lena – a liquid scintillator detector for low energy neutrino astronomy and proton decay marianne...
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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: