Saturday Video: Webcast of the faster-than-light talk at CERN

by Salman Hameed

I think it is quite evident that the news of the claim of faster-than-light neutrinos has traveled faster than the speed of light! Below is the webcast of the actual talk. It is a scientific talk and not intended to razzle-dazzle (okay - it is a bit dry and a bit boring). However, IF - and this a huge IF - the claim turns out to be true, then this talk will be a big part of the history of science. In some sense this, this is a good public demonstration of how science works: Here is an experiment that makes a provocative claim. Scientists, in general, are quite skeptical of the results, and want to make sure that physicists making the claim took care of all the variables (such as the accurate measurement of the distance between the relevant points, or the tidal bulging of the Earth's crust due to the Moon, etc.). The coming months will see an effort to replicate these results. If they are not replicated or if a flaw is found in the original study, then we will all forget about this sensational study. Or, we are going to see an interesting revolution in our basic understanding of physics - perhaps leading to the unification of the large-scale (general-relativity) and small-scale (quantum) physics.

I'm also on the skeptical side (also see this xkcd cartoon on making money betting against the neutrinos results). But it is fun to watch this episode unfold.

Here is the video of the CERN webcast (be warned of its dryness) and here is the link to the technical paper (also not meant to razzle-dazzle the public) from the pre-print server:


And if you are looking for an easier explanation of the experiment, check out this article by Dennis Overbye: After Report on Speed, A Rush of Scrutiny.

According to Dr. Autiero’s team, neutrinos emanating from a particle accelerator at CERN, outside Geneva, had raced to a cavern underneath Gran Sasso in Italy — a distance of 454 miles — about 60 nanoseconds faster than it would take a light beam. That amounts to a speed greater than light by about 25 parts in a million.

and here is a brief description of what was involved in getting the neutrinos produced and then detected:

Neutrinos are still a cosmic mystery. They are among the weirdest denizens of the weird quantum subatomic world. Not only are they virtually invisible and able to sail through walls and planets like wind through a screen door, but they are shape-shifters. They come in three varieties and can morph from one form to another as they travel along, an effect Dr. Autiero and his colleagues were trying to observe. 

Their experiment, known clunkily as Oscillation Project with Emulsion-Tracking Apparatus, or Opera, is a collaboration of 160 physicists from 11 countries, primarily Japan and Italy. It is based at the Gran Sasso laboratory, a center for underground physics experiments that need sheltering from cosmic rays. 

The action begins in a tank of hydrogen gas inside a building at CERN. Atoms in puffs of gas from the tank get stripped of their electrons, becoming naked protons, and then get sent on a Coney Island-style speed ride through a series of particle accelerators, eventually winding up in the main ring of the Large Hadron Collider — the mother of all particle accelerators. 

For the Opera experiment, some of the protons are siphoned off at an intermediate energy and slammed in pulses 10 microseconds long into a graphite target, where they produce a pulse of lesser particles called mesons. The mesons in turn decay into neutrinos, which then disappear into the Earth in the direction of Gran Sasso. There, the arriving neutrinos run into an assemblage of lead bricks and photographic emulsion. 

In theory, during the trip, which takes a few milliseconds, some of the neutrinos should shape-shift from a variety known as muon neutrinos to tau neutrinos. The goal of the Opera experiments was to study this transformation: In three years, the researchers have recorded some 16,000 neutrinos in their detector, but only one tau neutrino. 

Measuring the speed of the neutrinos was only a side ambition, explained Antonio Ereditato of the University of Bern, the head of the Opera collaboration. “Now it is becoming a main issue,” he said, adding, “we would like to see some tau neutrinos,” to appreciative laughter from the audience.

Read the full article here. Here is the schematic of the set-up: