Neutrino detection

1
Neutrino detection
Neutrinos are very special there is a lot of
them around but they are very difficult
to detect

• Therefore well talk about
• Neutrino interactions (cross sections)
• Going underground with detectors
• Techniques of very large detectors

From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
2
Cross sections
A cross section s is a measure of interaction
probability. A number of interactions is
Nint Ntarget s F
where F is a flux ( cm-2) of the projectile
particles. Hence s is measured in cm2. It can be
seen as an effective surface of a target. For
strong interactions s is 1barn10-24
cm2 Differential cross sections
distributions of energies and angles
of secondary particles
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
3
Neutrino cross sections
From Fermi theory the cross section for a CC
interaction
are the relative velocities in the initial and
final states
is
q is momentum in cms Fermi constant
For reaction
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
4
Neutrino cross sections
For a CC interaction
is
For reaction
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
5
Neutrino interaction length
or mean free path between collisions
For neutrinos of 1 GeV pathing Earth lets take
Energy needed for l to become of the size of
Earth
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
6
n interactions with nucleons

• Fermi theory did not involve intermediate
  bosons.
• G constant was determined from experiments
  (neutron lifetime)
• Modern theory of electro-weak interactions
  provides the same
• cross sections at not too large energies

At low energies only anti neutrinos on free
protons neutrinos only on neutrons, (but
those are always bound in nuclei
extra energy needed to compensate for
nuclear binding
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Neutrino scattering on electrons
NC
CC
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
8
ne cross sections low energies
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
9
nm cross sections low energies
m mass 106 MeV
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
10
Neutrino interactions at different energies

• A neutrino of energy E and wavelength lh/E can
  interact with
• 
  
• an electron on the atomic orbit
• a nucleus as a whole (when l is comparable
  to the nucleus size)
• a free proton or a nucleon bound in a nucleus
  (when l is comparable to the nucleon size)
• a quark (when l is much smaller than the
  proton size)

From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
11
nm cross sections high energies
QE (quasi-elastic) Single Pion production (reso
nances)
DIS (deep inelastic scattering)
at high energies
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
12
Angular distributions in n e- scattering
Lets look at Lorentz transformation from CMS to
LAB
independently of qcms
both neutrino and electron mostly forward
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
13
Angular distributions in n e- scattering
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
14
Angular distributions in n N scatteringat low
energies
From neutrinos to cosmic sources, D.
Kielczewska and E. Rondio
15
We have to go underground...
Flux of atmospheric muons below the surface of
Earth
One order of magnitude per 650 m
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How to detect neutrinos i.e. products of their
interactions?

• Go underground to shield the detector from
  other particles
• Make your detector big
• use large volumes
  of cheap materials

Detection techniques

• radiochemical experiments
• water (light or heavy) record Cherenkov light
• scintillators record scintillation light
• liquid argon record drifting electrons from
  ionization
• iron slabs as targets and various detectors to
  record
• exiting particles

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Radiochemical experiments
First one ever used to detect solar neutrinos -
Davis-Pontecorvo reaction
or

• Produced isotopes are radioactive with not too
  long lifetime they are periodically extracted
  and counted
• No information on time of interactions or
  neutrino directions

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Davis experiment at Homestake
615 tons of CCl4 ran from 1968 for about 30
years Nobel prize in 2002

• 37Ar has half-life time for electron capture of
  35 days
• Argon atoms have to be extracted and counted
• - about 1 atom per 2 days

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Solar Neutrino Spectrumthresholds for different
thechniques

• radiochemical
• (Gallium Chlorine)
• low threshold
• only event rates counted
• no time information
• no direction
• Cherenkov detectors
• time and direction
• higher threshold

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WaterCherenkov detectors
BOREXINO, KAMLAND(2) Liquid Scintillator

• Super-Kamiokande
• SNO

n

• cheap material
• directionality
• time of every event
• threshold 4-5 MeV

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Cerenkov Light Emission
(where n is the refractive index of the medium)
Charged particles with velocities
produce the electromagnetic shock-wave along the
conical wavefront at an angle

there is a thereshold effect we get light if
e.g. in water total energy above
1.5 mass
It is used to measure particle velocity (angle
gives b) for slow particles, for relativistic
particles the angle is always very similar (in
water about 42 deg) can be
used to measure particle direction
and vertex reconstruction (the point from
which light is emitted
at the earliest)
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Super-Kamiokande detector

• 50,000 tons of ultra-pure water
• 1000 m underground
• 11,146 photomultipliers (PMT)
• 20 dimension
• 1,885 PMTs in outer layer

42m
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Photomultipliers (PMTs)
Dimension 20 Time uncertainty 1nsec
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Super-Kamiokande during water filling
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Stopping Muon in Super-Kamiokande

• colors time of every hit PMT corrected for
  photon flight time
• muon like from the sharp ring edge
• energy from sum of all PMT signals
• stopped from the ring empty inside
• no signal in outer detector
• second ring decay electron

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muon stopping in the detector
Colors charge at each PMT which measures numbe
r of photons
provide event energy
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two tracks
two tracks passing rings filled tracks
leaving the detector
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muon passing at the adge
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What can be seen in a Cherenkov detector
looking at gs

• gs are not directly seen by PMTs while
• electrons give light if above threshold
• BUT
• gs produce electromagnetic cascades
• they convert to e, e- pairs
• electrons emit bremstrahlung gs
• electron energy is degraded, they
• undergo multiple Coulomb scattering
• light is emitted in directions different
  from original
• in effect
• electrons or gs produce Cherenkov rings more
  smeared than muons or pions

this is only schematic drawing in reality angle
between e and e- is ZERO degree

• low energy particles (below threshold) are not
  visible
• neutrons are only visible by products of their
  interactions

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Particle identification
electrons, gammas
muons, pions, protons
Used in atmospheric ? detection
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Solar neutrinos in SuperKamiokande
Cherenkov light directionality allows
reconstruction of neutrino direction
(approximatly)
neutrinogram of the Sun made in the mine
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PMT photo
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SNO (Sudbury Neutrino Observatory)

• Water detector with a difference
• 2 km underground
• 1000 tonnes D2O
• 104 - 8 PMTs
• 6500 tons H2O

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Results from D2O
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SNO under construction
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n Reactions in SNO
Charged Current Reaction ? 6-9 events per
day ? ne flux and energy spectrum ? Some
directional sensitivity (1 - 1/3COSqe) Neutral
Current Reaction ? 1-2 or 6-8 events per day
(different detection mechanisms) ? Total solar
8B active neutrino flux Elastic Scattering
Reaction ? 1-2.5 events per day
? Directional sensitivity (very
forward peaked)
ne
e-
W
n
p
n
n
Z
n/p
n/p
ne
ne
n
n
ne
e-
W
Z
W
e-
e-
ne
e-
e-
e-
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Scintillator detectors

• in a good scintllator a charged particle emits
  much more scintillation light than Cherenkov
  light
• scintillation light is emitteded isotropically,
• there is practically no energy threshold
• gives precise time of photon arrival which can be
  used for reconstruction of interaction point
• no information about track direction
• wave length depends on the material

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LSND
Liquid Scintilator Neutrino Detector
tank with mineral oil, PMTs on all walls In
Los Alamos,
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Karmen
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MiniBooNE (nm??e) Experiment at Fermilab

• Use protons from the 8 GeV booster ? Neutrino
  Beam ltEngt 1 GeV
• Detector
• 12 m sphere filled with mineral oil and PMTs
• Located at 500m from neutrino source.
• hunderds events signal if LSND is verified
• If signal observed, add second detector at
  appropriate distance(MiniBooNE ? BooNE Exp.)

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Principle of a sandwich detector
Large mass from layers of passive
material for hadronic interactions
iron, concreet, rocks for
electromagnetic interactions
lead Detection in active layers
scintillators drift detectors
silicon detectors
nuclear emulsions ...
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Macro
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Sudan 2
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Minos far detector

• 8m octagonal steel scintillator tracking
  calorimeter
• Sampling every 2.54 cm
• 4cm wide strips of scintillator
• 2 sections, 15m each
• 5.4 kton total mass
• 55/?E for hadrons
• 23/?E for electrons
• Magnetized Iron (B1.5T)
• 484 planes of scintillator
• 26,000 m2

One Supermodule of the Far Detector Taking data
since July with magnetic field. Second
Supermodule 1/4 complete.
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OPERA Detector
2 kTon (Pb) 0.04 kTon emulsion
56 emulsion films / brick

• To the full detector
• 2 supermodules
• 31 walls / supermodule
• 52 x 64 bricks /wall
• 200 000 bricks

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Liquid Argon TPC(Time Projection Chamber)
detector ICARUS with 600 tons liquid Ar ready for
installation in underground laboratory in Gran
Sasso (Italy)
Technique for possible future detectors,
possibility to use it in the magnetic field. Very
interesting for search for proton decay.
Important feature three dimentional image of
all tracks almost no energy threshold
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ICARUS
PMT
Electric Field
UV Light
Ionizing Track
Ionisation electrons may drift over large
distances (meters) in a volume of highly purified
liquid Argon (O2 eq. less than 0.1 ppb !) under
the action of an electric field. With an
appropriate readout system (i.e. a set of fine
pitch wire grids) is it possible to realize a
massive, continuously sensitive bubble chamber
?
Drifting
e-
in LAr
E1
Screen Grid
Induction wire Signal (schematic) Waveform
wire pitch
Charge
E2
d
Induction Plane
T0
Tpeak
time
Tdrift
Amplifier
E3
Light
Collection Plane
d
PMT Signal
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ICARUS Detector T600

• box filled with
• liquid argon
• (temp. about 187oC)
• drift electric field
• 500V/cm
• wire spacing
• 3mm
• cleaning of argon continous
• to get large electron life time
• a module with 300 tons of argon tested with
  cosmic muons in 2001
• we are involved in it

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Solar neutrino detectors
name location mass
reaction start
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Experiments with n from accelerators
name accelerator det. technique
distance mass K2K
KEK water Cherenkov
250 km 50kt MiniBoone Fermilab
liquid scintillator 0.5 km
MINOS Fermilab
iron/scintillator 750 km 4.5kt
(NuMi)

Icarus CERN liquid
argon TPC 730 km 3 kt


Opera CERN
lead/emulsion 730 km 2 kt


longer term future JHF to
SuperKamiokande
300 km 500kTon
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Neutrino telescopessearch for dark matter and
cosmic n sources
Detector Location
Detection method Amanda South pole
Cherenkov light in ice Ice Cube
1km3 Baikal
Russia Cherenkov
light,water Antares Mediteranian Sea
Nestor