First results fromthe Double Chooz experiment
Masaki Ishitsuka (TokyoTech)
November 25, 2011
ICRR seminarNeutrino oscillations
Flavor transition occurs as a consequence of (1) finite mass and(2) mixing of mass eigenstates and weak interaction eigenstates:
cij=cosθij, sij=sinθij

0  c13
s23  0
c 23 −s13e iδν e  1 0  ν µ  = 0 c 23  0 −sν τ  23

θ23:
P(νµ→νµ) byAtm. ν & ν beam€

0 s13e−iδ  c12
10  −s12
0c13  0

θ13:
P(νe→νe) by Reactor νθ13& δ:P(νµ→νe) by ν beam

In two flavor scheme:

1.27 × Δm 2 [eV 2 ] × L [m]P(ν α → ν α ) = 1− sin 2θ sin 
E[MeV]

20 ν1  0ν 2  1ν 3 θ12:P(νe→νx) byReactor ν & solar νNeutrino oscillation parameters:
MNS matrix:
3 mixing angles: θ12, θ23, θ13
1 phase: δ => CP-violation in ν-sector
Mass scales:
2 mass difference scales: Δm122, Δm2322s12c120sin22θΔm2

Current understandings• Mass squared dufferences• Δm212 ~ 8x10-5eV2• |Δm322| ~ |Δm312|~2.5x10-3eV2• Mixing angles• θ12 ~ 34o• θ23 ~ 45o• θ13 < 12o (sin22θ13 < 0.15)• CP violation (δCP) ➙ unknown• Mass hierarchy ➙ unknown• Absolute mass scale ➙ unknown

Current understandings• Mass squared dufferences• Δm212 ~ 8x10-5eV2• |Δm322| ~ |Δm312|~2.5x10-3eV2• Mixing angles• θ12 ~ 34o• θ23 ~ 45o• θ13 < 12o (sin22θ13 < 0.15)• CP violation (δCP) ➙ unknown• Mass hierarchy ➙ unknown• Absolute mass scale ➙ unknown

Measurement of θ13
is essential

Two approaches to search for θ13
 Reactor neutrino experiments: Double Chooz, Daya-Bay, RENO…
2

22 Δm 31L
−3P [ν e → ν e ] ≅ 1− sin 2θ13 sin  + O(10 ) 4E 

• Sensitive to θ13 ➙clean measurement of θ13
 Long baseline neutrino experiments using νµ beam: T2K, NOvA …

€[P ν µ (ν µ ) → ν e (ν e )]a(x) = 2GF N e (x)J r ≡ c12 s12c132 s13c 23 s23

€
€

222
 Δm 31  Δm 31
L 1 2L
22 Δm 21L= sin 2θ s sin  − s12 sin 2θ13 s23  sin
 4E  2
 2E   2E 2222
 Δm21
 Δm21L   Δm 31
LL  2  Δm 31
L
+ 2J r cos δ sin
  4J r sin δ sin 
 2E   2E  2E 
 4E 2 2  Δm 31L
22 4 Ea(x)± cos2θ13 sin 2θ13 s23 sin2
 4E 
 Δm 31 2213 232222
 Δm 31
 Δm 21a(x)L 2L
L222
sin 2θ13 cos2θ13 s23 sin + c 23 sin 2θ12 
2
 2E 
 4E 

• Sensitive to θ13, δCP, mass hierarchy, θ23➙ Parameters degeneracy➙ Determination of δCP using νµ and anti-νµ beams

Parameter degeneracy

Ambiguity

Indication of electron neutrino appearance（non-zero θ13）from T2K experiment (June, 2011)• 2.5σ significance of non-zero θ13• 0.03 (0.04) < sin22θ13 < 0.28 (0.34) at 90% C.L. for normal (inverted)hierarchy (assuming Δm223=2.4 x 10-3 eV2, δCP=0, sin22θ23=1.0)

Measurement of θ13using reactor neutrinos
2
 Δm 31L−3P ν e → ν e ≅ 1− sin 2θ13 sin  + O(10 ) 4E []Δm312€

22sin22θ13

sin 2 2θ13 = 0.1
2Δm31= 2.5 ×10−3 eV 2€•

Simple 2 flavor oscillation formula is valid at 1km baseline– P(νe→νe) as a function of Δm312(well known) and θ13 (unknown)– Matter effects are negligible– Independent to CP-violation phase⇒ Clean measurement of θ13

Strategy2
 Δm 31
L−3P ν e → ν e ≅ 1− sin 2θ13 sin  + O(10 ) 4E []22

Systematic errors onneutrino flux interaction x-sec
 # of target protons
 detection efficiency
€sin 2 2θ13 = 0.1
2Δm31= 2.5 ×10−3 eV 2

are canceled by two
detectors technique.

€νeChooz原子炉
4.27GWth x 2 cores

Near Detector<L> 400m
450ν/day
120m.w.e.
Early 2013

Far Detector<L> 1050m
65ν/day
300m.w.e.
April 2011

Strategy2
 Δm 31L−3P ν e → ν e ≅ 1− sin 2θ13 sin  + O(10 ) 4E []22

Far/Near ratio（3 years）
Simulation€

sin 2 2θ13 = 0.1

sin 2 2θ13 = 0.1

2Δm31= 2.5 ×10−3 eV 2

€

2Δm31
= 2.5 ×10−3 eV 2€

νeChooz原子炉
4.27GWth x 2 cores

Near Detector<L> 400m
450ν/day
120m.w.e.
Early 2013

Far Detector<L> 1050m
65ν/day
300m.w.e.
April 2011

Double Chooz experiment

νeChooz原子炉
4.27GWth x 2 cores

Near Detector<L> 400m
450ν/day
120m.w.e.
Early 2013

Far Detector<L> 1050m
65ν/day
300m.w.e.
April 2011

Double Chooz collaboration

Double Chooz collaboration meeting @ Kobe Univ.

Detection of reactor neutrinos• Inverse beta decay reaction

ν e + p → e+ + n• Reaction threshold: 1.8MeV• 65 events/day (far detector)€Background are largely suppressed byrequiring delayed coincidence
Prompt signal:
Positron and annihilation γ’s（1-8MeV）
Neutrino energy: Eν = Evis + 0.8MeV
Delayed signal:
γ’s from neutron capture on Gd（8MeV)Time correlation：
τ = 30 µsec

Double Chooz detector

Double Chooz検出器

ν-Target（10.3m3 Gd loaded (1g/l) liquid scintillator）

Target for neutrino signals

Double Chooz detector

Double Chooz検出器

γ-Catcher（22.3m3 liquid scintillator）
Measurement of 8MeV γ’s from n-Gd
capture in target volume
ν-Target（10.3m3 Gd loaded (1g/l) liquid scintillator）

Target for neutrino signals

Double Chooz detector

Double Chooz検出器

Buffer（110m3 mineral oil & 390 PMTs）
Reduction of fast neutron andenvironmental γ’s from PMT and outsideAcrylic Vessel
γ-Catcher（22.3m3 liquid scintillator）
Measurement of 8MeV γ’s from n-Gd
capture in target volume
ν-Target（10.3m3 Gd loaded (1g/l) liquid scintillator）

Target for neutrino signals

Double Chooz detector

Double Chooz検出器
Inner Veto
（90m3 liquid scintillator & 78 PMTs）

Detection of cosmic ray muons andshield to fast neutrons
Steel Vessel & PMT support structure
Buffer（110m3 mineral oil & 390 PMTs）
Reduction of fast neutron andenvironmental γ’s from PMT and outside
Acrylic Vessel
γ-Catcher（22.3m3 liquid scintillator）
Measurement of 8MeV γ’s from n-Gd
capture in target volume
ν-Target（10.3m3 Gd loaded (1g/l) liquid scintillator）

Target for neutrino signals

Double Chooz detector

Double Chooz検出器
Steel shield (15cm thick)
Inner Veto
（90m3 liquid scintillator & 78 PMTs）

Detection of cosmic ray muons andshield to fast neutrons
Steel Vessel & PMT support structure
Buffer（110m3 mineral oil & 390 PMTs）
Reduction of fast neutron andenvironmental γ’s from PMT and outside
Acrylic Vessel
γ-Catcher（22.3m3 liquid scintillator）
Measurement of 8MeV γ’s from n-Gd
capture in target volume
ν-Target（10.3m3 Gd loaded (1g/l) liquid scintillator）

Target for neutrino signals

Double Chooz detector

Double Chooz検出器

Outer Veto（Plastic scintillator） [not used in this analysis]
Identification of cosmic ray muons
Steel shield (15cm thick)
Inner Veto
（90m3 liquid scintillator & 78 PMTs）

Detection of cosmic ray muons andshield to fast neutrons
Steel Vessel & PMT support structure
Buffer（110m3 mineral oil & 390 PMTs）
Reduction of fast neutron andenvironmental γ’s from PMT and outsideAcrylic Vessel
γ-Catcher（22.3m3 liquid scintillator）
Measurement of 8MeV γ’s from n-Gd
capture in target volume
ν-Target（10.3m3 Gd loaded (1g/l) liquid scintillator）

Target for neutrino signals

Milestones
May 2008 – October 2010
December 2010
April 2011

July 2011

Far detector construction
Far detector filling completed
Far detector commissioned
Start physics data taking
Near laboratory construction started
Outer Veto commissioned

November 2011

FIRST RESULTS

June 2012
Beginning 2013

Near laboratory expected delivery
Near detector expected
Data taking with two detectorsConstruction @ DC far lab.

Inner veto PMT installedBuffer PMT installed

Installation of acrylic vesselTarget and γ-catcher
acrylic vessels installedBufferγ-catcherTarget

Lid closureAll PMT equippedSteel shield installedOuter Veto partially installedOuter Veto commissioned

Preliminary

Data taking

Electronics
HV-Splitter

Photomultiplier tubes
ID: 390 PMTs (R7081MOD)
IV: 78 PMTs (R1408)

sig.

Frontend Electronics

customsig.

(by CIEMAT)

custom (by Drexel U. & LLNL)

HVHV

HV-Supply
SY1527LC & A1535P(by CAEN)Trigger & Clockcustom(by RWTH-Aachen)ν-FADCVX1721(by CAEN&APC)µ-FADC
custom(by CBPF)

Trigger pattern & clock+ OV readout(Hamamatsu M64 + Maroc2-chip)νDAQ
MVME3100 (by Emerson)

implemented in Ada

Electronics

Waveforms recorded by Flash-ADC

Event display（~8MeV）

Double Chooz Preliminary

Data taking efficiency

Fraction of analyzed data

Run Time: 101.5234 days from April 13th to September 18th
Live Time : 96.823 days (1 ms muon veto)Neutrino flux

Reactor neutrino flux calculation
Expected number of eventsexp"N

N p # Pth (t)(E,t) =% &f
2 %
4$ L
Ef

Mean energy per fission（k=235U,238U,239Pu,241Pu）

E f = ∑α k (t) E kk!

Mean cross-section per fission€"f = "f#"f!

kBugey+ % (# kDC (t) $ # kBugey (t) ) " fk

= $ dE Sk (E) " IBD (E)0Neutrino flux prediction is based on Bugey 4 measurement withcorrection to Double Chooz (fission rates for each isotopes etc.)!

kThermal power
Thermal power (GW)

Preliminary
4.5
4.0
3.5
3.0
2.52.01.51.0Core B10.5

Core B20.0 020406080

100120140160Days after April 13, 2011

Systematic uncertainty: 0.46%

Systematic uncertainty on reactor
neutrino flux prediction
NpPreliminaryL

Pth"Bugey

Eper fission"per fission!

1.7% total error

TOTAL
00.2 0.4 0.6 0.8(2.7% in theoretical calculation
1 1.2 1.4 1.6 1.8 without Bugey4 measurement)
Relat Error (%)

Calibration

LED calibration system• Illuminate detector by LED light source fed into detector
through optical fibers• Embedded calibration system mainly used for stability
check of detector response

Energy calibration• Deploy 68Ge positron source in target
by Z-Axis system• Total 1.02MeV γ’s from annihilation(corresponds to the minimum energy
from inverse beta decay reaction)

Preliminary

Energy calibration• Deploy 8Ge positron source in
γ-catcher by guide tube system• Energy calibration in γ-catcher（γ-catcher scintilltor is made to give
similar light yield to target scintillator）

PreliminaryNon-linearity correction
PreliminaryNeutrino selection• Prompt signal• Delayed signal• CoincidenceMuon veto:

Selection criteria (1)• Δtµ > 1msec

Prompt Event:• Qmax/Qtot < 0.09 & RMS(Tstart)<40 ns• 0.7 < E < 12 MeV

Delayed Event:• Qmax/Qtot < 0.06 & RMS(Tstart)<40 ns• 6 < E < 12MeV

νeCoincidence:• Time coincidence: 2 < Δt < 100µs• No space coincidence cut

Multiplicity:• No trigger (>500keV) within 100µsec before prompt• Only one trigger (>500keV) within 400µsec after promptNeutrino selection• Prompt signal• Delayed signal• CoincidenceTrigger threshold

Promptenergy cut

Minimum energyof neutrino signal• Trigger efficiency• 50% @ 350keV• 100+0-0.4% above 700keV• Prompt energy cut efficiency > 99.9%

Neutrino selection• Prompt signal• Delayed signal• CoincidenceDelayed energy cut

Efficiency of delayed signal: 86.0 ±0.6 %Neutrino selection• Prompt signal• Delayed signal• CoincidenceTime coincidence• KeV neutrons thermalized within a few µs➙ captured on Gd with τ = 27µs
• Efficiency within [2,100] µs: 96.5 ±0.5 %Data quality

Prompt energy vs. delayed energy

Reconstructed vertex positions

PromptDelayed

dR: prompt vs. delayed

Neutrino candidate: event rate

• Background not subtracted➙ good agreement indicates low background level

BackgroundCosmic muon rate
Inner Detector: 13Hz

Preliminary

Inner Veto: 46Hz

Preliminary

Accidental BG
Single spectrum
PreliminaryγAccidental BG
Prompt energy after
off-timing coincidenceγ

Preliminary

Rate: 0.332 ±0.004 events/day

Correlated BG: cosmogenic
Cosmic-ray µ spallation products:
9Li, 8He➙ n+β decay with decay time of 200msec
completely mimic neutrino signal
9Li → e- + n + 8Be (n + e- < 11.9MeV)

Preliminary
Number of BG events estimated from timecorrelation with showering µ➙Consistent with reactor OFF measurement

Rate: 2.3 ±1.2 events/day

Correlated BG: fast neutron
Prompt signal:
Recoil proton
Delayed signal
8MeV γ’s from neutron capture on Gd

Preliminary

Number of BG events estimatedfrom the spectrum at high energy

Rate: 0.7 ±0.5 events/dayReactor OFF data
• 1 day data was taken with both reactor OFF• 3 events pass neutrino selection below 30MeV
1. Eprompt=9.8 MeV, Δt=201msec from showering muon(>600MeV), vertex close to muon track (15.4cm)
2. Eprompt=4.8 MeV, Δt=241msec from showering muon,vertex close to muon track (27.9cm)
3. Eprompt=26.5 MeV, no showering muon within 5sec
Number of events observed under rector OFF condition
was consistent with the estimated number of BG events

Neutrino oscillation analysis

2Definition of χResults

Rate Only:
Shape Only:
Rate & Shape:

sin22θ13 = 0.096 ±0.029(stat) ±0.073(syst)
sin22θ13 = 0.044 ±0.157
sin22θ13 = 0.086 ±0.029(stat) ±0.042(syst)➙ No-Oscillation Excluded at 92.9 %Results
Rate & Shape

Preliminary
Rate Only:
Shape Only:
Rate & Shape:

sin22θ13 = 0.096 ±0.029(stat) ±0.073(syst)
sin22θ13 = 0.044 ±0.157
sin22θ13 = 0.086 ±0.029(stat) ±0.042(syst)➙ No-Oscillation Excluded at 92.9 %Combined analysis:
T2K+Double Chooz

Combined analysis:
T2K+MINOS+CHOOZ+Double Chooz

Sensitivity

Near detector construction in progress!!

Comparison of rector neutrino experiments
Double Chooz

Daya BayRENO

923 m.w.e
120 m.w.e

ν-target10t ×2400m

230 m.w.e
291 m.w.e

ν-target20t ×8481m

1,985

4.27GWthm

2.3GWth

1,050m
2.9GWth300m.w.e

P=8.2GWth/2
L=1.05km
δsin22θ13=0.03
Far data taking
November 2011 first result

255 m.w.e
360m

P=11.6GWth/4
17.4GWth/6(2011~)
L~1.8kmδsin22θ13=0.01
Neardata taking

ν-target20t ×2675m.w.e

P=16.1GWth/6
L~1.4kmδsin22θ13=0.02
Near + Fardata taking

Measurement of Δm213
by reactor experiments

Conclusion• Double Chooz started physics data taking since April 2011
• First neutrino oscillation analysis results are presented
Rate+Shape: sin22θ13 = 0.086 ±0.029(stat) ±0.042(syst)
No oscillation excluded by 92.9% C.L.
• Near detector will be operational by early 2013
➙ Precise measurement of θ13 (sensitivity: sin22θ13< 0.03)