Borexino and Solar neutrinos

Borexino and Solar neutrinos

Igor MachulinRRC “Kurchatov Institute”

On behalf of the Borexino CollaborationQuarks2008/May/

Quarks2008/May/

Borexino collaboration

Kurchatov Institute(Russia)

Dubna JINR(Russia)

Heidelberg(Germany)

Munich(Germany)Jagiellonian U.

Cracow(Poland)

Perugia

Genova

APC Paris

MilanoPrinceton University

Virginia Tech. University

St.-Petersburg INF (Russia)

99,77%p + p d+ e+ +

e

0,23%p + e - + p d +

e

3He+3He+2p

3He+p+e+

+e

~210-5 %84,7%

13,8%

0,02%13,78%3He + 4He 7Be +

7Be + e- 7Li + e7Be + p 8B

+

d + p 3He +

7Li + p ->+

8B 8Be*+ e+ +e

2

Solar neutrinos from nuclear reactions in the Sun core , dominant pp cycle.

Quarks2008/May/ Igor Machulin , RRC “Kurchatov Institute “

Solar neutrinos from nuclear reactions in the Sun core, sub-dominant CNO cycle

LCNO / Lsun < 5-6%

(GALLEX/GNO+SAGE)

from CNO cycle had not yet been observed


…dominates in stars with more mass

than our sun…

=>Large astrophysical relevance

Solar neutrino spectrum according to the SSM (Bahcall-Serenelli 2005)

Borexino energy range for Solar neutrino measurements in Real-time

Quakrs2008/May/ Igor Machulin , RRC “Kurchatov Institute “

Oscillations and matter effects

Oscillation length ~ 102 km

=> oscillation smeared out

and non-coherent

Effective e 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 e suppression for those energies…

MSW Effect in Sun

Missing info herebefore BOREXINO

Now additionalImprovement on

uncertaintyon pp-e flux

Vaccum regime Matter regime

1 10 MeV

Experimental site for Borexino - Gran Sasso Laboratory

Laboratori Nazionali del Gran Sasso near L’Aquila, INFN.

Underground Lab provides shielding from cosmic background of 3500 m water equivalent


Water Tank: and n shield water Čherenkov detector208 PMTs in water2100 m3

20 legs

Scintillator:278 t PC+PPO (1,5 g/l) in150 m thick nylon vessel

Stainless Steel Sphere:2212 photomultipliers 1350 m3

2 Nylon vessels:Inner: 4.25 mOuter: 5.50 m

Borexino Detector Design

BOREXINO Design is based on the principles of graded shielding

Buffer :890 t PC+DMP(5

g/l)


PhotoMultiplierTube -PMT

Installation of PMTs on the sphere

Nylon vessel installation


Detector filling completed and data taking started- May 15th, 2007


Borexino Physics• Be-7 neutrino detection in real time mode

• pep, CNO and pp neutrino detection

• B-8 neutrino detection

• Measurement of neutrino magnetic moment

with the sensitivity of few* 10-11B level

• Geo and reactor antineutrinos

• Supernova detection

• Rare processes studies (electron decay, neutrino decay etc.)

e Lie Be 77

Monochromatic E=862 KeV

SSM=4.8x109 / (s*cm2)


Detection principles x + e- -> x + e-~10-44 cm2 Liquid scintillator (photon yield ~ 10000 photons/MeV)

High Light Yield = 500 photoelectrons/MeV Good energy resolution – 5% for 1 MeV

Very low energy threshold ~ 60 keV Good position reconstruction of eventsThe key requirement for measurements is the

extremely low radioactive contamination !To be less than Solar neutrino rate ~50 counts/(day*100 tons)

Simulated electron spectrum in Borexino

from Solar (SSM+LMA) and backgrounds

pp7Be

CNO, pep

8B

Electron recoil spectrum due to solar neutrino scattering


Light Yield and Energy Resolution

14C spectrum in Borexino detector(end point of decay-156 keV)

The Light Yield is calculated by global fit on the experimental Borexino spectrum:

14C – 156 keV end-point,

11C – + decay, Q=1.98 MeV

7Be Compton edge - 665 keV

210Po alpha peak resolution - 210Po

Light yield = 500 pe/MeV Energy resolution is obtained from

210Po alpha-decays peak ( Q=5.41 MeV, quenched by a factor ~13)

/E = 5% at 1 MeV

14C content in Borexino scintillator- 2.7 * 10-18 14C/12C


Cosmic muon rejection in Borexino

after μ cut

• Cosmic μ flux - 1.21±0.05 h-1m-2

• μ detected in Outer and Inner Detector • Outer Detector efficiency > 99%• Inner Detector μ analysis is based

on time pulse shape variables

• Estimated overall rejection factor: > 104

After cuts, background:

< 1 c/d/100 ton Measured μ angular distributions


Position reconstruction of events– Based on time of flight fit to the time distribution of detected photoelectrons– cross checked on selected events : 14C, 214Bi-214Po, 11C, external gammas, teflon laser

light diffusers on the Inner Vessel detector surface.

Spatial resolution of reconstructed events: 16 cm at 500 keV scaling as (Npe)-1/2

Quarks2008/May/

external eventson the surface

R=4.25m.

Radius (m)

1,25 m of scintillator in all directions assures a shielding for the background from the PMTs and the nylon of the vessel. Additional cut |z|<1.7m

Total effective fiducial volume after the position cut - 78.5 tons

Igor Machulin , RRC “Kurchatov Institute “

Radius cut

Internal events R<4.25m.

/ discrimination of events

particles

Small deformation due to averageSSS light reflectivity

particles

near the 210Po peak low energy side of the 210Po peak

2 gaussians fit 2 gaussians fit

Full separation at high energy

ns

Gatti parameter Gatti parameter Quarks2008/May/

GATTI Parameter is applied to the statistical subtraction of

Igor Machulin , RRC “Kurchatov Institute “

Background - 232Th content in scintillator

212Bi 212Po 208Pb

= 432.8 ns

2.25 MeV ~800 KeV eq.

=423±42 ns

232Th: (6.8+-1.5)×10-18 g/g – 0.25 cpd/100 tons

z (m

)

2 2cR x y (m)Time

(ns)


212Bi-212Po correlated events in the scintillator

Background - 238U content in scintillator

214Bi 214Po 210Pb

= 236 s

3.2 MeV ~700 KeV eq.

=240±8 s

Time (s)

2 2cR x y (m)

z (m

)

238U: (1.9+-0.3)×10-17 g/g - 2 cpd/100 tons


214Bi-214Po correlated events in the scintillator:

Background- other contaminants in scintillator

(~ 60 cpd/ton was inserted during the scintillation filling) - 210Po background is related neither to 238U contamination nor to 210Pb contamination -it is decaying with a 200 days-removed from the spectrum via discrimination technique

85Kr - -decayQ=687 keV

210Po - -decayQ=5.41 MeV , LY quenched by a factor~13

studied by delayed coincidence: 85Rb85Kr 85mRb

= 1.46 s - BR: 0.43%

514 keV

173 keV

the 85Kr contamination (29+-14) counts/day/100 ton


New experimental results for 192 days of live time (16 May 2007 – 12 April)

Cou

nts

/(5

ph

otoe

lect

ron

s *

day

* 1

00 t

ons)

– to be published these days at arXiv:08xxxxxv1


Photoelectron raw charge spectrum in Borexino

Spectral fit of the energy spectrum with statistical subtraction (192 days)


• Oscillation predictions for Mikheev-Smirnov Large Mixing Angle Solution:In Solar model BPS07(GS98) HighZ 48 ± 4 c/100t/dIn Solar model BPS07(AGS05) LowZ 44 ± 4 c/100t/d• No oscillation hypothesis

75 ± 4 c/100t/d

Survival probability for 7Be νe - Pee=0.56 ± 0.10

The no oscillation hypothesis Pee=1 is rejected at 4 level

BOREXINO new result192 days of live time

49 ± 3stat ± 4syst 7Be ν counts / (day · 100 ton)


BOREXINO

Prospects of Borexino- pep and CNO Solar fluxes - Main problem: 11C production by cosmic

11C 11B +e+ +e (Q = 1.98 MeV, T1/2=20.4min), tagging in 3-fold delayed coincidence , n (~ms) ,

track reconstruction + position of n-capture veto region around this

position for ~ 1 hour. Required rejection factor ~ 10

- neutrino magnetic moment search :

CNO

- 8B Solar flux measurements

pep11C

Sensitivity on at few * 10-11B level (like in best reactor experiments);

with Solar and dedicated measurement with artificial 51Cr source

Quarks2008/May/2008 Igor Machulin , RRC “Kurchatov Institute “

- Geo & reactor antineutrinos

Prospects of Borexino

- Supernova neutrinos detection

Detection channel Any hierarchy

Inverse-Beta Decay(E > 1.8 MeV)

79

-p ES(E > 0.25 MeV)

55

12C()12C* (E = 15.1 MeV)

17

Standard SN at 10kpc


Monitoring of CERN neutrino beam • The SPS CERN primary proton beam at 400

GeV is focused onto a graphite target, producing secondary mesons. Neutrinos are produced in a 900 m length vacuum tunnel by the decay in flight of high momentum p+ and K+ selected and focused towards the Gran Sasso Laboratory - 730 km .

• The neutrino beam contains predominantly muon neutrinos with an average energy of 17 GeV, and a contamination of anti e and anti-e at the level of 10-2. The beam to Gran Sasso will restart in summer 2008.

Direction of detected passing muons, generated by CERN beam in Borexino detector (Sept.-Oct. 2007)


Total Scintillator Mass 0.2

Fiducial Mass Ratio 6.0

Live Time 0.1

Detector Resp. Function

6.0

Cuts Efficiency 0.3

Total 8.5

Systematic (1σ) Error [%]

More Info

Spectral fit of the energy spectrum (192 days) before statistical subtraction


Neutrino Oscillations

(1,2,3)

( , , )

i i

i

U

neutrino mass eigenstates

neutrino flavor eigenstates e

cos , sinij ij ij ijc s

U:

Pontecorvo-Maki-Nakagawa-Sakata matrix (the analog of the CKM matrix in the hadronic sector of the Standard Model).

i : Non-zero only of neutrinos are Majorana particles and do not enter the oscillation phenomena regardless. If neutrinoless double beta decays occurs, these factors influence its rate.

The phase factor is non-zero only if neutrino oscillation violates CP symmetry.

The two neutrino case

cos sin

sin cosU

The probability that a neutrino originally of flavor will later be observed as having another flavor is given by:

222 2

2( ) sin 2 sin 1.267

m L GeVP t

eV km E

Oscillation parameters: Solarolar

Atmospheric

2m0.6 5 20.48.0 10 eV

0.6 3 20.52.4 10 eV

0 2.4

2.233.9

045 7

Solar neutrino oscillations and atmospheric oscillations are decoupled:

Chooz reeactor result - Theta(1,3) < 13O

Documents

Borexino and Solar neutrinos