RooDstD0BG.cxx

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/*****************************************************************************
 * Project: RooFit                                                           *
 * Package: RooFitModels                                                     *
 * @(#)root/roofit:$Id$
 * Authors:                                                                  *
 *   UE, Ulrik Egede,     RAL,               U.Egede@rl.ac.uk                *
 *   MT, Max Turri,       UC Santa Cruz      turri@slac.stanford.edu         *
 *   CC, Chih-hsiang Cheng, Stanford         chcheng@slac.stanford.edu       *
 *   DK, David Kirkby,    UC Irvine,         dkirkby@uci.edu                 *
 *                                                                           *
 * Copyright (c) 2000-2005, Regents of the University of California          *
 *                          RAL and Stanford University. All rights reserved.*
 *                                                                           *
 * Redistribution and use in source and binary forms,                        *
 * with or without modification, are permitted according to the terms        *
 * listed in LICENSE (http://roofit.sourceforge.net/license.txt)             *
 *****************************************************************************/
 
/** \class RooDstD0BG
    \ingroup Roofit
 
Special p.d.f shape that can be used to model the background of
D*-D0 mass difference distributions. It computes
 
\f[
  \mathrm{RooDSTD0}(m \, | \, m_0, A, B, C) =
    \left(1 - \exp\left(-\frac{m - m_0}{C}\right) \right)
    \cdot \left(\frac{m}{m_0}\right)^A + B
    \cdot \left(\frac{m}{m_0} - 1 \right)
\f]
**/
 
#include <RooDstD0BG.h>
 
#include <RooBatchCompute.h>
 
#include <TMath.h>
 
#include <cmath>
 
ClassImp(RooDstD0BG);
 
////////////////////////////////////////////////////////////////////////////////
 
RooDstD0BG::RooDstD0BG(const char *name, const char *title, RooAbsReal &_dm, RooAbsReal &_dm0, RooAbsReal &_c,
                       RooAbsReal &_a, RooAbsReal &_b)
   : RooAbsPdf(name, title),
     dm("dm", "Dstar-D0 Mass Diff", this, _dm),
     dm0("dm0", "Threshold", this, _dm0),
     C("C", "Shape Parameter", this, _c),
     A("A", "Shape Parameter 2", this, _a),
     B("B", "Shape Parameter 3", this, _b)
{
}
 
////////////////////////////////////////////////////////////////////////////////
 
RooDstD0BG::RooDstD0BG(const RooDstD0BG &other, const char *name)
   : RooAbsPdf(other, name),
     dm("dm", this, other.dm),
     dm0("dm0", this, other.dm0),
     C("C", this, other.C),
     A("A", this, other.A),
     B("B", this, other.B)
{
}
 
////////////////////////////////////////////////////////////////////////////////
 
double RooDstD0BG::evaluate() const
{
   double arg = dm - dm0;
   if (arg <= 0)
      return 0;
   double ratio = dm / dm0;
   double val = (1 - std::exp(-arg / C)) * std::pow(ratio, A) + B * (ratio - 1);
 
   return (val > 0 ? val : 0);
}
 
////////////////////////////////////////////////////////////////////////////////
/// Compute multiple values of D*-D0 mass difference distribution.
void RooDstD0BG::doEval(RooFit::EvalContext & ctx) const
{
   RooBatchCompute::compute(ctx.config(this), RooBatchCompute::DstD0BG, ctx.output(),
          {ctx.at(dm), ctx.at(dm0), ctx.at(C), ctx.at(A), ctx.at(B)});
}
 
////////////////////////////////////////////////////////////////////////////////
/// if (matchArgs(allVars,analVars,dm)) return 1 ;
 
Int_t RooDstD0BG::getAnalyticalIntegral(RooArgSet & /*allVars*/, RooArgSet & /*analVars*/,
                                        const char * /*rangeName*/) const
{
   return 0;
}
 
////////////////////////////////////////////////////////////////////////////////
 
double RooDstD0BG::analyticalIntegral(Int_t /*code*/, const char * /*rangeName*/) const
{
   // switch (code) {
   // case 1: {
   //    double min = dm.min(rangeName);
   //    double max = dm.max(rangeName);
   //    if (max <= dm0)
   //       return 0;
   //    else if (min < dm0)
   //       min = dm0;
   //
   //    bool doNumerical = false;
   //    if (A != 0)
   //       doNumerical = true;
   //    else if (B < 0) {
   //       // If b<0, pdf can be negative at large dm, the integral should
   //       // only up to where pdf hits zero. Better solution should be
   //       // solve the zero and use it as max.
   //       // Here we check this whether pdf(max) < 0. If true, let numerical
   //       // integral take care of. ( kind of ugly!)
   //       if (1 - exp(-(max - dm0) / C) + B * (max / dm0 - 1) < 0)
   //          doNumerical = true;
   //    }
   //    if (!doNumerical) {
   //       return (max - min) + C * exp(dm0 / C) * (exp(-max / C) - exp(-min / C)) +
   //              B * (0.5 * (max * max - min * min) / dm0 - (max - min));
   //    } else {
   //       // In principle the integral for a!=0  can be done analytically.
   //       // It involves incomplete Gamma function, TMath::Gamma(a+1,m/c),
   //       // which is not defined for a < -1. And the whole expression is
   //       // not stable for m/c >> 1.
   //       // Do numerical integral
   //       RooArgSet vset(dm.arg(),"vset");
   //       std::unique_ptr<RooAbsFunc> func{bindVars(vset)};
   //       RooRombergIntegrator integrator(*func,min,max);
   //       return integrator.integral();
   //    }
   // }
   // }
 
   assert(0);
   return 0.0;
}