GaussianTransferFunctionOnPt.cc

/*
 *  MoMEMta: a modular implementation of the Matrix Element Method
 *  Copyright (C) 2016  Universite catholique de Louvain (UCL), Belgium
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */


#include <momemta/Logging.h>
#include <momemta/Module.h>
#include <momemta/ParameterSet.h>
#include <momemta/Types.h>
#include <momemta/Math.h>

#include <Math/DistFunc.h>

class GaussianTransferFunctionOnPtBase: public Module {
    public:

        GaussianTransferFunctionOnPtBase(PoolPtr pool, const ParameterSet& parameters): Module(pool, parameters.getModuleName()) {
            m_reco_input = get<LorentzVector>(parameters.get<InputTag>("reco_particle"));

            m_sigma = parameters.get<double>("sigma", 0.10);
            m_sigma_range = parameters.get<double>("sigma_range", 5);
            m_min_Pt = parameters.get<double>("min_Pt", 0.);
        }

    protected:
        double m_min_Pt;
        double m_sigma;
        double m_sigma_range;

        // Input
        Value<LorentzVector> m_reco_input;
};

class GaussianTransferFunctionOnPt: public GaussianTransferFunctionOnPtBase {
    public:
        GaussianTransferFunctionOnPt(PoolPtr pool, const ParameterSet& parameters): GaussianTransferFunctionOnPtBase(pool, parameters) {
            m_ps_point = get<double>(parameters.get<InputTag>("ps_point"));
        }

        virtual Status work() override {
            // Estimate the width over which to integrate using the width of the TF at Pt_rec ...
            const double sigma_Pt_rec = m_reco_input->Pt() * m_sigma;

            const double cosh_eta = std::cosh(m_reco_input->Eta());
            double range_min = std::max(m_min_Pt, m_reco_input->Pt() - (m_sigma_range * sigma_Pt_rec));
            double range_max = m_reco_input->Pt() + (m_sigma_range * sigma_Pt_rec);
            double range = (range_max - range_min);

            double gen_Pt = range_min + range * (*m_ps_point);

            // To change the particle's Pt without changing its direction and mass:
            const double gen_E = std::sqrt(SQ(m_reco_input->M()) + SQ(cosh_eta * gen_Pt));

            output->SetCoordinates(
                    gen_Pt * std::cos(m_reco_input->Phi()),
                    gen_Pt * std::sin(m_reco_input->Phi()),
                    gen_Pt * std::sinh(m_reco_input->Eta()),
                    gen_E);

            // ... but compute the width of the TF at Pt_gen!
            const double sigma_Pt_gen = gen_Pt * m_sigma;

            // Compute TF*jacobian, where the jacobian includes the transformation of [0,1]->[range_min,range_max] and d|P|/dPt = cosh(eta)
            *TF_times_jacobian = ROOT::Math::normal_pdf(gen_Pt, sigma_Pt_gen, m_reco_input->Pt()) * range * cosh_eta;

            return Status::OK;
        }

    private:
        // Input
        Value<double> m_ps_point;

        // Outputs
        std::shared_ptr<LorentzVector> output = produce<LorentzVector>("output");
        std::shared_ptr<double> TF_times_jacobian = produce<double>("TF_times_jacobian");

};

class GaussianTransferFunctionOnPtEvaluator: public GaussianTransferFunctionOnPtBase {
    public:
        GaussianTransferFunctionOnPtEvaluator(PoolPtr pool, const ParameterSet& parameters): GaussianTransferFunctionOnPtBase(pool, parameters) {
            m_gen_input = get<LorentzVector>(parameters.get<InputTag>("gen_particle"));
        }

        virtual Status work() override {
            // Compute TF value
            *TF_value = ROOT::Math::normal_pdf(m_gen_input->Pt(), m_gen_input->Pt() * m_sigma, m_reco_input->Pt());

            return Status::OK;
        }

    private:
        // Input
        Value<LorentzVector> m_gen_input;

        // Outputs
        std::shared_ptr<double> TF_value = produce<double>("TF");

};

REGISTER_MODULE(GaussianTransferFunctionOnPt)
        .Input("ps_point")
        .Input("reco_particle")
        .Output("output")
        .Output("TF_times_jacobian")
        .Attr("sigma:double=0.10")
        .Attr("sigma_range:double=5")
        .Attr("min_Pt:double=0");

REGISTER_MODULE(GaussianTransferFunctionOnPtEvaluator)
        .Input("gen_particle")
        .Input("reco_particle")
        .Output("TF")
        .Attr("sigma:double=0.10")
        .Attr("sigma_range:double=5")
        .Attr("min_Pt:double=0");