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DPM theta cut off [message #13890] 
Mon, 27 August 2012 16:49 
donghee
Messages: 385 Registered: January 2009 Location: Germnay

firstgrade participant 
From: *kph.unimainz.de


Hello DPM expert,
I have couple of questions for DPM generator.
Now I'm trying to evaluate contributions of inelastic and elastic part from DPM generator with a particular beam momentum.
I used theta_min 0.01 degree for inelastic plus elastic mode during the DPM generation.
When I try to calculate the ratio of crosssection between total and elastic in DPM. I have too high elastic contribution due to
small theta cut off. (I'm now understanding theta_min in DPM direct represents theta cut off.)
Which kind of theta cut off value do I have to introduce to get correct ratio, which is pronounced in many reference, for instance, beam momentum 15GeV/c case the elastic cross section must to be 10mb.
I'm also wondering wheather the elastic cross section of 10 mb has been taken into account the coulomb contribution in the reference?[K.Nakmura et al. (PDG), J.Phys.G 37, 075021 (2010)]
I assume that coulomb and interference part of elastic process are used in the DPM model.
In order to make correct ratio between elastic and inelastic part, I have to apply correct theta cut off value during the generation in my understanding.
Thank you for your teaching in advance.
Donghee





Re: DPM theta cut off [message #13905 is a reply to message #13904] 
Wed, 29 August 2012 11:28 
Simone Bianco
Messages: 29 Registered: January 2009

continuous participant 
From: *cb.unibonn.de


Dear Donghee,
the work of Thomas and the results of some discussions of one year ago about the theta_min parameter were included in the PndDpmDirect class.
Johan introduced the parametrization of theta_min in the implementation of the ctor PndDpmDirect::PndDpmDirect(Double_t Mom, Int_t Mode, Long_t Seed):
PndDpmDirect::PndDpmDirect(Double_t Mom, Int_t Mode, Long_t Seed) {
//
// Calculate ThtMin first. For this we make a cutoff on the value of t of 1e2 GeV^2 (~100 MeV/c momentum)
// This estimated from a parametrization found in thesis of Thomas Wuerschig (figure 6.4, page 121):
// Roughly: 0.4 deg at 15 GeV/c and 4 deg at 1.5 GeV/c, lineair interpolation in double logscale.
//
Double_t logangle = TMath::Log(0.4)+(TMath::Log(15.)TMath::Log(Mom))*(TMath::Log(4)TMath::Log(0.4))/(TMath::Log(15)TMath::Log(1.5));
Double_t ThtMin = TMath::Exp(logangle);
PndDpmDirect(Mom, Mode, Seed, ThtMin) ;
}
so if you use this ctor you don't need to calculate by hands a value for theta_min, since this is automatically obtained as a function of the beam momentum.
I hope this helps.
Cheers,
Simone





Re: DPM theta cut off [message #13909 is a reply to message #13908] 
Wed, 29 August 2012 14:51 
donghee
Messages: 385 Registered: January 2009 Location: Germnay

firstgrade participant 
From: *kph.unimainz.de


Thanks Mathia for your kind correction.
Anyhow, the case of studying the range of 0.170.46 degree with DPM, one has to care this fact, when the efficiencies or some normalization of event rates are calculated.
Best wishes,
Donghee



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