Liquid Scintillator Technology Tobias Lachenmaier Universitt - PowerPoint PPT Presentation

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

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

LENA (Low Energy Neutrino Astronomy) Liquid scintillator Desired energy resolution 50 kt LAB/PPO+ bisMSB → 30% optical coverage Inner vessel (nylon) → 3000m² effective photo- Radius r = 13m sensitive area Buffer Light yield ≥ 200 pe/MeV 15kt LAB, Δr =2m Cylindrical steel tank, e.g. The tracking option adds to 55000 PMTs (8“) with the requirements of the PMT Winston Cones (2x area) array and electronics: r = 15m, height = 100m, → more, but smaller, optical coverage: 30% faster PMTs Water cherenkov muon veto → full waveform digitizing 5,000 PMTs, Δr > 2m to shield fast neutrons Pyhäsalmi Cavern egg-shaped for increased stability design Rock overburden: 4000 mwe

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

A galactic SN in LENA A galactic SN in LENA ca 15.000 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

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 + ✓ 8900 1.8 n e 12 C → 12 N e - ( ✓ ) 200 17.3 _ n e 12 C → 12 B e + ( ✓ ) 130 13.4 n 12 C → 12 C* n ✗ 860 15.1 n p → p n ✓ 2200 1.0 n e - → e - n ✓ 700 0.2 Michael Wurm, TUM Physics with LENA 6/24

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 7/24

Scientific Gain of SN Observation Scientific gain of SN detection Neutrino physics Astrophysics  Survival probability of n e in  Observe neutronisation burst neutronisation burst  Cooling of the neutron star P ee ≈ 0 → normal mass hierarchy flavor-dependent spectra  Resonant flavor conversions in and luminosity, time-dev. the SN envelope: hierarchy, q 13  Propagation of the shock wave  Earth matter effect: by envelope matter effects n mass hierarchy, q 13  SNEWS  Observation of collective neutrino oscillations  more exotic effects ... Michael Wurm, TUM Physics with LENA 8/24

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)

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 b n-emitters: 9 Li  neutrons from atm. n ‘s (NC on 12 C)  fast neutrons Scientific Gain Expected rate: 2-15 ev/year in fid. vol.  first detection of DSN (in energy window from 10-25MeV)  information on SN n spectrum

Solar Neutrinos in LENA Detection Channel [Borexino, arXiv:0805.3843] elastic n e scattering, E > 0.2MeV Background Requirements  U/Th concentration of 10 -18 g/g 7 Be- n 11 C (as achieved in Borexino)  shielding of >3500 mwe 210 Bi for CNO/pep- n measurement CNO/pep- n 85 Kr 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) (18kt)  probe the MSW effect in the vacuum transition region → new osc. physics _  search for n e → n e conversion

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

Influence of detector location K. Loo Michael Wurm, TUM Physics with LENA 13/24

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.

Sensitivity to proton decay p → K + ν Simulated energy spectrum of 20000 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.

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. Angular resolution of a few degrees, in principal very accurate energy resolution. J. Learned

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

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

Borexino Angular Resolution M. Wurm

Tracking 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 • 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 J. Learned, arXiv/0902.4009, J. Peltoniemi, arXiv/0909.4974

Photoelectrons in the optical model Photoelectron distributions

Photoelectrons in the optical model

Tracking tests with Geant4 optical model • Procedure: maximize log-likelihood value of photon pattern depending on all track parameters • First preliminary results: 100-500 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 100-750 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. D. Hellgartner

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 electrons (1.2 GeV) muons (1.2 GeV)  additional information, more powerful for n e selection

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: D E/E = 9%/sqrt(E/MeV)  for 300 MeV muon  D E/E ≈ 0.5%

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°, D x origin = 2cm