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Double Chooz: Outer Veto Sophie Berkman Nevis Labs, Columbia University Sophie Berkman Nevis Labs, Columbia University.

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Presentation on theme: "Double Chooz: Outer Veto Sophie Berkman Nevis Labs, Columbia University Sophie Berkman Nevis Labs, Columbia University."— Presentation transcript:

1 Double Chooz: Outer Veto Sophie Berkman Nevis Labs, Columbia University Sophie Berkman Nevis Labs, Columbia University

2 Outline 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

3 Neutrino 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

4 What 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 )=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

5 Neutrino Mixing with 3 flavors

6 Double Chooz Measure θ 13 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 θ 13 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 -

7 Muon Background 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 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

8 Double 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

9 Outer 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

10 PMT 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

11 Characterization 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

12 Before 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%

13 Gain 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

14 Scintillator 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

15 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

16 Efficiency 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

17 Efficiency 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 RequireEffic. 3-fold91% 4-fold94% 5-fold96% RequireEffic. 3-fold83% 4-fold83% 5-fold90% Large SpacerSmall Spacer Conclusion: more efficient with more coincidences, and with smaller spacer.

18 Cross 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

19 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

20 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

21 Strips at Position 3 PH=206. 4pe= PH=281.7 pe=8.049 PH = pe=6.337 PH =305.3 Pe=8.723 Conclusion: Four strips have different pulse heights because of polishing of fibers or scintillator

22 Strip 4 at four different positions 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)

23 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 =76.88 Pe=2.197 Mean=106.4 Pe=3.040 Mean=305.3 Pe=8.723

24 Attenuation Length Find using PH vs. distance data Find by fitting plot of PH vs distance to exponential Strip noT0 small spacer T0 no spacer T0 grease T2 grease T2 grease (gain online) aver age per strip

25 Conclusion 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.

26 Bibliography/Picture Permissions Camilleri, Leslie. Slides. Shaevitz, Mike. Reactor Neutrino Experiment and the Hunt for the Little Mixing Angle. 30 Nov Sutton, Christine. Spaceship Neutrino. Camilleri, Leslie. Slides. Shaevitz, Mike. Reactor Neutrino Experiment and the Hunt for the Little Mixing Angle. 30 Nov Sutton, Christine. Spaceship Neutrino.

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28 Efficiency Test 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%


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