Double Chooz Preliminary Results: Neutrino Experiment Detects Disappearance of Neutrinos

The most common particle in the Universe is also the most mysterious, but it seems that scientists might have got something correctly predicted about it. Neutrinos have been noticed to disappear’ in the Double Chooz experiment and this is being interpreted as the manifestation of the elusive neutrino oscillation signature. Electron anti-neutrinos have been noticed to simply disappear meaning that they are actually turning into tau anti-neutrinos, which we have no way of detecting. Technically, scientists are measuring the third mixing angle’ or θ13.

The Double Chooz experiment

Oscillations of  neutrinos

Neutrinos are strange because they do not behave in conventional’ ways. One form of neutrinos can change into another, provided neutrinos have mass, however small it might be. There are three types of neutrinos electron neutrinos, muon neutrinos and tau neutrinos. The names are given according to the particle they accompany in a doublet.

Experimental evidence suggests that one form of neutrinos changes into another and this is through a process called see-saw’ mechanism. In other words, the neutrino exists in a mixed’ state and we detect only one of the constituent states. (If you think this is weird, just know that this is the staple bread-butter of quantum mechanics.) The amount of mixing is given by angles. The electron (type 1) and muon (type 2) type neutrinos mix via the mixing angle θ12. The muon (type 2) and tau (type 3) neutrinos mix via the θ23 angle. The electron and the tau neutrinos mix via the angle θ13, which happens to be out angle of interest.   We know that θ13 is very small, but we want to know how small it really is. The fact that it is non-zero is, in itself, remarkable.

Neutrino oscillations. The subscripted letters refer to the type of neutrinos.

The value of the mixing angle and the consequence of that

One of the experiments measuring the θ13 is the Double Chooz experiment. It just released the first set of results and it gives a definitive value for this third mixing angle. The value, given in terms of sine squared of double the angle, is

sin22θ13  = 0.085  +  0.029(stat)  +  0.042(syst),

where the last two numbers represent errors and need not concern us too much at the moment.

The T2K experiment. The walls are lined with photo-detectors. The entire chamber will be filled with water when in operation.

What is interesting is the fact that the other giant experiment in the field of neutrinos the T2K experiment also gives similar results.

The value of θ13 is not zero and the two results corroborate one another to give a 3-sigma level confidence on that fact. There are neutrino oscillations between the electron type and the tau type.

This is a theoretically significant result for scientists, who are knee-deep with questions about neutrinos and their properties (and, before you ask, the faster-than-light results are the least of the worries). This will put further constraints on the neutrino masses.

Further details about the Double Chooz preliminary results can be found here:

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Debjyoti Bardhan

Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.