Neutrino Scattering Experiment at BNL
Yorikiyo Nagashima
Osaka University, Osaka, Japan
The Standard Model was proposed between 1961 and 1967, but it was not
recognized as such until 1978, when at ICHEP78 in Tokyo, R. Taylor from SLAC
presented the asymmetry of the polarized electron Deuteron scattering data and singled
it out from other experimentally equally viable models. C. Baltay from Yale, in the same
conference, demonstrated that all the Weinberg angles measured in variety of
experiments more or less agreed. The ICHEP 78 was also a scene when the first
scientific results of the 12 GeV Proton Synchrotron at KEK was presented. This marked
the Japanese debut to the world high energy society.
The next year, the Japan-US collaboration project began, and BNL E734 was among
the first approved programs. An urgent topic at that time was to measure the Weinberg
angle in the pure leptonic reaction and confirm if it was the universal constant. The
reaction is free from QCD correction and was considered the most fundamental test of
the model. The detector (fig.3) was a 170 ton liquid scintillator/proportional tube
electromagnetic calorimeter followed by a gamma catcher and muon detector. As the
electron energy E and its scattering angle was constrained by E2 < 2me, the signal was
a single forward going shower. The obtained data and their theoretical expression are
given in fig.4. From the measured data, values of the neutral coupling constants gV and
gA which contain the Weinberg angle are determined with four-fold ambiguity. It was
resolved by combining data from the reactor neutrino and the muon pair production by
electron positron annihilation (fig 5, right). The measured value was
sin2W = 0.199 ±0.0１8(stat) ±0.013(syst)
and confirmed the validity of the Standard Model in the pure leptonic sector. Similar
results were obtained by the CHARM/CERN experiment.
The Weinberg angle was also determined in the elastic (bar)-p scattering and
confirmed the Standard Model in the semi-leptonic sector. The process is parity
violating and the cross section includes the axial vector form factor whose mass
parameter was determined as mA=1.06±0.05 GeV/c2. Another result was the upper
limit of the second-class current which is forbidden by the Standard Model. It is
complementary to that obtained by the nuclear beta decay as the process is at much
higher value of the momentum transfer Q2.
The third topic was the neutrino oscillation e (fig.6). The excluded region
was comparable to the present values at large mixing angle and about a few factors
above the LSND/MiniBooNE results. Note the data were obtained in the 1980’s.
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BNL E734
Precision (then) Measurements
of the Neutral Current Reactions
Determination of the Weinberg Mixing Angle
e  e and e  e
p  p and p  p
Neutrino Oscillation
Other themes
Axial Vector Form factor
Neutrino Magnetic Moment
Search for Heavy neutrino
Second Class Current
Figure 1: Topics of this talk
Figure 2: List of E734 participants
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E734 Detector
Liquid Scintillator Calorimetor:
4 m x 4 m x 0.1 m (16 cells), 112 modules, total 170 tons,
+ Proportinal Drift Tubes
~2  interactions/burst (1.4 s)
(~16, 25X0)
Figure 3: Layout of E734 Detector
BKG
BKG
Figure 4: Differential distributions in 2 for the neutrino and antineutrino scattering with
electrons. Data are points with error bars.
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Present PDG value (e)
E734
LEP EWWG Phys. Rep. 427 (2006) 257
Figure 5: Left: Values of gA and gV with four fold ambiguity obtained from E734.
Right: constraints from world experiments on gA-gV circa 1987 and 2002 (insert).
Neutrino Oscillation
L=110m <E>=1.2 GeV
Figure 6: constraints obtained by E734 and other experiments. Bands are finite results
from LSND and Mini-BooNE
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