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Take one small black hole

New Scientist

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Written by Zeeya Merali

THEY must be eternal optimists. How else would you explain the plan by physicists to look for a hypothetical particle, the Higgs boson, by sifting through the remnants of an evaporating mini black hole, which itself may or may not exist?

The Higgs boson, which is thought to give all other particles their mass, was first proposed in the 1960s, but has so far escaped detection. One of the primary goals of the Large Hadron Collider (LHC), the particle accelerator being built at CERN near Geneva, Switzerland, will be to search for the Higgs in the shower of particles generated when two high-energy proton beams collide. It wont be easy. Physicists predict that the Higgs will be created just once in every 10 trillion collisions. With an estimated 800 million collisions a second when the LHC is running, thats still just a handful of Higgs a day, so seeing one is a really remote possibility.

This prompted Gouranda Nayak and Jack Smith of Stony Brook University in New York to look for alternatives. Could the Higgs be found, they wondered, in debris left behind by mini black holes, which physicists think could be created in the LHC if the universe has extra dimensions? Although the chances of making mini black holes are slim, preparations for detecting them are already under way (New Scientist, 23 April 2005, p 38). Black hole production has long odds, but high stakes, says Ben Allanach, a physicist at the University of Cambridge.

Theory predicts that, once created, a mini black hole would immediately evaporate in a blaze of Hawking radiation, releasing all manner of particles in the process, including the Higgs. It sounds crazy, but if mini black holes can be created then the Higgs must be produced, says Smith.

Whats more, if gravity comes into play in particle interactions at energies of a few tera-electronvolts (TeV), as some theories of quantum gravity suggest, then Nayak and Smiths calculations show that far more Higgs bosons will be produced by mini black holes than by conventional collisions (Physical Review D, vol 74, p 014007). Energies of a few TeV can be achieved in the LHC.

Thats exciting, says Horatiu Nastase, a theoretical particle physicist at Brown University in Providence, Rhode Island, who works on mini black holes. Nobody suspected that the Higgs signature from black holes could potentially be so large.

Cigdem Issever of the University of Oxford, who is heading the hunt for mini black holes as part of the ATLAS experiment at the LHC, hopes to spot the fleeting presence of an evaporating black hole by looking for events in which many particles are suddenly sprayed out in every direction like a firework. Unfortunately, finding a Higgs in this outburst will be just a problematic as finding one in the aftermath of the collision of proton beams. The real difficulty is identifying the Higgs, she says.

We dont know its mass. She believes that Nayak and Smiths mechanism will work best if used in tandem with the conventional search. So when physicists suspect they have created the Higgs by normal collisions and can estimate its mass, Issever could check whether a similar particle has been produced by a mini black hole.

Issever points out that Nayak and Smiths idea could become crucial for finding the Higgs if physicists dont find it via normal collisions before the energy of the LHC proton beams crosses the threshold for producing black holes. Past this point, finding the Higgs the conventional way will become impossible. Once black holes are produced, any new particles thrown into the mix will be swallowed by them, so you wont be able to study normal particle collision processes, says Issever. In that case, black hole production will be the only way to make the Higgs.

Ironically, the detection of a mini black hole would upstage the Higgs boson. It would be the find of the century, says Allanach. Their presence would confirm the existence of extra dimensions and provide experimental evidence for string theories. Creating a mini black hole and then sifting through the rubble for the Higgs would be like discovering America for the first time, and being fascinated that there are daisies there, he says. ¡ñ



Claire Bowles
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