Liquid Scintillator Technology Tobias Lachenmaier Universität Tübingen

Transcription

1 Liquid Scintillator Technology Tobias Lachenmaier Universität Tübingen 11th International Workshop on Next Generation Nucleon Decay and Neutrino Detectors December 13-16, 2010, Toyama, Japan

2 Outline The LENA project Detector layout Physics Potential Low energy physics topics GeV energy range physics Particle Tracking in Liquid Scintillator Detectors Technical design

3 LENA (Low Energy Neutrino Astronomy) Liquid scintillator 50 kt LAB/PPO+ bismsb Inner vessel (nylon) Radius r = 13m Buffer 15kt LAB, Δr =2m Cylindrical steel tank, e.g PMTs (8 ) with Winston Cones (2x area) r = 15m, height = 100m, optical coverage: 30% Water cherenkov muon veto 5,000 PMTs, Δr > 2m to shield fast neutrons Cavern egg-shaped for increased stability Rock overburden: 4000 mwe Pyhäsalmi design Desired energy resolution 30% optical coverage 3000m² effective photosensitive area Light yield 200 pe/mev The tracking option adds to the requirements of the PMT array and electronics: more, but smaller, faster PMTs full waveform digitizing

4 Low Energy Physics Neutrinos from galactic Supernovae Diffuse Supernova neutrinos Solar neutrinos Geoneutrinos Reactor neutrinos Indirect dark matter search Physics in the GeV energy range Proton decay search Long baseline neutrino beams Atmospheric neutrinos

5 A galactic SN in LENA A galactic SN in LENA ca events for a galactic SN high statistics energy dispersive time dispersive flavour resolving Antielectron n spectrum with high precision Electron n flux with ~ 10 % precision Total flux via neutral current reactions Separation of SN models independent from (collective) oscillations in NC reactions

6 A galactic SN in LENA For standard SN (10kpc, 8M ): ca. 13k events in 50kt target Channel Rate Threshold (MeV) Spectrum _ n e p n e n 12 e C 12 N e ( ) _ n 12 e C 12 B e ( ) n 12 C 12 C* n n p p n n e - e - n Michael Wurm, TUM Physics with LENA

7 Scientific Gain of SN Observation Scientific gain of SN detection Astrophysics Observe neutronisation burst Cooling of the neutron star flavor-dependent spectra and luminosity, time-dev. Propagation of the shock wave by envelope matter effects SNEWS Michael Wurm, TUM Physics with LENA

8 Scientific Gain of SN Observation Scientific gain of SN detection Astrophysics Observe neutronisation burst Cooling of the neutron star flavor-dependent spectra and luminosity, time-dev. Propagation of the shock wave by envelope matter effects SNEWS Neutrino physics Survival probability of n e in neutronisation burst P ee 0 normal mass hierarchy Resonant flavor conversions in the SN envelope: hierarchy, q 13 Earth matter effect: n mass hierarchy, q 13 Observation of collective neutrino oscillations more exotic effects... Michael Wurm, TUM Physics with LENA

9 Diffuse Supernova Neutrino Background Regular galactic Supernova rate: 1-3 per century intergrated neutrino flux generated by SN on cosmic scales redshifted by cosmic expansion flux: ~100/cm 2 s of all flavours rate too low for detection in current neutrino experiments _ In LENA: 4-30 n e events per year (in 50kt target mass)

10 Diffuse Supernova Neutrino Background Detection via Inverse Beta Decay _ n e +p n+e + allows discrimination of most single-event background limiting the detection in SK Remaining Background Sources _ reactor and atmospheric n e s cosmogenic bn-emitters: 9 Li neutrons from atm. n s (NC on 12 C) fast neutrons Expected rate: 2-15 ev/year in fid. vol. (in energy window from 10-25MeV) Scientific Gain first detection of DSN information on SNn spectrum

11 Solar Neutrinos in LENA (18kt) 7 Be-n 210 Bi 85 Kr [Borexino, arxiv: ] 11 C CNO/pep-n Detection Channel elastic ne scattering, E > 0.2MeV Background Requirements U/Th concentration of g/g (as achieved in Borexino) shielding of >3500 mwe for CNO/pep-n measurement Scientific Motivation determination of solar parameters (e.g. metallicity, contribution of CNO) search for temporal modulations in 7 Be-n (on a per mille level) probe the MSW effect in the vacuum transition region new osc. physics _ search for n e n e conversion

12 Geo neutrinos Detect anti-neutrinos of the U, Th decay chains (inverse b-decay energy threshold is 1.8 MeV). Expected event rate at Pyhäsalmi : 2000 events/year in 50 kt Background from reactors: 700 events/year in 50 kt in the relevant energy window measure flux from crust and mantle determine U/Th ratio disentangle continental/oceanic crust with more than one detector location only detector within LAGUNA able to detect geo-neutrinos

13 Influence of detector location K. Loo Michael Wurm, TUM Physics with LENA

14 Search for proton decay observation would be de-facto discovery of Grand Unification current limits dominated by Super-Kamiokande. Want to improve at least factor of 10.

15 Sensitivity to proton decay p K + ν Simulated energy spectrum of proton decay events into Kaon channel (light yield 180 p.e./mev) Two peaks: Kaon + Muon ~ 257 MeV Kaon + Pions ~ 459 MeV Energy-cut efficiency E =99.5%, bound protons of 12 C included. Variety of other channels can be tested.

16 Particle Tracking in LENA Potential at higher energies depends on tracking and PID capabilities (all ionizing particles are visible) HE particles create along their track a light front very similar to a Cherenkov cone. Single track reconstruction based on: Arrival times of 1 st photons at PMTs Number of photons per PMT Sensitive to particle types due to the ratio of track length to visible energy. J. Learned Angular resolution of a few degrees, in principal very accurate energy resolution.

17 Tracks of Cosmic Muons in Borexino incl. correction for muon time-of-flight origin entry point exit point exit point Cherenkov-like light-front of the muon is visible in the Inner Detector!

18 Proof of principle: Borexino Reconstructed tracks from CNGS beam in Borexino No simulation: real data! Borexino is actually a low E calorimetry detector; not optimized for tracking at all LENA will be designed for tracking capability Michael Wurm

19 Borexino Angular Resolution M. Wurm

20 Tracking in liquid scintillator detectors J. Learned, arxiv/ , J. Peltoniemi, arxiv/ 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 We have developed an optical model of the detector, and two event reconstruction programs for tracking: Scinderella by J. Peltoniemi Tracking algorithm for the Geant4 LENA optical detector model by D. Hellgartner

21 Photoelectrons in the distributions optical model

22 Photoelectrons in the optical model

23 Tracking tests with Geant4 optical model D. Hellgartner Procedure: maximize log-likelihood value of photon pattern depending on all track parameters First preliminary results: MeV 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 on direction MeV single-track electrons: all uncertainties comparable to muon events but for some events, the direction is reconstructed with wrong sign (starting point at end of track). We are working on this right now.

24 Lepton flavour identification Muon-decay electron: muon has to decay sufficiently late energy threshold to discriminate spallation neutrons n e rejection efficiency >99.63% (95%C.L.) n m acceptance: 85% Pulse-shape discrimination: rise time and peak width additional information, more powerful for n e selection electrons (1.2 GeV) muons (1.2 GeV)

25 Performance for energy reco (muons) The main fit routine maximizes probability of charge and arrival time PDFs: First estimate is used as input. Energy fit: based on calculation of expected photon number per PMT, includes: - particle de/dx - particle quenching - light absorption and scattering - PMT photoefficiency - relative coordinates resulting energy resolution: DE/E = 9%/sqrt(E/MeV) for 300 MeV muon DE/E 0.5%

26 Tracking Performance (muons) The main fit routine maximizes probability of charge and arrival time PDFs: First estimate is used as input. Track fit: relies on first-photon arrival times, log-likelihood maximization determination of PDF includes: - time spectrum of scintillation - PMT time jitter - finite size of PMTs - delays by light scattering for 300 MeV muon: Df = 3.1, Dx origin = 2cm

27 Resolution of high energy events CC events from HE n s usually involve: Quasi-elastic scattering Single-pion production Deep inelastic scattering Resulting light front/pmt signals are superposition of single-particle tracks. E < 1 GeV E = 1-2 GeV E > 5 GeV Multi-Particle Approach: (Juha Peltoniemi, arxiv: ) Fit MC events with combinations of test particle tracks. Single-event tracking as input. Use full pulse-shape information of the individual PMTs to discern the particles. Decay particles and capture processes (n s) provide additional information. CC neutrino reaction cross-sections on Carbon, MiniBooNE, hep-ex/

28 Tracking performance Single Tracks: 2GeV n m quasielastic scattering Flavor recognition almost absolute Position resolution: few cms Angular resolution: few degrees Energy resolution: ca. 1% for 2-5 GeV range, depends on particle, read-out information Multiparticle Events: 3 tracks are found if separated more tracks very demanding muon tracks always discernible overall energy resolution: few % track reconstruction less accurate Michael Wurm, TUM 4GeV n m deep-inelastic scattering Physics with LENA

29 LENA as far detector Baseline CERN to Pyhäsalmi: 2288 km (>10 3 km for mass hierarchy) 1 st oscillation maximum 4 GeV on-axis detector Beam properties wide band: energy 1-6 GeV beam power: 3.3 x pot/yr 5 yrs n + 5 yrs n Preliminary GLoBES result _ 3s sensitivity on q 13, d CP, mass hierarchy for sin 2 (2q 13 )>5x10-3 Michael Wurm, TUM Physics with LENA

30 LENA as far detector Results for Wide Band Beam Detector Size: 50 kt sufficient, 100 kt would be better Energy resolution of about 3% fully sufficient, <5% does not improve results n m p - P p + Vertical orientation is small disadvantage (<10% reduction in target mass) Baseline of >1200 km required for mass hierarchy m - Improved background rejection not important, beam contamination is the bottle-neck

31 Pre-feasibility study within LAGUNA Pre-feasibility study (within LAGUNA) ROCKPLAN, Finland, together with TU München: pre-feasibility study for a LENA detector at Pyhäsalmi depth of m possible geological study completed vertical detector position infrastructure (ventilation, electricity, etc.) considered construction time of cavern ~ 4 yrs first cost and time estimate for the whole project

32 Cavern/tank construction New: ROCKPLAN tank + excavation study for Pyhäsalmi Based on existing 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 crosssection Higher volume for Water Cherenkov detector M. Tippmann

33 Detector construction: tank 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, 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 M. Tippmann

34 Photo sensors/winston cones Borexino Winston Cone CTF Winston Cone Attach Parabolic Concentrators ( Winston Cones ) to increase effective area of PMTs by a factor of ca. 2 increases number of detected photons / MeV deposited increased resolution Limits field of view by introducing an acceptance angle can be used to limit field of view to fiducial volume coming soon: study the influence on detector performance with the optical Geant4 Monte Carlo simulation of LENA M. Tippmann

35 PMT encapsulation Pressure at tank bottom might be too high for PMT glass envelopes Try if thicker glass envelope (4mm) fulfills pressure tests Develop pressure encapsulation Can use standard PMTs Integrate Winston Cones + µ metal shielding into design Starting points for development e.g. Borexino encapsulation with pressureresistant window instead of thin PET foil window M. Tippmann

36 Conclusions a large-volume liquid-scintillator detector like LENA is a multipurpose neutrino observatory very rare event search as well as high-statistics measurements of (astrophysical) sources track reconstruction at GeV energies opens up the possibility for neutrino beam physics and atmospheric neutrino detection work on liquid scintillator mostly completed, optimization of PM configuration on-going

37 LENA White Paper

38 Backup slides

39 LENA as Long Baseline Detector Baseline CERN to Pyhäsalmi: 2288 km (>10 3 km for mass hierarchy) 1 st oscillation maximum 4.2 GeV on-axis detector Beam properties wide band (1-6 GeV): E max =1.5 GeV power: 3.3 x pot/yr, 1.5 MW _ 5 yrs n + 5 yrs n Preliminary GLoBES result 3s sensitivity on q 13, d CP, mass hierarchy for sin 2 (2q 13 )>5x10-3

40 LENA as Long Baseline Detector Baseline CERN to Pyhäsalmi: 2288 km (>10 3 km for mass hierarchy) 1 st oscillation maximum 4.2 GeV on-axis detector Beam properties wide band (1-6 GeV): E max =1.5 GeV power: 3.3 x pot/yr, 1.5 MW _ 5 yrs n + 5 yrs n Preliminary GLoBES result 3s sensitivity on q 13, d CP, mass hierarchy for sin 2 (2q 13 )>5x10-3

41 Sensitivity to Mixing Angle θ 13 1s 2s 3s discovery potential

42 Sensitivity to CP-Violating Phase 1s 2s 3s discovery potential

43 Sensitivity to Mass Hierarchy

44 Europe: LAGUNA LAGUNA Collaboration Consortium composed of 21 beneficiaries in 9 countries 9 university entities (ETHZ, Bern, Jyväskylä, OULU, TUM, UAM, UDUR, USFD, UA) 8 research organizations (CEA, IN2P3, MPG, IPJ PAN, KGHM CUPRUM, GSMiE PAN, LSC, IFIN-HH) 4 private companies (Rockplan, Technodyne, AGT, Lombardi) Additional university participants (IPJ Warsaw, Silesia, Wroclaw, Granada)

45 Europe: LAGUNA

46 Europe: LAGUNA