Pionic hydrogen atoms

Here r is the Bohr radius of the pionic hydrogen atom with i b = 222.56 fm, Qo = 0.142 fm-1 is a kinematical factor and P=1.546 0.009 is the Panofsky ratio [6]. 6e and dr are electromagnetic corrections, which have recently been calculated with a potential model with an accuracy of about 0.5% [7], In a recent study the problem of the electromagnetic corrections is discussed and the potential model ansatz is critizised [8]. 

Recent experiments determined the velocity state of the pionic hydrogen atom at the moment of the charge exchange reaction [23]. These results constrain the input parameters for the cascade calculations as well as the direct X-ray measurements from muonic hydrogen. The results of the cascade calculations can then be used to correct for the influence of the Doppler broadening. 

The exotic hydrogen isotopes (see O Table 28.2) provide numerous interesting processes, like the transfer of the exotic particle from a hydrogen isotope to a heavier nucleus the formation of exotic molecules, which makes the muon catalysis of nuclear fusion possible or measuring the electron density on the hydrogen in molecules using the pionic hydrogen atom. 

As pionic hydrogen atoms found important applications in chemistry most of this chapter is devoted to that particular topic and the rest of hadronic atoms is only briefly summarized. 

Deser S., Goldberger M. L., Baumann K. and Thirring W. Energy Level Displacements in Pi-Mesonic Atoms, Phys. Rev. 96, 774-776 (1954) Anagnostopoulos D. F. et al., Precision measurements in pionic hydrogen, Nucl. Phys. A 721, 849-852 (2003). 

In conclusion it can be stated that the results from scattering data and atom experiments are still contradictory and therefore need further investigation. From the side of the atom experiments it should be clarified whether the shift and the width values of pionic hydrogen and deuterium are true strong interaction effects and are not spoiled by the interaction of the pionic atom with the surrounding molecules. In other words the shift and the width measurements for pionic hydrogen and deuterium should be extrapolated to zero pressure. In a second step state of the art electromagnetic corrections should be applied. 

The still necessary increase in accuracy requires an additional effort. A simultaneous spectroscopy of pionic and muonic hydrogen atoms is planned as the muonic X-rays do not show any strong interaction broadening, but exhibit Doppler broadening similar to pionic atoms. A method was found to measure pionic and muonic X-rays simultaneously. The reduced masses of pionic and muonic hydrogen exhibit almost the same ratio as two lattice plane differences of quartz. With a two crystal set up the pionic and muonic X-rays can be Bragg reflected to the same CCD detector. 

In this work, we have presented the present status of the pion mass measurement from light exotic atoms, and as well as preliminary results for the pionic hydrogen strong interaction shift and width measurement. We have shown that such high accuracy measurements can only be performed in conjunction with highly-charged ion measurements, that provide the necessary spectrometer characterization. As... 

Pion chemistry, i.e., the use of pionic hydrogen in physical chemistry, was invented in Dubna more than 40 years ago (Petrukhin et al. 1967). As shown by the experimental studies of Petrukhin et al., the probability, Wz, that a pion stopped in a compound containing Z-H groups will be absorbed by a proton, i.e., hydrogen bound by Z atoms, depends on the... 

It is evident that the LMM picture is an extremely simple and rough approximation the processes involved are not independent and, as shown byO Fig. 28.9,0 Eq. (28.14) reflects just one of the possible paths for the pion to follow in a simple system of hydrogen bound by a heavier Z atom. For the correct interpretation of pion-chemistry results, the primordial populations of pionic bound states and pion transfer to heavier atoms were studied in gas mixtures with and without hydrogen (Horvath 1984b Muroyama et al. 1999). On the basis of these data several efforts were made to improve on the LMM model, the latest and most successful ones were that by Imanishi et al. (1988) and Shinohara et al. (1996). 

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