Download MET Calibration with W+jets / GMSB

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