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physics

The proton in transformation

A study demonstrates how an accelerated particle can originate others

If it were to remain stationary, free from any electric or magnetic force and at zero degrees Absolute (-273º Celsius), the proton, one of the particles of the atomic nucleus, would remain stable. And so it could remain forever, according to the current theoretical models. The scenario is more exciting awhen the proton is submitted, for example, to an electric field: it begins to accelerate and can self-destruct. The explanation of this, from the proton’s point of view – as if an observer were seated on top of it -, is part of a study that was highlighted in the 8th of October issue of Physical Review Letters, signed by George Matsas of the Theoretical Physics Institute of the São Paulo State University (IFT-Unesp), and by his doctorate student Daniel Vanzella, today at the Gravitation and Cosmology Center of Wisconsin University in the United States.

To give an explanation of the disintegration or decaying of the proton, the study by Matsas and Vanzella mathematically confirmed the so called Fulling-Davies-Unruh effect, presented as a hypothesis in 1976: an inert observer at rest in the laboratory would not see anything if he were to be in a vacuum at zero Absolute, whilst an accelerated observer would observe elementary particles in movement, as if he were in a microwave oven with millions of protons, neutrons and electrons hitting him. The researchers based themselves on this effect to explain the disintegration of the proton from the point of view of an accelerated observer seated upon it. Under these conditions, he would watch the appearance of particles that simply don’t exist for inert observers – one more mystery of quantum mechanics.

At low temperature, the proton absorbs an electron and an anti-neutrino and forms a neutron. “As the acceleration increases, the proton feels a higher environmental temperature and other processes of disintegration become more probable”, says Matsas. The proton can then transform itself into a neutron, this time through the capture of an electron, in a process that emits a neutrino, a type of particle apparently without mass. Another possibility is the absorption of an anti-neutrino and to give birth to a neutron and a positron, a particle with the same characteristics an electron, but with the opposite electrical charge.

Matsas and Vanzella also calculated the time for the disintegration oftheproton for observers at rest in the laboratory which only sees the proton in movement. In the end, they observed that the time for disintegration coincided with the results obtained for observations in movement on the proton. “If the effect didn’t exist, there would be no way of explaining the disintegration of the accelerated proton from the point of view of an observer seated upon it”, says Matsas. The transformation into a neutron and other particles immensely smaller is extremely quick – it takes a tenth of a second. However, it can only occur if the proton has been submitted to a gigantic acceleration, equivalent to the number 5 followed by 34 zeros in centimeters per second per second something only conceivable in pulsars, highly energetic cosmic objects.

“Only under astrophysics conditions would there be a chance of observing the disintegration of the proton”, says the Unesp researcher. On the Earth, it is still not possible to reach this acceleration, not even with the best accelerators in the world such as at the Fermi Laboratory in the USA, or the French Swiss Large Hadron Collider (LHC), under construction. In the meantime, the proton continues to be a stable particle. “On the Earth”, says Matsas, “the time that the proton would need to disintegrate would be greater than the actual life of the universe”.

The project
Postulations in Field Theory in Curved Space (nº 97/13261-2); Modality
Post Graduate Scholarship; Coordinator George Emanuel Avraam Matsas – Theoretical Physics Institute/Unesp; Investment R$ 81,283.69

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