Determination of Breit-Wigner features of the S 11 (1535), S 11 (1650), and P 11 (1710) nucleon resonances
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EMENTARY PARTICLES AND FIELDS Theory
Determination of Breit–Wigner Features of the S11(1535) (1535), S11(1650) (1650), and P11 (1710) Nucleon Resonances Е. V. Balandina* , E. M. Leikin, and N. P. Yudin† Institute of Nuclear Physics, Moscow State University, Vorob’evy gory, Moscow, 119992 Russia Received November 2, 2006
Abstract—Basic Breit–Wigner features of the S11 (1535), S11 (1650), and P11 (1710) nucleon resonances are evaluated in a model-independent way on the basis of the results obtained previously from a partialwave analysis of eta-meson photoproduction on protons. PACS numbers: 13.60.Le, 14.20.Gk DOI: 10.1134/S1063778808010201
The present study completes the partial-wave analysis performed previously in [1–3], where we examined the latest data on processes of eta-meson photoproduction on protons. Specifically, we applied there the procedure of an energy-independent analysis to angular distributions for the process γp → ηp that were measured in [4–7]. In that analysis, we employed a linear nonparametric model in the form of an expansion of angular distributions in a series in Legendre polynomials {Eq. (1) in [1]}. In this expansion, the coefficients a0 (W ), where W is the c.m. energy, are given by the sum of the squares of relevant multipole amplitudes {Eq. (2) in [1]}. In order to describe the dependence of a0 on the energy W , use is made of traditional Breit–Wigner formulas similar to those quoted in [2, 8]. The resonance masses WR , the total resonance widths ΓR , and the helicity amplitudes A1/2 serve there as adjustable resonance parameters. Our partial-wave analysis of experimental data obtained in [4] covers the range of c.m. energies between 1490.16 and 1724.15 MeV, where nucleon resonances characterized by identical spin and isospin [S11 (1535), S11 (1650), and P11 (1710)] lie. This energy range was broken down into intervals in which the measurements in question were performed, and the quality of description of the S11 (1535) nucleon resonance on the basis of one of the parametric models (which features one, two, or three resonances) was determined in each of these intervals. Table 1 presents the χ2 /ν values (ν is the number of degrees of freedom) that characterize the quality of description † *
Deceased. E-mail: [email protected]
of the S11 (1535) nucleon resonance by these models in the above energy intervals ∆W and which ensure the verification of the hypothesis that the choice of this model was reasonable. For the nucleon-resonance parameters estimated within the various parametric models, the values that are the most reliable according to the data in Table 1 are given in Table 2. In all cases, estimates obtained from experimental data reported in [4] are within the statistical errors. Similar procedures were implemented upon adding, in nearly the same energy range, two more sets of data from independent experiments—these were data from the experiments reported in [4, 5] and data from four experiments reported in [4–7]. It was legitimate to combine these data since all regression co
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