The recent results of solar neutrino measurement in Borexino Yusuke - PowerPoint PPT Presentation

The recent results of solar neutrino measurement in Borexino Yusuke Koshio On behalf of Borexino collaboration

Why solar neutrinos? • Neutrino physics n e survival Probability (Pee) – MSW-LMA scenario is our current understandings 0.7 Precise determination of the Before Borexino neutrino oscillation parameters 0.5 – Any other possibility?  Day/Night asymmetry 0.3  Survival probability in n e 1 10 • Solar astrophysics E n (MeV) – Verify the Standard Solar Model (SSM) Direct measurements for sub-MeV solar neutrino flux  Does CNO cycle really happen in the sun?  pep (1.1%) and pp (0.6%) are predicted with higher precision. – Study the metallicity (High or Low) controversy  Differences are ~10% in 7 Be, ~20% in 8 B, ~30% in CNO LowNu 2011/11/9 2

Solar neutrino spectrum Flux (cm -2 sec -1 MeV -1 ) (Bahcall-Pena-Garay-Serenelli 2008) BOREXINO pp • Precise measurement < 5% 7 Be uncertainties (10% in previous) • Day/Night asymmetry 13 N pep 15 O Can be seen? CNO 8 B 17 F hep 7 Be Neutrino energy (MeV) LowNu 2011/11/9 3

Laboratori Nazionali del Gran Sasso Assergi, (AQ), Abruzzo, Italy 120km from Roma LNGS Outside laboratory 1300m underground (3500m w.e.) Borexino detector + fluid plants Underground labs LowNu 2011/11/9 4

BOREXINO Liquid scintillator: 270 t PC+PPO (1.5g/l) Experimental in a 150 m m thick target : Inner nylon vessel (R=4.25m) • Solar Neutrinos Buffer region: PC+DMP quencher (5g/l) The wide energy 4.25m<R<6.75m range in real time are measurable. Outer nylon vessel: R=5.50m • Geo Neutrinos ( 222 Rn Barrier) • SuperNova Stainless Steel Sphere: neutrinos R=6.75m • Long/Short base 2212 8” PMTs with line neutrinos light guide cone. 1350m 3 • etc… Water tank: g and n shield m water cherenkov detector 208 PMTs in water 2100m 3 LowNu Data taking started in 2007 2011/11/9 5

Detection principle Solar neutrinos are detected through n solar + e  n + e elastic scattering on electrons Scintillation lights are emitted  High light yield (~500 p.e. /MeV)  Good timing response  Pulse shape discrimination b ut…  No neutrino direction  No way to distinguish between neutrinos and b/g backgrounds Extreme radiopurity is required (NIM A, 609, 1 (2009) 58) LowNu 2011/11/9 6

Detector calibration globe box assembly 7 CCD cameras; determine the absolute umbilical cord source position <2cm Source insertion movable arm PMT radioactive source g b a n 222 Rn loaded dopant dissolved in small water vial Am-Be liq. scint. vial n 57 Co 139 Ce 203 Hg 85 Sr 54 Mn 65 Zn 60 Co 40 K 14 C 214 Bi 214 Po n-p n+Fe + 12 C Energy 1.1 0.122 0.165 0.279 0.514 0,834 1.1 1.4 0.15 3.2 (7.6) 2.2 4.94 ~7.5 (MeV) 1.3 clear tag from Bi-Po LowNu fast coincidence 2011/11/9 7

Position and Energy calibration Reconstructed position shift from nominal R Z -3cm -0.3cm Using the 184 points of Rn calibration data, the fiducial volume uncertainty is 1.3% The energy scale uncertainty is 1.5% LowNu 2011/11/9 8

Results in 7 Be neutrino

Reduction and signal extraction MC; signal + intrinsic BG 14 C 750 days of data 210 Po with 100ton norm. No cut FV cut soft a/b cut 11 C 7 Be+ 85 Kr ext.bkg A spectral fit was applied by solar neutrino signals and all the intrinsic backgrounds LowNu 2011/11/9 10

Result of 7 Be solar neutrino rate w/o Po subtraction 7 Be rate (E=862 keV line) in 750 days of data +1.5 46.0 ± 1.5 (stat) (sys) - 1.6 counts/(day x 100t) (total uncertainty is 4.7%) Source of systematic error Trigger eff. And stability <0.1 % with Po subtraction Live time 0.04% Scintillator density 0.05 % Sacrifice of cuts 0.10 % previous Fiducial volume +0.5 6% – 1.3% Fit methods 2.0 % 6% Energy response 2.7 % Total syst. error +3.4 8.5% – 3.6% LowNu 2011/11/9 11

Implication on solar physics • Metallicity controversy Fit to the available all solar neutrino data leaving free High Low ( f = F / F (SSM) ) f Be and f BO Hard to discriminate • Other solar neutrino sources Each solar neutrino flux can be calculated with solar luminosity constraint. M.C.Gonzalez-Garcia, M.Martoni, J.Salvado JHEP 05(2010)072 / 0910.4584 +0.02 F pp = (6.06 )x10 10 cm -2 s -1 (f pp = 1.013) - 0.06 F CNO < 1.3x10 9 cm -2 s -1 (f CNO < 2.5) at 95%C.L. LowNu 2011/11/9 12

Day/Night asymmetry in 7 Be rate • In the MSW scenario, the flux rate in Night should be higher than Day because of the regeneration effect. • In the 7 Be energy region, no effect expected in MSW- LMA region, but large in MSW-LOW region (~20%). Day (positive Sun altitude) 360.25 days Night (negative Sun altitude) 380.63 days No significant effect was found  N D  Adn  ( N D ) / 2    0 . 001 0 . 012 ( stat .) 0 . 007 ( sys .) LowNu 2011/11/9 13

Neutrino oscillation analysis All solar w/o BX All solar with BX Only Borexino excluded by BX D/N asymmetry 68.27, 90%C.L. LOW solution excluded Confirm LMA scenario at >8 s by BX data by BX data alone LowNu 2011/11/9 14

Results in pep and CNO

A challenging task • Low signal rates with large backgrounds – A few cpd/100ton for signal, while 11 C as a 11 C dominant BG for pep is 210 Bi ~28 cpd/100ton. pep – External BG of 208 Tl, 214 Bi from PMTs, CNO stainless steel sphere… Cosmogenic 11 C • How to separate? m + 12 C  11 C+n+ m – Three Fold Coincidence – e+/e- pulse shape captured by proton (2.2MeV g ) discrimination – Position distribution 11 B+e + + n e ( t ~30min) – Spectrum LowNu 2011/11/9 16

Three Fold Coincidence • Veto using space-time correlation m – 2 m sec cylindrical veto along its track Neutron production g e + Spherical cut (r=1m) around g - 2hrs after m Optimal compromise: 91% rejection of 11 C keeping 48.5% residual exposure LowNu 2011/11/9 17

e+/e- pulse shape discrimination Positrons have different time profile and event topology with electrons. • Form positoronium (51.2%, 3.12ns) (Phys.Rev.C 83(2010)015504) Annihilation g s • LowNu 2011/11/9 18

External background • Recognized by position and energy Calibration data vs MC distribution by MC simulation • Simulation validated with calibration data Radial of high activity external 228 Th source (arXiv 1110.1217) Energy Good agreement LowNu 2011/11/9 19

Results of the spectrum fitting pep rate: 3.1 ± 0.6(stat.) ± 0.3(sys.) count/day/100ton  (1.6 ± 0.3) x 10 8 cm -2 s -1 Main systematics: fit configuration / energy scale First direct observation. (98%C.L.) CNO rate: < 7.9 count/day/100ton  < 7.7x 10 8 cm -2 s -1 (95%C.L. upper limit) Strongest constraint (f CNO < 1.4) LowNu 2011/11/9 20

n e survival Probability (Pee) Consistent with MSW-LMA scenario LowNu 2011/11/9 21

CNO measurement in future • Similar spectra as 210 Bi difficult to separate… 210 Bi Reduce as much as possible CNO • Borexino phase II – We have undertaken a series of purification campaigns (mainly water extraction and nitrogen stripping) to decrease radioactive backgrounds since July 2010. – Significant removal of 210 Bi was found. – Operation is now on-going. LowNu 2011/11/9 22

Summary • Precise measurement (<5% uncertainty) of the 7 Be solar neutrino has achieved thanks to the internal source calibration. • The analysis techniques have been able to suppress backgrounds. • First direct measurement of pep neutrinos, and strongest constraint to CNO flux. • Purification efforts are now on-going, which should improve the pep flux measurement and directly observe the CNO neutrinos. LowNu 2011/11/9 23

Thank you for your attention (USA) UMass Amherst (USA) LowNu 2011/11/9 (USA) 24

Backup

CNGS n velocity • Activity is in progress to check the OPERA result about the CNGS neutrino velocity • Need some hardware upgrade • Ready for the 2012 beam • Check the data already collected. – T ime resolution was not accurate enough… – Independent way from OPERA all the steps of the measurement • Also available to collaborate with OPERA LowNu 2011/11/9 26

Metallicity controversy inside the sun • “Improved” calculation of the solar composition changes the fluxes. – Z/X=0.0229(GS98)  0.0165(AGS05) (X:hydrogen, Y:helium, Z:others) GS98 AGS05 – But, disagree with helioseismology ?? 5.97x10 10 6.04x10 10 pp • Observed 8 B flux       1.41x10 8 1.45x10 8 pep 0 . 1 6 2 1 5 . 3 10 cm s  8 0 . 2 B 7.90x10 3 8.22x10 3 hep • Precise 7 Be flux may useful 7 Be 5.07x10 9 4.55x10 9 information. ~10% • CNO n observation may solve 8 B 5.94x10 6 4.72x10 6 13 N 2.88x10 8 1.89x10 8 the problem. – Study in progress in Borexino ~30% 15 O 2.15x10 8 1.34x10 8 – One of goal for SNO+ 17 F 5.84x10 6 3.25x10 6 LowNu 2011/11/9 27

a/b discrimination PMT hit timing distribution LowNu 2011/11/9 28

Significance of result (pep) LowNu 2011/11/9 29

Significance of result (CNO) LowNu 2011/11/9 30

Significance of result in pep and CNO analysis LowNu 2011/11/9 31