Highlights from SuperKEKB Phase 2 Commissioning

Abstract: SuperKEKB is an electron-positron asymmetric-energy collider to search new physics phenomena appeared in B-meson decays. In order to accomplish this purpose, 40 times the luminosity as high as the KEKB collider is demanded. The strategy is that the vertical beta function at the IP is squeezed down to 1/20 and the beam currents double those of KEKB while keeping the same beam-beam parameter. The vertical beta function at the interaction point(IP) will be much smaller than the bunch length, however, the hourglass effect which degrades the luminosity will be reduced by adopting a novel "nano-beam" scheme. First of all, the Phase 2 commissioning was focused on the verification of nano-beam scheme. Secondary, beam related background at the Belle II detector was also studied for the preparation of the pixel vertex detector installed before the Phase 3 operation. The preliminary results and accomplishments of the commissioning in Phase 2 will be reported in this article.