Liquid Scintillator Detector Lena Low Energy Neutrino Astronomy L. Oberauer, TUM

Detector properties to be achieved Very good optical properties (light yield, absorption-, scattering-length...) Optical coverage ca. 30 % photoelectron yield 200 pe / MeV or better energy resolution ca. 7 1 MeV energy threshold ca. 250 keV large dynamic range (sub-MeV – GeV physics) Low background cosmic ray shielding (depth > 4000 mwe) self-shielding (external gamma-, neutron background) radiopurity delayed coincidence technique (e.g. Bi-Po, inverse beta-decay) pulse-shape discrimination (separation alpha/neutron/beta- gamma)

Detector location LAGUNA: European site + design study for a next generation neutrino and p-decay detector 7 preselected sites Proposed experiments: GLACIER, LENA, MEMPHYS LENA (d>4000mwe) Pyhäsalmi, LSM

Tank construction: Cavern construction Tank + excavation study for Pyhäsalmi 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

Detector construction Tank design Conventional Steel Tank + well known, straightforward to build, robust - expensive, single passive layer defense Sandwich Steel Tank + cost effective, room for cooling, fast install, laser welds - mechanically challenging Sandwich Concrete Tank + robust, mechanically strong - Slow to build; steel plates and rebar prevent continuous casting Hollow Core Concrete Tank + room for cooling, - Not very much experience

Scintillator

Scattering Length Results  isotropic and anisotropic contributions measured  anisotropic scattering in good agreement with Rayleigh expectation  correct wavelength- dependence found  literature values for PC, cyclohexane correctly reproduced Results for =430nm Michael Wurm LAB (plus CH or C12) is fulfilling the requirements

Liquid Scintillator properties Emission spectra Teresa Marrodan, PhD thesis MLL accelerator lab Munich Light yield LAB (PPO, bis-Msb) ca. 10,000 ph/MeV Attenuation length (430nm) > 15m Absorption length ca. 20m (or better) PE yield 200 / MeV reachable !

Photomultiplier and Electronics

Area Inner Detector: m² Targeted optical coverage: 30% → 3130 m² effective photosensitive area PMTs probably the only photosensor type Durable for at least 30 years AND Utilizable until start of construction Important properties: Transit time spread, afterpulsing, gain, dynamic range, area, quantum efficiency, dark noise, peak-to-valley-ratio, early + pre- pulsing, late pulsing, pressure resistance, long term stability, low radioactivity, price Photo sensors : Photosensor requirements Pressure resistant encapsulation design (P > 15 bar) ready Acryl window

Example: PMT timing behavior Normal Pulses Early Pulses Pre-Pulses Late Pulses Transit Time Spread (FWHM, spe) Dark Noise 12

Electronics Requirements large dynamic range (0.3 < pe < 100) nsec – resolution zero deadtime Solutions under investigation FADCs for all channels (2 ns sampling time) FADCs for PMT-groups customized ASIC boards for PMT-groups (investigate by Pmm2 group for MEMPHIS)

14 LENA Physics Goals Proton Decay Galactic Supernova Burst Diffuse Supernova Neutrino Background Long baseline neutrino oscillations Solar Neutrinos Geo neutrinos Reactor neutrinos Neutrino oscillometry Atmospheric neutrinos Dark Matter indirect search L. Oberauer, TUM

LENA and proton decay High efficiency and very good background rejection for p  K + K and  from successive K decay K ->  (68 %) K -> 2 and 3  (31 %) (12 nsec) K 

Main background: atmospheric neutrino interactions in the target Background rejection: pulse shape discrimination Rise time distribution proton decays (MC) Rise time distribution atmospheric neutrinos (MC)

P -> K +

19 LENA and a galactic supernova

Event analysis e spectrum (inverse beta decay on H #1) with very high statistics – basically free of background e spectrum (inverse beta decay on 12 C) – {#2+#3 – norm.#1} with ~ (5-10) % accuracy Total flux of all active neutrinos (via 12 C-nc reaction #4)   sum spectrum plus antineutrinos (#6- e - e ) Everything as function of time Separation of SN models (due to large NC statistics – independent from oscillation physics) Information on Mass hierarchy, Theta_13 (see talk by A. Mirizzi)

all flavors     and anti-particles dominate Possible threshold Neutrino elastic scattering off protons From John Beacom

22 LENA and the Diffuse Supernova Background Excellent background rejection ( e p->e + n) Energy window 10 to 30 MeV. High efficiency (100% with 50 kt target) Discovery potential in LENA ~5 to 20 events per year are expected (model dependent) L. Oberauer, TUM M. Wurm et al., Phys.Rev.D 75 (2007)

DSNB background studies Cosmogenic produced neutrons no problem if d > 4000 mwe < 0.2 events / year Cosmogenic produced beta-neutron emitter (e.g. 9 Li) no problem if d > 4000 mwe < 0.1 events / year Atmospheric neutrino CC reaction 10 < E / MeV < 30 Atmospheric neutrino NC reaction – neutron production data from KamLAND severe bg: reduction by pulse shape discrimination and statistical subtraction ? Laboratory experiments indicate that a strong bg-reduction can be achieved Preliminary results: Monte-Carlo simulation based on recent results of PSD parameter on LAB scintillators n-scattering TOF exp. at MLL (Garching) preliminary

24 LENA and Geo-neutrinos LENA is the only detector within Laguna able to determine the geo neutrino flux In LENA we expect between 300 to 3000 events per year (~ 1500 / year) Good signal / bg ratio rather low reactor flux Separation of U/Th Test of geological models L. Oberauer, TUM

Geo-Neutrinos: Separation U / Th contribution > 5 sigma after 5 years at Pyhäsalmi

Neutrino oscillometry Sterile neutrinos S.K. Agarwallaa, J.M. Conrad, M.H. Shaevitz arXiv: v1 Source pion decay at rest E = 40 MeV and Dm 2 = 1.5 eV 2  L osc ~ 65m  Appearance of n e  LENAs “golden channel”  BG reactor neutrinos < 10 MeV  Also n e can be detected via delayed coincidence ( 12 C reaction)  Oscillation can be observed in LENA as function of the distance to the source

...with alternative – monoenergetic - neutrino sources (Y. Novikov et al.) Like 51 Cr, 37 Ar preliminary

28 CNGS neutrino induced muons in BOREXINO CERN 730km Direction from CERN (azimuth = 0 degree) real Data – no Monte-Carlo ! BOREXINO is NOT optimized for tracking ! Water Cherenkov Scintillator Track reconstruction

29 Separation between e- and  -like events possible Pulse shape discrimination (risetime, width) Track reconstruction Muon decay  e  Measuring the Michel electron Work under process electrons (1.2 GeV) muons (1.2 GeV) L. Oberauer, TUM

Single track reconstruction (MC studies): 3° angle resolution 0.5% energy resolution (at 300 MeV)

Next steps… Study of CERN to Pyhäsalmi superbeam (within Laguna-lbno)   e appearance experiment E ca. 4 GeV (d = 2300 km) Mass hierarchy, CP-violation, Theta_13 Problematic bg: NC  production (decay into 2 gammas resembles e reaction) Under study: Event topology variables to seperate electrons from π 0 (e.g. asymmetry variable, rise time, mean time, tof-corrected first hit times,...)

32 Conclusions Feasibility studies very promising Detector location, tank design Scintillator, photomultiplier, electronics Low energy neutrino physics: Reactor, Solar, Supernova, DSNB, Geo High energy physics: proton-decay, long-Baseline - oscillations (work under process) Rich R&D-program still on-going “White paper” published in April authors, 35 institutions L. Oberauer, TUM