The Sudbury Neutrino Observatory: Observation of Flavor Change for Solar Neutrinos. Art McDonald, Professor Emeritus Queen’s University, Kingston, Ontario, Canada
Neutrinos from the Sun The middle of the sun is so hot that the centers of the atoms (nuclei) fuse together, giving off lots of energy and neutrinos. The neutrinos penetrate easily through the dense material in the Sun and reach the earth.
Understanding How the Sun Burns Hans Bethe Willy Fowler Basic Theory 1939 Theory, Experiments 1950’s, 60’s Nobel Laureate 1967 Nobel Laureate 1983 We stand on the Shoulders of Giants
Pioneers of Solar Neutrino Physics: Davis, Bahcall, Pontecorvo & Gribov 1968: Gribov and Pontecorvo suggest flavor change (oscillation) of 1968: Davis’ Measurements with Chlorine-based electron neutrinos to muon detector show 3 times fewer than Bahcall’s calculations. neutrinos as a possible Ray Davis: Nobel Laureate 2002 reason.
SOLAR FUSION CHAIN 1984: Chen proposes heavy water to search for direct evidence of flavor transformation for neutrinos from 8 B decay in the Sun. Electron neutrinos and all active neutrinos are measured separately to show flavor change independent of solar model calculations.
Spokespersons 1985 McDonald Sinclair: 1984 1987:US UK 1984 Ewan: 1989:Director Chen : Canada US SNO Collaboration Meeting, Chalk River, 1986 PROPOSAL TO BUILD A NEUTRINO OBSERVATORY IN SUDBURY, CANADA D. Sinclair, A.L. Carter, D. Kessler, E.D. Earle, P. Jagam, J.J. Simpson, R.C. Allen, H.H. Chen, P.J. Doe, E.D. Hallman, W.F. Davidson, A.B. McDonald, R.S. Storey, G.T. Ewan, H.-B. Mak, B.C. Robertson Il Nuovo Cimento C9, 308 (1986)
How does SNO detect neutrinos from the Sun? Billions of them stream out every second from the nuclear reactions powering the Sun and strike our detector. Once an hour they make a burst of light that we can detect.
Unique Signatures in SNO (D 2 O) (1 in 6400 molecules in ordinary water are D 2 O. We used >99.75% D 2 O) Electron Neutrinos (CC) ν e +d → e - +p+p E thresh = 1.4 MeV Equal Sensitivity All Types (NC) ν x + d → ν x + n+p E thresh = 2.2 MeV 3 ways to detect neutrons Comparing these two reactions tells if electron neutrinos have changed their type. Radioactivity must be carefully Elastic Scattering from Electrons controlled because gamma ν x +e - → ν x +e - rays can also break apart ν x , but enhanced for ν e x 6 deuterium and produce a free 10 times lower count rate neutron. Points away from the Sun
3 neutron (NC) detection methods (systematically different) Phase I (D 2 O) Phase II (salt) Phase III ( 3 He) Nov. 99 - May 01 July 01 - Sep. 03 Nov. 04-Dec. 06 n captures on 2 tonnes of NaCl 400 m of proportional 2 H(n, γ ) 3 H n captures on counters 35 Cl(n, γ ) 36 Cl 3 He(n, p) 3 H Effc. ~14.4% NC and CC separation Effc. ~40% Effc. ~ 30% capture by energy, radial, and NC and CC separation Measure NC rate with directional by event isotropy entirely seperate distributions detection system. 35 Cl+n 5 cm 8.6 MeV 2 H+n 6.25 MeV n 3 H p 3 He n + 3 He → p + 3 H 3 H 36 Cl
Sudbury Neutrino Observatory (SNO) Neutrinos are very difficult NEUTRINO to detect so our detector had to be very big with low radioactivity, deep underground. 1000 tonnes of heavy 34 m water: D 2 O or $ 300 million on Loan for $1.00 ~ Ten Stories 9500 light sensors High! 12 m Diameter Acrylic Container 2 km below Ultra-pure the Water: H 2 O. ground Urylon Liner and Radon Seal
To study Neutrinos with little radioactive background, we went 2 km underground to reduce cosmic rays and built an ultra-clean detector: SNO VALE’S CREIGHTON MINE NEAR SUDBURY, ONTARIO Nickel ore
SNO: One million pieces transported down in the 3 m x 3 m x 4 m mine cage and re-assembled under ultra-clean conditions. Every worker takes a shower and wears clean, lint-free clothing. 70,000 showers during the course of the SNO project
Water systems were developed to provide low radioactivity water and heavy water: 1 billion times better than tap water. Less than one radioactive decay per day per ton of water!! Steven Hawking’s Visit Posed some special Challenges – INCO Designed a special Rail car for him. (Stainless steel with Lots of nickel, of course)
WE OBSERVED NEUTRINOS FROM THE SUN WITH ALMOST NO RADIOACTIVE BACKGROUND SUMMED DATA After Calibration: ELECTRON NEUTRINOS ELECTRON NEUTRINOS AT EARTH ARE ALL NEUTRINO TYPES ONLY 1/3 OF ALL NEUTRINOS Electron kinetic energy (MeV) Data from Pure Heavy Water Phase in 2002
Excellent Agreement With the SOLAR Solar Model MODEL Calculations SNO USED LESS THAN ONE HEAVY CHANCE IN 10 WATER TO MILLION MEASURE FOR “NO TWO CHANGE IN SEPARATE NEUTRINO THINGS TYPE” ELECTRON ALL NEUTRINO NEUTRINOS TYPES A CLEAR DEMONSTRATION NEUTRINOS CHANGE THEIR TYPE: 2/3 OF THE ELECTRON NEUTRINOS HAVE CHANGED TO MU, TAU NEUTRINOS ON THE WAY FROM THE SOLAR CORE TO EARTH. THIS REQUIRES THAT THEY HAVE A FINITE MASS.
SNO Energy Calibrations 6.13 MeV 19.8 MeV Detailed Detector Mapping with LaserBall, 16 N, 252 Cf, 238 U, 232 Th β ’s from 8 Li γ ’s from 16 N and t(p, γ ) 4 He 252 Cf neutrons Radioactivity: Rn and encapsulated U and Th
Measuring U/Th Content Ex-situ Ion exchange ( 224 Ra, 226 Ra) Membrane Degassing ( 222 Rn) count daughter product decays In-situ Low energy data analysis Separate U and Th Chains Using Event isotropy Th Chain U Chain Numbers of background neutrons from gamma rays breaking apart deuterium are measured to be 3 times smaller than the signal. Uncertainty from this is less than Isotropy 10% of the neutrino measurement.
As measured 1999-2003 D 2 O As simulated in 1987 D 2 O NaCl
SNO Results for Salt Phase Flavor change determined by > 7 σ. New physics beyond ν µ , The Standard Model of ν τ Elementary Particles! The Total Flux of Active Electron neutrinos Neutrinos is measured + + φ = 0 . 06 0 . 08 independently (NC) and agrees 1 . 68 ( stat. ) ( syst. ) − − CC 0 . 06 0 . 09 well with solar model + + φ = 0 . 21 0 . 38 4 . 94 ( stat. ) ( syst. ) − − NC 0 . 21 0 . 34 Calculations: + + φ = 0 . 22 0 . 15 2 . 35 ( stat. ) ( syst. ) − − 0 . 22 0 . 15 ES 5.82 +- 1.3 (Bahcall et al), − − 6 2 1 (In units of 10 cm s ) 5.31 +- 0.6 (Turck-Chieze et al) φ + = ± 0 . 029 CC 0 . 34 0 . 023 ( stat. ) Electron Neutrinos are only 1/3 of Total − φ 0 . 031 NC
Phase 3: 400 m of Ultra Low Background Neutron Counters installed in the heavy water by a remotely controlled submarine Light Sensors Neutron Detectors The original The Neutron Counters were a great Submarine … success (after a lot of hard work by Hamish Robertson and his team). Yellow, of course! The yellow paint was much too radioactive. Well, maybe not!
Including other solar neutrino measurements 1989 on 2001 on 1968 on 1992 on Kamiokande , SNO Bahcall et al.
Solar Neutrino Problem Year 2000 Experimental sensitivity: primarily or exclusively electron neutrinos Theory pp ν 8 B ν 7 Be, 8 B ν
Solar Neutrino Problem Resolved all ν x Theory ν e only
NEUTRINO OSCILLATIONS AND NEUTRINO MASS Neutrino Flavors (Electron, Muon, Tau) can be expressed as combinations of Masses (1,2,3) Tau Neutrino Quantum Muon mechanics Neutrino states Electron Neutrino After traveling there is a The mass fractions Created in a unique finite probability to be change as the Flavor State detected as a different neutrino travels flavor type
Combining SNO with other solar measurements Solar Fluxes: Bahcall et al Experiment vs Solar Models The analysis concludes that the electron neutrinos are converted to a pure Mass 2 state by interaction with the dense electrons in the sun via the Mikheyev-Smirnov-Wolfenstein (MSW) effect. This interaction determines that Mass 2 is greater than Mass 1 as well as determining ∆ m 12 2 and the mixing parameter θ 12
DEAP/CLEAN 3600 kg Ar, The Future: SNOLAB New large scale MiniCLEAN 500 kg Ar, Ne: Cube Hall project. Dark Matter HALO Phase II 60 to 800 times lower SuperNovae Cryopit µ fluxes than Now:PICO-2L, Gran Sasso, Kamioka. DAMIC:Dark Matter 2016: SuperCDMS Dark Matter Now: PICO-60: Dark Matter New SNO+: Double Beta, solar,geoneutrinos Area Ladder Labs Low Background counting facility Utility Area Personnel SNO facilities Cavern All Lab Air: Class < 2000 Christchurch May 28 th , 2008 SNOLAB @ Neutrino 2008
Recommend
More recommend
