章 飞虹ZHANG FeiHong
Ph.D. student from
Institute of High Energy Physics, Beijing
INTERNATIONAL SCHOOL OF SUBNUCLEAR PHYSICS 2012
Erice, 23 June – 2 July 20121
Before Hunting—Introduction
Target—The Third Type of Neutrino
Oscillation
Rifle—Detector
Adjusting Rifle—Calibration
Prey Searching—Neutrino Selection
Some Other Things in Our Gun
Sight—Background
Score—Latest Result of Collaboration
Neutrino Hunting
2
Flavour and mass
eigenstates need not
correspond:
• How they interact
• How they propagate
3
1
,
i
iiU
3
Atmospheric Solar Majorana
phase
CP phase & q13
Atmospheric
accelerator
solar
reactor
Double beta
decays
reactor
accelerator
Target of Daya
Bay Experiment
Relative measurement to cancel Corr. Syst. Err.
2 near sites, 1 far site Multiple Antineutrino Detector (AD) modules at each site to reduce Uncorr. Syst. Err.
Three zones modular structure
Far: 4 modules,near: 2 modules Multiple muon detectors to reduce veto eff. uncertainties
Water Cherenkov: 2 layers
RPC: 4 layers at the top + telescopes 4
Raw data from detector need to be calibrated before analysis Energy information from ADC
Time information from TDC Time Calibration for ADs
Use high intensity LED runs to calibrate time offsets of 192 PMTs.
Use LED intensity scan runs to get time walk.
A measurement is designed to help understanding time walk of FEE board.
An example of
time offsets
After time offset
calibration, time
resolution in LED
run can be 1ns.
Pulse
Generator
FEE
FEE
Fake PMT
Signal
Reference
Signal
An example of time walk fit. LEDs
at different position are compared.5
Anti-neutrinos are detected via
the inverse beta decay (IBD)
reaction nepe
6
Reject Flashers
Prompt: 0.7 MeV < Ep < 12 MeV
Delayed: 6.0 MeV < Ed < 12 MeV
Capture time: 1 μs < Δt < 200 μs
Muon Veto:
Pool Muon: Reject 0.6 ms
AD Muon (>20 MeV): Reject 1 ms
AD Shower Muon (>2.5 GeV):
Reject 1 s
Multiplicity:
No other signal > 0.7 MeV in -200
μs to 200 μs of IBD.
Good agreement with MC. 7
Theoretical Calculation:
Start with a delayed-like signal, whose energy is in (6, 12) MeV, the probability of
forming an accidental background is
in which P1 is the probability of accidentally having 1 prompt signal, P0 is the
probability of passing multiplicity cut. Both follow Poisson distribution. Then the
total accidental background count is
The final equation is like this
8
Fast neutrons produced by cosmic muons external to the AD. They
may enter the AD and mimic IBD signal:
Prompt: Recoil proton(s) produced by slowing neutron
Delayed: Capture of the neutron
Estimate contribution to selected IBD candidates
Loose prompt energy cut, and extrapolate from prompt energy
distribution in 12~100 MeV range.
Check extrapolation by tagging fast neutron with water pool system.
9
Cosmic m produced 9Li/8He b-decay + neutron emitter
t(8He/9Li ) = 171.7ms/257.2ms
8He/9Li, Br(n) = 12%/48%, 9Li
dominant
Measurement: Time-since-last-muon fit
Improve the precision by reducing
the muon rate:▪ Select only muons with an energy deposit
>1.8MeV within a [10us, 200us] window
▪ Issue: possible inefficiency of 9Li
Results w/ and w/o the reduction is
studied
10
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For every background, we all at least have one alternative method or independent
analysis from another collaborator for double check.
The whole IBD analysis is also done in an alternative way with different energy
reconstruction algorithm. Results are consistent.
AD1 AD2 AD3 AD4 AD5 AD6
Antineutrino
candidates69121 69714 66473 9788 9669 9452
DAQ live time (day) 127.5470 127.3763 126.2646
Efficiency em*em 0.8015 0.7986 0.8364 0.9555 0.9552 0.9547
Accidentals (/day) 9.73±0.10 9.61±0.10 7.55±0.08 3.05±0.04 3.04±0.04 2.93±0.03
Fast neutron (/day) 0.77±0.24 0.77±0.24 0.58±0.33 0.05±0.02 0.05±0.02 0.05±0.02
8He/9Li (/day) 2.9±1.5 2.0±1.1 0.22±0.12
Am-C corr. (/day) 0.2±0.2
13C(α, n)16O (/day) 0.08±0.04 0.07±0.04 0.05±0.03 0.04±0.02 0.04±0.02 0.04±0.02
Antineutrino rate
(/day)
662.47
±3.00
670.87
±3.01
613.53
±2.69
77.57
±0.85
76.62
±0.85
74.97
±0.84
> 200k antineutrino interactions!
sin22θ13 = 0.089 ±0.010 (stat) ±0.005 (syst)
Weighted Baseline [km]
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
expec
ted
/ N
det
ecte
dN
0.9
0.95
1
1.05
1.1
1.15
E H 1 E H 2
E H 3
13q22sin
0 0.05 0.1 0.15
2c
0
10
20
30
40
50
60
70
s1s3
s5
Entr
ies
/ 0
.25M
eV
0
500
1000
1500
2000Far hall
Near halls (weighted)
Prompt energy (MeV)0 5 10
Far
/ N
ear
(wei
ghte
d)
0.8
1
1.2No oscillation
Best Fit
See a clear deficit in the far site due to oscillations
Most precise measurement of q13 to date:
Deficit consistent
with oscillations!
Shape analysis is
preliminary.
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First q13 paper: PRL 108, 171803 (2012).
The latest results with more details will be submitted to
Chinese Physics C soon.
Besides,
Please don’t hurt wild animals!
Neutrino hunting is much more fascinating!
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Gd-doped
liquid scintillator
liquid
scintillator
γ-catcher
mineral oil
5 m
Calibrationunits
192 PMTs
The detectors are ~100ton three-zone cylindrical modules:
Zone Mass Liquid Purpose
Inner
acrylic
vessel
20 t
Gd-doped
liquid
scintillator
Anti-
neutrino
target
Outer
acrylic
vessel
20 tLiquid
scintillator
Gamma
catcher (from
target zone)
Stainless
steel
vessel
40 t Mineral Oil Radiation
shielding
15
16
PMTs
Four layers of
RPCs
Attenuates ambient neutrons as well as gammas
Serves as a Cerenkov detector to tag cosmic ray muons (thus reducing background)
Double purpose:
EH1 (Daya Bay Near Hall) EH3 (Far Hall)
Peak energy of different
sources
Low-intensity LED PMT gains, good stability ( 1 oC temperature
control)
60Co at the center raw energies
Time dependence corrected / Different from different ADs
60Co at different R & Z to obtain the correction function,
Space dependence corrected / Unique for all the ADs
Correct for energy non-linearity: normalize to neutron capture peak
17~% level residual non-uniformities
• Spontaneous light emission by PMT• ~ 5% of PMT, ~5% of event• Rejection: pattern of fired PMTs
– Topology: a hot PMT + near-by PMTs and opposite PMTs
FlashersAnti-neutrinos
Inefficiency to neutrinos:
0.024% 0.006%(stat)
Contamination: < 0.01%Contain the hottest PMT18
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Simulated neutron
capture position
Estimation Procedure:- Measure uncorrelated gamma rays from
ACU in data
- Estimate ratio of correlated/uncorrelated rate
using simulation
- Assume 100% uncertainty from simulation
Weak (0.5 Hz) neutron source in ACU can also mimic IBD via inelastic scattering and capture on iron:
20
Example alpha
rate in AD1
238U 232Th 235U 210Po
Bq 0.05 1.2 1.4 10
Near Site: 0.04+-0.02 per day, B/S (0.006±0.004)%
Far Site: 0.03+-0.02 per day, B/S (0.04±0.02)%
Potential alpha source:
238U, 232Th, 235U, 210Po
Each of them are measured in-
situ:
U&Th: cascading decay of
Bi(orRn) – Po – Pb
210Po: spectrum fitting
Combining (α,n) cross-section,
correlated background rate is
determined.
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