[Rivet] JIMMY parameters in AGILe

[Jonathan Butterworth]

Hi Holger,

Holger Schulz wrote:
> Hi,
> 
> I was trying to reproduce some plots Arthur Moraes showed
> in a talk recently:
> 
>     http://hermes.ihep.su:8001/pool/atlas/multipart/reports/UE-jimmy.pdf
> 
> On slide 6 he proposes a tuning of the parameters PTJIM, JMRAD(73)
> and JMRAD(93). In AGILe their is neither JMRAD(73), nor JMRAD(91).
> So I had a look in the source file and added in the PRRAD section the
> two missing parameters. However, I do not know how to translate
> the parameter setting of Arthur's talk JMRAD(73)=2.2 to a proper
> PRRAD value.

JMRAD() is the array defining the area of the particles in units of 
GeV^-2 (inverse radius squared!)

73=proton
91=antiproton

in the herwig numbering scheme.

PRRAD in Agile is a shorthand used to set these parameters such that
JMRAD(73)=JMRAD(91)=PRRAD.

In the c++ for Agile (FHerwigJimmy.cc you can see:

} else if (name == "PRRAD") {
55 	      getLog() << Log::INFO << "Setting 1/(Proton radius)2 (PRRAD) = 
" << asDouble(value) << endl;
56 	      FC_JMPARM.JMRAD[72] = asDouble(value);
57 	      FC_JMPARM.JMRAD[74] = asDouble(value);
58 	      FC_JMPARM.JMRAD[90] = asDouble(value);
59 	      FC_JMPARM.JMRAD[92] = asDouble(value);

This actually also set the neutron area, not that it is relevant.
The offset by one is just from c++ starting arrays at 0 when fortran 
starts them at 1.

> 
> If I want to generate events at cms energies other than 1800 GeV,
> I guess I have to evaluate the formula given on slide 6 for PTJIM,
> right?

yes, as Frank says...

> 
> Holger
> 
> Holger
> 
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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. Jonathan Butterworth,              http://www.hep.ucl.ac.uk/~jmb/
Physics and Astronomy Department                  Tel: +44 20 7679 3444
ATLAS, CERN                                       Tel: +41 22 76  72340
University College London                 Gower St, London WC1E 6BT, UK
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