Latest results from the Double Chooz experiment with near and far - - PowerPoint PPT Presentation

Latest results from the Double Chooz experiment with near and far detectors

Masaki Ishitsuka (Tokyo University of Science) On behalf of the Double Chooz Collaboration September 11th, 2019 16th international Conference on Topics in Astroparticle and underground physics (TAUP) Toyama, Japan

1

Reactor neutrinos

• Reactor is a free and rich !

𝜉# source

• β-decays in a commercial fission reactor core produce 1020 ν/sec
• Reactor !

𝜉#

$s are detected via inverse β-decay (IBD) reaction

• Cross-section is well known
• Prompt signal: 𝑓' + annihilation γ’s (𝐹) ≈ 𝐹signal + 0.8MeV)
• Delayed signal:
• Total 8 MeV 𝛿$𝑡 from n-Gd (well above natural radioactivity)
• 2 MeV 𝛿 from n-H capture
• Background is strongly suppressed by requiring time/space correlation

̅ 𝜉#

γ

p n

Gd

𝑓'

Detector Reactor

γ

γ’s from n-capture

ΔT

Prompt signal Delayed signal

2

Precision measurement of 𝜄;< with reactor ! 𝜉#

• Simple two flavor oscillation formula is valid at ~1km distance
• 𝑄

̅ 𝜉# → ̅ 𝜉# ≈ 1 − sinD 2𝜄;< sinD

FGHI JKL

• Direct measurement of θ13 from energy dependent deficit

(no parameter degeneracy and matter effects)

sinD 2𝜄;< = 0.1 ∆𝑛<;

D

= 2.5×10R<eVD

𝐭𝐣𝐨𝟑 𝟑𝜾𝟐𝟒

3

CHOOZ experiment

• CHOOZ experiment measured “Reactor-ON” – “Reactor-OFF” (= BG)

spectrum at 𝑀~1km

• Rate compared with an integrated flux measured at 15m

(Bugey4: Phys. Lett. B338, 383 (1994)

• No significant deficit observed:

𝑆 = 1.01 ± 2.8%(stat) ± 2.7%(syst)

• Phys. Lett. B466, 415 (1999)

Current reactor combined

4

Double Chooz experiment

Far Detector L = 1050m 10m3 target 300m.w.e. Since 2011 Near Detector L = 400m 10m3 target 120m.w.e. Since 2015

νe

Chooz Reactors 4.27GWth x 2 cores

5

Improvements from CHOOZ

• Stable Gd loaded liquid scintillator → Improve statistics with stable operation
• 4 layers detector structure with buffer region to suppress background from

PMT and surrounding rock → Improve background reduction

• Experimental setup with multi-detectors → Improve systematics

2MeV 3MeV 4MeV

Near Detector Far Detector

6

Brazil

CBPF UNICAMP

France

APC (IN2P3) CEA/IRFU: SPP SPhN SEDI SIS SENAC CENBG (IN2P3) LNCA (IN2P3/CEA) Subatech (IN2P3)

Germany

EKU Tübingen MPIK Heidelberg RWTH Aachen TU München Tohoku U. Tokyo Inst. Tech. Tokyo Metro. U. Tokyo U. Science Kitasato U. Kobe U.

Japan Russia

INR RAS RRC Kurchatov

Spain

CIEMAT-Madrid

USA

Alabama U. ANL Chicago U. Drexel U. Hawaii U. Notre Dame U. Virginia Tech.

Double Chooz collaboration

Spokesperson:


• A. Cabrera (IN2P3/CNRS)

Project Manager:

• Ch. Veyssière (CEA)

web: doublechooz.in2p3.fr

97 scientists 25 institutions (Americas, Asia, Europe)

7

Double Chooz Detector

From the innermost volume:

• 𝜉-target (NT): Gd loaded liquid scintillator (10 m<)
• 𝛿-catcher (GC): Liquid scintillator (22 m<) → 𝜉 target volume with n-H capture
• Buffer: Mineral oil (110 m<) monitored with inward facing 390 10-inch PMT
• Inner Veto (IV): Liquid scintillator (90 m<) monitored with 78 8-inch PMT

+ Outer Veto (OV): Plastic scintillator strips on top of the detector

8

Signal & Background ̅ 𝜉#

γ

p n

Gd

H n-Gd capture n-H capture

𝜐 ~30𝜈s 8MeV 2.2MeV 𝜐 ~200𝜈s

IBD signal

e+

9

Signal & Background ̅ 𝜉#

γ

p n

Gd

H n-Gd capture n-H capture

𝜐 ~30𝜈s 8MeV 2.2MeV 𝜐 ~200𝜈s

IBD signal

p

e+

n

Accidental BG Cosmogenic BG

Random coincidence

• f two signals

𝛿 + 𝛿 𝛿 + n-capture

𝜈

Fast neutron: p-recoil + n-capture 𝛾 + 𝑜 emitter (9Li, 𝜐 = 257ms): electron + n-capture

9Li

10

Background reduction

→ Detection of total neutron capture

Powerful background reduction by

• Requirement of time

and spatial correlations + ANN

• Various active vetoes

FD ND Events/day 110 820 Signal to BG 11 20

• Cosmogenic (muon-induced) BG are dominant in final sample
• Validity of BG reduction confirmed with reactor off data

11

Reactor power vs. rate

• Simple setup with two reactors
• Reactor rate modulation analysis
• Direct measurement of background

with reactor-OFF data

• Precise measurement of !

𝜉# yield

𝜏

j = (5.71 ± 0.06)×10RJ<cmD/nission

Phys.Lett. B735 (2014) 51-56

12

Total neutron capture detection

• Initial analyses used n-Gd capture and n-H capture separately
• New approach to collect all neutron captures (n-Gd, n-C and n-H)
• To improve statistics with extend effective target mass (GdT + GC)
• To suppress systematics associated with detection (e.g. Gd-fraction)

13

Three reactor experiments in the world

1,050m 400m FD: 300m.w.e ND: 120 m.w.e 4.27GWth 360m 1,146m 1,985m 1,600m ND:291 m.w.e FD: 923 m.w.e 2.9GWth ND: 255 m.w.e 481m 1,380m 750m 750m 290m FD: 675m.w.e ND: 230 m.w.e 2.3GWth

Reactor Detector

Double Chooz Daya Bay RENO

Nearly iso-flux condition: 𝑀p;Rqr 𝑀p;Rsr ≈ 𝑀pDRqr 𝑀pDRsr

B1 B2

• 𝜄;< is measured by reactor experiments with <1% systematic uncertainties
• Reactor 𝜄;< is used as input to current and future neutrino experiments

aiming for precise measurement of neutrino mixing including 𝜀uv and MH

• Validation by multi-experiments with different systematics are important

14

Three reactor experiments in the world

sinD 2𝜄;< = 0.1 ∆𝑛<;

D

= 2.5×10R<eVD

2MeV 3MeV 4MeV

Double Chooz Daya Bay RENO

15

Double Chooz detector layout

FD-I (single-detector phase)

481days

+ FD-II (multi-detectors phase)

384 days

Reactor B1 B2

Google Earth

ND

DC: nearly iso-flux setup ⇒ reactor flux error highly suppressed with multi-detectors

16

Measured spectrum

arXiv:1901.09445

Far detector Near detector

17

• Energy dependent deficit consistent with neutrino oscillation with 𝜄;<
• Clear spectral distortion especially around 5MeV
• Impact to 𝜄;< was evaluated → negligible impact to multi-detector analysis

Measured spectrum

arXiv:1901.09445

FD ND

18

• Energy dependent deficit consistent with neutrino oscillation with 𝜄;<
• Clear spectral distortion especially around 5MeV
• Impact to 𝜄;< was evaluated → negligible impact to multi-detector analysis

𝜄;< measurement

sinD 2𝜄;< = 0.105 ± 0.014(𝑡𝑢𝑏𝑢. +𝑡𝑧𝑡𝑢. )

Breakdown of the uncertainties

Uncertainty Single syst. Total - x Rector flux 0.0081 (7.6%) 0.0112 Detection 0.0073 (6.8%) 0.0113 Energy 0.0018 (1.7%) 0.0121 Background 0.0018 (1.7%) 0.0134 ∆𝑛##

D

0.0018 (1.7%) 0.0140 Statistics 0.0054 (5.0%) Total 0.0141 (13.3%)

Reference

• Daya Bay

sinD 2𝜄;< = 0.0856 ± 0.0029

• RENO

sinD 2𝜄;< = 0.0896 ± 0.0067

PRL121, 241805 (2018) PRL121, 201801(2018)

19

𝜄;< measurement

• Cross-check analyses including rate only and shape only fits were carried out

→ consistent results show robustness of 𝜄;< measurement

sinD 2𝜄;< = 0.105 ± 0.014(𝑡𝑢𝑏𝑢. +𝑡𝑧𝑡𝑢. )

20

Spectral distortion

• Significant distortion was observed in reactor neutrino spectrum
• Three experiments with different background compositions reported

similar distortion → unlikely due to background

• The cause is not yet understood

DC, arXiv:1901.09445

21

Summary

• Double Chooz reported 𝜄;< measurement with multi-detectors
• Double Chooz employed total neutron detection method to improve

statistics and suppress systematic uncertainties associated with the detection including Gd-fraction

• Uncertainties of flux prediction are largely cancelled in nearly iso-flux

condition in Double Chooz

• Significant spectral distortion was observed but we demonstrated the

impact to 𝜄;< measurement is negligible in multi-detectors analysis

• Prospects
• Double Chooz detectors already finished their operation but the

analyses are still ongoing for the final results

22

backup

23

Reactor model: rate

• Several past experiments reported rate observation lower than

prediction (Huber-Mueller model) by ~6% → reactor anomaly

Light Sterile Neutrinos: A White Paper, arXiv:1204.5379

With a new neutrino mass state

24

Reactor model: rate

• Several past experiments reported rate observation lower than

prediction (Huber-Mueller model) by ~6% → reactor anomaly

• Data taken with different fuel-compositions indicate the deficit

is in neutrinos from 235U

Daya Bay

PRL118, 251801 (2017)

RENO

arXiv:1806.00574 (2018)

25