C_z$ from CLAS.
• The analysis incorporates a large dataset of photo- and pion-induced reactions, including beam, target, and recoil asymmetries.
• Pole positions are extracted from the $S$-matrix via residues of the $T$-matrix, with helicity amplitudes and phases calculated as residues at the pole locations.
• Two classes of solutions are found, both requiring a $P_{13}$ resonance with masses at $1870 \pm 15$ MeV and $1960 \pm 15$ MeV, respectively.
• The resonance's properties are constrained by fitting to data, with the final mass and width reported as $M = 1915 \pm 50$ MeV and $\Gamma = 180 \pm 40$ MeV, covering both solution classes.
• Branching ratios and helicity couplings are calculated for decay modes including $\pi N$, $\eta N$, $K\Lambda$, $K\Sigma$, and $D_{13}(1520)\pi$.

Experimental results

Research questions

• RQ1 Does the new CLAS data on double polarization observables provide further evidence for the existence of the $N(1900)P_{13}$ resonance?
• RQ2 Can the observed data be consistently described by including an additional $P_{13}$ resonance not present in previous fits?
• RQ3 What are the pole positions, widths, and branching ratios of the $N(1900)P_{13}$ resonance, and how do they compare to PDG listings?
• RQ4 Why is the $N(1900)P_{13}$ resonance difficult to observe in $\pi N$ elastic scattering, and how does its low elasticity affect detection?
• RQ5 Is the $N(1900)P_{13}$ resonance more consistent with symmetric three-quark models or diquark-quark models?

Key findings

• The analysis reveals two solution classes, both requiring a $P_{13}$ resonance with pole positions at $1870 \pm 15$ MeV and $1960 \pm 15$ MeV, respectively.
• The resonance mass and width are determined as $M = 1915 \pm 50$ MeV and $\Gamma = 180 \pm 40$ MeV, covering both solution classes.
• The elastic width is estimated at 10% or less, explaining the difficulty in observing the state in $\pi N$ elastic scattering.
• Branching ratios to $\Lambda K^+$ and $\Sigma K^+$ are found to be 5–15%, consistent with the PDG's $\Lambda K^+$ branching fraction of $2.4 \pm 0.3$%.
• The $N(1900)P_{13}$ resonance is unlikely to be explained by diquark-quark models, as it is predicted by symmetric three-quark models.
• Helicity couplings $A_{1/2}$ and $A_{3/2}$ are found to be small and negative in one solution, indicating weak coupling to the $\pi N$ channel.