June 2006

June 28

Worked on the TChain-ing correctly the root files. Our previous FWLight scripts were producing seg. faults when trying to access the events. I found this page in the CMS TWiki:

https://uimon.cern.ch/twiki/bin/view/CMS/WorkBookJetReco#FWLite_with_TChain

and used the method described in the files analyzeJets_headChain.C and analyzeJetsChain.C. My (final?) version of the root script looked like:

gSystem->Load("libPhysicsToolsFWLite");
AutoLibraryLoader::enable();

TChain chain("Events");
chain->Add(filenames);

// Number of entries in chain
Int_t nevent = chain.GetEntries();

// Open first file and set addresses. This needed in addition to what is done in event loop.
chain.GetEvent(0);

// Declare HepMCProduct
edm::HepMCProduct prod;
chain.SetBranchAddress("edmHepMCProduct_PythiaSource__TEST.obj",&prod);

int treenumber = 0;
double p_mom, p_eta, p_id;

// Loop over events
for ( int ev = 0; ev < nevent; ++ev )
{
// Begin magic from Phillipe Canal to insure that for each file
// we read the first entry twice. Necessary, for the chain to work.
int current = chain.LoadTree(ev);
if (treenumber!=current)
{
chain.GetEvent(ev);
chain.SetBranchAddress("edmHepMCProduct_PythiaSource__TEST.obj",&prod);
treenumber = current;
}
// End magic from Phillipe Canal.

chain.GetEvent(ev);

// Iterate over the particles of the current event

for (HepMC::GenEvent::particle_const_iterator p = prod.getHepMCData().particles_begin(); p != prod.getHepMCData().particles_end(); ++p ) {

(...) // particle iteration loop

} // End current event loop
} // End iteration over events.

Executing this script gives warnings like this:

Error in <TTree::SetBranchStatus>: unknown branch -> edmHepMCProduct_PythiaSource__TEST.obj

The number of the warnings is as much as the number of root files we have TChained (edit: warnings are #files-1). With tests that have been made so far though, it doesn't seem to affect our histograms.

Note: The above is for CMSSW 0_6_0. Moving to 0_7_2 will probably require to use gSystem->Load("libFWCoreFWLite.so"); instead.

June 26

Not much to say... I've been trying to make my root scripts more elaborate.

I have an updated version of the Powerpoint presentation (some plots have finally Et removed). The PlotCombined root script now plots each background set with a different color (e+e-, neutrinos). Also, the scaling of the graphs changed slightly. Now to do the scaling, the sum of the cross sections of each set is being used times the number of events.

Week 3

June 23

Created 2 highest Pt e+e- plots. Signal, Background Set 1, Set 2, Top, Drell-Yan.
* Script stops searching @50th particle to save time.

Finished(?) script to produce combined signal/background plots. Will be online during the weekend hopefully.

Powerpoint presentation with the progress so far (under development!)

June 22

Started producing background plots. Plotted all background sets separately. (until I get organized better look at my files)

Plotted the highest Pt electrons for the signal.

Work in progress: Script to plot signal+background together.

Scaling of the histograms: Multiplication of the cross section given by Pythia times the number of events.

TODO: 1) Plot 2 highest Pt electrons. 2) Remove Et from graphs - keep only Pt (DONE - new plots will be ok).

June 20

Looking for background processes in Pythia... current selection:

'MSUB(12)=1 ! fi fibar -> fk fkbar',
'MSUB(15)=1 ! fi fibar -> g Z0',
'MSUB(16)=1 ! fi fjbar -> g W+',
'MSUB(22)=1 ! fi fibar -> Z0 Z0',
'MSUB(23)=1 ! fi fjbar -> Z0 W+',
'MSUB(25)=1 ! fi fibar -> W+ W-',
'MSUB(30)=1 ! fi g -> fi Z0',
'MSUB(31)=1 ! fi g -> fk W+',
'MSUB(81)=1 ! fi fibar -> Qk Qkbar',
'MSUB(82)=1 ! gg -> Qk Qkbar',
'MSUB(84)=1 ! g gamma -> Qk Qkbar'

June 19

So, the Drell-Yan process is the collision between two quarks giving a virtual photon and subsequently a lepton and an antilepton pair as a product.

Quoting this paper (Phys. Rev. Lett. 56, 1327), my process, a Z with larger transverse momentum opposite a missing transverse momentum of the same size, has litte background in the SM.

Notes:
K-factor: The fraction (NLO cross section)/(LO cross section) --- NLO: Next Leading Order

Week 2

* Final selection of process: Higgs -> ZZ -> eeνν

• Find and set Pythia parameters to produce the above process.

Parameter selection so that only the Higgs->ZZ process exists. Also, Added constraints so that one of the Zs decays to e+e- and the other to (any) two neutrinos.

• Using root scripts ploting Etran, Ptran and eta (for electrons/positrons and neutrinos)

Currently at the stage of identifying background processes. t-tbar and the Drell-Yan process (?->look it up!) important backgounds.

Root notes:

Getting the events from the root file:

TTree* events = (TTree*) (f.Get("Events"));
TBranch* MCBranch = events->GetBranch("edmHepMCProduct_PythiaSource__TEST.obj");
edm::HepMCProduct prod;
MCBranch->SetAddress(&prod);

To iterate over all particles in a root file:

for (HepMC::GenEvent::particle_const_iterator p = prod.getHepMCData().particles_begin();
p != prod.getHepMCData().particles_end(); ++p )
{
...
}

Useful properties of particles:

(*p)->ParticleID(); What particle are we dealing with?
(*p)->momentum().perp();Transverse component of momentum
(*p)->momentum().eta();Pseudorapidity
(*p)->momentum().et();Transverse energy
(*p)->momentum().Mother();The mother of the particle

Week 1

A small roundup of what happened the first week...

• Selected a Higgs decay channel (higgs -> ZZ -> llνν).

• Setting up a CMSSW project to work with...

scramv1 project CMSSW CMSSW_0_6_0;
cd CMSSW_0_6_0/src;

• Checking out code from the CSSSW repository using cvs:

cmscvsroot CMSSW; cvs login;
cvs co -r CMSSW_0_6_0 IOMC;

cd IOMC/GeneratorInterface/test;
eval `scramv1 runtime -sh`; Needed after logon to run a project.
cmsRun mcinput.cfg; Generate events.

• Learned how to setup a process is CMSSW, by changing MSUB (processes), MDME (decays) values.
• Creating Root scripts to plot transverse energy/momentum and eta of particles.

Very useful: Filip Moortgat's presentation on Generator Interface in CMSSW.

Also, attended the June 7th CMSSW tutorial. And here's the workbook of the tutorial.