Results from Borexino

Results from Borexino

Davide Franco CNRS-APC

NOW 2012September 9-16, 2012

Davide Franco – APC CNRS – NOW2012

Detector layout and radiopurity

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

Carbon steel plates

Scintillator:270 t PC+PPO in a 150 m thick nylon vessel

Stainless Steel Sphere:2212 PMTs 1350 m3

Nylon vessels:Inner: 4.25 mOuter: 5.50 m


Detection principles and signature

Borexino detects solar via their elastic scattering off electrons in a volume of highly purified liquid scintillator Mono-energetic 0.862 MeV 7Be neutrinos: main target Mono-energetic 8B, pep, CNO and possibly pp neutrinos

Detection via scintillation light: Very low energy threshold Good position reconstruction Good energy resolutionBUT… No direction measurement The induced events can’t be

distinguished from other events due to natural radioactivity

RadioIsotope Concentration or FluxName Source Required Achieved

cosmic ~ 10-10 <10-10

14C Intrinsic PC/PPO ~ 10-18 ~ 10-18

238U Dust < 10-16 g/g ~ 2 10-17

232Th Organometallic (?) (in scintillator) ~ 7 10-18

210Po Surface contam. ~ 1485Kr Air (nitrogen) < 1 c/d/100 t = 25±3

Extreme radio-purity of the scintillator is a must!


Detector Calibration

May 2007

Detector response vs position:100 Hz 14C+222Rn in scintillator in >100 positions

Quenching and energy scale:Beta: 14C, 222Rn in scintillatorAlpha: 222Rn in scintillatorGamma: 139Ce, 57Co, 60Co, 203Hg, 65Zn, 40K, 85Sr, 54MnNeutron: AmBe

MC-G4BxData

Pulse shape of 14C events

LY ~ 500 p.e./MeV Ph.Y. ~ 12000 photons/MeV

Data - MC


7Be neutrino (862 keV) rate @ 4.6%Phys. Rev. Lett. 107, (2011) 141302

740 live days

MC Fit

Analytical Fit

Systematics


Implication of the 7Be measurement

No oscillation excluded @ 5.0 Assuming MSW-LMA: f7Be= 0.97± 0.09 fpp = 1.013 +0.003

-0.010

fCNO < 1.7% (95 % C.L.)

Pee = 0.51 ± 0.07 @ 867 keV no power to resolve low/high metallicity problem

< 5.4 10-11 b

Neutrino magnetic moment limit:


The Day-Night Asymmetry

Adn = 0.001 ± 0.012 (stat) ± 0.007 (syst)

LOW ruled out at 8.5

A neutrino “regeneration” is expected only in the LOW

solution


8B neutrinos with the lowest threshold: 3 MeV

2.6 MeV ’s from 208Tl on PMT’s and in the buffer

All volume

R < 3 m (100 tons)

Energy spectrum in Borexino (after subtraction)

Expected 8B rate in 100 tons of liquid scintillator above 2.8 MeV:0.26±0.03 c/d/100 tons

> 5 distant from the 2.6 MeV peak S/B ratio < 1/6000!!!

live-time: 246 days


8B neutrino rate measurement

raw spectrum

cut

FV cut

cosmogenic, neutron, 214Bi and 10C cuts

208Tl

3.0-16.3 MeV 5.0-16.3 MeV

Rate [c/d/100 tons] 0.22±0.04±0.01

0.13±0.02± 0.01

ESexp [106 cm−2s−1] 2.4±0.4±0.1 2.7±0.4±0.2

ESexp/ES

th 0.88±0.19 1.08±0.23


First observation of pep neutrinos

+ 12C → + 11C + n+ p → d +

→11B + e+ + e

Three Fold Coincidence (TFC): space-time veto removes 90% of 11C

paid with 50% loss of exposure

11C ~ 30 min


o-Ps in scintillators

Measurements of the o-Ps mean-life and formation

probability in scintillators with the PALS technique

D. Franco, G. Consolati, D. Trezzi, Phys. Rev. C83 (2011) 015504

Pulse shape induced distortion

MC

~ 3 nsp ~ 50%


Multivariate maximum likelihood fit

Energy spectral fit

Radial fitPulse shape fit

Pulse shape test


pep neutrinos: results

pep neutrinos: Rate: 3.1 ± 0.6(stat) ± 0.3(sys) cpd/100 t Assuming MSW-LMA: Φpep = 1.6 ± 0.3 108 cm-2 s-1

No oscillations excluded at 97% C.L. Absence of pep solar ν excluded at 98%

CNO neutrinos: only limits, correlation with 210Bi; CNO limit obtained assuming pep @ SSM CNO rate < 7.1 cpd/100 t (95% c.l.) Assuming MSW-LMA: ΦCNO < 7.7 108 cm-2 s-1 (95% C.L.)

the strongest limit to date not sufficient to resolve metallicity problem

Δχ2 profile for fixed pep and CNO rates

Borexino limit


The Borexino Solar neutrino spectroscopy


Status and future perspectives

Since July 2010, purification campaigns:• Nitrogen stripping successful in 85Kr removal:85Kr < 8.8 cpd / 100 t (2007-2010: 31.2 ± 5) • moderate success in 210Bi removal by water extraction:

210Bi : (16 + 4) cpd / 100 t (2007-2010: 41.0 ± 2.8) • unprecedented 238U and 232Th radio-purity:

238U < 9.7 10-19 g/g and 232Th < 2.9 10-18 g/g • 210Po natural decreasing:

~5 cpd / t Borexino phase II started:• Solar neutrino program:

- Improve 7Be, 8B → test of MSW- Confirm pep at more than 3 σ - Improve upper limit on CNO → probe metallicity- Attempt direct pp measurement

• more statistics for an update of geo-neutrino measurement;• another long-term scientific goals under discussion (sterile?)


A glance at the Borexino physics results

Neutrino speed: Measurement of CNGS muon neutrino speed with Borexino, submitted

Pep & CNO limit : First evidence of pep solar neutrinos by direct detection in Borexino, Phys. Rev. Lett. 108 (2012) 051302. 7Be ADN: Absence of day--night asymmetry of 862 keV 7Be solar neutrino rate in Borexino and MSW oscillation parameters, Phys. Lett. B 707 (2012) 22. 7Be @ 5%: Precision measurement of the 7Be solar neutrino interaction rate in Borexino, Phys. Rev. Lett. 107 (2011) 141302.

Solar antinu limits: Study of Solar and other unknown anti-neutrino fluxes with Borexino at LNGS, Phys. Lett. B696 (2011) 191-196.

Geo-nu: Observation of Geo-Neutrinos, Phys. Lett. B687 (2010) 299-304.

8B > 3 MeV: Measurement of the solar 8B neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector, Phys. Rev. D82 (2010) 033006.

7Be @ 10%: Direct Measurement of the Be-7 Solar Neutrino Flux with 192 Days of Borexino Data, Phys. Rev. Lett. 101 (2008) 091302.

7Be @ 17%: First real time detection of Be-7 solar neutrinos by Borexino, Phys. Lett. B658 (2008) 101-108

+ muon modulation + cosmogenics + axions + Pauli principle + magnetic moment + ….


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


Backup


Geo-neutrinos: results

Null hypothesis rejected at 4.2

Documents

Results from Borexino