rf314_paramfitrange.py

## \ingroup tutorial_roofit_main

## \notebook

## Multidimensional models: working with parameterized ranges in a fit.

## This an example of a fit with an acceptance that changes per-event

##

## `pdf = exp(-t/tau)` with `t[tmin,5]`

##

## where `t` and `tmin` are both observables in the dataset

##

## \macro_image

## \macro_code

## \macro_output

##

## \date February 2018

## \authors Clemens Lange, Wouter Verkerke (C++ version)

import ROOT

# Define observables and decay pdf

# ---------------------------------------------------------------

# Declare observables

t = ROOT.RooRealVar("t", "t", 0, 5)

tmin = ROOT.RooRealVar("tmin", "tmin", 0, 0, 5)

# Make parameterized range in t : [tmin,5]

t.setRange(tmin, ROOT.RooFit.RooConst(t.getMax()))

# Make pdf

tau = ROOT.RooRealVar("tau", "tau", -1.54, -10, -0.1)

model = ROOT.RooExponential("model", "model", t, tau)

# Create input data

# ------------------------------------

# Generate complete dataset without acceptance cuts (for reference)

dall = model.generate({t}, 10000)

# Generate a (fake) prototype dataset for acceptance limit values

tmp = ROOT.RooGaussian("gmin", "gmin", tmin, 0.0, 0.5).generate({tmin}, 5000)

# Generate dataset with t values that observe (t>tmin)

dacc = model.generate({t}, ProtoData=tmp)

# Fit pdf to data in acceptance region

# -----------------------------------------------------------------------

r = model.fitTo(dacc, Save=True, PrintLevel=-1)

# Plot fitted pdf on full and accepted data

# ---------------------------------------------------------------------------------

# Make plot frame, datasets and overlay model

frame = t.frame(Title="Fit to data with per-event acceptance")

dall.plotOn(frame, MarkerColor="r", LineColor="r")

model.plotOn(frame)

dacc.plotOn(frame)

# Print fit results to demonstrate absence of bias

r.Print("v")

c = ROOT.TCanvas("rf314_paramranges", "rf314_paramranges", 600, 600)

ROOT.gPad.SetLeftMargin(0.15)

frame.GetYaxis().SetTitleOffset(1.6)

frame.Draw()

c.SaveAs("rf314_paramranges.png")