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

detector size: 100 m length 30 m Ø 50 kt liquid scintillator PXE as default option 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 LENA – detector outline 100 m 30 m L. Oberauer et al.,NPB 138 (2005) 108 alternative: vertical tanks 25 kt each

Why liquid scintillator for 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 ( , n) LY(  ) ~ 1/10 LY(  ) => 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)

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

LENA - solar neutrinos high statistics solar neutrino spectroscopy (fiducial volume 18 kt): – 7 Be ~ 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 – 8 B- e ~ 360 events per year from CC reaction on 13 C (~ 1% ab.)  distortion of 8 B-  spectrum precise determination of solar fusion reactions and oscillation parameters experience gained with Borexino e + 13 C -> 13 N + e - Q thr = 2.2 MeV back decay (  =863 s): 13 N -> 13 C + e + + e Ianni et al. Phys.Lett. B627 (2005) 38-48

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

Supernova Neutrinos Core collapse Supernova: M prog ≥ 8 M Sun,  E ≈ MeV 99% of the energy is carried away by neutrinos Neutrinos with ~ 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 ( burst several hours before optical burst) Real-time spectroscopy of different -flavours T. Janka e e x

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

LENA - Diffuse Supernova Neutrino Background DSN give information about star formation rate Super-Kamiokande limit ( 19.3 MeV) close to theoretical expectations (KamLAND: cm-2 s-1 for 8.3 MeV<E<14.8MeV) use delayed coincidence e p -> e + n advantage of LENA: - low reactor neutrino background  threshold ~ 9 MeV (SK 19 MeV) - distinction btw. e / e possible predicted SRN rate in LENA ~ 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)

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

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

Geo-Neutrinos 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 Detection via p + e  n + e + Hochmuth et al. Astrop.Phys 27, 21 (2007)

Studies of liquid scintillator properties 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 Investigated scintillators: Phenyl-xylyl-ethane (PXE) Linear Alkylbenzene (LAB)  = 0.86  = 0.99

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

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

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

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 muon veto + anti-Compton passive shielding only Diploma thesis, M. Hofmann, TUM, 2007

LAGUNA Large Apparatus for Grand Unification and Neutrino Astrophysics 30m 100m MEMPHYS Water Čerenkov Detector 500 kt target in 3 shafts, 3x 81,000 PMs LENA Liquid-Scintillator Detector 13,500 PMs, 50 kt target GLACIER Liquid-Argon Detector 100 kt target, 20m drift length, LEM-foil readout 28,000 PMs for Čerenkov- and scintillation light coordinated R+D design study in European collaboration on-going application for EU funding ~ 20 participating institutes scientific paper: (hep-ph)

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

LENA - geoneutrinos 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? Detection via p + e  n + e + core enhanced  (rad) minimal maximum ref hep-ph

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/

Requirements of the liquid scintillator 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  high light yield  high transparency  fast decay time  high transparency  long-term stability  material compatibility detectors should feature:

Shock propagation neutrinos