By the way, when I wrote the first question yesterday I thought I would not need to explain it in detail, but it just occurred to me that a disclaimer would be useful. Here it is:
I offer these questions as a self-test of one's knowledge in particle physics. I am not part of the INFN selection committee. I have no connection to the selection committee, nor any insider information on how the exam will be structured. All I know about it is what is contained in the official call, available to everybody. I do have some previous experience with INFN selections of researchers, but this needs not be relevant for the present one.
Okay, I hope the above is clear (these days there's always some sorry soul around who tries to cast the blame on bloggers... As I explained many times in the past, rumors and leaks come from other sources, not from bloggers, who are by definition doing everything they do in the light of the day).
So here is today's question.
A 2-TeV proton-antiproton collider experiment composed of a gaseous tracking chamber surrounded by electromagnetic and hadronic calorimeters collects 100 inverse picobarns of data. In the resulting dataset the experiment detects one peculiar event that features two energetic electron candidates with transverse energy above 50 GeV each, two photon candidates with transverse energy above 50 GeV each, and significant missing transverse energy also in the 50 GeV ballpark.
Consider all thinkable physics- and detector-related sources of the detected signature and discuss their chance to be the true source of the observation. Make all the credible assumptions you need about the system you deem appropriate.