1. 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

2. Neutrinos undergo only weak interactions:
Neutrinos as probes ?
Interactions w w,e w,e,s
Charge /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

3. Neutrino Mixing 2 mixing angles are measured: Q12 ~ 340 Q23 ~ 450
Flavor eigenstates =
Mixing matrix x
Mass eigenstates
2 mixing angles are measured: Q12 ~ Q23 ~ 450
m23 – m22 ~ 2.6 x 10-3 eV2 atmospheric n and accelerator n exp.
m22 – m21 ~ 8 x 10-5 eV solar and reactor n experiments
Open: Q13 ? CP violating phase d ?
Absolute mass scale (mn < 2.2 eV) ? Mass hierarchy ?

4. Intrinsic n parameters (particle physics)
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)

5. Natural Neutrino Sources
(experimentally verified)
Sun
(since 1970)
Atmosphere (since ~1990)
Earth (since 2005)
Supernovae (1987)

6. Natural Neutrino Sources
(not yet verified)
Big Bang
Active galactic nuclei ?
Supernovae remnants ?,
Gamma ray bursts ?,
Supernovae relic neutrinos ?...

7. Energy Spectra of Astrophysical Neutrinos
low energy ~ 1 GeV ? high energy
Non-thermal sources
Thermal sources

8. The dominating solar pp - cycle
H. Bethe
W. Fowler
pp - 1
pp -2
pp -3

9. 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

10. Solar Neutrinos Neutrino Energy in MeV GALLEX GNO SAGE Integral whole
spectrum
no spectral
information
BOREXINO
Since august 2007
7-Be neutrinos
SuperK, SNO
Directional
information

11. History of solar neutrino experiments at 2007
All experiments were successful
Discovery of neutrino
oscillations
Probing thermal
fusion reactions

12. 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
MeV
Vaccum regime Matter regime

13. This effect is only possible for m2 > m1
=> Information on mass hierarchy in the m2 m1 system

14. BOREXINO Neutrino electron scattering n e -> n e
Liquid scintillator technology (~300t):
Low energy threshold (~60 keV)
Good energy resolution 1 MeV)
Sensitivity on sub-MeV neutrinos
Online since May 16th, 2007

15. Borexino Collaboration
Genova
Milano
Princeton University
Perugia
APC Paris
Virginia Tech. University
Munich
(Germany)
Dubna JINR
(Russia)
Kurchatov
Institute
(Russia)
Jagiellonian U.
Cracow
(Poland)
Heidelberg
(Germany)

16. BOREXINO in the Italian Gran Sasso Underground Laboratory in the mountains of Abruzzo, Italy,
~120 km from Rome
Laboratori
Nazionali del
Gran Sasso
LNGS
Shielding
~3500 m.w.e
External Labs
Borexino Detector and Plants

17. BOREXINO Detector layout
Stainless Steel Sphere:
2212 PMTs + concentrators
1350 m3
Scintillator:
270 t PC+PPO in a 150 mm
thick nylon vessel
Water Tank:
g and n shield
m water Č detector
208 PMTs in water
2100 m3
Nylon vessels:
Inner: 4.25 m
Outer: 5.50 m
Excellent shielding of external background
Increasing purity from outside to the central region
Carbon steel plates

18. The ideal electron recoil spectrum due to solar neutrino scatteringpp
7-Be
CNO, pep 8B

19. Energy Spectrum (no cuts)
14C dominates below 200 KeV
210Po NOT in eq. with 210Pb
Arbitrary units
Mainly external gs and ms
Photoelectrons
Statistics of this plot: ~ 1 day

20. Muon cuts
Problem: muons going through the buffer may create pulses in the neutrino energy window via Cherenkov light
350 PMS without light concentrators
Npe (no-cone) / Npe (all)
is higher for muons
Sensitive cut (“Deutsch-cut”) on muons using the Inner Detector
Additional cuts on pulse shape applicable
Neutrino candidates
muons

21. 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

22. Fiducial volume cut Preliminary
Rejection of external background (mostly gammas)
R < 3.3 m (100 t nominal mass)
Radial distribution
z vs Rc scatter plot
Preliminary R2
gauss FV

23. Spectrum after muon and fiducial volume cuts
210Po (only, not in eq. with 210Pb!)
14C
85Kr+7Be n
11C
Last cut: 214Bi-214Po and Rn daughters removal

24. 238U and 232Th 212Bi-212Po 212Bi 212Po 208Pb b a t = 432.8 ns 214Bi
2.25 MeV
~800 KeV eq.
214Bi
214Po
210Pb b a
t = 236 ms
3.2 MeV
~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: < g/g
232Th: < g/g

25. a/b Separation in BOREXINO
a particles
Full separation at high energy
b particles ns
pe; near the 210Po peak
2 gaussians fit
a/b Gatti parameter

26. 7Be signal: fit without a/b subtraction
210Po peak not included in this fit
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
Fit components:
7Be n
85Kr
CNO+210Bi combined
Light yield left free
7Be n
CNO + 210Bi
85Kr
These bins used to limit 85Kr content in fit

27. 7Be signal: fit a/b subtraction of 210Po peak
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

28. 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

29. BOREXINO and n-Oscillations
No oscillation hypothesis
75 ± c/100t/d
Oscillation (so-called Large Mixing Solution)
49 ± c/100t/d
BOREXINO experimental result
47 ± 7stat ± 12sys c/100t/d

30. Survival probability Pee for solar ne
Transition of vacuum to matter dominated n - oscillations predicted by MSW-effect
It implies m2 > m1
Pee
Gallium experiments: 8B and 7Be neutrinos subtracted !
1.0
0.8
0.63 ± 0.19
BOREXINO
0.6
0.4
0.34 ± 0.04
SNO, SuperKamiokande
0.2
< 0.44
0.86
Energy in MeV

31. 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 pp-neutrinos and 8B-neutrinos below 5.5 MeV
Additional features: Geo neutrinos & reactor neutrinos & Supernova neutrinos (~100 events) for a galactic SN type II

32. CNO and pep Neutrinos Problem: muon induced 11C nuclei
11C -> 11B e+ ne (Q = 1.0 MeV, T1/2=20.4min)
Aim: tag via 3-fold delayed coincidence
m, n (~ms) reconstruct position of n-capture veto region around this position for ~ 1 hour. Required rejection factor ~ 10
m track reconstruction

33. 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

34. 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 thermo-nuclear fusion processes (Solar Neutrinos)
Test of geophysical models (“Geo-neutrinos”)

35. LAGUNA Large Apparatus for Grand Unification and Neutrino Astrophysics
100m
LAGUNA Large Apparatus for Grand Unification and Neutrino Astrophysics
30m
coordinated F&E “Design Study” European Collaboration, FP7 Proposal
APPEC Roadmap
LENA liquid scintillator 13,500 PMs for 50 kt target Wasser Čerenkov muon veto
MEMPHYS Water Čerenkov 500 kt target in 3 tanks, 3x 81,000 PMs
GLACIER liquid-Argon 100 kt target, 20m driftlength, 28,000 PMs foor Čerenkov- und szintillation

36. 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)

37. OBSERVING SN NEUTRINOS
n emission
Flavor conversion
Shock wave
EARTH
OBSERVING SN NEUTRINOS
sensitive to SN dynamics -> matter induced oscillation
Core Collapse
Event rate spectra
f : from simulations of SN explosions
P : from n oscillations + simulations (density profile)
s : (well) known
e : under control

38. Supernova neutrino luminosity (rough sketch)
T. Janka, MPA
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!

39. Galactic Supernova neutrino burst in LENA

40. Event rates in LENA

41. 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: x103 10kpc Aims - physics of the core-collapse (neutronisation burst, n cooling …) - determine neutrino parameters - look for matter oscillation effects (envelope, shock wave, Earth)

42. 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?

43. Separation of SN models ?
Yes, independent from oscillation model ! neutral current reactions in LENA
e.g. TBP KRJ LL
12C:
n p:
Lawrence, Livermore
Berkeley,Arizona
Garching, Munich
for 8 solar mass progenitor and 10 kpc distance

44. Conclusions
Low Energy Neutrino Astronomy is very successful (Borexino direct observation of sub-MeV neutrinos)
Strong impact on questions in particle- and astrophysics
New technologies (photo-sensors, extremely low level background…)
Strong European groups