There is a wide variety of phenomena that could signal the production of black holes in the proton-proton collisions of the LHC. The one considered by the latest article by ATLAS is just one of them -the production of photon-jet pairs of high combined mass, which could result from the decay of a black hole that would not have time to thermalize. But in truth ATLAS does the opposite: they search for gamma-jet events of high mass, without specifically focusing on black holes. They thus produce aspecific limits on the rate of processes that would yield that signature, and that is, I think, a very good thing.
Indeed, exclusive searches for very specific final states predicted by particular new physics models are useful but a bit narrow-minded. With the large amount of data now available in ATLAS and CMS, and with the failure of fashionable models of new physics to provide predictions that stand the experimental test, it is quite reasonable to study the data in a more inclusive fashion, concentrating on rather generic signatures and determining if the corresponding data agree with the Standard Model background or if they depart from it.
ATLAS considered their while 8-TeV data sample and produced a spectrum of the invariant mass of energetic photons recoiling against a jet. The photon signature at high energy is quite clean, so backgrounds are mainly due to the compton-like scattering process of a quark-gluon collision yielding a quark and a photon; a second background is due to hadronic jets fragmenting in such a way that the leading particle is a photon. These are not "direct" photons, in the sense that they are not the direct result of the hard scattering process, but are secondary by-products of the final state partons.
Despite the above distinction, the analysis is performed in such a way that the background processes are estimated from the data themselves - a smooth distribution of invariant mass is their collective result, so one may search that smooth spectrum for a Gaussian bump signalling the presence of a resonance or other turn-on phenomena.

Using by now well-tested technology of limit setting with the CLs criterion, ATLAS proceeds to interpret the data in terms of an exclusion of the cross section for quantum black holes and excited quarks as a function of the mass scale of those processes (see e.g. the figure below). However, they also produce a limit for a generic narrow resonance as a function of its mass, so that a future model can compare to the ATLAS result without the need for a new analysis.

All in all a nice analysis, and I must say I wish I saw more of these signature-based searches. Specifically, I would like to see searches that consider the data even more inclusively, and multivariate techniques that take care of evidencing region of multi-dimensional parameter space of the observable quantities where the data disagree with background expectations. But such searches are still viewed with suspicion in the HEP community, partly because the mindset is still aligned with that of our now aging mentors, who learned how to hunt for new physics when computers still munched hole-punched data cards. Those new ideas will take time to win over the scientific consensus.
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