LENA – a liquid scintillator detector for Low Energy Neutrino Astronomy and

proton decay

Marianne Göger-Neff NNN07

TU München Hamamatsu

• 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

• 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

LENA – detector outline

100 m

30 m

L. Oberauer et al.,NPB 138 (2005) 108

alternative:vertical tanks25 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 noabsorption in matter

direct informationabout their origin

BUT: hard to detect

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-e ~ 360 events per year

from CC reaction on 13C (~ 1% ab.) distortion of 8B-spectrum

precise determination of solar fusion reactions and oscillation parameters

experience gained with Borexino

e + 13C -> 13N + e-

Qthr = 2.2 MeV

back decay (=863 s):13N -> 13C + 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 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

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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

( burst several hours before optical burst)

Real-time spectroscopy of different -flavours

T. Janka

0 10 20 30 40 50 60

0

0.02

0.04

0.06

e

e

x

LENA – Supernova Neutrinos

Possible reactions Event rate for a 8M⊙ Supernovain liquid scintillator: in 10 kpc distance (KRJ, no osc.):

e + p n + e+ (Q=1.8 MeV) 8700 e spectroscopy

e + 12C 12B + e+ (Q=13.4 MeV) 200

e + 12C 12N + e- (Q=17.3 MeV) 130 e spectroscopy

x + 12C 12C* + x 12C + (15.1 MeV) 950 total flux

x + e- x + e- (Ethr = 0.2 MeV) 700mainlye,ex + p x + p (Ethr = 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 10000 to 24000 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 (< 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 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

~ 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

T (K+) = 105 MeV

(K+) = 12.8 nsec

K+ -> (63.5 %) K+ -> (21.2 %)

T (+) = 152 MeV T (+) = 108 MeV T () = 110 MeV

+ -> e+ e (= 2.2 s)

e+ e (= 2.2 s)

event structure: p -> K+

LENA – proton decay

• proton decay predicted by GUT, SUSY theories

• SUSY predicts dominant decay mode p (p->K+)~ 1034 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 10-5

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 1034 years (90% CL)

Current SK limit: 2.3 x 1033 years (90% CL)=> 40 events in 10 years in LENA (<1 backgr. ev.)

T. Marrodan et al., Phys. Rev. D 72,

075014 (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 PPOT. 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 > 10 m @ 430 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 2008

+ muon veto + anti-Compton

passive shielding only

Diploma thesis, M. Hofmann, TUM, 2007

LAGUNALarge Apparatus for Grand Unificationand Neutrino Astrophysics

30m

100m

MEMPHYSWater Čerenkov Detector

500 kt target in 3 shafts,3x 81,000 PMs

LENALiquid-Scintillator Detector13,500 PMs, 50 kt target

GLACIERLiquid-Argon Detector100 kt target, 20m drift length, LEM-foil readout28,000 PMs for Čerenkov- and scintillation light

coordinated R+D design studyin European collaborationon-going application for EU funding~ 20 participating institutesscientific paper: 0705.0116 (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-ph0509136

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

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