- 3069 - PARTICLE PHYSICS - fundamental particles? Physicists working at CERN have observed a rare decay of the Higgs boson, expanding our understanding of the quantum universe. Scientists have found evidence of this massive particle decaying into two leptons and a photon. What are these fundamental particles?
--------------- 3069 - PARTICLE PHYSICS - fundamental particles?
- But what are leptons? How have scientists ‘observed’ this decay? And what does it tell us about the Higgs boson?
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- More than a hundred years ago, the first sub-atomic particle was discovered. We called it an “electron“.
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- As scientists probed deeper into the matter, we discovered two more particles: protons and neutrons. By 1947, physicists were aware of seven elementary particles: electron, photon, proton, neutron, kaon, and meson.
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- An elementary particle is one that isn’t composed of any smaller particles. It was several years later when we found that protons and neutrons are not elementary. They are further composed of ‘quarks“.
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- The year 1950 left theoretical particle physics in a mess. Experimentalists were happy. Each year, they were discovering several elementary particles. In the 1950s, there was a joke among physicists that the year’s Nobel Prize for Physics must go to a researcher who did not discover a new particle!
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- Theoretical physicists were in trouble because they didn’t know how to group these particles. They had to come up with a theory. Else, they would keep drowning in the soup of elementary particles.
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- The 1960s saw triumphs in theoretical particle physics. According to physicists, everything you see around is a result of four fundamental forces. The first is gravity. It is responsible for the motion of astronomical objects. The Moon goes around the Earth; the Earth goes around the Sun; the Sun revolves around the galactic center.
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- The force that governs the motion of celestial objects is gravity. It also keeps you grounded. The theory that explains gravity is the general theory of relativity given by Einstein. However, in this remarkably successful theory, gravity is described as a curvature of “spacetime“, instead of a “force“.
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- The second is the electromagnetic force. For quite a long time, electricity and magnetism were thought to be different forces. But, the relationship between the two was discovered. Scottish physicist James Clerk Maxwell brought together the four equations that show how the two forces are mingled with each other. The four Maxwell’s equations describe the single “electromagnetic force“.
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- “Quantum Gravity” is the hardest problem in physics. IIt is combining Special Relativity & Quantum Mechanics.
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- The third on the list is the “weak nuclear force’ responsible for the radioactive decay of atoms. The theory of the weak force is Fermi’s theory of beta decay. Finally, we have the “strong nuclear force” that binds the nucleus together.
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- After years of brainstorming and hard work, physicists successfully combined three of the four fundamental forces into a complex theory called the Standard Model. The three forces are the electromagnetic force, the weak force, and the strong force. These are the elementary particles of the standard model.
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- Standard Model of Physics has two types of particles: “Fermions” and “bosons“. All the fermions have a half-integer spin, and the bosons have an integral spin. There are six types of “quarks“. Different combinations of quarks and anti-quarks make up different composite particles. For example, two ‘up quarks’ and a ‘down quark’ make up a “proton“.
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- The elementary particles are the six leptons: electron, muon, tau, and the three neutrinos. Quarks make up the protons and the neutrons, that further make up the nucleus of all the atoms.
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- Electrons revolving around the nucleus form these atoms. Quarks and leptons are basically the building blocks of the universe. There are bosons. They are the force carriers.
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- The photon mediates the electromagnetic force, the gluon mediates the strong force, and finally the W and the Z bosons are the carriers of the weak force.
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- The Higgs boson does not intermediate any of the four fundamental forces. This heavyweight of the standard model gives mass to all the other particles. The universe is thought to be filled with a quantum field called the Higgs field. As the particles travel in this Higgs field, they interact with it. The more the particle interacts with this Omni-present field, the heavier it becomes.
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- The particles that do not interact with the Higgs field, such as photons, are massless.
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- The quantum excitation of the “Higgs field” is known as the “Higgs boson“. Theorized in the 1960s, it took more than 50 years and about $14 billion to search for this exotic particle.
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- On July 4, 2012, scientists working at CERN’s Large Hadron Collider announced they had discovered the Higgs boson, the last missing piece of the Standard Model of physics.
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- The recently observed rare decay of the Higgs boson into a photon and a pair of leptons is known as the “Dalitz decay“. In this type of decay, after its short life, the Higgs boson quickly turns into one photon and what scientists call a “virtual photon.”
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- That “virtual photon,” also known as an “off-shell photon” then immediately turns into something like, two leptons. This “virtual photon,” has a very small non-zero mass, while regular photons are completely massless.
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- By studying rare particle decays researchers can explore the possibility of new physics that stretches beyond the Standard Model. The Standard Model explains a lot of things about our physical universe, but it doesn’t include gravity or dark matter.
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- Dark matter, which emits no light and cannot be directly observed, is thought to make up about 80% of all matter in the known universe, but scientists do not yet know exactly what it is. Get busy students you have a lot more to learn.
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March 1, 2021 PARTICLE PHYSICS - fundamental particles? 3069
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