EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
CERN-PPE/93-65
15 April 1993
Neutrino Electron Scattering
y x
GabyRadel and Rolf Beyer
y
DESY, Hamburg, Germany
x
CERN, Geneva, Switzerland.
(to appear in Mod. Phys. Lett. A)
Abstract
This article reviews exp erimental results obtained from studies of neutrino elec-
tron scattering and shows in particular the imp ortant input from these exp eri-
ments to the improved knowledge of weak neutral currents and the con rmation
of the Standard Mo del at tree level. Sp ecial emphasis is put on recent high pre-
cision e-exp eriments, whose results on electroweak parameters allow, in combi-
2
nation with precise results obtained at higher Q , a test of the Standard Mo del
at the level of higher order corrections.
Neutrino Electron Scattering
Gaby Radel and Rolf Beyer
Intro duction
The rst observation of a handful of e-scattering events by the Gargamelle bubble chamber [1]in
1973 was a turning p oint in elementary particle physics. The existence of weak neutral currents was
demonstrated. A phenomenon which could not b e explained by the long-standing Fermi-typ e theory
of weak interactions but was predicted by a combined electroweak theory, formulated by Glashow,
Weinb erg, and Salam [2]: the so-called 'Standard Mo del' of electroweak interactions. Since then
several exp eriments with the aim of studying the elastic scattering of neutrinos on electrons have b een
p erformed, all of which added further supp ort to the Standard Mo del.
The rst generation of e-exp eriments, p erformed in the 1970's, were exp eriments dedicated to
the con rmation of the Standard Mo del at tree level. Integral cross sections and rst values for the
2
electroweak mixing angle, sin ,were obtained. These early exp eriments were either p erformed at
W
accelerators in or b eams or at nuclear reactors, where e scattering was observed for the rst
e
time. However, all these exp eriments su ered from rather p o or statistics, due to the very low cross
section of e scattering. In 1980 the numb er of observed events by all exp eriments was in the order
of 100.
The situation changed in the 1980's with the second generation of exp eriments. They were counter
exp eriments with large target mass dedicated neutrino detectors utilizing high intensity neutrino
b eams. The statistics collected were an order of magnitude higher than for the previous generation,
thus making it p ossible to measure kinematical distributions and di erential cross sections. With
the last exp eriment in this series (CHARM I I [3]) electroweak parameters were measured to such
an accuracy that testing the Standard Mo del at higher orders b ecame p ossible. In addition limits
on quantities b eyond the Standard Mo del could b e derived. At last neutrino electron scattering
nowadays is used even as an exp erimental to ol to detect solar neutrinos [4], thus testing the Standard
Solar Mo del.
From a theoretical p oint of view the pro cess of e-scattering is comparatively simple. In the rst,
theoretical, section of this article we de ne the relevant quantities to describ e e-scattering in the
theoretical frame, of the Standard Mo del at tree level. Going to higher orders we make some remarks
on radiative corrections as well as physics b eyond the Standard Mo del.
On the other hand, exp erimentally e-scattering is a very dicult task due the smallness of its