First measurement of coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV

Abstract

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonancelike behavior is observed in the excitation function for W γd = 2.38-2.61 GeV, where the d * (2380) dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be 0.034 µb for the dibaryon resonance at W γd = 2.37 GeV (90% confidence level) in the γd → π 0 π 0 d reaction.

Photo-absorption on deuteron contributed by d∗(2380) resonance

“…[40,[86][87][88][89][90]). Even if we can make up for the underestimation of the quark model in some way, the photoabsorption cross section of γd → π 0 π 0 d from the ∆∆ component of d * is around 1 ∼ 2 nb, which is still about one order of magnitude smaller than the currently data of about 28 nb measured by ELPH and A2 at MAINZ [91][92][93][94]. The small signal might be submerged in the contribution from the background, which comes from the other mechanisms, for instance, the conversion of the very small hidden-color configuration in deuteron to a dominated hidden-color configuration in d * , the coupling of the photon to the meson exchange current, and so on.…”

“…Moreover, an experiment on the γd → π 0 π 0 d at the incident energy of 0.55 ∼ 1.15 GeV has been carried out in the Research Center for Electron Photon Sciences (ELPH) at Tohoku University, Japan, and the new data on dibaryon were released. It is shown that a signal of the d * (2380) state with the width of 70 MeV was clearly exhibited in the mass spectrum of π 0 π 0 d, and the corresponding cross section at this resonant point is about 28 nb [93,94]. Compared with the observations, our estimated cross section for the total photon absorption is about 20 times smaller than the data, since the branching ratio of d * → π 0 + π 0 + d is about 14%.…”

Deuteron photodisintegration by polarized photons in the region of the d⁎(2380)

“…The γd → dπ 0 π 0 reaction was recently measured by the A2 collaboration at MAMI [14] and by the Tohoku Collaboration [15]. Both measurements gave similar results σ(γd → d * → dπ 0 π 0 ) ≈ 20 -30 nb (on top of σ(γd → dπ 0 π 0 ) ∼ 15 nb of conventional processes).…”

Study of non-strange dibaryon resonances via coherent double neutral-pion photoproduction on the deuteron

“…The required constraints were energy and three-momentum conservation between the initial and final states and two γγ invariant masses (the neutral-pion rest mass, m π 0 ). Events in which the χ 2 probability was higher than 0.4 were selected to prevent contamination from the background processes [11]. Here, sideband background subtraction was performed because accidental coincidence events exist between the photon-tagging counter and FOREST.…”

“…The details of the analysis for the 0.9-GeV primary electrons including evaluation of the systematic uncertainties are described in Ref. [11]. …”