Presentation on theme: "22 Feb 2008UCL Physics Meeting1 WW CSC update Adam, Erkcan, Jon, Peter."— Presentation transcript:
22 Feb 2008UCL Physics Meeting1 WW CSC update Adam, Erkcan, Jon, Peter
22 Feb 2008UCL Physics Meeting2 Outline 2-jet W reconstruction Central jet veto and smart(er) overlap removal Atlfast lepton efficiency corrections Curse of EV & Root Final WW mass plots and summary
22 Feb 2008UCL Physics Meeting3 Hadronic Ws from 2 jets The updated algorithm: Check if mass of hardest jet is within the mass single jet W mass window. If so, check whether it satisfies the y-scale cut. If not, try reconstructing from 2 jets. 2-jet reconstruction: Loop through all pairs of jets in the event. Identify the pair with highest combined Pt (use vector sum). See if it falls into the 2-jet W mass window (different mean and width).
22 Feb 2008UCL Physics Meeting4 1-jet and 2-jet masses… Different means and widths for the mass windows.
22 Feb 2008UCL Physics Meeting5 Y-value for 2-jet scenario? Question: Could we use define a y-value for the 2-jet Ws? Use the 4-momenta of the two jets, to calculate the relative transverse momentum of one against the other (k T ). Choose the smaller k T and divide to the P T of the reconstructed W. This is the equivalent of sqrt(y 12 ).
22 Feb 2008UCL Physics Meeting6 Y-value for signal vs. bkg. Small difference after the mass cuts.
22 Feb 2008UCL Physics Meeting7 Y-value vs. Mass An additional 5-10% improvement after a little optimization. signalw+jets bg
22 Feb 2008UCL Physics Meeting8 Central Jet Veto Significant discrepancy between fast and full sim in the central jet veto efficiency: ~98% vs. ~75%. Reason: Electrons misidentified as jets in the full sim. Solution: Reject any jet that overlaps with an isEM=medium object ( R<0.4).
22 Feb 2008UCL Physics Meeting9 A Lesson about Eventview (ie. Smart(er) Overlap Removal) Question: You use EV, isn’t overlap removal handling this automatically? Answer: Yes by default, but we don’t use it! Why? –EV overlap removal work on classes of objects, ie. first insert all your electrons and then insert jets which are not overlapping with them. => Not smart! –First reconstruct your hadronic W from any jets. Then require that the lepton used for leptonic W reconstruction not overlap with this/these jet(s). Efficiency for signal: ~99%. Blindly use EV overlap removal: Loose ~20% of your signal. –Apply electron overlap removal afterwards for your “secondary” jets (like central jets, tag jets, etc.)
22 Feb 2008UCL Physics Meeting10 Atlfast Lepton Efficiency Altfast has too high lepton efficiency…
22 Feb 2008UCL Physics Meeting11 Atlfast Correction… First order correction as a function of the true P T. Leptonic W reco eff –full sim: ( 48.8 +- 0.8 )% –fast sim before fix: ( 72.2 +- 0.3 )% –fast sim after fix: ( 56.6 +- 0.3 )%
22 Feb 2008UCL Physics Meeting12 Last Minute Obstacle (or the Curse of ROOT and EVtuples) Finalized all cuts, scripts to run everything automatically and to produce final plots and even the latex tables! But… –Root fails to chain some of the signal ntuples! –These roottuples are mostly produced on our local batch farm. (Surprise: Grid ones ok.) –Each TFile is fine on its own, but when you try to chain them, your process goes into an infinite loop. –Adam filed bug report to Root guys, but we are unable to isolate the problem. –We don’t have time!!!
22 Feb 2008UCL Physics Meeting13 Solution to ROOT problem Use hexeditor to compare “good” ROOT files with “bad” ones. Somehow the exact unix path to the tuples ingrained into the TFiles. Try hexediting: Doesn’t work. Finally: A macro to read the TTrees and clone them into new TFiles, then merge them into single huge TFile: Single file, no need for TChaining any longer.
22 Feb 2008UCL Physics Meeting14 Conclusions Now everything working smoothly. Finished WW analysis. Have running code for WZ analysis. => To be finalized by next Tuesday.
22 Feb 2008UCL Physics Meeting15 Final m WW plot (example updated)