Validation of the neutrino oscillation model and first real ...static.sif.it/.../public/files/congr10/mc/ranucci.pdfBologna - 22 September, 2010 Gioacchino Ranucci - I.N.F.N. Sez

Bologna - 22 September, 2010 Gioacchino Ranucci - I.N.F.N. Sez. di Milano

Validation of the neutrino oscillation model and first real

observation of geoneutrinos with Borexino

1-Solar neutrinos and the SSM2-Performances of the Borexino detector3-Validation of the neutrino oscillation model throughthe solar neutrino measurements4-Observation of geoneutrinos

Gioacchino Ranucci - I.N.F.N. Sez. di Milano

on behalf of the Borexino Collaboration

SIF 2010 - Bologna


Neutrino production in the Sun

pp

ν from:pp

pep7Be8B

hep

The pp chain reactionThe CNO cycle

There are different steps in which energy (and neutrinos) are produced

Monocrhomatic ν’s(2 bodies in the final state)

In our star > 99% of the energy is created in this reaction

In the Sun < 1% More important in heavier stars

CNOν from:13N 15O 17F


Neutrino production in the Sun

Neutrino energy spectrum as predicted bythe Solar Standard Model (SSM)

John Norris Bahcall(Dec. 30, 1934 – Aug. 17, 2005)

•7Be: 384 keV (10%)• 862 keV (90%)

•Pep: 1.44 MeV

Surface metallicitycomposition controversy still open: High Z vs Low Z

http://en.wikipedia.org/wiki/December_30

http://en.wikipedia.org/wiki/1934

http://en.wikipedia.org/wiki/August_17

http://en.wikipedia.org/wiki/2005


Solar neutrino experiments: a more than four decadeslong saga

•Radiochemical experiments:

Homestake (Cl)

Gallex/GNO (Ga)

Sage (Ga)

•Real time Cherenkov experiments

Kamiokande/Super‐Kamiokande

SNO

•Scintillator experiments

Borexino


Long standing discrepancy between measured and predicted fluxes: SNPCulminated with a crystal clear proof that neutrino oscillates

Phys.Rev.Lett.101:111301,2008

Neutrino oscillations !

•MSW matter enhanced flavor conversion•LMA solution

SOLAR PLUSKAMLAND (Reactor ν’s)

519.021.0

2 1059.7 −+− ×=Δm

3.12.112 4.34 +

−=θ


“Solar” Issues still to be settled before Borexino

Extend to low energies the real time spectroscopic detection of solarneutrinos, also for 8B (SNO and Superkamiokande detected only solar ν’s above 4-5 MeV)

•Direct experimental determination of the following fluxes7Be (main Borexino motivation)CNO peppp

•Direct observation at low energy of the transition from vacuum tomatter dominated oscillation regimes (further test of the MSW-LMA solution tested up to now only for the high energy 8B ν’s)

Metallicity controversy about the solar surface composition (Flux value)


Other Physics Reachs (red that covered in the talk)

A powerful low background instrument like Borexino proved to be suited to

enrich its physics potential with goals beyond the main topic of solar neutrino

studies

-Geoneutrinos anti-ν’s from radioactive elements in the Earth’s crust and mantle

- Limit on anti-ν’s from the Sun

- Limit on non-Paulian transitions

- Limit on Neutrino magnetic moment


Borexino is located at LaboratoriNazionali of Gran Sasso nearL’Aquila, shielded by 1400 m ofrocks (3500 m water equivalent)

Experimental site


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


Physics and detection principles

Borexino aims to measure low energy solar neutrinos in real time byelastic neutrino-electron scattering in a volume of highly purified liquidscintillator

Mono-energetic 0.862 MeV 7Be ν is the main targetPep, CNO and possibly pp νGeoneutrinosSupernova ν

Detection via scintillation lightAdvantages:

Very low energy thresholdGood position recostructionGood energy resolution

Drawbacks:No direction measurementsν induced events can’t be distinguished from other β due to natural

radioactivity

Extreme radiopurity of the scintillator238U and 232Th : 10-16 g/g , nat K : 10-14 g/g


Detector design and layout

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

20 legsCarbon steel plates

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

Stainless Steel Sphere:2212 photomultipliers 1350 m3

Nylon vessels:Inner: 4.25 mOuter: 5.50 m

Design based on the principle of graded shilding


Radiopurity construction requirementsDetector and plants materials

Low intrinsic radioactivityLow radon emanation Chemical compatibility with PC

Pipes, vessels and pipesElectropolishedCleaned with filtered detergents

(Detergent-8, EDTA)Pickled and passivated with acidsRinsing with ultrapure water (class

20 – 50 MIL STD 1246 )Leak tightness

Leak rate < 10-8 atm cc /sNitrogen blanketing on critical

elements like pumps, valves, bigflanges

Double seal metal gaskets

Thorrn-EMI photomultipliersLow radioactivity Shott borosilicate

glass (type 8246)1.1 ns time gitter for good spatial

resolution(Al) light cones for uniform light

collection in the fiducial volumemu-metal shilding for the earth

magnetic field384 PMTs with no cones for muon

identification in the buffer region

Nylon vesselsGood chemical and mechanical

strength (small buoyancy)Low radioactivity (< 1 count/day/100

tons)Contruction in low 222Rn clean

roomHigh purity nitrogen storage

Clean roomsMounting room in class 100Inner detector in class 1.000 Outer detector in class 100.000


Nylon vesselsRequirements:

Chemical resistance to PC,PPO, DMP,water

Mechanical strength (20MPa – 5°ΔT)Optical transparency (350-450 nm)Low intrinsic radioactivity (U, Th, K)Clean fabrication (<3 mg dust)Low permeability ti RnLeak tightness

Solutions and results:Sniamid Nylon-6 film125 μm thick filmIndex of refract. = 1.53 with >90%

trasmittanceU, Th less than 2 pptUmidification to decrese the Tg glass

transition temperature (brittle state)


Auxiliary plants

Water plantInverse osmosis CDI deionizer Ultra-Q filter down to class 10Nitrogen stripping column 2 m3/h production rateU, Th: < 10-14 g/g222Rn: ~ 1 mBq/m3226Ra: <0.8 mBq/m318.2-18.3 MΩ/cm at 20°C

Distillation plants6 stages distillation column operating

at reduced pressure (80 mbar at 95°C)High reflux rate in the columnProduction rate up to 1000 l/hCounter current gas stripping column

with structure packingHumidified with water vapor 60-70%

Filling stationsSurface cleanlinessOperational flexibility

Nytrogen plantsExtremely pure for 39Ar 85Kr










Filled detector

PC filling completedMay 15th, 2007


Data acquisition ν-e scattering•The data taking with the whole scintillator started may 15th, 2007

•The main trigger fires with ≥ 25 PMTs detecting each 1 p.e., at least ,within 66-99 ns; En. threshold: ≈60 keV-the time and charge of each PMT, detected in 16.2ms, arerecorded

•Typical triggering rate: 11 cps (dominated by 14C)

•The time is measured by a TDC (res.≈0.5 ns); the charge by 8 bits ADC

•The OD gives a veto when ≥ 6 PMT fire (99.8 %of probability of mrejection)-- within 150 ns (after a m crossing the PC all events in 2 ms are rejected).The m rate in scintillator plus buffer is 0.055 s-1.

•The time and the total charge are measured, and the position is reconstructed for each event . Absolute time is also provided (GPS)

•Up to now accumulated about 900 live days of data taking


The Light Yield has been evaluated first fitting the 14C spectrum. ( β decay-156 keV,

end point)Borex. Coll. NIM A440,2000

The light yield has been evaluated also by taking it as free parameter in a global fit on the total spectrum(14C,210Po, σ 210Po ,

7Be ν Compton edge)

LY≈500 p.e./MeV(taking into account the β quenching factor)

Energy resolution: 5%/ √E(MeV)Position resolution: 16 cm at 500 keV(scaling as )Fid. Vol. definition ~ 75.5 tons

Detector performances

Np.e.−1/ 2


Intrisic background levels

238U: (1.6±0. 1) 10-17 g/gfrom214Bi-214Po

85Kr β decay- 687 keV

8 events 29±14 c/d

85Rb85Kr 85mRb

τ= 1.46 μs - BR: 0.43%

514 keV

β

173 keV

γ

232Th: (6.8±1.5) 10-18 g/gfrom 212Bi-212Po

210Po- α, Q=5.41 Mev quenched by ≈13-no evidence of 210Bi,initially 80 c/d/t

natK ≤3 10-14 g/gFrom spectrum


Initial assessment of the energy scale and position reconstruction via self-calibration through internal signals

Precise determination of the fiducial volume and energy scale: source calibration

Calibration campaign (in 2009) • External sources inserted in the detector at various positions:

•8 gamma sources (57Co,139Ce,203Hg,85Sr,54Mn,65Zn,40K,60Co)

energy range up to 2 MeV

•plus a neutron source (Am-Be) with capture gammas ( H,12C,56Fe,54Fe)

2-10 MeVChecks of the reconstruction codes and MC tuning

Bologna - 22 September, 2010

Detector calibration


Low energy (0.14-2 MeV)

•R(m)

Systematic errors-

1.5% for both the energy scale and the fiducial volume(from the previous ±6%)

Above 2 MeV

A little worse due to slight less precision in the calibration


0.032+/-0.001 0.002897+/-0.0006741


Spectral fit in ≈ 192 daysfor 7Be flux

Expected energy spectrum The unavoidable background isincluded: 14C, 11C

Raw p.e. charge spectrum after the basic cuts and subtr.

-μ and μ−correlated activities-fiducial volume;-222Rn daughters;−α subtraction (Gatti filter)


BOREXINO: 192 days - free parameters:7Be,14C, CNO+210Bi,11C,85Kr;-fixed at the SSM values:pp, pep – α subtracted spectrum


BOREXINO: 192 days - free parameters:7Be,14C, CNO+210Bi,11C,85Kr;-fixed at the SSM values:pp, pep – α unsubtracted spectrum


Systematic (before calibration)F.V. definition from the IV: uniform background sources(14C,222Rn, capture of cosmogenic n), 229Rn decay emitted by nylon, diffuser balls on the IV surface, laser activated.

Detector response function

49± 3stat± 4syst cpd/100tons for 862 keV 7Be solar νF(7Be)=(5.12 ±0.51)x109cm-2s-1 SSM; H.M.(5.08±0.56) x109cm-2s-1

L.M.(4.55 ±0.5) x109cm-2s-1

Goal:5%Totalerror

No osc:75 ± 5 cpd/100tons

8B with lower threshold at 3 MeV (488 live days)

•Background in the 3.0-16.5 MeV Cutsenergy range

••@Muon cut + 2 mms dead time to reject

induced neutrons (240 μs)•@Fiducial volume•@Muon induced radioactive nuclides:6.5 s

veto after each crossing muon (~30% deadtime)-10C (τ=27.8 s) tagged with the Three-fold coincidence with the μ parent and theneutron capture)-11Be (τ=19.9 s) statisticallysubtracted

•@214Bi-214Po coincidences rejected (τ=237 μs- 222Rn daughter)

•@208Tl from 212Bi-212Po (B.R.64%-τ=431ns) we evaluate the 208Tlproduction via



Phys. Rev. D, 82 (2010) 033006


Exp. 8B spectrum vs models


After two years of Borexino data taking: probe and striking confirmation of the

MSW matter-vacuum transition in a same detector via both 7Be and 8B signal

•Pee(Vac) - Pee(matter)= 0.27 (1.9σ)


The day night asymmetry in the 7Be energy region

MSW mechanism: ν interaction in the Earth could lead to a νe regeneration effect

Solar νe flux higher in the night than in the day

The amount of the effect depends on the detector latitude,

•the oscillation parameter values and the energy of the neutrinos;

• Actual LMA solution : a very small effect is effect is expected

• NOTE: a large effect was expected when the LOW solution was allowed ( in 2002, after the first SNO results and before the Kamland results)

•LMA and LOW predictions: Large difference for the ADN effect and small difference for the 7Be flux

•LOW is now already excluded but Borexino alone could exclude a large portion of the LOW space parameters (without Kamland) if the ADN for 7Be is very small

• Some numbers from J. Bahcall et al., JHEP07(2002)054

2/)( DNDNADN

+−

=N = νe flux during night time (average over 1 year)D = νe flux during day time (average over 1 year)

Observable LMA (+- 3 σ) LOW (+- 3 σ)7Be v-e scattering 0.64-0.05

+0.09 0.58+-0.05ADN(%) 7Be 0.0+0.1

-0.0 23+10-13

272 10 eVm −≈Δ


Mass Varying Models P.C. de Holanda JCAP07 (2009) 024

day

night

23.02/)(

−=+

−=

DNDNADN

The day night asymmetry in the 7Be energy region:not standard oscillation scenario

Expected effect in Borexino(including the vμ,τ detection)


The day night analysis

Binned ADN : signal and background are included

Be7 signal region Background dominated region


The day night result

From the day and night spectra fit of the 0.862 MeV 7Be neutrions

)(073.0007.02/)(

statDNDNADN −+=

+−

=

Preliminary result (systematic effects are still under evaluation):

•The MaVaN prediction is disfavoured within 3 sigma•ADN is well consistent with zero: further confirmation of the LMA!•Unique measurement for solar 7Be neutrinos


Geo-neutrinos: anti-neutrinos from the Earth

U, Th and 40K in the Earth release heat together with anti-neutrinos, in a well fixedratio:

Earth emits antineutrinos whereas Sun shines in neutrinos.

A fraction of geo-neutrinos from U and Th (not from 40K) are above threshold for inverse β on protons:

Different components can be distinguished due to different energy spectra: e. g. anti-νwith highest energy are from Uranium.

p e n 1.8 MeV+ν + → + −


Classical antineutrino detection in liquid scintillation detectors

Presenter

Presentation Notes

Geo-neutrinos: what are they? By definition geoneutrinos are the antineutrinos from natural radioactivity inside the Earth. U, Th and 40K in the Earth release heat together with anti-neutrinos: the important point is the well fixed ratio between the heat and anti-neutrinos. If you consider for example the U 238: the decay chain include 8 alpha decay and 6 beta decay, that release 6 anti-neutrinos. The half life is comparable with the age of the Earth, the antineutrino maximal energy is about 3.3 MeV and the Q value of the decay chain is about 52 MeV. At the end you have the antineutrinos production rates for unit mass and unit time, and heat production rates for unit mass and unit time. So the Earth emits mainly antineutrinos while Sun shines in neutrinos. The order of magnitude of the flux of geo-neutrinos is 10^6 per square cm per second. A fraction of geo-neutrinos from ONLY U and Th are above threshold for inverse b on protons. In the next we will not consider the 40K decay. Different components can be distinguished due to different energy spectra: e. g. anti-n with highest energy are from Uranium.


How detect the geo-neutrinos in Borexino


Probes of the Earth’s interior

• Samples from the crust (and the upper portion of mantle) are available for geochemical analysis.

• Seismology reconstructs density profile (not composition) throughout all Earth.

• Deepest hole is about 12 km

Geo-neutrinos: a new probe of Earth's interior

• They escape freely and instantaneously from Earth’s interior.

• They bring to Earth’s surface information about the chemical composition of the whole planet.


Presenter

Presentation Notes

Probes of the Earth’s interior: what do we have available for our investigation? Direct investigation. If we consider that the deepest hole is about 12 km and the ray of the Earth is about 6400 km, we are able to investigate only a thin layer of the Earth. LEGGI The geochemistries base on them different models about Earth’s evolution, mantle circulation and planet dynamics. Seismology reconstructs density profile throughout all Earth but not composition. In this scenario geo-neutrino is a new probe of Earth’s interior. They escape freely and instantaneously from Earth’s interior. They bring to Earth’s surface information about the chemical composition of the whole planet. The topic of geo-neutrino can be saw as a bridge between the Earth Science and Physics as emphasized by the cover of Nature of a couple years ago.

Open questions about natural radioactivity in the Earth

•1 - What is the radiogenic contribution to terrestrial heat production?

•2 - How much U and Th in the crust?

•3 - How much U and Th in the mantle?

•4 - What is hidden in the Earth’s core?

(geo-reactor,40K, …)

•5 - Is the standard geochemical model (BSE)

consistent with geo-neutrino data?


Presenter

Presentation Notes

Open questions about natural radioactivity in the Earth. What is the radiogenic contribution to terrestrial heat production? The total terrestrial heat production is estimated about 40 TW, but how much of this comes from radiogenic and how much of this comes from non radiogenic… 2) How much U and Th is in the crust? 3) How much U and Th is in the mantle? Now we estimate that half of the total amount of the Uranium mass on the Earth is in the crust. 4) What’s hidden in the Earh’s core? May be a geo-reactor or additional 40K, U or Th, that permits to solve the problem of the suorce of energy for driving the terrestrial dynamo. 5) Is the standard geochemical model BSE consistent with geo-neutrino data? The BSE model means Bulk Silicate Earth model and represent the standard geochemical paradigm.

Geo-ν: predictions of the BSE Reference Model

Signal from U+Th[TNU]

Mantovani et al. (2004)

Fogli et al. (2005)

Enomoto et al. (2005)

Pyhasalmi 51.5 49.9 52.4Homestake 51.3

Baksan 50.8 50.7 55.0Sudbury 50.8 47.9 50.4

Gran Sasso 40.7 40.5 43.1Kamioka 34.5 31.6 36.5Curacao 32.5Hawaii 12.5 13.4 13.4

• 1 TNU = one event per 1032 free protons per year

• All calculations in agreement to the 10% level

• Different locations exhibit different contributions of radioactivity from crust and from mantle

•Fiorentini et al. - JHep. 2004


Presenter

Presentation Notes

By using the canonical model what are the predictions about geo-neutrinos? Here you have a map of the predicted geo-neutrinos events: the color scale indicate the number of events normalized to 10^32 protons year. In the table you can see the expected signal at a few location in which the geo-neutrinos could be detected. The unit which is used is TNU Terrestrial Neutrino Units. A signal of 1 TNU corresponds to one event per 10^32 free protons per year. 10^32 proton is about 1 Kton of liquind scintillator. You can see that the calculations performed by different group are in agreement to the 10% level. Note that different locations exhibit different contributions of radioactivity from the crust and from the mantle.

Running and planned experiments

• Several experiments, either running or under construction or planned, have geo-ν among their goals.

• Figure shows the sensitivity to geo-neutrinos from crust and mantle together with reactor background.

•0•50

•100•150•200•250 Mantle

CrustReactor

•Sig

nal

[TN

U]

•Homestake

•Baksan

•0•50

•100•150•200•250 Mantle

CrustReactor

•Sig

nal

[TN

U]


Presenter

Presentation Notes

Here you have the potential of different detectors in the world. Now a quick view about few details of some experiment.


Look for possiblesources of fake anti‐νevents(prompt + delayed):

2.Background from other sources



•MC spectra for •likelihood function •Unbinned ML best fit

• Data set: from Dec 2007 to Dec 2009•Total live time: 537.2 live days•Fiducial exposure after muon cuts and including detection efficiency: 252.6 ton-year•21 anti-ν candidates selected



Best-fit parameters from the likelihood analysis

•BSE•Max radiogenic

•Min radiogenic

•68%, 90% and 99.73% C.L.

9.9−3.4+4.1events

Nreact= 10.7−3.4+4.3

99.997% → 4.2σ

•Total heat flow : •31+1 TW or 44+1 TW

•Phys. Letters B 687(2010)299

base line of 1000kmNo oscillation of reactor neutrinos rejected at 2.9σ


Geoneutrinoevidence at 4.2 σ


CONCLUSIONS>> After a long quest for the ultimate radiopurity,

Borexino joined the solar neutrino arena with the first real time detection of 7Be solar neutrinos, marking a fundamental milestone in the field of ultra low background techniques

>> Such a success allowed to validate the MSW-LMA neutrino oscillation model, by detecting for the first time in a same detector the predicted transition from “matter” to “vacuum” oscillation regimes

>> The first three years of operation of Borexinoculminated also with the striking observation of Geoneutrinos with an evidence as high as 4.2 σ

Documents

Validation of the neutrino oscillation model and first real ...static.sif.it/.../public/files/congr10/mc/ranucci.pdfBologna - 22 September, 2010 Gioacchino Ranucci - I.N.F.N. Sez