Double Chooz: Outer VetoDouble Chooz: Outer Veto

Sophie BerkmanNevis Labs, Columbia

University

Sophie BerkmanNevis Labs, Columbia

University

OutlineOutline

• Neutrino Oscillations• Double Chooz • Outer Veto• Some Studies

– PMT Characterization– Scintillator Tests

• Efficiency• Cross-Talk• Pulse Height vs. Distance

• Neutrino Oscillations• Double Chooz • Outer Veto• Some Studies

– PMT Characterization– Scintillator Tests

• Efficiency• Cross-Talk• Pulse Height vs. Distance

Neutrino OscillationsNeutrino Oscillations

• 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 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

What it means that neutrinos oscillateWhat it means that neutrinos oscillate

In a 2-neutrino simplification:• Mass states = 1, 2

• Flavor (weak) states = , e

In a 2-neutrino simplification:• Mass states = 1, 2

• Flavor (weak) states = , e

Probability of oscillation:

P( -> e)=sin2(2θ)sin2(1.27m2L/E)

Θ=mixing angle

m2=difference in squares of neutrino masses

L=distance of oscillation E=energy of neutrinos

Neutrino Mixing with 3 flavors

Neutrino Mixing with 3 flavors

Double Chooz Double Chooz

• Measure θ13

• Reactor experiment– Look at e from reactors

• Disappearance experiment - reactors only produce e

• Two Detectors - identical, cancel uncertainties in neutrino flux and cross-section – Near - unoscillated

neutrino flux– Far - after oscillation

• Measure θ13

• Reactor experiment– Look at e from reactors

• Disappearance experiment - reactors only produce e

• Two Detectors - identical, cancel uncertainties in neutrino flux and cross-section – Near - unoscillated

neutrino flux– Far - after oscillation

-

Muon BackgroundMuon Background

• Double Chooz looks for inverse beta decay e+ p n + e+

– Double coincidence of neutron capture and positron signal (within ~100s)

• 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

• Double Chooz looks for inverse beta decay e+ p n + e+

– Double coincidence of neutron capture and positron signal (within ~100s)

• 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

Double Chooz DetectorsDouble Chooz Detectors

• 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

• 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

7m

7m

Outer VetoOuter Veto• 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

• 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

PMT CharacterizationPMT Characterization

• 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

• 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

Characterization ProcessCharacterization Process

• 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

• 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

Before and After CharacterizationBefore and After Characterization

Conclusion: characterization process narrows the spread of the pulse height distributions. Use to determine if bad PMTs.

Spread=18% Spread=2.9%

Gain Constant DistributionGain Constant Distribution

Conclusion: Centered around 16 (ie. Adjustment by factor of 1)

•Gain Constant = measure of gain adjustment•Gain constant of 16 means adjust by a factor of 1

Scintillator SetupScintillator Setup

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

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

Some Standard Modifications

Some Standard Modifications

• 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

• 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

Efficiency TestEfficiency Test

#Entries=326

#Entries=359

= 91%

Efficiency =

•Events over 1pe for triggered strip/trigger counter•Repeat with more coincidences

Trigger on trigger counters

Trigger on trigger counters and one strip

Efficiency ResultsEfficiency Results• Repeated for more coincidences• Large spacer: ~4.3pe• Small spacer: ~5.2pe

• Repeated for more coincidences• Large spacer: ~4.3pe• Small spacer: ~5.2pe

Require Effic.

3-fold 91%

4-fold 94%

5-fold 96%

Require Effic.

3-fold 83%

4-fold 83%

5-fold 90%

Large Spacer Small Spacer

Conclusion: more efficient with more coincidences, and with smaller spacer.

Cross TalkCross Talk

• 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

• 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

PH distribution before and after addition - no spacer, strip 2

PH distribution before and after addition - no spacer, strip 2

Conclusion:cross-talk is on average ~10% and #pe increases to: ~5-8pe in the nearest position

Pulse Height vs Distance Setup

Pulse Height vs Distance Setup

• 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

• 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

Strips at Position 3Strips at Position 3

PH=206.4pe=5.897

PH=281.7pe=8.049

PH = 221.8pe=6.337

PH =305.3Pe=8.723

Conclusion: Four strips have different pulse heights because of polishing of fibers or scintillator

Strip 4 at four different positions

Strip 4 at four different positions

Mean =246.8Pe=7.051

Mean=269.9Pe=7.711

Mean=308.3Pe=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)

Trigger Counters at Position 3

Trigger Counters at Position 3

Conclusion: Trigger counters have lower PH than strips because light will be lost from muons that hit them at the edge

Mean =76.88Pe=2.197

Mean=106.4Pe=3.040

Mean=305.3

Pe=8.723

Attenuation LengthAttenuation Length

•Find using PH vs. distance data

•Find by fitting plot of PH vs distance to exponentialStrip no T0 small

spacer T0 no spacer

T0 grease

T2 grease

T2 grease (gain online)

average per strip

1 260.11 127.66 162.52 177.54 160.55 177.67

2 204.9 174.82 220.29 229.37 336.92 233.26

3 281.66 236.95 212.73 209.66 280.37 244.27

4 364.54 302.58 296.6 268.95 255.62 297.66

Conclusion and ThanksConclusion and Thanks• 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

• 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.

Bibliography/Picture Permissions

Bibliography/Picture Permissions

• Camilleri, Leslie. Slides. • Shaevitz, Mike. Reactor Neutrino Experiment and the

Hunt for the Little Mixing Angle. 30 Nov 2007.• Sutton, Christine. Spaceship Neutrino.

• Camilleri, Leslie. Slides. • Shaevitz, Mike. Reactor Neutrino Experiment and the

Hunt for the Little Mixing Angle. 30 Nov 2007.• Sutton, Christine. Spaceship Neutrino.

Efficiency TestEfficiency Test1. 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%