First Results from
BOREXINO and
Prospects of Low Energy
Neutrino Astronomy
Oxford University and RAL
November 20th and 21st
Lothar Oberauer, Physikdepartment E15, TU München
Charge
Interactions
Neutrinos as probes ?
0
w
w,e
-1
w,e,s
+2/3 -1/3
Neutrinos undergo only
weak interactions:
No deflection in electric or magnetic fields,
extremely penetrating => n‘s are perfect
carriers of information from the centers of
astrophysical objects
Neutrino Mixing
Flavor eigenstates
n e   1 0
  
n     0 c23
n   0  s
23
  
=
Mixing matrix
x
Mass eigenstates
 i

0  c13
0 s13e  c12 s12 0 n 1 


 
s23  0
1
0   s12 c12 0 n 2 
c23   s13ei 0 c13  0
0 1 n 3 
2 mixing angles are measured: Q12 ~ 340 Q23 ~ 450
m23 – m22 ~ 2.6 x 10-3 eV2
atmospheric n and accelerator n exp.
m22 – m21 ~ 8 x 10-5 eV2
solar and reactor n experiments
Open: Q13 ? CP violating phase  ?
Absolute mass scale (mn < 2.2 eV) ? Mass hierarchy ?
Neutrino oscillations (i.e. flavor transitions)
and matter depending effects
May complicate interpretation of
astrophysical processes
Access to n intrinsic properties not
available in laboratory experiments !
Low energy n
astronomy
Intrinsic n parameters
(particle physics)
Natural Neutrino Sources
(experimentally verified)
Sun
(since 1970)
Earth
(since
2005)
Atmosphere
(since ~1990)
Supernovae (1987)
Natural Neutrino Sources
(not yet verified)
Big Bang
Active galactic
nuclei ?
Supernovae remnants ?,
Gamma ray bursts ?,
Supernovae relic neutrinos ?...
Energy Spectra of Astrophysical Neutrinos
low energy
~ 1 GeV ?
Thermal sources
Non-thermal sources
high energy
The dominating solar pp - cycle
H. Bethe
W. Fowler
pp - 1
pp -2
pp -3
The sub-dominant solar CNO - cycle
…dominates in stars with
more mass as our sun…
=>Large astrophysical
relevance
“bottle-neck” reaction
slower than expected
(LUNA result)
Solar CNO-n
prediction
lowered by factor ~ 2 !
 Impact on age of
globular clusters
Solar Neutrinos
4 p  He  2e  2n e  26.7 MeV
4
GALLEX
GNO
SAGE
Integral
whole
spectrum

BOREXINO
Since august 2007
7-Be neutrinos
no spectral
information
Neutrino Energy in MeV
SuperK, SNO
Directional
information
History of solar neutrino
experiments at 2007
All experiments were successful
•Discovery of neutrino
oscillations
•Probing thermal
fusion reactions
Oscillations and matter effects
Oscillation length ~ 102 km
=> oscillation smeared out
and non-coherent
Effective ne mass (due to
forward scattering on
electrons) is enhanced by a
potential A
A ~ GFNeE2
=> for E > 1 MeV
matter effect dominates
and leads to an enhanced
ne suppression for those
energies…
Missing info here
before BOREXINO
Now additional
Improvement on
uncertainty
on pp-ne flux
1
Vaccum regime
10 MeV
Matter regime
BOREXINO
Neutrino electron scattering
n e > n e
Liquid scintillator technology (~300t):
Low energy threshold (~60 keV)
Good energy resolution (~4.5% @ 1 MeV)
Sensitivity on sub-MeV neutrinos
Online since May 16th, 2007
Borexino Collaboration
Genova
Milano
Princeton University
APC Paris
Perugia
Dubna JINR
(Russia)
Kurchatov
Institute
(Russia)
Virginia Tech. University
Munich
(Germany)
Jagiellonian U.
Cracow
(Poland)
Heidelberg
(Germany)
BOREXINO in the Italian Gran
Sasso Underground Laboratory in
the mountains of Abruzzo, Italy,
~120 km from Rome
Laboratori
Nazionali del
Gran Sasso
LNGS
External Labs
Shielding
~3500 m.w.e
Borexino Detector and Plants
BOREXINO Detector layout
Scintillator:
270 t PC+PPO in a 150 m
thick nylon vessel
Nylon vessels:
Inner: 4.25 m
Outer: 5.50 m
Stainless Steel Sphere:
2212 PMTs +
concentrators
1350 m3
Water Tank:
g and n shield
 water Č detector
208 PMTs in water
2100 m3
Excellent
shielding of
external
background
Carbon steel plates
Increasing purity
from outside to the
central region
The ideal electron recoil spectrum due
to solar neutrino scattering
pp
7-Be
CNO, pep
8B
Arbitrary units
Energy Spectrum (no cuts)
14C
dominates below 200 KeV
210Po
NOT in eq. with 210Pb
Mainly external gs and s
Photoelectrons
Statistics of this plot: ~ 1 day
Problem: muons going
through the buffer may
create pulses in the
neutrino energy window
via Cherenkov light
Muon cuts
350 PMS without light
concentrators
Npe (no-cone) / Npe (all)
is higher for muons
Sensitive cut (“Deutschcut”) on muons using the
Inner Detector
Additional cuts on pulse
shape applicable
Neutrino
candidates
muons
Outer Detector efficiency
OD-efficiency ~
99%
Total muon
rejection power
(incl. cuts ID) ~
99.99%
Preliminary, exact
numbers require
more detailed
studies
muons
Distribution of
events without
OD-muon flag
Fiducial volume cut
Rejection of external background (mostly gammas)
R < 3.3 m (100 t nominal mass)
Radial distribution
z vs Rc scatter plot
R2
gauss
FV
R  x2  y 2  z 2
Rc  x 2  y 2
Spectrum after muon and fiducial volume cuts
210Po
14C
(only, not in eq. with 210Pb!)
85Kr+7Be
n
11C
Last cut: 214Bi-214Po and Rn daughters removal
238U
232Th
and
212Bi-212Po
 = 432.8 ns
212Bi
b
a
212Po
208Pb
~800 KeV eq.
2.25 MeV
 = 236 s
214Bi
b
3.2 MeV
a
214Po
210Pb
~700 KeV eq.
232Th
Events are mainly in the south vessel
surface (probably particulate)
212Bi-212Po
214Bi-214Po
Only 3
bulk candidates (47.4d)
238U:
< 2. 10-17 g/g
232Th:
< 1. 10-17 g/g
a/b Separation
in BOREXINO
a particles
Full separation at high energy
b particles
ns
250-260 pe; near the 210Po peak
2 gaussians fit
a/b Gatti parameter
signal: fit without a/b
subtraction
Po peak not included in this fit
7Be
210

Strategy:




Fit the shoulder region only
Area between 14C end
point and 210Po peak to
limit 85Kr content
pep neutrinos fixed at
SSM-LMA value
7Be
CNO + 210Bi
Fit components:
 7Be
n
 85Kr


CNO+210Bi combined
Light yield left free
These bins used to
limit 85Kr
content in fit
n
85Kr
signal: fit a/b subtraction of
210Po peak
7Be
 210Po
background is
subtracted:




For each energy bin, a
fit to the a/b Gatti
variable is done with two
gaussians
From the fit result, the
number of a particles in
that bin is determined
This number is
subtracted
The resulting spectrum is
fitted in the energy range
between 270 and 800keV
The two analysis yield
fully compatible
results
BOREXINO 1st result
(astro-ph 0708.2251v2)

Scattering rate of 7Be solar n on electrons
7Be
n Rate: 47 ± 7STAT ± 12SYS c/d/100 t
BOREXINO and n-Oscillations
No oscillation hypothesis
75 ± 4
c/100t/d
 Oscillation (so-called Large Mixing Solution)
49 ± 4
c/100t/d
 BOREXINO experimental result
47 ± 7stat ± 12sys
c/100t/d

Survival probability Pee for solar ne
Pee
Gallium experiments: 8B and 7Be
neutrinos subtracted !
1.0
0.8
0.63 ± 0.19
0.6
BOREXINO
Transition of
vacuum to matter
dominated n 
oscillations
predicted by
MSW-effect
It implies m2 > m1
0.4
0.34 ± 0.04
SNO, SuperKamiokande
0.2
< 0.44
0.86
5.5 - 15
Energy in MeV
Prospects of BOREXINO

Improvement of systematical uncertainty
up to now it is dominated by uncertainty on fiducial volume
=> calibrations
 7Be



flux measurement with 10% uncertainty => 1%
accuracy for pp-neutrinos ! (BOREXINO + LMA
parameters + solar luminosity)
Theoretical uncertainty on pp-neutrino flux ~ 1%
=> high precision test of thermal fusion processes
Aim to measure CNO and pep-neutrinos, perhaps ppneutrinos and 8B-neutrinos below 5.5 MeV
Additional features: Geo neutrinos & reactor neutrinos &
Supernova neutrinos (~100 events) for a galactic SN
type II
CNO and pep Neutrinos

Problem: muon induced
11C nuclei
> 11B e+ ne (Q = 1.0 MeV,
T1/2=20.4min)
11C

Aim: tag via 3-fold
delayed coincidence
, n (~ms)
reconstruct
position of n-capture
veto
region around this position for
~ 1 hour. Required rejection
factor ~ 10
 track reconstruction
LAGUNA
Large Apparatus for Grand Unification and
Neutrino Astronomy
 Future Observatory for n-Astronomy at low
energies
 Search for proton decay (GUT)
 Detector for “long-baseline” experiments

Astrophysics
Details of a gravitational collapse
(Supernova Neutrinos)
 Studies of star formation in former
epochs of the universe („Diffuse
Supernovae Neutrinos Background“
DSNB)
 High precision studies of thermonuclear fusion processes (Solar
Neutrinos)
 Test of geophysical models (“Geoneutrinos”)

LAGUNA
Large Apparatus for Grand Unification
and Neutrino Astrophysics
LENA
liquid scintillator
13,500 PMs for 50 kt target
Wasser Čerenkov muon veto
coordinated F&E “Design Study”
European Collaboration,
FP7 Proposal
APPEC Roadmap
MEMPHYS GLACIER
Water Čerenkov liquid-Argon
500 kt target in 3 tanks,
3x 81,000 PMs
100 kt target, 20m driftlength,
28,000 PMs foor Čerenkov- und szintillation
LENA: Diffuse SN Background
ne + p -> e+ + n
Delayed coincidence
Spectral information
Event rate depends on
-Supernova type II rates
-Supernova model
Range: 20 to 220 / 10 y
Background: ~ 1 per year
M. Wurm et al., Phys. Rev D 75 (2007) 023007
Supernova neutrino luminosity (rough sketch)
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. Info
on all
neutrino flavors and energies desired!
T. Janka, MPA
Galactic
Supernova
neutrino burst in
LENA
Event rates in LENA
SN Neutrino predicted rates
vary with …
- distance and progenitor mass
(here: 10 kpc, 8 solar masses)
- the used SN neutrino model
(mean energies, pinching)
- neutrino physics
(value of q13, mass hierarchy)
variation: 10-19 x103 ev @ 10kpc
Aims
- physics of the core-collapse
(neutronisation burst, n cooling …)
- determine neutrino parameters
- look for matter oscillation effects
(envelope, shock wave, Earth)
Matter effects in
the Earth
•mass hierarchy
•theta_13
Matter effects in
the SN:
•mass hierarchy
and theta_13
•time development
of the shock
wave?
Separation of SN models ?

Yes, independent from oscillation model !
neutral current reactions in LENA
e.g.
TBP
KRJ
LL
12C:
700
950
2100
n p:
1500
2150
5750
for 8 solar mass progenitor and 10 kpc distance
Conclusions
Low Energy Neutrino Astronomy is very
successful (Borexino direct observation
of sub-MeV neutrinos)
 Strong impact on questions in particleand astrophysics
 New technologies (photo-sensors,
extremely low level background…)
 Strong European groups
