杏吧原创

Mirroring the universe (Image: Claudia Marcelloni/CERN)

PHYSICS may be shifting to the right. Tantalising signals at CERN鈥檚 Large Hadron Collider near Geneva, Switzerland, hint at a new particle that .

Like your hands, some fundamental particles are different from their mirror images, and so have an intrinsic handedness or 鈥渃hirality鈥�. But some particles only seem to come in one of the two handedness options, leading to what鈥檚 called 鈥渓eft-right symmetry breaking鈥�.

In particular, W bosons, which carry the weak nuclear force, are supposed to come only in left-handed varieties. The debris from smashing protons at the LHC has revealed evidence of unexpected right-handed bosons.

After finding the Higgs boson in 2012, the collider shut down for upgrades, allowing collisions to resume at higher energies earlier this year. At two of the LHC鈥檚 experiments, the latest results appear to contain four novel signals. Together, they could hint at a W-boson-like particle, the W鈥�, with a mass of about 2 teraelectronvolts. If confirmed, it would be the first boson discovered since the Higgs.

The find could reveal how to extend the successful but frustratingly incomplete standard model of particle physics, in ways that could explain the nature of dark matter and why there is so little antimatter in the universe.

The strongest signal is an excess of particles seen by the ATLAS experiment (), at a statistical significance of 3.4 sigma. This falls short of the 5 sigma regarded as proof of existence (see 鈥�Particle-spotting at the LHC鈥�), but physicists are intrigued because three other unexpected signals at the independent CMS experiment could point to the same thing.

鈥淭he big question is whether there might be some connection between these,鈥� says at Fermilab in Chicago. In a paper posted online last month, Dobrescu and , also at Fermilab, showed how the signals could fit naturally into modified versions of left-right symmetric models (). They restore left-right symmetry by introducing a suite of exotic particles, of which this possible W鈥� particle is one.

Another way to fit the right-handed W鈥� into a bigger theory was proposed last week by at the University of Manchester, UK, and at the University of Maryland. They invoke just a few novel particles, then restore left-right symmetry by giving just one of them special properties ().

Some theorists have proposed that these exotic particles instead hint that the Higgs boson is not fundamental particle. Instead, it could be a composite, and some of its constituents would account for the observed signals.

鈥淚n my opinion, the most plausible explanation is in the context of composite Higgs models,鈥� says at CERN. 鈥淚f this scenario is true, that would mean there are new symmetries and new forces just around the corner.鈥�

鈥淚f the Higgs is really a composite particle, that would mean new forces just around the corner鈥�

The next step is for the existence of the right-handed W鈥� boson to be confirmed or ruled out. Dobrescu says that should be possible by October this year. But testing the broader theories could take a couple of years.

Other LHC anomalies have disappeared once more data became available. That could happen again, but at the University of Melbourne, Australia, says this one is more interesting.

鈥淭he fact that the data hint at a very sensible and well-motivated standard model extension that has been studied for decades perhaps is reason to take this one a bit more seriously,鈥� he says.

This article appeared in print under the headline 鈥淣ew boson caught right-handed?鈥�