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LENA – a liquid scintillator detector for L ow E nergy N eutrino A stronomy and proton decay

LENA – a liquid scintillator detector for L ow E nergy N eutrino A stronomy and proton decay. Detector outline Physics potential: solar neutrinos Supernova neutrinos diffuse Supernova neutrino background proton decay geoneutrinos R&D on liquid scintillators Outlook.

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LENA – a liquid scintillator detector for L ow E nergy N eutrino A stronomy and proton decay

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  1. LENA – a liquid scintillator detector for Low Energy Neutrino Astronomy and proton decay • Detector outline • Physics potential: • solar neutrinos • Supernova neutrinos • diffuse Supernova neutrino background • proton decay • geoneutrinos • R&D on liquid scintillators • Outlook Marianne Göger-Neff NNN07 TU München Hamamatsu

  2. LENA – detector outline 100 m • detector size: 100 m length 30 m Ø • 50 kt liquid scintillator PXE as default option • 13500 PMTs 30 % coverage • light yield ~ 120 pe for events in center • water Cerenkov muon veto 2m of active shielding • located at > 4000 mwe Pyhäsalmi mine, Finland Nestor site, Mediterranean Sea 30 m alternative: vertical tanks 25 kt each L. Oberauer et al.,NPB 138 (2005) 108

  3. Why liquid scintillator for n detection? Neutrinos interact only weakly... => low count rate experiments => detectors must have large mass, good shielding, good background discrimination Liquid scintillators offer... • high light yield (~50 times more than water Cerenkov) => low energy threshold • quenching of heavy particles (a, n) LY(a) ~ 1/10 LY(b,g) => background suppression • liquid at ambient temperatures: => advantageous for detector construction and handling => several purification methods applicable (distillation, water extraction, nitrogen sparging, column chromatography) • easily available in large amounts, reasonable price (~ 1€/l)

  4. Neutrino Astronomy neutrinos are ideal probes for astronomy: neutral: no deflection by B-fields almost no absorption in matter direct information about their origin BUT: hard to detect

  5. LENA - solar neutrinos high statistics solar neutrino spectroscopy (fiducial volume 18 kt): • 7Be ~ 5400 events per day • test of small flux variations on short time scales, e.g. due to density profile fluctuations, look for coincidences with helioseismological data ! • test of day/night asymmetry (MSW effect in the earth) • pep ~ 150 events per day • solar luminosity in neutrinos • CNO ~ 200 events per day • important for heavy stars • 8B-ne ~ 360 events per year from CC reaction on 13C (~ 1% ab.) • distortion of 8B-n spectrum precise determination of solar fusion reactions and n oscillation parameters experience gained with Borexino ne + 13C -> 13N + e- Qthr = 2.2 MeV back decay (t=863 s): 13N -> 13C + e+ + ne Ianni et al. Phys.Lett. B627 (2005) 38-48

  6. Detection of pep and CNO neutrinos • transition region important to discriminate MSW from NSI • need low 11C background to detect pep and CNO neutrinos • at least 4000 mwe. • discriminate 11C by 3fold coincidence ( µ + n + 11C) Borexino coll. PhysRevC 74, 045805(2006) • about 90% reduction can be reached by local cuts around µ track and n capture position Friedland, Lunardini, Peña-Garay hep-ph/0402266

  7. Supernova Neutrinos • Core collapse Supernova: Mprog ≥ 8 MSun, E ≈ 1059 MeV • 99% of the energy is carried away by neutrinos • 1058 Neutrinos with <E> ~ 10 MeV within few s Neutrinos provide information on: 1. Supernova physics: Gravitational collapse mechanism Supernova evolution in time Cooling of the proto-neutron star Shock wave propagation 2. Neutrino properties Neutrino mass (time of flight) Oscillation parameters (matter effects) 3. Early alert for astronomers (n burst several hours before optical burst) Real-time spectroscopy of different n-flavours T. Janka ne ne nx

  8. LENA – Supernova Neutrinos Possible reactions Event rate for a 8M⊙ Supernova in liquid scintillator: in 10 kpc distance (KRJ, no osc.): ne + p  n + e+ (Q=1.8 MeV) 8700 ne spectroscopy ne + 12C 12B + e+ (Q=13.4 MeV) 200 ne + 12C 12N + e- (Q=17.3 MeV)130 ne spectroscopy nx + 12C 12C* + nx  12C + g(15.1 MeV)950 total n flux nx + e-nx + e- (Ethr = 0.2 MeV) 700 (mainly ne, ne) nx + p nx + p (Ethr = 0.2 MeV) 2200 total energy spectrum (mainly nm, nt) Beacom et al. Phys.Rev.D 66(2002)033001 for different models (TBP, LL, KRJ) and different oscillation scenarios the total rate changes from 10000 to 24000 events Diploma thesis by J. Winter, TUM 2007, to be published

  9. LENA - Diffuse Supernova Neutrino Background • DSN give information about star formation rate • Super-Kamiokande limit (< 1.2 cm-2 s-1 for E > 19.3 MeV) close to • theoretical expectations (KamLAND: 3.7 102 cm-2 s-1 for 8.3 MeV<E<14.8MeV) • use delayed coincidencene p -> e+ n • advantage of LENA: • - low reactor neutrino background •  threshold ~ 9 MeV (SK 19 MeV) • - distinction btw. ne/ ne possible • predicted SRN rate in LENA • ~ 6 - 10 counts per year • limit after 10 years: • < 0.3 cm-2 s-1 for 10 MeV < E < 19 MeV • < 0.13 cm-2 s-1 for 19 MeV < E < 25 MeV M. Wurm et al. Phys.Rev. D75 (2007) 023007

  10. LENA – proton decay • proton decay predicted by GUT, SUSY theories • SUSY predicts dominant decay mode tp (p->K+n)~ 1034 years • K+ is invisible in water Cerenkov detectors • event structure:

  11. LENA – proton decay Event structure: 3-fold coincidence, use energies, time and position correlation, pulse shape analysis m Cutting at a rise time of 9 ns Acceptance ~ 60% Background suppression (atmospheric nm -> m) ~5 x 10-5 K T. Marrodan et al., Phys. Rev. D 72, 075014 (2005) Expected background: < 0.1 ev/year (K production by atmospheric n) Limit after 10 years: 4 x 1034 years (90% CL) Current SK limit: 2.3 x 1033 years (90% CL) => 40 events in 10 years in LENA (<1 backgr. ev.)

  12. Geo-Neutrinos Detection via p +nen + e+ Neutrino flux and spectrum depend on the distribution of radioactive elements in the Earth‘s crust and mantle (mainly U, Th) => input data for Earth models = neutrino geophysics First geo-neutrinos detected by KamLAND • => in LENA 400 – 4000 ev/year • scaled from KamLAND Hochmuth et al. Astrop.Phys 27, 21 (2007)

  13. Studies of liquid scintillator properties Investigated scintillators: Phenyl-xylyl-ethane (PXE) Linear Alkylbenzene (LAB) • Light Yield • Choice of right solvent • Optimization of fluor concentration • Transparency • Measurement of attenuation and • scattering length • Influence of scintillator purification • Fluorescence Decay Time • Optimizing scintillator response time • => time and position resolution • Alpha quenching • => alpha-beta discrimination • Radiopurity and purification methods • Ge spectroscopy (+ NAA) to screen various • materials and study effects of purification • Long term stability r = 0.99 r = 0.86

  14. Light yield and decay time • measure number of photoelectrons per MeV and exponential decay time constants for different solvent/fluor mixtures • under study: PXE/LAB/dodecane PPO/PMP/bisMSB PXE + 2g/l PPO T. Marrodan, PhD thesis,, TUM, in preparation

  15. Scintillator emission spectrum • excitation by UV light with deuterium lamp • excitation by 10 keV electrons T. Marrodan, PhD thesis,, TUM, in preparation

  16. Light propagation • Measurement of attenuation length • separate scattering and absorption: measure angular dependence with polarized/unpolarized light • attenuation length > 10 m @ 430 nm scattering and absorption lengths > 20 m M. Wurm, diploma thesis, TUM, 2005

  17. Radiopurity UGL in Garching, 15 mwe shielding 150% HPGe detector with NaJ anti-Compton + µ-veto panels radiopurity screening of various materials extension of the UGL planned 2008 passive shielding only + muon veto + anti-Compton Diploma thesis, M. Hofmann, TUM, 2007

  18. LAGUNALarge Apparatus for Grand Unificationand Neutrino Astrophysics LENALiquid-Scintillator Detector13,500 PMs, 50 kt target 100m coordinated R+D design studyin European collaborationon-going application for EU funding ~ 20 participating institutes scientific paper: 0705.0116 (hep-ph) 30m MEMPHYSWater Čerenkov Detector500 kt target in 3 shafts,3x 81,000 PMs GLACIERLiquid-Argon Detector100 kt target, 20m drift length, LEM-foil readout28,000 PMs for Čerenkov- and scintillation light

  19. Summary and Outlook • LENA : multi-purpose detector for low energy neutrino astronomy and proton decay • evaluation of physics potential: solar neutrinos  Supernova neutrinos  diffuse SN background  geoneutrinos  proton decay  atmospheric neutrinos  reactor neutrinos  beta beams / nu factory  • detector design under study: scintillator development photosensors & electronics optimum tank size and shape optimum location • R&D is funded in SFB/TR 27 ‘Neutrinos and beyond’ and in excellence cluster ‘Origin and structure of the universe’ • joint European effort: LAGUNA

  20. LENA - geoneutrinos Detection via p +nen + e+ • source of the terrestrial heat flow • contribution of natural radioactivity • distribution of U, Th, K in crust, mantle and core • hypothetical natural reactor at the Earth‘s center? maximum core enhanced ref minimal Q (rad) hep-ph0509136

  21. Supernova Neutrinos earth matter effect: if SN neutrinos pass through the Earth before being the detector, see wiggles in spectrum Dighe, Keil & Raffelt hep-ph/0304150

  22. Requirements of the liquid scintillator n detectors should feature: • high light yield • high transparency • low energy threshold • good energy resolution • precise position reconstruction • correlated events with short delay • good background separation  different pulse shapes for alphas/betas • low background from radioactivity  high radiopurity • long measuring time (~5-10 years) • safety in underground laboratories  high flash point • fast decay time • high transparency  long-term stability  material compatibility

  23. Shock propagation neutrinos

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