On Fri, 31 Mar 2006, Christopher Crawford wrote:
>> -Mascarad+Epel issue
>> +Mascarad only produces the radiative tail starting at a cutoff
>> energy for the radiated photon (ad hoc set to 10 MeV).
>
> Chi and Vitaliy, is Mascarad implemented in MC this way? I'm just checking
> that both the hard and soft parts have been integrated out to the cutoff
> energy, and that both both parts are included in the radiative cross section
> past that. The original Mascarad did not generate cross sections in this
> manner.
>
>> +Electron momentum generated with Mascarad is thus shifted relative
>> to the unradiated momentum by at least 10 MeV.
>> +Average momentum shift of electrons due to internal radiation
>> convoluted with resolution can only be correctly estimated by
>> Montecarlo if Mascarad is properly combined with the unradiated
>> yield.
>
> We can get this straight from the original Mascarad code, by calculating the
> radiated cross section as a function of cutoff energy and then taking the
> derivative to get the W-spectrum (and then convoluting with the BLAST
> W-resolution). Note that the momentum shift depends on the cutoff energy
> used in the analysis (not the 10 MeV), and you must be consistent. I'm
> calculating it this way for the geometrical offsets code.
>
>> +The proper combination of Mascarad with Epel needs to be established.
>
> This is just a matter of running the original Mascarad to calculate the
> radiated elastic cross section with the cutoff set to 10 MeV. It is probably
> best to add an elastic channel with the <10MeV radiation-corrected cross
> section. Chi, don't we already have this channel?
The discussion above sounds a bit funky... Way too complicated for
what a radiation code should do in my opinion. Why should it start
producing the tail only after 10 MeV? So what happened to Bloch-Nordsieck?
If a cutoff is implemented, it should match the bin size in the variable
one is trying to correct. And what does "integrated out to the cutoff
energy mean"? Does it mean that the correction amounts to a simple factor
up to this relatively high cutoff? I also do not see how the cutoff
relates to a direct *shift* in energy to first order. Finally, I am
not sure the procedure suggested by Chris is optimal. I think that
the sequence of calculating the radiated XS and convoluting it with
the experimental resolution is incorrect; if I am not mistaken,
this issue was raised already a while ago. Convoluting a radiated
theoretical observable with the corresponding measured spectrum
may imply double counting, and may just mean the emperor MC's
new clothes!
Best regards,
Simon
-- Simon Sirca Dept of Physics, University of Ljubljana Tel: +386 1 4766-574 Jadranska 19 Fax: +386 1 2517-281 1000 Ljubljana, Slovenia
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