Neutrino detection

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Neutrino detection

Laura Rossetto

Experimental techniques for particle astrophysics

January 27

^th

2011

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• I – About neutrinos

 short history of neutrino discovery

 different neutrino sources

 neutrino oscillation

 characteristics of neutrino detection

• II – Neutrino experiments Cherenkov detectors:

 SuperKamiokaNDE

 Sudbury Neutrino Observatory (SNO)

 IceCube

Scintillation detectors:

 KamLAND

 Borexino

• III – Neutrinos from SN1987A

 SNEWS

Outline

Laura Rossetto – January 27^th2011

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• The existence of this particle was postulated by Pauli in 1930 to preserve the conservation of energy, momentum and angular momentum in the b decay ( n  p + e^– + n_e )

• the term neutrino was coined by Fermi in 1934

• first detection in 1956 in the so-called Cowan-Reines experiment:

n created in a nuclear reactor were detected in a tank of water through the inverse b decay anti-n_e + p  n + e⁺

• Frederick Reines received the Nobel Prize in Physics in 1995

• n_m first detected in 1962 by Lederman, Schwartz and Steinberg  Nobel Prize in Physics in 1988

• discovery of the solar neutrino problem in 1967  Davis, Nobel Prize in Physics in 2002

• detection of anti-n_e from SN1987a  Koshiba, Nobel Prize in Physics in 2002

• n_t first detected in 2000 by the DONUT collaboration at FermiLab

 observation of missing energy in t decays

 the latest particle of the Standard Model to have been directly observed!!!

I – Neutrino history

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• Cosmic neutrino energy spectrum

 10^-12 eV – 10²⁰ eV

• low energy

 n produced in the Big-Bang

• E ~ 10⁶ eV

 n produced by Supernovae

 solar n

• 10⁸ eV < E < 10¹¹ eV

 atmospheric n

• above ~ 10¹¹ eV

 n from extragalactic sources

• highest energy

 decay products of p’s produced via interactions of cosmic rays with background microwave photons

I – Neutrino energy spectrum

4 Laura Rossetto – January 27^th2011

F. Halzen and S.R. Klein, 2010, Review of Scientific Instruments, 81

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• First experimental evidence in the Homestake Gold Mine experiment (South Dakota) in 1967

• the leader of the experiment was Raymond Davis who received the Nobel Prize in Physics in 2002

• the idea was to detect solar n_e emitted by the decay of ⁸B and ⁷Be in the Sun via the reaction

37Cl + n_e  ³⁷Ar + e^–

• the experiment was built in the mine at 1478 m underground and it consisted of 100000 gallon tank of perchloroethylene C₂Cl₄ , rich in chlorine

• first results: upper limit 3SNU , 1 SNU = 10^–36 captures (target atom)^–1 s^–1

• predictions from the standard solar model (Bahcall & Shaviv, 1967)  7.5 ± 3 SNU

• the solar neutrino problem  the n_e produced in the Sun turned to be only 1/3 of those expected

 results confirmed by KamiokaNDE, Gallex, SNO, KamLAND

 later on this luck of n was interpreted as neutrino oscillation

I – Solar neutrino problem

R. Davis, 2003, ChemPhysChem, 4

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I – Neutrino oscillation

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= U n_e

n_m n_t

( ) ( )

ⁿⁿn¹²₃

c₁₂ = cosJ₁₂, s₁₂ = sinJ₁₂, J₁₂  mixing angle 1–2 c₁₃ = cosJ₁₃, s₁₃ = sinJ₁₃, J₁₃  mixing angle 1–3 c₂₃ = cosJ₂₃, s₂₃ = sinJ₂₃, J₂₃  mixing angle 2–3

The probability of a neutrino changing its flavour is:

• First pointed out by Pontecorvo in 1957

• oscillation  the 3 n species are constituted by a mixing of 3 mass eigenstates (1, 2, 3)

• the mixing matrix is:

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I – Neutrino oscillation

Observed values of oscillation parameters:

• SNO (solar neutrinos) and KamLAND (nuclear reactor neutrinos)

 Sen²(2J₁₂) = 0.82 ± 0.07

 Dm²₁₂ = 8.0 · 10^–5 eV²

T. Araki et al., 2005, Physical Review Letters 94, 081801

• Super–KamiokaNDE (atmospheric neutrinos)

 Sen²(2J₂₃) > 0.92

 1.5 · 10^–3 < Dm²₂₃ < 3.4 · 10^–3 eV²

Y. Ashie et al., 2005, Physical Review D 71, 112005

• CHOOZ (nuclear reactor neutrinos)

 Sen²(2J₁₃) < 0.2 at 90% C.L.

 assuming Dm²₁₃ = 2 · 10^–3 eV²

S. Eidelman et al., 2004, Particle Data Group, Physics Letters B, 592 M. Apollonio et al., 2003, The European Physical Journal C 27, 331

n_en_m

n_mn_t

n_en_t

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• Neutrino detectors must be underground

 large background radiation from cosmic rays interaction in the atmoshpere

• very large detector is required

 very small neutrino cross section (s ~ 10

^–41

cm

²

)

• flavour identification is needed

 atmospheric n

_m

>> atmospheric n

_e

and n

_t

• good energy resolution

 important for identifying where neutrinos are produced (i.e. atmospheric n, Supernovae n, extragalactic sources)

I – Characteristics of neutrino detectors

8 Laura Rossetto – January 27^th2011

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• Cherenkov detectors

 charged-current interactions: n

_e

+ n  p + e

^–

, anti-n

_e

+ p  n + e

⁺

 elastic scattering: n

_x

+ e

^–

 n

_x

+ e

^–

 positrons and electrons emitted Cherenkov light

 KamiokaNDE – SuperKamiokaNDE

 Sudbury Neutrino Observatory (SNO)

 AMANDA – IceCube

 Antares, NEMO, NESTOR – KM3NeT

• Liquid scintillation detectors

 detection of the fluorescence light emitted by excited substance (usually fluoride organic compound): anti-n

_e

+ p  n + e

⁺

 KamLAND

 Borexino

 CHOOZ

 LVD

I – Characteristics of neutrino detectors

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Cherenkov detectors Liquid scintillation detectors

Production of light 100 photons/MeV 10000 photons/MeV

Direction information YES NO

Costs low high

Dimensions 50 ktons – 1 km³ (SuperKamiokaNDE –

IceCube)

up to 1 kton

I – Characteristics of neutrino detectors

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II – Super-KamiokaNDE

• 50 ktons water Cherenkov

detector located at the Kamioka observatory, Japan

• rock overburden of 2700 m.w.e.

• two concentric cylindrical detectors

• inner detector  11146 PMTs

• outer detector  cylindrical shell of water 2.6 – 2.75 m thick;

1885 outward-facing PMTs (4p active veto, thick passive radioactivity shield)

42 m

39.3 m

Mt. Ikenoyama

http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html

• Evolution of the previous KamiokaNDE = Kamioka Nucleon Decay Experiment

• atmospheric n observed via charged–current interactions

• it measured Dm²₂₃ and J₂₃

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II – Super-KamiokaNDE

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42 m

39.3 m

Mt. Ikenoyama

• Evolution of the previous KamiokaNDE = Kamioka Nucleon Decay Experiment

• atmospheric n observed via charged–current interactions

• it measured Dm²₂₃ and J₂₃

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II – Super-KamiokaNDE

Inner detector Outer detector

n_m event n_m + N  X + m

a Cherenkov ring is emitted

n_e event n_e + e^–  n_e + e^–

the emitted electron generates an

electromagnetic shower which is very similar to a Cherenkov ring

The outer PMTs permit to distinguish between neutrino and cosmic ray particle

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II – Sudbury Neutrino Observatory (SNO)

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• Built at 2070 m (~ 6000 m.w.e.) below ground in the Creighton mine near Sudbury, Canada

• two concentric spherical detectors immersed in water (H₂O) within a 30 meter barrel-shaped cavity

• 1000 tons of heavy-water (D₂O) contained by a 12 m diameter transparent acrylic vessel (inner sphere)

• 9600 PMTs mounted on a

geodesic support structure which surrounds the heavy-water vessel

http://www.sno.phy.queensu.ca/

Heavy-water Cherenkov detector designed to detect solar neutrino and to observe the neutrino oscillation flavours (Dm²₁₂ and J₁₂)

Acrylic vessel (D₂O)

Inner H₂O (1.7 kT)

Outer H₂O (5.7 kT)

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proton – proton chain in which solar neutrinos are produced

(Standard Solar Model)

II – Sudbury Neutrino Observatory (SNO)

Charged current reaction n_e + D  p + p + e^–

• it occurs only for n_e at solar neutrino energies ( ~ 100 keV – 10 MeV)

• the recoil e^– energy is strongly correlated with the incident n energy  precise measurement of the ⁸B n energy spectrum

W

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II – Sudbury Neutrino Observatory (SNO)

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Neutral current reaction n_x + D  p + n + n_x

• it’s sensitive to all n flavours

• it provides a direct measurement of the total flux of ⁸B n from the Sun

Electron scattering e^– + n_x  e^– + n_x

• the recoil e^– direction is strongly correlated with the direction of the incident n (direction to the Sun)

• it’s sensitive to all n flavours

• s(n_e) ~ 6.5 s(n_m , n_t)

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II – IceCube

• 1 km³ of Antarctic ice acts as a large tracking calorimeter

• 86 vertical strings arranged on an hexagonal grid (covering 1 km² of the surface) with 60 DOMs each; the total number of DOMs is 5160

• DOMs are attached to the strings every 17 m between 1450 m and 2450 m DOMs

• DeepCore  6 strings situated on a denser 72 m triangular grid

• strings deployed in the ice using hot-water drill

• the complete IceCube will observe several hundred n/day with E > 100 GeV;

DeepCore will observe n with energy up to

~ 10 GeV

Construction will be completed in January 2011

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II – IceCube

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• Each PMT is enclosed in a transparent pressure sphere  Digital Optical Module (DOM)

• a DOM also contains a digitally controlled high voltage supply and a data acquisition system

• IceTop  surface air-shower array consisting of 160 ice-filled tanks (2 tanks for each string), each instrumented with 2 DOMs

• IceTop detects cosmic-ray air showers with a threshold of about 300 TeV

Tanks of the IceTop array

A.Achterberg et al., 2006, Astroparticle Physics, 26

35 cm

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II – IceCube

~ km–long muon tracks from n_m ~ 10m–long cascade from n_e , n_t

• IceCube detects n by observing the Cherenkov radiation from the charged particles produced by n interactions

• m tracks from n_m are ~ km–long  the m direction can be determined accurately (IceCube angular resolution is better than 1° for long tracks)

• tracks from n_e and n_t are shorter  leptons and nuclear targets produce showers

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II – IceCube

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1. 2.

3.

Simulated events of 3 types of neutrino interactions in IceCube:

1. n_m + N  X + m 2. n_e + N  cascade

3. n_t + N  t + cascade₁ 

 cascade₁ + cascade₂

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II – KamLAND

http://kamland.stanford.edu/Pictures/Pictures.html T. Araki et al., 2005, Nature, 436

• KamLAND  Kamioka Liquid scintillator AntiNeutrino Detector

• observation of anti-n_e emitted by nuclear reactors

• a 13-m-diameter transparent balloon containes 1 kton of ultrapure liquid scintillator

• the balloon is suspended in non-scintillating oil and surrounded by 1879 PMTs

• a 3.2 kton water-Cherenkov detector surrounds the containment sphere, absorbing g rays and neutrons from the surrounding rock and detecting cosmic-ray m

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II – KamLAND

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http://kamland.stanford.edu/Pictures/Pictures.html T. Araki et al., 2005, Nature, 436

• anti-n_e are detected via inverse b decay: anti-n_e + p  e⁺ + n

• observation of n oscillation: it detected 258 anti-n_e candidate events with

E > 3.4 MeV compared to 365.2 ± 23.7 events expected in the absence of n oscillation

• most precise measurement of J₁₂ and Dm²₁₂

• first detector that measured the anti-n_e produced in the Earth from the ²³⁸U and ²³²Th (geoneutrini)

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II – Borexino

G. Alimonti et al., 2009 , Nuclear Instruments and Methods in Physics Research A, 600

• Large volume liquid scintillator detector

• it performed measurements of solar n from ⁷Be and ⁸B through n_eelastic scattering

• located deep underground (~ 3600 m.w.e.) at the Gran Sasso Laboratory, Italy

• 278 tons of liquid scintillator contained in a spherical nylon vessel

• the scintillation light is detected via 2212 PMTs located on the inner spherical surface

• the sphere is enclosed in a tank filled with 2100 tons of water as shielding for g and

13.7 m

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III – Supernova neutrinos

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• Explosion of the supernova SN1987A in the Large Magellanic Cloud on February 23^rd 1987

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III – Supernova neutrinos

• Explosion of the supernova SN1987A in the Large Magellanic Cloud on February 23^rd 1987

• a signal associated with the supernova was detected by 4 neutrino detectors:

KamiokaNDE–II (Japan)  Cherenkov water detector

Irvine–Michigan–Brookhaven (IMB, USA)  Cherenkov water detector

Baksan Scintillation Telescope (BST, north Caucasus)  liquid scintillator detector Liquid Scintillator Detector (LSD, Mont Blanc)

• LSD detected 5 pulses with a duration of 7s at 2h 52min 36.8s U.T.

(imitation rate = 1.78 · 10^–3/day)

• IMB, Kamiokande–II and BST detected a second burst delayed by 4.7 hours in comparison with the LSD one

 Koshiba received the Nobel Prize in Physics in 2002 for the first real time observation of supernova neutrinos

• the events detected by IMB, Kamiokande–II and BST are consistent among them

• the events detected by LSD remain still a mystery!!

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III – Supernova neutrinos

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• Standard core–collapse scenario of a supernova: n create during the formation of the neutron star (e^– + p  n_e + n) and then in greater abundance during the rapid cooling phase; theoretical

calculations predict an average neutrino energy ~ 15 MeV which correspond to a total number of n emitted ~ 10⁵⁷ – 10⁵⁸ in few seconds

 this standard scenario cannot explain all the events detected in correlation to the SN1987a

• a new scenario have been proposed: a massive rotating star breaks into 2 fragments with masses M ~ 20 M₀ and m ~ (1 – 2) M₀ ; the massive component continues to collapse and produces the first neutrino burst during the proto-neutron star formation; the low mass star approaches the massive component and because of gravitational losses it will be disrupted

 its matter is accreted by the massive star, thus producing the second neutrino burst

• the problem is still not solved!

Events detected Energy (MeV) Time (U.T.) Dt (s)

LSD 5 5.8 – 7.8 2:52:36.8 7

IMB 8 15 – 40 7:35:41 –

Kamiokande–II 12 6.3 – 35.4 7:35 13

BST 5 12 – 23.3 7:36:12 9

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III – SNEWS

• Waiting the next galactic supernova ...

• SNEWS = SuperNova Early Warning System

• the SNEWS project involves several neutrino detectors currently running or nearing completion, like Super–KamiokaNDE, SNO, LVD, IceCube,

Borexino, etc.

• the idea is to create an alert network linking several neutrino detectors in coincidence

 provide an early warning on the next galactic supernova

• neutrino detection of the next supernova will be very important in

understanding the core–collapse scenario, and perhaps explaining the events

detected during the SN1987A

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• I – About neutrinos

 when and how neutrinos were discovered

 the solar neutrino problem and its solution  neutrino oscillation

 characteristics of neutrino detection

• II – Neutrino experiments

 Cherenkov detectors (Super–KamiokaNDE, SNO, IceCube)

 Scintillation detector (KamLAND, Borexino)

• III – SN1987A neutrinos

 neutrinos emitted from a supernova were detected for the first time

 waiting the next galactic supernova  SNEWS

 new results from neutrino experiments, like IceCube, will probably permit to understand better cosmic rays acceleration in astrophysical sources

Summary

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Bibliography

Articles:

• Y. Ashie et al., Measurement of atmospheric neutrino oscillation parameters by Super-Kamiokande I, Physical Review D 71, 112005 (2005)

• B. Aharmim et al., Determination of the n_eand total ⁸B solar neutrino fluxes using the Sudbury Neutrino Observatory Phase I data set, Physical review C 75, 045502 (2007)

• F. Halzen and S.R. Klein, IceCube: an instrument for neutrino astronomy Review of scientific instruments 81, 081101 (2010)

• A. Achterberg, First year performance of the IceCube neutrino telescope Astroparticle Physics 26, 155 – 173 (2006)

• T. Araki et al., Measurement of neutrino oscillation with KamLAND: evidence of spectral distortion, Physical Review Letters 94, 081801 (2005)

• T. Araki et al., Experimental investigation of geologically produced antineutrinos with KamLAND, Nature 436, 499 – 503 (2005)

• M. Aglietta et al., Neutrino Astrophysics and SN1987A, Il Nuovo Cimento 13, 365 – 374 (1990)

• K.S. Hirata et al., Observation in the Kamiokande-II detector of the neutrino burst from the supernova

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Bibliography

• G. Alimonti et al., The Borexino detector at the Laboratori Nazionali del Gran Sasso, arXiv:0806.2400v1, 2008

• G. Bellini et al., Measurement of the solar ⁸B neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector, arXiv:0808.2868v3, 2010

• C. Arpesella et al., Direct measurement of the ⁷Be solar neutrino flux with 192 Days of Borexino data, Physical Review Letters 101, 091302 (2010)

Websites:

• Super-KamiokaNDE home page http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html

• Sudbury Neutrino Observatory (SNO) home page  http://www.sno.phy.queensu.ca/

• KamLAND home page  http://kamland.stanford.edu/

• IceCube home page http://icecube.wisc.edu/

• SNEWS home page  http://snews.bnl.gov/news.html