NDM03, 10 June 2003

J. Dunmore, University of Oxford

Event Isotropy in the Salt Phase of SNO

Jessica DunmoreUniversity of Oxford

NDM03, Nara - 10 June 2003

NDM03, 10 June 2003

J. Dunmore, University of Oxford

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

p

pd

x

e e

x

x

n

pd

x

detected particle

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Detecting Electrons• Relativistic electrons typically produce single

cone of Cherenkov light detected by PMTs.

Fit vertex

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Detecting Neutrons• Pure D2O: neutron capture on deuterons

n

t*

d t(6.3 MeV)

e

Comptonscatter

'

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Simulated Neutron Event in D2O

• Neutron events in pure D2O look very similar to electrons.

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Detecting Neutrons• Pure D2O: neutron capture on deuterons

n

t*

d t(6.3 MeV)

e

Comptonscatter

'

n

36Cl*

‘s

35Cl

(8.6 MeV)

36Cl

• Salt D2O: neutron capture on 35Cl

Distribution of no. ’s

1 2 3 4 5 6 7 8 9

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Simulated Neutron Event in Salt

• Neutron events in salt are more isotropic than electrons.

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Simulated Neutron Event in D2O

• Neutron events in pure D2O look very similar to electrons.

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Definition of A measure of the isotropy: is the average angle between all hit pairs.

ij

ij

ij

ik

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Distributions

CCNC

ij

Nhit Range 50-60

NDM03, 10 June 2003

J. Dunmore, University of Oxford

• Use higher orders of Spherical Harmonics– Define Harmonic Beta Parameters as

where Pl is the lth order Legendre Polynomial,

ij is the angle between hits i and j.

eg.

is very closely related to < ij >

Can we do better?

cosl l ij i jP

1 cos ij i j

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Harmonic Beta Parameters

– Using a combination of 1and 4 gives better separation power than using .

1 32

4 5

ij

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Signal Extraction PDFs

CCNC

CCNC

Maximum likelihood will be used to separate CC and NC events

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Correction to Monte Carlo

• The Monte Carlo had more backscattered light than the data.

more isotropic 14 less isotropic

UncorrectedCorrected

2.4% difference in mean

• Comparison between 16N calibration data and Monte Carlo showed a 2.5% difference between mean 1+44 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.

NDM03, 10 June 2003

J. Dunmore, University of Oxford

Isotropy Calibration

• Calibration sources show excellent agreement between data and Monte Carlo.

1+44

Cf DataCf MC

NDM03, 10 June 2003

J. Dunmore, University of Oxford

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.