Special Report - Race for the Higgs is on

As scientists at the Large Hadron Collider confirm the physics we already know, Fermilab say they’re closing in on the Higgs boson – Laboratory News investigates what’s new in particle physics

CERN’s Large Hadron Collider (LHC) has been running for three months and so far it’s been rediscovering what we already know about physics - albeit at unprecedented speeds.

Meanwhile, a team of researchers at Fermilab in the US say they have made a giant leap forward in discovering the elusive Higgs boson, the God particle that could answer the questions of how the universe was created.

CERN announced their first results from the LHC at the 35th International Conference on High Energy Physics (ICHEP) in Paris in July, making it clear that measurements from the four major experiments are rediscovering the particles that lie at the heart of the Standard Model.

“Rediscovering our ‘old friends’ in the particle world shows that the LHC experiments are well prepared to enter new territory,” said CERN director-general Rolf Heuer. After all, if the LHC hadn’t found the ‘old friends’ who would believe that it was capable of finding something never before seen.

“It seems that the Standard Model is working as expected,” Heuer said, “Now it’s down to nature to show us what is new.”

But, as pointed out by Katie Yurkewicz from symmetry breaking – a blog from Fermilab and the SLAC National Accelerator Lab in the US – many of these measurements are new. The LHC is operating at 3.5TeV per beam – that’s three and a half times more energy than ever before – and the new higher-energy measurements are providing new information to the scientific community and helping to improve theoretical models describing how particles and forces interact.

“Such models are continually refined to more accurately reflect the way the universe works, and are also used to predict where new particles may be hiding,” Yurkewicz said, “The more accurate the model, the better the chance that physicists will look in the right place for new particles, and the sooner the world might hear of a discovery.”

Experiments around the LHC were rediscovering particles within days of the collider being ramped up to its new higher energy; ATLAS was seeing W and Z bosons; LHCb has seen hundreds of b particles containing beauty quarks; and the groundwork has been laid for heavy lead ion collisions later in the year at ALICE.

With several experiments geared towards finding the Higgs boson, the LHC is desperate to find the elusive particle, and Fermilab think they’ve managed to narrow down its possible mass range. Two projects – DZero and CDF – separately analysed more than 500,000 billion proton-anti-proton collisions to produce joint exclusion limits for the Higgs particles mass.

“As we continue to collect and analyse data, the experiments will either exclude the Standard Model Higgs boson in the entire mass range, or we’ll go on to see first hints of its existence. There is less and less room for the Higgs boson to hide now,” said Stefan Söldner-Rembold spokesperson for DZero.

Although the Standard Model predicts the Higgs boson, it doesn’t predict it’s mass. Results from Fermilab eliminate masses in the range 158-175GeV/C2 with a confidence of 95%. Combined with other studies, the Higgs mass is likely to be in the 114-158 GeV/C2 and 175-185 GeV/C2 range.

Measuring the Higgs mass is expected to be a major achievement at CERN; a heavier Higgs (over 140GeV/C) is likely to result in decay to pairs of Z or W bosons, which have a distinctive signal in the detector. Lighter Higgs would decay to b-quarks, which would be more difficult to spot against other events.
Meanwhile, plans for a new generation electron-positron collider capable of shooting particles straight have been proposed. The tunnel would measure 50km, cost €10 billion and could be based in Japan, Russia, USA or even with the LHC at CERN. The International Linear Collider aims to compliment the LHC and unlock the mysteries of the universe.

Whatever the future holds, it seems it will bright for particle physics.