Z' Statistical tools

Working Twiki on the use of the standard Z' statistical tools for limit setting and significance calculations in CMS. The focus of this Twiki is on the use of these tools for the Z'->ee analysis

Master reference (G. Kukartsev Twiki):

https://twiki.cern.ch/twiki/bin/viewauth/CMS/RooStatsZprime

Getting started on lxplus

The Z' statistical tools require a well-configured recent version of the ROOT package (>=5.27), with ROOSTATS and PYROOT support. There are several ways to achieve this. I found the simplest method was to source a recent version of CMSSW (>= CMSSW_4_1_X) which links to the required version of ROOT. Note that the standard Z' statistical tools Twiki generally refers to code running on the FNAL lpc cluster

Worked example using CMSSW_4_1_4

Set up ROOT version + ROOTSTATS + PYROOT

> cd cms_releases/CMSSW_4_1_4/src

> cmsenv

Check out Exost statistical package

> svn co svn+ssh://[your_cern_login]@svn.cern.ch/reps/exost

> cd exost

Source setup script for CMSSW installation

> source setup/cmssw_setup.[c]sh

> cd workdir

Check out the Z' code

> setenv CVSROOT ':gserver:cmssw.cvs.cern.ch:/cvs/CMSSW'

> kinit

> cvs co -d twobody UserCode/GenaKukartsev/twobody

> cd twobody

Making a workspace

> exost -a workspace -c dielectron_ratio.cfg

Note that when using the ROOT installation linked to CMSSW, you may see the following harmless messages when executing this command:

=[Model]: It seems like you are running in a nonstandard ROOT environment,=

=[Model]: likely, the one that comes with CMSSW.=

=[Model]: Certain harmless RooFit warning messages are turned off.=

> cp myWS.root ws_dielectron_ratio.root

Check configuration of the workspace

> exost -a mcmc -c dielectron_ratio.cfg

(success: the code should compile and execute without crashing)

A quick test of the limit setting code:

> root

> .L twobody.C+

> limit("dielectron","observed",1000, "test", 1, 10000, 100, "")

Interpreting dielectron_ratio.cfg

Input file: must have branch named "mass", "weight" branch is optional

systematics:

mass_kappa = [1.01]; fix; -> 1% error on energy scale

running code:

limit("dielectron","observed",1000, "test", 1, 10000, 100, "")

limit("dielectron","expected",1000, "test", 2, 10000, 100, "")

Simple script to compute observed limit for a given Z' mass:

void mass(Int_t masslim){

gSystem->Load("[path to your exost installation]/exost/workdir/twobody/twobody_C.so");

char txt[20];

sprintf(txt,"_mass_%04d",masslim);

limit("dielectron","observed",float(masslim),txt,25,1000000,100,"");

}

Output files and limit plots

Running the above macro will produce an output root file (.ascii) with:

a) mass; b) limit on xsec ratio

(one per job)

plotting file expects a concatenated list

> ./merge_ascii.py {input file list} [to stdout]

> ./merge_ascii.py -f {output file>}  {input file list}

> ./plots.py -p {output plot name} -d  {input dir}

> ./limit_plots.py see here for definition of input ascii file

{plotter.py is worker file}

Significance calculation

see:

https://twiki.cern.ch/twiki/bin/view/CMS/RooStatsZprime#Significance_and_trials_factors

-- DavidPetyt - 27 Mar 2009

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