LENALENALow Energy Neutrino AstronomyLow Energy Neutrino Astronomy

ASPERA Technology ForumASPERA Technology ForumMunich, 2010/10/22Munich, 2010/10/22

Marc TippmannMarc TippmannTechnische Universität MünchenTechnische Universität München

LAGUNAMEMPHYS: Water Cherenkov Detector, 0.5Mton

GLACIER: Liquid Argon TPC, 100kton

LENA: Liquid Scintillator Detector, 50kton

• LAGUNA = Large Apparatus for Grand Unification and Neutrino Astrophysics

• LAGUNA design study: feasibility and physics potential of 3 next-generation neutrino + p-decay detectors on 7 sites within Europe

• Proposed experiments: GLACIER, LENA, MEMPHYS

• Design study has been carried through

• Will request subsequent design study:focussing on detector design and neutrino oscillometry with a CERN neutrino beam

LAGUNA

LENALENALow Energy Neutrino AstronomyLow Energy Neutrino Astronomy

Low Energy PhysicsLow Energy Physics• Neutrinos from galactic Neutrinos from galactic

SupernovaeSupernovae• Diffuse Supernova neutrinosDiffuse Supernova neutrinos• Solar neutrinosSolar neutrinos• GeoneutrinosGeoneutrinos• Reactor neutrinosReactor neutrinos• Indirect dark matter searchIndirect dark matter search

Physics in the GeV energy Physics in the GeV energy rangerange•Proton decayProton decay•Long baseline neutrino beamsLong baseline neutrino beams•Atmospheric neutrinosAtmospheric neutrinos

LENA (Low Energy Neutrino Astronomy)LENA (Low Energy Neutrino Astronomy)Detector layout:Detector layout:

Liquid scintillatorLiquid scintillator46kt LAB/PPO+ bisMSB46kt LAB/PPO+ bisMSB

Inner vessel (nylon)Inner vessel (nylon)Radius (r) = 13mRadius (r) = 13m

Buffer Buffer 15kt LAB, Δr =2m15kt LAB, Δr =2mCylindrical steel tank, Cylindrical steel tank, 55,000 PMTs (8“) with 55,000 PMTs (8“) with Winston Cones (2x area)Winston Cones (2x area)

r = 15m, height = 100m, r = 15m, height = 100m, optical coverage: 30%optical coverage: 30%

Water cherenkov muon vetoWater cherenkov muon veto5,000 PMTs, Δr > 2m to shield 5,000 PMTs, Δr > 2m to shield fast fast

neutronsneutronsCavern egg-shaped for increased stabilityCavern egg-shaped for increased stabilityRock overburden: Rock overburden: 4000 mwe4000 mwe

Requirements on photo sensors• Sensor performance• Environmental properties• Availability until start of

construction• Cost-performance-ratio

Requirements on photo sensors• Sensor performance• Environmental properties• Availability until start of

construction• Cost-performance-ratio

Desired energy resolution Desired energy resolution → → 30% optical coverage 30% optical coverage →→ 3000m² effective photo-3000m² effective photo-sensitive areasensitive areaLight yield ≥ 200 pe/MeVLight yield ≥ 200 pe/MeV

PMTs are probably the only PMTs are probably the only photo sensor type which can photo sensor type which can fulfil all requirement classes fulfil all requirement classes

Sensor performanceSensor performancePreliminary requirements for PMTsPreliminary requirements for PMTs

• Transit time spread (TTS)Transit time spread (TTS): lower : lower →→ improves time + position resolution and improves time + position resolution and tracking tracking →→ TTS < 3.0ns (single pe, FWHM)TTS < 3.0ns (single pe, FWHM)

• Bremsstrahlung Afterpulses (fast AP)Bremsstrahlung Afterpulses (fast AP): can : can blur out proton decay coincidence blur out proton decay coincidence ((ττkaonkaon=13ns) =13ns) → → probability fast AP < 5% (?)probability fast AP < 5% (?)

• Ionic Afterpulses (slow AP) Ionic Afterpulses (slow AP) can corrupt can corrupt position reconstruction of neutrons position reconstruction of neutrons knocked out of C12 by muons knocked out of C12 by muons →→ decreases decreases exclusion probability of C11, whichexclusion probability of C11, which is main is main background for background for CNO + pep CNO + pep νν-flux -flux →→ probability Ionic AP < 5%, probability Ionic AP < 5%, maybe even < 1% (?)maybe even < 1% (?)

• Dark Noise RateDark Noise Rate: DN worsens energy : DN worsens energy resolution and can cause fake events by resolution and can cause fake events by random coincidencesrandom coincidences → → DN < 15Hz/cm² DN < 15Hz/cm² Michael Wurm, TUM, LENA - PMm² meeting 07/04/2009

Type: Bialkali (HQE) photocathode, borosilicate (low background) glass, hemispherical window, diameter 5“-10“

Type: Bialkali (HQE) photocathode, borosilicate (low background) glass, hemispherical window, diameter 5“-10“

• Single photo electron peak-to-valley ratio (p/V)Single photo electron peak-to-valley ratio (p/V): : higherhigher →→ single photon pulses have less overlap single photon pulses have less overlap with noise with noise →→ more pulses usable more pulses usable →→ p/V > 2p/V > 2

• GainGain: same as for p/V : same as for p/V →→ gain > 3 10∙gain > 3 10∙ 66 • Dynamic rangeDynamic range: Detector must be able to detect : Detector must be able to detect

events with only one photon on most hit PMTs as events with only one photon on most hit PMTs as well as HE events (muon, proton decay, neutrino well as HE events (muon, proton decay, neutrino beam) beam) → →

1pe – >0.17pe/(cm² effective photosensitive area) (?)1pe – >0.17pe/(cm² effective photosensitive area) (?)= 1pe – >100pe for 8“ PMT with 2x Winston Cone= 1pe – >100pe for 8“ PMT with 2x Winston Cone

• Quantum efficiency + collection efficiencyQuantum efficiency + collection efficiency: : higher higher →→ energy resolution and to a lesser energy resolution and to a lesser extent position + time resolution improve and extent position + time resolution improve and energy threshold decreases; energy threshold decreases; Losses through back-scattering: Losses through back-scattering: Should be Should be minimalminimal→→ (?)(?)

• Early Pulses, Prepulses + Late PulsesEarly Pulses, Prepulses + Late Pulses: : worsen time + position resolution, tracking worsen time + position resolution, tracking (assumes “first pulses = first photons“) (assumes “first pulses = first photons“) →→ EP <1% , LP < 4%EP <1% , LP < 4%

Sensor performanceSensor performancePreliminary requirements for PMTsPreliminary requirements for PMTs

• Radioactive contaminationRadioactive contamination– 238238U U < 3 10∙< 3 10∙ -8-8 g/g, g/g,– 232232Th Th < 1 10∙< 1 10∙ -8-8 g/g, g/g,– natnatK K < 2 10∙< 2 10∙ -5-5 g/g g/g

• Pressure resistancePressure resistance: : > 13-15bar> 13-15barat the moment no PMTs meet the pressure requirements at the moment no PMTs meet the pressure requirements →→ increase glass thickness or use pressure encapsulations increase glass thickness or use pressure encapsulations

• Long-term reliability for 30+ yearsLong-term reliability for 30+ years

• Area per sensorArea per sensor: : Smaller Smaller →→ higher granularity, dynamic range of sensor need higher granularity, dynamic range of sensor need not be as high, transit time spread in general smallernot be as high, transit time spread in general smaller

Bigger Bigger →→ less sensors + channels less sensors + channels →→ cost-performance-ratio cost-performance-ratio better (if not too big)better (if not too big)

→→ generally sensor area as small as affordable generally sensor area as small as affordable

need more test PMTS from several series to assess currently achievable performance + simulations to establish final limits

Sensor performanceSensor performancePreliminary requirements for PMTsPreliminary requirements for PMTs

PMT diameter

Number of PMTs using 2x Winston Cones

5“ 165,000

8“ 55,000

10“ 41,000

Environmental propertiesEnvironmental properties

Borexino Outer Detector Borexino Outer Detector PMT encapsulationPMT encapsulation

Cost-performance-ratio (CPR)Cost-performance-ratio (CPR)• Crucial variable for energy, position and time Crucial variable for energy, position and time

resolution:resolution:

• Total costs Total costs QQNNPMTsPMTsQQlight yield light yield → → lower light yield; lower light yield; however: lower light yield however: lower light yield → → worse physics worse physics performanceperformance

• Possibilities of improving the CPR Possibilities of improving the CPR →→ lower costslower costs– Light concentrators : Light concentrators : Winston Cones Winston Cones →→ enlarge PMT enlarge PMT

area by max. a factor 2 area by max. a factor 2 → → less PMts; WC bigger than less PMts; WC bigger than that that → → field of view smaller than fiducial volume field of view smaller than fiducial volume → → limits physics limits physics

– High QE photocathodes High QE photocathodes → → less PMtsless PMts– High CE electron optics High CE electron optics → → less PMtsless PMts– PMT arraysPMT arrays: front-end readout electronics + HV : front-end readout electronics + HV

distribution on FPGA in detector for matrices of 16 distribution on FPGA in detector for matrices of 16 PMTs PMTs →→ greatly reduces number of cables + channels greatly reduces number of cables + channels → l→ lowers incidental costsowers incidental costscollaboration with MEMPHYS within PICS-frameworkcollaboration with MEMPHYS within PICS-framework

– Automatize production Automatize production (glass encapsulation, dynode (glass encapsulation, dynode chain)chain)

• Total PMT costsTotal PMT costs: : Question for manufacturers!Question for manufacturers! How much would it cost for 5“/ 8“/ 10“ PMTs with all How much would it cost for 5“/ 8“/ 10“ PMTs with all these cost reduction measurements?these cost reduction measurements?

PMT R&DPMT R&D• Close collaboration with manufacturers needed Close collaboration with manufacturers needed

during design phase (ongoing, until end of 2013) to during design phase (ongoing, until end of 2013) to fulfil requirements fulfil requirements →→ if necessary R&D if necessary R&D

• Desired photo sensor R&D at the moment:Desired photo sensor R&D at the moment:– Lower fast + ionic afterpulsingLower fast + ionic afterpulsing– High QE photocathodesHigh QE photocathodes– High CE electron opticsHigh CE electron optics– Automatize productionAutomatize production (glass encapsulation, dynode (glass encapsulation, dynode

chain) -> lower production costschain) -> lower production costs– Higher pressure resistanceHigher pressure resistance: thicker glass or spherical : thicker glass or spherical

shape; or develop pressure encapsulationsshape; or develop pressure encapsulations

→ → new PMT type for LENA would be bestnew PMT type for LENA would be best• Very similar PMT requirementVery similar PMT requirements for other planned

neutrino experiments (KM3NET, LBNE, MEMPHYS,HyperKamiokande, GLACIER) →→ common benefit from these R&D projects + larger common benefit from these R&D projects + larger production facilitiesproduction facilities

• Direct benefits for products on the market from Direct benefits for products on the market from higher QE, higher CE, automatized production, higher QE, higher CE, automatized production, larger production facilities, …larger production facilities, …

→ Extensive collaboration(s) of experiments + manufacturers possible! Goal: develop next-generation PMTs → share the costs, EU funding?

Timeline + RisksTimeline + Risks• TimelineTimeline: :

– decision on photo sensor type until end of 2013decision on photo sensor type until end of 2013– production time begin 2014 – mid 2019production time begin 2014 – mid 2019– photo sensor installation mid 2019 – begin 2020photo sensor installation mid 2019 – begin 2020

• RisksRisks: no potential show-stoppers, proven : no potential show-stoppers, proven technologytechnology

• Challenges: Challenges: – Scintillator: optical transparency + radiopurityScintillator: optical transparency + radiopurity– PMTs: afterpulse reduction, pressure resistancePMTs: afterpulse reduction, pressure resistance

→ → all in all making good progressall in all making good progress