Compton scattering off proton in the third resonance region

Abstract

Compton scattering off the proton in the third resonance region is analyzed for the first time, owing to the full combined analysis of pion- and photo-induced reactions in a coupled-channel effective Lagrangian model with K-matrix approximation. Two isospin $I=3/2$ resonances $D_{33}(1700)$ and $F_{35}(1930)$ are found to be essential in the range of 1.6 - 1.8 GeV. The recent beam asymmetry data of Compton scattering from the GRAAL facility are used to determine the helicity couplings of these resonances, and strong constraints are coming also from $\pi N$ and $K\Sigma$ photoproduction data. The possible spin and parity of new narrow resonances is discussed.Comment: 7 pages, 2 figs, 2 tabs, publish versio

Photo- and electro-production of narrow exotic states: from light quarks to charm and up to bottom

“…A renowned narrow structure at around 1680 MeV close to KΣ threshold was found by Graal group in η photoproduction off neutron [37] and confirmed by many other experiments [38][39][40][41][42]. It was explained by coupledchannel effects due to S 11 (1650) and P 11 (1710) in a Kmatrix approximation coupled-channel model [43,44], which was further used to study Compton scattering off the proton [45]. Alternative interpretations were the interference in the 1/2 − wave -S 11 (1535) and S 11 (1650) -in chiral quark model [46] and Bonn-Gatchina analysis [47,48], and loop contributions from associated strangeness threshold openings [49].…”

“…Whether these states correlate with each other is under investigation. A coupled-channel calculation showed that the narrow structures in Compton scattering γp → γp are feeble after considering carefully all the contribution of known N * and ∆ * [45]. In this paper as an exemplar of the major obstacles we further demonstrate a full set of beam polarization of proton Compton scattering up to the third resonance region in Sec.…”

“…in terms of K f a = V f a accommodating the reaction mechanism of the pion-and photo-induced reactions in the resonance region [43,44,192,193]. The summation over intermediate states a(b) is running only over hadronic states but neglecting the γN so gauge invariance of the Compton amplitude is easily retained [45,164]. Thus, unitarity holds with the merit of technical simplicity and flexibility but at the cost of analyticity.…”

“…This is realized for the first time with the help of the techniques at hand after fixing properly the isospin I = 3/2 amplitude by the KΣ channel [211]. It results into a refined extraction of the amplitudes of Compton scattering off the proton [45]. After a full combined analysis of pion-and photoinduced reactions, beam polarization of proton Compton scattering can be fairly described without free parameters as shown by the solid lines in Fig.…”

“…3. Selected angular bins have been already published [45]. The leading contribution stems from P 33 (1232) and D 13 (1520) in first and second resonance region.…”