Status in 2021 and request for beamtime in 2022 for CERN NA63

In the NA63 experiment of April 2018 reliable data was taken for 40 and 80 GeV electrons and positrons aligned to the h100i axis of a diamond crystal of thickness 1.5 mm, as well as for 40 and 80 GeV electrons on a 1.0 mm thick diamond aligned to the h100i axis. The 2017 + 2018 results have been published in Phys. Rev. D. and a shorter paper is in the making for a special issue on "Strong Field Quantum Electrodynamics with high power lasers and particle beams" in New Journal of Physics. For the 2017 data, a paper has been published in Phys. Rev. Research in 2019, and our experimental findings have inspired another paper published in Phys. Rev. Lett. For the year 2022 we request 2 weeks of beamtime in the SPS H4 to do a measurement of trident production, e− ! e−e+e−, in strong crystalline fields. We requested 2 weeks of beam time in 2021, but high demand prevented NA63 from getting beam time allocated and we therefore submit our request again. The trident process is closely related to the production of muon pairs, e− ! e−μ+μ−, and single crystals may prove to be an attractive source to obtain muons of high intensity and small emittance, as required for a muon collider. The trident results obtained in 2009, and published in 2010, are strongly at odds with theory (factor 3-4 discrepancy). Since then we have acquired and have been using MIMOSA-26 position-sensitive detectors with a resolution about a factor 40 higher than the drift chambers used in 2009, and now with true multi-hit capability, a significant advantage when looking for trident events. Thus we have substantial improvements in our equipment that enable a much more precise measurement

Status for 2017, CERN NA63

In the NA63 experiment of May-June 2017 the purpose was to look for the effect of classical radiation reaction as described in \cite{DiPiazza20171} but for 50 GeV positrons aligned to the (110) plane of silicon crystals of varying thicknesses in the range 1-6 mm. The data which was taken during the run shows promising results, but the final verdict awaits accurate calculations of the theoretically expected spectra, and a final analysis. For the 2016 results on quantum radiation reaction obtained by CERN NA63, we have submitted a manuscript, which is presently under refereeing \cite{Wist17}

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

Status for 2018, CERN NA63

In the NA63 experiment of April 2018 the purpose was to look for the effect of the derivative term, the so-called Schott-term, in classical radiation reaction as described in \cite{DiPiazza20171}. Data was taken for 20, 40 and 80 GeV electrons and positrons aligned to the $\langle100\rangle$ axis of a diamond crystal of thickness 1.5 mm, as well as for 40 and 80 GeV electrons on a 1.0 mm thick diamond aligned to the $\langle100\rangle$ axis. The data which was taken during the run shows encouraging results, but await a thorough analysis. For the 2017 data, the analysis is still ongoing, but expected to be finished within the coming few months. The results look very promising, but no final conclusion can be drawn at the present stage. For the 2016 results on quantum radiation reaction obtained by CERN NA63, the results have been published in Nature Communications \cite{Wist17}

Status for 2019, CERN NA63

In the NA63 experiment of April 2018 data was taken for 20, 40 and 80 GeV electrons and positrons aligned to the h100i axis of a diamond crystal of thickness 1.5 mm, as well as for 40 and 80 GeV electrons on a 1.0 mm thick diamond aligned to the h100i axis. Off-line analysis has shown that the direction of the crystallographic axis cannot be found with certainty for the 2018 data for 20 GeV, and thus this data set has been discarded. However, the comparison between data and theoretical simulations performed for several angular settings for the 40 and 80 GeV data show remarkable agreement with calculations including the Landau Lifshitz force with a few quantum corrections. A draft of a paper for submission will be finished within the coming month. For the 2017 data, the analysis is finished, shows good results, and a draft of a paper for submission will be finished within the coming month