kamland update

KamLAND Update

Lauren HsuLawrence Berkeley National Laboratory

June 17, 2005

LEPP Journal Club

KamLAND Update - Lauren Hsu

I. Introduction

II. Role of Reactor Experiments in Neutrino Oscillations

II. KamLAND Overview and Results on 2nd Reactor Analysis

III. The Future of KamLAND Reactor Measurements

IV. Other Future Measurements: Geo-neutrinos and Be7

Outline

KamLAND

Inside the Kamioka Mine

KAMioka Liquid scintillator Anti-Neutrino Detector

Surrounded by 53 Japanese Nuclear Reactors

Detecting reactor anti-neutrinos 1 km beneath Mt. Ikeyama


Physics Reach of KamLAND


The KamLAND Collaboration

Tohoku U.

LBNLStanfordCalTechKS State U.U. of TNU. of ALTUNLDrexel U. of NMU. of HI

IHEP

CENBG


• Role of Reactor Experiments in Neutrino Oscillations


Neutrino Oscillations Review

Like quarks, neutrino flavor and mass eigenstates are not the same:

Simplified expression for two flavor oscillations in a vacuum:

P(ll’) = sin22 sin2(1.27m2(eV2)L(m)/E (MeV))

UMNSP =

oscillations imply neutrinos have mass!

1 0 00 e-i/2 00 0 e-i(/2+)

cos12 sin12 0-sin12 cos12 0 0 0 1

1 0 00 cos23 sin23

0 -sin23 cos23

cos13 0 e-isin13

0 1 0-e-isin13 0 cos13

Solar and KamLAND Atmospheric Future reactor oraccelerator

Majorana phases


Sampling of -Oscillation Experiments

Reactor(KamLAND)

tan12 & m 12

e disappearance+ appearance

Energy: ~5-15 MeV

Baseline: 1.5108 km

By no means comprehensive!

m23 & sin223

v (?) disappearance

Energy: ~ GeV

Baseline: 15 -13,000 km

2

m23 & sin223

vu (?) disappearance

Energy: ~ GeV

Baseline: 250 km

2

m12 & sin212

e disappearance

Energy: few MeV

Baseline: 180 km

-

22


Neutrino Mass Heirarchy

m2

?

e

0.0

m21

m22

m23

m12

m23= (1-3)10-3 eV2

= (7.90.06)10-5 eV2

atmospheric

Solar and KamLAND2

2

Normal or Inverted?


Reactor Anti-Neutrino Experiments

• Disappearance Experiment• Detect anti neutrino via inverse beta-decay• Energy range ~few MeV• Reactor anti-neutrino experiments performed since 1950’s• Detector relatively simple and basic design unchanged

Why a Reactor Neutrino Experiment?

No matter effectsMan-made source

Opportunity to study anti-neutrino vs neutrino oscillations

Basics


Anti-Neutrino Production in Reactors

Net thermal power output by all Japanese Nuclear Reactors is 200 GW.

• Anti-neutrinos produced in beta decay of daughter isotopes resulting from fission

• Production of anti-neutrinos well understood theoretically and fission yields precisely monitored by power companies (to 2% uncertainty)

Averaged Relative Fission Yields:

235U:238U:239Pu:241Pu = 0.563: 0.079: 0.301:0.057

235U + n X1 + X2 + 2n

No need for a near detector to monitor flux!


Un-Oscillated Reactor Neutrino Spectrum

Verified to 2% accuracy by earlier generation of reactor anti-neutrino experiments

Why KamLAND?

More Overburden: Avoids Cosmogenic Backgrounds

Long Baseline – optimizes sensitivity to oscillations

Large (1 kTon!) – combats1/R2 drop-off in intensity

KamLAND sees ~1 anti-neutrino event/day at an effective baseline of 180 km.

KamLAND Optimizations:


The First KamLAND Result

PRL 90 (2003) 021802Before KamLAND

KamLAND is the first reactor experiment to observe e disappearance!-


Physics Implications for the First Result


III. KamLAND Overview and Results on 2nd Reactor Analysis


The KamLAND Detector

(1879)


The Target Volume

• Serves as both the target and the detector, > 1031 protons• 20% Pseudocume + 80% Mineral Oil + 1.5 g/l PPO • Optimal light yield while maintaining long attenuation length (~20 m).

• Separates target LS volume from buffer oil• 135 m Nylon/EVOH (ethylene vinyl alcohol copolymer)• Supported by kevlar ropes

Liquid Scintillator:

Balloon:

Welding the Balloon


KamLAND Photo-Multipliers

• 1325 17” tubes

• 554 20” tubes (since 2/03)

• Transit time spread < 3 ns

• Separated from inner buffer by acrylic panels

• 200 17” hits for 1 MeV energy deposit

PMT and acrylic panel installation


The Outer Detector

• 3.2 kT water Cerenkov detector (~200 PMT’s)• Detects 92% of muons passing through inner detector• Buffers inner detector from spallation products and radioactivity in rock.


Anti-Neutrino Signal Detection

Coincident energy deposits are a distinct signature of inverse beta-decay:

e + p e+ + n

Delayed Energy: n-capture releases 2.2 MeV , ~200 s later

Prompt Energy: positron energy deposit (K.E. + annihilation ’s)


Selecting Candidate Events

Candidate Coincidence Events: t = [0.5, 1000]s

Apply Time and Spacial Cuts to Obtain Candidate Coincidence Events

e energy obtained from E = Eprompt + 0.8 MeV-


Basic KamLAND Data Reconstruction

Energy Reconstruction:• Energy Number of Hit PMT’s• Correction for Vertex Position• Corrections for Quenching and Cerenkov

Vertex Reconstruction• Determined by Very Precise Timing of Hits (~ few ns):• Inherent Detector Resolution ~15cm.• Based on push-pull minimization algorithm.

Energy and Vertex fitter Calibrated w/ Co60, Ge68, Zn65, and AmBe deployed along the z-axis.

How much energy deposited and where?


Energy Calibration


Energy Estimation

Only observe e above 3.4 MeV(Eprompt = 2.6 MeV)

Correcting for Nonlinearity of Energy Scale

-

Muon Tracking

Reconstruction of Tracks:• Pattern recognition based on expected timing of inner detector hits• Good agreement with simulation of muons passing through detailed mountain topography

Rate of Muons hitting KamLAND is ~1 Hz


Uncorrelated Backgrounds

• From radioactive isotopes in detector and surrounding material. • Activity concentrated near balloon• Fiducial volume cut defined at r = 5.5m

Uncorrelated backgrounds:

Lots of steel in the chimney region!


Correlated Cosmogenic Backgrounds

Muons interacting with material produce neutrons and delayedneutron - emitters

Spallation Products

He8 thought to be a negligeable contribution


13C(,n)16O Background

low energy

4.4 MeV

~6 MeV

Background Prompt E (MeV)


KamLAND Reactors

Total reactor power uncertaintyin analysis is 2%(conservative estimate)


Dip in Nuclear Power Output

KamLAND

no

-osc

rat

e e

eve

nts

/day

Falsified saftey records prompted shutdown of several nuclear power plants


Looking for Correlations in Un-Oscillated Rate Changes


What Were Improvements?

• More Statistics: 515.1 live days compared to 145.1 live days.

• 13C(,n)16O background discovered and included in analysis

• Better Optimized Cuts (fiducial volume increased from 5m to 5.5m)

• Addition of 20” tubes (improved energy resolution from 7%/E(MeV) to 6%/E(MeV))

• Reactor off-time allowed for study of correlation of signal with reactor flux.

Second results includes re-analysis of same data-sample used in first


Observation of Spectral Distortion from Neutrino Oscillations

Measurement of Energy Spectral Distortion Due to Oscillation: PRL 94 081802 (2005)

258 events observed365 expected


Looking for Oscillatory Behavior

0.7% goodness of fit1.8% goodness of fit

Simplified expression for two flavor oscillations in a vacuum:

P(ll’) = sin22 sin2(1.27m2(eV2)L(m)/E (MeV))


Unparalled Sensitivity to m12

PRL 94 081802 (2005)

2

Extract Oscillation Parameters and Combine with Solar Data

Solar + KamLAND: m12 =7.9 10-5 eV2, tan212 =0.4 2 +0.6-0.5

+0.10-0.07

PR

L 94 081802 (2005)


IV. The Future of KamLAND Reactor Measurements


Future Improvements: Reactor Analysis

Systematic Unc. on Rate %

Fiducial Volume 4.7

un-oscillated e spectrum (theor.) 2.5

Energy Threshold 2.3

Reactor Power 2.1

Cut Efficiency 1.6

Fuel Composition 1.0

Cross Section 0.2

Livetime 0.06

Total 7.1

Compare to statistical uncertainty: 6.7%

Further Improvements Require Reducing Systematic Uncertainty!

Better understanding of 13C(,n)16O will also improve shape analysis


Full Volume Calibration

• A new full-volume calibration device• Off-axis calibration to improve energy and vertex estimation• Reduce fiducial volume uncertainty

Testing 4 at LBNL

Source placement uncertainty of 2 cm will measure fiducial volume to 2-3% uncertainty


A Muon Tracker

• Gold-plated muon events will cross-check the muon track- reconstruction.

• Three layer tracking chamber prop tubes

• ~200 events per day in coincidence with inner detector

• x-y resolution of 2-3 cm.

• assembled by graduate student(s) at LBNL.


A Full-Detector Simulation

Goal: A Tuned Full-Detector SimulationGeant4 visualization of

KamLAND

Helps to reduce systematic uncertaintyfor next analysis and increase understanding of detector


A Change in Effective Baseline?

Shika upgrade will be complete in 2006. Impact on baseline will depend on the oscillation parameters!

(sin212, m2)12


Projected Future Sensitivity

KamLAND will continueto make the most sensitivemeasurements on m2 for the forseeable future

12


V. Other Future Measurements: Geo-neutrinos and Be7


Geo-Anti-Neutrinos

16 TW of Heat predicted from decay of 238U and 232Th concentrated in earth’s crustTotal Heat radiated by Earth is ~44 TW

surface heat flux measurementsFirst search for geologically produced e!-


A Measurable Spectrum Below

2.6 MeV

Th + U signal

reactor - e

background

-

Geo-neutrino analysis is very sensitive to quenched neutronsfrom 13C(,n)16O background


Be7 Phase: 2nd KamLAND Phase


An Ambitious Purification Project

Detecting e

Via elastic Scattering(no coincidence tosuppress radioactivebackgrounds)


Purification R&D

• $10 million must be spent this year • Construction of Purification Hall already begun• 3 Distillation towers will be installed.

Kr removal is through Hebubbling and Kr trap~10-4 achieved

Current R&D shows promising results.


Post Purification Goal


Timeline for KamLAND

Excavation of new purification chamber started in April and nearly finished.


Summary

• KamLAND is the first experiment to observe disappearance of reactor anti-neutrinos (99.998% significance).

• Latest results (summer 2004) show evidence for spectral distortion. combined solar-experiment and KamLAND results give:

m2 = 7.9 10-5eV2 and tan2 = 0.40

• Future reactor measurements will benefit from full-volume calibration, a muon tracker, full-detector Monte Carlo, and purification.

• Expect results soon on geo-neutrinos – the first limit ever for observation of anti-neutrinos produced from the earth.

• Phase II of KamLAND: 7Be neutrinos from the sun. Purification stage is already beginning, and measurements to start in 2007.

+0.6-0.5

+0.10-0.0712 12


AcknowledgementsAlmost all pieces of this talk borrowed liberally from

my KamLAND colleagues

Reference:

http://www.ba.infn.it/~now2004/talks/12_09_04/plen/KamLAND.pdf

http://www.ba.infn.it/~now2004/talks/12_09_04/plen/KamLAND.pdf


Mozumi 4/05

KL Control Room

to Kamioka Mine

kamland update

Documents

reactor neutrino experiment

neutrino flavor

antineutrino eventday

neutrino oscillationsii

kamland overview

kamland optimizations

kamland resultprl

reactor analysisiii