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Missing Transverse Energy Calibration in W/Z(+jets) Events Jason Nielsen Santa Cruz Institute for Particle Physics University of California, Santa Cruz UC Davis HEFTI Workshop on Missing Energy Signals at LHC April 1, 2009 Missing Energy Calibration • Goals for calibration: – Resolution (measured for at least one point) – Linearity (requires at least two points) – Extrapolation (unknown requirements) • Z/W (+jet) events provide a known true missing transverse energy • Assume for now that any effects of MET on acceptance can be unfolded/corrected • Also assume backgrounds are small (Z), or can be measured in-situ (W) J. Nielsen Davis Missing Energy 2009 2 MET Scale from Z(ee) Events • Define projection axis along Z momentum – Note this is anti-parallel to the hadronic recoil system • Elong gives measure of energy scale, Eperp gives angular resolution – Find that Elong is the challenge J. Nielsen Davis Missing Energy 2009 3 Artificial Z Decays to Neutrinos • Replace one lepton from Z by neutrino to simulate W decay with nonzero MET • In simulation, true MET is the ET of removed lepton • In collider data, will remove calorimeter deposits associated with lepton J. Nielsen Davis Missing Energy 2009 4 MET in W Events • Choice of measuring W mass or calibrating MET! • MET smearing does not completely wash out sensitivity to W transverse mass • Numerical methods for convoluting mass with resolution functions – Resolutions measured in early W/Z analyses J. Nielsen Davis Missing Energy 2009 5 Results from Many Samples • Check samples with larger true MET: top pairs, SUSY LSPs, high-mass tau pairs • These high-MET samples don’t have a “truth” handle which is known a priori – taken from simulation J. Nielsen Davis Missing Energy 2009 6 Extrapolation to Higher Energies • These data-driven methods are limited to the lowenergy bulk of the MET distribution • How to get to the 300 GeV regime? J. Nielsen Davis Missing Energy 2009 7