Bad News For Extra-Dimensional String Theory

"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 pain -
staking 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 MD of the putative unification of the gravi -
tational and electroweak interactions. (CMS collaboration,
http://arxiv.org/abs/1012.3375 )

From Physics Today, Feb, 2011 - Fair use excerpt for non-commercial educational use only.