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Large Hadron COllider Readies For New Search

May 18, 2010

If commissioning work goes well, the Large Hadron Collider could soon start a search for new sub-atomic particles, as early as the end of this summer, a leading physicist told BBC News.

Among the first candidates for discovery are two boson particles that have been predicted to exist.

The $10 billion machine has seen a half billion proton collisions since beams crossed for the first time in November 2009.

The LHC is designed to search for the elusive Higgs boson and study new physics predicted to exist at the 1,000 gigaelectronvolt (GeV) scale (approximately 1,000 times larger than the mass of a proton).

One of the first predictions for new discoveries are for particles known as W prime and Z prime bosons. These are heavier than typical W and Z bosons, which are responsible for weak interactions.

The weak interactions are one of the four fundamental interactions of nature, alongside gravity, the strong interaction and electromagnetic force.

The W and Z bosons were discovered at CERN in the 1980s using a 100 GeV (gigaelectronvolt) mass scale. In order to detect higher-mass particles, physicists needed to build a more powerful “atom-smasher”, which was how the LHC came into existence.

If all goes well, the machine could be sensitive enough to probe the 1,000 GeV scale within a few months, according to Dr Tony Weidberg, a particle physicist at the University of Oxford, UK.

The collider will operate at 3.5 TeV (teraelectronvolts) this year and next year – about half the energy it was designed for. But engineers have been steadily increasing the intensity – or luminosity – of the beams.

The discovery of higher-mass W and Z bosons would shed important new light on interactions of sub-atomic particles. The lower-mass versions fall into a category called gauge particles, which are associated with a particular form of “handedness”.

In this scheme, particles can be described as left-handed, right-handed or as combinations of both. The W boson is described by physicists as “left-handed”.

“We’re into speculation here, but one possibility is that the Universe is really symmetric at high energies and that there are right-handed W bosons as well,” said Dr Weidberg. “For some reason, they happen to be much heavier than the left-handed W bosons we know.”

The LHC is right on course to be exploring the 1,000 GeV mass range during its first run — scheduled to last 18 to 24 months — according to Dr James Gillies, director of communications at CERN. But it is still too early to tell if it will happen this year or not.

LHCb, another large detector, will focus on exploring the nature of anti-matter. The detector recently identified a pair of sub-atomic particles known as Charm and Strange Beauty.

Dr Tara Shears, who works on LHCb, said that sighting the Strange Beauty particle was particularly exciting for her team. “This is the first of a type of particle that we’re going to use to try to give us a handle on anti-matter and why it behaves differently to normal matter,” the University of Liverpool researcher told BBC News.

“We’re going to use matter and anti-matter versions of this particular particle to really probe our understanding of what’s going on in a way that we haven’t been able to with other experiments,” she added.

Dr Weidberg said the LHC would probably not be sensitive enough to conduct searches for the Higgs boson until 2011 at the earliest.

Image Caption: LHCb is an experiment set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe we inhabit today. Courtesy CERN

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