Solar neutrino spectroscopy and oscillation with Borexino Davide Franco APC-CNRS LPNHE November 17, 2011 – Paris

Outline The Solar neutrino physics The physics of Borexino The detector The “radio-purity” challenge The reached goals ( 7 Be, 8 B, pep and geo-, day/night,...) Future goals in the Solar sector Sterile neutrinos, superluminal (?) Davide Franco – APC-CNRS

Neutrino Production In The Sun Davide Franco – APC-CNRS pp chain: pp, pep, 7 Be, hep,and 8 B CNO cycle: 13 N, 15 O, and 17 F

Solar Neutrino Spectra Davide Franco – APC-CNRS SNO SuperK (real time) HomestakeGallex GNO Sage Borexino (real time)

The Standard Solar Model before/after 2004 Davide Franco – APC-CNRS The Standard Solar Model, based on the old metallicity derived by Grevesse and Sauval (Space Sci. Rev. 85, 161 (1998)), was in agreement within 0.5 in % with the solar sound speed measured by helioseismology. Latest work by Asplund, Grevesse and Sauval (Nucl. Phys. A 777, 1 (2006)) indicates a lower metallicity by a factor ~2. This result destroys the agreement with helioseismology < 2004> 2004

What about neutrinos? [cm -2 s -1 ] pp (10 10 ) pep (10 10 ) hep (10 3 ) 7 Be (10 9 ) 8 B (10 6 ) 13 N (10 8 ) 15 O (10 8 ) 17 F (10 6 ) GS AGS  -1%-2%-3%-9%-18%-27%-30%-38% Davide Franco – APC-CNRS Solar neutrino measurements can solve the problem!

Borexino physics goals Davide Franco – APC-CNRS First ever observations of sub-MeV neutrinos in real time Balance between photon luminosity and neutrino luminosity of the Sun X CNO neutrinos (direct indication of metallicity in the Sun’s core) pep neutrinos (indirect constraint on pp neutrino flux) Low energy (3-5 MeV) 8 B neutrinos X Tail end of pp neutrino spectrum Test of the matter-vacuum oscillation transition with 7 Be, pep, 8 B Day/night effect Limit on the neutrino magnetic moment SNEWS network for supernovae Evidence (>3  ) of geoneutrinos X Sterile neutrinos X Superluminal neutrinos done X in progress done X in progress

Borexino Collaboration Davide Franco – APC-CNRS Kurchatov Institute (Russia) Dubna JINR (Russia) Heidelberg (Germany) Munich (Germany) Jagiellonian U. Cracow (Poland) Perugia Genova APC Paris Milano Princeton University Virginia Tech. University

Davide Franco – APC-CNRS Laboratori Nazionali del Gran Sasso Assergi (AQ) Italy ~3500 m.w.e Borexino External Lab

Detection principles and signature Borexino detects solar via their elastic scattering off electrons in a volume of highly purified liquid scintillator Mono-energetic MeV 7 Be are the main target, and the only considered so far Mono-energetic pep, CNO and possibly pp will be studied in the future Detection via scintillation light: Very low energy threshold Good position reconstruction Good energy resolution BUT… No direction measurement The induced events can’t be distinguished from other  events due to natural radioactivity Extreme radiopurity of the scintillator is a must! Davide Franco – APC-CNRS Typical rate (SSM+LMA+Borexino)

Borexino Background Low background nylon vessel fabricated in hermetically sealed low radon clean room (~1 yr) Rapid transport of scintillator solvent (PC) from production plant to underground lab to avoid cosmogenic production of radioactivity ( 7 Be) Underground purification plant to distill scintillator components. Gas stripping of scintlllator with special nitrogen free of radioactive 85 Kr and 39 Ar from air All materials electropolished SS or teflon, precision cleaned with a dedicated cleaning module Natural water~ 10 Bq/kg in 238 U, 232 Th and 40 K Air~ 10 Bq/m 3 in 39 Ar, 85 Kr and 222 Rn Typical rock~ Bq/kg in 238 U, 232 Th and 40 K Davide Franco – APC-CNRS Expected solar neutrino rate in 100 tons of scintillator ~ 50 counts/day (~ Bq/kg) Just for comparison: BX scintillator must be 9/10 order of magnitude less radioactive than anything on earth!

Detector layout and main features Davide Franco – APC-CNRS Water Tank:  and n shield  water Č detector 208 PMTs in water 2100 m 3 20 legs Carbon steel plates Scintillator: 270 t PC+PPO in a 150  m thick nylon vessel Stainless Steel Sphere: 2212 PMTs 1350 m 3 Nylon vessels: Inner: 4.25 m Outer: 5.50 m

Davide Franco – APC-CNRS PMTs: PC & Water proof Installation of PMTs on the sphere Nylon vessel installation

Counting Test Facility Davide Franco – APC-CNRS CTF is a small scale prototype of Borexino: ~ 4 tons of scintillator 100 PMTs Buffer of water Muon veto Vessel radius: 1 m CTF demonstrates the Borexino feasibility

Davide Franco – APC-CNRS May 15, 2007

Borexino background Davide Franco – APC-CNRS RadioIsotopeConcentration or FluxStrategy for Reduction NameSourceTypicalRequiredHardwareSoftwareAchieved  cosmic~200 s -1 m -2 ~ UndergroundCherenkov signal < at sea level Cherenkov detectorPS analysis(overall) Ext.  rock Water Tank shieldingFiducial Volumenegligible Int.  PMTs, SSS Material SelectionFiducial Volumenegligible Water, Vessels Clean constr. and handling 14 CIntrinsic PC/PPO~ ~ Old Oil, check in CTFThreshold cut ~ UDust~ g/g < g/g Distillation, Water Extraction ~ ThOrganometallic (?)(dust)(in scintillator)Filtration, cleanliness ~ BeCosmogenic ( 12 C)~ Bq/t< Bq/tonFast procurement, distillationNot yet measurable? 40 KDust,~ g/g< g/g scin.Water ExtractionNot yet measurable? PPO(dust)< g/g PPODistillation 210 PbSurface contam. Cleanliness, distillationNot yet measurable? from 222 Rn decay (NOT in eq. with 210 Po) 210 Po Surface contam. Cleanliness, distillationSpectral analysis ~ 14 from 222 Rn decay  stat. subtraction ~ 0.01 c/d/t 222 Rnair, emanation from~ 10 Bq/l (air)< 1 c/d/100 tWater and PC N 2 stripping,Delayed coincidence< 0.02 c/d/t materials, vessels~100 Bq/l (water)(scintillator)cleanliness, material selection 39 ArAir (nitrogen)~17 mBq/m 3 (air)< 1 c/d/100 tSelect vendor, leak tightnessNot yet measurable? 85 Kr Air (nitrogen)~ 1 Bq/m 3 in air< 1 c/d/100 tSelect vendor, leak tightnessSpectral fit = 25±3 (learn how to measure it)fast coincidence = 29±14

Expected Spectrum Davide Franco – APC-CNRS

The starting point: no cut spectrum Davide Franco – APC-CNRS

Calibrations: Monte Carlo vs Data Gamma sources in the detector center MC-G4Bx Data Pulse shape of 14 C events Uncertainties on: energy scale ~ 1.5% fiducial volume: +0.6% - 1.3% Data MC

Cosmic muons and induced neutrons Davide Franco – APC-CNRS PSD

The  /  discrimination and the 210 Po puzzle Davide Franco – APC-CNRS  particles  particles ns Different response in the scintillation emission time depending on the particle nature   210 Po The puzzle: high 210Po contamination not in equilibrium with its “father”: 210Bi

After the selection cuts Davide Franco – APC-CNRS

Final fit: 740 days of statistics Davide Franco – APC-CNRS Analytical Model MC Model

7 Be- result Davide Franco – APC-CNRS

7 Be- result Davide Franco – APC-CNRS R: 46.0±1.5 stat syst cpd/100 t f Be = 0.97 ± 0.05 P ee = R: 46.0±1.5 stat syst cpd/100 t f Be = 0.97 ± 0.05 P ee = Under the luminosity constraint:  pp = ( )x10 10 cm -2 s -1 CNO <1.7% (95% C.L.) Under the luminosity constraint:  pp = ( )x10 10 cm -2 s -1 CNO <1.7% (95% C.L.)

Davide Franco – APC-CNRS The Day-Night regeneration LOW LMA A neutrino “regeneration” is expected only in the LOW solution Exposure DayNight

The Day-Night Asymmetry Davide Franco – APC-CNRS A dn = ± (stat) ± (syst) LOW ruled out at 8.5 

Neutrino Magnetic Moment Davide Franco – APC-CNRS EstimateMethod μ B SuperK 8B8B<11 Montanino et al. 7 Be<8.4 GEMMAReactor<5.8 Borexino 7 Be<5.4 EM current affects cross section: spectral shape sensitive to μ ν sensitivity enhanced at low energies (c.s.≈ 1/T) A fit is performed to the energy spectrum including contributions from 14 C, leaving μ as free parameter of the fit Neutrino-electron scattering is the most sensitive test for  search

8 B neutrinos with the lowest threshold: 3 MeV Davide Franco – APC-CNRS 2.6 MeV  ’s from 208 Tl on PMT’s and in the buffer All volume R < 3 m (100 tons) Energy spectrum in Borexino (after  subtraction) Expected 8 B rate in 100 tons of liquid scintillator above 3.0 MeV: 0.26±0.03 c/d/100 t Expected 8 B rate in 100 tons of liquid scintillator above 3.0 MeV: 0.26±0.03 c/d/100 t > 5  distant from the 2.6 MeV  peak A. Friedland 2005

Background in the MeV range Davide Franco – APC-CNRS Cosmic Muons External background High energy gamma’s from neutron captures 208 Tl and 214 Bi from radon emanation from nylon vessel Cosmogenic isotopes 214 Bi and 208 Tl from 238 U and 232 Th bulk contamination Raw Spectrum live-time: 246 days Count-rate: 1500 c/d/100 ton S/B ratio < 1/6000!

Summary of the Cuts and Systematic CutCounts >3 MeV Counts > 5 MeV None Muon cut FV cut Cosmogenic cut C removal Bi removal Tl and 11 Be sub Measured 8 B BPS09(GS98) 8 B BPS09(AGS05) 8 B Davide Franco – APC-CNRS *MSW-LMA:  m 2 =7.69×10 −5 eV 2, tan 2  =0.45 Systematic errors: 3.8% from the determination of the fiducial mass 3.5% (5.5%) uncertainty in the 8 B rate above 3.0 MeV (5.0 MeV) from the determination of the light yield (1%) raw spectrum  cut FV cut cosmogenic, neutron, 214 Bi and 10 C cuts 208 Tl P ee ( 8 B) = 0.29 ± 0.10 (8.6 MeV)

The 8 B spectrum Davide Franco – APC-CNRS Borexino data ( 7 Be and 8 B) confirm neutrino oscillation at 4.2 , No discrimination between log and high metallicity SSM’s Borexino data ( 7 Be and 8 B) confirm neutrino oscillation at 4.2 , No discrimination between log and high metallicity SSM’s

Geo-neutrinos Davide Franco – APC-CNRS Geo-neutrino spectrum Positron spectrum S/B ratio ~ 1 (entire energy spectrum) S/B ratio ~ 1 (entire energy spectrum) Expectations geo- : 6.3 cpy / 300 t reactor- : 5.7 cpy / 300 t Expectations geo- : 6.3 cpy / 300 t reactor- : 5.7 cpy / 300 t reactors geo

Geo-neutrinos: results Null hypothesis rejected at 4.2  Davide Franco – APC-CNRS

pep neutrinos: the 11 C background Davide Franco – APC-CNRS  + 12 C →  + 11 C + n + p → d +  → 11 B + e + + e Expectations in [ ] MeV pep- ~ 0.01 cpd / t 11 C ~ 0.15 cpd / t Expectations in [ ] MeV pep- ~ 0.01 cpd / t 11 C ~ 0.15 cpd / t Required 11 C rejection factor > 15 Required 11 C rejection factor > 15

11 C rejection: the three-fold coincidence technique Davide Franco – APC-CNRS Coincidence among the muon father, the neutron capture and the 11 C decay problem 1: 11 C meanlife ~ 30 min problem 2: ~5% of 11C production without neutron emission Coincidence among the muon father, the neutron capture and the 11 C decay problem 1: 11 C meanlife ~ 30 min problem 2: ~5% of 11C production without neutron emission  PC+P PO 11 C n 

pep neutrinos after the TFC Davide Franco – APC-CNRS

11 C rejection: a new PSD Davide Franco – APC-CNRS Pulse Shape Discrimination (PSD) for e + /e - may meet a general interest in the neutrino community However scintillators have almost equal response to e + /e - in the energy region of interest (<10 MeV) standard PSD can not be applied!! Pulse Shape Discrimination (PSD) for e + /e - may meet a general interest in the neutrino community However scintillators have almost equal response to e + /e - in the energy region of interest (<10 MeV) standard PSD can not be applied!! Ionization Positron Electron No way (up to now!!) to disentangle electron (positron) induced signal and positron (electron) background in scintillator

Exploiting positronium formation... Davide Franco – APC-CNRS In matter positrons may either directly annihilate or form a positronium state Positronium has two ground states: para-positronium (p-Ps) mean life in vacuum of ~ 120 ps singlet - 2 gamma decay ortho-positronium (o-Ps) mean life in vacuum of ~ 140 ns triplet - 3 gamma decay In matter o-Ps has a shorter mean life, mainly because of: spin-flip: conversion to p-Ps due to a magnetic field pick off: annihilation on collision with an anti-parallel spin electron Note!! the 3 body decay channel is negligible in matter Even a short delay ( few ns ) in energy depositions between positron (via ionization) and annihilation gammas (via Compton scattering) can provide a signature for tagging (a subset of) positrons

o-Ps in scintillators Davide Franco – APC-CNRS Measurements of the o-Ps meanlife and formation probability in scintillators with the PALS technique D. Franco, G. Consolati, D. Trezzi, Phys. Rev. C83 (2011) Pulse shape induced distortion MC

The o-Ps technique in Borexino Davide Franco – APC-CNRS

pep neutrinos: results Davide Franco – APC-CNRS the fit the subtraction pep-n flux = (1.6 ± 0.3)x10 8 cm -2 s -1 CNO-n flux < 7.4x10 8 cm -2 s -1 pep-n flux = (1.6 ± 0.3)x10 8 cm -2 s -1 CNO-n flux < 7.4x10 8 cm -2 s -1

The Borexino Solar neutrino spectroscopy Davide Franco – APC-CNRS

Next future: sterile neutrinos? Davide Franco – APC-CNRS Several anomalies/hints for  m 2 ~ 1 eV 2 : reactor anomaly gallium anomaly LSND MiniBooNE cosmological constraints Several anomalies/hints for  m 2 ~ 1 eV 2 : reactor anomaly gallium anomaly LSND MiniBooNE cosmological constraints

A neutrino/anti-neutrino source in Borexino Davide Franco – APC-CNRS The physics Neutrino magnetic moment Neutrino-electron non standard interactions ν e - e weak couplings at 1 MeV scale Sterile neutrinos at 1 eV scale Neutrino vs anti-neutrino oscillations on 10 m scale The physics Neutrino magnetic moment Neutrino-electron non standard interactions ν e - e weak couplings at 1 MeV scale Sterile neutrinos at 1 eV scale Neutrino vs anti-neutrino oscillations on 10 m scale The location A: underneath - D = 825 cm - No change to present configuration B: inside - D = 700 cm - Need to remove shielding water C: center - Major change - Remove inner vessels The location A: underneath - D = 825 cm - No change to present configuration B: inside - D = 700 cm - Need to remove shielding water C: center - Major change - Remove inner vessels

The Icarus pit Davide Franco – APC-CNRS pit tunnel

The source candidates Davide Franco – APC-CNRS Source [MeV] R FV [m] Interaction channel L osc [m] Δ m 2 =0.1 eV 2 L osc [m] Δ m 2 =1.5 eV 2 N ev /MCiN background 51Cr ES ~ days ~ days 37Ar ES201.3~ days ~ days 90Sr-90Y ES211.4~ year ~ year 90Y IBD493.3~ year ~12 1 year 106Rh IBD ~ year ~12 1 year Sources in the Icarus Pit

Davide Franco – APC-CNRS An example: 5 MCi 51 Cr in the Icarus Pit ( Δ m 2,sin 2 2  SBL  eV 2,0.15)

Conclusion Borexino opened the study of the solar neutrinos in real time below the barrier of natural radioactivity (5 MeV) Three measurements reported for 7 Be neutrinos Best limits for pp and CNO neutrinos, combining information from SNO and radiochemical experiments First real time measurement of pep First observation of 8 B neutrino spectrum below 5 MeV First observation of geoneutrinos Best limit on neutrino magnetic moment Potential in sterile neutrinos Superluminal neutrinos Davide Franco – APC-CNRS …and do not forget the technological success of the high radio-purity scintillator!