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P.A. Zolnierczuk
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We report a search for d^* dibaryon production by double-radiative capture on pionic deuterium. The experiment was conducted at the TRIUMF cyclotron using the RMC cylindrical pair spectrometer, and detected gamma-ray coincidences following pion stops in liquid deuterium. We found no evidence for narrow dibaryons, and obtained a branching ratio upper limit, BR < 6.7 times 10^{-6} (90% C.L.), for narrow d^* production in the mass range from 1920 to 1980 MeV. Replaced with Physics Letter B accepted version and corrected normalization.
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We report measurements of double radiative capture in pionic hydrogen and pionic deuterium. The measurements were performed with the RMC spectrometer at the TRIUMF cyclotron by recording photon pairs from pion stops in liquid hydrogen and deuterium targets. We obtained absolute branching ratios of $(3.02 pm 0.27 (stat.) pm 0.31 (syst.)) times 10^{-5}$ for hydrogen and $(1.42 pm ^{0.09}_{0.12} (stat.) pm 0.11 (syst.)) times 10^{-5}$ for deuterium, and relative branching ratios of double radiative capture to single radiative capture of $(7.68 pm 0.69(stat.) pm 0.79(syst.)) times 10^{-5}$ for hydrogen and $(5.44 pm^{0.34}_{0.46}(stat.) pm 0.42(syst.)) times 10^{-5}$ for deuterium. For hydrogen, the measured branching ratio and photon energy-angle distributions are in fair agreement with a reaction mechanism involving the annihilation of the incident $pi^-$ on the $pi^+$ cloud of the target proton. For deuterium, the measured branching ratio and energy-angle distributions are qualitatively consistent with simple arguments for the expected role of the spectator neutron. A comparison between our hydrogen and deuterium data and earlier beryllium and carbon data reveals substantial changes in the relative branching ratios and the energy-angle distributions and is in agreement with the expected evolution of the reaction dynamics from an annihilation process in S-state capture to a bremsstrahlung process in P-state capture. Lastly, we comment on the relevance of the double radiative process to the investigation of the charged pion polarizability and the in-medium pion field.
The strong interaction shift and broadening in pionic deuterium have been remeasured with high statistics by means of the (3p-1s) X-ray transition using the cyclotron trap and a high-resolution crystal spectrometer. Preliminary results are (-2325+/-31) meV (repulsive) for the shift and (1171+23/-49} meV for the width, which yields precise values for the pion-deuteron scattering length and the threshold parameter for pion production.
The strong interaction shift $epsilon$ and broadening {Gamma} in pionic deuterium have been determined in a high statistics study of the {pi}D(3p - 1s) X-ray transition using a high-resolution crystal spectrometer. The pionic deuterium shift will provide constraints for the pion-nucleon isospin scattering lengths extracted from measurements of shift and broadening in pionic hydrogen. The hadronic broadening is related to pion absorption and production at threshold. The results are epsilon = (-2356 {pm} 31)meV (repulsive) and {Gamma}1s = (1171+23/-49) meV yielding for the complex {pi}D scattering length a = [-(24.99 {pm} 0.33) + i (6.22+0.12/-0.26)]x10-3/m{pi}. From the imaginary part, the threshold parameter for pion production is obtained to be {alpha} = (251 +5/-11) {mu}b. This allows, in addition, and by using results from pion absorption in 3He at threshold, the determination of the effective couplings g0 and g1 for s-wave pion absorption on isoscalar and isovector NN pairs.
A search for the muon catalyzed fusion reaction dd --> ^4He +gamma in the ddmu muonic molecule was performed using the experimental mu CF installation TRITON and NaI(Tl) detectors for gamma-quanta. The high pressure target filled with deuterium at temperatures from 85 K to 800 K was exposed to the negative muon beam of the JINR phasotron to detect gamma-quanta with energy 23.8 MeV. The first experimental estimation for the yield of the radiative deuteron capture from the ddmu state J=1 was obtained at the level n_{gamma}leq 2times 10^{-5} per one fusion.
The 12C+16O resonant radiative capture reaction has been studied at 5 bombarding energies between Elab = 15.4 and 21.4 MeV, around the Coulomb barrier, at the Triumf laboratory (Vancouver, Canada) using the Dragon 0{deg} spectrometer and the associated BGO array. The most remarquable result is the previously unobserved decay path through 28Si doorway states of energies around 12 MeV leading to the measurement of new capture cross-sections. The feeding of specific, deformed states in 28Si from the resonances is discussed, as well as the selective feeding of 1^+ T=1 states around 11 MeV.
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