I follow Simon's question. I do not see why W should be shifted that much.
aki
Simon Sirca wrote:
> 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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