First results from borexino and prospects of low energy neutrino astronomy
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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


First results from borexino and prospects of low energy neutrino astronomy

Neutrinos as probes ?

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

Flavor eigenstates

=

Mixing matrix

x

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 ?


First results from borexino and prospects of low energy neutrino astronomy

Intrinsic n 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 !


First results from borexino and prospects of low energy neutrino astronomy

Natural Neutrino Sources

(experimentally verified)

Sun

(since 1970)

Atmosphere (since ~1990)

Earth (since 2005)

Supernovae (1987)


First results from borexino and prospects of low energy neutrino astronomy

Natural Neutrino Sources

(not yet verified)

Big Bang

Active galactic nuclei ?

Supernovae remnants ?,

Gamma ray bursts ?,

Supernovae relic neutrinos ?...


First results from borexino and prospects of low energy neutrino astronomy

Thermal sources

Non-thermalsources

Energy Spectra of Astrophysical Neutrinos

low energy ~ 1 GeV ? high energy


First results from borexino and prospects of low energy neutrino astronomy

The dominating solar pp - cycle

H. Bethe

W. Fowler

pp - 1

pp -2

pp -3


The sub dominant solar cno cycle

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


First results from borexino and prospects of low energy neutrino astronomy

Neutrino Energy in MeV

Solar Neutrinos

GALLEX

GNO

SAGE

Integral

whole

spectrum

no spectral

information

BOREXINO

Since august 2007

7-Be neutrinos

SuperK, SNO

Directional

information


First results from borexino and prospects of low energy neutrino astronomy

  • History of solar neutrino experiments at 2007

  • All experiments were successful

  • Discovery of neutrino

  • oscillations

  • Probing thermal

  • fusion reactions


Oscillations and matter effects

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 10 MeV

Vaccum regime Matter regime


Borexino

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

Milano

Perugia

Borexino Collaboration

Genova

Princeton University

APC Paris

Virginia Tech. University

Munich

(Germany)

Dubna JINR

(Russia)

Kurchatov

Institute

(Russia)

Jagiellonian U.

Cracow

(Poland)

Heidelberg

(Germany)


First results from borexino and prospects of low energy neutrino astronomy

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


Borexino detector layout

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


First results from borexino and prospects of low energy neutrino astronomy

The ideal electron recoil spectrum due to solar neutrino scattering

pp

7-Be

CNO, pep

8B


Energy spectrum no cuts

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


Muon cuts

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


Outer detector efficiency

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

Fiducial volume cut

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


Spectrum after muon and fiducial volume cuts

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


238 u and 232 th

t = 236 ms

t = 432.8 ns

b

b

a

a

212Bi

214Bi

212Po

214Po

210Pb

208Pb

~700 KeV eq.

~800 KeV eq.

3.2 MeV

2.25 MeV

238U and 232Th

212Bi-212Po

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/b Separationin 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


7 be signal fit without a b subtraction

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


7 be signal fit a b subtraction of 210 po 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

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 (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 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 p ee for solar n e

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

5.5 - 15

Energy in MeV


Prospects of borexino

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


Cno and pep neutrinos

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


Laguna

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

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”)


First results from borexino and prospects of low energy neutrino astronomy

LAGUNALarge Apparatus for Grand Unificationand Neutrino Astrophysics

100m

30m

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

  • 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


First results from borexino and prospects of low energy neutrino astronomy

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!


First results from borexino and prospects of low energy neutrino astronomy

Galactic Supernova neutrino burst in LENA


First results from borexino and prospects of low energy neutrino astronomy

Event rates in LENA


First results from borexino and prospects of low energy neutrino astronomy

SN Neutrino predicted ratesvary 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)


First results from borexino and prospects of low energy neutrino astronomy

  • Matter effectsin 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 ?

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

    e.g. TBPKRJLL

    12C: 700 950 2100

    n p: 1500 2150 5750

Lawrence, Livermore

Berkeley,Arizona

Garching, Munich

for 8 solar mass progenitor and 10 kpc distance


Conclusions

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


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