νeνe νeνe νeνe νeνe νeνe νeνe Distance (L/E) Probability ν e 1.0 ~1800 meters (@ 3 MeV)...

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Transcript of νeνe νeνe νeνe νeνe νeνe νeνe Distance (L/E) Probability ν e 1.0 ~1800 meters (@ 3 MeV)...

Page 1: νeνe νeνe νeνe νeνe νeνe νeνe Distance (L/E) Probability ν e 1.0 ~1800 meters (@ 3 MeV) Reactor Oscillation Experiment Basics Unoscillated flux observed.
Page 2: νeνe νeνe νeνe νeνe νeνe νeνe Distance (L/E) Probability ν e 1.0 ~1800 meters (@ 3 MeV) Reactor Oscillation Experiment Basics Unoscillated flux observed.

νe

νe

νe

νe

νe

νe

Distance (L/E)

Pro

babi

lity

ν e

1.0

~1800 meters(@ 3 MeV)

Reactor Oscillation Experiment Reactor Oscillation Experiment BasicsBasics

Unoscillated flux Unoscillated flux observed hereobserved here

Well understood, isotropic source Well understood, isotropic source of electron anti-neutrinosof electron anti-neutrinos Oscillations observed Oscillations observed

as a deficit of as a deficit of ννee

sin22θ13

)4/(sin θ2sin1)νν( ν213

213

2 ELmP ee

νe

νe

νe

νe

νe

νe

Detectors are located Detectors are located underground to shield underground to shield against cosmic rays.against cosmic rays.

πEν /2Δm213

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The Existing Limit on The Existing Limit on θθ1313

sinsin22221313< 0.13 at 90% CL< 0.13 at 90% CL

Come from the Chooz and Palo Verde reactor experimentsCome from the Chooz and Palo Verde reactor experiments

Neither experiments found evidence for Neither experiments found evidence for ee oscillation oscillation

The null result eliminated The null result eliminated →→ee as the primary mechanism for as the primary mechanism for

the atmospheric deficitthe atmospheric deficit

ν213

213

2x 4Δsinθ2sin)νν( ELmP e

Remember the oscillation Remember the oscillation probabilityprobability

So these experiments are sensitive to So these experiments are sensitive to sinsin2222θθ1313 as a function of as a function of ΔΔmm22

1313

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CHOOZCHOOZ

• Homogeneous detectorHomogeneous detector

• 5 ton, Gd loaded, scintillating 5 ton, Gd loaded, scintillating target target

• 300 meters water equiv. shielding300 meters water equiv. shielding

• 2 reactors: 8.5 GW2 reactors: 8.5 GWthermalthermal

• Baselines 1115 m and 998 mBaselines 1115 m and 998 m

• Used new reactors Used new reactors →→ reactor off reactor off data for background measurementdata for background measurement

Chooz Nuclear Reactors, FranceChooz Nuclear Reactors, France

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Palo VerdePalo Verde

• 32 mwe shielding (Shallow!)32 mwe shielding (Shallow!)

• Segmented detector: Segmented detector: Better at handling the Better at handling the cosmic rate of a shallow site cosmic rate of a shallow site

• 12 ton, Gd loaded, scintillating 12 ton, Gd loaded, scintillating targettarget

• 3 reactors: 11.6 GW3 reactors: 11.6 GWthermalthermal

• Baselines 890 m and 750 mBaselines 890 m and 750 m

• No full reactor off runningNo full reactor off running

Palo Verde Generating Station, AZPalo Verde Generating Station, AZ

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CHOOZ and Palo Verde ResultsCHOOZ and Palo Verde Results

• sin2213< 0.18 at 90% CL (at m2=2.0×10-3)

• Future experiments should try to improve on these limits by at least an order of magnitude.

Down to sin2213 0.01

In other words, a 1% measurement is needed!

<~

• Neither experiments found evidence for e oscillation.

• This null result eliminated →e as the primary mechanism for the Super-K atmospheric deficit.

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Nuclear Reactors as a Neutrino SourceNuclear Reactors as a Neutrino Source

A typical commercial reactor, A typical commercial reactor, with 3 GW thermal power, with 3 GW thermal power, produces 6×10produces 6×102020 ννee/s/s

The observable The observable ee spectrum is spectrum is

the product of thethe product of the fluxflux and theand the cross sectioncross section..

Nuclear reactors are a very intense sources of Nuclear reactors are a very intense sources of ννee coming from coming from

the the -decay of the neutron-rich fission fragments.-decay of the neutron-rich fission fragments.

Arb

itra

ry

Flux Cross

Sectio

n

Observable ν Spectrum 

From Bemporad, Gratta and Vogel

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The reaction process is inverse The reaction process is inverse ββ-decay-decay

Two part coincidence signal is crucial for background reduction.Two part coincidence signal is crucial for background reduction.

Minimum energy for the primary signal of 1.022 MeV from Minimum energy for the primary signal of 1.022 MeV from ee++ee−−

annihilation at process threshold. annihilation at process threshold.

Positron energy spectrum implies the anti-neutrino spectrumPositron energy spectrum implies the anti-neutrino spectrum

In pure scintillator the neutron would capture on hydrogenIn pure scintillator the neutron would capture on hydrogen

Scintillator will be doped with gadolinium which enhances captureScintillator will be doped with gadolinium which enhances capture

e p→ e+n n capture

Reactor Neutrino Event SignatureReactor Neutrino Event Signature

n H → D (2.2 MeV)

n mGd → m+1Gd ’s (8 MeV)

Eν = Ee + 0.8 MeV ( =mnmp+me1.022)

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With GdWithout Gd

With GdWithout Gd

Why Use Gadolinium?Why Use Gadolinium?Gd has a huge neutron capture cross section. So you get faster capture times and smaller spatial separation. (Helps to reduce random coincidence backgrounds)

Also the 8 MeV capture energy (compared to 2.2 MeV on H) is distinct from primary interaction energy.

~30 μs

~200 μs

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Inverse Inverse ββ-decay -decay makes a nice makes a nice coincidence coincidence signal in the signal in the detector.detector.

First burst of First burst of light from the light from the positron.positron.

10’s of 10’s of μμs later…s later…

Delayed burst of Delayed burst of light from light from neutron capture.neutron capture.

Gd15764

Neutrino Interactions in the DetectorNeutrino Interactions in the Detector

νe

pn

Gd15864

e+

e-

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2

2

nearnear

farfar

LN

LNR

far

bgfar

stat N

NN

far

bgratebgbg N

N

1

npair

A Simple Sensitivity ModelA Simple Sensitivity Model

Where Where NN is the number of observed signal events, is the number of observed signal events, LL is the is the baseline and baseline and εε is the relative efficiency (≈1). Then… is the relative efficiency (≈1). Then…

222bgstatR

Where…Where…

< 1< 1– 3– 3σσRR means an effect is observedmeans an effect is observed

StatisticsStatistics Relative Relative NormalizationNormalization

BackgroundBackground

How Do You Measure a Small Disappearance?How Do You Measure a Small Disappearance?

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Statistics Statistics

Ways to optimize statistics…Ways to optimize statistics…

• Reactor power Reactor power Daya Bay is one of the most powerful nuclear plants in the Daya Bay is one of the most powerful nuclear plants in the world with 6 cores online by 2011 world with 6 cores online by 2011

• Detector massDetector massWith a total of 80 tons at the far site and no fiducial mass cut With a total of 80 tons at the far site and no fiducial mass cut Daya Bay will be an order of magnitude larger than any Daya Bay will be an order of magnitude larger than any previous short baseline reactor neutrino experimentprevious short baseline reactor neutrino experiment

• Run time Run time Three years run time will be two years more than previous Three years run time will be two years more than previous experimentsexperiments

• Optimized baseline for known value of Optimized baseline for known value of ΔΔmm22

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Relative NormalizationRelative NormalizationThe use of a near detector eliminates the normalization The use of a near detector eliminates the normalization uncertainty due touncertainty due to

• Inverse Inverse ββ-decay -decay reaction cross section reaction cross section

• neutrino production in the reactor coreneutrino production in the reactor core

• reactor powerreactor power

Truly identical detectors would eliminate the remaining sources Truly identical detectors would eliminate the remaining sources of normalization uncertainty which areof normalization uncertainty which are

• detector efficiency detector efficiency

• gadolinium fraction (neutron detection efficiency)gadolinium fraction (neutron detection efficiency)

• free proton count (neutrino target size and density)free proton count (neutrino target size and density)

• geometric acceptancegeometric acceptance

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BackgroundBackground

1.1. Fast neutron Fast neutron ── fast neutron enters fast neutron enters detector, creates prompt signal, detector, creates prompt signal, thermalizes, and is capturedthermalizes, and is captured

2.2. ββ+n decays of spallation isotopes +n decays of spallation isotopes ─ such as ─ such as 99Li and Li and 88He with He with ββ+n +n decay modes can be created in decay modes can be created in μμ 1212C spallation eventC spallation event

The vast majority of backgrounds are directly related to cosmic The vast majority of backgrounds are directly related to cosmic raysrays

There are three types of background:There are three types of background:

1.1. Random coincidence Random coincidence ── two unrelated events happen close two unrelated events happen close together in space and timetogether in space and time

(1%)

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Random Coincidence BackgroundRandom Coincidence Background

Assuming KamLAND Assuming KamLAND concentrations of concentrations of 4040K, K, 232232Th and Th and 238238U and 450 U and 450 mwemwe

Calculated rates for Braidwood.

Plot by Hannah Newfield-Plunkett

The rate of coincident events can be determined by studying the The rate of coincident events can be determined by studying the rates for positron and neutron capture like events in the detectorrates for positron and neutron capture like events in the detector

The singles rates from long lived spallation isotopes and the U, Th The singles rates from long lived spallation isotopes and the U, Th and K decay chains is shown below. and K decay chains is shown below.

Hannah was a bright high school student who worked with me for a couple of summers and is now a Cornell undergraduate student.

Positron-like events are Positron-like events are between ~2 and 8 MeVbetween ~2 and 8 MeV

Neutron events are ~6 to ~10 Neutron events are ~6 to ~10 MeV and include neutron MeV and include neutron captures from muon induced captures from muon induced neutrons which are not shownneutrons which are not shown

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Fast Neutron BackgroundsFast Neutron Backgrounds

1.1. Two neutron captures from the same cosmic Two neutron captures from the same cosmic ── This This should be tagged the vast majority of the time, but it should be tagged the vast majority of the time, but it sets the tag window for tagged muons at 100 sets the tag window for tagged muons at 100 μμs.s.

2.2. Proton recoil off fast neutron ─ dominate effect.Proton recoil off fast neutron ─ dominate effect.

3.3. Fast neutron excitation of Fast neutron excitation of 1212C C ── interesting, but not interesting, but not significantly different than 2. Energy spectrum peaks significantly different than 2. Energy spectrum peaks at particular values (like 4.4 MeV, first at particular values (like 4.4 MeV, first 1212C excited C excited state)state)

There are three main processes for the prompt “positron-There are three main processes for the prompt “positron-like” eventslike” events

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Tagging Muons at Daya BayTagging Muons at Daya BayThe basic idea is to tag muons that pass near the detector so The basic idea is to tag muons that pass near the detector so that we can reject the fast neutron background. Neutrons from that we can reject the fast neutron background. Neutrons from farther away should be mostly ranged out.farther away should be mostly ranged out.

n

p

n

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Correlated Spallation IsotopesCorrelated Spallation Isotopes

Isotopes like Isotopes like 99Li and Li and 88He can He can be created in be created in μμ spallation on spallation on 1212C and C and can decay to can decay to ββ+n +n

KamLAND found that the KamLAND found that the spallation is almost exclusively spallation is almost exclusively 99LiLi

This production is correlated This production is correlated with with μμ’s that shower in the ’s that shower in the detectordetector

from the thesis of Kevin McKinnyfrom the thesis of Kevin McKinny

Therefore we can account for these events by looking at the Therefore we can account for these events by looking at the separation in time of candidate events from energetic showers separation in time of candidate events from energetic showers muon showers.muon showers.

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Background SummaryBackground Summary

Total expected background rates: Total expected background rates:

far site < 0.4 events/det/dayfar site < 0.4 events/det/day

Daya Bay site < 6 events/det/dayDaya Bay site < 6 events/det/day

Ling Ao site < 4 events/det/dayLing Ao site < 4 events/det/day

(1%)

(a)

(d)

(c)

(b)

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Sensitivity To Shape Deformation Sensitivity To Shape Deformation

90%CL at Δm2 = 3×10-3 eV2

Assumes negligible background; Assumes negligible background; σσcalcal relative near/far energy calibration relative near/far energy calibration

σσnormnorm relative near/far flux relative near/far flux

normalizationnormalization

Huber et al hep-ph/0303232

Statistical error only

Fit uses spectral shape only

Exposure (ton GWth year)

sin

2 2θ 13

Sen

siti

vity

400 8000

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For three years of Daya Bay data and For three years of Daya Bay data and ΔΔmm22 ≈≈ 2.5 2.5××1010-3-3 eV eV22

90% CL limit at sin90% CL limit at sin2222θθ1313 < 0.008 < 0.008

3 3 σσ discovery for sin discovery for sin2222θθ1313 > 0.015 > 0.015

Daya Bay Projected SensitivityDaya Bay Projected Sensitivity

Sensitivity to sin22θ13

Source of Uncertainty %Far Statistical per Det. 0.3Near Statistical per Det. 0.1Reactor Related 0.1Relative Normalization 0.38Background (Near) 0.3Background (Far) 0.1

With Swapping

0.0060.006

0.0130.013

0.12

Page 22: νeνe νeνe νeνe νeνe νeνe νeνe Distance (L/E) Probability ν e 1.0 ~1800 meters (@ 3 MeV) Reactor Oscillation Experiment Basics Unoscillated flux observed.

The reactor oscillation experiment is what is known as a The reactor oscillation experiment is what is known as a disappearance experiment since it is only sensitive to the disappearance experiment since it is only sensitive to the original neutrino type (original neutrino type (ννee))

Electron neutrinos oscillate into Electron neutrinos oscillate into ννμμ or  or ννττ which can’t which can’t

produce a produce a μμ or or ττ at reactor energies at reactor energies

Therefore, when oscillations occur a fraction of neutrinos Therefore, when oscillations occur a fraction of neutrinos seem to disappearseem to disappear

Another class of experiments, known as appearance Another class of experiments, known as appearance experiments, experiments, areare sensitive to the new neutrino types sensitive to the new neutrino types

But the expression for the oscillation probability is much But the expression for the oscillation probability is much more complicated in these experimentsmore complicated in these experiments

Non-Reactor Handles on Non-Reactor Handles on θθ1313

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The oscillation probability for The oscillation probability for ννμμ→ν→νee is given by is given by

P(P(ννμμννee) = sin) = sin22θθ2323 sin sin2222θθ1313 sin sin22(1.27 (1.27 ΔΔmm131322 L/E) L/E)

+ cos+ cos22θθ2323 sin sin2222θθ1212 sin2(1.27 sin2(1.27 ΔΔmm121222 L/E) L/E)

± J sin ± J sin δδ sin(1.27 sin(1.27 ΔΔmm131322 L/E) L/E) (CP Violating Term)(CP Violating Term)

+ J cos + J cos δδ cos(1.27 cos(1.27 ΔΔmm131322 L/E) L/E)

where J = coswhere J = cosθθ2323 sin 2 sin 2θθ1212 sin 2 sin 2θθ2323 ××

sin(1.27 sin(1.27 ΔΔmm131322 L/E) sin(1.27 L/E) sin(1.27 ΔΔmm1212

22 sin 2 sin 2θθ1313 L/E) L/E)T2K (Japan)T2K (Japan)

• Appearance Appearance ννμμ→ν→νee (or (or ννμμ→ν→νee with separate running) with separate running)

• Off-axis beam results in a mono-energetic Off-axis beam results in a mono-energetic ννμμ beam beam

• Long baseline (300 – 900 km)Long baseline (300 – 900 km)• Needs a very large detectorNeeds a very large detector

Accelerator Based Accelerator Based θθ1313 Oscillation Experiments Oscillation Experiments

NOAMINOS

NONOννA (Fermilab)A (Fermilab)

Page 24: νeνe νeνe νeνe νeνe νeνe νeνe Distance (L/E) Probability ν e 1.0 ~1800 meters (@ 3 MeV) Reactor Oscillation Experiment Basics Unoscillated flux observed.

ννee Appearance Probability Appearance Probability

)27.1sin()27.1(sinδsin

θ2sinθ2sinθsinθcos)ννP()νP(ν212

213

2

23131223eμeμ

ELmELm

)27.1sin()27.1cos()27.1sin(

δcosθ2sinθ2sinθsinθcos

)27.1sin()27.1(sin

δsinθ2sinθ2sinθsinθcos

)27.1(sin2θsinθcosθcos

)27.1(sin2θsinθsin)νP(ν

212

213

213

23131223

212

213

2

23131223

212

212

213

223

2

213

213

223

2eμ

ELmELmELm

ELmELm

ELm

ELm

CPCP Asymmetry… Asymmetry…

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The The θθ2323 Degeneracy Problem Degeneracy ProblemAtmospheric neutrino measurements are sensitive to sinAtmospheric neutrino measurements are sensitive to sin2222θθ2323

But the leading order term in But the leading order term in ννμμ→ν→νee oscillations is oscillations is

If the atmospheric oscillation is not exactly maximal If the atmospheric oscillation is not exactly maximal (sin(sin2222θθ2323≠1) then sin≠1) then sin22θθ2323 has a twofold degeneracy has a twofold degeneracy

ν223

223

2xμ 4sinθ2sin)νν( ELmP

ν213

213

223

2eμ 4sinθ2sinθsin)νν( ELmP

45º 90º2θ 2θθθ

sin2 sinsin2222θθ2323

sinsin22θθ2323

No 2!

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Daya Bay (3 yrs) + Nova Nova only (3yr + 3yr) Double Chooz + Nova 90% CL

Daya Bay +T2K

T2K only (5yr,-only)

Double Chooz+T2K

90% CL

More On More On DegeneraciesDegeneraciesThere are additional degeneracies due to the unknown CP phase There are additional degeneracies due to the unknown CP phase and the unknown sign of the mass hierarchyand the unknown sign of the mass hierarchy

Combining experimental results can resolve these degeneraciesCombining experimental results can resolve these degeneracies

Need the more sensitive reactor experiment to resolve degeneraciesNeed the more sensitive reactor experiment to resolve degeneracies

McConnel & ShaevitzMcConnel & Shaevitz

hep-ex/0409028hep-ex/0409028

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Sensitivity to CPV and Mass HierarchySensitivity to CPV and Mass Hierarchy

The accelerator experiments may be sensitive to CP violation and The accelerator experiments may be sensitive to CP violation and the mass hierarchy, but if Daya Bay sets a limit on sinthe mass hierarchy, but if Daya Bay sets a limit on sin2222θθ1313 these these

questions can not be resolved by Noquestions can not be resolved by Noννa and T2K.a and T2K.

??

McConnel & ShaevitzMcConnel & Shaevitz

hep-ex/0409028hep-ex/0409028

Daya Bay Daya Bay