Neutrino

1
Low Energy Challenges in SK-III

• Neutrino
• Oscillation
• Workshop

Michael Smy UC Irvine
Conca Specchiulla, September 11th 2006
2
Super-Kamiokande

• 50kt Water Cherenkov Detector with 11,146 20 f
  PMTs
• located in Kamioka mine at 36.430N latitude and
  137.310 longitude 2,400 m.w.e underground

• 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 ns, proton decay

Courtesy Y. Oyama
3
Super-K Is Repaired!
now finished!
began in fall 2005
despite some weather problems!
Mozumi Mine Entrance
Village of Dou near Atotsu Mine Entrance
Michael Smy, UC Irvine
4
Conca Specchiula, 11th September 2006
5
Motivation 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
6
Solar Neutrino Problem
Michael Smy, UC Irvine
7
Solar Neutrino Problem Explained by SNO and
Super-K as Neutrino Flavor Conversion!
Michael Smy, UC Irvine
8
Solar Neutrino Oscillation Parameters
SolarKamLAND
KamLAND
99.73
Solar
95
Michael Smy, UC Irvine
9
Solar 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
10
How 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
11
SK-I Angular distributions
5.0-5.5MeV
5.5-6.0MeV
Rn, g
8.0-8.5MeV
ne search
spallation
14-20MeV
Courtesy Y. Takeuchi
12
SK-I Backgrounds
Courtesy M. Nakahata
13
How 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
14
Vertex Reconstruction
Michael Smy, UC Irvine
15
New Vertex Fit BONSAI

• Before Clusfit, Kaifit,
  Hayai maximize
• (choose center of
• timing window for t0)
• BONSAI use likelihood better maximization

Michael Smy, UC Irvine
16
BONSAI Performance in SK-II
LINAC v(-3.9,-0.7,12.0)m 5 MeV
cm
BONSAI 2.0
Clusfit
SK-II Monte Carlo
Kaifit
LINAC v(-12.1,-0.7,-0.1)m 5 MeV
BONSAI 2.0
Clusfit
Kaifit
LINAC v(-12.1,-0.7,-12.1)m 5MeV
BONSAI 2.0
Clusfit
Kaifit
Energy (MeV)
Michael Smy, UC Irvine
17
BONSAI Performance in SK-I
LINAC v(-3.9,-0.7,12.0)m 5 MeV
cm
BONSAI 2.0
Clusfit
SK-II Monte Carlo
Kaifit
LINAC v(-12.1,-0.7,-0.1)m 5 MeV
BONSAI 2.0
Clusfit
Kaifit
LINAC v(-12.1,-0.7,-12.1)m 5MeV
BONSAI 2.0
Clusfit
Kaifit
Energy (MeV)
Michael Smy, UC Irvine
18
SK-I Reduction BONSAI Fid. Cut
These Events already passed 2m dwall cuts from
Hayai (online), Kai-Fit (online), Kai-Fit
(offline) Clusfit (offline) as well as an 8m dg
cut!!
SK-I 4.5-5 MeV
Michael Smy, UC Irvine
19
Event Selection(Tested at SK-II)
Michael Smy, UC Irvine
20
Reconstruction Quality
Good Calibration Events

• Timing residual goodness 0bad, 1good
• Direction goodness azimuthal symmetry 0good,
  1bad
• Reject non-Cherenkov events and misreconstructed
  events

Low Energy Sample
Michael Smy, UC Irvine
21
Reconstruction Quality
Good Calibration Events

• Timing residual goodness 0bad, 1good
• Direction goodness azimuthal symmetry 0good,
  1bad
• Reject non-Cherenkov events and misreconstructed
  events
• Hyperbolical cut gt2-gd2gt0.25

Low Energy Sample
Michael Smy, UC Irvine
22
Solar Peak at SK-II at 7MeV
Livetime 622 Days
Livetime 622 Days
Michael Smy, UC Irvine
23
Recoil Electron Spectrum
MC
f8B2.33x106/cm2s
fhep15x103/cm2s
ADN-1.81.61.2
ADN-6.34.3(stat)
8B n MC only
8B n MC only
Michael Smy, UC Irvine
24
SK-II
SK-ISK-II
SK-I
Michael Smy, UC Irvine
25
Background Studies
Michael Smy, UC Irvine
26
Lantern Mantle Source

• contains large amounds of 208Tl
• produces 60kBq of 2.6MeV gs

300 Lantern Mantles
Michael Smy, UC Irvine
27
Lantern Mantle Source in SK-II

• x-1661.45 cm y-70.7 cm
  z1559.8 cm
• gt6 MeV

Michael Smy, UC Irvine
28
Lantern Mantle Source in SK-III
BONSAI
BONSAI

• x-71 cm y71 cm
• z1830 cm

Clusfit
Clusfit
BONSAI
BONSAI
Clusfit
Clusfit
Michael Smy, UC Irvine
29
Conclusions

• 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