- 3729 - QUARKS - the bottom of atomic discoveries. Quarks are the building blocks of visible matter in the universe. If we could zoom in on an atom in your body, we would see that it consists of electrons swarming in orbits around a nucleus of protons and neutrons.
--------------------- 3729 - QUARKS - the bottom of atomic discoveries.
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- ( See Review 3728 - discovering the atom )
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- If we could zoom in on one of those protons or neutrons, we'd find that they themselves are made up of a trio of particles that are so small that they have almost no size at all, and are little more than points. These point-like particles are the “quarks“.
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- Quarks are elementary particles. Like the electron, they are not made up of any other particles.
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- The existence of quarks was first theorized in 1964 in the work of two physicists, Murray Gell-Mann and George Zweig, who were both at the California Institute of Technology (CalTech) but who came to the conclusion that quarks exist independently of one another. Contrary to how science is often portrayed in the media, Gell-Mann and Zweig's conclusions were not an "a-ha!" moment but were instead built on the back of many years of hard work and careful discoveries by the particle physics community.
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- By the 1950s, physicists were building up a library of known particles. This theory ultimately became known as the Standard Model, but in order to get there several vital discoveries had to be made, including that of quarks.
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- Most puzzling was the existence of particles called “hyperons“, which were unstable and decayed very quickly, but not into the particles they were expected to decay into. Gell-Mann realized that there must be an unknown quantum property at work, which he named "strangeness" because of the unexpectedness of it all.
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- “Quantum numbers“, like “strangeness“, charge and spin, have to be conserved. If a particle with a specific quantum number decays, then its by-products must add up to those quantum numbers that the decayed particle had.
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- The quantum numbers of a given particle have "degrees of freedom", basically the range of values that these numbers can have. These degrees of freedom are called “multiplets“, and the pattern in which these multiplets could be arranged between different particles led Gell-Mann and Zweig to believe that the particles and their multiplets could be explained if each particle was formed from two or three smaller particles.
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- Zweig called these tiny, elementary particles "aces", but the name didn't catch on. Gell-Mann, who was ever one for cooky and memorable names, called them quarks.
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- These quarks were referred to as "up", "down" and "strange" quarks. The up and down doesn't really refer to anything, while the strange quark had a quantum number of strangeness of –1, hence why it is called "strange", whereas the up and down quarks have a strangeness of 0.
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- In 1968 at the Stanford Linear Accelerator Center (SLAC) in California. Experimenters fired electrons, and then later muons, at protons, and found evidence that the electrons and muons were scattering off three smaller particles contained within the protons, each of these smaller particles having their own electric charge. These particles are the “quarks“.
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- There are six types, or flavors, of quarks in total. Besides the up, down and strange quarks, there are also "charm", "top" and "bottom" quarks. Each one has its own set of quantum numbers, and their masses are very different, with the up and down quarks being the least massive, and the top quark being the heaviest with a mass over 61,000 times more massive than the up quark.
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- Quarks are always bound together by the strong nuclear force, which allows them to form composite particles called “hadrons“. Particles made of two quarks are called “mesons“, and particles made of three quarks are called “baryons“, which include protons (two up and one down quark) and neutrons (one up and two down quarks).
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- There are particles called “tetra quarks” that are made of four quarks, and “pentaquarks” that have five quarks, and some of them are almost stable, but do eventually decay.
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- To fit into quantum physics theory, the behavior of quarks is governed by a model called “quantum chromo dynamics“, or QCD for short. The "chromo" in the name refers to "color". not as in red, green or blue, but the name given to a particular quantum number that quarks possess.
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- Think of color as playing the same role in the strong force as electric charge plays in the electromagnetic force. So, like colors repel and unlike colors (i.e. a color and its anti-color) attract, forming stable pairs of quarks, and like other quantum numbers, it must also be conserved.
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- The strong force that binds quarks inside hadrons is carried by another kind of tiny elementary particle called “gluons“, which are exchanged between the quarks. To separate individual quarks requires an enormous amount of energy .
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- This amount of raw energy only existed in nature about 10 billionths of a second to about a millionth of a second after the Big Bang, when the temperature was approximately 3.6 trillion degrees Fahrenheit.
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- During this brief, early period, the baby universe was filled with a form of matter known as a quark–gluon plasma, a particle soup of free-floating quarks and gluons. As the temperature and pressure quickly dropped as the baby universe expanded, the quarks became bound together, forming hadrons that ultimately formed the basis of all visible matter that we see today in the cosmos, from stars and galaxies to planets and people.
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- Although the quark–gluon plasma only existed 13.8 billion years ago in the immediate aftermath of the Big Bang, scientists have successfully recreated it in particle accelerator experiments by smashing two heavy nuclei, such as that of lead, into each other close to the speed of light. The first time that this was achieved was at CERN's Super Proton Synchrotron in the year 2000.
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- The one other location in nature where conditions could be so extreme that quarks become unbounded is in a hypothetical object called a "quark star". If they exist, then quark stars are a kind of extreme neutron star, which are the most compact objects known in the universe that haven't collapsed under gravity to form a black hole.
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- A “neutron star” is born in a supernova, which is a violent explosion signaling the destruction of a massive star. While the outer layers of the star are blown away, the star's core collapses under gravity and the pressure there becomes so great that protons with their positive electric charge merge with negatively charged electrons, their charges canceling out to form neutral neutrons.
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- Neutron stars are about 6 miles in diameter, and a spoonful of neutron star material can have as much mass as a mountain. However, it may be possible for the cores of dying stars to become even more compact. In this scenario, neutrons would break apart, releasing their quarks to freedom. This would be a “quark star“.
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- However, for now, quark stars remain purely hypothetical; astronomers have not conclusively discovered one yet, although there are a handful of candidates that appear to have slightly different properties to ordinary neutron stars, such as a smaller diameter and a greater mass.
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- One candidate is an object that actually wasn't formed in a supernova but from the merger of two neutron stars that produced a gravitational-wave event known as GW 190425, which was picked up by the LISA and Virgo gravitational-wave detectors here on Earth in 2019.
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- The mass of the merged object is between 3.11 and 3.54 solar masses. This is too massive to be a neutron star which in theory can't get more massive than about 2.4 solar masses, but, isn't massive enough to be a blackhole, which needs to be about five solar masses at minimum. Could it be a quark star instead?
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- One other possibility is that some neutron stars could be hybrid objects, with ordinary neutron star material in their outer layers and quark matter deep in their cores. I left this for my grandchildren to figure out.
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- November 1, 2022 QUARKS - the bottom of atomic discoveries? 3729
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