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LENA Detector development

LENA Detector development. ANT2010, Santa Fe 2010/09/18 Marc Tippmann Technische Universität München. Most relevant topics at the moment. LENA (Low Energy Neutrino Astronomy ). Detector layout : Liquid scintillator ca. 50kt LAB Inner vessel ( nylon ) R adius (r) = 13m

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LENA Detector development

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  1. LENADetector development ANT2010, Santa Fe 2010/09/18 Marc Tippmann Technische Universität München

  2. Most relevant topics at the moment

  3. LENA (Low Energy Neutrino Astronomy) Detectorlayout: Liquid scintillator ca. 50kt LAB Innervessel (nylon) Radius (r) = 13m Buffer (inactive liquid scint.) Δr =2m Cylindricalsteel tank, 48k PMTs (8“) with Winston Cones (2x area) r = 15m, height = 100m, opticalcoverage: 30% Watercherenkovmuonveto 5000 PMTs, Δr> 2m toshield fast neutrons Cavern egg-shapedforincreasedstability Rock overburden: 4000 mwe Physicsobjectives: Low energy: • Neutrinos from galactic Supernova • Diffuse Supernova neutrinos • Solar neutrinos • Geoneutrinos • Reactor neutrinos • Indirect dark matter search Higher energy: • Proton decay • Long-baseline neutrino / beta beams • Atmosphericneutrinos

  4. Detector construction

  5. Detector construction LAGUNA: • European site + design study for a next generation neutrino and p-decay detector • 7 preselected sites • Proposed experiments: GLACIER, LENA, MEMPHYS Includes cavern design study

  6. Detector construction: Cavern construction • New: Rockplan tank + excavation study for Pyhäsalmi • Based on Technodyne study → substantial improvements • Worked out excavation process and extra structures to fulfill safety requirements: • 2 access tunnels, spherical work tunnel, 1 or 2 new shafts • Long term rock stability simulations → elliptical horizontal cross-section and kink in vertical cross-section • → Higher volume for Water Cherenkov detector

  7. Detector constructionTank design Conventional Steel Tank + well known, straightforward to build, robust - expensive, single passive layer defense, a lot of elements and connections Sandwich Steel Tank + cost effective, room for cooling, fast install, high QA/QC, laser welds - a lot of welding, little used solution, mechanically challenging Sandwich Concrete Tank + well known, straightforward to build, robust, improved physics - steel plates and rebar prevent continuous casting, slow to build Hollow Core Concrete Tank + room for cooling, mechanically strongest, improved physics, quick build - little used solution, active leak prevention may lead to sustained pumping

  8. Liquid Scintillator properties Extensively covered last year on ANT09 by Michael Wurm → only new results Liquid Scintillator properties are essentially understood + known Only particular measurements remain to be done Started to repeat measurements with higher precision

  9. Liquid scintillator propertiesAttenuation length vs. wavelength Michael Wurm 10m Attenuation length (m) Wavelength (nm) Martin Hofmann • Already measured with a 1m scintillator tube (10nm accuracy) + 10cm cell (1nm) → transparency considerably increases with wavelength → need longer tube • → New experiment with ≈10m tube length • Is being set up at new Munich underground lab (≈ 10mwe rock overburden) • All parts ordered, most have arrived • Should be able to start measurements within the next months 1m

  10. Liquid Scintillator propertiesDecay time constants • Paolo Lombardi has set up a new experiment in Milan • Measured time behavior of different scintillators (PC, LAB, DIN) with varying PPO concentration • → Cross-check with Munich experiment possible • Measurements on LAB in both experiments in good agreement in some variables, deviation in others → maybe due to different manufacturers / batches→will study this further Paolo Lombardi, LENA Meeting 2010-07-05 preliminary

  11. Liquid Scintillator propertiesEmission spectra Paolo Lombardi, LENA Meeting 2010-07-05 • Measurements done in Perugia by Fausto Ortica and Aldo Romani • → Cross-check with Munich experiment possible • Very good agreement of results for LAB with 1.5 resp. 2g/l PPO Teresa Marrodan, PhD thesis

  12. Photo sensors

  13. Photo sensors: Photo sensor requirementsPMT timing behavior Transit Time Spread (FWHM, spe) Normal Pulses Early Pulses Late Pulses Pre-Pulses Dark Noise

  14. Photo sensors: Photosensor requirements • Area InnerDetector: 10430 m² Targetedopticalcoverage: 30% →3130 m² effectivephotosensitivearea • PMTsprobablytheonlyphotosensortype • Meeting thephysicalrequirements • Having a lowenough cost /(area*photon detection efficiency) • Durable for at least 30 years AND • Utilizable untilstartof construction Importantproperties: Transit time spread, afterpulsing, gain, dynamicrange, area, quantum efficiency, darknoise, peak-to-valley-ratio, early + pre-pulsing, late pulsing, pressure resistance, long term stability, low radioactivity, price

  15. Photo sensors: Photosensor requirementsNecessaryparametersfor PMTs

  16. Photo sensors: PMT characterizationSelection of feasible PMT models for LENA • Manufacturers available for 100k+ PMTs: • Hamamatsu Photonics • Electron Tubes Enterprises Ltd. • Study most promising PMTs withdiametersfrom 3“-10“ • Measured until now: • Hamamatsu: R6091(3“), R6594(5“), R5912(8“) and R7081(10“) • ETEL: 9351(8“)

  17. Photo sensors: PMT characterization • Borexino PMT testing facility @LNGS: • Excellent time resolution: 410nm laserdiode light source, pulse FWHM <30ps, triggeroutputjitter <100ps; electronicsjitter ≈45-90ps →total time resolution <140ps • Can measureupto 32 PMTs simultaneously • Repaired + reactivated setup • Further improved setup: • Use second channel to measure fast AP up to ≈25-30 ns after primary pulse, triggered by pulse in first channel • Low noise preamp near PMT →increased p/V by a factor of 2

  18. Photo sensors: PMT characterizationResults: ComparisonR6594(+) vs. R7081(+) 5“ 10“

  19. Photo sensors: PMT characterization -Comparison PMTs

  20. Photo sensors: PMT characterization Improve + extend Munich PMT testing setup PMT testsetupat TUM, Garching (currently) • FlashADC (10bit, upto 8 Gigasample/s = 125ps time resolution, 4 channels) →excellent • Currently using LED (430nm peak-wavelength) with moderate relaxation time (≈5-10ns) drivenby 5ns FWHM voltage pulse →bad → Build in fast lightpulserdevelopedby George Korga: fast LED drivenbyAvalanche Diode -> total time jitter FWHM ≈1ns orlower • Medium term: build in ps laser diode→ time jitter ≈30ps → Confirm results from Italy → Can measure in addition pulseshape + fast afterpulses (Δt<30ns) + prepulses • Status: coincidence running; working with two students on improving readout + evaluation software

  21. Paolo Lombardi, LENA Meeting 2010-07-05 Photo sensors: PMT characterizationHQE measurements • (Another) experimental setup of Paolo Lombardi in Milan to characterize PMTs: • Picosecond laser (405nm) • 8bit 1GS/s FADC • Measured Hamamatsu super-bialkali PMTs (~34% peak-QE): R6594-SEL, R5912-SEL, R7081-SEL • → Direct comparison with standard photocathode PMTs measured @ Borexino PMT testing facility possible

  22. Photo sensorsWinston Cones • Attach Compound Parabolic Concentrators („Winston Cones“) to increase effective area of PMTs by a factor of 2-8(!) → increases number of detected photons / MeV deposited → increased resolution • Limits field of view by introducing an acceptance angle (conservation of etendue) → can be used to limit field of view to fiducial volume • …coming soon: study influence on detector performance with the Geant4 Monte Carlo simulation of LENA (software development finished + working) Borexino Winston Cone CTF Winston Cone

  23. Photo sensorsPressure encapsulations • Pressure at tank bottom might be too high for PMT glass envelopes → • a) Try if thicker glass envelope (4mm) fulfills pressure tests • b) Develop pressure encapsulations → • Can use standard PMTs • Integrate Winston Cones + µ metal shielding into design • Starting points for development e.g. Borexino encapsulation with pressure-withstanding window instead of thin PET window with pressure-resistant window in front • Development will commence soon

  24. Electronics

  25. Electronics: PMT arrays • Employ PMT arrays with central on-site front-end electronics on chip → Reduce number of channels (only 1 cable for data + voltage); however voltage not adjustable for individual PMTs after installation + can read out pulse shape only for sum of PMT channels • Currently under development in PMm² project • PICS collaborationbetween LENA + MEMPHYS • →can useexisting R&D of PMm² (3 years) for LENA! • PMm²: 16 PMs(12“) + frontendelectronics (PARISROC) J.E. Campagne, LENA - PMm² meeting 07/04/2009

  26. Electronics: PMT arraysPMm² frontendelectronics: PARISROC • Triggerless • Individual channels • Charge + time measurement • Variable gainofpreamplifier • Common HV for PMs • 1/3pe 100% efficiency • 1ns time resolution • 16 triggerchannelsor 1 OR-trigger-output • 2 gains per channel (not showedhere): 0-10pe & 0-300pe • Scaleability

  27. Electronics: PMT arrays • Advantages: • Data transfer digital →lessattenuation • Lower cost (less cables, voltage in cablessmaller, bundledfrontendelectronicsreducesdataprocessingcost/channel) • Disadvantages: • Same HV foreach PMT withinmodule→countermeasures: partial compensation via individual gainadjustment, combinesimilar PMTs for a module • Different physicalrequirementsfor PMT Arrays →adopt R&D of PMm² asfaraspossible + adaptsetupwhereneccessary

  28. Software

  29. SoftwareTracking in Liquid Scintillator Detectors • Light front generated by GeV particles resembles a Cherenkov cone → directionality → can use arrival time of first photons on PMTs and total photon count for tracking • → Can be used for p decay, neutrino beams and atmospheric neutrinos • Have developed two event reconstruction programs for tracking: • „Scinderella“ by Juha Peltoniemi • Tracking script for the Geant4 LENA optical detector model by Dominikus Hellgartner J. Learned, arXiv/0902.4009, J. Peltoniemi, arXiv/0909.4974

  30. Software: Tracking in Liquid Scintillator Detectors: „Scinderella“ • Single-Particle Tracks (leptons, CC QES): excellent reconstruction • Multi-Particle Vertices (deep inelastic neutrino scattering creates pions, 1-5GeV): new reconstruction algorithm fits a superposition of the light fronts generated by MC sample tracks to the overall PMT signal • → for ≤ 3 pions good track reconstruction at ≤ 5% E resolution possible • → LSD is good tracking detector at E > 1GeV: excellent flavour recognition, E resolution typically < 5%, very good for neutrino beams: sin²(2ϑ) > 10-2 – 10-3if not lower • If pulse-shape of PMT signals available even better • Detector simulation software based on Java developed by Juha Peltoniemi • Can do both event simulation and event reconstruction • Event simulation → record observation time of photons in PMTs • Track reconstruction by comparing light pattern produced by test track with that of track from simulation → minimalization of deviation Reco of 4GeV  deep-inelastic sample event J. Peltoniemi

  31. Software: Tracking in Liquid Scintillator DetectorsTracking script for Geant4 optical model • Developed by Dominikus Hellgartner based on work done by Michael Wurm on tracking in Borexino • Procedure: minimize log-likelihood value of photon pattern depending on all track parameters • → Look at even lower energies than 1GeV: • First preliminary results: • a) 100 500MeV single-track muons: very good track reconstruction with <≈1+/-2cm position uncertainty and 0.1+/-0.1ns time uncertainty for the starting point and 2.5° direction deviation • b) 100 750MeV single-track electrons: all uncertainties comparable to muon events, however one problem occurring: for some events, the direction is reconstructed with wrong sign → starting point at end of track → outliers; are working on this right now Dominikus Hellgartner

  32. Software: Tracking in Liquid Scintillator DetectorsProof of principle: Borexino • Borexino is actually a low E calorimetry detector; not optimized for tracking at all • LENA will be designed for tracking capability • Reconstructed tracks from CNGS beam in Borexino • No simulation: • real data! Michael Wurm

  33. Summary • Pyhäsalmi site study finished → elliptical cavern, steel or concrete tank • Liquid scintillator properties mostly known, setting up attenuation length precision measurement at the moment • Photo sensor: 5“-10“ PMTs (which type will be decided shortly) with Winston Cones and pressure encapsulations • Bundle PMTs to arrays to save channels • Geant4 detector simulation is running, have to measure last missing properties for optical model • Liquid Scintillator Detectors are actually quite good at tracking

  34. Backup slides

  35. Detector constructionExcavation

  36. Scattering Length Results • no hints for Mie-scat. • anisotropic scattering in good agreement with Rayleigh expectation • correct wavelength- dependence found • literature values for PC, cyclohexane correctly reproduced Results for l=430nm LS = 22±3 m after purification in Al2O3-column Michael Wurm

  37. Liquid Scintillator propertiesQuenching factors Gamma Quenchinglight output of low-energeticelectrons (E<200keV) by small-angle Compton scattering …in progress q Timo Lewke, Jürgen Winter Proton Quenching using neutron recoils(AmBe-source, n-generator) …coming soon scintillator sample

  38. Proton decay Large impact on proton decay (into K+n) detection efficiency: Signal of kaon (t=13ns) and of its decay products (mostly muons) must be separated by rise time analysis Background Source:Atmospheric Muon-Neutrinos Kaon Muon Efficiency ranges from 56% to 69% for typical rise times of 7 to 10 ns

  39. Proton decay

  40. Software: Tracking in Liquid Scintillator Detectors: „Scinderella“ • Single-Particle Tracks • excellent flavour recognition • Positional accuracy: a few cm • Angular accuracy: a few degrees • initial neutrino energy + momentum can be determined at 1%(?) accuracy from lepton track (CC QES) • Multi-Particle Vertices • - deep-inelastic scattering of neutrinos creates pions (1-5 GeV) • - new reconstruction algorithm fits a superposition of the light fronts generated by MC sample tracks to the overall PMT signal • - resolution of vertices featuring ≤ 3 ‘s is possible at % accuracy • - recoil protons/neutrons quenched, not invisible, allowing a calorimetric measurement of the event energy deposited. • - time-resolved response of individual PMTs needed for optimum result

  41. Software: Tracking in Liquid Scintillator DetectorsTracking script for Geant4 optical model • Developed by Dominikus Hellgartner based on work done by Michael Wurm on tracking in Borexino • Procedure: • For muon: separate track signal + decay signal: look for second peak in detected photons vs. time -> time cut • Determine start values for fits: • Energy →from number of photons of track; barycenter fit → position on track; first PMT hit → crude direction: vertical or horizontal • Vertical: Fit point-like source from first hit times for PMT-ring containing minimum hit time PMT → starting point → with barycenter fit direction → with energy track length → track • Horizontal: TOF-correction to barycenter → direction from most negative first hit times; table of position of charge barycenter vs track E (input from other simulations) → with energy track • Main fit: minimize log-likelihood value depending on all track parameters • → Look at even lower energies than 1GeV: • First preliminary results: • a) 100 500MeV single-track muons: very good track reconstruction with <≈1+/-2cm position uncertainty and 0.1+/-0.1ns time uncertainty for the starting point and 2.5° direction deviation • b) 100 750MeV single-track electrons: all uncertainties comparable to muon events, however one problem occurring: for some events, the direction is reconstructed with wrong sign → starting point at end of track → outliers; are working on this right now Dominikus Hellgartner

  42. Requirements on PMTs in LENA

  43. Other types of photosensors • Avalanche Photodiode (APD): solid state equivalent to PMTs; price/area too high; Dark Noise very high, if not cooled; low amplification • SiPM: array of small APDs; excellent tts (FWHM < 0.5ns), excellent energy resolution, high QE(?), immense cost/area; huge dark count (some 100kHz up to several MHz) • Cupid/ Hybrid Photo-Detector: Photocathode just like in PMTs, e- however focussed on APD in center instead of dynode chain; problems with huge DN? Still working on fixing that • Microchannel Plate (MCP): Photocathode, e- accelerated along very thin etched channels perpendicular to cathode, coated with metal on inside, thickness of coating varies along axis -> increasing voltage along flight path, e- crashes on walls + knocks out more e- -> amplification

  44. Other types of photosensors • Quasar: Photocathode, solid scintillator block in center with a small PMT looking at it; apply very high voltages (typ.25-30kV) -> e- creates scintillation light in crystal -> light signal on PMT advantages: small jitter even for large photocathode area, excellent energy resolution, …, price=? Already used in BAIKAL, however needs further development • Hybrid-Gas Photomultiplier: photocathode in vacuum, e- accelerated through mebrane into Thick Gas Electron Multiplier (THGEM) -> accelerated through holes in metal-covered plate, different voltage on upper+ lower side -> very high field inside holes -> e- scatters off gas atoms -> produces further e- -> amplification; use several THGEMs in series for higher amplification still under development, needs several more years to be ready for production

  45. PhotomultiplierTubes (PMTs)Principleofoperation • Extremely sensitive lightdetectorscapableofdetectingsinglephotons • Photon →photoelectron(pe) →amplifiedby ≈10^7 in dynodechain • Gain = amplificationfactor

  46. PMTsOcurringeffects + basicparameters • Afterpulse: delayed additional pulse causedbytheprimary pulse • Ion Afterpulses: typically 0.3-15µs later • Bremsstrahlung Afterpulses:typ. 30-60ns later • Dark Noise: electronsemittedfromcathodewithoutincidentphoton; mostlythermionicemission Primary Pulses (Next laser pulse) Ion Afterpulses Dark Noise

  47. PMTsOcurring effects + basic parameters • Single photoelectron (spe) spectrum: 3 components: normal pulses, underamplifiedpulses + noise • Peak-to-valley-ratio (p/V): ratiobetweenvalueofmaximumandvalley noise under- amplified pulses spe (normal pulses) Peak 2 pe Valley

  48. PMTsVoltagebehavior • Two different modesofapplyingvoltage: a) Photocathode atground potential → positive voltage on anode →needcapacitorto separate DC voltagefromelectronics b) Negative voltageappliedtophotocathode→anodeatground potential →signalcanbesentdirectlytoelectronics • Advantage: faster • Disadvantage: DN higher • Dynamic Range: numberofphotonsincidentatthe same time on thecathode, whichcanbedetected • Raisevoltage→gainrises, transit time decreases, jitterdecreases, however: AP rise, DN risesifvoltageisveryhigh (fieldemission), dynamicrangedecreases → find optimumworkingpoint

  49. PMTs in LENA • Transit time spreadmust below→tracking • Bremsstrahlung Afterpulses (fast AP) canblur out protondecaycoincidence • Ion Afterpulses (slow AP) canpreventpositionreconstructionofneutrons→decreasesdetection rate ofcosmogenics (C11): C11 ismainbackgroundforCNO-ν-flux Michael Wurm, TUM, LENA - PMm² meeting 07/04/2009

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