Reproducing 2.09 Results

Running the standard job (5 Mev e$^-$ in D$_2$O ) will at once reveal that 3.00 produces markedly different PMT hit patterns to 2.09. This is largly the result of two major changes to:-

• The PMT response functions.

• The attenuation lengths and isothermal compressibilities (and, hence, the Rayleigh scattering) in H$_2$O and D$_2$O .

To change back to the 2.09 PMT response fuctions use the command:-

@select_2_09_pmt_response

To change back to the 2.09 attenuation lengths and isothermal compressibilities use:-

titles media_2_09.dat

The PMT response function previously used was found to be in error according to the measured curves of Rob Boardman. The differences arise from 2 sources:-

1. The QE curve for the wrong tube was used which did not correspond to the Schott 8246 glass used in the post-production SNO tubes and also had a lower peak efficiency

2. The single pe collection efficiency of the PMT, which Boardman measured as being relatively low (55%), was not taken into account.

After both these effects are taken into account, this results in an overall average loss of about 30% in light level, with proportionally more light produced at lower wavelengths.

The attenuation lengths in H2O and D2O have been dropped to practically zilch and, instead, the isothermal compressibilities (and, hence, the Rayleigh scattering) have been increased to 2 times the theortical values. This is in line with the current best-guess assumptions that:-

1. The H2O and D2O should really both be very clean with little absorption.

2. Any observed light ``extinction'' would be almost entirely due to approximately isotropic scattering from very small particles.

3. We should do about as well as the lowest extinction values ever measured, which corresponds to a scattering level of about twice the theoretical Rayleigh limit.

4. Any potential absorption effects should be the same in D2O as in H2O for wavelengths below about 400nm.