NON-STRANGE DIBARYONS STUDIED IN COHERENT DOUBLE NEUTRAL-MESON PHOTOPRODUCTION

T. Ishikawaa, H. Fujimuraa, H. Fukasawaa, R. Hashimotoa Q. Hea, Y. Hondaa, T. Iwatab, S. Kaidaa, H. Kandac, J. Kasagia A. Kawanod, S. Kuwasakia, K. Maedac, S. Masumotoe M. Miyabea, F. Miyaharaa, K. Mochizukia, N. Muramatsua A. Nakamuraa, K. Nawaa, S. Ogushia, Y. Okadaa, Y. Onoderaa K. Ozawaf , Y. Sakamotod, M. Satoa, H. Shimizua, H. Sugaia K. Suzukia, Y. Tajimab, S. Takahashia, Y. Taniguchia Y. Tsuchikawaa, H. Yamazakia, R. Yamazakia, H.Y. Yoshidab


Introduction
The structure of hadrons is one of the most important subjects to be studied in the non-perturbative domain of quantum chromodynamics. A B = 2 system (dibaryon) is an interesting object to study its basic configuration from a molecule-like state consisting of two baryons such as the deuteron to a spatially-compact hexaquark hadron state. Understanding dibaryons would not only give a clue to the solution of the current problem in hadron physics but also provide an insight into the nuclear equation of state and the interior of a neutron star [1].
The search for dibaryons has a long history [2]. Recent observations of the d * (2380) dibaryon [3,4] with M = 2.37 GeV, Γ = 0.07 GeV, and I (J π ) = 0 (3 + ) in the pn → π 0 π 0 d reaction have opened the door to study non-strange dibaryons. The d * (2380) may be attributed to a spatially compact hexaquark hadron state and/or an isoscalar ∆∆ quasi-bound state D 03 , which was predicted by Dyson and Xuong [5] as a member of the sextet nonstrange dibaryons D I J with isospin I and spin J. Many experimental investigations of the sextet members have been made, and candidates for almost all the members * e-mail: ishikawa@lns.tohoku.ac.jp are found: the deuteron D 01 , the 1 S 0 -NN virtual state D 10 , an isovector ∆N state D 12 in the π + d → pp reaction [6][7][8][9], an isotensor ∆N state D 21 in the quasi-free pp → π + π − pp reaction [10], and an I = 3 ∆∆ dibaryon D 30 in the pp → π − π − π + π + pp reaction [11]. However, the dibaryonic interpretations of the experimental data for some members are still questionable.
From now on, we focus on D 12 which is a key state of the sextet dibaryons. Experimentally, the evidence for D 12 is given as the 3 P 2 multipole strength at M = 2. 18 GeV in π ± d elastic scattering by a partial-wave analysis [7]. The corresponding 1 D 2 -pp amplitude also shows the same structure in the π + d → pp reaction [8]. The SAID group provides a pole for D 12 [9] from a combined analysis of πd elastic scattering, the π + d → pp reaction, and pp elastic scattering. Hoshizaki shows the D 12 state is required to explain the pp and πd phase parameters [12], and excludes the interpretation of the state as a cusp or a virtual state [13]. Platonova and Kukulin also claim that conventional meson-exchange models do not explain the pp → π + d reaction [14]. Recently, preliminary results for D 12 candidates observed in the γd → π + π − d reaction are reported [15,16], showing a peak with M = 2.1-2.2 GeV and Γ ≃ 0.1 GeV in both the π ± d invariant-mass distribu-tions. The peak position is close to the sum of the N and ∆ masses, and the width is much narrower than the ∆ width. Although these considerations and observations seem to show the existence of D 12 , a possibility of quasi-free (QF) ∆ production cannot be excluded in the interpretation of the experimental data.
There is no doubt that the π ± d system has a resonancelike structure around 2.15 GeV. We study the γd → π 0 π 0 d reaction, aiming to find and observe D 12 in the π 0 d subsystem. Possible production mechanisms for the γd → π 0 π 0 d reaction are classified as follows: Figure 1. Possible mechanisms for the γd → π 0 π 0 d reaction. The R IS and R IV denote isoscalar and isovector dibaryons, respectively. The N p and N s stand for the participant and spectator nucleons in the quasi-free process, respectively.
In the QF-ππ production mechanism, coalescence into a deuteron requires that the two π 0 s should be emitted so as to compensate for the momentum given to N p . In this case, the angular distribution of deuteron emission in the γd center-of-mass (CM) frame shows strongly backward peaking. As for the QF-π production mechanism, the condition for coalescence into R IV makes the distribution sideway peaking at the incident photon energy around 1 GeV. A completely-different rather-flat distribution is obtained in the dibaryon and direct-ππ production mechanisms. It should be noted that the angular distributions are mainly determined by the deuteron or R IV masses and that the other detailed kinematic conditions do not affect the behaviors of the angular distributions. The most serious background of QF N * or ∆ excitation is kinematically separable from the dibaryon production mechanism.

Experiment
A series of meson photoproduction experiments [21] were carried out using the energy-tagged photon beams [22] at the Research Center for Electron Photon Science (ELPH), Tohoku University, Japan. The photon beam was produced by a bremsstrahlung process with a carbon fiber (radiator) with a diameter of 11 µm from the 0.93 and 1.20 GeV circulating electrons in a synchrotron called the STretcher Booster (STB) ring [23]. Each produced photon was energy-tagged by measuring the trajectory of the corresponding post-bremsstrahlung electron with a photontagging detector STB-Tagger II in the bending magnet just after the radiator location. The tagging energy of the photon beam ranged from 0.57 to 0.88 and from 0.74 to 1.15 GeV for 0.93-and 1.20-GeV circulating electrons, respectively. The target used in the experiments was liquid deuterium with a thickness of 45.9 mm. The incident photon energies for the two circulating electron energies give γd center of mass energies W γd s from 2.38 to 2.61 and from 2.51 to 2.80 GeV. The lowest photon energy for the 0.93-GeV circulating electrons corresponds to the centroid of the d * (2380) resonance.
All the final-state particles in the γd → π 0 π 0 d reaction were measured using an electromagnetic calorimeter (EMC) complex, FOREST [24]. FOREST consists of three different EMCs as shown in Fig. 2: the forward EMC consists of 192 pure CsI crystals, the central consists of 252 lead scintillating fiber modules, and the backward consists of 62 lead glass Cherenkov counters, respectively. A plastic scintillator hodoscope (PSH) is placed in front of each calorimeter to identify charged particles. The solid angle of FOREST is approximately 88% in total. The typical photon-tagging rates were 2.8 and 20 MHz, and the photon transmittance ratios (so-called tagging efficiency) were approximately 42% and 53% [22] for the 0.93 and 1.20 circulating electrons, respectively. The trigger condition of the data acquisition (DAQ) was made for detecting more than one final-state particles in coincidence with a photon-tagging signal. The details of the trigger condition are described elsewhere [24]. The average trigger rates were 1.1 and 1.7 kHz, and the average DAQ efficiency were 85% and 79% for the 0.93 and 1.20 circulating electrons, respectively.

Total cross sections
The analysis of the γd → π 0 π 0 d reaction was made in the same way as in Refs. [25,26]. We selected the events containing four neutral particles and a charged particle, and applied a kinematic fit with six constraints: fourmomentum conservation, and every γγ invariant mass being the π 0 mass. Sideband-background subtraction was performed for accidental-coincidence events detected in STB-Tagger II and FOREST. Events in which the χ 2 probability was higher than 0.4 were selected to reduce those from background processes. The most competitive background process was the QF γp ′ → π 0 π 0 p reaction having 100 times higher cross section at maximum [27]. To remove the events from this background process, we made the lower limit of the χ 2 probability relatively higher as 0.4.
The total cross section of the γd → π 0 π 0 d reaction can be obtained from the equation which uses the number of events for the γd → π 0 π 0 d reaction N π 0 π 0 d , the effective number of incident photons N ′ γ , the number of target deuterons per unit area N τ = 0.237 b −1 , the acceptance of the final state π 0 π 0 d → γγγγd detection η acc , and the branching ratio of the neutral pion to the two-photon decay BR(π 0 → γγ). The number of incident photons N γ is determined by multiplying the number of photon-tagging signals after the counting-loss correction by the corresponding photon transmittance. The N ′ γ is a product of multiplying N γ and the DAQ efficiency. The acceptance of γγγγd detection is estimated by a Monte-Carlo simulation based on Geant4 [28]. Here, the event generation is modified from pure phase-space generation to reproduce the following three measured distributions: the ππ invariant mass M ππ , the πd invariant mass M πd , and the deuteron emission angle cos θ d in the γd-CM frame. Fig. 3 shows the total cross section σ as a function of the γd CM energy W γd . The systematic uncertainty of σ includes the uncertainty of event selection in the kinematic fit, that of acceptance owing to the uncertainties of the M ππ , M πd , and cos θ d distributions in event generation of the simulation, that of detection efficiency of deuterons, and that of normalization resulting from the numbers of target deuterons and incident photons. . Total cross section σ as a function of W γd . The circles (cyan) and squares (blue) show σs obtained in Ref. [25] and in Ref. [26], respectively. The horizontal error of each data point corresponds to the coverage of the incident photon energy, and the vertical error shows the statistical error of σ. The solid and dotted curves (green) show theoretical calculations given in Ref. [19] and in Ref. [20] based on the QF-ππ production mechanism, respectively. The dashed curve (red) shows the fitted function (5) expressed by a sum of three Breit-Wigner peaks and phase-space contributions. Each contribution is shown in a dashed dotted curve (red). The lower hatched histograms show the systematic errors of σ.
The excitation function is not monotonically increasing but shows resonance-like behavior peaked at around 2.47 and 2.63 GeV. The two-peak structure is similar to the excitation function of the γN → π 0 π 0 N reaction with two peaks at the γN-CM energy W γN of ∼1.5 and ∼1.7 GeV [17,18], corresponding to the second-and thirdresonance regions of the nucleon. A naive interpretation of this behavior may be a QF excitation of the nucleon in the deuteron, followed by coalescence into the deuteron. The solid curve in Fig. 3 shows a calculation performed by Fix and Ahrenhövel (FA) based on the QF-ππ produc- tion mechanism [19]. The calculation reproduces the data surprisingly well. A calculation performed by Egorov and Fix based [20] on the QF-ππ mechanism also gives a similar excitation function as shown in Fig. 3 (dotted curve). However, as discussed later in section 4.2, the kinematic condition for the obtained data completely differs from the QF-ππ and QF-π production mechanisms. Although the measured cross sections are wellreproduced in the FA calculation, the discrepancy seems observed in the lowest incident photon energy region (∼0.57 GeV). This discrepancy may be explained by excitation of the d * (2380) dibaryon resonance. The d * (2380) contribution is estimated by fitting the function to the data obtained for the 0.92 GeV circulating electrons, where BW(W γd ) denotes the relativistic Breit-Wigner function [29] corresponding to the expected d * (2380) contribution with a centroid of M = 2.37 GeV and a width of Γ = 68 MeV. The σ FA stands for the total cross section in the FA calculation. The χ 2 /dof of the fit is 10.1/15, and the obtained parameter is The d * (2380) contribution is not statistically significant, and the upper limit of the total cross section is found to be 34 nb at W γd = 2.37 GeV (90% confidence level).

Differential cross sections
The differential cross sections, dσ/dM ππ , dσ/dM πd , and dσ/dΩ d , are obtained for each group of photon-tagging channels divided into four groups. All the differential cross sections obtained are plotted in Fig. 2 in Ref. [26].
Here, we focus on the M πd and dσ/dΩ d distributions for the highest photon-tagging group. The M πd distribution is investigated to determine the mass and width of a peak near 2.15 GeV. The differential cross section as a function of the deuteron emission angle dσ/dΩ d is shown to study the reaction mechanism for the γd → π 0 π 0 d reaction.

M πd distribution
The M πd distribution shows two peaks for the higher incident photon energies. The centroid of the low-mass peak is ∼ 2.15 GeV independently of the incident energy. However, that of the high-mass peak decreases with a decrease in the incident energy, and finally the two peaks are merged into a bump. The high-mass peak reflects the appearance of the 2.15-GeV peak in the M πd distribution between the other pion and deuteron (reflection). This interpretation becomes obvious by looking at the correlation between the two M πd s (see Fig. 3(b) in Ref. [26]). The M πd distribution of the FA calculation shown in Fig. 4 (dotted) also shows a similar distribution having two peaks, which are caused by QF π 0 ∆ production.
We have analyzed the M πd distribution in detail. We consider the sequential (dibaryon and QF-π production  (2.14 ) IV GeV R (2.14 ) IV GeV R mechanisms) and non-sequential (QF-ππ and direct-ππ production meachisms) processes of two-π 0 emission. Here, the contribution from the latter process is assumed to be proportional to the phase space. The mass and width are determined by fitting a function, expressed as a sum of a Breit-Wigner (BW) peak, its reflection, and phase-space contributions, to the M πd data. The function is given by convolution of a Gaussian with an experimental mass resolution of σ M = 0.011 GeV, and where V PS (m 1 , m 2 ) expresses the phase-space contribution, represents the BW amplitude with mass M and width Γ. The acceptance is taken into account depending on M ππ , M πd , and cos θ d to estimate V PS (m 1 , m 2 ). The parameters obtained are M = 2.14±0.01 GeV and Γ = 0.09±0.01 GeV. The mass is slightly lower than the sum of the N and ∆ masses (∼ 2.17 GeV), and the width is narrower than that of ∆ (∼ 0.12 GeV) [30]. It should be noted that the FA calculation does not reproduce the M πd distribution, either. The centroid of the second peak is higher at higher incident energy.

Angular distribution of deuteron emission
A great difference between the FA calculation based on the QF-ππ mechanism and the experimental data appears in the angular distribution of deuteron emission dσ/dΩ d in Fig. 5 a gradually-increasing behavior with decrease of cos θ d . While the FA calculation based on the QF-ππ production mechanism provides a strongly backward-peaking behavior. The QF-π production mechanism, giving a sideway peak in dσ/dΩ d at high incident energies in Fig. 5 (dotted curve in magenta), is also rejected. A sideway peak corresponding to the QF-π production mechanism is not observed in the experimental distribution. Since neither backward nor sideway peaks are not observed in the dσ/dΩ d distribution, the sequential and nonsequential processes in section 4 one-to-one correspond to the dibaryon and direct-ππ production mechanisms, respectively. We conclude that the peak at 2.14 GeV in the M πd spectrum is attributed to a dibaryon state, which can be generated in neither the QF-ππ production mechanism nor the QF-π production mechanism. This conclusion gives the dominant sequential process γd → R IS → π 0 R IV → π 0 π 0 d, and motivates the following interpretation for the resonance-like structure in Fig. 3: a dibaryon state can be formed from a deuteron and a photon; the generated state may be a loosely-coupled molecular state; it plays a role as a doorway to a more complicated dibaryon state. Of particular importance is the fact that there is no spectator nucleon in the observed reaction. We fit a function expressed by a sum of three BW peaks and phase-space contributions to the data. The function is given by where σ PS (W γd ) denotes σ for the phase-space contribution, L M,Γ (W γd ) represents a BW function with the centroid of M and width of Γ. Here, three BW peaks are summed up at a cross section level. The M 0 = 2.37 GeV and Γ 0 = 0.07 GeV are fixed to the values for d * (2380) [4], and the absolute values for σ PS (W γd ) are determined to fit the phase-space component in each M πd spectrum (see Fig. 4). The fitted function and each contribution to it are also plotted in Fig. 3

Spin-parity
Information on the spin-parity of the dibaryon states has been deduced from angular distributions of π 0 s obtained for the events from M πd = 2.05-2.25 GeV in Fig. 4. We define π 1 and π 2 as follows: π 2 is one of the two pions giving 2.05 ≤ M πd < 2.25 GeV, and π 1 is the other pion. Here, we assume π 1 is emitted first in the dominant dibaryon production mechanism, leaving the π 2 d system with 2.05 ≤ M πd < 2.25 GeV, and π 2 is emitted subsequently. We combine the data of the two highest-energy groups, which covers W γd from 2.66 to 2.80 GeV, to analyze angular distributions. Thus, we expect the reaction sequence γd → R IS (2.63 GeV) → π 1 R IV (2.14 GeV) → π 1 π 2 d together with the direct π 1 π 2 production mechanism. Fig. 6(a) shows the deduced π 1 angular distribution after the acceptance correction is applied in the γd-CM frame with the z axis taken along the incident photon direction. The experimental distribution is well-reproduced by a sum of two terms, constant and proportional to cos θ. This cos θ dependence can be understood as a result of interference between π 1 -emission amplitudes with different parities. The π 2 angular distribution in the rest frame of the π 2 d system (π 1 -π 2 angular correlation) after the acceptance correction is applied is shown in Fig. 6(b), where the z axis is defined to be opposite to the direction of π 1 emission. Unlike Fig. 6(a), the distribution shows almost 90 • symmetry. This implies that the 2.14-GeV resonance is made of a single J π state or mixed states with the same parity (no interference between different parities). The FA calculation (provided in the same kinematic condition) completely fails to reproduce both the angular distributions, due to the difference in the underlying reaction mechanism as discussed previously (QF-ππ production mechanism adopted in the FA calculation is not observed in the experiment). A sharp peak at 0 • in Fig. 6(a) is the reflection of the backward peak in dσ/dΩ d . In Fig. 6(b), the distribution takes an upward-convex shape being opposite to the experiment. We calculate the π 1 and π 2 angular distributions for the reaction sequence γd → R 1 → π 1 R 2 → π 1 π 2 d using the density matrix (statistical tensor) formalism [31], where spins of R 1 and R 2 are denoted by J 1 and J 2 , respectively. The formalism incorporates the exchange symmetry between π 1 and π 2 . A possible contribution from Yield (a.u.) cosθ π2 Figure 6. Acceptance-corrected angular distributions for π 1 in the γd-CM frame (z axis: the photon beam direction) (a), and for π 2 in the π 2 d rest frame (z axis: the opposite direction to π 1 ) (b). Events with M π 2 d = 2.05-2.25 GeV and W γd = 2.66-2.80 GeV are selected. The lower hatched histograms (cyan) show the corresponding systematic errors. The dashed curves (green) show the corresponding distributions in the FA calculations. The angular distributions are plotted with a shaded band (red) for J π 2 = 1 + , 2 + , and 3 − , and with dotted and dash-dotted curves (black) for J π 2 = 1 − and 2 − , respectively. The solid horizontal lines (magenta) show the phase-space contributions.
non-sequential direct π 0 π 0 production mechanism is assumed to be proportional to the phase-space contribution, of which the fraction is determined from the M πd spectrum in Fig. 4 for each photon-tagging group. Since the π 2 angular distribution is almost symmetric with respect to cos θ π 2 = 0, the interference effect may be small. Thus, the contributions from the sequential dibaryon production and non-sequential direct π 0 π 0 production mechanisms are summed up incoherently. A set of the ampli-tudes of sequential processes A ΛΛ is determined for all the Λ = (L 0 , J 1 , L 1 , J 2 , L 2 ) combinations to reproduce the measured π 1 and π 2 angular distributions simultaneously (20 data points), where L 0 , L 1 , and L 2 ≤ 2 denote angular momenta carried by the incident photon, π 1 emission, and π 2 emission, respectively. An amplitude for a mixed state is given by A ΛΛ ′ = (A ΛΛ A Λ ′ Λ ′ ) 1/2 . The S -wave NN * molecular states are assumed to play a role as a doorway to R 1 since all the observed isoscalar dibaryons are close to the sum of NN * masses as discussed in section 6. Here, the considered N * s are D 15 (1675), F 15 (1680), and P 13 (1720), which give dominant contributions in the γN → π 0 π 0 N reaction in the relevant energy region [18]. Hence, J π 1 s under consideration are 1 + , 2 ± , and 3 ± . Additionally, R 2 is assumed to be a single resonance, namely J 2 = J ′ 2 and L 2 = L ′ 2 . In Fig. 6, also shown are the angular distributions calculated for J π 2 = 1 ± , 2 ± , and 3 + . The J π 2 = 0 ± assignments are already excluded because of an isotropic distribution for π 2 emission. The assignments of J π 2 = 1 + , 2 + , and 3 − show almost the same quality to reproduce the angular distributions (29 < χ 2 < 32). We reject the J π 2 = 1 − and 2 − assignments, giving worse distributions (χ 2 = 47 and 55), respectively, with a confidence level of higher than 99.7% (3σ), and leave the possibility of J π 2 = 1 + , 2 + and 3 − . Regarding J π 1 , major components are 1 + (∼70%) and 2 − (∼20%) for the case of J π 2 = 1 + and 2 + , while they are distributed widely to J π 1 = 1 + , 2 ± , and 3 + for J π 2 = 3 − . The J π 2 = 2 + assignment not only coincides with the energy dependence of the 3 P 2 -πd amplitude, but also supports the existence of the predicted D 12 state at 2.14 GeV. The J π 2 = 3 − assignment is consistent with the energy dependence of the 3 D 3 -πd amplitude (about a half strength of 3 P 2 ). There is no experimental sign for a 1 + state, although two isovector 0 − and 2 − states at 2.2 GeV have been reported recently [32]. Most probably, R IS (2.63 GeV) is a mixing state between J π 1 = 1 + (∼70%) and 2 − (∼20%), and J π 2 = 2 + for R IV (2.14 GeV).

Discussion
A rather-flat angular distribution of deuteron emission completely differs from the QF-ππ and QF-π production mechanisms. In addition, the M πd distributions shows a peak at 2.14 GeV. The present work suggests a sequential process γd → R IS → π 0 R IV → π 0 π 0 d is dominant with two 2.47-and 2.63-GeV R IS and a 2.14-GeV R IV . Fig. 7 shows the deuteron hadronic excited spectrum. The three R IS s are photo-excited from the deuteron with masses of 2.37, 2.47, and 2.63 GeV. The spin-parity of R IS (2.37 GeV) is 3 + , and that of R IS (2.63 GeV) is found to be most probably a mixing of 1 + and 2 − . The R IS (2.63 GeV) decays into R IV (2.14 GeV) by emitting π 0 with angular momenta of 0 and 1, and the R IV (2.14 GeV) decays into the deuteron by emitting π 0 with an angular momentum of 1.  The spin-parity of R IS (2.37 GeV) is 3 + , and that of R IS (2.63 GeV) is found to be a mixing of 1 + and 2 − . The R IS (2.63 GeV) decays into R IV (2.14 GeV) by emitting π 0 with angular momenta of 0 and 1, and the R IV (2.14 GeV) decays into the deuteron by emitting π 0 with an angular momentum of 1. The left-side levels show the sum of the nucleon and nucleon resonance masses, and the right-side levels show the masses of the dibaryon sextet member predicted by Dyson and Xuong [5], and the sum of the two baryon masses.
R IS (2.47 GeV) mass. The NN(1675)D 15 , NN(1680)F 15 , and NN(1720)P 13 masses are close to the R IS (2.63 GeV) mass. Thus, we consider the possibility that the S -wave NN * molecular states may play a role as a doorway to the three R IS states. The R IS (2.37 GeV), or d * (2380), has been considered as a mixing state between a spatially compact hexaquark hadron state and an isoscalar ∆∆ quasi-bound state. The R IV would be also attributed to be the N∆ quasi-bound state since its mass is lower than the N∆ mass, and its width is narrower than that of ∆. The dibaryon sextet picture predicted by Dyson and Xuong [5] is now established owing to strong evidence for the existence of the 2.14-GeV isovector dibaryon in the π 0 d channel. Additionally, our work shows evidence of the 2.47 and 2.63-GeV isoscalar dibaryons in the π 0 π 0 d channel. These findings would give a base to explore dibaryon states lying at higher masses.
To study dibaryon states, it is advantageous to find two neutral mesons and the deuteron in the final state. The γd → π 0 ηd reaction also satisfy this condition. The angular distribution of deuteron emission in this reaction also shows rather flat, suggesting dibaryon production mechanism seems dominant. Since the available phase space is very limited in this reaction at incident energies below 1.2 GeV, it is difficult to determine the mass, width, and spinparity of the intermediate dibaryon states using the current data. The maximum energy for circulating electrons in the synchrotron at ELPH has increased after the 2011 earthquake, allowing us to study the γd → π 0 ηd reaction in more detail.

Summary
The total and differential cross sections have been measured for the γd → π 0 π 0 d reaction at E γ = 0.75-1.15 GeV. The measured angular distribution of deuteron emission is rather flat, suggesting that a sequential process γd → R IS → π 0 R IV → π 0 π 0 d is dominant. The total cross section σ as a function of W γd shows isoscalar dibaryons R IS with masses of 2.47 and 2.63 GeV. The σ for R IS with a mass of 2.37 GeV corresponding to the d * (2380) dibaryon observed by the WAST-at-COSY collaboration is found to be 18.4 ± 9.2 nb at the central mass. The π 0 d invariantmass distributions show an isovector dibaryon R IV with a mass of 2.14 GeV. Most probably, R IS (2.63 GeV) is interpreted as a mixing state between J π 1 = 1 + (∼70%) and 2 − (∼20%), and J π 2 = 2 + for R IV (2.14 GeV). The details of the analysis and discussion can be found elsewhere [26].