Sophie Berkman
Nevis Labs, Columbia University

• Neutrino Oscillations
• Double Chooz
• Outer Veto
• Some Studies
– PMT Characterization
– Scintillator Tests
• Efficiency
• Cross-Talk
• Pulse Height vs. Distance

• In the standard model neutrinos are massless leptons - cannot mix.
• BUT - neutrinos oscillate so by the current interpretation:
– Neutrinos have mass
– Lepton family number is not conserved

In a 2-neutrino simplification:
• Mass states =  1,  2
• Flavor (weak) states = 

,  e
Probability of oscillation:
P( 

->  e
)=sin 2 (2 θ )sin 2 (1.27
 m 2 L/E)
Θ =mixing angle
 m 2 =difference in squares of neutrino masses
L=distance of oscillation E=energy of neutrinos

• Measure θ
13
• Reactor experiment
– Look at reactors
 e from
• Disappearance
only produce  e
• Two Detectors identical, cancel uncertainties in neutrino flux and cross-section
– Near - unoscillated neutrino flux
– Far - after oscillation

• Double Chooz looks for inverse beta decay
–  e
+ p n + e +
– Double coincidence of neutron capture and positron signal (within ~100  s)
• Cosmic muon background
– Muon interacts to form neutrons
– Neutrons knock protons out of scintillator
– Protons emit light as they move through scintillator and neutron captured by gadolinium
– Looks like inverse-beta decay signal

7m
7m
• Target: liquid scintillator, doped with Gadolinium n capture
• Gamma catcher: measure gammas from n capture
• Buffer: holds PMTs, shields detector from PMT radiation
• Inner veto: reject fast neutron/muon background
• Outer Veto: atmospheric muons

• Reject atmospheric muon background
• Stacked scintillator strips
• Wavelength shifting fibers
• Light transmitted to PMT and DAQ
• Nevis: developing electronics/software
• All tests done in light tight boxes

• Why Characterize?
– Want all pixels to respond in the same way to light
– Pulse height of 350 ADC counts
• 350ADC counts =10pe * 35 ADC/pe

• Take Baseline with laser off
• Turn laser on and allow it to stabilize for 30 min
• Adjust HV to get an average pulse height for all pixels to be 350 ADC counts
• Adjust gain across preamplifiers to get a mean pulse height of 350 ADC counts across each individual pixel
• Turn off the laser and allow it to stabilize for 30 minutes
• Take noise data for different DAC thresholds

Spread=18%
Spread=2.9%
Conclusion: characterization process narrows the spread of the pulse height distributions. Use to determine if bad PMTs.

•Gain Constant = measure of gain adjustment
•Gain constant of
16 means adjust by a factor of 1
Conclusion: Centered around 16 (ie. Adjustment by factor of 1)

• Four stacked strips 1.5m long
• Four sets of trigger counters
• Wavelength Shifting fibers
• Fiber Holder

• Spacers to protect the face of the
PMT
– Large spacer = space of 1.27mm
– Small spacer = space of 0.48mm
– No spacer = space of 0.000mm
• Optical Grease

Trigger on trigger counters and one strip
Efficiency =
#Entries=326
#Entries=359
= 91%
Trigger on trigger counters
•Events over 1pe for triggered strip/trigger counter
•Repeat with more coincidences

• Repeated for more coincidences
• Large spacer: ~4.3pe
• Small spacer: ~5.2pe
Large Spacer
Require
3-fold
Effic.
83%
Small Spacer
Require Effic.
3-fold 91%
4-fold 83% 4-fold 94%
5-fold 90% 5-fold 96%
Conclusion: more efficient with more coincidences, and with smaller spacer.

• Optical Cross talk: the amount surrounding pixels receive light from the illuminated pixel
• # pe smaller than expected
• Add pulse heights in surrounding pixels to the signal pixel
• Can find maximum #pe without crosstalk
• Note: different numbers of surrounding pixels for different pixels

no spacer, strip 2
Conclusion:cross-talk is on average ~10% and
#pe increases to: ~5-8pe in the nearest position

• Noticed dependence on distance from previous studies
• All strips at all positions
• Use optical grease without spacer
• Require 5-fold coincidence
• 1 photoelectron cut on non signal strip/trigger

PH=206.
4pe=5.89
7
PH=281.7
pe=8.049
PH = 221.8
pe=6.337
PH =305.3
Pe=8.723
Conclusion: Four strips have different pulse heights because of polishing of fibers or scintillator

Mean =246.8
Pe=7.051
Mean=269.9
Pe=7.711
Mean=308.3
Pe=8.809
Mean=355.1
Pe=10.14
Conclusion: Pulse Height increases as move closer to the
PMT because more light will reach the PMT from closer positions. (Higher PH than previous because of Trigger 2)

Mean =76.88
Pe=2.197
Mean=106.4
Pe=3.040
Mean=305.3
Pe=8.723
Conclusion: Trigger counters have lower PH than strips because light will be lost from muons that hit them at the edge

Attenuation Length
•Find using PH vs. distance data
•Find by fitting plot of PH vs distance to exponential
Strip no T0 small spacer
T0 no spacer
T0 grease
T2 grease
T2 grease
(gain online)
1
2
3
260.11
204.9
281.66
127.66
174.82
236.95
162.52 177.54 160.55
220.29 229.37 336.92
212.73 209.66 280.37 aver age per strip
177.
67
233.
26
244.
27
4 364.54 302.58 296.6 268.95 255.62 297.
66

• Process for characterizing PMTs works well and will be possible to implement for all outer veto PMTs
• Still generally not as many photoelectrons as expected, but we can use optical grease/other trigger modes to increase the number
Thanks to everyone I worked with this summer for teaching me so much about physics and for this extraordinary opportunity to work on Double Chooz.

• Camilleri, Leslie. Slides.
• Shaevitz, Mike. Reactor Neutrino Experiment and the Hunt for the Little Mixing Angle. 30 Nov 2007.
• Sutton, Christine. Spaceship Neutrino.

1.
Find the mean of the pulse height distribution in strip 1 when both trigger counters have at least 1pe
2.
Find the mean pulse height distribution in strip 1 when both trigger counters and strip 2 have at least 1pe.
3.
Efficiency = Second Mean/First mean
4.
Require more strips to have 1pe
5.
Look at efficiencies with different requirements for events
6.
Repeat with large and small spacer
Conclusion:
More efficient with more requirements.
-Large Spacer went from 83-90%
-Small Spacer went from 91-96%