The MINOS Experiment Andy Blake Cambridge University.
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Transcript of The MINOS Experiment Andy Blake Cambridge University.
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The MINOS Experiment
Andy BlakeCambridge University
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Neutrinos are the most abundant particles in the universe …
… but the most difficult to detect !
Three flavours – electron, muon, tauWeakly interacting (absorbed by ~10 light years Pb)
Extremely small mass (< 10-36 kg)
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Neutrino OscillationsQuantum mechanical phenomenon –the weak eigenstates can be amixture of the free eigenstates
If neutrinos really mix and have mass,flavour oscillations occur during flight.The oscillation probability is given by:
(L = distance travelled, E = energy, M2 = mass difference squared)
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One example - Atmospheric Neutrinos
• Produced from interactions of cosmic rays with the atmosphere.
• Expect ~ isotropic and e
• and e measured by Japanese Super-Kamiokande experiment (50kT water cerenkov detector)
• Found deficit in upward-going but upward-going travel longer distance to detector so - oscillations may be taking place.
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Main Injector Neutrino Oscillation Search
Soudan Underground Laboratory
Fermi National Accelerator Laboratory
• Produce beam at Fermilab (nr. Chicago).
• Measure beam in two detectors: (1) 1 km away (1kT near detector at Fermilab, IL) (2) 730km away (5kT far detector at Soudan, MN)
• Compare measurements and look for oscillations.
• Beam scheduled to switch on early 2005.
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Wilson Hall for Scale
Target HallNear Detector Hall
Absorber Hall
Proton carrierDecay volume
Muon Monitors
How do you make a neutrino beam … ?
• Fire ~ 1013 protons per second at ~ 50g graphite target.
• Select pions from the resultant spray of secondary particles.
• Focus pions into tight beam.
• Let pions decay inside 600m evacuated pipe to produce muons and neutrinos.
• At end of pipe, absorb muons in rock, leaving just neutrinos!
• Just have to aim beam pipe at your detectors!
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How do you detect a neutrino beam … ?
• 5.4 kT calorimeter (8m x 8m x 30m).
• 485 inch-thick planes of steel.
• ~ 1T magnetic field.
• 93,000 strips of plastic scintillator.
• Muon neutrinos interact inside detector to produce muons, which leave trails of ionization and induce photon emissions in scintillator.
• Photons detected by 1450 PMTs.
• Signal amplified and digitized by sensitive electronics.
• Signature of neutrino interaction: (1) muon track with contained vertex (2) timing + direction consistent with neutrino beam from Fermilab
• Expect to detect ~103 of ~1013 neutrinos that pass through far detector each year.
The Soudan Detector
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How do you measure neutrino oscillations … ?
• Measure energy spectrum at near and far detector.
• Use near spectrum to predict far spectrum for no oscillations.• Look for oscillation dip in ratio of far spectrum to far prediction.
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Cambridge Involvement in MINOS
Far detector neutrino event
Monte Carlo neutrino event
my first atmospheric neutrino !
• Currently 3 staff + 2 graduate students + 1 postdoc.
• Significant software commitments (1) DAQ control software (2) Monte Carlo simulation (3) Data reconstruction + analysis
• Analysis of atmospheric neutrinos.
• Analysis of beam neutrinos.
Oscillation analysis
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New Physics … ?
• The eleventh commandment - “thou shalt not violate CPT in your theories”. • CPT symmetry requires that and have identical properties.
• Separate measurements of and oscillations possible at MINOS.
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An alternative view … Alternative mass hierarchy for neutrinos and anti-neutrinos …
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Summary
• Over the last 5 years, our understanding of neutrino physics has increased hugely.
• Over the next 5 years, a new generation of neutrino experiments will make precise measurements.
• MINOS will be a major part of this experimental effort.
• Cambridge will continue to make significant contributions.