Observation of the geo-ν's and reactor anti-ν's in Borexino Yury Suvorov INFN (LNGS) / RRC...

Observation of theObservation of thegeo-ν's and reactor anti-ν'sgeo-ν's and reactor anti-ν's

in Borexino in Borexino

Yury SuvorovYury SuvorovINFN (LNGS) / RRC Kurchatov INFN (LNGS) / RRC Kurchatov

Inst.Inst.

APC 28th April 2010, Paris

((on behalf of the Borexino collaborationon behalf of the Borexino collaboration))


Historical introductionHistorical introductionGamoGamoww in the letter to Reines (1953) in the letter to Reines (1953)::

“Dear Fred,...your background neutrinos may just be coming from high energy β-decaying members of U and Th families in the crust of the Earth.”

G. Marx, N. Menyard Mitteilungen der G. Marx, N. Menyard Mitteilungen der Sternwarte, Budapest, 48 (1960):Sternwarte, Budapest, 48 (1960):

First estimation of the anti-neutrino fluxes from U,Th and K.

М.А.Мarkov М.А.Мarkov ““НейтриноНейтрино””, М., Nauka (1964), М., Nauka (1964)::

First proposal to use the reaction of inverse β decay for the geo-nu registration.

Gernot Eder Nucl Phys 78 (1966) Terrestrial Gernot Eder Nucl Phys 78 (1966) Terrestrial neutrinos:neutrinos:

Idea to determine chemical composition of some elements by the study of the emited neutrinos.


Geo-Geo-ν'sν's

Emax(K) = 1.3 MeV

Emax(U) = 3.26 MeV

Emax(Th) = 2.25 MeVEarth shines mainly in the Earth shines mainly in the anti-ν's.anti-ν's.

Geo-neutrinos are Geo-neutrinos are the electron anti-the electron anti-neutrinos produced neutrinos produced in the beta decays in the beta decays of of 4040K, K, 238238U and U and 232232Th Th isotopes, which are isotopes, which are naturally present in naturally present in the Earth interior.the Earth interior.


GeoGeo-ν fluxes around -ν fluxes around the worldthe world

36.531.634.5Kamioka

55.050.750.8Baksan

50.447.950.8Sudbury

43.140.540.7Gran Sasso

32.5Curacao

13.4

52.4

Enomoto et al. (2005)

12.5

51.3

51.5

Mantovani et al. (2004)

13.4

49.9

Fogli et al. (2005)

Signal from U+Th[TNU]

Hawaii

Homestake

Pyhasalmi

1 TNU = 1 ev in 101 TNU = 1 ev in 1032 32 protons / yrprotons / yr

Importance of the geological location of the detector Importance of the geological location of the detector (Crust/Mantle)(Crust/Mantle)Expected in Borexino rate is about Expected in Borexino rate is about 5 ev/yr5 ev/yr


KamLANDKamLAND20052005 – First try of – First try of““Experimental Experimental investigation of investigation of geologically produced anti-geologically produced anti-neutrinos” neutrinos” Nature 436, 499-503 (28 July 2005)Nature 436, 499-503 (28 July 2005)

““Assuming a Th/U mass Assuming a Th/U mass concentration ratio of 3.9, concentration ratio of 3.9, the 90 per cent confidence the 90 per cent confidence interval for the total interval for the total number of geoneutrinos number of geoneutrinos detected is 4.5 to 54.2.”detected is 4.5 to 54.2.”

20082008 - new results based on the - new results based on the greater statistics yield 73±27 ev (~ greater statistics yield 73±27 ev (~ 2.5σ)2.5σ)

““The indication of an excess of low-The indication of an excess of low-energy anti-neutrinos consistent with energy anti-neutrinos consistent with an interpretation as geo-neutrinos an interpretation as geo-neutrinos persists.” persists.” Phys. Rev. Lett. 100 (2008) 221803Phys. Rev. Lett. 100 (2008) 221803


Heidelberg(Germany)

Kurchatov Institute(Russia)

Dubna JINR(Russia)

Munich (Germany)Jagiellonian U.

Cracow(Poland)

Perugia

Genova

APC Paris

Milano

Princeton University

Virginia Tech. University

Borexino collaborationBorexino collaboration

About 160 collaborators from 6 About 160 collaborators from 6 countriescountries

Borexino detectorBorexino detector

Stainless Steel Sphere (d= 13.7 m, Volume = 1340 m3)


2212 8” ETL 9351 PMTs mounted inside the SSS

Water Tank (d=18 m, V = 2400 m3) Shielding from γ and n. Water Cerenkov detector (Muon Veto) 208 PMTs 20 supporting legs

Two Nylon balloons:

Inner Vessel (8.5 m, V = 340 m3) filled with 278 tons of scintillator (PC + 1.5 g/l of PPO)

Inner Buffer (11.5 m) filled with PC + DMP


Anti-ν detectionAnti-ν detection

Inverse beta decay reactionInverse beta decay reaction. .

Correlated in space and time pair of signals: Correlated in space and time pair of signals:

EEthth=1.806 MeV=1.806 MeV

1) 1) Prompt signalPrompt signal:: Positron + 2 Positron + 2 γγ from annihilation with efrom annihilation with e--, , EEγγ=0.511 =0.511 MeVMeV

After t~250μs After t~250μs

2) 2) Delayed signalDelayed signal:: Neutron capture Neutron capture on Hydrogenon Hydrogen - γ of - γ of EEγγ=2.2 MeV=2.2 MeV

The unprecedentedly low intrinsic radioactivity of The unprecedentedly low intrinsic radioactivity of Borexino, the high photon yield and large number of Borexino, the high photon yield and large number of

free target protons (~ 1.7x10free target protons (~ 1.7x103131) offer a unique tool for ) offer a unique tool for the anti-ν study in the MeV energy range.the anti-ν study in the MeV energy range.

+e+np+ν ~


AntiAnti-ν sources -ν sources

Electron anti-Electron anti-νν from from thethe

Nuclear Power Nuclear Power plantsplants

Electron anti-Electron anti-νν from from

The Earth The Earth InteriorInterior


Reactor antiReactor anti-ν's-ν's

Knowledge of the exact duty cycle and the fuel Knowledge of the exact duty cycle and the fuel composition of the nuclear plants is of the crucial composition of the nuclear plants is of the crucial importance!importance!

Nominal thermal power and monthly load factors for Nominal thermal power and monthly load factors for each European plant from the IAEA and EDF.each European plant from the IAEA and EDF.

Main contribution from from 194 European nuclear 194 European nuclear plants.plants. 245 plants from the rest 245 plants from the rest of the world give 2.5 %.of the world give 2.5 %.

3 most powerful power 3 most powerful power plants in France giveplants in France give 13% of the total signal.13% of the total signal.

Mean-base line: 1000 kmMean-base line: 1000 km((~~60% of total flux)60% of total flux)


Reactor antiReactor anti-ν spectrum-ν spectrumExpected inExpected in Borexino Borexino::

In the whole spectrum andIn the whole spectrum and in case in case of of 100% detection efficiency:100% detection efficiency:

Without oscill.Without oscill. : : 9.9±0.59.9±0.5 events/(events/(100 ton yr100 ton yr))

With oscillationsWith oscillations: : 5.7±0.35.7±0.3 events/(events/(100 ton yr100 ton yr) )

~~15 cpy15 cpy

Only 35% in the geo-neutrino Only 35% in the geo-neutrino window ~window ~5 cpy!5 cpy!

The diff. reactor anti-The diff. reactor anti-ν spectrum in ν spectrum in units of (anti-units of (anti-νν/MeVcm/MeVcm22))

Sys. errors on the expected Sys. errors on the expected signalsignal

ii - P.huber,T.Shwetz, Phys.Rev D70 (2004)- P.huber,T.Shwetz, Phys.Rev D70 (2004)


Geo-Geo-ν signal in Borexinoν signal in Borexino

Emax(K) = 1.3 MeV

Emax(U) = 3.26 MeV

Emax(Th) = 2.25 MeV

Expected in Borexino signal from the geo-ν's Expected in Borexino signal from the geo-ν's obtained from the BSE model (obtained from the BSE model (Mantovani et Mantovani et

al. 2004al. 2004): ):

2.5 events/100ton yr2.5 events/100ton yr

Ideal expected spectrumIdeal expected spectrum


Calibrations 2008-2009Calibrations 2008-2009

Energy scale and quenching:Energy scale and quenching:

: 14C, 222Rn in scintillator

: 222Rn in scintillator

: 139Ce, 57Co, 60Co, 203Hg, 65Zn, 40K, 85Sr, 54Mn

NeutronNeutron: 241Am-9Be (protons recoil study)

Detector response vs position:Detector response vs position:100 Bq 14C+222Rn in scintillator in >100 positions.Improved position reconstruction. We reduced the reduced the

error on the FV down to 3.8%error on the FV down to 3.8% (old value 6%)

Detailed study of the detector. Over 300 Detailed study of the detector. Over 300 on-on-

axisaxis and and off-axisoff-axis positions. positions.

Improved understanding of energy scale:

(from 120 keV 120 keV up toup to 9.3 MeV 9.3 MeV)

Monte Carlo code is tuned to take into account non-linearities of the

energy scale (ionization quenching, electronics)


MC spectra Geo+Reactors MC spectra Geo+Reactors

The expected prompt positron event spectrum in Borexino after The expected prompt positron event spectrum in Borexino after taking into account the position and energy response of the taking into account the position and energy response of the

detector, MC.detector, MC.


Candidates selectionCandidates selection

1) Q1) Qprompt prompt > 410 p.e.> 410 p.e.

2) 700 p.e. < Q2) 700 p.e. < Qdelayed delayed

<1250 p.e.<1250 p.e.

3) ∆R< 1m 3) ∆R< 1m

4) 20µs < ∆t < 1280µs4) 20µs < ∆t < 1280µs

5) R5) RIV IV – R– R

prompt prompt > 0.25m > 0.25m

The data set used for the analysis is The data set used for the analysis is 537.2 live days537.2 live days

(Dec. 2007 - Dec. 2009)(Dec. 2007 - Dec. 2009)

Total detection efficiency determined with MC isTotal detection efficiency determined with MC is

0.850.85±0.01±0.01


BaBackground sourcesckground sources

Radiogenic fake anti-ν'sRadiogenic fake anti-ν's 1) (α,n) reaction 1) (α,n) reaction

Cosmogenic fake anti-ν's Cosmogenic fake anti-ν's ((muon muon induced backgroundinduced background)) 1) Fast neutrons;1) Fast neutrons; 2) Spallation isotopes (2) Spallation isotopes (99Li,Li,88He)He)

Accidental coincidencesAccidental coincidences

Search for the background capable to mimic the Search for the background capable to mimic the anti-ν signature (anti-ν signature (fakefake anti-ν's) anti-ν's)


Fake anti-ν (Fake anti-ν (210 210 Po)Po)

0.00.021±0.00221±0.002 ev/(100 t yr) ev/(100 t yr)

210210Po is the main contaminant in Borexino Po is the main contaminant in Borexino ( (~~12 cpd/t on avarage in present data 12 cpd/t on avarage in present data set);set);

Low abundance of Low abundance of 1313C (1.1 %);C (1.1 %);

Probability for the reaction to occur: (5.0Probability for the reaction to occur: (5.0±±0.3) 100.3) 10-8-8

1313C(α,n)C(α,n)1616O reactionO reaction

Two correlated in time and Two correlated in time and space events:space events:

PromptPrompt - beta from decay of - beta from decay of 1616O, O, or recoil proton;or recoil proton;

DelayedDelayed – gamma from the – gamma from the neutron capture on neutron capture on 11H;H;


Fast neutronsFast neutrons

Flux of fast neutrons from the Flux of fast neutrons from the surrounding rock in Hall C was surrounding rock in Hall C was studied with MC. Measurements studied with MC. Measurements obtained by Macro and LVD obtained by Macro and LVD (D.M. Mei and A. Hime, Phys. Rev. D 73, 053004 (2006)) as an input for the simulations.as an input for the simulations.

Fast neutrons can also fake the Fast neutrons can also fake the anti-ν signal (two signals anti-ν signal (two signals correlated in space and time):correlated in space and time):

1) recoil proton 1) recoil proton 2) gamma from the neutron 2) gamma from the neutron capture.capture.

Borexino shieldingBorexino shielding::2 m of water and2 m of water and

2.5 m of PC (buffer)2.5 m of PC (buffer)

Muons can generate neutrons Muons can generate neutrons from the from the Rocks, Water.Rocks, Water.


Muon induced fast Muon induced fast nn's's

µµµµ

µµ µµ µµ

nn nnnn

nn

nn

Hall C, LNGS

~ 3800 mwe~ 3800 mwe

ΦΦµµ = 1.2 = 1.2 µ/mµ/m22/hr/hr

<E<Eµµ> = 320 GeV> = 320 GeV

RRµ µ IVIV

≈≈ 4200 cpd 4200 cpd

ΦΦrockrocknn = = 7.3x10 7.3x10-10-10cmcm-1-1ss-1-1

<E<Erockrocknn> = 90 MeV> = 90 MeV

- Muon Veto - Muon Veto inefficiency is 99.5 % inefficiency is 99.5 %

- 2ms veto after each - 2ms veto after each WT muon remove more WT muon remove more then 99.5% of WT then 99.5% of WT neutrons;neutrons;

< 0.01 ev / (100 ton yr) < 0.01 ev / (100 ton yr) (90% C.L.)(90% C.L.)


Fast Fast nn's from the rock's from the rockOverall statistics of 5x10Overall statistics of 5x1066 neutrons generated on the neutrons generated on the surface Water Tank. 10 MeV < En < 3.5 GeV. surface Water Tank. 10 MeV < En < 3.5 GeV.

160 events in the IV (reduction factor ~10160 events in the IV (reduction factor ~1044))

< 0.04 ev / (100 ton yr) < 0.04 ev / (100 ton yr) (90% C.L.)(90% C.L.)

Only 1 pair of correlated in time events (fake anti-Only 1 pair of correlated in time events (fake anti-neutrino)neutrino)


Spallation IsotopesSpallation Isotopes

Cosmic ray muons Cosmic ray muons crossing the crossing the scintillator can create scintillator can create the radioactive the radioactive isotopes by the isotopes by the spallation of the spallation of the 1212C C atoms.atoms.

Some of these isotopes Some of these isotopes can decay via can decay via -n -n cascade perfectly cascade perfectly mimicking anti-nu mimicking anti-nu signature.signature.Expected in Borexino rate: Expected in Borexino rate: (0.096 ± (0.096 ±

0.019) ev/d0.019) ev/d (T.Hagner et all Ast. Phys. 14 (2000) 33-47)


99Li-Li-88He isotopesHe isotopes


99Li-Li-88He isotopesHe isotopes

Application of 2s veto (8 tau) after each passing muon sufficiently Application of 2s veto (8 tau) after each passing muon sufficiently removes all such events, however this brings to the removes all such events, however this brings to the 10% reduction of 10% reduction of the expositionthe exposition..

Dedicated study: 2s window after each muon. 51 candidates selected in Dedicated study: 2s window after each muon. 51 candidates selected in the whole period. Measured rate: the whole period. Measured rate: 15.4 events (100 ton yr)15.4 events (100 ton yr)

Remaining background from Li-He: Remaining background from Li-He: < 0.03± 0.02 ev/100t/y < 0.03± 0.02 ev/100t/y


Accidental coincidencesAccidental coincidences

0.080± 0.010 ev/(100t 0.080± 0.010 ev/(100t y)y)

The same energy cuts The same energy cuts for the prompt and for the prompt and delayed signals as in the delayed signals as in the anti-ν selection.anti-ν selection.

Off-time coincidence Off-time coincidence window of (2-20) s.window of (2-20) s.

Search for the time Search for the time corellated backgroundcorellated backgroundtime window of 2ms - time window of 2ms - 2s2s

Energy spectrum of the acc. Energy spectrum of the acc. coincidencecoincidence

<0.003 ev/(100t y)<0.003 ev/(100t y)


Background Background summarysummary

Expected signal from geo+reactors:Expected signal from geo+reactors: ~~5 + 5 + ~1~15 5


Selected anti-ν candidatesSelected anti-ν candidates

- Data set: from Dec. 2007 to Dec. 2009- Data set: from Dec. 2007 to Dec. 2009

- Total live time: 532.7 days- Total live time: 532.7 days

- Cosmogenic veto: 2s after each detected - Cosmogenic veto: 2s after each detected muon is muon is removed (~10% of live time)removed (~10% of live time)

- The fiducial exposure after all cuts: - The fiducial exposure after all cuts: 252.6 ton yr252.6 ton yr

- Total number of selected anti-ν - Total number of selected anti-ν candidates: candidates: 2121


21 selected candidates21 selected candidates


21 selected candidates21 selected candidatesExpected background is 0.40Expected background is 0.40±0.05!±0.05!

Signal/Background ~ Signal/Background ~ 50:150:1


Reactor anti-ν signalReactor anti-ν signalExpected reactor anti-ν signal in the Expected reactor anti-ν signal in the

reactor anti-ν window (E>1300 p.e.) 65% reactor anti-ν window (E>1300 p.e.) 65% of totalof total::

WithoutWithout oscillations: oscillations: 16.316.3±1.1 events±1.1 events

WithWith oscillation: oscillation: 9.49.4±0.6 events±0.6 events

Background: Background: 0.090.09±0.06 events±0.06 events

Observed:Observed: 6 events 6 events

Borexino

KamLANDChooz

Future

Exclusion of the non-oscillation hypothesis at 99.6% C.L.Exclusion of the non-oscillation hypothesis at 99.6% C.L.

Long mean-base line:Long mean-base line:

- effective distance is - effective distance is ~~1000 km 1000 km

- flux of 10- flux of 1055cmcm-2-2ss-1-1

GeoGeo ..

ReactorsReactors

65%65%35%35%


Observed Geo-Observed Geo-νν signal signal

In the geo-neutrino window E<1300 p.e:In the geo-neutrino window E<1300 p.e:

Expected from reactors Expected from reactors anti-νanti-ν : 5.0: 5.0±0.3±0.3 events events

Expected background : Expected background : 0.31±0.050.31±0.05 eventsevents

Observed:Observed: 1515 events events

GeoGeo ReactorsReactors

The best estimates for the The best estimates for the geo-geo-νν and and reactor anti-ν are:reactor anti-ν are:

events

events

68.3% (99.73) C.L.


Observed Geo-Observed Geo-νν signal signalevents

Scaling the obtained best estimation with Scaling the obtained best estimation with exposure of the 252.6 ton yr, the best Borexino exposure of the 252.6 ton yr, the best Borexino

measurement of the geo-ν signal becomes:measurement of the geo-ν signal becomes:

(F.Mantovani, G. Fiorentini, '04)(G.L.Fogli, '06)(C.G. Rothschild, '98)

Rate in events/(100 ton yr)Rate in events/(100 ton yr)

ByBy studying the profile of the studying the profile of the log-likelihood with respect to log-likelihood with respect to

the Nthe Ngeo geo we reject the null we reject the null hypothesis for geo-hypothesis for geo-νν signal signal at at

more then 3more then 3

Phys. Lett. B 687 (2010) 299-304Phys. Lett. B 687 (2010) 299-304

Hypothesis of a geo-reactor present in theHypothesis of a geo-reactor present in theEarth’s Core: Earth’s Core:

upper limit for a 3 TW at 95% C.L.upper limit for a 3 TW at 95% C.L.


Summary and Summary and PerspectivesPerspectives

First observation of geo-ν's with more then First observation of geo-ν's with more then 33σσ..

First indication of the electron anti-ν disappearance First indication of the electron anti-ν disappearance on the long on the long (1000 km) base line (2.9 (1000 km) base line (2.9 σσ).).

The possible presence of the natural geo-reactor The possible presence of the natural geo-reactor of > 3TW is excluded at 95% C.L.of > 3TW is excluded at 95% C.L.

Spectroscopic study of the geo-ν signal:Spectroscopic study of the geo-ν signal:

- Fully radiogenic or Min. radiogenic model?- Fully radiogenic or Min. radiogenic model? - U/Th mass ratio measurement?- U/Th mass ratio measurement?

The EndThe End

Observation of the geo-ν's and reactor anti-ν's in Borexino Yury Suvorov INFN (LNGS) / RRC...

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Transcript of Observation of the geo-ν's and reactor anti-ν's in Borexino Yury Suvorov INFN (LNGS) / RRC...