First MINOS results from the NuMI beam Page: 1 of 5
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First MINOS Results from the NuMI Beam
Nathaniel Tagg, for the MINOS Collaboration
Tufts University, 4 Colby Street, Medford, MA, USA 02155
As of December 2005, the MINOS long-baseline neutrino oscillation experiment collected data with an exposure
of 0.93 x 1020 protons on target. Preliminary analysis of these data reveals a result inconsistent with a no-
oscillation hypothesis at level of 5.8 sigma. The data are consistent with neutrino oscillations reported by
Super-Kamiokande and K2K, with best fit parameters of Om23 = 3.05-0.55 x 10-3 and sin2 2823 = 0.8812 15.
The MINOS long-baseline neutrino oscillation ex-
periment  was designed to accurately measure neu-
trino oscillation parameters by looking for vN disap-
pearance. MINOS will improve the measurements
of Am223 first performed by the Super-Kamiokande
[2, 3] and K2K experiments . In addition, MINOS
is capable of searching for sub-dominant vN -> ve os-
cillations, can look for CPT-violating modes by com-
paring v, to zN, oscillations, and is used to observe
atmospheric neutrinos .
The MINOS experiment uses a beam of v, created
at Fermilab National Laboratory and directed at the
Soudan mine in northern Minnesota, a distance of
735 km. The composition and energy spectrum of the
beam is measured in two detectors, the Near (1 km
downstream from the target) and the Far (735 km
downstream), allowing for precision measurements of
the spectral distortion of the beam.
2. The NuMI Neutrino Beam
The Fermilab Main Injector has a minimum cycle
time of 1.87 s, with a maximum intensity of 4 x 1013
protons per pulse for a maximum average power of
0.4 MW of power on the target. Protons are extracted
from the Main Injector in a single turn, taking ~ 10ps.
The NuMI neutrino beam  is created by directing
these protons onto a water-cooled segmented graphite
target. Secondary pions from the proton-carbon in-
teractions are deflected into the forward direction by
two parabolic focusing elements (horns) before being
allowed to decay in a 675 m evacuated decay volume.
Undecayed secondaries are stopped by an absorber
wall at the end of this volume. The primary proton
beam is monitored for position and intensity on target.
The secondary hadrons and muons are monitored for
position and intensity to ensure good alignment and
composition of the beam.
The NuMI beam has been in operation since late
2004. Near the end of 2005, a total exposure of
0.93 x 1020 protons were delivered to the target. This
exposure was used in the following analysis. At the
end of the run period in March 2006, the maximum in-
tensity delivered to the target was in excess of 25 x 1012
protons per pulse, with a maximum target power of
3. The MINOS Detectors
The MINOS Near and Far detectors are constructed
to have nearly identical composition and cross-section.
The detectors consist of sandwiches of 2.54 cm thick
steel and 1 cm thick plastic scintillator, hung verti-
cally. The polyethylene scintillator is in the form of
4 cm-wide strips, with a co-extruded TiO2 reflective
coating. Along one side of each strip a groove holds
a glued wavelength-shifting optical fibre. Scintillation
light created in the scintillator is caught by the fibre,
shifted, and transported efficiently to the end of the
strip. Clear readout fibres carry the light to multi-
anode photomultipliers for readout.
The detectors act as tracking, sampling calorime-
ters. Strips in adjacent planes are oriented orthogo-
nally, allowing events to be reconstructed in two trans-
verse views. Both detectors are equipped with magnet
coils which generate -1.2 T toroidal magnetic fields,
which act to contain long muon tracks and provide
curvature information for estimating energies.
The Near detector has a total mass of one kiloton,
and 282 of these steel planes, 153 of which are instru-
mented. It uses sampling electronics to distinguish
neutrino events in time, due to the large instantaneous
intensity during a beam spill. The Far detector masses
5.4 kilotons, and consists of 485 steel planes, 484 of
which are instrumented. Because of the low rate in
the Far detector, the strips are read out via an 8-fold
4. Data Selection
Charged-current vN events in the MINOS detectors
appear as long muon tracks accompanied by short
hadronic showers near the event vertex. The two
other distinguishable event classes are neutral-current
events, which appear only as short, sparse hadronic
showers, and ve charged-current events, which appear
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Tagg, Nathaniel & U., /Tufts. First MINOS results from the NuMI beam, article, May 1, 2006; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc882568/m1/1/: accessed April 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.