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FCCeeHiggsStudies

ZH recoil studies (mass and xsec measurement)

The FCCee Higgs studies consists of two main steps:

  1. Analysis of Ntuples (Whizard/Pythia + Delphes) using the FCCee framework tools
  2. Statistical analysis with Combine

Analysis

Analysis framework based on RDataframe to run over all the Ntuples.

For each session, run

source initFCC.sh

Combine

Installation standalone version of Combine: instructions see comments in initCombine.sh (lxplus7). For each session, run

source initCombine.sh

The main scripts are stored in the fitAnalysis directory.

Steps to run Combine (provided the necessary recoil distributions obtaind from step 1):

  1. Prepare datacard (text file) and make workspace (ROOT file).
  2. Convert datacard + workspace to Combine workspace
  3. Run the necessary grid scans

Step 1 Datacard can be found in fitAnalysis/combine/datacard.txt. It contains the signal and background process, their links to the RooFit workspaces and a list of nuisance parameters to be taken into account. The workspace is generated using fitAnalysis/fitAnalysis/makeWS_2CBG.py. It basically models the signal and backgrounds with RooFit objects, as well as the systematics.

Step 2 Conversion of workspace to a Combine workspace:

text2workspace datacard.txt -o ws.root

This command is attached to the end of the makeWS_2CBG.py file. It produces the Combine workspace ws.root, which is used for all Combine commands and run the fits.

Step 3 Using the ws.root, one can run a single fit to the signal strength (r):

combine -M FitDiagnostics -t -1 --expectSignal=1 ws.root -m 125 -v 10 --X-rtd ADDNLL_CBNLL=0

It does a likelihood fit and returns the signal strength with the uncertainty. As we inject 1 unit of signal (--expectSignal=1), the fit result should give identical results.

To run a grid scan for the signal strength between 0.95 and 1.05 (100 points equally spaced), run:

combine -M MultiDimFit -t -1 --setParameterRanges r=0.95,1.05 --points=100 --algo=grid ws.root --expectSignal=1 -m 125 --X-rtd TMCSO_AdaptivePseudoAsimov -v 10 --X-rtd ADDNLL_CBNLL=0

For a grid scan using the Higgs mass as parameter of interest (between 124.99 and 125.01 GeV) use:

combine -M MultiDimFit -t -1 --setParameterRanges MH=124.99,125.01 --points=%d --algo=grid ws.root --expectSignal=1 -m 125 --redefineSignalPOIs MH --X-rtd TMCSO_AdaptivePseudoAsimov -v 10 --X-rtd ADDNLL_CBNLL=0

A script to run, analyze and make plots of the grid scans can be found at fitAnalysis/gridScans.py.