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Exploring the Past, Present, and Future of the Borexino Project

This presentation discusses the scientific phases, solar neutrino measurements, and expected interaction rates in the Borexino project. It also covers the calibration, purification tests, and temperature stabilization in different phases of the project.

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Exploring the Past, Present, and Future of the Borexino Project

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

  2. Borexino: scientificphases 2007 2017 2015 2011 2010 2015 ??? ~Nov. ~mid. ~Feb. May May Oct. ~ 2010 now PHASE 1 Purifications PHASE 2 • 5% 7Be n measurement • absenceof 7Be day night • lowthreshold8B • first pepdetection • best upperlimit on CNO • geonmeasurement • muons, cosmogenics • limiton rare processes • evidence of 7Be nseasonalmodulation • calibration • more geonresults • background reduction In progress now • pp • seas. results (preliminary) • more precise7Be,8B. pep (in progress) • Rare processes SOX, sterile n + distillation (under discussion) PHASE 3 • calibration • more purificationtests • temperature stabilization • CNO Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  3. Solar nspectrum and expectedinteractionrates in Borexino Expectedrates in Borexino • Precise solar nmeasurementmay discriminate between solar models • CNO : high potentialdiscovery… the mostdifficult to detect! • 7Be : high precisionneeded CNO Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  4. Solar n and nesurvivalprobabilityPee: MSW and Non Standard Interactions (NSI) Pee Pee MaVanmodels Non standard forwardscattering LMA and standard model 1 10 • NSI betweenn and electronsmodifyPee vs E (MSW) • NSI affects the shape of the elasticscattering cross section(seenextslides) • S.K. Agarwalla et al JHEP 12 079 (2012) PRD 88: 053010 (2013) Long rangeinteractions 1 10 Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  5. Borexino: real time n detector with liquidscintillator 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+DMPquencher 4.25 m < R < 6.75 m • anti-ndetection: • Inverse Beta Decay (IBD) Water Tank: g and n shield m water Č detector 208 PMTs in water • “promptsignal” • e+: energyloss + annihilation • (2 g 511 KeVeach) • “delayedsignal” • n capture on H afterthermalization; 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

  6. Real time solar ndetection pep pp CNO 8B 7Be 8B detect en. thres. (Lowest) (106 cm-2 s-1) (108 cm-2 s-1) (108 cm-2 s-1) (109cm-2 s-1) (1010cm-2 s-1) 2.344 ± 0.034 neequiv.1 (1.4%) SK 3.5 MeV SNO 5.25 ± 0.16+0.11-0.13 Total active2n (3.8%) 3.5 MeV Kamland 2.77 ± 0.26± 0.32 neequiv.3 (15%) 3.26 ± 0.5 (15%) neequiv8 5.5 MeV < 7.7 LMA-MSW included5 6.6 ± 0.7 (10.6%) LMA-MSW included7 1.6 ± 0.3 (19%) LMA-MSW included5 Borexino 3.10 ± 0.15 (5%) neequiv6 2.4 ± 0.4 ± 0.1 neequiv.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)

  7. G. Bellini et al., PhysRec D 112007(2014) How do weseen in Borexino? • No direction: keytool in the SNO and SK analysis • Energy (from number of PMT hits or phe) : - high energyresolution and fit of the energyspectra • - recognize the signal on the basis of the spectralshape • - needverylow background! • Position reconstruction (from PMT time) : - definition of the Fiducial Volume (from the PMT time meas.) • - distinguishsignal from back on the basis of the spatialdistribution • of the events • Pulseshapediscrimination: distinguishsignal and back on the basis of the time profile of the emitted light • + explore time and spacecorrelationsbetweenevents to remove or evaluate background • (214Bi-214Po, 212Bi-212Po, 85Kr, 11C 3 foldcoincidence, muondaugthers) • In situ calibration with radiocativesources + accurate detector modeling (Monte Carlo and analyticalmodels) Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  8. PHASE 1: position reconstructioncalibration (from PMT time measurements) • Rn source deployed in 182 positions • True position with laser light and CCD The position resolutionas a function of the energy The accuracy of the absolute position reconstruction: differencebetweentrue 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

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

  10. PHASE 1: pulseshapediscrimination Distribution of the parameter (Gatti filter) used to discriminate a from b The time profile of the emitted light for a and b 1) ab (obtained with time tagged214Bi-214Po) 2) b+ b- 11C decays by b+ e+ slow down, capture e-, Lifetime in the liquidisfew ns e+ scintillationdelayed (compared to e-)

  11. Phase I solar nresults: 5% accuracy on 7Be ninteraction 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 sevidence of oscillation Theor. uncertainty on 7Be flux : 7% Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  12. 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

  13. Phase I solar nresults: absence of day night asymmetry for 7Be n interaction rate • neregeneration by interaction with e: D/N effectis 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 Day time G. Bellini et al., Borexino Collaboration, Phys. Lett. B707 (2012) 22. Solar data alone select the LMA-MSW ifoneincludes the Borexino D/N result (no use of CPT) LMA-MSW LMA-MSW All solar n withoutBx withoutKamland All solar n with Bx withoutKamland Night time Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  14. Phase I solar nresults: first pepn detection and best limit on CNO • pep signal is ten time lowerthan7Be • About 3cpd/100t • CNO: rate similar to pep G. Bellini et al., Borexino Collaboration, Phys. Rev. Lett. 108 (2012) 051302.. • Most important background • 11C : • 210Bi : • External background (g from PMT): • Play againstexternal background • calib. with external232Th source • Monte Carlo simulation • Include the radialdistribution of events in the fit 7Be 11C 210Bi pep Ext back The effect of the 3 foldcoinc. The eec • Play against11C • 3 foldcoinc • Pulseshapeparam in the fit CNO • 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

  15. Phase I solar nresults: first pepn 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 LowMet.) Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

  16. PHASE I solar nresults: 8B flux with the lowestenergythreshld G. Bellini et al., BorexinoCollaboration,PRD 82. 108 (2010) 033006 • 208Tl (from the 232Thdecaychain) limits the energythreshold • lowsignal rate (Borexinois small…) 3 MeV electron energythreshold: the lowest ! Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  17. Purification of the scintillator : (betweenphase 1 and 2) • 6 puricationcycles • 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 Arbitrayunits • 232Th (from 212Bi-Po) • < 9 10-19g/g 95% C.L. • PHASE 1: 3 10-18 g/g • 85Kr (from spectralfit) • < 7 cpd/100t 95% C.L. • PHASE 1: 30.4±5.3±1.5 • 210Bi (from spectralfit) • 25±2 cpd/100t • PHASE 1: 41.8±2.8 • 210Po • 102cpd/100t • PHASE 1: 104cpd/100t Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

  18. PhaseII solar nresults: ppneutrinos !!! See the Oleg’s talk Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

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

  20. More about Non Standard Interactions (NSI) NSI change the ne-e differentialelasticscattering cross section • Bounds on the parameters with PHASE 1 data • betterlimits 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

  21. Phase I (and preliminary for PHASE 2) solar nresults : annualmodulation of the 7Be nsignal Expectedoscillationamplituteof 7Be nsignal: 6.8% peak-to-peak max flux: Jan. 3rd 47.5 e=0.0167 7Be ncpd/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., PhysRec D 112007(2014) Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  22. PHASE 1: annualmodulation of the 7Be nsignal Difficultanalysis in PHASE 1 due to unstable210Bi G. Bellini et al., Borexino Collaboration, Phys. Rev. C (2014) ?????. best fit 1s 2s expectedvalue Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

  23. PHASE 2: annualmodulation of the 7Be nsignal (preliminaryresults) 7Be signal and background: annualmodulation 210Bi time stability in PHASE 2 Expected time curve Preliminary Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

  24. DreamingaboutCNO neutrinos…….. 1) Reduce 210Bi by purification: partiallyachieved 2) Infer the 210Bi activity from the 210Po vs time 210Bi-210Po out of equilibrium: wesee an high 210Po rate b (63 KeV) a b 206Pb 210Bi 210Po 210Pb 5 days T1/2=22y stable 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, typicalBorexinorates • Needed: • 210Po activitynottoo high: actualvalues are OK • stableconditions for long time (1-2 years..) • no 210Po sources Constrain on 210Bi rate due to 210Po time decay Standard spectralfit

  25. 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

  26. Notonly 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! • Cleansignature by IBD • Geon: they probe the U,Th content of the Earth (no K) • Multidisciplinary research: particle physics&geophysics Likelihoodfit: geov + reactor No geon signal: rejected at 4.5 s C.L. • Eventselection and results • Search for coincidence (energy, time and spacecuts) • Large Fiducial Volume: distance from the vessel <25 cm • Exposure 613±26 ton year • 46 candidates • 14.3 +- 4.4 geo nevents • 31.2-6.1+7 reactorevents • 33.3±2.4 expectedreactorevents • 0.70±0.18 others back geon geon reactor reactors 1MeV≈ 500 p.e.

  27. Geon: implicationsabout Earth models For each element (U,Th) the expecetd geonsignalS 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 radiogenicheat) in a model dependent way (red and blue plot) TNU=1ev/ (y 1032 protons) Borexinoresults • 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

  28. Notonly solar n! Search for sterile-n in Borexino (SOX) Experimentalhints for sterile neutrinos Severalunexpectedsignalsat 3 s level: Accelerator anomaly (3.8 s) LSND and MiniBoone Excess of lowenergyneevents from a nmbeam Appearancesignalat a new short baseline? Galliumanomaly (2.8 s) Calibrationruns with radiocativesources in Gallex/SAGe Deficit of the detectedne R= 0.76+-0.09 Reactoranomaly (2.5 s) Re-evaluation of reactor antine spectra Rate deficit at short baseline (10-100m) R= 0.927+-0.230 Disapperance of electron neutrinosinto sterile neutrinos?? Light sterile neutrinos: a whitepaper Xiv:1204.5379 Gemma Testera (INFN Ge) - LNGS Sept. 5th, 2014

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

  30. nand anti-n neutrino sources to search for sterile nsignal SOX: Short distance neutrino Oscillations with BoreXino) • SOX A: • Source belowBorexino: 8.25 m from the center • No changes in the detector We are working on twosources: 51Cr nesource 44Ce anti- ne(in collaboration with Saclaygroup) End 2015: start data taking with 44Ce 8.25 m Oscillationlenght of the order of the Borexinosize

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

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

  33. The expectedsensitivity sin2(2 q14) sin2(2 q14)

  34. Summary, conclusions and perspectives • Borexinois the onlyreal time experimentwhodetectedn over all the solar spectrum • The results are relevant to both solar physics and neutrino physics • PHASE 2 with lower background than PHASE 1 almostconcluded: data analysis in progress • 7Be (goingtoward 3-3.5 % accuracy) • pep • 8B • seasonalmodulation • geo n • several rare processes • ….whilewaiting for a Supernova all the time • ! First ppneutrinosdetection in real time ! • A new calibrationisscheduled for the beginning of 2015: needed to reduce the uncertainties • Effort in progress toward the CNO detection : • weneedstableconditions • control of the temperature • furtherpurification of the scintillator (under discussionwithin the collaboration) • Sterile nsearch with radiocative source: start soon (end 2015) Gemma Testera (INFN Ge) - LNGS Sept. 5th 2014

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