Brumfiel in Nature, “No black holes at LHC”

“The end of the world is not nigh after all. Flouting predictions from some theorists, microscopic black holes have so far failed to appear inside the Large Hadron Collider (LHC), scientists there have revealed. The result will be posted this week on arXiv.org. Scientists at the Compact Muon Solenoid (CMS) detector now say they found no signs of mini black holes at energies of 3.5–4.5 TeV. Physicist Guido Tonelli, the detector’s spokesperson, says that by the end of the next run, the LHC should be able to exclude the creation of black holes almost entirely.” Geoff Brumfiel, “No black holes, but extra time at LHC,” News, Nature 468: 876, 14 December 2010.

“Predictions of mini black holes forming at collision energies of a few teraelectronvolts (TeV) were based on theories that consider the gravitational effects of extra dimensions of space. Although the holes were expected to evaporate quickly, some suggested that they might linger long enough to consume the planet. The find is one of a stream of recent papers from the LHC, made possible by the machine’s unexpectedly high performance.”

The technical paper is The CMS Collaboration, “Search for Microscopic Black Hole Signatures at the Large,” CERN-PH-EP/2010-073, 2010/12/15. Submitted to Physics Letters B.

“A search for microscopic black hole production and decay in pp collisions at a center of mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 /pb. Limits on the minimum black hole mass are set, in the range 3.5 – 4.5 TeV, for a variety of parameters in a model with large extra dimensions, along with model-independent limits on new physics in these final states. These are the first direct limits on black hole production at a particle accelerator.”

“One of the exciting predictions of theoretical models with extra spatial dimensions and low scale quantum gravity is the possibility of copious production of microscopic black holes in particle collisions at the CERN Large Hadron Collider (LHC). The model with large, flat, extra spatial dimensions proposed by Arkani-Hamed, Dimopoulos, and Dvali, referred to as the ADD model, predicts microscopic black hole formation in particle collisions. At LHC energies, this cross section can reach 100 pb for energies about 1 TeV. The exact cross section cannot be calculated without knowledge of the underlying theory of quantum gravity and is subject to significant uncertainty. When a black hole is formed, some fraction of the colliding parton energy may not be trapped within the event horizon and will be emitted in the form of gravitational shock waves, which results in energy, momentum, and angular momentum loss. Once produced, the microscopic black holes would decay thermally via Hawking radiation, democratically (with equal probabilities) to all standard model (SM) degrees of freedom. Quarks and gluons are the dominant particles produced in the black hole evaporation (>75%), because they have a large number of color degrees of freedom. The remaining fraction is accounted for by leptons, W and Z bosons, photons, and possibly Higgs bosons. Emission of gravitons by a black hole in the bulk space is generally expected to be suppressed.

The microscopic black holes produced at the LHC would be distinguished by high multiplicity, democratic, and highly isotropic decays with the final-state particles carrying hundreds of GeV of energy. Most of these particles would be reconstructed as jets of hadrons. Observation of such spectacular signatures would provide direct information on the nature of black holes as well as the structure and dimensionality of space-time.

The search for black holes is based on 7 TeV c.m. pp collision data recorded by the Compact Muon Solenoid (CMS) detector at the LHC between March and October 2010, which correspond to an integrated luminosity of 34.7± 3.8 /pb. No black holes were found. The lower limits on the black hole mass at 95% CL range from 3.5 to 4.5 TeV for values of the Planck scale up to 3.5 TeV in the model with large extra dimensions in space.”

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