374
L. Camilleri
neutral currents required the rejection of events containing muons in the final state.
Muons were defined as satisfying one of the following categories:
• a particle leaving the visible volume without undergoing a nuclear scatter
• a particle which stops in the chamber and decays to an electron
• a negative particle stopping in the chamber without producing visible products
(44% of negative muons are absorbed in the nucleus).
The hypothesis that the observed neutral current candidates could have been due to
neutral hadrons entering the chamber was rejected as this would have resulted in a
decrease of their number as a function of depth within the chamber, an effect that
was not observed.
A 12-foot bubble chamber [118] (a 26 m 3 cylinder) was used in the neutrino
beam at the Argonne Zero Gradient Synchrotron (ZGS). It was the first chamber to
use a superconducting magnet.
The superconducting technology was then used in subsequent bubble chambers.
BEBC (the Big European Bubble Chamber) was a 33.5 m 3 bubble chamber,
Fig. 8.19, operating in a 3.5 T magnetic field and was exposed to the CERN neutrino
beams. It was equipped with an External Muon Identifier (EMI) [119] consisting of
proportional wire chambers placed behind an iron absorber and covering an area
6 m high and 25 m wide. A muon candidate track observed within the chamber was
confirmed as a muon if, when its trajectory was extrapolated to the EMI, a hit was
found within a distance consisting with multiple scattering. In order to reduce the
miss-classification of events due to the random association of a neutral current event
with a background muon in the EMI, an Internal Picket Fence [120] of proportional
tubes placed between the chamber body and the magnet cryostat provided timing
information for all events occurring within BEBC with a resolution of 230 ns full
width. The tubes operated within the BEBC magnetic field. The chamber was used
with fillings of liquid hydrogen, liquid deuterium or a neon-hydrogen mixture. This
allowed the study of both νp and νn interactions. It was also used with a 3 m 3 Track
Sensitive Target (TST) which, when filled with hydrogen within a neon-hydrogen
environment provided a sample of clean interactions within the hydrogen which
could be compared to interactions in the neon for which nuclear effects had to be
taken into account. In addition the heavier neon allowed a more efficient detection
of secondaries.
The 15-foot bubble chamber at Fermilab ran in a magnetic field of 3.0 T. When
filled with a neon-hydrogen mixture [121] (61.7% atomic neon and 38.3% atomic
hydrogen) it provided a 23 ton target with a density of 0.75 g · cm −3 , an interaction
length of 125 cm and a radiation length of 40 cm. It was also fitted with an external
muon identifier.
L. Camilleri
neutral currents required the rejection of events containing muons in the final state.
Muons were defined as satisfying one of the following categories:
• a particle leaving the visible volume without undergoing a nuclear scatter
• a particle which stops in the chamber and decays to an electron
• a negative particle stopping in the chamber without producing visible products
(44% of negative muons are absorbed in the nucleus).
The hypothesis that the observed neutral current candidates could have been due to
neutral hadrons entering the chamber was rejected as this would have resulted in a
decrease of their number as a function of depth within the chamber, an effect that
was not observed.
A 12-foot bubble chamber [118] (a 26 m 3 cylinder) was used in the neutrino
beam at the Argonne Zero Gradient Synchrotron (ZGS). It was the first chamber to
use a superconducting magnet.
The superconducting technology was then used in subsequent bubble chambers.
BEBC (the Big European Bubble Chamber) was a 33.5 m 3 bubble chamber,
Fig. 8.19, operating in a 3.5 T magnetic field and was exposed to the CERN neutrino
beams. It was equipped with an External Muon Identifier (EMI) [119] consisting of
proportional wire chambers placed behind an iron absorber and covering an area
6 m high and 25 m wide. A muon candidate track observed within the chamber was
confirmed as a muon if, when its trajectory was extrapolated to the EMI, a hit was
found within a distance consisting with multiple scattering. In order to reduce the
miss-classification of events due to the random association of a neutral current event
with a background muon in the EMI, an Internal Picket Fence [120] of proportional
tubes placed between the chamber body and the magnet cryostat provided timing
information for all events occurring within BEBC with a resolution of 230 ns full
width. The tubes operated within the BEBC magnetic field. The chamber was used
with fillings of liquid hydrogen, liquid deuterium or a neon-hydrogen mixture. This
allowed the study of both νp and νn interactions. It was also used with a 3 m 3 Track
Sensitive Target (TST) which, when filled with hydrogen within a neon-hydrogen
environment provided a sample of clean interactions within the hydrogen which
could be compared to interactions in the neon for which nuclear effects had to be
taken into account. In addition the heavier neon allowed a more efficient detection
of secondaries.
The 15-foot bubble chamber at Fermilab ran in a magnetic field of 3.0 T. When
filled with a neon-hydrogen mixture [121] (61.7% atomic neon and 38.3% atomic
hydrogen) it provided a 23 ton target with a density of 0.75 g · cm −3 , an interaction
length of 125 cm and a radiation length of 40 cm. It was also fitted with an external
muon identifier.