No microscopic black holes yet

No microscopic black holes yet. From among 10¹³ proton–proton collisions at 7 GeV in its first year of operation, the Large Hadron Collider (LHC) at CERN has as yet yielded no evidence of black hole production. The detectable creation of microscopic black holes at the LHC follows from speculative but attractive theories that seek to explain the puzzling weakness of gravity by positing curled-up extra spatial dimensions accessible only to gravitons. In such theories, the intrinsic strength of gravity would be comparable to those of the electromagnetic and weak interactions at energies near 1 TeV, where electroweak unification occurs. But now the collaboration that runs the LHC’s Compact Muon Solenoid (CMS) detector, having found no evidence of black holes, has published the first experimental lower limits on their masses. A black hole produced in a 7-TeV collision would decay by Hawking radiation within 10⁻²⁷ s into perhaps half a dozen extraordinarily energetic particles—mostly quarks and gluons manifesting themselves as jets of hadrons. Such a spectacular decay would be conspicuous not only by the number of emerging ultrahigh-energy jets, but also by their unusually isotropic distribution. Even in the absence of true black hole events, however, 10¹³ collisions will create many imposters. So determining limits on black hole production requires painstaking estimation of the resulting backgrounds. The figure shows the minimum black hole mass deduced from the CMS null result as a function of two parameters of the extra-dimension theories: the number n of extra spatial dimensions, and the characteristic mass scale M _D of the putative unification of the gravitational and electroweak interactions. (August 2010, page 42 )