Evolution of the Antineutrino Flux and Spectrum, and Search for Light Sterile Neutrinos at Daya Bay - Christopher White - CERN Indico
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Evolution of the Antineutrino Flux and Spectrum,
and Search for Light Sterile Neutrinos at Daya Bay
Christopher White
on behalf of the Daya Bay Collaboration
LLWI 2019
Reactor Anti-Neutrinos Measurements Relative Measurements versus Absolute Measurements
Antineutrino Detection
• Antineutrinos are detected via the Inverse Beta Decay (IBD) reaction:
νe + p → e+ + n
~30μs
~8MeV
signal
− Coincidence between positron and neutron signals allows for
powerful background rejection
− Energy of positron preserves information about energy of incoming νe
Antineutrino Detection
• Antineutrinos are detected via the Inverse Beta Decay (IBD) reaction:
νe + p → e+ + n
~30μs
~8MeV
signal
− Coincidence between positron and neutron signals allows for
powerful background rejection
− Energy of positron preserves information about energy of incoming νe
Reactor Antineutrino Anomaly
Phys.Rev. D87 (2013) no.7, 073018
There is tension between
the flux and spectrum predictions
and experimental measurements
Daya Bay Detectors
• The antineutrino detectors (ADs) are “three-zone” cylindrical modules
immersed in water pools:
inner water shield
RPCs outer water shield
PMTs
Tyvek
Gd-doped
Liquid
Scintillator
192 8” (LS) LS
PMTs
Mineral Oil
AD
AD support stand
concrete
Energy resolution: Double purpose: shield the ADs
σE/E ≅ 8.5%/√E[MeV] and veto cosmic ray muons
NIM A 811, 133 (2016) NIM A 773, 8 (2015)
Improved Energy Response Model
• A model is needed to convert reconstructed positron energy to
antineutrino energy
• Energy response is non-linear Old
electronics
mainly due to two reasons:
both in - Normal quenching + Cerenkov
the light in liquid scintillator
order of FADC
10%! - Response of the electronics
EH1-AD1
• Carried out two key measurements:
1.08
Electronics nonlinearity
Gamma data
- End of 2015: installation of a full 1.06 137
Cs FADC data
FADC readout system in EH1- 54
Mn
Best fit model
1.04
AD1, taking data simultaneously 68
a direct measurement of the
with standard electronics electronics non-linearity!
Ge
1.02
n-H
208
40 Tl
K
1 n-12C
- Early 2017: deployment of 60Co 60
Co
calibration sources with different 0.98 n-56Fe2
encapsulating materials, to 0.96
16
O*
constrain optical shadowing effects 0 1 2 3 4 5 6 7 8
Visible energy [MeV]
Improved Energy Response Model
1.1
Scintillator nonlinearity
• The model is built based on n-12C
16
O*
various gamma peaks and the
1.05 n-56Fe2
208
Tl
n-H
continuous 12B spectrum 1
60
Co
40
K
Single gamma source
- Validated with low energy β+γ 0.95
137
54
Mn Multiple gamma source
Best fit model
spectra from 212Bi and 214Bi
Cs
68
Ge
0.9
Data / best fit
0 1 2 3 4 5 6 7 8 9
- Halved uncertainty of absolute 1.02
1
Effective single γ energy [MeV]
energy scale to ~0.5% 0.98
0 1 2 3 4 5 6 7 8 9
Effective gamma energy [MeV]
Events / 0.25 MeV
Full nonlinearity
1.04 14000
Data
Best fit model
12000 Total
1.02
12
10000 B
12
1 N: 3.3%
8000
6000
0.98
4000
0.96 Best fit + 68% C.L. (in 2015) 2000
Data / best fit
0.94 1.05 0 2 4 6 8 10 12 14
Reconstructed Energy [MeV]
16
Best fit + 68% C.L. (in 2018)
1
0.92 0.95
0 2 4 6 8 10 12 0 2 4 6 8 10 12 14 16
Positron energy [MeV] Reconstructed energy [MeV]
Absolute Antineutrino Flux
• Previous measurement of the absolute reactor ve flux compared to the
Huber+Mueller expectation:
systematics-dominated from
Rdata/pred = 0.946 ± 0.020 (exp.) absolute detection efficiency
• New strategy: take new neutron calibration data and use it to constrain the
“neutron detection efficiency” εn
ACU=Automated Calibration Unit
previous efficiency values
εn
Carried out an extensive calibration
campaign in late 2016 / early 2017
Deployed two neutron sources (241Am-13C and
241Am-9Be) along three vertical calibration axes
Absolute Antineutrino Flux
Chinese Physics C, 2017, 41(1)
• Reactor antineutrino yield: f = (5.91+/-0.09)x10-43 cm2/fission
ILL+Vogel Huber+Mueller
R = 1.001+/-0:015+/-0.0026 R = 0.952+/-0.014+/- 0.023
(exp) (model) (exp) (model)
21Search for a Light Sterile Neutrino
A minimal extension of the 3-ν model that includes one sterile neutrino
will create a higher frequency oscillaJon paKern, as shown below.
4 2 2
% Δm 2
31 L ( 2 2
% Δm 2
41E
(
P(ν e → ν e ) ≅ 1− cos θ14 sin 2θ13 sin ' * − sin 2θ14 sin ' *
& 4Eν ) & 4Eν )
Introduction
• If exists, Daya Bay would see additional rate and spect
distortion from sterile neutrinos
1
EH1
EH2
EH3
P( ν →ν )
3 ν best fit
e
3 ν + sterile (illustration)
0.95
e
0.9
0 0.2 0.4 0.6 0.8
L / E [km/MeV]
eff νSearch for a Light Sterile Neutrino
In collaboration with MINOS (Bugey-3)
Phys. Rev. Lett, 117 151801 (2016)Evolution of Neutrino Flux and Spectrum
✦ Calculate
effective fission fraction
observed by each detector
✦ Compare IBDs from periods of
differing effective fission fractions
✦ Doing
this by combining periods of
common fission fraction F239Unambiguous Observation of Fuel Evolution
Unambiguous Observation of Fuel Evolution
Thank You
The Daya Bay Reactor Neutrino Experiment
The Daya Bay Collaboration
Asia (23)
Beijing Normal Univ., CGNPG, CIAE, Congqing Univ.,
Dongguan Univ. Tech., ECUST, IHEP, Nanjing Univ., North America (15)
Nankai Univ., NCEPU, NUDT, Shandong Univ., Brookhaven Natl Lab, Illinois Institute of Technology,
Shanghai Jiao Tong Univ., Shenzhen Univ., Tsinghua Iowa State, Lawrence Berkeley Natl Lab, Princeton,
Univ., USTC, Xian Jiaotong Univ., Zhongshan Univ., Siena College, Temple University, UC Berkeley, Univ.
Chinese Univ. of Hong Kong, Univ. of Hong Kong, of Cincinnati, Univ. of Houston,
National Chiao Tung Univ., National Taiwan Univ., UIUC, Univ. of Wisconsin, Virginia Tech, William &
National United Univ. Mary, Yale
Europe (2) South America (1)
Charles University, JINR Dubna ~230 Collaborators Catholic University of Chile 16You can also read
