Transcript LENA – proton decay

LENA – a liquid scintillator detector for
Low Energy Neutrino Astronomy and
proton decay
• Detector outline
• Physics potential:
• solar neutrinos
• Supernova neutrinos
• diffuse Supernova neutrino background
• proton decay
• geoneutrinos
• R&D on liquid scintillators
• Outlook
Marianne Göger-Neff
TU München
NNN07
Hamamatsu
LENA – detector outline
• 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
L. Oberauer et al.,NPB 138 (2005) 108
alternative:
vertical tanks
25 kt each
Why liquid scintillator for n detection?
Neutrinos interact only weakly...
=> low count rate experiments
=> detectors must have large mass, good shielding,
good background discrimination
Liquid scintillators offer...
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high light yield (~50 times more than water Cerenkov)
=> low energy threshold
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quenching of heavy particles (a, n)
LY(a) ~ 1/10 LY(b,g)
=> background suppression
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liquid at ambient temperatures:
=> advantageous for detector construction and handling
=> several purification methods applicable (distillation,
water extraction, nitrogen sparging, column chromatography)
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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):
–
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-n
~ 360 events per year
from CC reaction on 13C (~ 1% ab.)
 distortion of 8B-n spectrum
ne + 13C -> 13N + eQthr = 2.2 MeV
back decay (t=863 s):
13N -> 13C + e+ + n
e
e
Ianni et al. Phys.Lett. B627 (2005) 38-48
precise determination of solar fusion reactions and n oscillation parameters
experience gained with Borexino
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transition region important
to discriminate MSW from NSI
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need low 11C background
to detect pep and CNO
neutrinos
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at least 4000 mwe.
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discriminate 11C by
3fold coincidence
( µ + n + 11C)
Borexino coll. PhysRevC 74, 045805(2006)
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about 90% reduction can
be reached by local cuts around
µ track and n capture position
Friedland, Lunardini, Peña-Garay
hep-ph/0402266
Detection of pep and CNO neutrinos
Supernova Neutrinos
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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
T. Janka
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
(n burst several hours before optical burst)
Real-time spectroscopy of different n-flavours
ne
0.06
ne
0.04
nx
0.02
0
0
10
20
30
40
50
60
LENA – Supernova Neutrinos
Possible reactions
in liquid scintillator:
Event rate for a 8M⊙ Supernova
in 10 kpc distance (KRJ, no osc.):
ne + p  n + e+ (Q=1.8 MeV)
8700
ne + 12C  12B + e+ (Q=13.4 MeV)
200
ne + 12C  12N + e- (Q=17.3 MeV)
130
nx + 12C  12C* + nx  12C + g(15.1 MeV)
950
nx + e-  nx + e(mainly ne, ne)
nx + p  nx + p
(mainly nm, nt)
700
(Ethr = 0.2 MeV)
(Ethr = 0.2 MeV)
2200
ne spectroscopy
ne spectroscopy
total n flux
total energy spectrum
Beacom et al. Phys.Rev.D 66(2002)033001
for different models (TBP, LL, KRJ) and different oscillation scenarios
the total rate changes from 10000 to 24000 events
Diploma thesis by J. Winter, TUM 2007, to be published
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 ne p -> e+ n
• advantage of LENA:
- low reactor neutrino background
 threshold ~ 9 MeV (SK 19 MeV)
- distinction btw. ne/ ne 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
LENA – proton decay
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proton decay predicted by GUT, SUSY theories
SUSY predicts dominant decay mode tp (p->K+n)~ 1034 years
K+ is invisible in water Cerenkov detectors
event structure:
event structure:
p -> K+ n
T (K+) = 105 MeV
t (K+) = 12.8 nsec
K+ -> m nm
(63.5 %)
T (m+) = 152 MeV
K+ ->   (21.2 %)
T () = 110 MeV
T (+) = 108 MeV
  gg
m+ -> e+ ne nm (t = 2.2 ms)
  m nm
m  e+ nm ne (t = 2.2 ms)
LENA – proton decay
Event structure: 3-fold coincidence, use energies,
time and position correlation, pulse shape analysis
m
Cutting at a rise time of 9 ns
Acceptance ~ 60%
K
Background suppression
(atmospheric nm -> m) ~5 x 10-5
T. Marrodan et al., Phys. Rev. D 72,
075014 (2005)
Expected background: < 0.1 ev/year (K production by atmospheric n)
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.)
Geo-Neutrinos
Detection via p + ne  n + e+
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
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)
r = 0.99
Linear Alkylbenzene (LAB)
r = 0.86
Light yield and decay time
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measure number of photoelectrons per MeV
and exponential decay time constants
for different solvent/fluor mixtures
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under study: PXE/LAB/dodecane
PPO/PMP/bisMSB
PXE + 2g/l PPO
T. Marrodan, PhD thesis,,
TUM, in preparation
Scintillator emission spectrum
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excitation by UV light with deuterium lamp
excitation by 10 keV electrons
T. Marrodan, PhD thesis,,
TUM, in preparation
Light propagation
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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
passive shielding only
+ muon veto + anti-Compton
Diploma thesis, M. Hofmann, TUM, 2007
LENA
LAGUNA
Large Apparatus for Grand Unification
and Neutrino Astrophysics
Liquid-Scintillator Detector
13,500 PMs, 50 kt target
coordinated R+D design study
in European collaboration
on-going application for EU funding
~ 20 participating institutes
scientific paper: 0705.0116 (hep-ph)
MEMPHYS GLACIER
Water Čerenkov Detector
500 kt target in 3 shafts,
3x 81,000 PMs
Liquid-Argon Detector
100 kt target, 20m drift length, LEM-foil readout
28,000 PMs for Čerenkov- and scintillation light
Summary and Outlook
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LENA : multi-purpose detector for low energy neutrino astronomy and
proton decay
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evaluation of physics potential: solar neutrinos
Supernova neutrinos
diffuse SN background
geoneutrinos
proton decay
atmospheric neutrinos
reactor neutrinos
beta beams / nu factory
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detector design under study:
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R&D is funded in SFB/TR 27 ‘Neutrinos and beyond’
and in excellence cluster ‘Origin and structure of the universe’
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joint European effort: LAGUNA
scintillator development
photosensors & electronics
optimum tank size and shape
optimum location
LENA - geoneutrinos
Detection via p + ne  n + e+
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source of the terrestrial heat flow
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contribution of natural radioactivity
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distribution of U, Th, K in crust, mantle and core
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hypothetical natural reactor at the Earth‘s center?
maximum
core enhanced
ref
minimal
hep-ph0509136
Q (rad)
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
n detectors should feature:
• low energy threshold
• good energy resolution
 high light yield
 high transparency
• precise position reconstruction
• correlated events with short delay
 fast decay time
 high transparency
• good background separation
 different pulse shapes
for alphas/betas
• low background from radioactivity
 high radiopurity
• long measuring time (~5-10 years)
 long-term stability
 material compatibility
• safety in underground laboratories
 high flash point
Shock propagation neutrinos