THE PARTICLE ZOO

The Discovery of Particles and Particle Accelerators

Prior knowledge regarding the constituent particles of the atom (protons, neutrons and electrons) alongside familiarity with the ideas of conservation of energy, charge and mass should enable you to understand particle physics. We’ll be looking at particles classified as hadrons (baryons and mesons) and leptons, each with its own antiparticle and each with their own interactions that occur between particles.

Subatomic particles such as the proton, neutron and electron were identified as major components of the atom, and further particles have been identified too, such as quarks that make up protons and neutrons and particles such as muons, leptons and neutrinos. 

It all seems pretty confusing, and it only gets far more discombobulating – variable “fields” have been observed in the universe that have incredibly important roles in the functioning of the universe, such as: magnetic fields, electrical fields, gravitational fields and more. 

And scientists are looking for more. 

If you haven’t come across the search for a particle called the Higgs boson – a particle potentially responsible for the “field” giving mass to some particles but not others – then you’re missing out. The world’s largest particle accelerator began operations in Europe in 2008, and the search for new particles and fields is expanding.

Likewise, exchange particles called mesons were hypothesized by Japanese physicist Hidekei Yukawa, who predicted the existence of these exchange particles to be of a range of no more than 10⁻¹⁵m and with a mass between that of a proton and electron. 

A cloud chamber photograph obtained by Carl Anderson was thought to have shown a meson, but instead the heavy electron was discovered – the muon – due to the track length of 40mm lasting longer than that of a strong-interacting particle. Years later British physicist Cecil Powell discovered pions, or pi mesons – "microscopic tracks were found in photographic emulsions exposed to cosmic rays at high altitude" (AQA Physics A, Nelson Thornes, 2008).

• The Stanford Linear Accelerator in California permits electrons to accelerate over 3km through 50,000mV. When these electrons collide with a "target", particle-antiparticle pairs are created.
• The Large Hadron Collider at CERN has a circumference of 27km and is designed in a ring structure underground, differing from a linear accelerator as hadrons are accelerated at more than 7000GeV. Protons, neutrons and mesons go under the hadron subsection.

The search has extended to looking for particles and fields coinciding with dark energy and dark matter. It is known that dark matter fills the universe, exerting a gravitational pull on the regular matter (like stars and planets) surrounding it. But it’s undetectable – no radio waves, no heat – basically no form of energy - is produced from dark matter – therefore physicists are eager to defy the laws of physics and find evidence for dark energy particles or fields.

Ultimately, scientists would need incredibly powerful particle accelerators and a lot of luck in discovering dark energy particles/ fields. In the meantime a new field has been described, called quintessence. 

"One key difference from the vacuum energy is that quintessence would vary with time, so it might not show up at all in the early universe, but exert a powerful influence today. " (http://hetdex.org/dark_energy/)

Several hypotheses exist and all is debatable. NOW BACK TO THE MAIN STORY, THE PARTICLE ZOO! 

Muons, Pions and Kaons 

• Muons: heavy electrons, a negatively charged particle, a rest mass of over x200 regular electron
• Pions: positively charged or negatively charged or neutral, a rest mass greater than a muon but less than a proton
• Kaons: positively charged or negatively charged or neutral, a rest mass greater than a pion but less than a proton