High purity 100 GeV electron identification with synchrotron radiation

E Depero,M Hösgen,F Dubinin,A Fabich,D.V Peshekhonov,B Radics,A Rubbia,V.D Samoylenko,V.A Polyakov,D Cooke,P Crivelli,S Emmenegger,S.V Donskov,V Lysan,P Ulloa,A Gardikiotis,D Banerjee,B Ketzer,Yu.V Mikhailov,A Toropin ,A Karneyeu ,V.e Burtsev ,V Matveev ,В Фролов ,S Kuleshov ,R R Dusaev ,V O Tikhomirov ,V A Kramarenko ,M Kirsanov ,A.g Chumakov ,S Gninenko ,D Tlisov ,G A Vasquez ,Valery E Lyubovitskij ,B I Vasilishin ,A Dermenev ,V D Peshekhonov ,V V Myalkovskiy ,I Konorov

doi:10.1016/j.nima.2017.05.028

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 π− 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 ∼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.

Highlights

Many high energy experiments require pure electron beams
The dipole magnets installed in series produce a total integrated magnetic field of 7 T⋅m [2] resulting in a nominal displacement for the incoming electrons at the synchrotron radiation detector (SRD)/electromagnetic calorimeter (ECAL) positions of 31/34 cm from the undeflected beam axis
The SRD was placed between the undeflected and the deflected beam axis at a distance of approximately 9 cm from both (Fig. 4). This separation minimizes the possibility for Bremsstrahlung photons and neutral particles produced by interactions of the beam particle with materials upstream and for particles in the beam halo to hit the SRD

Summary

Introduction

Many high energy experiments require pure electron beams. The available energy of pure primary beams from electron machines is limited. Secondary electron beams can provide higher beam energies with a uniform time structure. In secondary beams a contamination of particles other than electrons below a level of few % is basically unavoidable. An example is the NA64 experiment at CERN in which it is mandatory to suppress hadron and muon contamination in the electron beam since such particles can generate irreducible background processes mimicking the experimental signature of a dark photon [1,2]. NA64 uses 100 GeV electrons from the H4 SPS beam line at CERN which is one of the best existing beam lines at this energy in terms of beam purity [3]

Methods

Results

Conclusion