Status and plans for 2016, CERN NA63

Abstract

In the NA63 experiment of May 2015 the purpose was primarily to measure the photon spectrum of channeled electrons in diamond with relevance to using diamond as a pair production target for future linear colliders and secondarily to look for the effect of radiation reaction as described in [Di Piazza et al.(2015)Di Piazza, Wistisen, and Uggerhøj]. The setup was designed to be able to be efficient from photon energies as low as ~40MeV. This was estimated based on requiring the energy of a deflected particle in the magnet to stay within the final detector ’M6’, see figure 1, i.e. a deflection of ~1cm at ’M6’ should correspond to 40 MeV. This was, however, not achieved in the experiment. A large drop off of efficiency is seen already at 1.5GeV as seen in figure 4. We have since investigated the cause of this and made a detailed simulation of the whole setup. The most significant effect for the large difference in the expected and achieved lower energy cut off is due to the fact that Bethe-Heitler pair production tends to give one of the produced particles a large fraction of the energy and the subsequently large multiple Coulomb scattering of the low energy particle of the produced pair within the ’Converter foil’ (see figure 1) is so large that it escapes the detectors ’M3’ to ’M6’. This can be partly alleviated by making a more compact setup, i.e. moving the last 4 MIMOSA detectors closer together and possibly acquiring a smaller magnet. However, due to the small size of the MIMOSA detectors it becomes difficult to measure energies below 1GeV. This is not the relevant energy regime for the investigation of a pair production scheme and we therefore wish to focus on the investigation of classical radiation reaction for the run in the summer of 2016. The 100GeV electron data which was taken during the 2015 run shows very promising results in this regard and a redesigned experiment based on what we learned during the 2015 run are expected to give results which can test the Landau Lifshitz equation of classical radiation reaction [Landau(2013)]