neutrino detectors - university of warwick · neutrino detectors ... particles below threshold and...
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Neutrino Detectors
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So, you want to build a neutrino detector?
How many events do you need to do the physics?
Determines detector mass
Determines the target type
What kind of interaction? e,
, CC, NC?
What do you want to measure?
Energy? Final state particles? This influences detector technology
What sort of backgrounds do have to deal with?
More influence on technology – usually conflicting with signal requirements.
How much cash do you have? (most important)
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Neutrino Flavour Identification
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Types of Interactions
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Usual collider detector
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Usual collider detector
Know when and where the interaction will occur. So can design a detector around that point
Neutrinos will interact anywhere
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Detector TechniquesYou can never detect the neutrinos themselves – you haveto detect the products of their interactions and work back.
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Neutrinos interaction anywhere there is mass. More mass, more interactions. Combined with small cross-sections thismeans that detection mass must be large (and therefore cheap) and usually you need to go underground for shielding
Usually large containers of matter surrounded by detectionelements
Radiochemical experiments
Water (H20 or D
20) experiments
Scintillator detectors
Tracking calorimeters
Detector Techniques
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Radiochemical Experiments
This technique uses the production of radioactive isotopes.
Davis-Pontecorvo experiment was the first attempt to use this to look at solar neutrinos
eCl37
Ar 37e
eGa71
Ge37e
The isotopes Ar or Ge are radioactive. In this type ofexperiment the isotopes are chemically extracted andcounted using their decay
Disadvantage is that there is no information on interactiontime, neutrino direction or flavours other than
e
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The Davis Experiment
The very first solar neutrino experiment in the Homestakemine in South Dakota
615 tonnes of CCl4Ran from 1968 to 1994
Individual argonatoms are capturedand counted.
1 atom per 2 days.
Threshold : 814 keV
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Standard Solar Model
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Water ExperimentsWater is a very cheap target material – these experimentsdetect charged particles using Cerenkov radiation.
If a charged particle moves througha material with > 1/n it producesan EM shockwave at a particular angle.
cos=1/ n
The shockwave can be detected and used to measure the particle direction and vertex.Particles below threshold and neutral particles are not detected
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Super-Kamiokande
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Photomultiplier Tubes
50 cm
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Cerenkov light detected as a ring or circle by PMTs
Vertex from timing
Direction from cone
Energy from summed light
No neutrals or charged particles under Cerenkov threshold
Low multiplicity events
Principle of operation
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Directionality
For simple events , the direction of the ring can be used to point back to the neutrino source
Proof that these neutrinos werecoming from the sun
-
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Neutrino-GramImage of the sun 1 kilometer underground
Actual size of sun
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Muons vs Photons
The secondary photon interactions smear out the edge ofCerenkov cone and provide particle identification as well.
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Colours = time of hitEvent energy = sum ofPMT signals
Electron-like : has a fuzzy ring
Muon-like : has a sharp edged ring andparticle stopped in detector.
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ProblemsAny particle below threshold is not seenNeutral particles are not observedMulti-ring events are extremely hard to reconstruct
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Oops
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SNO – A twist
1000 tonnes of D20
6500 tons of H20
Viewed by 10,000 PMTS
In a salt mine 2km undergroundin Sudbury, Canada
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Reactions in SNO
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Deep Water Detectors -KM3Net
Sited off Toulon in the Mediterranean @2400m depth
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Scintillator DetectorsEmission of a pulse light following ionisation
Organic liquids and plastics
Inorganic crystals
Nobel liquids
In a good scintillator, much more light is emitted by scintillation than by the Cerenkov process.Scintillation light is isotropic and there is no threshold.No information on directionality,the emission
wavelength depends on the scintillator material, and thescintillator is usually highly toxic.
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KamLANDExternal container filled
with 3.2 kton H2O
Inner sphere filled with 2 kton of mineral oil
Inside transparent balloon filled with 1 kton of liquid scintillator
Located 1km deep in the Kamioka mine, just up the street from Super-Kamiokande
Very pure – background is a major problem.
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Event Displays epe+
n
np d
200 ms later
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Tracking Detectors and Calorimeters
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Energy Determination
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Magnetic Tracking
pt=0.3 B[T ]r [m ]
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NuTeVIron Sampling calorimeter : CDHS,CHARM,CCFR,NUTEV,MINOS
Typically used for high energy (> a few GeV) beamsIron plates (target) interspersed by scintillator planesMuon tracked and radius of curvature measured in toroidHadronic energy summed from active detector but single
track resolution is not achievable
FermiLab
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NuTeV
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Liquid Argon TPCs
3D tracking with excellent resolutionCalorimetry from energy deposition in filler materialFiller can be gas or liquid. Neutrino Physics looking at liquid argon TPCs
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Summary
Type of neutrino detectors depend on target, event rate, neutrino energies, interaction type and costFour “main” techniques
radiochemical (low threshold but no direction or timing information)
water cerenkov (high threshold, cheap target mass, direction and timing but only low multiplicity events)
scintillator (no threshold but no directionality unless enhanced by water cerenkov)
tracking detectors and calorimeters (high energy events - full reconstruction of events)