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Register a new userObservation of the Charge Symmetry Breaking d + d -> 4He + pi0 Reaction Near Threshold
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We report the first observation of the charge symmetry breaking d + d -> 4He + pi0 reaction near threshold at the Indiana University Cyclotron Facility. Kinematic reconstruction permitted the separation of 4He + pi0 events from double radiative capture 4He + gamma + gamma events. We measured total cross sections for neutron pion production of 12.7 +- 2.2 pb at 228.5 MeV and 15.1 +- 3.1 pb at 231.8 MeV. The uncertainty is dominated by statistical errors.
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We consider the reaction g+d -> pi+d in a wide energy range around and above the eta-meson photoproduction threshold at backward CM angles of the outgoing pion. Our theoretical analysis is essentially motivated by the recent measurements of the CLAS Collaboration at Jefferson Lab, where this kinematical region of the reaction has been thoroughly studied for the first time and a cusps in the energy dependence of the differential cross section in the region of Eg = 600-800 MeV has been observed. Our preliminary and qualitative analysis, based on single- and double-scattering diagrams, shows that the observed structure can be explained by the contribution of the double-scattering diagram with intermediate production of the eta meson. The effect, to a considerable extent, is formed due to the contribution of N(1535) resonance to the amplitudes of subprocesses on the nucleons.
The total cross section of the p d -> p d eta reaction has been measured at two energies near threshold by detecting the final proton and deuteron in a magneti spectrometer. The values are somewhat larger than expected on the basis of two simple theoretical estimates.
To investigate the interaction between the nucleon $N$ and nucleon resonance $N(1535)1/2^-$, the $eta d$ threshold structure, connected to the isoscalar $S$-wave $N$-$N(1535)1/2^-$ system, has been experimentally studied in the $gamma{d}${$to$}$pi^0eta{d}$ reaction at incident photon energies ranging from the reaction threshold to 1.15 GeV. A strong enhancement is observed near the $eta d$ threshold over the three-body phase-space contribution in the $eta d$ invariant-mass distribution. An analysis incorporating the known isovector resonance $mathcal{D}_{12}$ with a spin-parity of $2^+$ in the $pi^0d$ channel has revealed the existence of a narrow isoscalar resonance-like structure $mathcal{D}_{eta d}$ with $1^-$ in the $eta d$ system. The Breit-Wigner mass of $mathcal{D}_{eta d}$ is found to be $2.425^{-0.006}_{+0.003}$ GeV, located just close to the $eta d$ threshold, and the width is $0.034_{-0.003}^{+0.004}$ GeV. The $mathcal{D}_{eta d}$ would be a predicted isoscalar $1^-$ $eta NN$ bound state from the $eta NN$ and $pi NN$ coupled-channel calculation, or $eta d$ virtual state owing to strong $eta d$ attraction.
The forward--backward asymmetry in n p --> d pi^0, which must be zero in the center-of-mass system if charge symmetry is respected, has been measured to be [17.2 +/- 8 (stat) +/- 5.5 (sys)] * 10^{-4}, at an incident neutron energy of 279.5 MeV. This charge symmetry breaking observable was extracted by fitting the data with GEANT-based simulations and is compared to recent chiral effective field theory calculations, with implications regarding the value of the u d quark mass difference.
The first measurement of the p n -> d omega total cross section has been achieved at mean excess energies of Q = 28 and 57 MeV by using a deuterium cluster-jet target. The momentum of the fast deuteron was measured in the ANKE spectrometer at COSY-Juelich and that of the slow spectator proton p(sp) from the p d -> p(sp) d omega reaction in a silicon telescope placed close to the target. The cross sections lie above those measured for p p -> p p omega but seem to be below theoretical predictions.
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