The SUSY 2012 conference starts in Beijing today. It is the biggest supersymmetry conference of the year and we expect to see the latest results using the 5/fb gathered in 2012 at 8 TeV before the last technical stop. Actually at least some of the results have already appeared with three new conference notes from ATLAS this morning here, here and here. CMS released their results earlier, see their twiki page .
Because of the high masses being searched for the extra TeV of energy over last year’s 7 TeV actually provides 2 to 3 rimes as much sensitivity, so even without combining the new results with the similar amount of data collected last year we get significantly better depth. Sadly there is nothing yet observed in these notes beyond standard model expectations. This is disappointing but there may be other searches released later and there are always places for SUSY to hide from the LHC.
The most promising anomaly at this time is the 1.8 times SM excess in the diphoton channel seen in the Higgs search which currently has 2.5 sigma significance BSM in ATLAS and 1.5 sigma in CMS. If the peaks coincided the combined significance would be about 2.8 sigma but they are at slightly different masses so the combined result is actually no better than ATLAS on its own. You could argue that this might be a callibration error and the 2.8 sigma is good. In any case there will be twice as much data available in a few weeks and we will see if the excess is a statistical fluctuation or not. Looking at the four individual results from the two experiments and last year vs this year they can be plotted on a mass vs signal scale roughly as follows
The green line is the standard model expectation, blue circles are CMS and red are ATLAS. Black is the unofficial combination. The results are comparable to throwing 4 dice and getting four sixes. Was it a fluke or were the dice loaded, and if so, how?
If the effect is not statistical it could easily be a combination of systematic errors. This would most likely be due to errors in the theoretical calculations that would affect both experiments. (TS pointed out this paper which fingers QCD uncertainties) Many people would suggest we wait for the dice to be rolled again and then look at systematics more carefully before taking this too seriously. However, by time that has happened the long shutdown will be on us. If there is a possibility for something to be seen here it makes sense to look at what it could be. Theorists might then make predictions that could be tested this year if triggers can be adjusted in time.
I am assuming that the excess in the diphoton channel is due to extra particles that affect the Higgs decay loop and that the production rate via gluon fusion is close to SM predictions. This may be wrong but it is what the data looks like so far. That being the case, the Higgs diphoton loop can most easily be enhanced if there is a new charged particle that adds to the loop. A boson would probably add to the cross-section while a fermion would subtract from it but some knowledgeable theorists say that “vector-like” fermions are also a possibility and who am I to argue. It must be colourless to avoid spoiling the gluon fusion production rate. It could carry lepton number which would affect its decay possibilities. Mass would be greater than 105 GeV otherwise it would be produced via mediated photons at LEP, but less than about 300 GeV to have a significant affect on the loop. Best candidates are scalar leptons like the stau or charged scalars like a charged Higgs, but vectors such as a W’ are also possible. These things have been searched for and already excluded in the required mass range, but only under model specific assumptions. Hadron colliders ahve big blind spots especially when particles decay via jets. There is still hope that something is being missed.