Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Neutrino directionality in liquid scintillatordetectors
Application to geoneutrinos detection
Vincent Fischer
CEA/IRFU/SPP
Neutrino Geosciences 2015June 17th, 2015
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 1 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Outline
1 Neutrino directionality with IBD
2 Geoneutrino directional detection
3 Perspectives and conclusion
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 1 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Motivations
Neutrino directionality consists of retrieving the direction of aneutrino flux
Easily achievable with ν scattering in Čerenkov detectors
Potential of directionality with Inverse Beta Decay →• Locating supernovae before optical observation• Studying geo-neutrinos from the Earth’s crust and mantle• Detecting and monitoring nuclear reactors
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 2 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
The Inverse Beta Decay process
• Inverse beta decay: ν̄e + p → e+ + n• Higher cross section than other ν interactionsσIBD ∼ 10−43cm2
• Signature → Prompt signal (e+ energydeposition) followed by delayed signal (neutroncapture on Gd or H at 8 or 2.2 MeV).
• Look for: Energy signature (∼Eν [MeV] forprompt, ∼8 MeV or 2.2 MeV for delayed), timeand space coincidence → Huge backgroundreduction !
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 3 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Directionality with IBD
Positron• Positron energy:Ee = Eν − (Mn −Mp) + σ (Eν , cos θ)
• Emission angle:dσ
d cos θ ∼ 1 + Vea (Eν) cos θ• At low energies → Backward emission on
average
→ ν̄e interaction ' Prompt event• At higher energies → Forward emission
→ Non relevant for geoneutrinos
From Vogel&Beacom, PRD, VOLUME 60, 053003
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 4 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Directionality with IBD
Neutron• Neutron kinetic energy:Tn ' EνEeMn−Mp (1− Ve cos θ)
• Emission angle:
cos θn,max =
√2Eν∆−(∆2−m2e)
Eν
• Forward emission but energy-dependantspread
• Moderation + Diffusion + Capture →Delayed event
• Neutron diffusion smears directionalinformation → Statistical-only behavior
From Vogel&Beacom, PRD, VOLUME 60, 053003
Diffusion length of thermal neutron (mm)
Probability
0 500 1000 1500 2000 2500 30000
0.5
1
1.5
2
2.5
3
3.5x 10
−3
Unloaded0.1%Gd-loaded
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 5 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Directionality with IBD
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 6 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Application: Reactor experiments
• Observed by CHOOZ and DoubleChooz
• Low energy neutrinos:• Negligible positron displacement• Strong forward neutron emission
• Double Chooz results → Seeprevious talk
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 7 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Application: Supernovae early pointing
• Early pointing of supernovae• Energy range → 0-100 MeV• Important number of IBD
interactions
• Almost background-free• Subject of a dedicated study
V. Fischer, T. Chirac, T. Lasserre, C.Volpe et al.
Prompt directional detection of galacticsupernova by combining large liquid
scintillator neutrino detectors
arXiv:1504.05466 [astro-ph.IM]
Distance to the Supernova [kpc]
An
gu
lar
err
or
[°]
2 4 6 8 10 12 14 16 18 20
10
20
30
40
50
60
70
80
KamLAND (1kt)
SNO+ (0.8kt)
Borexino (0.3kt)
DayaBay (0.3kt)
DoubleChooz (0.05kt)
RENO (0.1kt)
MiniBoone (0.7kt)
JUNO (20kt)
LENA (50kt)
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 8 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Outline
1 Neutrino directionality with IBD
2 Geoneutrino directional detection
3 Perspectives and conclusion
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 8 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Geo-neutrinos
• Emitted by consecutive β-decays inTh, U and K chains
• Originate from the Earth crust andmantle
• Strong interest in measuring 40Kneutrinos
• Above IBD threshold (1.8 MeV) →Only 232Th and 238U neutrinos
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 9 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Hypothetical georeactor
• Postulated by J.M. Herndon• Incompatible with usual BSE model• Self-sustained 3-10 TW nuclear
reactor
• 4 km radius at the center of Earth’score
• U-driven reactor → Typical reactorspectrum
• Could be proven/discarded usinggeoneutrinos
• Current limit (Borexino):< 4.5 TW (95% C.L.)
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 10 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Previous geo-neutrino detections
KamLAND
• From March 2002 to November2012
• S/B (geo-ν/reactor) ∼ 0.032(before 2012)
• Rate: 30 ± 7 TNU (116+28−27 events)
Borexino
• From December 2007 to August2012
• S/B (geo-ν/reactor) ∼ 0.23• Rate: 38.8 ± 12 TNU (14.3 ± 4.4
events)
1 TNU = 1 Terrestrial Neutrino Unit = 1 ν̄e.(1032H)−1.y−1
= 0.113 ×106 ν̄e.cm−2.s−1
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 11 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Detectors of interest
KamLAND:
• 1000 t (Japan)• 2700 mwe
Borexino:
• 270 t (Italy)• 3800 mwe
Thick continental crust
HanoHano:
• 10 kt (Hawaii)• 3000-5000 mwe
Thin oceanic crust
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 12 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Expected signals
Borexino/KamLAND
• Important reactor background (S/B� 1)
• Limited size and expected lifetime• Sensitivity to local crust (within
500 km)
HanoHano• Low reactor background (S/B ∼
10)
• Important size• Sensitivity to mantle/georeactor
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 13 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Simulation - Overview
• Goal: Simulation of a geoneutrinos detection and sourcereconstruction
• Development of a fast and reliable toy Monte Carlo for the IBDreaction
• Energy spectrum and cross-section → Detected spectrum
• IBD kinematics & GEANT4 inputs → Precise (e+,n) generation
• Fit of angular distributions → Direction in (θ, φ)
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 14 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Simulation - Geoneutrinos simulation• Main energy spectra considered:
• Geoneutrino spectrum → Th:U (3.9:1) ν̄e spectra above IBDthreshold at 1.8 MeV
• Georeactor spectrum → 235U neutrino spectrum (similar to nuclearreactor spectrum)
• Cross sections:• Strumia & Vissani → Precise well above 100 MeV and in agreement
with Vogel & Beacom
Eν [MeV]
Flu
en
ce
[A
.U.]
0 2 4 6 8 100
0.5
1
1.5
2
2.5
3
3.5x 10
5
Geoneutrinos (Th/U=3.9)
Georeactor (235
U)
Eν [MeV]
Cro
ss
se
cti
on
[c
m2]
0 20 40 60 80 1000
1
2
3
4
5
6
7
x 10−40
κ Ee . p
e
Vogel&Beacom
Strumia&Vissani
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 15 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Simulation - IBD kinematics
• Simulation of (e+,n) behavior in liquid scintillator• Use of GEANT4 inputs → Energy-dependant mean path lengths• Reconstruction effects: Vertex and energy resolutions
Path length [mm]
Pro
ba
bil
ity
0 100 200 300 400 500 60010
−4
10−3
10−2
10−1
100
Ee= 10.0 MeV
Ee= 30.0 MeV
Ee= 50.0 MeV
Ee= 70.0 MeV
Ee= 90.0 MeV
Tn [MeV]
Ne
utr
on
ra
ng
e [
mm
]
0 5 10 15 2010
1
102
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 16 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Simulation - Direction retrieval• Direction vector for each event:
−−→Xevt =
−−−−−→Xdelayed −
−−−−−→Xprompt
→ (θ,φ) angular distributions• Generation of two datasets: a model (high stat.) and a realistic
dataset in different directions
• χ2 minimization on both angular distributions → Find best-fit (θ,φ)and associated errrors
• χ2 formula →χ2 (φ, θ) =
∑Ni
∑Nj (Yi −Mi (φ, θ))
(V −1
)ij
(Yj −Mj (φ, θ))
Azimuthal angle [°]
Pro
ba
bil
ity
−180 −135 −90 −45 0 45 90 135 180
0.025
0.03
Zenith angle [°]
Pro
ba
bil
ity
−90 −45 0 45 900
0.05
0.1
Cosine projection over initial direction
Pro
ba
bil
ity
−1 −0.5 0 0.5 10.04
0.05
0.06
# of events
An
gu
lar
err
or
[°]
102
103
104
0
10
20
30
40
50
60
70
80
90
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 17 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Results - Georeactor
• Goal: Locate an hypothetical georeactor• 4 TW georeactor, point-like neutrino source• Event rate: 15.2 ν̄e.y−1.kt−1
• Energy cut @ 3.3 MeV → 73 % efficiency• No backgrounds taken into account
Exposure [y]
An
gu
lar
err
or
[°]
0 10 20 30 40 50 60 70 80 90 1000
10
20
30
40
50
60
70
80
90Borexino (0.27 kt)
KamLAND (1 kt)
HanoHano (10 kt)
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 18 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Results - Crust and mantle neutrinos
• Event rate →• Borexino: 38.1 TNU (observed)• KamLAND: 30.1 TNU (observed)• HanoHano: 7.7 TNU (expected mantle ν rate)
• Hemispherical source → Reconstruction of the distributionbarycenter
• No backgrounds, 100% efficiency
Exposure [y]
An
gu
lar
err
or
[°]
0 10 20 30 40 50 60 70 80 90 1000
10
20
30
40
50
60
70
80
90Borexino (0.27 kt)
KamLAND (1 kt)
HanoHano (10 kt)
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 19 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Results - Summary
• Requires large scale detectors and long exposure time to provide asomewhat useful directional information
• Underground detector → Almost all neutrinos come from below• High reactor background → Impossibility to separate local crust and
reactor events
• IBD directionality in LS is not suitable for an application togeoneutrinos
• Low anisotropy of the IBD reaction• Low statistic• High background
• Precise directionality would help distinguish crust/mantle/georeactorgeo-ν especially far from reactors and continental crust
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 20 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Outline
1 Neutrino directionality with IBD
2 Geoneutrino directional detection
3 Perspectives and conclusion
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 20 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
New detector concepts
Segmented detectors
• Existing concept: PROSPECT, MiniTimeCube, PANDA, etc...• Detector divided into several cells• Very precise track and position reconstruction → Good directional
capabilities
Water-based liquid scintillator detectors
• Advanced Scintillator Detector Concept (ASDC)• Mixing of scintillating molecules and water• High light yield (LS) and strong directional capabilities (Čerenkov)
Hydrogeneous TPC
• Concept in development → see arXiv:1405.1308• 3D imaging of positron and neutron interactions• Evt-by-evt directional information at low energies
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 21 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Conclusion
• IBD is the most suitable reaction to detect geoneutrinos
• However, providing directional information seems hardly achievable
• Directional information must be provided on an evt-by-evt basis →TPC, scattering, ... ?
• Interest: Distinguish crust/mantle/georeactor? neutrinos
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 22 / 23
Neutrino directionality with IBD Geoneutrino directional detection Perspectives and conclusion
Thanks
Thank you for your attention !
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 23 / 23
Back-up
Simulation - Validation tests
ToyMC vs IBD kinematics
Generated emission angle vs theory
Eν [MeV]
<co
s θ
e>
0 20 40 60 80 100
0
0.05
0.1
0.15
0.2
Vogel and Beacom
← Positron
Neutron →E
ν [MeV]
<co
s θ
n>
0 20 40 60 80 1000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
(cosθn)min
− Vogel and Beacom
< cosθn >
(cosθn)min
ToyMC vs GEANT4
Best observable: Projections on neutrino axis
Ee [MeV]
Mean
pro
jecti
on
over ν
axis
[m
m]
0 10 20 30 40 50 60 70 80−20
0
20
40
60
80
100
Positron
Neutron
← GEANT4
ToyMC →
Eν [MeV]
Mean
pro
jecti
on
over ν
axis
[m
m]
0 20 40 60 80 100−20
0
20
40
60
80
100
120
Positron
Neutron
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 1 / 9
Back-up
Directionality methods
Direction information comes from the detection reaction2 favorite reactions: Electron scattering (ν + e− → ν + e−) and IBD
(ν̄e + p → e+ + n)
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 2 / 9
Back-up
Event in organic TPC
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 3 / 9
Back-up
Large Scale Scintillator Detectors
KamLAND, Borexino, SNO+Spherical detectors, large size(KamLAND and SNO+: 1000t,Borexino: 300t)Deep underground, very low backgroundrate
LVD and MiniBooneLVD: 1000 t of scintillator, deep underground, main goal: supernovadetectionMiniBoone: 680 t at sea level
The future: JUNO and LENAJUNO: Spherical, 20 kt, construction startedLENA: 50 kt, project ongoing
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 4 / 9
Back-up
Super-Kamiokande
• 50 kt (22.5 fiducial) WaterČerenkov
• 13’000 PMT’s• Detection via ν-e− scattering• About 8’000 events expected (IBD
+ scattering) for galactic SN
• Pointing ability: 8 degrees at10 kpc (95% C.L.)
• Best current SN detector
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 5 / 9
Back-up
Application to SN detection
Supernova detection
Type II (core-collapse) supernova emits ∼ 1057 neutrinos.Current detectors will detect thousands of IBD events for a galacticsupernova.→ Possibility to perform a directionality measurement
InterestProvides information even if visible light is absorbed by galactic disk.During a core-collapse SN, neutrinos arrive several hours before visiblelight.→ Early pointing of the region of interest over the sky→ Better accuracy using combinations of detectors
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 6 / 9
Back-up
Results
Distance to the Supernova [kpc]
An
gu
lar
err
or
[°]
2 4 6 8 10 12 14 16 18 20
10
20
30
40
50
60
70
80
KamLAND (1kt)
SNO+ (0.8kt)
Borexino (0.3kt)
DayaBay (0.3kt)
DoubleChooz (0.05kt)
RENO (0.1kt)
MiniBoone (0.7kt)
JUNO (20kt)
LENA (50kt)
Distance to the Supernova [kpc]
An
gu
lar
err
or
[°]
5 10 15 20 25 30 35 40 45 50
10
20
30
40
50
60
SNEWS
Existing
Near future
All
• Large angular uncertainty for current individual detectors• Combination of current detectors → 45◦(68% C.L.) @ 10 kpc• In a near future (∼ 2018) → 12◦(68% C.L.) @ 10 kpc
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 7 / 9
Back-up
Type II Supernova
• Core collapse of massive stars (M > 8M�)• Chain fusion of H into Fe → Core collapse (see slide on SN phases)• 99 % of energy emitted as neutrinos (6 flavors) in a 10 s time
window → ∼ 1053 neutrinos• Neutrino conversion and oscillation effects → Modify amplitude and
shape of the energy spectrum
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 8 / 9
Back-up
Type II Supernova phases• Hydrogen burning phase (main phase) withstand gravitation• After this phase, gravity takes over and the increase of density
induces He fusion• He fuses till the creation of a Fe core• Density rises till the core reaches the Chandrasekhar mass (1.4M�)• Electron capture on protons giving neutrons and neutrinos →
Neutron star creation and iron core collapse• Fall of the outer shells on the core→ Shockwave and matter ejection
Vincent Fischer : CEA/IRFU/SPP Neutrino directionality in liquid scintillator detectors 9 / 9
Neutrino directionality with IBDGeoneutrino directional detectionPerspectives and conclusionAppendix