章 飞虹ZHANG FeiHong

zhangfh@ihep.ac.cn

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

11

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.

12

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!

13

14

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

19

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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