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/*****************************************************************************
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* Project: CMS detector at the CERN
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*
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* Package: PhysicsTools/TagAndProbe/RooCMSShape
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*
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*
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* Authors:
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* Nadia Adam, Princeton - neadam@princeton.edu
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* Adam Hunt, Princeton - ahunt@princeton.edu
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* Kalanand Mishra, Fermilab - kalanand@fnal.gov
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*
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* Description:
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* Defines a probability density function which has exponential decay
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* distribution at high mass beyond the pole position (say, Z peak)
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* but turns over (i.e., error function) at low mass due to threshold
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* effect. We use this to model the background shape in Z->ll invariant
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* mass.
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* History:
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*
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*
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* Copyright (C) 2008 FNAL
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*****************************************************************************/
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#include "RooCMSShape.h"
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RooCMSShape::RooCMSShape(const char *name, const char *title,
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RooAbsReal& _x,
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RooAbsReal& _alpha,
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RooAbsReal& _beta,
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RooAbsReal& _gamma,
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RooAbsReal& _peak) :
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RooAbsPdf(name,title),
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x("x","x",this,_x),
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alpha("alpha","alpha",this,_alpha),
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beta("beta","beta",this,_beta),
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gamma("gamma","gamma",this,_gamma),
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peak("peak","peak",this,_peak)
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{ }
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RooCMSShape::RooCMSShape(const RooCMSShape& other, const char* name):
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RooAbsPdf(other,name),
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x("x",this,other.x),
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alpha("alpha",this,other.alpha),
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beta("beta",this,other.beta),
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gamma("gamma",this,other.gamma),
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peak("peak",this,other.peak)
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{ }
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Double_t RooCMSShape::evaluate() const
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{
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// ENTER EXPRESSION IN TERMS OF VARIABLE ARGUMENTS HERE
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//Double_t erf = TMath::Erfc((alpha - x) * beta);
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Double_t erf = RooMath::erfc((alpha - x) * beta);
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Double_t u = (x - peak)*gamma;
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if(u < -70) u = 1e20;
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else if( u>70 ) u = 0;
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else u = exp(-u); //exponential decay
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return erf*u;
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}
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