Electron in a helium atom was replaced by a pion

Physicists experimentally confirmed and explored exotic metastable atom system consisting of a pion and an electron and a helium nucleus. Further study of this object will allow to greatly increase the accuracy of determination of masses of elementary particles and to test the Standard model. Article published in the journal Nature.

Exotic atoms is a special quantum-mechanical system with electromagnetic communication. If in normal atoms the charge carriers are electrons and protons, in the exotic replace them with other elementary particles. Typically, these objects are destroyed in a split second, so you can monitor the system and make measurements extremely difficult. At the same time data that can provide an exotic atoms are of great significance for physics. In particular, they allow to determine the mass of the particles is many times more precisely than is possible in other experiments, as well as to record and study phenomena that go beyond the Standard model.

One of the possible types of exotic mesonic atoms are atoms. In such systems one of the electrons is replaced by a negatively charged meson — hundreds of times heavier a particle that consists of a quark and an antiquark. Usually the life time of the Mesic atom does not exceed 10-12 seconds, but are known and more stable representatives of this class. Among these centenarians scientists distinguish π4He+ system of the pion, the electron and the helium nucleus. Due to the quantum laws, this object is destroyed only on the scale of nanoseconds — that is a thousand times more stable than conventional mesonic atoms. This feature allows researchers to have time to take measurements and to obtain the necessary information. However, until recently, the object existed only on paper reliably to detect it in practice, no one could.

A group of researchers from Germany and Switzerland under the leadership of Masaki Hori (Masaki Hori) from the Institute of quantum optics max Planck Society for the first time experimentally confirmed the formation of the π4He+. To do this, physicists have used the world’s most powerful source of pions and the target of superfluid helium chilled. Equipment produced in the European organization for nuclear research (CERN) and delivered the Paul Scherrer Institute specifically for the experience.

Peonies in the experiment occurred during the irradiation of graphite by protons accelerated — this method allowed us to generate tens of millions of particles per second. Then they headed towards the target by means of a system of magnets, and a special filter were selected from the generated beam the extra components — muons and electrons. Finally the peonies, which flew to the target, partially faced with its atoms and forms a π4He+. For the latest discovery, scientists sent the helium laser beam — the lack of bubbles in the superfluid substance allowed him to achieve exotic atoms almost without scattering. Physicists have found the frequency of the radiation so that the energy of the photons coincide with the energy of the abrupt transition of the π4He+ in the excited state. As a result of this transition of the exotic atom becomes unstable, and the core helium absorbs the pion, and then breaks up into pieces that scatter in opposite directions. The researchers were able to record these pieces on a special detector, also manufactured at CERN, and thus confirm the detection of the π4He+.

In addition, the authors were able to determine the frequency of the resonance transition, which led to the destruction of the exotic atom, however, the measured value does not coincide with the theoretically predicted. Scientists explain this by the collisions of atoms, which lead to the perturbation of energy levels and shifts the resonance frequency: this effect of physics already encountered earlier. The researchers note that when they will be able to adjust for this offset, the experimental data will allow to determine the mass of a pion with an accuracy of 10-8 — a hundred times more than was possible until now. This creates new opportunities to verify and correct theoretical predictions.

Earlier we talked about how the Standard model coped with the description of the rare decay of the D meson and in CERN decided to refuse from using Microsoft software.

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