Photon energy dependence of left-right asymmetry parameters of Kr 4p photoelectrons in the vicinity of 3d resonant excitations

Complete text of publication follows. A left-right asymmetry was observed experimentally for the outer s-shell photoelectrons of noble gases and of the H2 molecule in our previous studies (see the cited articles for the definition of 'left' and 'right' as well as for the details of the experimental method). Recently, the angular distribution of 4p photoelectrons of Kr was measured with linearly polarized synchrotron radiation in the photon energy range (90 - 94.4 eV) of the 3d-1 → np resonant excitations in order to determine the anisotropy parameters. Now, also the left-right asymmetry parameters have been determined from the measured spectra of Ref. [3]. The experiment was performed at beamline BW3 of the DORIS III storage ring at HASYLAB (Hamburg, Germany). The emitted electrons were analyzed using the ESA-22D electrostatic electron spectrometer. Fig. 1 shows the measured left-right asymmetry parameters (ALR) of the two fine structure components of Kr 4p photoelectrons. The asymmetry parameters (ALR) are increasing with increasing photon energies reaching a maximum value of 0.04, definitely different from zero when considering the error bars. Furthermore, the left-right asymmetry parameters oscillate around the (3d3/2,5/2)-1 → 5p resonant excitation for both fine structure components. Currently, we do not know what kind of interaction can produce a left-right asymmetry in photon-atom collisions but the shape of the oscillations shows interference between the unknown and the resonant excitation channels. One of the most important observations is that the sign of ALR changes from positive to negative and then back again to positive just within a narrow photon energy range of only 250 meV around the (3d5/2)-1 → 5p resonant excitation. Within such a narrow range artificial asymmetry of the experimental setup is totally unconceivable. Acknowledgements. The authors thank the DORIS III staff for providing excellent working conditions. This work was supported by the NKTH-OTKA (Grant No. K67719), and by the European Community-Access to Research Infrastructure Action of the Improving Human Potential Program. Financial support by DESY is gratefully acknowledged.