A bremsstrahlung-identification technique for cosmic-ray electrons and positrons.pdf

NUCLEAR INSTRUMENTS AND METHODS 122 (x974) 575-585; ~ NORTH-HOLLAND PUBLISHING CO.
A BREMSSTRAHLUNG-IDENTIF1CATION TECHNIQUE FOR COSMIC-RAY
ELECTRONS AND POSITRONS
ANDREW BUFFING1-ON, CHARLES D. ORTH and E F. SMOOI
Space Sciences am/Lawrence Berkeley Laboratory, UnicersiO' (~[' Cal~/brnia, Berkeley, California 94720, .
Received 19 September 1974
We introduce a new technique to separate energetic e ~ and e- using this technique for cosmic-ray e + spectral measurements in
from a background of other particles. The technique utilizes a the energy range from 5 to 50 GeV. Calibrations of the apparatus
selective trigger, radiation of bremsstrahlung photons by inci- at particle accelerators and the method of flight data analysis
dent e ±, ic deflection of the e + after photon emission, and are also described. Our balloon-borne apparatus provides an
the separate detection of both the e ± and the photons in a shower efficiency of about 50% for the detection of e ~ and a proIoll
detector. Descriptions are given of a balloon-borne apparatus rejection of about 10 ~
1. Introduction ground particles is not much greater than 10 -3 . Placing
In this paper we introduce a new technique for iden- several e + identification techniques ill series can of
tifying and separating energetic e + (positrons) and e- course provide better background rejection. A single
(negatrons, electrons) in the primary cosmic rays while application of our new technique results in rejections
providing powerful rejection of the plentiful back- of about 10 s
grourid of heavier particles. Many other techniques for Our technique is based on the simultaneous detection
identifying e + already exist. Cherenkov counters, for both of a particle and its panying bremsstrahlung
example, monly employed both at accelerators ~) radiation. This radiation is characteristic ore -+ but not
and in cosmic-ray measurements2). Visual examination of heavier background par