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![Page 1: A long baseline neutrino oscillation search - MINOS Reinhard Schwienhorst School of Physics and Astronomy University of Minnesota.](https://reader036.fdocuments.us/reader036/viewer/2022081515/56649e2b5503460f94b19306/html5/thumbnails/1.jpg)
A long baseline neutrino oscillation search -
MINOS
Reinhard Schwienhorst
School of Physics and Astronomy
University of Minnesota
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MIMINNOOSS::
• Introduction
• What are neutrinos?
• Why should neutrinos oscillate?
• How can we search for neutrino oscillations?
• What is the Main Injector?
• How do we search for neutrino oscillations in MINOS?
OutlineOutline
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Neutrinos in the standard Neutrinos in the standard model of particle physicsmodel of particle physics
• Three flavors/generations
• Massless (in the standard model)• The standard model gives no
explanation for these characteristics• The standard model is the fundamental
building block of everything we observe in nature
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Neutrinos are not part of Neutrinos are not part of the atomthe atom
• Everything is made out of atoms– molecules, DNA, we, books,
houses, cars, planets, stars, …
• neutrinos are “extra” particles
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Neutrino interactionsNeutrino interactions
• Neutrinos only participate in “weak interactions”– 1013 neutrinos fly through the
human body, 1 interacts– same as:
1013 tennis balls (fill the state of MN) thrown at you, only 1 hits you.
– Chances of winning the lottery:10-8 It is 100,000 more likely to win the lottery
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Neutrino OscillationsNeutrino Oscillations
• Not part of the standard model
• mass eigenstates might not be flavor eigenstates– flavor eigenstates interact– mass eigenstates travel through
space
• example: oscillations between 2 neutrinos:
square
circle
mass eigenstates: flavor eigenstates:
red
green
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2-neutrino oscillations2-neutrino oscillations
• Example: produce only red neutrinos
• they propagate as circles (75% of them) or squares (25% of them)
red
• Observe (far away from the source):– 63% of the time red
– 37% of the time green!
• red has oscillated into green!
observer75%
25%
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2-neutrino oscillations2-neutrino oscillationsand quantum mechanicsand quantum mechanics
• The probability changes with distance to the source.
• The probability has sinusoidal shape
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3 3.5 4
distance from the source
pro
babi
lity
probability to observe red
probability to observe green
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Neutrino Oscillations, Neutrino Oscillations, the whole storythe whole story
• 3 different flavors• oscillations depend on distance,
neutrino energy, mixing• Neutrino oscillations can
answer a few physics mysteries:– neutrinos may constitute dark
matter in the universe.– They can solve the solar neutrino
puzzle and– explain atmospheric neutrino ratio
• Most Physicists believe neutrinos are massive
• To date no massive neutrino has been found
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Solar neutrino puzzleSolar neutrino puzzle• Observed electron neutrino flux
from the sun is smaller than predicted
• (possible) explanation:neutrino oscillation
5.0flux predicted
flux observed
Atmospheric neutrino ratioAtmospheric neutrino ratio
• Neutrinos from the upper atmosphere
• ratio of electron neutrinos to muon neutrinos is smaller than predicted
• explanation:neutrino oscillation
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Atmospheric neutrino Atmospheric neutrino ratioratio
• Measured by several experiments
• best measurement by the SuperKamiokande detector in Japan
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Atmospheric neutrinosAtmospheric neutrinos
earth
SuperK detector
neutrino
neutrino
•Experimental result:•more green neutrinos from the top than from the bottom
•Explanation: neutrino oscillations!
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Main InjectorMain Injector
• Particle accelerator at Fermilab near Chicago
• accelerates protons and smashes them into a pencil
• that produces many neutrinos– 1018 neutrinos/m2 per year– stand in the beam: 1 interaction
every 5 minutes
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• Neutrino beam from Fermilab to Soudan, MN
The MINOS projectThe MINOS project
Earth
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MINOS detector in the MINOS detector in the Soudan mineSoudan mine
headframe
Mine shaft
MINOS cavern
Fermilab
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MINOS detectorMINOS detector
• 8m by 8m by 25m– size of a 4 story building– 1inch steel plates
• 6,000 tons of steel
• magnetized
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Oscillation search with Oscillation search with MINOSMINOS
• Produce only red neutrinos at Fermilab – (muon neutrinos)
• identify the type of interaction at Soudan– separate red from green
(electron neutrinos, muon neutrinos, tau neutrinos)
• also record the energy dependence – same as distance dependence
• calculate:– difference in neutrino masses– mixing parameter
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MINOS measurement MINOS measurement potentialpotential
mixing parameter
neut
rino
mas
s di
ffer
ence
atmosphericneutrinos
MINOSsensitivity
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GoalsGoals
• Build the detector by 2002
• Collect enough data to confirm or rule out neutrino oscillations in 2 years
• Measure oscillation parameters in detail over the next 20 years
• personal goals:– finish my thesis this summer– continue to work on MINOS as a
postdoc
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Neutrino (Flavor) oscillations
• Simple quantum mechanics
• Flavor eigenstates:
• Each is a superposition of mass eigenstates:
with:– : a mass eigenstate with mass – : a unitary matrix– : a flavor eigenstate
e , ,
U
1
3
m
U
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Flavor oscillationsFlavor oscillations
• Time development of :
• and of :
with
( ) ( )t e UiE t
0
1
3
( ) ( )t e iE t 0
E m p2 2
Oscillation ProbabilityOscillation Probability• In practical units
P Lm L
E
'( ) sin sin .2 2
2
2 127
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Oscillation probability for m^2=0.001eV^2
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14 16 18 20
E (GeV)
P(E
)
Oscillation probability for m^2=0.01eV^2
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 10 20 30 40 50 60
E (GeV)
P(E
)
Oscillation probabilities for sin^2(2)=1, L=730km
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Oscillation testsOscillation tests
• CC/total or T test
– measures disappearance– has the highest sensitivity
• energy measurement of CC events– muon energy through range and
bending in a B field– measures disappearance
• Near/far comparison– reduces systematics on other tests– CC rate comparison measures
disappearance
r
CC interactions
CC and NC interactions
# muon tracks
all events
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Minos detector layout each steel plane is 2-4cm thick each active detector readout plane has 400 readout channels