signal_bkg_mass_fit.py

#  Copyright (c) 2022 zfit

import zfit

# create space
obs = zfit.Space("x", limits=(-10, 10))

# parameters
mu = zfit.Parameter("mu", 1.0, -4, 6)
sigma = zfit.Parameter("sigma", 1.0, 0.1, 10)
lambd = zfit.Parameter("lambda", -0.06, -1, -0.01)
frac = zfit.Parameter("fraction", 0.3, 0, 1)

# model building, pdf creation
gauss = zfit.pdf.Gauss(mu=mu, sigma=sigma, obs=obs)
exponential = zfit.pdf.Exponential(lambd, obs=obs)
model = zfit.pdf.SumPDF([gauss, exponential], fracs=frac)

# data
n_sample = 10000

data = model.create_sampler(n_sample, limits=obs)
data.resample()

# set the values to a start value for the fit
mu.set_value(0.5)
sigma.set_value(1.2)
lambd.set_value(-0.05)
frac.set_value(0.07)

# create NLL
nll = zfit.loss.UnbinnedNLL(model=model, data=data)

# create a minimizer
minimizer = zfit.minimize.Minuit()
result = minimizer.minimize(nll)
print(result)

# do the error calculations, here with minos
param_hesse = result.hesse()
param_errors, new_result = result.errors()
print(result.params)