Hi Chris,
I am neither questioning the Bardin & Shumeiko approach nor
the physics behind mascarad; I am worried about coupling mascarad
to our MC. Let me therefore reformulate my simple questions, hoping
that someone can answer them without pointing just at Afanasev's PRD.
- Does the radiative correction implemented in our simulation
amount to a single number below the selected cutoff? If yes,
is there an agreed-upon procedure to determine this cutoff?
- How and why exactly does the large electron energy shift
that was mentioned come about?
- Is the XS radiated by mascarad being convoluted with the
*measured* experimental resolution in the MC?
Thanks,
Simon
>> 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!
On Fri, 31 Mar 2006, Christopher Crawford wrote:
> 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
>
>
-- 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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