SNO II: Salt Strikes Back Joseph A. Formaggio University of Washington NuFACT’03 Update from the Sudbury Neutrino Observatory

Beyond a Reasonable Doubt… Our understanding of neutrinos has changed in light of new evidence: Neutrinos no longer massless particles (though mass is very small) Experimental evidence from three different phenomena: Solar Atmospheric Accelerator Reactor Data supports the interpretation that neutrinos oscillate. Murayama

Solar Neutrino Experiments Chlorine flux = 34% SSM Gallium flux = 57% SSM Super-K flux = 47% SSM EXPERIMENTAL RESULTS Need to measure x sloar flux, independently of e or solar model

The SNO Experiment

Mapping the Sun with ’s Neutrinos from the sun allow a direct window into the nuclear solar processes. Each process has unique energy spectrum Only electron neutrinos are produced SNO sensitive to 8 B neutrinos Light Element Fusion Reactions p + p  2 H + e + + e p + e - + p  2 H + e 2 H + p  3 He +  3 He + 4 He  7 Be +  7 Be + e -  7 Li +  + e 7 Li + p   +  3 He + 3 He  4 He + 2p 99.75% 0.25% 85%~15% 0.02% 15.07% ~10 -5 % 7 Be + p  8 B +  8 B  8 Be* + e + + e 3 He + p  4 He + e + + e

The SNO Collaboration G. Milton, B. Sur Atomic Energy of Canada Ltd., Chalk River Laboratories S. Gil, J. Heise, R.J. Komar, T. Kutter, C.W. Nally, H.S. Ng, Y.I. Tserkovnyak, C.E. Waltham University of British Columbia J. Boger, R.L Hahn, J.K. Rowley, M. Yeh Brookhaven National Laboratory R.C. Allen, G. B ü hler, H.H. Chen * University of California, Irvine I. Blevis, F. Dalnoki-Veress, D.R. Grant, C.K. Hargrove, I. Levine, K. McFarlane, C. Mifflin, V.M. Novikov, M. O'Neill, M. Shatkay, D. Sinclair, N. Starinsky Carleton University T.C. Andersen, P. Jagam, J. Law, I.T. Lawson, R.W. Ollerhead, J.J. Simpson, N. Tagg, J.-X. Wang University of Guelph J. Bigu, J.H.M. Cowan, J. Farine, E.D. Hallman, R.U. Haq, J. Hewett, J.G. Hykawy, G. Jonkmans, S. Luoma, A. Roberge, E. Saettler, M.H. Schwendener, H. Seifert, R. Tafirout, C.J. Virtue Laurentian University Y.D. Chan, X. Chen, M.C.P. Isaac, K.T. Lesko, A.D. Marino, E.B. Norman, C.E. Okada, A.W.P. Poon, S.S.E Rosendahl, A. Schülke, A.R. Smith, R.G. Stokstad Lawrence Berkeley National Laboratory M.G. Boulay, T.J. Bowles, S.J. Brice, M.R. Dragowsky, M.M. Fowler, A.S. Hamer*, A. Hime, G.G. Miller, R.G. Van de Water, J.B. Wilhelmy, J.M. Wouters Los Alamos National Laboratory J.D. Anglin, M. Bercovitch, W.F. Davidson, R.S. Storey * National Research Council of Canada J.C. Barton, S. Biller, R.A. Black, R.J. Boardman, M.G. Bowler, J. Cameron, B.T. Cleveland, X. Dai, G. Doucas, J.A. Dunmore, H. Fergani, A.P. Ferrarris, K. Frame, N. Gagnon, H. Heron, N.A. Jelley, A.B. Knox, M. Lay, W. Locke, J. Lyon, S. Majerus, G. McGregor, M. Moorhead, M. Omori, C.J. Sims, N.W. Tanner, R.K. Taplin, M.Thorman, P.M. Thornewell, P.T. Trent, N. West, J.R. Wilson University of Oxford E.W. Beier, D.F. Cowen, M. Dunford, E.D. Frank, W. Frati, W.J. Heintzelman, P.T. Keener, J.R. Klein, C.C.M. Kyba, N. McCauley, D.S. McDonald, M.S. Neubauer, F.M. Newcomer, S.M. Oser, V.L Rusu, S. Spreitzer, R. Van Berg, P. Wittich University of Pennsylvania R. Kouzes Princeton University E. Bonvin, M. Chen, E.T.H. Clifford, F.A. Duncan, E.D. Earle, H.C. Evans, G.T. Ewan, R.J. Ford, K. Graham, A.L. Hallin, W.B. Handler, P.J. Harvey, J.D. Hepburn, C. Jillings, H.W. Lee, J.R. Leslie, H.B. Mak, J. Maneira, A.B. McDonald, B.A. Moffat, T.J. Radcliffe, B.C. Robertson, P. Skensved Queen’s University D.L. Wark Rutherford Appleton Laboratory, University of Sussex R.L. Helmer, A.J. Noble TRIUMF Q.R. Ahmad, M.C. Browne, T.V. Bullard, G.A. Cox, P.J. Doe, C.A. Duba, S.R. Elliott, J.A. Formaggio, J.V. Germani, A.A. Hamian, R. Hazama, K.M. Heeger, K. Kazkaz, J. Manor, R. Meijer Drees, J.L. Orrell, R.G.H. Robertson, K.K. Schaffer, M.W.E. Smith, T.D. Steiger, L.C. Stonehill, J.F. Wilkerson University of Washington

Somewhere in the Depths of Canada...

Sudbury Neutrino Observatory 2092 m to Surface (6010 m w.e.) PMT Support Structure, 17.8 m cm PMTs ~55% coverage within 7 m 1000 Tonnes D 2 O Acrylic Vessel, 12 m diameter 1700 Tonnes H 2 O, Inner Shield 5300 Tonnes H 2 O, Outer Shield Urylon Liner and Radon Seal

Unique Signatures Charged-Current (CC) e +d  e - +p+p E thresh = 1.4 MeV e only Elastic Scattering (ES) x +e -  x +e - x, but enhanced for e Neutral-Current (NC) x +d  x +n+p E thresh = 2.2 MeV x

Results from Pure D 2 O Measurement of 8 B flux from the sun. Final flux numbers:  NC SNO * = 5.09  8B SSM * = * in units of 10 6 cm -2 s -1

SNO Phase II - Salt Enhanced NC sensitivity  n ~55% above threshold n+ 35 Cl  36 Cl+ ∑  Systematic check of energy scale E ∑  = 8.6 MeV NC and CC separation by event isotropy NC sensitivity  n ~14.2% above threshold n+ 2 H  3 H+  Energy near threshold E  = 6.25 MeV NC and CC separation by energy, radial, and directional distributions D2OD2O Salt

Advantages of Salt Neutrons capturing on 35 Cl provide much higher neutron energy above threshold. Gamma cascade changes the angular profile. Higher capture efficiency Same Measurement, Different Systematics n 36 Cl * 35 Cl 36 Cl 

Steps to a Signal Calibrations Optics Energy Neutron Capture Backgrounds Internal photo-disintegration PMT  -  External neutrons and other sources Signal Extraction Charged current (CC) Neutral Current (NC) Elastic Scattering (ES)

Sources of Calibration Use detailed Monte Carlo to simulate events Check simulation with large number of calibrations: Calibration Pulsed Laser 16 N 252 Cf 8 Li AmBe U & Th Sources Radon Spike Simulates nm optics 6.13 MeV  neutrons <13 MeV  decay 4.4 MeV ,n) source 214 Bi & 208 Tl ( ,  ) Rn backgrounds

Optical Calibration The PMT angular response and attenuation lengths of the media are measured directly using laser+diffuser (“laserball”). Attenuation for D 2 O and H 2 O, as well as PMT angular response, also measured in-situ using radial scans of the laserball. Exhibit a change as a function of time after salt was added to the detector.

16 N Calibration Source Energy response of the detector determined from 16 N decay. Mono-energetic  at 6.13 MeV, accompanied by tagged  decay. Provides check on the optical properties of the detector. Radial, temporal, and rate dependencies well modeled by Monte Carlo.

16 N Energy Response In addition to 16 N, additional calibration sources are employed to understand energy response of the detector. Muon followers 252 Cf 8 Li 24 Na Systematics dominated by source uncertainties, optical models, and radial/asymmetry distributions Energy Scale = + 1.1%* 252 Cf 8 Li Energy Resolution = + 3.5%* *Preliminary

Neutron Response Use neutron calibration sources ( 252 Cf and AmBe) to determine capture profile for neutrons. 252 Cf decays by  emission or spontaneous fission. Observe resulting  cascade from neutron capture on 35 Cl. Monte Carlo agrees well with observed distributions. Neutrons/fission =

Neutron Efficiency Salt Preliminary Capture efficiency increase by 4-fold in comparison to pure D 2 O phase. Systematics include: source position energy response source strength modeling Less than 3% total systematic uncertainty on capture.

Backgrounds Calibrations Optics Energy Neutron Capture Backgrounds Internal photo-disintegration PMT  -  External backgrounds and other sources Signal Extraction Charged current (CC) Neutral Current (NC) Elastic Scattering (ES)

3.27 MeV   MeV  Uranium An Ultraclean Environment Highly sensitive to any  above neutral current (2.2 MeV) threshold. Sensitive to 238 U and 232 Th decay chains “I will show you fear in a handful of dust.” -- T.S. Eliot Thorium MeV 

U / Th and Other Backgrounds Other Backgrounds Fission from possible U and Cf contamination Atmospheric neutrinos 24 Na from the vessel 13 C( ,n) 16 O from acrylic  activation from radon embedded on the surface of the acrylic vessel. Measured from neutron radial profile and internal e + e - high-energy gamma conversion from 16 O. Salt provides unique window of sensitivity to external neutrons. Uranium and Thorium Two methods: In-situ: Low Energy Data Separate 208 Tl and 214 Bi based on event isotropy Ex-situ: Ion exchange ( 224 Ra, 226 Ra) Membrane degassing Count daughter product decays Preliminary salt measurements yield background levels at par with what was measured in D 2 O

Steps to a Signal Calibrations Optics Energy Neutron Capture Backgrounds Internal photo-disintegration PMT  -  External Neutrons and other backgrounds Signal Extraction Charged current (CC) Neutral Current (NC) Elastic Scattering (ES)

NC E higher Less Rad. Sep. Directionality Unchanged Isotropy Separation Energy R3R3 cos  sun  ij Variables: E, R 3, cos  sun,  ijUnconstrained 8 B Shape Constrained Changes in Signal Extraction Based on data taken from May 27, 2001 to October 10, Total 254 live days of neutrino data. Previous analysis used energy, radial, and solar angle distribution to separate events. Introduction of salt moves neutron energy higher (but disrupts radial separation). New statistical separation using event isotropy, allowing both energy dependent and independent analyses.

Fit Result Uncertainties (Monte-Carlo) 10%5.3%3.8% R,  sun,Iso 10%4.6%3.3% E,R,  sun,Iso 10%6.3%4.2% E,R,  sun 10%8.6%3.4% E,R,  sun ES Stat. Error NC Stat. Error CC Stat. Error Variables D 2 O results Simulated Salt Phase Results Published D 2 O energy-unconstrained statistical error was 24% Simulations assume 1 yr of data with central values and cuts from D 2 O phase results

What’s Inside Pandora’s Box?

Day – Night Contours (%) Projected SNO Assuming D 2 O NC Result Probability Contours De Holanda, Smirnov hep-ph/

Coming Soon... SNO III: Return of the Neutron

SNO Phase III The Neutral Current Detectors Physics Motivation Event-by-event separation. Measure NC and CC in separate data streams. Different systematic uncertainties than neutron capture on NaCl. NCD array as a neutron absorber. Detection Principle 2 H + x  p + n + x MeV (NC)  3 He + n  p + 3 H x n Array of 3 He counters 40 Strings on 1-m grid 398 m total active length NCD PMT

Counters Ultraclean nickel counters of varying length, connected as “string”. Mixture of 3 He (85%) and CF 4 (15%). Anchored to the bottom of the acrylic vessel. Radioassayed and polished to reduce U and Th backgrounds.

The Remotely Operated Vehicle A remote controlled submarine will be used to deploy the NCDs in the acrylic vessel. The bottom end of the NCD string will be pulled to the floor of the acrylic vessel directly below the neck with a pulley. The ROV will then move the bottom end of the string along the floor of the acrylic vessel to its anchor point and anchor it.

Future Solar Physics Salt Phase: More precise measurements of CC/NC ratio, due to increased sensitivity to neutrons. Ability to extract solar flux with and without assumptions regarding the energy spectrum. Final systematics and backgrounds currently being evaluated. NCD Phase: Event-by-event separation of charged current and neutral current events. Model-independent extraction of charged current and neutral current flux. Begin deployment of counters in October.

ROV Training

Using Angular Information Use semi energy-independent variable  14 to separate neutrons from electrons via angular distributions. Allows one to reconstruct the energy profile of NC and CC events w/o use of energy constraint. Powerful check on the spectral shape of 8 B Monte Carlo

SNO during Construction

Masses and Mixings P ee ~ 1-sin 2 (2  ) sin 2 (1.27  m 2 L / E) Physics:  m 2 & sin 2 (2  ) Experiment: Distance (L) & Energy (E)    e e e 

Three Pieces For a full understanding of neutrino properties, it is necessary to determine: The mixing parameters and phases The neutrino masses The physics governing mass e µ  hierarchicaldegenerate Higgs Field Precision measurements!

Signal Extraction CC ES NC 576.5

Summary of Backgrounds

Status All the NCDs are underground. The 156 NCDs that will be deployed have been identified. Pre-deployment welding is in progress. The DAQ is operational and has been taking data from complete unwelded strings of NCDs underground. All of the electronics are underground and operational. The current estimated deployment date is October 2003, subject to removal of salt.

What is changing? Why? Combination of both attenuation length and reflectors changing over time. Change in optics accounts for why there was a large drop in energy response. Attenuation length change correlated with change in water chemistry Reflectors consistent with both a sudden drop in response, as well as a gradual decay. Possible causes: petal degradation, temperature change Prediction from attenuation 16 N measured energy

Radon Spike Further aim at understanding backgrounds to lower energy threshold. Required to understand the detector uniformity and low energy tails. Injection of 50 ml of solution at 25 grid points in vessel 2.2 million Rn atoms/liter

16 N Calibration Source Energy response of the detector determined from 16 N decay. Mono-energetic  at 6.13 MeV, accompanied by tagged  decay. Provides check on the optical properties of the detector. Radial, temporal, and rate dependencies well modeled by Monte Carlo.