Sensitivity study of the Hbb and Hcc couplings for e+e- collisions at FCC

-- LeaHeckmann - 2017-09-04

This page describes the methodology for determining the precision of BR(Hbb) and BR(Hcc) by simulating CMS at TLEP at 240 GeV with an integrated luminosity of 3500 fb⁻1.

The first section will describe how to obtain the necessary toolkits. Afterwards the simulation and analysis will be divded in three steps:

  • Generate signal and background for Hbb and Hcc using Pythia8
  • Simulate the CMS detector response using Delphes
  • Run the data selection anaylsis and fit usint root and RooFit

How to obtain the necessary tools

Pythia8

Pythia can be downloaded from this website.
Follow the the instructions in the worksheet to install it together with the interface for HepMC.

Delphes

Download Delphes from this website and use the instructions in the workbook to install it.

ExRootAnalysis

Simulation steps

Run Pythia8

This section describes how to generate signal and background events for various processes. First make sure you understand what to edit in a Pythia cards. Some examples of Pythia cards are in


/BSMGen/data/pythiaCards/

In this case, we generated HZ and ZZ events, forcing the Z to decay to muon pair and the Z/H to decay to b pair.


In the main program settings, the number of generated events may be modified as desired. In this card, we generated 100,000 events in both the HZ and ZZ cards.


! This file contains commands to be read in for a Pythia8 run.
! Lines not beginning with a letter or digit are comments.

! 1) Settings that could be used in a main program, if desired.
Main:numberOfEvents = 100000 ! number of events to generate
Main:numberToList = 0 ! number of events to print
Main:timesToShow = 20 ! show how far along run is
Main:timesAllowErrors = 30 ! max number of allowed errors
Main:showChangedSettings = on ! print changed flags/modes/parameters
Main:showChangedParticleData = on ! print changed particle and decay data

The LHC beam parameters may be modified depending on the center of mass energy desired in the generation.


! 2) LHC beams parameter settings.
Beams:idA = 11 ! first beam, p = 2212, pbar = -2212
Beams:idB = -11 ! second beam, p = 2212, pbar = -2212
#Beams:eCM = 91. ! CM energy of collision for Z pole run
#Beams:eCM = 161 ! CM energy of collision for WW run
Beams:eCM = 240. ! CM energy of collision for HZ run
#Beams:eCM = 350. ! CM energy of collision for tt run

In the Pythia cards, the settings for hard process generation can be finely-tuned to the specific processes you want to study. For particle identification, PDG Codes are used. Here, the Standard Model Higgs is set to decay to H and Z, where various decay modes are switched on and off depending on what we want to observe in simulation.


! 3) Settings for the hard-process generation
HiggsSM:ffbar2HZ = on
23:onMode = off ! switch off all Z decays
23:onIfAny = 13 ! switch on Z->mu mu only
25:onMode = off ! switch off all H decays
25:onIfAny = 5 ! switch on all decays to b's
#25:offIfAny = 23 ! switch off H-> Z gamma. Only H->gamma gamma is left

! 4) Settings for the event generation process in the Pythia8 library.
PartonLevel:MI = on ! no multiple interactions
PartonLevel:ISR = on ! no initial-state radiation
#PartonLevel:ISR = off ! no initial-state radiation
PartonLevel:FSR = on ! no final-state radiation
HadronLevel:Hadronize = on ! no hadronization

! 5) Non-standard settings; exemplifies tuning possibilities.
#SpaceShower:pT0Ref = 2.0 ! dampening of pT -> 0 divergence
#MultipleInteractions:pT0Ref = 3.0 ! dampening of pT -> 0 divergence
25:m0 = 125.0 ! Higgs mass


The solutions to the Pythia cards can be found below and in the attachments.



! This file contains commands to be read in for a Pythia8 run.
! Lines not beginning with a letter or digit are comments.

! 1) Settings that could be used in a main program, if desired.
Main:numberOfEvents = 100000 ! number of events to generate
Main:numberToList = 0 ! number of events to print
Main:timesToShow = 20 ! show how far along run is
Main:timesAllowErrors = 30 ! max number of allowed errors
Main:showChangedSettings = on ! print changed flags/modes/parameters
Main:showChangedParticleData = on ! print changed particle and decay data

! 2) LHC beams parameter settings.
Beams:idA = 11 ! first beam, p = 2212, pbar = -2212
Beams:idB = -11 ! second beam, p = 2212, pbar = -2212
#Beams:eCM = 91. ! CM energy of collision for Z pole run
#Beams:eCM = 161 ! CM energy of collision for WW run
Beams:eCM = 240. ! CM energy of collision for HZ run
#Beams:eCM = 350. ! CM energy of collision for tt run

! 3) Settings for the hard-process generation
HiggsSM:ffbar2HZ = on
23:onMode = off ! switch off all Z decays
23:onIfAny = 13 ! switch on Z->mu mu only
25:onMode = off ! switch off all H decays
25:onIfAny = 5 ! switch on all decays to b's
#25:offIfAny = 23 ! switch off H-> Z gamma. Only H->gamma gamma is left

! 4) Settings for the event generation process in the Pythia8 library.
PartonLevel:MI = on ! no multiple interactions
PartonLevel:ISR = on ! no initial-state radiation
#PartonLevel:ISR = off ! no initial-state radiation
PartonLevel:FSR = on ! no final-state radiation
HadronLevel:Hadronize = on ! no hadronization

! 5) Non-standard settings; exemplifies tuning possibilities.
#SpaceShower:pT0Ref = 2.0 ! dampening of pT -> 0 divergence
#MultipleInteractions:pT0Ref = 3.0 ! dampening of pT -> 0 divergence
25:m0 = 125.0 ! Higgs mass




! This file contains commands to be read in for a Pythia8 run.
! Lines not beginning with a letter or digit are comments.

! 1) Settings that could be used in a main program, if desired.
Main:numberOfEvents = 100000 ! number of events to generate
Main:numberToList = 0 ! number of events to print
Main:timesToShow = 20 ! show how far along run is
Main:timesAllowErrors = 30 ! max number of allowed errors
Main:showChangedSettings = on ! print changed flags/modes/parameters
Main:showChangedParticleData = on ! print changed particle and decay data

! 2) LHC beams parameter settings.
Beams:idA = 11 ! first beam, p = 2212, pbar = -2212
Beams:idB = -11 ! second beam, p = 2212, pbar = -2212
Beams:eCM = 240. ! CM energy of collision

! 3) Settings for the hard-process generation
WeakDoubleBoson:ffbar2gmZgmZ = on
23:onMode = off ! switch off all decays
23:onIfAny = 5 13 ! switch on Z->mumu and Z->bb only
22:onMode = off ! switch off all decays



! 4) Settings for the event generation process in the Pythia8 library.
PartonLevel:MI = on ! no multiple interactions
PartonLevel:ISR = on ! no initial-state radiation
#PartonLevel:ISR = off ! no initial-state radiation
PartonLevel:FSR = on ! no final-state radiation
HadronLevel:Hadronize = on ! no hadronization

! 5) Non-standard settings; exemplifies tuning possibilities.
#SpaceShower:pT0Ref = 2.0 ! dampening of pT -> 0 divergence
#MultipleInteractions:pT0Ref = 3.0 ! dampening of pT -> 0 divergence


Once you have modified the cards appropriately, run the following to generate a HepMC file using Pythia.


cd BSMGen
source setup.sh
# see the attached cards
./GenPythiaToHepMC XXX.pythia XXX.hepmc > log_hz.log
./GenPythiaToHepMC YYYpythia YYY.hepmc > log_zz.log

Run Delphes

This section describe how to run a Delphes simulation (CMS) on your generated signal and background events. First make sure you understand how Delphes works. The DELPHES Tutorial for FCC is very helpful in learning the basics of Delphes. An essential component of Delphes simulation is the detector card. In this project, a new b-tagging efficiency formula was extrapolated from the values in a prior study.



cd -
cd Delphes
cp XXXCMScard cards/
./DelphesHepMC cards/XXCMS.tcl outputZZ.root inputZZ.hepmc
./DelphesHepMC cards/XXCMS.tcl outputZH.root inputZH.hepmc


Run Analysis

This section describe how to run the simple analysis on the reconstructed samples.

Before proceeding, install the ExRootAnalysis packages into your Delphes directory by doing the following:



svn checkout https://server06.fynu.ucl.ac.be/sources/ExRootAnalysis/trunk ExRootAnalysis
cd ExRootAnalysis
make


For more information on ExRootAnalysis, see the User Manual.

Once the simulation has been run, you are ready for analysis. The zh_analysis_FCC.cpp macro is a basic macro that interprets the simulated events and calculates the invariant masses of Z and H, number of jets for various cases, and a profile of b-jet probability and PT to evaluate the efficiency formula that was used. NormalizePlot.cpp normalizes the plots created in the previous macro to the desired luminosity of the simulation. Finally, RooFitAnalysis.cpp combines the normalized plots, creates a fit over it, and calculates the uncertainty of the Higgs measurements.



cd -
mkdir Analysis
cd Analysis
cp XXXmacros .
................


List of references

  1. Prospective Studies for LEP3 with the CMS Detector
  2. First Look at the Physics Case of TLEP


This topic: CMSPublic > CMSCommunicationsGroup > CMSCommunicationsProjects > WebHome > SWGuide > FCCeeHbbHccAnalysis
Topic revision: r2 - 2017-09-04 - LeaAlinaHeckmann
 
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