|Search for new physics in the exclusive
Photon+MET channel in RunII
The photon plus missing transverse energy signal is comparatively rare in the Standard Model. The production is dominated by the higher-order electroweak Z+gamma process. This signature is a sensitive place to search for new high-energy invisible particles because photons radiated by incoming partons in a collision can be the only tag available to us in the detection of such processes. Photons are also good candidates to be produced in the decay chains of new particles and appear in such popular models as Large Extra Dimensions, anomalous Z+gamma couplings, heavy right-handed neutrinos, and so on.Authors:
One model of new physics that can produce such a signature is the compactified Large Extra Dimensions (LED) model of Arkani-Hamed, Dimopoulos, and Dvali (ADD). In such a model, gravitons are produced directly in processes such as qqbar->gamma+G, where G is the emitted graviton. The emitted graviton will be undetected, leaving the final state of a single photon. We perform a general search in this final state, and separately optimize the cut on the photon Et to gain the best sensitivity to the ADD model.
This search for new physics is based on ~2.0 fb-1 of data collected with a trigger requiring photon Et> 18 GeV and MET > 18 GeV and requiring base kinematic cuts of photon Et > 50 GeV and MET > 50 GeV. The optimization for the ADD model yields photon Et > 90 GeV. We observe 40 events after this optimization, in agreement with the background estimate of 46.7 events. The acceptance to find and identify a central photon is 68 +/- 3% and the acceptance of analysis clean-up cuts is 63%. The kinematic acceptance for the optimized search, calculated with a Z+gamma sample generated with a photon with ET > 20 GeV and |eta|<2, is 2.7%. For Z+gamma production the LO cross-section is equal to NLO+0jet cross-section for a jet rejection threshold of 15 GeV, which is applied in this analysis. As a result we use the LO MadGraph generator to estimate the Z+gamma cross section, which is 1065 fb for generated photons with ET > 20 GeV and |eta| < 2.
M Goncharov, V Krutelyov, R Culbertson, A Pronko