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In situ MET performance in early data

In situ MET performance in early data. Overview of ATLAS studies presented in the CSC era To bring everybody up-to-date so that we can discuss which area might be of interest for us. Minimum bias data. First thing to do, look at data supposedly without real missing Et

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In situ MET performance in early data

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  1. In situ MET performance in early data • Overview of ATLAS studies presented in the CSC era • To bring everybody up-to-date so that we can discuss which area might be of interest for us David - CAT SUSY / MET Meeting

  2. Minimum bias data • First thing to do, look at data supposedly without real missing Et • Need to get rid of non-collision events (beam-gas, cosmics, beam-halo) first • Mean missing Et from minbias simulations: 3-4 GeV • Plot MET Ex, MET direction phi, Sigma_MET vs. SumEt Just like Moritz has already shown: David - CAT SUSY / MET Meeting

  3. Minimum bias data • Next logical steps would then be to extend MET resolution vs SumEt to higher SumEt values with QCD dijets • Consistency check between 2 very different event topologies • Moritz started looking at this minbias stuff • We thought there is more to do and contribute in the area of MET performance in the presence of pile-up (much related to minbias of course) N.Kanaya, http://indico.cern.ch/conferenceDisplay.py?confId=41367 David - CAT SUSY / MET Meeting

  4. MET in Z->ee, mumu E.Dobson • Production cross section .. • Select Z->ll events, assume no real missing Et, investigate MET performance as a function of hadronic activity • Take hadronic recoil into account, plot missing Et projected onto the l+l- bisector and the orthogonal axis • Obtain measure for MET resolution, check for possible bias as function of recoil pt • 16k selected events for 10/pb expected (cf. CSC note) Bias from underestimation of hadronic recoil David - CAT SUSY / MET Meeting

  5. MET in Z->tautau And after their cuts: 210 signal over 16 background events for 100/pb in 66 to 116 GeV inv. mass range… Not for this year! David - CAT SUSY / MET Meeting

  6. MET in Z->tautau Reconstruct Z invariant mass assuming m_tau=0, directions of both neutrino systems (measured by MET) are coincident with the measured tau decay products Background subtracted mass peak • Assume Z mass peak position is only a function of MET scale • For 0.8 GeV precision on the Z mass, MET scale can be determined to 8% (assuming 3sigma precision) David - CAT SUSY / MET Meeting

  7. MET in W->lnu • Assume neutrino pt equals MET • Get transverse mass templates from simulations, convolved with MET resolution and scale, in bins of SumEt • Fit templates to measured transverse mass distributions to get MET resolution and scale from best fit David - CAT SUSY / MET Meeting

  8. MET in W->lnu • W->munu events, for 30/pb • No SumEt binning done, background not considered David - CAT SUSY / MET Meeting

  9. MET in semi-leptonic ttbar • Possible to investigate MET in W transverse mass, and difference in pt between leptonic and hadronic top (after full kinematic fit of final state) • They claim 7000 selected events in 200/pb • Even longer term, many other influences (e.g. jet energy scale) David - CAT SUSY / MET Meeting

  10. MET in QCD dijet events • Not done for the note • After minbias the first sample we’ll look at to learn about MET • Also assume ideally zero MET in such events • Cannot probe if we reonstruct real MET correctly, but can go up high in SumEt • Need to select events which you believe have 2 jets, back-to-back, and hence should have 0 MET • E.g. exactly 2 jets, no 3rd jet above x GeV • Df > 160 deg • Such events are also the first approach to get the jet response flat in eta, i.e. get the relative jet-energy scale right (back-to-back jets have to be balanced in energy), so we cannot use exactly the same events to test the MET scale, only the resolution David - CAT SUSY / MET Meeting

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