neutrino directionality in liquid scintillator detectors · 2015. 6. 30. · cea/irfu/spp neutrino...

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


Outline

1 Neutrino directionality with IBD

2 Geoneutrino directional detection

3 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



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 !



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




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



Application: Reactor experiments

• Observed by CHOOZ and DoubleChooz

• Low energy neutrinos:• Negligible positron displacement• Strong forward neutron emission

• Double Chooz results → Seeprevious talk



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)



Outline






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



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.)



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



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



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



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)



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



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



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



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)



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)



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



Outline






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



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



Thanks

Thank you for your attention !


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


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)


Back-up

Event in organic TPC


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


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


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


Back-up

Results


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)


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


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


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


Neutrino directionality with IBDGeoneutrino directional detectionPerspectives and conclusionAppendix

neutrino directionality in liquid scintillator detectors · 2015. 6. 30. · cea/irfu/spp neutrino...

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