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Search for q 13 at Daya Bay . On behalf of the Daya Bay Collaboration Deb Mohapatra Virginia Tech. Outline. The neutrino mixing matrix and the mixing angle θ 13 Reactor neutrino experiments Daya Bay experimental setup Expected signal and background rates

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search for q 13 at daya bay

Search for q13 at Daya Bay

On behalf of the Daya Bay Collaboration

Deb Mohapatra

Virginia Tech

outline
Outline
  • The neutrino mixing matrix and the mixing angle θ13
  • Reactor neutrino experiments
  • Daya Bay experimental setup
  • Expected signal and background rates
  • Systematics and sensitivity
  • Current status
  • Summary
the neutrino mixing mns matrix

Atmospheric

Reactor

Solar

The neutrino mixing (MNS) matrix
  • The MNS matrix relates the mass eigenstates(n1, n2 andn3) to the flavor eigenstates (ne, nmandnt)

Last unknown

matrix element

  • It can be described by three 2D rotations

Majorana Phases

  • Ifθ13is zero there is no CP violation in neutrino mixing
existing limit on q 13
Existing limit on q13

Hints for q13 ≠ 0

Global Fit Results

Sin2q13 = 0.016 ± 0.010 or Sin22q13 = 0.06 ± 0.04

[ E. Lisi, et al., arXiv: 0905.3549 ]

allowed region

nuclear reactors as antineutrino source
Nuclear reactors as antineutrino source
  • Fission process in nuclear reactor produces huge number of low-energy antineutrino
  • A typical commercial reactor, with 3 GW thermal power, produces 6×1020νe/s
  • Daya Bay reactors produce 11.6 GWth now, 17.4 GWth in 2011

From Bemporad, Gratta and Vogel

  • The observable antineutrino spectrumis the product of the fluxand the cross section

Antineutrino spectrum

Arbitrary

Cross Section

Flux

measuring 13 with reactor antineutrinos
Measuring 13 with reactor antineutrinos

Reactor anti-neutrinos survival probability:

Small-amplitude oscillation due to 13integrated over E

Solar oscillation

due to 12

θ13

Δm213≈Δm223

far

detector

near

detector

slide7

Daya Bay: Experimental setup

Far site

Overburden: 355 m

Empty detectors: to be moved to underground

halls via access tunnel.

Filled detectors: to be transported between

halls via horizontal tunnels.

900 m

Ling Ao Near

Overburden: 112 m

465 m

Ling Ao II

cores

Water

hall

Construction

tunnel

810 m

Ling Ao

cores

Liquid

Scintillator

hall

295 m

Entrance

Daya Bay Near

Overburden: 98 m

Daya Bay

cores

Total tunnel length ~ 3000 m

slide8

Far site

Overburden: 355 m

Ling Ao Near

Overburden: 112 m

Ling Ao II

cores

Ling Ao

cores

Daya Bay Near

Overburden: 98 m

Daya Bay

cores

Daya Bay: Experimental setup

  • 8 identical anti-neutrino detectors ( two at each near site and four at the far site) to cross-check detector efficiency
  • Two near sites sample flux from reactor groups

9 different baselines under the assumption of point size reactor cores and detectors

(Starting 2011)

Halls

Cores

antineutrino detector ad

5 meters

5 meters

~ 12% / E1/2

Antineutrino Detector (AD)
  • Three-zone cylindrical design
    • Target: 20 ton 0.1% Gd-doped Liquid Scintillator (LS)
    • Gamma catcher: 20 ton LS
    • Buffer : 40 ton (mineral oil)
  • 192 low-background 8” PMTs
  • Reflectors at top and bottom
  • AD sits in a pool of

ultra-pure water

Calibration System

Mineral Oil

LS

Gd-Loaded LS

1.55 m

1.99 m

PMT

2.49 m

muon veto system
Muon veto system

Cerenkov

Water Pool (2Zone)

RPC’s

AD

PMTs

(962)

  • Two tagging systems to detect cosmic ray and fast neutron background: 2.5 meter thick two-section water shield and RPCs
  • Efficiency 99.5% with uncertainty <0.25%
antineutrino event signature in ad
Antineutrino event signature in AD

Inverse b-decay

  • Two part coincidence is crucial for background reduction
  • Neutron capture on Gd provides a secondary burst of light approximately 30 μs later

epe+ + n(prompt)

 + p  D + (2.2 MeV) (delayed)

~ 0.3b

  • + GdGd* Gd+ ’s(8 MeV) (delayed)

~ 50,000b

measuring 13 with reactor antineutrinos at daya bay
Measuring 13 with reactor antineutrinos at Daya Bay

Measured

Ratio of

Rates

Proton Number Ratio

sin22q13

± 0.3%

Storage

Tank

+ flow & mass measurement

Near

Far

target mass measurement

ISO Gd-LS weighing tank

filling platform with clean room

pump stations

Coriolis mass flowmeters < 0.1%

load cell

accuracy < 0.02%

filling “pairs” of detectors

20-ton ISOtank

detector

Target mass measurement

200-ton Gd-LS reservoir

measuring 13 with reactor antineutrinos at daya bay1
Measuring 13 with reactor antineutrinos at Daya Bay

Measured

Ratio of

Rates

Detector

Efficiency

Ratio

Proton Number Ratio

sin22q13

± 0.3%

Storage

Tank

+ flow & mass measurement

± 0.2%

Near

Far

Calibration systems

ad calibration system
AD calibration system

Automated calibration system

→ routine weekly deployment of sources

LED light sources

→ monitoring optical properties

e+ and n radioactive sources

→ energy calibration

  • 68Ge source
  • Am-13C + 60Co source
  • LED diffuser ball

automated calibration system

energy calibration

6 MeV

1 MeV

Prompt Energy Signal

Delayed Energy Signal

10 MeV

8 MeV

Energy calibration

e+ threshold: stopped positron signal using 68Ge source (2x0.511 MeV)

e+ energy scale: 2.2 MeV neutron capture signal (n source, spallation)

6 MeV threshold:n capture signals at 8 and 2.2 MeV (n source, spallation)

6 MeV cut for delayed neutrons: 91.5%,

uncertainty 0.22% assuming 1% energy uncertainty

1 MeV cut for prompt positrons: >99%,

uncertainty negligible

slide17

Backgrounds

  • Fast neutron ─ fast neutron enters detector, creates prompt signal, thermalizes, and is captured
  • β+n decays of9Li and 8He created in AD via μ - 12C spallation

9Li

Antineutrino Signal

  • Random coincidence ─ two unrelated events happen close together in space and time
slide18

Signal, background and systematic

  • Signal rates:
    • far site < 90 events/det/day
    • DayaBay site < 840 events/det/day
    • Ling Ao site < 740 events/det/day

(1%)

  • Total expected background rates:
    • far site < 0.4 events/det/day
    • Daya Bay site < 6 events/det/day
    • Ling Ao site < 4 events/det/day

Systematic and

statistical

budgets summary

daya bay sensitivity to sin 2 2 13
Daya Bay sensitivity to sin22θ13

Sin22θ13 < 0.01 @ 90% CLin

3 years of data taking

2011start data taking with full experimentnominal running period: 3 years

site preparation
Site preparation

staging area

surface assembly building

tunnel

assembly pit

cleanroom

test assembly

assembly pit

entrance portal

fabrication and delivery of detector components
Fabrication and delivery of detector components

detector tank

acrylic target vessels

slide22

Gd-Liquid scintillatortest production

Daya Bay experiment uses 200 ton 0.1% gadolinium-loaded liquid scintillator (Gd-LS).

4-ton

test batch

production

0.1% Gd-LS in 5000L tank

Gd-LS will be produced in multiple batches but mixed in reservoir on-site, to ensure identical detectors.

summary daya bay is the most sensitive reactor 13 experiment
Summary Daya Bay is the most sensitive reactor 13 experiment.
  • Daya Bay will reach a sensitivity of ≤ 0.01 for sin2213
  • Civil and detector construction are progressing. Data taking will begin in summer 2010 with 2 detectors at near site.
  • Full experiment will start taking data in 2011.
the daya bay collaboration
The Daya Bay Collaboration

Europe (3) (9)

JINR, Dubna, Russia

Kurchatov Institute, Russia

Charles University, Czech Republic

North America (14)(73)

BNL, Caltech, George Mason Univ., LBNL,

Iowa state Univ. Illinois Inst. Tech., Princeton,

RPI, UC-Berkeley, UCLA, Univ. of Houston,

Univ. of Wisconsin, Virginia Tech.,

Univ. of Illinois-Urbana-Champaign

Asia (18) (125)

IHEP, Beijing Normal Univ., Chengdu Univ.

of Sci. and Tech., CGNPG, CIAE, Dongguan

Polytech. Univ., Nanjing Univ.,Nankai Univ.,

Shandong Univ., Shenzhen Univ.,

Tsinghua Univ., USTC,

Zhongshan Univ., Hong Kong Univ.,

Chinese Hong Kong Univ., National Taiwan Univ., National Chiao Tung Univ., National United Univ.

~ 210 collaborators

Thank You

slide26

Background Summary

(a)

(d)

(c)

(b)

(1%)

detector related s ystematic uncertainties
Detector-related systematic uncertainties

Relative

measurement

Absolute

measurement

Ref: Daya Bay TDR

experimental sensitivity calculation
Experimental sensitivity calculation
  • Scan in Dm2 – Sin22q13
  • Minimize c2 at each point
global fit to to sin 2 2 13
Global fit to to sin22θ13

[ P. Huber, et al., arXiv: 0907.1896 ]