The MINOS Experiment

Andy BlakeCambridge University

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)

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)

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.

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.

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!

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

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.

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

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 …

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.