ROOT Analysis example : top mass

ROOT analysis example for a short ttbar analysis (+ the required ntuples) using MakeClass are available here:

/afs/f9.ijs.si/home/liza/CERN/tretjeleto/wiki_analysis/wiki_root_structured

Physics

The code and ntuples are from the Underlying Event tuning effects on semileptonic ttbar analysis study. The ntuples are Pythia events, produced with decreased (min.root)/ increased (max.root) value of the one of the main UE tuning parameters PARP(82). This parameter controls Multiple Interactions behaviour for small pt (see Pythia manual for details). Higher value of the cutoff corresponds to less UE activity, hence less soft jets. Due to the UE contribution to the jet energy it also results in a lower value of the reconstructed top mass. In order to see these effects execute histo.C macro on the min_max.root file, which is the result of the analysis. Note that for the UE tuning PARP(82) is usually varied by ~ 10 % rather than a factor of 2, which is a quite extreme variation.

Analysis

Analysis is built around the main file rootaant_skeleton.C, which is the skeleton of the analysis and uses other files in order to perform the analysis:

• for selection, removal of overlap and truth matching:

do_selection.C
do_ol_removal.C
do_truth_info.C
do_truth_match.C

• t and W mass reconstruction:

do_pre_truthmatch_reco.C (top mass reco using truth matching)
do_truthmatch_reco.C         (top mass reco using truth matching)

do_highest3_reco.C (top mass reco from 3 jets combo that result in highest pt 4-vector)

do_2jW_t_reco.C (W mass reco - related)
do_Wbassoc1_reco.C (W mass reco - related)
do_Wmass_reco.C (W mass reco - related)

It also uses some matching / combination functions.

The analysis can be run by executing macro.C from within root.

-- LizaMijovic - 16 Feb 2009