LENA - Institute for Nuclear Theory · LENA (Low Energy Neutrino Astrophysics) Idea: A large (~30 kt) liquid scintillator underground detector for Galactic supernova neutrino detection

LENALENA

Low Energy Neutrino Astrophysics

F. Von Feilitzsch, L. Oberauer, W. Potzel

Technische Universität München

LENALENA

((Low Energy Low Energy Neutrino Neutrino AstrophysicsAstrophysics))

IdeaIdea: A : A large large (~30 (~30 ktkt) liquid ) liquid scintillatorscintillatorunderground detectorunderground detector for for

Galactic supernovaGalactic supernovaneutrino detectionneutrino detection

Relic supernovaeRelic supernovaeneutrino detectionneutrino detection

Terrestrialneutrino detection

Search forProton Decay

Solar NeutrinoSpectroscopy

Neutrinoproperties

Possible locations for Possible locations for LENA ?LENA ?

Underground mine

~ 1450 m depth, lowradioactivity, lowreactor n-background !

Access via trucks

Pylos Pylos (Nestor Institute) in (Nestor Institute) in GreeceGreece

P - decay event

Galactic Supernova neutrinodetection with Lena

protons). off scattering (elastic (6)

electrons) off scattering (elastic (5)

MeV) 15.1 E(Q CC with (4)

MeV) 17.3 (Q (3)

MeV) 13.4(Q (2)

MeV) 1.8 (Q (1)

x

xx

12*12*1212x

1212e

1212

pp

ee

CC

NeC

BeC

nep

x

x

e

e

+Æ+

+Æ+

==+Æ+Æ+

=+Æ+

=+Æ+

=+Æ+

--

-

+

+

nn

nn

gnn

n

n

n

g

Electron Antineutrinospectroscopy

Electron n spectroscopy~ 65~ 65

Neutral current interactions; info on all flavours~ 4000 and ~ 2200~ 4000 and ~ 2200

~7800~7800

~ 480~ 480

Event rates for Event rates for a SN a SN type IIa type IIa in in the galactic center the galactic center (10 (10 kpckpc))

Supernova Supernova neutrino luminosity neutrino luminosity ((rough sketchrough sketch))

Relative size of the different luminositiesis not well known: it depends onuncertainties of the explosionmechanism and the equation of state ofhot neutron star matter

T. Janka, MPA

T. Janka, MPA

Luminosities from core collapses of 11 to 25 solar masses

SupernovaSupernovadiagnosticsdiagnostics by nmeasurements:

• a direct view intothe SN-core

• high high statisticsstatistics onnnee and and nnxx , timeand energyresolution

• perhaps a way tounravel the secretsof the explosionmechanism

Supernova Supernova explosion explosion and and neutrino interactionsneutrino interactions

Gas infall from thecollapsing star dampsshock expansion

Gas between NeutronStar and the shock iscooled and heated byneutrinos

Only when theneutrino heating isstrong enough anexplosion can betriggered

from T. Janka, MPA Garching

Inverse beta decay on p can be tagged by delayedcoincidence in a liquid scintillator

prompt event: Ev – 0.77 MeVn spectroscopy

Delayed event:MeV)2.2(g+Æ+ dpn

180_sec180_sec

Ev > 1.8 MeV

Position reconstruction of both events indicates direction toSupernova! ...good statistics necessary (experiencies @ reactorexperiments)

nepe +Æ+ +n

ne interaction;delayeddelayedcoincidencecoincidence with11.0 msec

All n flavours; mono-energetic 15.1 MeVgamma line

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 SupernovaSupernovaneutrino spectrumneutrino spectrum

• easy to separate from high energy signals

Visible proton recoil spectrum in a liquid scintillator

all flavors

nm, nt and anti-particles

dominate

J. Beacom, astro-ph/0209136

SNN-detection and neutrino oscillations

Modulations in the energyspectrum due to mattereffects in the Earth Dighe, Keil, Raffelt (2003)

Preconditions for observation of thosemodulations

• SN neutrino spectra ne and nm,t are different

• distance L in Earth large enough

• very good statistics

• very good energy resolution

Anti-electron-neutrino spectra for 2000 events in each detector

Only ~1000 ~1000 eventsevents required for SC

Scintillator

good resolution

WaterCherenkov

Dighe, Keil, Raffelt (2003)

…frequency k of the modulations independentfrom the shape of the spectrum and indepent intime, 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 ?

SupernovaeSupernovae RelicRelic Neutrinos (SRN) Neutrinos (SRN)

••Flux dependsFlux depends on on thetheevolutionevolution of of the starthe starformationformation rate rate

••Flux estimates varyFlux estimates varybetweenbetween

10 to 20 cm10 to 20 cm-2-2 sec sec-1-1

••No No signal observed signal observed sosofarfar

••Best Best limit comes fromlimit comes fromSKSK

ne

SRN - SRN - spectrum as observed spectrum as observed inininverse beta decay reactioninverse beta decay reaction

SK-threshold

LENA-LENA-

thresholdthreshold

~ 9 MeV !~ 9 MeV !

LENA: LENA: delayeddelayedcoincidencecoincidenceprompt eprompt e++ and anddelayed delayed n.n.

This reducesThis reducesbackgroundbackgroundand and hence thehence thethresholdthreshold!!

LENA SNRLENA SNRrate:rate:

~ 6 ~ 6 countscounts/y/y

((better as better as SKSKby factor by factor ~6)~6)

Background:

Nuclearreactors!

SRN

No background forLENA !

Reactor SK

Reactor bgLENA !

Atmospheric neutrinos

LENA SNR rate:LENA SNR rate:

~ 6 ~ 6 countscounts/y/y

Sensitivity Sensitivity on on proton decayproton decay

p K p K nn

• This decay mode is favoured in SUSYSUSY theories

• The primary decay particle K is invisible inWater Cherenkov detectors

• It and the K-decay particles are visible inscintillation detectors

• Better energy solution further reducesbackground

P P -> -> KK+ + nn event structureevent structure:: T (K+) = 105 MeV

t (K+) = 12.8 nsec

KK++ -> m-> m++ n n ( (63.5 %) K63.5 %) K++ -> p-> p+ + p p00 (21.2 %) (21.2 %)

T (m+) = 152 MeV T (p+) = 108 MeV electromagnetic shower

E = 135 MeV

mm+ + -> -> ee++ n n (t = 2.2 mn n (t = 2.2 ms) s) pp++ -> m -> m++ n n (T = 4 MeV)

mm+ + -> -> ee++ n n (t = 2.2 mn n (t = 2.2 ms)s)

••3 - 3 - fold coincidence fold coincidence !!

••the first the first 2 2 events are monoenergetic events are monoenergetic !!

••useuse time- and time- and position correlation position correlation !!

HowHow good good can onecan one separate separate thethe

first two eventsfirst two events ? ?

........results results of a of a first first Monte-Carlo Monte-Carlo calculationcalculation

K

m

time (nsec)

K

m

P decay into K and n

Signal in LENA

Background

Rejection:

• monoenergetic K- and m-signal: DE/E ~ 1 % !

• position correlation

• pulse-shape analysis

(after correction on

reconstructed position)

• SuperKamiokandeSuperKamiokande has 170 170 background events in 14891489days (efficiency 33% 33% ))

•In LENALENA, this would scale down to a background of ~ 5 / y~ 5 / y andafter PSD-analysis this could be suppressed in LENALENA to

~ ~ 0.25 / y0.25 / y ! (efficiency ~ ~ 70%70% )

•A 30 kt detector (~ 10103434 protons as target) would have a

sensitivity of t t << a a few few 10103434 yearsyears for the K-decayK-decayafter ~10 years measuring time

•The minimal SUSYSUSY SU(5) SU(5) model predicts the K-decayK-decay mode tobe dominantdominant with a partial lifetime varying from 10102929y to 10y to 1035 35 yy !

actual best limit from SKSK: t < 6.7 x 1032 y (90% cl)

...some more aspects of Lena

Complementary to highenergy neutrino astronomy

Long term (~decades)experiment

Large European intiative