LENA Low Energy Neutrino Astrophysics

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Deirdre Andrews
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1 LENA Low Energy Neutrino Astrophysics F. Von Feilitzsch, L. Oberauer, W. Potzel Technische Universität München

2 LENA (Low Energy Neutrino Astrophysics) Idea: : A large (~30 kt) ) liquid scintillator underground detector for Galactic supernova neutrino detection Solar Neutrino Spectroscopy Relic supernovae neutrino detection Neutrino properties Search for Proton Decay Terrestrial neutrino detection

3 Possible locations for LENA? Underground mine ~ 1450 m depth, low radioactivity, low reactor n- background! Access via trucks

4 Pylos (Nestor Institute) in Greece

5 P - decay event

6 Galactic Supernova neutrino detection with Lena (1) (2) (3) (4) (5) (6) n n n n n n e e e x x x + + p Æ C C e C - Æ Æ e e e Æn Æn + p Æn + + x - x x + n B e + p N C - * (Q = 1.8 MeV) (Q = 13.4 MeV) Electron n spectroscopy (Q = 17.3 MeV) ~ * 12 with C Æ C + g (Q = E = 15.1 MeV) (elastic scattering off (elastic scattering off Electron Antineutrino spectroscopy electrons) protons). g ~7800 ~ 480 Neutral current interactions; info on all flavours ~ 4000 and ~ 2200 Event rates for a SN type IIa in the galactic center (10 kpc)

7 Relative size of the different luminosities is not well known: it depends on uncertainties of the explosion mechanism and the equation of state of hot neutron star matter Supernova neutrino luminosity (rough sketch) T. Janka, MPA

8 Luminosities from core collapses of 11 to 25 solar masses T. Janka, MPA Supernova diagnostics by n measurements: a direct view into the SN-core high statistics on n e and n x, time and energy resolution perhaps a way to unravel the secrets of the explosion mechanism

9 Supernova explosion and neutrino interactions Gas infall from the collapsing star damps shock expansion Gas between Neutron Star and the shock is cooled and heated by neutrinos Only when the neutrino heating is strong enough an explosion can be triggered from T. Janka, MPA Garching

10 Inverse beta decay on p can be tagged by delayed coincidence in a liquid scintillator n + p Æ e + + e n E v > 1.8 MeV prompt event: E v 0.77 MeV n spectroscopy Delayed event: n + p Æ d 180_sec + g (2.2MeV) Position reconstruction of both events indicates direction to Supernova!...good statistics necessary reactor experiments)

11 All n flavours; monoenergetic 15.1 MeV gamma line n e interaction; delayed coincidence with 11.0 msec

12 Neutrino proton elastic scattering recoil p kinetic energies ~ few MeV quenching reduces this to ~ 1 MeV (and below) low threshold required (~ 0.2 MeV or so) (aim of Borexino, KamLAND for solar n) proton recoil spectrum reflects the Supernova neutrino spectrum easy to separate from high energy signals

13 Visible proton recoil spectrum in a liquid scintillator all flavors n m, n t and anti-particles dominate J. Beacom, astro-ph/

14 SNN-detection and neutrino oscillations Modulations in the energy spectrum due to matter effects in the Earth Dighe, Keil, Raffelt (2003)

15 Preconditions for observation of those modulations SN neutrino spectra n e and n m,t are different distance L in Earth large enough very good statistics very good energy resolution

16 Scintillator good resolution Water Cherenkov Anti-electron-neutrino spectra for 2000 events in each detector Only ~1000 events required for SC Dighe, Keil, Raffelt (2003)

17 frequency k of the modulations independent from the shape of the spectrum and indepent in time, but... SuperK is not good enough in energy resolution KamLAND is not large enough Required: Liquid scintillator experiment ~ 10 kt (or larger!) Megaton Cherenkov detector?

18 Supernovae Relic Neutrinos (SRN) n e Flux depends on the evolution of the star formation rate Flux estimates vary between 10 to 20 cm -2 sec -1 No signal observed so far Best limit comes from SK

19 LENA- threshold ~ 9 MeV! Background: Nuclear reactors! SRN - spectrum as observed in inverse beta decay reaction SK-threshold LENA: delayed coincidence prompt e + and delayed n. This reduces background and hence the threshold! LENA SNR rate: ~ 6 counts/y (better as SK by factor ~6)

20 Reactor SK Reactor bg LENA! No background for LENA! LENA SNR rate: SRN ~ 6 counts/y Atmospheric neutrinos

21 Sensitivity on proton decay p K n This decay mode is favoured in SUSY theories The primary decay particle K is invisible in Water Cherenkov detectors It and the K-decay particles are visible in scintillation detectors Better energy solution further reduces background

22 P -> K + n event structure: T (K + ) = 105 MeV t (K + ) = 12.8 nsec K + -> m + n (63.5 %) K + -> p + p 0 (21.2 %) T (m + ) = 152 MeV T (p + ) = 108 MeV electromagnetic shower E = 135 MeV m + -> e + n n (t = 2.2 ms) m p + -> m + n (T = 4 MeV) m + -> e + n n (t = 2.2 ms) m

23 33 - fold coincidence! the first 2 events are monoenergetic! use time- and position correlation! How good can one separate the first two events?...results of a first Monte-Carlo calculation

24 P decay into K and n K m m K Signal in LENA time (nsec)

25 Background Rejection: monoenergetic K- and m- signal: DE/E ~ 1 %! position correlation pulse-shape analysis (after correction on reconstructed position)

26 SuperKamiokande has 170 days (efficiency 33% ) In LENA 170 background events in 1489 LENA, this would scale down to a background of ~ 5 / y and after PSD-analysis this could be suppressed in LENA to ~ 0.25 / y! (efficiency ~ 70% ) A 30 kt detector (~ protons as target) would have a sensitivity of t < a few years for the K-decay after ~10 years measuring time The minimal SUSY SU(5) model predicts the K-decay mode to be dominant with a partial lifetime varying from y to y! actual best limit from SK: t < 6.7 x y (90% cl)

27 ...some more aspects of Lena Complementary to high energy neutrino astronomy Long term (~decades) experiment Large European intiative

Ay 122 - Fall 2004. The Sun. And The Birth of Neutrino Astronomy. This printout: Many pictures missing, in order to keep the file size reasonable

Ay 122 - Fall 2004. The Sun. And The Birth of Neutrino Astronomy. This printout: Many pictures missing, in order to keep the file size reasonable Ay 122 - Fall 2004 The Sun And The Birth of Neutrino Astronomy This printout: Many pictures missing, in order to keep the file size reasonable Why Study the Sun? The nearest star - can study it in a greater