Researchers added extra energy to the proton to produce a pair of quarks, which then yielded new particles. In this illustration, a strange/anti-strange quark pair (s and ?) yields a Lambda (^) hyperon and Kaon (K+ meson). The researchers found that strange/anti-strange quark pairs were produced about one-third as often as pairs of up/anti-up (u) and down/anti-down (d) quarks. Credit: Image courtesy of Jefferson Lab
A suppression of strange quark production vs up and down quark production had previously been noted, and for the 1st time, the result has been verified when a single pair is produced.
Protons are composed of 3 quarks – 2 up quarks and 1 down quark bound together by the “strong force” – 1 of the 4 natural forces in our universe. Due to a quirk of the strong force, an accelerator can produce new particle pairs from the proton by imparting extra energy to the particles, with a beam of electrons. Researchers found that when enough energy is provided for a single pair of up, down, or strange quarks, the new particles are far more likely to be made of the proton’s primary quarks (up/anti-up or down/anti-down) than of strange quarks, the next most-prolific quark found in nature.
Less strange quark production than up, down quark production by a factor of 3 had previously been noted in experiments at very high energies, eg at LHC, CERN. It is now verified when a single pair is produced, evidence for universal nature of the quark pair creation process.
One of the biggest mysteries of the structure of ordinary matter revolves around the force that binds the smallest particles of matter together. The strong force is one of the 4 fundamental forces, along with gravity, the weak force, and electromagnetism. The strong force binds together the quarks that build the protons and neutrons inside the nucleus of every atom in the visible universe. The strong force is so strong, in fact, that it will never allow a quark to be found alone: All quarks are bound with other quarks inside composite particles = confinement.
In this experiment, a 5.5-GeV beam of electrons was directed onto a target of liquid hydrogen with a single proton in its nucleus. They collected data on interactions that produced a single pair of quarks that yielded a +ve charged particle measured in the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer, along with a neutral particle identified by its missing mass. These interactions included a proton and a neutral pion (for up/anti-up), a neutron and positive pion (for down/anti-down), and a Lambda and a Kaon (for strange/anti-strange). The strange/anti-strange quark pairs were produced 1/3 as often as their light-quark counterparts, consistent with results from much higher energy, thus providing insight into confinement. http://science.energy.gov/np/highlights/2015/np-2015-08-b/
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