Hi Simon,
You have to understand how MASCARAD (or POLRAD, the same thing)
works. It uses the Bardin & Shumeiko approach, but a cutoff is still
required in MC generators. See my talk, at
http://blast.lns.mit.edu/PRIVATE_RESULTS/USEFUL/ANALYSIS_MEETINGS/
meeting_050630/rc_overview.ppt
--Chris
_______________________________________
TA-53/MPF-1/D111 P-23 MS H803
LANL, Los Alamos, NM 87545
505-665-9804(o) 665-4121(f) 662-0639(h)
_______________________________________
On Mar 31, 2006, at 15:13:52, Simon Sirca wrote:
> 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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