NEVER mind the Large Hadron Collider at CERN, its ageing predecessor may have discovered a new and unexpected kind of particle. The announcement last week from the Tevatron particle accelerator at Fermilab in Batavia, Illinois, provided some excitement amid the frustration of ongoing repairs to the LHC.
The Tevatron smashes protons and anti-protons together at high speed inside a 1.5-centimetre-wide “beam pipe”. Particles created by the collision are tracked by surrounding layers of electronics, whose output is then examined by researchers working on the Collider Detector at Fermilab project. In this instance, the CDF team was looking at bottom quarks and bottom antiquarks, whose decay products include at least two charged particles called muons.
The team was in for a big surprise. Firstly, they saw far more muons coming from the collisions than expected. But crucially, some of these muons seemed to have been created outside the beam pipe: they had left no trace in the innermost layer of the detector.
Advertisement
The CDF team says it is unable to explain such muons using the standard model of particle physics, or from what they know of their detector (). However, “we haven’t ruled out a mundane explanation for this, and I want to make that very clear”, says CDF spokesman Jacobo Konigsberg. He adds that the effect needs to be verified by other experiments.
If the effect is real, it means that some unknown particle with a lifetime of about 20 picoseconds was produced in the collision, travelled about 1 centimetre through the side of the beam pipe, and then decayed into muons.
“A centimetre is a long way for most kinds of particles to make it before decaying,” says Dan Hooper of Fermilab. “It’s too early to say much about this. That being said, if it turns out that a new ‘long-lived’ particle exists, it would be a very big deal.”
“It’s too early to say much about this, but if it turns out that a new ‘long-lived’ particle exists, it would be a very big deal”
So what could it be? In a recent paper, Neal Weiner of New York University and colleagues sought to explain recent observations of radiation and antiparticles from the Milky Way by positing particles of dark matter – the enigmatic stuff thought to make up a large proportion of the universe – that interact with each other by exchanging “force-carrying” particles ().
These latter particles would have a mass of about 1 gigaelectronvolt – roughly the same as the mysterious CDF particle. Could they be one and the same? “We’re trying to figure that out,” says Weiner. “But I would be excited regardless.”
