J. Dunmore, University of Oxford NDM03, 10 June 2003 Event Isotropy in the Salt Phase of SNO Jessica Dunmore University of Oxford NDM03, Nara - 10 June 2003

J. Dunmore, University of Oxford NDM03, 10 June 2003 Reactions in SNO Charged Current e + d  p + p + e  Elastic Scattering x + e   x + e  Neutral Current x + d  x + p + n x = e,  CC ES NC e ee p p d x ee ee x x n p d x detected particle

J. Dunmore, University of Oxford NDM03, 10 June 2003 Detecting Electrons Relativistic electrons typically produce single cone of Cherenkov light detected by PMTs. Fit vertex

J. Dunmore, University of Oxford NDM03, 10 June 2003 Detecting Neutrons Pure D 2 O: neutron capture on deuterons n t*t*  d t (6.3 MeV) ee Compton scatter ''

J. Dunmore, University of Oxford NDM03, 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 NDM03, 10 June 2003 Detecting Neutrons Pure D 2 O: neutron capture on deuterons n t*t*  d t (6.3 MeV) ee Compton scatter '' n 36 Cl *  ‘ s 35 Cl (8.6 MeV) 36 Cl Salt D 2 O: neutron capture on 35 Cl Distribution of no.  ’s

J. Dunmore, University of Oxford NDM03, 10 June 2003 Simulated Neutron Event in Salt Neutron events in salt are more isotropic than electrons.

J. Dunmore, University of Oxford NDM03, 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 NDM03, 10 June 2003 Definition of A measure of the isotropy: is the average angle between all hit pairs.  ij  ik

J. Dunmore, University of Oxford NDM03, 10 June 2003 Distributions CC NC Nhit Range 50-60

J. Dunmore, University of Oxford NDM03, 10 June 2003 Use higher orders of Spherical Harmonics –Define Harmonic Beta Parameters as where P l is the l th order Legendre Polynomial,  ij is the angle between hits i and j. eg. is very closely related to Can we do better?

J. Dunmore, University of Oxford NDM03, 10 June 2003 Harmonic Beta Parameters –Using a combination of  1 and  4 gives better separation power than using. 11 33 22 44 55

J. Dunmore, University of Oxford NDM03, 10 June 2003 Signal Extraction PDFs CC NC CC NC Maximum likelihood will be used to separate CC and NC events 

J. Dunmore, University of Oxford NDM03, 10 June 2003 Correction to Monte Carlo The Monte Carlo had more backscattered light than the data. more isotropic   14  less isotropic Uncorrected Corrected 2.4% difference in mean Comparison between 16 N calibration data and Monte Carlo showed a 2.5% difference between mean  1 +4  4 values. Electron multiple scattering cross section in EGS4 is missing the Mott terms arising from electrons being 1/2 spin particles – a significant part of the discrepancy.

J. Dunmore, University of Oxford NDM03, 10 June 2003 Isotropy Calibration Calibration sources show excellent agreement between data and Monte Carlo.  1 +4  4 Cf Data Cf MC

J. Dunmore, University of Oxford NDM03, 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.