Presentation on theme: "Double Chooz: Outer Veto"— Presentation transcript:
1Double Chooz: Outer Veto Sophie BerkmanNevis Labs, Columbia University
2Outline Neutrino Oscillations Double Chooz Outer Veto Some Studies PMT CharacterizationScintillator TestsEfficiencyCross-TalkPulse Height vs. Distance
3Neutrino Oscillations In the standard model neutrinos are massless leptons - cannot mix.BUT - neutrinos oscillate so by the current interpretation:Neutrinos have massLepton family number is not conserved
4What it means that neutrinos oscillate In a 2-neutrino simplification:Mass states = 1, 2Flavor (weak) states = , eProbability of oscillation:P( -> e)=sin2(2θ)sin2(1.27m2L/E)Θ=mixing anglem2=difference in squares of neutrino massesL=distance of oscillation E=energy of neutrinos
5Neutrino Mixing with 3 flavors How do you measure delta? By measuring neutrinos and antineutrinos
6Double Chooz Measure θ13 Reactor experiment Look at e from reactors Disappearance experiment - reactors only produce eTwo Detectors - identical, cancel uncertainties in neutrino flux and cross-sectionNear - unoscillated neutrino fluxFar - after oscillation-
7Muon Background Double Chooz looks for inverse beta decay e+ p n + e+Double coincidence of neutron capture and positron signal (within ~100s)Cosmic muon backgroundMuon interacts to form neutronsNeutrons knock protons out of scintillatorProtons emit light as they move through scintillator and neutron captured by gadoliniumLooks like inverse-beta decay signal
8Double Chooz Detectors 7m7mTarget: liquid scintillator, doped with Gadolinium - n captureGamma catcher: measure gammas from n captureBuffer: holds PMTs, shields detector from PMT radiationInner veto: reject fast neutron/muon backgroundOuter Veto: atmospheric muons
9Outer Veto Reject atmospheric muon background Stacked scintillator stripsWavelength shifting fibersLight transmitted to PMT and DAQNevis: developing electronics/softwareAll tests done in light tight boxes
10PMT Characterization Why Characterize? Want all pixels to respond in the same way to lightPulse height of 350 ADC counts350ADC counts =10pe * 35 ADC/pe
11Characterization Process Take Baseline with laser offTurn laser on and allow it to stabilize for 30 minAdjust HV to get an average pulse height for all pixels to be 350 ADC countsAdjust gain across preamplifiers to get a mean pulse height of 350 ADC counts across each individual pixelTurn off the laser and allow it to stabilize for 30 minutesTake noise data for different DAC thresholdsLaser - stabalize for thermal reasons
12Before and After Characterization Spread=18%Spread=2.9%Conclusion: characterization process narrows the spread of the pulse height distributions. Use to determine if bad PMTs.
13Gain Constant Distribution Gain Constant = measure of gain adjustmentGain constant of 16 means adjust by a factor of 1Conclusion: Centered around 16 (ie. Adjustment by factor of 1)
14Scintillator Setup Four stacked strips 1.5m long Four sets of trigger countersWavelength Shifting fibersFiber Holder
15Some Standard Modifications Spacers to protect the face of the PMTLarge spacer = space of 1.27mmSmall spacer = space of 0.48mmNo spacer = space of 0.000mmOptical Grease
16Efficiency Test Trigger on trigger counters and one strip #Entries=326 = 91%#Entries=359Trigger on trigger countersEvents over 1pe for triggered strip/trigger counterRepeat with more coincidences
17Efficiency Results Repeated for more coincidences Large spacer: ~4.3pe Small spacer: ~5.2peLarge SpacerSmall SpacerRequireEffic.3-fold91%4-fold94%5-fold96%RequireEffic.3-fold83%4-fold5-fold90%Conclusion: more efficient with more coincidences, and with smaller spacer.
18Cross TalkOptical Cross talk: the amount surrounding pixels receive light from the illuminated pixel# pe smaller than expectedAdd pulse heights in surrounding pixels to the signal pixelCan find maximum #pe without crosstalkNote: different numbers of surrounding pixels for different pixels
19PH 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
20Pulse Height vs Distance Setup Noticed dependence on distance from previous studiesAll strips at all positionsUse optical grease without spacerRequire 5-fold coincidence1 photoelectron cut on non signal strip/trigger
21Strips at Position 3 PH=281.7pe=8.049 PH=206.4pe=5.897 PH =305.3 All four strips at position 3.Conclusion: Four strips have different pulse heights because of polishing of fibers or scintillator
22Strip 4 at four different positions Mean =246.8Pe=7.051Mean=269.9Pe=7.711Mean=355.1Pe=10.14Mean=308.3Pe=8.809Conclusion: 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)
23Trigger Counters at Position 3 Mean=106.4Pe=3.040Mean =76.88Pe=2.197Conclusion: Trigger counters have lower PH than strips because light will be lost from muons that hit them at the edgeMean=305.3Pe=8.723
24Attenuation Length Find using PH vs. distance data Find by fitting plot of PH vs distance to exponentialStrip noT0 small spacerT0 no spacerT0 greaseT2 greaseT2 grease (gain online)average per strip1260.11127.66162.52177.54160.55177.672204.9174.82220.29229.37336.92233.263281.66236.95212.73209.66280.37244.274364.54302.58296.6268.95255.62297.66
25Conclusion and ThanksProcess for characterizing PMTs works well and will be possible to implement for all outer veto PMTsStill generally not as many photoelectrons as expected, but we can use optical grease/other trigger modes to increase the numberThanks to everyone I worked with this summer for teaching me so much about physics and for this extraordinary opportunity to work on Double Chooz.
26Bibliography/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.
28Efficiency Test Conclusion: More efficient with more requirements. Find the mean of the pulse height distribution in strip 1 when both trigger counters have at least 1peFind the mean pulse height distribution in strip 1 when both trigger counters and strip 2 have at least 1pe.Efficiency = Second Mean/First meanRequire more strips to have 1peLook at efficiencies with different requirements for eventsRepeat with large and small spacerConclusion:More efficient with more requirements.-Large Spacer went from 83-90%-Small Spacer went from 91-96%