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First Results from BOREXINO and Prospects of Low Energy Neutrino Astronomy. Oxford University and RAL November 20 th and 21st Lothar Oberauer, Physikdepartment E15, TU München. Neutrinos as probes ?. Interactions w w,e w,e,s. Charge 0 -1 +2/3 -1/3.

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First results from borexino and prospects of low energy neutrino astronomy

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

Neutrinos as probes ? Neutrino Astronomy

Interactions w w,e w,e,s

Charge 0 -1 +2/3 -1/3

Neutrinos undergo only weak interactions:

No deflection in electric or magnetic fields, extremely penetrating => n‘s areperfect carriers of information from the centers of astrophysical objects

Neutrino mixing
Neutrino Mixing Neutrino Astronomy

Flavor eigenstates


Mixing matrix


Mass eigenstates

2 mixing angles are measured: Q12 ~ 340 Q23 ~ 450

m23 – m22 ~ 2.6 x 10-3 eV2atmospheric n and accelerator n exp.

m22 – m21 ~ 8 x 10-5 eV2 solar and reactor n experiments

Open: Q13 ? CP violating phase d ?

Absolute mass scale (mn < 2.2 eV) ? Mass hierarchy ?

Intrinsic Neutrino Astronomyn parameters (particle physics)

Low energy n astronomy

  • 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 !

Natural Neutrino Sources Neutrino Astronomy

(experimentally verified)


(since 1970)

Atmosphere (since ~1990)

Earth (since 2005)

Supernovae (1987)

Natural Neutrino Sources Neutrino Astronomy

(not yet verified)

Big Bang

Active galactic nuclei ?

Supernovae remnants ?,

Gamma ray bursts ?,

Supernovae relic neutrinos ?...

Thermal sources Neutrino Astronomy


Energy Spectra of Astrophysical Neutrinos

low energy ~ 1 GeV ? high energy

The dominating solar pp - cycle Neutrino Astronomy

H. Bethe

W. Fowler

pp - 1

pp -2

pp -3

The sub dominant solar cno cycle
The sub-dominant solar CNO - cycle Neutrino Astronomy

  • …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

Neutrino Energy in MeV Neutrino Astronomy

Solar Neutrinos







no spectral



Since august 2007

7-Be neutrinos

SuperK, SNO



Oscillations and matter effects
Oscillations and matter effects Neutrino Astronomy

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


Now additional

Improvement on


on pp-ne flux

1 10 MeV

Vaccum regime Matter regime

BOREXINO Neutrino Astronomy

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

Milano Neutrino Astronomy


Borexino Collaboration


Princeton University

APC Paris

Virginia Tech. University



Dubna JINR





Jagiellonian U.





BOREXINO in the Italian Gran Sasso Underground Laboratory in the mountains of Abruzzo, Italy,

~120 km from Rome


Nazionali del

Gran Sasso



~3500 m.w.e

External Labs

Borexino Detector and Plants

Borexino detector layout
BOREXINO Detector layout the mountains of Abruzzo, Italy,

Stainless Steel Sphere:

2212 PMTs + concentrators

1350 m3


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

Energy spectrum no cuts
Energy Spectrum (no cuts) scattering

14C dominates below 200 KeV

210Po NOT in eq. with 210Pb

Arbitrary units

Mainly external gs and ms


Statistics of this plot: ~ 1 day

Muon cuts
Muon cuts scattering

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


Outer detector efficiency
Outer Detector efficiency scattering

OD-efficiency ~ 99%

Total muon rejection power (incl. cuts ID) ~ 99.99%

Preliminary, exact numbers require more detailed studies


Distribution of events without OD-muon flag

Fiducial volume cut
Fiducial volume cut scattering

Rejection of external background (mostly gammas)

R < 3.3 m (100 t nominal mass)

Radial distribution

z vs Rc scatter plot





Spectrum after muon and fiducial volume cuts
Spectrum after muon and fiducial volume cuts scattering

210Po (only, not in eq. with 210Pb!)


85Kr+7Be n


Last cut: 214Bi-214Po and Rn daughters removal

238 u and 232 th

t scattering = 236 ms

t = 432.8 ns











~700 KeV eq.

~800 KeV eq.

3.2 MeV

2.25 MeV

238U and 232Th


232Th Events are mainly in the south vessel surface (probably particulate)



Only 3

bulk candidates (47.4d)

238U: < 2. 10-17 g/g

232Th: < 1. 10-17 g/g

A b separation in borexino
a scattering/b Separationin BOREXINO

a particles

Full separation at high energy

b particles


250-260 pe; near the 210Po peak

2 gaussians fit

a/b Gatti parameter

7 be signal fit without a b subtraction
7 scatteringBe 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


These bins used to limit 85Kr content in fit

7 be signal fit a b subtraction of 210 po peak

210 scatteringPo 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

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

The two analysis yield fully compatible results

Borexino 1st result astro ph 0708 2251v2
BOREXINO 1st result scattering(astro-ph 0708.2251v2)

  • Scattering rate of 7Be solar non electrons

    7Be n Rate: 47 ± 7STAT ± 12SYS c/d/100 t

Borexino and n oscillations
BOREXINO and scatteringn-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 p ee for solar n e
Survival probability P scatteringee for solar ne

Transition of vacuum to matter dominated n - oscillations predicted by MSW-effect

It implies m2 > m1


Gallium experiments: 8B and 7Be neutrinos subtracted !



0.63 ± 0.19




0.34 ± 0.04

SNO, SuperKamiokande


< 0.44


5.5 - 15

Energy in MeV

Prospects of borexino
Prospects of BOREXINO scattering

  • 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

Cno and pep neutrinos
CNO and pep Neutrinos scattering

  • 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

LAGUNA scattering

  • 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 scattering

  • 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”)

LAGUNA scatteringLarge Apparatus for Grand Unificationand Neutrino Astrophysics



coordinated F&E “Design Study”European Collaboration,FP7 Proposal

APPEC Roadmap

LENAliquid scintillator13,500 PMs for 50 kt targetWasser Čerenkov muon veto

MEMPHYSWater Čerenkov500 kt target in 3 tanks,3x 81,000 PMs

GLACIERliquid-Argon100 kt target, 20m driftlength,28,000 PMs foor Čerenkov- und szintillation

Lena diffuse sn background
LENA: Diffuse SN Background scattering

  • 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) scattering

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!

SN Neutrino predicted rates scatteringvary 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 @ 10kpcAims- physics of the core-collapse (neutronisation burst, n cooling …)- determine neutrino parameters- look for matter oscillation effects (envelope, shock wave, Earth)

  • Matter effects scatteringin 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
Separation of SN models ? scattering

  • Yes, independent from oscillation model ! neutral current reactions in LENA

    e.g. TBP KRJ LL

    12C: 700 950 2100

    n p: 1500 2150 5750

Lawrence, Livermore


Garching, Munich

for 8 solar mass progenitor and 10 kpc distance

Conclusions scattering

  • 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