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Re: 4/27 physics meeting...



Hi,

in PYTHIA, photoproduction includes 3 processes:
a) gamma+q - hard process
b) VDM
c) Generalized VDM (gamma-->qqbar)

The target fragmentation can be a complex system with, say a proton
in the state. The effective mass of everything but this proton 
can be large.

On the attached plot the left picture shows the effective mass
of everything but the proton for all events Egamma>6 GeV.
The right picture is a subsample with a requirement that the proton
is produced directly in the vertex, but not via a cascade.
Using the NTUPLE produced by bggen one can select ITYP(4,ip)=K(ip,3)=0,
where ip is the proton number in the list. The right plot contains
omega, rho, phi and a continuum up to 2.5 GeV.

Eugene

On Mon, 27 Apr 2009, Richard Jones wrote:

> Hello all
>
> Following the question I raised about the odd spectral shape of mX for 
> gamma,p -> X,nucleon today during the talk by M. Dugger, I decided to look at 
> this spectrum for myself to see if the bump at 3 GeV/c^2 was being produced 
> by the parametric MC or if it was coming from Pythia.  I added some plots to 
> the wiki page for today's meeting.  Please see the notes that I posted there 
> for details.  The question I end up asking is, does Pythia know about the 
> rapidity gap in diffractive production?  If not, we will need to take these 
> kinds of mass distributions with a big grain of salt.
>
> http://www.jlab.org/Hall-D/software/wiki/index.php/April_27,_2009_(11AM),_Physics_Working_Group#Comment_on_Pythia_mass_distributions_-_R._Jones 
> <http://www.jlab.org/Hall-D/software/wiki/index.php/April_27,_2009_%2811AM%29,_Physics_Working_Group#Comment_on_Pythia_mass_distributions_-_R._Jones>
>
> -Richard Jones
>

BGGEN eff mass