Highligth on the past, present and future of the Borexino project Gemma Testera (INFN Genova) On behalf of the Borexino Collaboration LNGS Sept. 5th, 2014 Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Borexino: scientific phases 2010 2007 May 2010 May 2011 Oct. 2015 ~Feb. 2015 ~Nov. 2017 ~mid. ??? ~ now PHASE 1 Purifications 5% 7Be n measurement absence of 7Be day night low threshold 8B first pep detection best upper limit on CNO geon measurement muons, cosmogenics limit on rare processes evidence of 7Be n seasonal modulation calibration PHASE 2 more geon results background reduction In progress now pp seas. results (preliminary) more precise 7Be, 8B. pep (in progress) Rare processes SOX, sterile n + distillation (under discussion) calibration more purification tests temperature stabilization PHASE 3 CNO Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

and expected interaction rates in Borexino Solar n spectrum and expected interaction rates in Borexino Expected rates in Borexino n Diff % pp 0.8 pep 2.1 7Be 8.8 8B 17.7 13N 26.7 15O 30.0 17F 38.4 Precise solar n measurement may discriminate between solar models CNO : high potential discovery… the most difficult to detect! 7Be : high precision needed CNO Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Solar n and ne survival probability Pee: MSW and Non Standard Interactions (NSI) MaVan models Non standard forward scattering LMA and standard model 1 10 NSI between n and electrons modify Pee vs E (MSW) NSI affects the shape of the elastic scattering cross section (see next slides) S.K. Agarwalla et al JHEP 12 079 (2012) PRD 88: 053010 (2013) Long range interactions 1 10 Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Borexino: real time n detector with liquid scintillator Stainless Steel Sphere: R = 6.75 m 2212 PMTs Scintillator: 270 t PC+PPO (1.5 g/l) in a 150 mm thick inner nylon vessel (R = 4.25 m) n detection: elastic scattering on electrons Buffer region: PC+DMP quencher 4.25 m < R < 6.75 m anti-n detection: Inverse Beta Decay (IBD) Water Tank: g and n shield m water Č detector 208 PMTs in water “prompt signal” e+: energy loss + annihilation (2 g 511 KeV each) “delayed signal” n capture on H after thermalization; 2.2 g The smallest radioactive background of all the neutrino detectors: 9-10 orders of magnitude smaller than the every-day environment Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

Real time solar n detection pp pep 7Be CNO 8B 8B detect en. thres. (Lowest) (1010 cm-2 s-1) (109 cm-2 s-1) (108 cm-2 s-1) (108 cm-2 s-1) (106 cm-2 s-1) 2.344 ± 0.034 ne equiv.1 (1.4%) SK 3.5 MeV SNO 5.25 ± 0.16+0.11-0.13 Total active2 n (3.8%) 3.5 MeV Kamland 3.26 ± 0.5 (15%) ne equiv8 2.77 ± 0.26± 0.32 ne equiv.3 (15%) 5.5 MeV Borexino 6.6 ± 0.7 (10.6%) LMA-MSW included7 3.10 ± 0.15 (5%) ne equiv6 1.6 ± 0.3 (19%) LMA-MSW included5 < 7.7 LMA-MSW included5 2.4 ± 0.4 ± 0.1 ne equiv.4 (17%) 3. MeV 1) Y. Koshio (SK Coll.) Neutrino 2014 talk 2) B. Aharmim et al (SNO Coll.) Phys. Rev. C 88 025501 (2013) 3) S. Abe et al (Kamland Collaboration) Phys. Rev. C 84 035804 (2011) 4) G. Bellini et al (Borexino Collaboration) Phys. Rev. D 82, 3 (033006) 2010 5) G. Bellini et al., (Borexino Collaboration) Phys. Rev. Lett. 108 (2012) 051302.. 6) G. Bellini et al., (Borexino Collaboration) Phys. Rev. Lett. 107 (2011) 141362. 7) G. Bellini et al. (Borexino Collaboration) Nature 512 383 (2014) 8) A. Gando et al. (Kamland Collaboration) arxiv:1405.6190v1 (May2014)

How do we see n in Borexino? G. Bellini et al., Phys Rec D 112007(2014) How do we see n in Borexino? No direction: key tool in the SNO and SK analysis Energy (from number of PMT hits or phe) : - high energy resolution and fit of the energy spectra - recognize the signal on the basis of the spectral shape - need very low background! Position reconstruction (from PMT time) : - definition of the Fiducial Volume (from the PMT time meas.) - distinguish signal from back on the basis of the spatial distribution of the events Pulse shape discrimination: distinguish signal and back on the basis of the time profile of the emitted light + explore time and space correlations between events to remove or evaluate background (214Bi-214Po, 212Bi-212Po, 85Kr, 11C 3 fold coincidence, muon daugthers) In situ calibration with radiocative sources + accurate detector modeling (Monte Carlo and analytical models) Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Fiducial Volume error: +0.5 -1.3% PHASE 1: position reconstruction calibration (from PMT time measurements) Rn source deployed in 182 positions True position with laser light and CCD The position resolution as a function of the energy The accuracy of the absolute position reconstruction: difference between true and reconstructed source position Vertical coordinate z y x x coordinate (and similar for y) Mean: -0.01 cm Rms : 0.87 cm 1MeV Fiducial Volume error: +0.5 -1.3% 10 cm@ 1MeV (electron equiv) Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

PHASE 1: energy (PMT hits or phe) calibration Energy calibration: g sources in the center Data and MC 214Po source (from Rn) in 182 positions: difference between data and MC Inside the FV R<3m X R>3m The energy scale in the FV Energy resolution ≈500 phe/MeV (electron equivalent) Quenching determined from calibration data

PHASE 1: pulse shape discrimination Distribution of the parameter (Gatti filter) used to discriminate a from b The time profile of the emitted light for a and b 1) a b (obtained with time tagged 214Bi-214Po) 2) b+ b- 11C decays by b+ e+ slow down, capture e-, Lifetime in the liquid is few ns e+ scintillation delayed (compared to e-)

Phase I solar n results : 5% accuracy on 7Be n interaction rate G. Bellini et al., Borexino Collaboration, Phys. Rev. Lett. 107 (2011) 141362. Use of PSD to subtract the 210Po peak 11C 210Bi ne flux reduction 0.62 +- 0.05 5 s evidence of oscillation Theor. uncertainty on 7Be flux : 7% Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Physics implication of the solar n Borexino results: high and low metallicity solar models High met. (1s) Low met. (1s) Data Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

Phase I solar n results : absence of day night asymmetry for 7Be n interaction rate ne regeneration by interaction with e: D/N effect is a consequence of MSW not expected for 7Be in the LMA-MSW model large effect expected in the “LOW” solution (excluded by solar exp + Kamland) no contradiction with the recent SK results G. Bellini et al., Borexino Collaboration, Phys. Lett. B707 (2012) 22. Solar data alone select the LMA-MSW if one includes the Borexino D/N result (no use of CPT) LMA-MSW LMA-MSW Day time Night time All solar n without Bx without Kamland All solar n with Bx without Kamland Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Phase I solar n results : first pep n detection and best limit on CNO pep signal is ten time lower than 7Be About 3cpd/100t CNO: rate similar to pep G. Bellini et al., Borexino Collaboration, Phys. Rev. Lett. 108 (2012) 051302.. pep 7Be 11C 210Bi CNO Ext back Most important background 11C : 210Bi : External background (g from PMT): Play against external background calib. with external 232Th source Monte Carlo simulation Include the radial distribution of events in the fit The effect of the 3 fold coinc. Play against 11C 3 fold coinc Pulse shape param in the fit The eec Residual 11C: 2.5 +- 0.3 cpd/100t (9+-1)% of the original value 48.5% of the original exposure preserved Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Phase I solar n results : first pep n detection and best limit on CNO G. Bellini et al., Borexino Collaboration, Phys. Rev. Lett. 108 (2012) 051302.. 210Bi cpd/100t CNO 210Bi CNO cpd/100t Sensitivity to CNO limited by 210Bi: similar spectral shape 5.24 High Met; 3.76 Low Met.) Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

PHASE I solar n results : 8B flux with the lowest energy threshld 208Tl (from the 232Th decay chain) limits the energy threshold low signal rate (Borexino is small…) G. Bellini et al., Borexino Collaboration,PRD 82. 108 (2010) 033006 3 MeV electron energy threshold: the lowest ! Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Purification of the scintillator : (between phase 1 and 2) 6 purication cycles Water extraction Nitrogen stripping (May 2010-2011) 238U (from 214Bi-Po) < 8 10-20 g/g 95% C.L. PHASE 1: 5 10-18 g/g Arbitray units 232Th (from 212Bi-Po) < 9 10-19 g/g 95% C.L. PHASE 1: 3 10-18 g/g 85Kr (from spectral fit) < 7 cpd/100t 95% C.L. PHASE 1: 30.4±5.3±1.5 210Bi (from spectral fit) 25±2 cpd/100t PHASE 1: 41.8±2.8 210Po 102 cpd/100t PHASE 1: 104 cpd/100t Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

Phase II solar n results : pp neutrinos !!! See the Oleg’s talk Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Borexino Solar Neutrino results and the oscillation physics Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

More about Non Standard Interactions (NSI) NSI change the ne-e differential elastic scattering cross section Bounds on the parameters with PHASE 1 data better limits are expected with reduced background and more statistics S.K. Agarwalla et al JHEP 12 079 (2012) Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Expected oscillation amplitute of 7Be n signal: Phase I (and preliminary for PHASE 2) solar n results : annual modulation of the 7Be n signal Expected oscillation amplitute of 7Be n signal: 6.8% peak-to-peak max flux: Jan. 3rd 47.5 e=0.0167 7Be n cpd/100t 46 44.5 Time (years) Counts in a energy region dominated by 210Bi Spectral fit in sub-periods: too large stat. errors Analysis method: Select a proper energy region, group data in time bins and search for a periodical component Enlarge the fiducial volume (with respect to the 7Be flux meas.) 3 methods (consistent results) Fit of the rate vs time Lomb Scargle analysis Empirical Mode Decomposition G. Bellini et al., Phys Rec D 112007(2014) Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

PHASE 1: annual modulation of the 7Be n signal Difficult analysis in PHASE 1 due to unstable 210Bi G. Bellini et al., Borexino Collaboration, Phys. Rev. C (2014) ?????. best fit 1s 2s expected value Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

PHASE 2: annual modulation of the 7Be n signal (preliminary results) 7Be signal and background: annual modulation 210Bi time stability in PHASE 2 Expected time curve Preliminary Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Dreaming about CNO neutrinos…….. 1) Reduce 210Bi by purification: partially achieved 2) Infer the 210Bi activity from the 210Po vs time 210Bi-210Po out of equilibrium: we see an high 210 Po rate 210Pb 210Bi 210Po 206Pb b (63 KeV) b a stable T1/2=22y 5 days 138 days Look at the 210Po time decay: the rate at regime is due to 210Bi F. Villante et al.,Phys. Lett. B 701 (2011) Simulation: 100 t X 1 year, typical Borexino rates Needed: 210Po activity not too high: actual values are OK stable conditions for long time (1-2 years..) no 210Po sources Standard spectral fit Constrain on 210Bi rate due to 210Po time decay

Studies of the 210Po decay Temperature of the Hall Temperature on top of the SSS 210Po of the vessel moves inside the IV due to convection induced by temperature changes Solutions under discussion 210Po in the Fiducial Volume Temperature at the bottom of the SSS July2014 Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

Not only solar n! Geo-n in Borexino: anti ne from inside the Earth Energy spectrum of geon neutrinos En>1.8 MeV Low flux: 3 order of magnitude less than 7Be solar n! Clean signature by IBD Geon: they probe the U,Th content of the Earth (no K) Multidisciplinary research: particle physics&geophysics reactor geon Likelihood fit: geov + reactor Event selection and results Search for coincidence (energy, time and space cuts) Large Fiducial Volume: distance from the vessel <25 cm Exposure 613±26 ton year 46 candidates 14.3 +- 4.4 geo n events 31.2-6.1+7 reactor events 33.3±2.4 expected reactor events 0.70±0.18 others back No geon signal: rejected at 4.5 s C.L. geon reactors 1MeV≈ 500 p.e.

Geon : implications about Earth models For each element (U,Th) the expecetd geon signal S in one site on the Earth’s surface is the sum of 3 contributions It depends on local geology We are interested in the Mantle contribution which is related to the U,Th mass (or radiogenic heat) in a model dependent way (red and blue plot) TNU=1ev/ (y 1032 protons) Borexino results LOC (TNU) ROC (TNU) DATA (TNU) MANTLE (TNU) U+Th (TW) Kamland 17.7±1.4 7.3±1.4 31.1±7.3 6.1±7.6 13±9 Borexino 9.7±1.3 13.7 ±2.5 38.8±12.0 15.4±12.3 23±14 Data not yet precise enough to select Earth models New multidisciplinary area, large interest from the geo- community Mantle (BX+Kamland) 7.7+-6.2 TNU (1s) Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

Not only solar n! Search for sterile-n in Borexino (SOX) Experimental hints for sterile neutrinos Several unexpected signals at 3 s level: Accelerator anomaly (3.8 s) LSND and MiniBoone Excess of low energy ne events from a nm beam Appearance signal at a new short baseline? Gallium anomaly (2.8 s) Calibration runs with radiocative sources in Gallex/SAGe Deficit of the detected ne R= 0.76+-0.09 Reactor anomaly (2.5 s) Re-evaluation of reactor antine spectra Rate deficit at short baseline (10-100m) R= 0.927+-0.230 Disapperance of electron neutrinos into sterile neutrinos?? Light sterile neutrinos: a white paper Xiv:1204.5379 Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

Dm214 (eV2) Add 2 new parameters sin2(2 q14) Plot taken from arxiv 1303.353 (2013) (Opera collaboration) Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

n and anti-n neutrino sources to search for sterile n signal SOX: Short distance neutrino Oscillations with BoreXino) SOX A: Source below Borexino: 8.25 m from the center No changes in the detector We are working on two sources: 51Cr n e source 44Ce anti- n e (in collaboration with Saclay group) End 2015: start data taking with 44Ce 8.25 m Oscillation lenght of the order of the Borexino size

Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

The SOX signal 1) Disappearance: - need accurate calibration of the source activity - measure heat (calorimeter) with 1-2% accuracy (in construction) 2) See spatial oscillations of the source count rate 51Cr source: example with Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

The expected sensitivity sin2(2 q14) sin2(2 q14)

Summary, conclusions and perspectives Borexino is the only real time experiment who detected n over all the solar spectrum The results are relevant to both solar physics and neutrino physics PHASE 2 with lower background than PHASE 1 almost concluded: data analysis in progress 7Be (going toward 3-3.5 % accuracy) pep 8B seasonal modulation geo n several rare processes ….while waiting for a Supernova all the time ! First pp neutrinos detection in real time ! A new calibration is scheduled for the beginning of 2015: needed to reduce the uncertainties Effort in progress toward the CNO detection : we need stable conditions control of the temperature further purification of the scintillator (under discussion within the collaboration) Sterile n search with radiocative source: start soon (end 2015) Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014