# High purity 100 GeV electron identification with synchrotron radiation

## TL;DR

This paper introduces a novel technique using synchrotron radiation detection with BGO scintillators to identify 100 GeV electrons with high purity, achieving superior suppression of heavy particle contamination in high energy experiments.

## Contribution

The paper presents a new method for electron identification based on synchrotron radiation detection, significantly improving suppression of heavy particle contamination compared to previous techniques.

## Key findings

- Achieved a suppression factor of 10^{-5} for heavy particles.
- Electron detection efficiency of approximately 95%.
- Results agree well with Monte Carlo simulations.

## Abstract

In high energy experiments such as active beam dump searches for rare decays and missing energy events, the beam purity is a crucial parameter. In this paper we present a technique to reject heavy charged particle contamination in the 100 GeV electron beam of the H4 beam line at CERN SPS. The method is based on the detection with BGO scintillators of the synchrotron radiation emitted by the electrons passing through a bending dipole magnet. A 100 GeV $\pi^-$ beam is used to test the method in the NA64 experiment resulting in a suppression factor of $10^{-5}$ while the efficiency for electron detection is $\sim$95%. The spectra and the rejection factors are in very good agreement with the Monte Carlo simulation. The reported suppression factors are significantly better than previously achieved.