Pionic Transition Research Articles

Mass determination of the charged pion, using high precision X-ray spectroscopy

X-ray transitions in pionic nitrogen were measured using a curved crystal spectrometer. From the transition energy, calibrated with the help of the copper Ka1,2 electronic transition, a value for the charged pion mass of (139.57071± 0.00053) MeV/c2 was deduced. In order to reduce the uncertainty of the charged pion mass in the level of 1 ppm, we propose the determination of pionic transition energy based on the more precisely known energies and line shapes of muonic transitions.

Pionic transition from Y(4260) to Zc(3900) in a hadronic molecular scenario

We study the pionic transition from Y(4260) to Z c(3900), where Y(4260) and Z c(3900) are regarded as the weakly bound states of D $\bar{D}_{1}$ (2420) + H.c. and D $\bar{D}^{\ast}$ + H.c., respectively. The partial width of Y(4260) $ \rightarrow$ Z c(3900) $\pi$ is estimated to be of the order of MeV with the wave functions of the bound states, where the wave functions are simulated by the simple harmonic oscillator wave functions with equivalent root-mean-square radii.

Measurement of the charged pion mass using X-ray spectroscopy of exotic atoms

The $5g-4f$ transitions in pionic nitrogen and muonic oxygen were measured simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4\,bar. Due to the precise knowledge of the muon mass the muonic line provides the energy calibration for the pionic transition. A value of (139.57077\,$\pm$\,0.00018)\,MeV/c$^{2}$ ($\pm$\,1.3ppm) is derived for the mass of the negatively charged pion, which is 4.2ppm larger than the present world average.

New precision determination of the π − mass from pionic X-rays

The wavelength of the pionic 4f-3d transition in 24Mg has been measured with a curved crystal spectrometer at SIN. The average population of the electronic K-shell during the pionic transition has been determined from the line shape of the pionic X-ray peak which allows a precise calculation of the electron screening correction to the transition energy. The wavelength calibration is based on the 25.7 keV γ-ray standard in the decay of 161Tb ( λ = 48.334488 (64) pm). From the measured wavelength the new value of the pion-electron mass ratio is deduced to be m π −/ m e − = 273.12677 (71). The obtained accuracy of 2.6 ppm is by a factor of 2.5 better compared with the best previous measurement. With this new π −/e − mass ratio the upper limit for the muon neutrino mass is reevaluated.

Spectroscopy of hadrons containing one heavy quark

A simple model for hadrons containing one heavy quark is constructed, starting with the bag model. The model is hydrogenic in that the heavy quark is treated as a point source of color fields located approximately at the center of the bag. A spectrum of hadrons containing one charmed or one bottom quark is presented using bag parameters adjusted for the light hadron masses in addition to a mass parameter for each heavy quark. Electromagnetic and pionic transition rates and the D and F meson weak decay constants ƒ D and ƒ F are computed.

3d→2pPionic Transition inNi58andNi60

The $3d\ensuremath{\rightarrow}2p$ pionic x rays in ${\mathrm{Ni}}^{58}$ and ${\mathrm{Ni}}^{60}$ have been observed in order to measure effects due to the strong interaction between the pion and the nucleus. These isotopes were chosen because nuclear effects in the x-ray energy are expected to be large and the x-ray yield is appreciable. We see a large nuclear level shift and broadening, but no isotope effect within experimental error. The level shift is found to have a strong dependence on the neutron radius, and our results are consistent with the hypothesis of equal neutron and proton rms radii. We also compute the isotope shift for the $2p\ensuremath{\rightarrow}1s$ transition in ${\mathrm{O}}^{16}$ and ${\mathrm{O}}^{18}$ and find that experimental measurements require the neutron radius of ${\mathrm{O}}^{18}$ to be greater than the neutron radius of ${\mathrm{O}}^{16}$. However, uncertainties in the pion-nuclear interaction do not allow an accurate determination of the neutron radius.