Event Isotropy in the Salt Phase of SNO

Event Isotropy in the Salt Phase of SNO Jessica Dunmore University of Oxford NDM 03, Nara - 10 June 2003 J. Dunmore, University of Oxford NDM 03, 10 June 2003

Reactions in SNO p CC Charged Current ne ne + d p + e ES Elastic Scattering p d e nx nx e nx + e detected particle e nx NC Neutral Current nx + d nx + p + n nx p d n x = e, m, t J. Dunmore, University of Oxford NDM 03, 10 June 2003

Detecting Electrons • Relativistic electrons typically produce single cone of Cherenkov light detected by PMTs. Fit vertex J. Dunmore, University of Oxford NDM 03, 10 June 2003

Detecting Neutrons • Pure D 2 O: neutron capture on deuterons e g' n d J. Dunmore, University of Oxford g (6. 3 Me. V) t* Compton scatter t NDM 03, 10 June 2003

Simulated Neutron Event in D 2 O • Neutron events in pure D 2 O look very similar to electrons. J. Dunmore, University of Oxford NDM 03, 10 June 2003

Detecting Neutrons • Pure D 2 O: neutron capture on deuterons g' n g (6. 3 Me. V) d t* e Compton scatter t Distribution of no. g’s • Salt D 2 O: neutron capture on 35 Cl g ‘s n 35 Cl 36 Cl* J. Dunmore, University of Oxford (8. 6 Me. V) 36 Cl 1 2 3 4 5 6 7 8 9 NDM 03, 10 June 2003

Simulated Neutron Event in Salt • Neutron events in salt are more isotropic than electrons. J. Dunmore, University of Oxford NDM 03, 10 June 2003

Simulated Neutron Event in D 2 O • Neutron events in pure D 2 O look very similar to electrons. J. Dunmore, University of Oxford NDM 03, 10 June 2003

Definition of l A measure of the isotropy: is the average angle between all hit pairs. qij J. Dunmore, University of Oxford qik NDM 03, 10 June 2003

Distributions Nhit Range 50 -60 CC NC J. Dunmore, University of Oxford NDM 03, 10 June 2003

Can we do better? • Use higher orders of Spherical Harmonics – Define Harmonic Beta Parameters as where Pl is the lth order Legendre Polynomial, qij is the angle between hits i and j. eg. is very closely related to < qij > J. Dunmore, University of Oxford NDM 03, 10 June 2003

Harmonic Beta Parameters b 1 b 4 b 2 b 3 b 5 – Using a combination of b 1 and b 4 gives better separation power than using J. Dunmore, University of Oxford . NDM 03, 10 June 2003

Signal Extraction PDFs l Maximum likelihood will be used to separate CC and NC events. CC NC J. Dunmore, University of Oxford CC NC NDM 03, 10 June 2003

Correction to Monte Carlo • Comparison between 16 N calibration data and Monte Carlo showed a 2. 5% difference between mean b 1+4 b 4 values. • The Monte Carlo had more backscattered light than the data. • Electron multiple scattering cross section in EGS 4 is missing the Mott terms arising from electrons being 1/2 spin particles – a significant part of the discrepancy. J. Dunmore, University of Oxford Uncorrected Corrected 2. 4% difference in mean more isotropic b 14 less isotropic NDM 03, 10 June 2003

Isotropy Calibration • Calibration sources show excellent agreement between data and Monte Carlo. Cf Data Cf MC J. Dunmore, University of Oxford b 1+4 b 4 NDM 03, 10 June 2003

Conclusions • Using an isotropy parameter allows for the separation of electrons and neutrons in the salt phase via Maximum Likelihood techniques. • This gives statistical rather than event-by-event separation of CC and NC signals. • Using Harmonic Beta Parameters maximizes the separation power and is being used in the analysis of the salt data. • Calibration sources show excellent agreement between data and Monte Carlo. J. Dunmore, University of Oxford NDM 03, 10 June 2003