[EvtGen] Continuum Background Model

[Yongcheng Wu]

Hi John:
   Thanks so much for the explanations.
   I'll try to use PYTHIA decay mode.  Thanks!

Best!
Yongcheng

On 2018-01-16 1:17 PM, John Back wrote:
> Hello,
>
> The JSCONT model has been discontinued since it uses JetSet/Pythia6, 
> and EvtGen only supports Pythia8; we need to update the documentation 
> to mention this.
>
> However, I think you will be able to generate the events you want by 
> using a Pythia 8 decay mode which generates onium to 3 gluons, or 2 
> gluons and a photon, and hadronises them:
>
> Decay vpho
> 1.0 g g g PYTHIA 92;
> Enddecay
>
> or
>
> Decay vpho
> 1.0 gamma g g PYTHIA  92;
> Enddecay
>
> where vpho is the (parent) virtual photon. Since this has zero mass, 
> you need to define its energy to the e+e- beam energy (per event). For 
> example, in your C++ program where you call EvtGen you need to do 
> something like:
>
> // Define virtual photon parent particle 4-momentum (GeV)
> double E0 = 10.8;
> EvtVector4R pInit(E0, 0.0, 0.0, 0.0);
>
> EvtParticle* theParent = EvtParticleFactory::particleFactory(theId, 
> pInit);
> // Vector particle spin
> if (theParent->getSpinStates() == 3){theParent->setVectorSpinDensity();}
>
> // Generate the event
> evtGen.generateDecay(theParent);
>
> See validation/genRootDecayChain.cc and 
> validation/UpsilonFiles/UpsilonTo3g.dec as examples.
>
> From the old JSCONT model documentation, the angular distribution of 
> the jet was 1 + cos^2Theta. I don't think this will be done for the 
> new way shown above.
>
> Another limitation is that you can't specify the quark content of the 
> virtual photon decay; all quarks are allowed, and the integer 
> parameter used for the JSCONT model to define the quark flavour can't 
> be used anymore.
>
> If you find that the generated events contain problems, or the wrong 
> physics content, then we can try to see if we can convert and upgrade 
> the JSCONT model to work in Pythia 8, although this will not be an 
> easy nor quick process.
>
> Regards,
>     John.
>
> On 14/01/18 20:46, Yongcheng Wu wrote:
>> Dear EvtGen Authors:
>>
>>     I'm trying to use EvtGen to generate continuum background events at
>> Upsilon4S. According to your documentation (maybe it is not up to date
>> ), JSCONT model should be used. However, in the newest version of
>> EvtGen, it seems this model has been removed. Can you please tell me
>> that which model should I use for a continuum background events
>> generation? Thanks so much!
>>
>> Best!
>>

-- 
Yongcheng Wu (email: ycwu at physics.carleton.ca)
Department of Physics, Carleton University
1125 Colonel By Drive, Ottawa, ON, K1S 5B6, CANADA
phone: +1 613 298 1839