ROOT   Reference Guide
rf210_angularconv.py File Reference

## Namespaces

namespace  rf210_angularconv

## Detailed Description

Convolution in cyclical angular observables theta, and construction of p.d.f in terms of trasnformed angular coordinates, e.g.

cos(theta), the convolution is performed in theta rather than cos(theta)

(require ROOT to be compiled with –enable-fftw3)

pdf(theta) = ROOT.T(theta) (x) gauss(theta) pdf(cosTheta) = ROOT.T(acos(cosTheta)) (x) gauss(acos(cosTheta))

import ROOT
# Set up component pdfs
# ---------------------------------------
# Define angle psi
psi = ROOT.RooRealVar("psi", "psi", 0, 3.14159268)
# Define physics p.d.f T(psi)
Tpsi = ROOT.RooGenericPdf("Tpsi", "1+sin(2*@0)", [psi])
# Define resolution R(psi)
gbias = ROOT.RooRealVar("gbias", "gbias", 0.2, 0.0, 1)
greso = ROOT.RooRealVar("greso", "greso", 0.3, 0.1, 1.0)
Rpsi = ROOT.RooGaussian("Rpsi", "Rpsi", psi, gbias, greso)
# Define cos(psi) and function psif that calculates psi from cos(psi)
cpsi = ROOT.RooRealVar("cpsi", "cos(psi)", -1, 1)
psif = ROOT.RooFormulaVar("psif", "acos(cpsi)", [cpsi])
# Define physics p.d.f. also as function of cos(psi): T(psif(cpsi)) = T(cpsi)
Tcpsi = ROOT.RooGenericPdf("T", "1+sin(2*@0)", [psif])
# Construct convolution pdf in psi
# --------------------------------------------------------------
# Define convoluted p.d.f. as function of psi: M=[T(x)R](psi) = M(psi)
Mpsi = ROOT.RooFFTConvPdf("Mf", "Mf", psi, Tpsi, Rpsi)
# Set the buffer fraction to zero to obtain a ROOT.True cyclical
# convolution
Mpsi.setBufferFraction(0)
# Sample, fit and plot convoluted pdf (psi)
# --------------------------------------------------------------------------------
# Generate some events in observable psi
data_psi = Mpsi.generate({psi}, 10000)
# Fit convoluted model as function of angle psi
Mpsi.fitTo(data_psi)
# Plot cos(psi) frame with Mf(cpsi)
frame1 = psi.frame(Title="Cyclical convolution in angle psi")
data_psi.plotOn(frame1)
Mpsi.plotOn(frame1)
# Overlay comparison to unsmeared physics p.d.f ROOT.T(psi)
Tpsi.plotOn(frame1, LineColor="r")
# Construct convolution pdf in cos(psi)
# --------------------------------------------------------------------------
# Define convoluted p.d.f. as function of cos(psi): M=[T(x)R](psif cpsi)) = M(cpsi:
#
# Need to give both observable psi here (for definition of convolution)
# and function psif here (for definition of observables, in cpsi)
Mcpsi = ROOT.RooFFTConvPdf("Mf", "Mf", psif, psi, Tpsi, Rpsi)
# Set the buffer fraction to zero to obtain a ROOT.True cyclical
# convolution
Mcpsi.setBufferFraction(0)
# Sample, fit and plot convoluted pdf (cospsi)
# --------------------------------------------------------------------------------
# Generate some events
data_cpsi = Mcpsi.generate({cpsi}, 10000)
# set psi constant to exclude to be a parameter of the fit
psi.setConstant(True)
# Fit convoluted model as function of cos(psi)
Mcpsi.fitTo(data_cpsi)
# Plot cos(psi) frame with Mf(cpsi)
frame2 = cpsi.frame(Title="Same convolution in psi, in cos(psi)")
data_cpsi.plotOn(frame2)
Mcpsi.plotOn(frame2)
# Overlay comparison to unsmeared physics p.d.f ROOT.Tf(cpsi)
Tcpsi.plotOn(frame2, LineColor="r")
# Draw frame on canvas
c = ROOT.TCanvas("rf210_angularconv", "rf210_angularconv", 800, 400)
c.Divide(2)
c.cd(1)