arXiv subjects

C. F. Nielsen

Publications and source records attributed to C. F. Nielsen.

2 recordsLinked to original sources

arXiv2021

Single Particle Detection System for Strong-Field QED Experiments

Measuring signatures of strong-field quantum electrodynamics (SF-QED) processes in an intense laser field is an experimental challenge: it requires detectors to be highly sensitive to single electrons and positrons in the presence of the typically very strong x-ray and $γ$-photon background levels. In this paper, we describe a particle detector capable of diagnosing single leptons from SF-QED interactions and discuss the background level simulations for the upcoming Experiment-320 at FACET-II (SLAC National Accelerator Laboratory). The single particle detection system described here combines pixelated scintillation LYSO screens and a Cherenkov calorimeter. We detail the performance of the system using simulations and a calibration of the Cherenkov detector at the ELBE accelerator. Single 3 GeV leptons are expected to produce approximately 537 detectable photons in a single calorimeter channel. This signal is compared to Monte-Carlo simulations of the experiment. A signal-to-noise ratio of 18 in a single Cherenkov calorimeter detector is expected and a spectral resolution of 2% is achieved using the pixelated LYSO screens.

hep-ex↗

arXiv2019

Quantum radiation reaction in aligned crystals beyond the local constant field approximation

We report on experimental spectra of photons radiated by 50 GeV positrons crossing silicon single crystals of thicknesses 1.1 mm, 2.0 mm, 4.2 mm, and 6.2 mm at sufficiently small angles to the (110) planes that their motion effectively is governed by the continuum crystal potential. The experiment covers a new regime of interaction where each positron emits several hard photons, whose recoil are not negligible and which are formed on lengths where the variation of the crystal field cannot be ignored. As a result neither the single-photon semiclassical theory of Baier et al. nor the conventional cascade approach to multiple hard photon emissions (quantum radiation reaction) based on the local constant field approximation are able to reproduce the experimental results. After developing a theoretical scheme which incorporates the essential physical features of the experiments, i.e., multiple emissions, photon recoil and background field variation within the radiation formation length, we show that it provides results in convincing agreement with the data.

physics.plasm-ph↗