26 September 2011

Particle faster than light

Brand new data from CERN indicates a particle that moves faster than the speed of light. If this really were the case, it would be almost unbelievable news that breaks with everything that physicists have been relying on since Einstein put forward the theory of relativity, which says, that nothing can move faster than light.

Detector setup to capture neutrino beams generated at CERN The beam of neutrinos created at CERN travel over 700 km through the earth to Italy where they are captured in a 1300-ton detector, primarily consisting of lead.

A journey underground

The measurements were made in the experiment CNGS (CERN Neutrinos to Gran Sasso), which literally sends particles through the earth from CERN to the OPERA experiment in the Gran Sasso observatory, located 720 km away in Italy. The particles in question are called muon neutrinos and have the unique property that they very rarely interact with other particles and can therefore move great distances through, for example, soil and rocks as if it was air. A 1300-ton detector captures them in Italy, after which, using very precise GPS measurements, it is possible to calculate the time they have taken to travel the distance from CERN to Italy, calculated down to an accuracy of just 20 cm.

The Gran Sasso experiment  under construction

The Gran Sasso experiment as it looked during construction. The experiment is located in the mountains to prevent outside particles disturbing the experiment.

The measurements made in the OPERA experiment at Gran Sasso provide the speed of the muon neutrinos down to an accuracy of less than 10 ns (0.000000001 seconds). The result shows that the particles move about 60 nano-seconds too quickly.

Break with the theory of relativity

"If the result turns out to not be related to measurement uncertainties, it is a violation of the theory of relativity, which has formed the basis for all physics since the beginning of the 1900s. According to Einstein’s theories, the speed of light is the upper limit for how fast particles, as we know them, can move. A time different of 60 nano-seconds gives a deviation that is well over 2000 km/h above the speed of light”, explains particle physicist Ask Emil Løvschall-Jensen, Discovery Center at the Niels Bohr Institute.

Muon neutrinos created at CERN Muon neutrinos are created at CERN and sent towards Gran Sasso. The protons from the circular accelerator SPS, which normally accelerates protons in the large ring, LHC, are shot into a material, thus releasing pion- and kaon- particles. These decay naturally into neutrinos and finally you get a beam of pure muon neutrinos moving towards Gran Sasso.  

Tachyon a possible candidate

Ask Emil Løvschall-Jensen explains that if the result turns out to hold water, theoretical particle physicists are not entirely on bare ground. There is a proposal for a particle that can move faster than the speed of light. The so-called Tachyon, which got its name from the Greek word for quick, takhus, appears in several alternative theories. It has the unique property in that it acts with negative mass in the equations, which means that it will always move faster than the speed of light. 

Whether there really is talk of a violation of the theory of relativity or an error in the measurements requires further investigation. By the same token, researchers behind the result are inviting a number of other researchers to find errors in the measurements at a conference later today at CERN. Whatever the result, physicists the world over are waiting in anticipation for the ruling.