B2A400-TreeFit.py

#!/usr/bin/env python3
 
 
 
import basf2 as b2
import modularAnalysis as ma
import vertex as vx
from stdPi0s import stdPi0s
 
# create path
my_path = b2.create_path()
 
# load input ROOT file
ma.inputMdst(environmentType='default',
             filename=b2.find_file('B02D0pi0_D02pi0pi0.root', 'examples', False),
             path=my_path)
 
 
# use standard final state particle lists
#
# creates "pi0:eff40_Jan2020Fit" ParticleList
# see Standard Particles section at https://software.belle2.org/
stdPi0s(listtype='eff40_Jan2020Fit', path=my_path)
 
# reconstruct D0 -> pi0 pi0 decay
# keep only candidates with 1.7 < M(pi0pi0) < 2.0 GeV
ma.reconstructDecay(decayString='D0:pi0pi0 -> pi0:eff40_Jan2020Fit pi0:eff40_Jan2020Fit',
                    cut='1.7 < M < 2.0',
                    path=my_path)
 
# reconstruct B0 -> D0 pi0 decay
# keep only candidates with Mbc > 5.24 GeV
# and -1 < Delta E < 1 GeV
ma.reconstructDecay(decayString='B0:all -> D0:pi0pi0 pi0:eff40_Jan2020Fit',
                    cut='5.24 < Mbc < 5.29 and abs(deltaE) < 1.0',
                    path=my_path)
 
# perform MC matching (MC truth association)
ma.matchMCTruth(list_name='B0:all', path=my_path)
 
vx.treeFit(list_name='B0:all',
           conf_level=0,  # 0:keep only fit survivors, -1: keep all candidates; optimise this cut for your need
           ipConstraint=True,
           # pins the B0 PRODUCTION vertex to the IP (increases SIG and BKG rejection) use for better vertex resolution
           updateAllDaughters=True,  # update momenta of ALL particles
           massConstraint=['pi0'],  # mass constrain ALL pi0
           path=my_path)
 
# whatever you are interested in
#
# see analysis/VariableManager/ for implementation of the vars
variables = [
    'isSignal',  # MC truth
    'chiProb',  # pValue of the fit use this in your analysis to reject background
    "p",  # momentum (of the B0)
    "mcP",  # generated momentum
    "pErr",  # momentum uncertainty taking the full px, py, pz covariance into account
]
 
# safe the output
output_name = "B2A400-TreeFit.root"
my_path.add_module('VariablesToNtuple',
                   treeName='B0',
                   particleList='B0:all',
                   variables=variables,
                   fileName=output_name)
 
# Process the events
b2.process(my_path)
 
# print out the summary
print(b2.statistics)