Neutrino flux at Daya Bay

Neutrino flux at Daya Bay
Neutrino flux at Daya Bay
Liang Zhan, IHEP, China
Liang
Zhan IHEP China
On behalf of the Daya Bay Collaboration
SNAC, September 26‐28, 2011 – Blacksburg, Virginia, USA
1
Outline Introduction to Daya Bay
Daya Bay status
Neutrino flux calculation
Neutrino flux calculation
Impact of reactor antineutrino anomaly and sterile neutrino
• Measure sterile neutrino at Daya
Measure sterile neutrino at Daya Bay
•
•
•
•
2
The Daya Bay Collaboration
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An International Effort
Europe (3) JINR, Dubna, Russia
Kurchatov Institute, Russia
Charles University, Czech Republic
North America (16)
North America (16)
Brookhaven Natl Lab, Cal Tech, Cincinnati,
Houston, Illinois Institute of Technology,
Iowa State, Lawrence Berkeley Natl Lab,
Princeton, Rensselaer Polytech, UC
Berkeley, UCLA, Wisconsin, William & Mary,
Virginia Tech, Illinois, Siena College
~ 220 collaborators
220 collaborators
Asia (20)
IHEP, Beijing Normal Univ., Chengdu Univ. of
Sci and Tech, CGNPG, CIAE, Dongguan
Polytech Nanjing Univ Nankai Univ.,
Polytech, Nanjing Univ., Nankai
Univ
NCEPU, Shandong Univ., Shanghai Jiao
Tong Univ., Shenzhen Univ., Tsinghua Univ.,
USTC, Zhongshan Univ., Univ. of Hong
Kong, Chinese Univ. of Hong Kong, National
Taiwan Univ., National Chiao Tung Univ.,
National United Univ.
3
Daya Bay overview
• Aim to measure sin22θ13
to 0 01
to 0.01
• 8 movable and identical antineutrino detectors
• 6 x 2.9 GW
6 2 9 GWth reactor cores
Far site
Far site experiment hall
Baseline (m)
4
Daya Bay detectors
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5
Commissioning Daya Bay Near Site
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August 2011, Near site data taking
6
First look of AD Performance
• AmC‐60Co source at the center of AD1/AD2 for 10 hours
– Blue: AD1 data, Red: AD2 data
Preliminary
Preliminary
AD1 : τcap = 28.40±0.40 μs
AD2 : τcap = 28.21±0.35 μs
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First Look at Water Cherenkov Detectors
• PMT single rate less than required rate of 50 kHz
• The water Cherenkov detectors are stable and working as expectation g
p
Outer pool
Outer pool
Outer pool
Inner pool
Inner pool
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Prospects for Daya Bay
p
y
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Physics potential of Daya Bay
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p
y
y
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Reactor Neutrino Flux at a Glance
• Using PWR (Pressurized Water Reactor) as examples in the following. (3‐4)% U‐235 enrichment. > 95% is U‐238.
• Neutrinos from subsequent ‐decays of fission fragments. N ti
f
b
t d
f fi i f
t
U‐235 depletion
U‐235, U
235, U‐‐238
Pu‐‐239, Pu
Pu
239, Pu‐‐241
Isotope evolvement,
Neutrino spectra, ILL
Pu‐239 breeding
More neutrinos from a U‐235
a U
235 fission fission than than
Pu‐239
X
0.1%
Palo Verde
Peak at 4 MeV
Neutrino rate,
Palo Verde
g
g
Refueling outage
Power trips
Isotope evolvement
Visible spectrum, Vi
ibl
t
multiplied by inverse ‐decay ((IBD) Xsec.
)
Neutrino Flux Neutrino Flux Calculation
Calculation
Neutrino Flux S ( E ) 
istopes

fi Si ( E )
i
Wth
S ( E ) 
 i ( fi F ) ei
istopes
 (f
Core configuration
Thermal power
p
Operations
Temperature pressure
… …
Measurements
Calculations
F )Si ( E )
i
Wth   i fi ei ,
Heat balance test
Online calibration
i
F   i fi
E : Neutrino energy
fi : Fission rate of isotope i
Si(E) : Neutrino energy spectra/f
( i i /F): Fission fraction
(f
)
Wth : Reactor thermal power
ei : Energy release per fission
Thermal Power
Wth
Energy release/fission
Core Simulation
fi/F
Flux
Spent fuel Non‐equilibrium
Spectra of Isotopes
Spectra
of Isotopes
Si(E)
Thermal Power
• KME
KME, thermal power, , thermal power, Secondary Heat Balance
Secondary Heat Balance Method.
– The most accurate measurement.
– Offline measurement, weekly or monthly
– Generally cited with Generally cited with (0.6
(0.6‐‐0.7)% uncertainties in literature
in literature. . • KIT/KDO
KIT//KDO, thermal power. ,, thermal power. Good for analysis
p
Good for analysis.
y .
– Primary Heat Balance
– Online
– Weekly
Weekly calibrated to KME power.
calibrated to KME power
PKIT  PKME  0.1% FP
• RPN
RPN, nuclear power
, nuclear power
l
–
–
–
–
Ex‐core neutron flux monitoring
Ex‐
Online
Safety and reactor operation control
Daily calibrated to KIT/KDO power
PRPN  PKME  1.5%
1 5% FP
Core Simulation
• Qualified core simulation code is normally licensed, not available for scientific collaborations.
• Need a lot of information from the power plant as inputs, such as Need a lot of information from the power plant as inputs such as
configurations, fuel composition, operations (control rods movement, Boron dilution, etc), inlet temperature, pressure, flow rate etc
rate, etc.
• Fission fractions, as a function of burn‐up, could be a by‐product of the refueling calculation, provided by the power plant.
Burn‐up is the amount of energy in Mega Watt Days (MWD) released from unit
(MWD) released from unit initial mass (ton) of Uranium (TU).
For small power variation, fission fraction can be gotten without redoing the ou edo g e
simulation.
Provided by CNPRI
Spectra of Isotopes
•
•
•
Lack of data of the ‐decays of the complex fission fragments, theoretical calculation on the neutrino spectra of isotopes carries large uncertainties.
ILL measured the  spectra of U‐235, Pu‐239, and Pu‐241 fission by ILL measured the 
spectra of U 235 Pu 239 and Pu 241 fission by
thermal neutrons, and converted them to neutrino spectra. Normalization error 1.9%, shape error from 1.34% at 3 MeV to 9.2% at 8 MeV.
U‐238 relies on theoretical calculation, 10% uncertainty (P. Vogel et al., PRC24, 1543 (1981)). Normally U‐238 contributes (7‐10)% fissions.
ILL spectra
K. Schreckenbach et al. PLB118, 162 (1985)
A.A. Hahn et al. PLB160, 325 (1985)
Shape verified by Bugey‐3 data
Normalization improved to 1.6%
ILL spectra • In analysis, we need to rebin the ILL spectra, which can be done by parameterize or interpolate the spectra
yp
p
p
• Parameterization(P. Huber and T. Schwetz,PRD.70.053011)
Blue line: three parameter fit
Red line: six parameter fit
• Interpolation
– Four interpolation methods agree well below 7.8 MeV
g
– Identical to the original ILL value at the given data points
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Energy Release per Fission
•
Slightly varied for different cores due to neutron capture.
Uncertainties in (0.30-0.47)%.
Isotopes
Energy (MeV)
U-235
201.7±0.6
U-238
205.0±0.9
Pu-239
210.0±0.9
P 241
Pu-241
212 4±1 0
212.4±1.0
M.F. James, J. Nucl. Energy 23, 517 (1969)
Kopeikin et al, Physics of Atomic Nuclei, Vol. 67, No. 10, 1892 (2004)
Spent Fuel
• Spent fuel stored temporarily adjacent to the core, could be up to 10 years
up to 10 years.
• Similar to non
Similar to non‐‐equilibrium contributions, long
equilibrium contributions, long‐‐lived fragments in spent fuel will emit neutrinos continiously
in spent fuel will emit neutrinos in spent fuel will emit neutrinos continiously.
continiously.
Isotopes with E
p
ν >1.8 MeV and T1/2 1/2 > 10 h.
Spent fuel antineutrino spectrum, mainly contributes 1.8 ‐3.5 MeV, the ratio to reactor antineutrino is ~ 0.3%.
Impact of reactor flux uncertainty
p
y
• Correlated uncertainty (common to all reactors)
– Come from ILL spectrum normalization (1.9%), energy release per p
(
),
gy
p
fission(0.3%), and IBD cross section (0.2%).
– Cancel out for Daya Bay near‐far running
– Near detectors determine a common normalize factor of reactor flux.
• Uncorrelated uncertainty
– Dominated by power measurement (0.6%) and isotope fraction (
)
simulation (0.5%)
– Cancel out for an ideal experiment with N+1 detectors and N reactors.
– Most cancelled, only 5% residual for the final systematic error of Daya Bayy
A larger correlated flux uncertainty has no impact on Daya Bay sensitivity
Daya Bay sensitivity.
Default: 2%
Uncorrelated flux uncertainty most cancelled 18
Reactor antineutrino anomalyy
• Recent calculated reactor flux is larger than ILL by 3%. (T. A. Mueller et al., Phys. Rev. C 83, 054615, P.Huber, arXiv:1106.0687v3)
• The reactor antineutrino anomaly is an effect at 98.6% C.L. (G. Mention et al., Phys. Rev. D 83, 073006)
• A
A large correlated uncertainty has no impact on the Daya large correlated uncertainty has no impact on the Daya
Bay sensitivity.
• Using new reactor flux or the old ILL spectra also has no i
impact on the Daya Bay sin
h D
B
i 22θ13 sensitivity. ii i
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Sterile neutrino oscillation
• If there is sterile neutrino, the survival probability is 2
2
m31
L
2
2 mnew L
)  sin (2 new ) sin (
)
Pee  1  cos  new sin (213 ) sin (
4 E e
4 E e
4
2
2
• For short baseline (<100m) detector, the ambiguity from θ
h b l (
)d
h
b
f
θ13
oscillation can be eliminated. 2
mnew
L
Pee  1  sin
i (2 new ) sin
i (
)
4 E e
2
2
• The baselines for DYB site are 363m from DYB cores, 857 m from LA I cores, and 1307 m from LA II cores. The phase of sterile neutrino oscillation is averaged.
2
m31
L 1 2
)  sin (2 new )
Pee  1  cos  new sin (213 ) sin (
4 E e
2
4
2
2
Energy dependent Energy
dependent
deficit
Energy independent Energy
independent
deficit
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Daya Bay near site
• Two of the possible reasons for reactor antineutrino anomaly are
– Erroneous prediction of the reactor flux
– Sterile neutrino oscillation
Sterile neutrino oscillation
• DYB site can not distinguish the two reasons because sterile neutrino oscillation is averaged to be an energy independent flux deficit.
• DYB site has potential to separate the θ
DYB site has potential to separate the θ13 oscillation and sterile oscillation and sterile
neutrino oscillation according to the energy dependence.
6 months data, DYB site
Error bar is statistics error
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Measure sterile neutrino
• A possible experiment to measure sterile neutrino oscillation using radioactive source at Daya Bay Far site
using radioactive source at Daya Bay Far site.
• Four “identical” detectors help to reduce systematic error.
• Variable baseline and flexible baseline configuration Variable baseline and flexible baseline configuration
• Vertex resolution ~ 15 cm
Distance to ADs
Ev ~ 2.5 MeV
source
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Possible sources
Possible sources
•
EC Neutrino source
–
–
–
–
–
•
Mono‐energetic but low energy (<1 MeV), low energy threshold required
Known experience. The GALLEX experiment made a 62PBq 51Cr source for test.
ν‐e scattering cross section is smaller than inverse β decay reaction.
Not easy to reject radioactive background for Daya Bay
Not easy to reject radioactive background for Daya
Hundreds of events are expected with a ~100 PBq 51Cr source (half life = 28 days) at Daya Bay far site. A ti
Antineutrino source (preferred)
ti
( f
d)
– Isotopes produced by spent reactor fuel, such as 114Ce (see poster by Bryce et al., Searching for Sterile Neutrinos at Daya Bay With a PBq Antineutrino Source)
– Background rejection is easier.
– Re‐use Daya Bay detector/electronics
– 100
100‐200
200 events/day is expected events/day is expected
with a ~10 PBq source.
Potential EC Neutrino source
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Summary y
• Daya Bay near site is taking data and the complete r n (8ADs) ill start s mmer 2012
complete run (8ADs) will start summer 2012.
• Based on the inputs from ILL spectra and the data f
from the reactor power plant, the expected h
l
h
d
neutrino spectrum can be calculate.
• Reactor antineutrino anomaly and sterile neutrino has almost no impact on the sin22θ13
sensitivity due to near‐far cancellation.
d
f
ll
• Daya Bay has potential to measure sterile neutrino oscillation using source and four ADs at far site.
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