It is possible that we live in a world that has more than the usual 1 time + 3 space dimensions of everyday experience. Indeed, one way to explain the peculiar properties of gravity is that the universe extends in 4+n dimensional space (the bulk) while we are trapped in the familiar 4 dimensional world (the brane).   The movie shown here illustrates a process that might occur in such a scenario. The bulk here is shown as the big black void containing our brane, which is represented by the box grid populated by galaxies, stars and familiar elementary particles.
Two such particles, for example a proton and an antiproton, shown as generic blue balls, can collide on the brane, and if the energy is high enough, produce a graviton (the particle that mediates the force of gravity), along with jets of familiar elementary particles (all shown as generic blue balls). The graviton flies out of the brane (the big blue ball) carrying away energy and momentum. Because the graviton moves off into the extra dimensions, we call it a Kaluza-Klein particle. An observer on the brane witnessing the outcome of the collision would see the usual particles produced in such experiments, with a large imbalance of energy and momentum. Instead of detecting the Kaluza-Klein graviton directly, we observe its "missing energy" signature. This is similar to the way that the existence of neutrinos is inferred in collider experiments.
CDF searched in a sample of events characterized by large missing energy at center of mass energy 1.8 TeV and found no excess of such events as demonstrated below. Most of the observed events are attributed to Standard Model processes that produce neutrinos. .
The result of the analysis is to constrain at 95% C.L. the value of the effective Planck Scale for 2,4,6 extra dimensions to be greater than 1, 0.77, 0.71 TeV, which in turn constrains the size of the extra dimension to be smaller than the corresponding values shown in the table below: This is the best result from a direct graviton emission search at the Tevatron. Note that the Tevatron is now running at a higher energy (~ 2 TeV) and that we will soon have many times the data sample analyzed here. This will make us sensitive to an effective Planck Scale as high as 1.5 TeV for 2 extra dimensions.
This analysis is published in the arXive hep-ex/0309051 For more info mail Kevin Burkett and Maria Spiropulu at CDF Movie created by Liubo Borissov. Find a short documentory about detectors here.

CDF plain english summary of analysis
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