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The Warsaw Voice » The Polish Science Voice » February 23, 2012
Physics
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Exploring Gravity
February 23, 2012   
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Is gravity at work in the world of quanta? The KLOE-2 international experiment taking place in a laboratory in Frascati, Italy, may yield some clues. A team of scientists from the National Center for Nuclear Research (NCBJ) in ¦wierk near Warsaw and the Institute of Physics of Jagiellonian University in Cracow are jointly looking for evidence of gravity in the data at the quantum level.

Gravity is a powerful force, but its effects have never been observed in the quantum world. However, this may change soon. A team of scientists working at the Italian National Center for Nuclear Physics in Frascati, near Rome, started the KLOE-2 experiment in December 2011. The experiment is designed to investigate kaons, in particular to search for evidence of the influence of gravitational forces on elementary particles. The team of Polish scientists taking part in the collaborative project is led by Prof. Wojciech Wi¶licki from the National Center for Nuclear Research and by Prof. Paweł Moskal from the Institute of Physics of Jagiellonian University in Cracow. The quantum interferometery method, based on one of the most fundamental quantum mechanics phenomena, will be employed to observe the influence of gravity.

The KLOE-2 experiment involves colliding a beam of electrons with a beam of positrons (their electron anti-matter counterparts). The energy of the collisions is directed in such a way so that Phi zero mesons are produced. Composed of one quark and one anti-quark, mesons are unstable, and the Phi zero mesons generated almost immediately decay into two electrically neutral K zero mesons (kaons) emitted in opposite directions along a straight line. Having traversed a small distance, kaons decay into Pi mesons (pions) that are detected by the KLOE-2 experiment measurement setup.

There are two variants of neutral kaons: short-lived and long-lived ones. Since their masses differ slightly, a characteristic fluctuating spectrum of their decay times is observed. This spectrum is of great interest to scientists since it is related to a fundamental quantum phenomenon: quantum interference.

Quantum mechanics describes states of particles by means of so-called wave functions. The latter may be used to calculate the probability that the particle is in some determined state. If more than a single quantum object of the same type populates a given frame of reference, their individual wave functions overlap and cause interference. The effects of classical interference, for example of laser light beams, may be seen on a screen as a set of distinctive light/dark patterns. Quantum interference occurs as “waving” distributions of values of some related physical parameters. Characteristic interference patterns may for example be seen in the spectra of differences of kaon decay times.

“The quantum interference phenomenon is quite sensitive to any disturbances,” says the National Center for Nuclear Research’s Wi¶licki. Various interactions of particles with the surrounding world, or even the measurement act itself may make it vanish as a result of loss of coherence. “Let us imagine a cleverly constructed experiment like KLOE-2. We want to observe two electrically neutral interfering elementary particles—for example, two kaons—inside an isolated vacuum chamber. Their interactions with electromagnetic fields or with any residue particles inside the chamber may be reduced to insignificant levels. In such conditions, gravity remains the only non-eliminated external factor that could destroy coherence which would be manifested as a loss of interference patterns.”

The first collisions of particles produced as part of the KLOE-2 experiment have already been registered. Eight Polish physicists are analyzing the acquired data and interpreting the results. They estimate one year should be enough to acquire data sufficient for some preliminary conclusions.

“It would be great if we observed de-coherence, or better still, if we found its relationship with the direction of gravity,” says the Jagiellonian University’s Moskal.

“However, the results will be valuable even if we do not observe de-coherence because in such a case we will discover the most accurate upper experimental limit for quantum gravitational effects so far.”

The research of the Polish team is supported by a grant from the Polish Ministry of Science and Higher Education as well as structural funds from the European Union.
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