NuMI Neutrino Beams

On-axis neutrino beam

The NuMI neutrino  beam is being built as a flexible beam. By re-arranging the relative positions of the target and two focusing horns it will be possible to produce beams with different neutrino spectra. These beams are usually referred to as: low/medium/high energy beams.

Charged current event rates expected at the far detector position for different beam configurations under the no oscillations hypothesis are given for 1 kton/year exposure assuming 4x10**20 protons per year on the NuMI target.

Event rates in the near detector hall are approximately 1,000,000 times higher. Neutrino energy spectra at the near detector are very similar to those in the far detector.
 

Off-axis neutrino beams

Neutrinos are produced by the decays of pions and kaons focused into a nearly parallel beam by magnetic horns. The neutrino spectrum is therefore a reflection of the energy distribution of the decaying parent mesons, modulo a factor of 0.43.

What is special about off-axis beams?   For low energy beams, the energy of the  neutrinos produced at 'large'angles is only weakly dependent on the parent pion momentum, as illustrated in   fig .  Lines labeled '10 km' and '20 km' represent decay angles pointing to the detectors located at these transverse distances from the beam axis at the distance  of 735 km from the source.  (This phenomenon was pointed out in the Long Baseline Neutrino Oscillation Proposal for Experiment, E889, at Brookhaven.)

Beam spectra at  off-axis detectors

The spectra of numu CC events expected (in the absence of oscillations)  for 10 kton*year exposures at distances of 5, 10 and 20 km (transversely) from MINOS for a nominal medium energy beam are shown in Event spectra . The event energy spectra do not depend  on the beam setting (low/medium/high energy), but the event rates do.  This can be seen   by looking at the corresponding event spectra for the low  and high  energy beams. The significant reduction of the off-axis neutrino flux in the case of the nominal high energy beam is primarily due to the kinematic reduction of the flux as a function of the decay angle for higher energy pions.

Disappearance experiment with off-axis detectors

Detectors located at the same distance from Fermilab (taken to be 735 km) but at different distances from the beam
axis will probe neutrino oscillations at different L/E ranges. Comparison of the expected (open histogram) and the observed (hatched histogram) CC event spectra for 10 kton*years exposures for maximal mixing angles and different dm**2's
 

Electron neutrino background rates

 Electron neutrino background  is at the level of 0.5% of the numu event rates (at the peak of the numu spectrum).
This background originates from Ke3 decays and from muon decays. At  the peak of the expected numu neutrino event energy distribution this background is dominated (at 90% level) by the neutrinos produced in muon decays (open histogram shows all nue background event, shaded histograms show a contribution of Ke3 decays).These neutrinos are therefore directly related to the muon neutrinos observed in the near detector.
 

Numu event rates at different detector positions

New detectors can be located at different distances from Fermilab, hence optimizing the oscillation probability and/or the matter effects, and at different distances from the nominal beam axis, hence selecting the beam energy and spectrum. Event rates are given in 200 MeV neutrino energy bins for 4x10**20 protons on target and 1 kton detector .
vec files are in ascii format, eps files show the corresponding distribution.
 
L/ DR [km] 5 8 9 10 11 12 15 20
900  numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
850  numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
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800  numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
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735  numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
650  numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps
 numu.vec
 numu.eps

Nue background event rates at different detector positions

Electron neutrino (and antineutrino) events spectra for different detector locations. Event rates are given in 200 MeV neutrino energy bins for 4x10**20 protons on target and 1 kton detector.
vec files are in ascii format, eps files show the corresponding distribution.
 
L/ DR [km] 5 8 9 10 11 12 15 20
900  bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
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850  bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
800  bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
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 bck.vec
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 bck.vec
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 bck.vec
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 bck.vec
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735  bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
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 bck.vec
 bck.eps
650  bck.vec
 bck.eps
 bck.vec
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 bck.vec
 bck.eps
 bck.vec
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 bck.vec
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 bck.vec
 bck.eps
 bck.vec
 bck.eps
 bck.vec
 bck.eps

Nue signal event rates at different detector positions

Assume dm**2=3x10-3 eV**2 and full oscillation of muon neutrinos into electron neutrinos. Electron neutrino events spectra for different detector locations are convolutions of the numu neutrino flux shape and the oscillation probability. Event rates are given in 200 MeV neutrino energy bins for 4x10**20 protons on target and 1 kton detector .
vec files are in ascii format, eps files show the corresponding distribution.
 
L/ DR [km] 5 8 9 10 11 12 15 20
900  sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
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850  sig.vec
 sig.eps
 sig.vec
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 sig.vec
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 sig.eps
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800  sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
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 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
735  sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
 sig.vec
 sig.eps
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650  sig.vec
 sig.eps
 sig.vec
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 sig.eps

Baseline/position optimization


This is just an example of a possible optimization scheme. Assume that we want to maximize the sensitivity of the experiment to  nue appearance. Assume that the neutral current background is reduced below the nue contamination of the beam and that the latter is known. The sensitivity of the appearance experiment is limited by the statistical fluctuations of the (otherwise known) background. The figure of merit can be defined as the ratio of the number of expected nue signal events to the square root of number of the predicted background events.  Furthermore, for every detector position one may define different energy ranges to maximize the experiment sensitivity at this location.

The table shows the result of such an optimization procedure. The entries are:

All numbers refer to a 1 kton*year exposure.
 
L/DR [km] 5 8 9 10 11 12 15 20
900 136.6 
140.9 
1.1 
1.8 
5.2 
146.9 
90.8 
0.4 
2.0 
3.6 
144.6 
81.9 
0.3 
2.0 
3.4 
139.0 
68.6 
0.2 
1.8 
3.0 
129.9 
56.4 
0.2 
1.8 
2.8 
118.6 
43.8 
0.1 
1.8 
2.6 
71.2 
18.9 
0.1 
1.4 
2.0 
15.9 
4.8 
0.1 
0.6 
2.0 
850 135.3 
135.4 
1.0 
1.8 
4.8 
145.6 
88.3 
0.4 
2.0 
3.4 
146.1 
83.4 
0.3 
1.8 
3.2 
139.3 
64.4 
0.2 
1.8 
2.8 
129.8 
55.3 
0.2 
1.6 
2.6 
118.6 
43.5 
0.1 
1.6 
2.4 
67.5 
18.9 
0.1 
1.4 
2.0 
15.5 
5.3 
0.1 
0.6 
2.4 
800 134.6 
144.8 
1.2 
1.6 
4.8 
146.5 
98.0 
0.4 
1.8 
3.4 
145.0 
80.1 
0.3 
1.8 
3.0 
137.5 
58.9 
0.2 
1.8 
2.6 
130.6 
50.8 
0.2 
1.6 
2.4 
116.5 
38.0 
0.1 
1.6 
2.2 
63.6 
16.9 
0.1 
1.2 
1.8 
15.1 
5.0 
0.1 
0.2 
2.2 
735 133.2 
148.0 
1.2 
1.6 
4.6 
146.9 
88.8 
0.4 
1.8 
3.0 
142.6 
80.1 
0.3 
1.6 
2.8 
138.6 
58.9 
0.2 
1.6 
2.4 
126.1 
45.0 
0.1 
1.6 
2.2 
110.9 
36.1 
0.1 
1.4 
2.0 
57.7 
16.3 
0.1 
1.2 
1.8 
14.4 
4.8 
0.1 
0.2 
2.2 
650 130.8 
139.5 
1.1 
1.6 
4.0 
143.4 
81.1 
0.3 
1.6 
2.6 
143.0 
68.5 
0.2 
1.6 
2.4 
133.4 
58.6 
0.2 
1.4 
2.2 
115.9 
46.9 
0.2 
1.2 
2.0 
101.7 
32.9 
0.1 
1.2 
1.8 
49.8 
13.9 
0.1 
1.0 
1.6 
13.7 
4.4 
0.1 
0.4 
2.0 



Last updated on March 30, 2002.
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