Neutrino

Oscillation

Workshop

Conca Specchiulla, September 11th 2006Michael SmyUC Irvine

Low Energy Challenges in SK-IIILow Energy Challenges in SK-III

• 50kt Water Cherenkov Detector with 11,146 20” PMTs• located in Kamioka mine at 36.430N latitude and 137.310

longitude ~2,400 m.w.e underground

Super-KamiokandeSuper-Kamiokande

• April 1996-July 2001: (SK-I) Accident in November 2001 during maintenance Jan. 2003-Oct. 2005: SK-II (half PMT density) July 2006 – (SK-III)

• many physics topics; solar, atmospheric & accelerator ’s, proton decay Courtesy Y. Oyama

Super-K Is Repaired!Super-K Is Repaired!

Michael Smy, UC Irvine

began in fall 2005…

…now finished!

Village of Dou near Atotsu Mine Entrance Mozumi Mine Entrance

…despitesomeweatherproblems!

Conca Specchiula, 11th September 2006

Motivation for Lower ThresholdMotivation for Lower Threshold

1. Extend Solar Neutrino Recoil Electron Spectrum to 4 MeV

2. Measure Gadolinium neutron captures with high efficiency (effective energy spectrum peaks at 5 MeV)

3. Measure reactor anti-neutrinos above 3 MeV

Michael Smy, UC Irvine

Solar Neutrino ProblemSolar Neutrino Problem

Michael Smy, UC Irvine

Solar Neutrino Problem Solar Neutrino Problem Explained by SNO and Explained by SNO and Super-K as Neutrino Super-K as Neutrino Flavor Conversion!Flavor Conversion!

Michael Smy, UC Irvine

Solar 95%

99.73% KamLAND

Solar+KamLAND

Michael Smy, UC Irvine

Solar Neutrino Oscillation ParametersSolar Neutrino Oscillation Parameters

Solar Neutrino Future MeasurementsSolar Neutrino Future Measurements• Still missing: oscillation signature!• Lower energy real-time 8B neutrino measurement in

SK-III studies transition from vacuum oscillation to matter-dominated oscillations

Michael Smy, UC Irvine

How To Lower ThresholdHow To Lower Threshold• Must reduce backgrounds…• Reduced Radon emission due to

blast shields• Reduced Radon due to water flow

change• Software Improvements:

– Event Reconstruction– Event Selection– Background Studies

Michael Smy, UC Irvine

SK-I: Angular distributionsSK-I: Angular distributions

Rn,

5.0-5.5MeV 5.5-6.0MeV

8.0-8.5MeV

14-20MeV

spallation

e search

Courtesy Y. Takeuchi

SK-I BackgroundsSK-I Backgrounds

Courtesy M. Nakahata

How To Lower ThresholdHow To Lower Threshold• Must reduce backgrounds…• Reduced Radon emission due to

blast shields• Reduced Radon due to water flow

change• Software Improvements:

– Event Reconstruction– Event Selection– Background Studies

Michael Smy, UC Irvine

Vertex Vertex ReconstructionReconstruction

Michael Smy, UC Irvine

New Vertex Fit: BONSAINew Vertex Fit: BONSAI• Before: Clusfit, Kaifit,

Hayai maximize (choose center of timing window for t0)

• BONSAI: use likelihood; better maximization

n

i

xt

i

i

ex1

2

)(2

2

)(gdn

0)(tof)( txtxt iii

))((pdflog),( 0 xttx i

L

Michael Smy, UC Irvine

BONSAI Performance in SK-IIBONSAI Performance in SK-II

BONSAI 2.0

BONSAI 2.0

BONSAI 2.0

Clusfit

Clusfit

Clusfit

Kaifit

Kaifit

Kaifit

LINAC v=(-3.9,-0.7,12.0)m5 MeV

LINAC v=(-12.1,-0.7,-0.1)m5 MeV

LINAC v=(-12.1,-0.7,-12.1)m5MeV

Michael Smy, UC IrvineEnergy (MeV)

cm

SK-II Monte Carlo

BONSAI Performance in SK-IBONSAI Performance in SK-I

BONSAI 2.0

BONSAI 2.0

BONSAI 2.0

Clusfit

Clusfit

Clusfit

Kaifit

Kaifit

Kaifit

LINAC v=(-3.9,-0.7,12.0)m5 MeV

LINAC v=(-12.1,-0.7,-0.1)m5 MeV

LINAC v=(-12.1,-0.7,-12.1)m5MeV

Energy (MeV)

cm

SK-II Monte Carlo

Michael Smy, UC Irvine

Threshold Goal Threshold Goal

SK-I Reduction: BONSAI Fid. CutSK-I Reduction: BONSAI Fid. Cut

Michael Smy, UC Irvine

These Events already passed 2m dwall

cuts from Hayai (online), Kai-Fit(online), Kai-Fit (offline) & Clusfit(offline) as well as an 8m d cut!!

SK-I: 4.5-5 MeVd

dwall

Event SelectionEvent Selection(Tested at SK-II)(Tested at SK-II)

Michael Smy, UC Irvine

Reconstruction Reconstruction QualityQuality

• Timing residual goodness: 0=bad, 1=good

• Direction goodness: azimuthal symmetry 0=good, 1=bad

• Reject non-Cherenkov events and misreconstructed events

Michael Smy, UC Irvine

Good Calibration Events

Low Energy Sample

Reconstruction Reconstruction QualityQuality

• Timing residual goodness: 0=bad, 1=good

• Direction goodness: azimuthal symmetry 0=good, 1=bad

• Reject non-Cherenkov events and misreconstructed events

• Hyperbolical cut: gt2-

gd2>0.25Michael Smy, UC Irvine

Good Calibration Events

Low Energy Sample

Solar Peak at SK-II at 7MeVSolar Peak at SK-II at 7MeV

Michael Smy, UC Irvine

Livetime622 Days

Livetime622 Days

Recoil Electron SpectrumRecoil Electron Spectrum

Michael Smy, UC Irvine

88B B MC only MC only 88B B MC only MC only

8B=2.33x106/cm2shep=15x103/cm2s

MC:

ADN=-1.8±1.6±1.2% ADN=-6.3±4.3%(stat)

SK-ISK-II SK-I+SK-II

Michael Smy, UC Irvine

Background StudiesBackground Studies

Michael Smy, UC Irvine

Lantern Mantle SourceLantern Mantle Source• contains large amounds of 208Tl

• produces 60kBq of 2.6MeV ’s

Michael Smy, UC Irvine

300 Lantern Mantles

Lantern Mantle Source in SK-IILantern Mantle Source in SK-II

x=-1661.45 cm y=-70.7 cm z=1559.8 cm

>6 MeV

Michael Smy, UC Irvine

Lantern Mantle Source in SK-IIILantern Mantle Source in SK-III

Michael Smy, UC Irvine

x=-71 cm y=71 cm

z=1830 cm

Clusfit

BONSAI

Clusfit

BONSAI

ClusfitBONSAI Clusfit

BONSAI

ConclusionsConclusions

• energy threshold of 4 MeV for solar neutrinos is very ambitions for a large water Cherenkov detector…

• …but we learned a lot from SK-II how to live with small # of photo-electrons!– we have better vertex reconstruction– we have a better event selection– we have a better understanding of the backgrounds

Michael Smy, UC Irvine