Searches for gauge mediated supersymmetry at the Tevatron Page: 2 of 5
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Such a title is probably a bit misleading for the reader interested in a general search within
the Gauge-Mediated Supersymmetry, since the only contributions (one from each Tevatron collab-
orations) we have to report on   are indeed searches for new physics in diphoton events with
large missing transverse energy, interpreted in the framework of such a model.
Gauge-Mediated Supersymmetry is a popular and attractive model, mostly because it drasti-
cally reduces the number of parameters from more than 100 to only 5 in its minimal implementa-
tion. In these models, Supersymmetry (SUSY) breaking occurs well below the Planck scale in a
hidden sector of fields that are singlets under Standard Model (SM) gauge transformations. SUSY
breaking is communicated to the visible sector by messengers that participate in both SM inter-
actions and the dynamics of the hidden sector. SM superpartner masses are generated radiatively
and are proportional to the effective SUSY breaking scale A. The gravitino (C) mass arises from
the Super-Higgs mechanism and is much smaller than the masses of SM superpartners. The phe-
nomenology of such models is then characterised by the decay of the next-to-lightest supersymmet-
ric particle (NLSP) to its SM partner and a light gravitino. The important parameter in determining
this NLSP is the number of messengers Nnes which is chosen here equal to 1, insuring that the
NLSP is the lightest neutralino (x ). Assuming R-parity conservation, the primary process at the
Tevatron is chargino and neutralino pair production, with a smaller contribution from slepton pairs.
The produced superpartners initiate separate decay chains to the next-to-lightest SUSY particle x,
and its decay is assumed to occur promptly with the dominant branching fraction yielding a photon
and an essentially massless gravitino. The dominant feature of this model is thus xfx -> yyG
with additional activity (leptons and/or jets) motivating the search in the (yy + missing transverse
energy + anything) final state.
2. Event selection summary
Since both contributions are searches for the same final state, the event selection is rather sim-
ilar: selection of di-photon events, finding the event vertex, computation of the transverse missing
energy. We emphasize here only the improvements brought since their last publications on the
subject  .
2.1 Photon identification
The DO collaboration achieved an improved photon identification by using a neural net-
work , with five input variables, describing the shape and isolation of the shower, allowing a
good discrimination between true photons and misidentified jets, as can be seen on Fig. 1.
This technique, used also in other DO analyses, gives a factor around 2 improvement in rejec-
tion for same efficiency when compared with the previous photon identification tool, allowing an
improved formulation of the background model.
There are on average several interactions per beam crossing. It is therefore important to cor-
rectly identify the vertex which both photons are coming from, since a wrong vertex would imply
Searches for Gauge Mediated Supersymmetry at the Tevatron
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Lutz, Pierre & /Saclay. Searches for gauge mediated supersymmetry at the Tevatron, article, January 1, 2010; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc832340/m1/2/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.