Status for 2015, CERN NA63

We summarize the status for the CERN NA63 collaboration, where in 2015 we have had two runs at the CERN SPS, beamline H4: One with Ar ions at various energies around 75 GeV per nucleon, and one with electrons/positrons of 10-20 GeV. We previously refined and updated our theoretical analyses of bremsstrahlung and delta-electron emission from heavy, and medium-heavy, ultrarelativistic nuclei \cite{Mikk15}. We thus concluded that - although not quite as interesting as for Pb projectiles - projectiles of Ar and/or Xe were suitable for the investigation, and for establishing the method to eventually measure the charge distribution of short-lived ($ct\gtrsim3$m) fragments \cite{Mikk14}. However, as the preliminary data analysis shows, the signal - which requires an intact projectile - is about three orders of magnitude lower than the background, stemming from photon emission (possibly originating from $\pi^0$'s) in coincidence with projectiles that most likely are not intact after the collision. With the presently available equipment, we were unable to effectively veto this background. Furthermore, we have performed a measurement of positrons produced by electrons traversing an aligned diamond target. This mesurement may also be relevant in the context of establishing experimentally the existence of radiation reaction.