Nucleon resonances in the fourth-resonance region

Abstract

Abstract.Nucleon and ∆ resonances in the fourth resonance region are studied in a multichannel partial-wave analysis which includes nearly all available data on pion-and photo-induced reactions off protons. In the high-mass range, above 1850 MeV, several alternative solutions yield a good description of the data. For these solutions, masses, widths, pole residues and photo-couplings are given. In particular, we find evidence for nucleon resonances with spin-paritiesFor one set of solutions, there are four resonances forming naturally a spin-quartet of resonances with orbital angular momentum L = 2 and spin S = 3/2 coupling to J = 1/2, · · · , 7/2. Just below 1.9 GeV we find a spin doublet of resonances with J P = 1/2 − and 3/2 − . Since a spin partner with J P = 5/2 − is missing at this mass, the two resonances form a spin doublet which must have a symmetric orbital-angular-momentum wave function with L = 1. For another set of solutions, the four positive-parity resonances are accompanied by mass-degenerate negativeparity partners -as suggested by the conjecture of chiral symmetry restoration. The possibility of a J P = 1/2 + , 3/2 + spin doublet at 1900 MeV belonging to a 20-plet is discussed.

Transverse polarization ofΣ+(1189)in photoproduction on a hydrogen target in CLAS

“…This might indicate that the production mechanisms in these two regimes are different. Recently, several resonances have been shown to exist at around √ s ≈ 2 GeV [11,12]. This difference in polarization might be due to the resonance effects of the different contributing s-channel states in these two mass ranges.…”

“…The main results were obtained in the reactions γp → ΛK + , γp → Σ 0 K + , and γp → Σ + K 0 S [3][4][5][6][7][8][9][10]. Recently, several new resonances have been shown to exist [11,12] at around 2 GeV based on a multichannel partial-wave analysis of existing data on pion-and photon-induced inelastic reactions. In those reactions, hyperons were seen to be polarized normal to the production plane (a plane made by the momentum vector of the beam and the momentum vector of the hyperon, i.e., alonĝ n z =p beam ×p hyperon /|p beam ×p hyperon |) although neither beam nor target were polarized.…”

Experimental study ofηmeson photoproduction reaction at MAMI

“…In order to subtract a background coming from quasi-free reactions on 12 C and 16 O nuclei of the butanol target, measurements on a pure carbon and a liquid hydrogen target were used. Figure 4 shows our preliminary results for differential cross sections together with various theoretical predictions [4,5,[15][16][17] for different bins in the incoming photon energy as a function of the η meson polar angle in the centerof-mass system, θ * η . The present data agree well with previous measurements, but are much more precise.…”

“…The new preliminary data with statistical uncertainties (black circles) are compared to existing partial-wave analysis predictions (red lines: η-MAID [5], blue: SAID GE09 [4]). green: BG2011-02 [15], black: Giessen model [16], magenta: Tryasuchev model [17]. The energy labels on the bottom of each panel indicate the photon energy bins for our data.…”

(1+1)-dimensional entropic gravity

“…[5]). In an attempt to address this shortcoming, real photon beams have been used to excite nucleon targets, providing accurate data to constrain partialwave analyses (PWA) and reaction models used to extract information on the excitation spectrum [6][7][8][9][10][11]. This is the choice method for such studies, as the photon probe has a well-understood interaction (QED) and polarization degrees of freedom (linear and circular).…”