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---------------------- 2289 - Atoms have Protons and Protons have Quarks?.
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- If we could see inside an atom we would see a nucleus of protons with orbiting electrons. The electrons are fundamental particles as far as we know, but, the protons inside the nucleus are made up of even more fundamental particles. These even smaller particles are called quarks.
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- Quarks are particles that are not only hard to see, they are almost impossible to measure. These tiny particles are the basis of a group of subatomic particles called hadrons.
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- With every discovery in this field of particle physics in the past 50 years more questions arise about how quarks influence the universe's growth and ultimate fate.
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- Strange facts about quarks starts with when they were first formed. The first quarks appeared about 10^-12 seconds after the universe was formed in the Big Bang. At that same time the weak force separated from the electromagnetic force and the antiparticles of quarks appeared.
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- The mystery of quarks first arose in the 1960s when researchers in California using the Stanford University Linear Accelerator found that the electron beam was scattering more widely than their calculations had determined it should.
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- More research found that there were at least three locations where electrons scattered within the nucleon, meaning something was causing that scattering. That scattering is the basis for our understanding of quarks today.
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- Physicists refer to the different types of quarks as flavors: up, down, strange, charm, bottom, and top. The biggest differentiation between the flavors is their mass, but some also differ by charge and by spin.
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- For instance, while all quarks have the same spin of 1/2, three of them (up, charm and top) have charge 2/3, and the other three (down, strange and bottom) have charge minus 1/3.
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- And, just because a quark starts out as a flavor doesn't mean it will stay that way; down quarks can easily transform into up quarks, and charm quarks can change into strange quarks.
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-Quarks can't be measured, because the energy required produces an antimatter equivalent ,an antiquary, before they can be observed separately. The mass of quarks is best determined by techniques such as using a supercomputer to simulate the interactions between quarks and gluons, with gluons being the other fundamental particles that glue quarks together.
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- In 2014, researchers published the first observation of a charm quark decaying into its antiparticle, providing more information about how matter behaves. Because particles and antiparticles should destroy each other, one would think the universe should just have photons and other elementary particles. Yet antiphotons and antiparticles still exist, leading to the mystery of why the universe is made mostly of matter and not an equal amount of antimatter.
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- By far, the most common quarks you'll encounter are the up and down ones. They're the ones that bundle together in triplets to form protons (two ups and a down) and neutrons (two downs and an up).
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- To form the familiar positive charge of the proton and the neutral charge on the neutron, the quarks need fractional charges. The up quark has a charge of plus two-thirds, while the down quark is sitting at minus one-third.
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- What's even more confusing about the quarks is that they're surprisingly light. The up quark is a mere 0.2 percent the mass of the proton, while its partner the down quark is only around 0.5 percent of the proton mass. So how can these particles add up to the mass of a proton?
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- The answer is the force that binds quarks together, the strong nuclear force. This binding among the quarks is so strong it handily defeats the natural electric repulsion of the similarly charged quarks. And since energy is the same thing as mass, (E=mc^2), the mass of the proton is really due to the glue, and not the quarks themselves.
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- The up and down quarks are the smallest and the mot stable. The next largest quarks, strange and charm, are rarely found in any great abundance in nature. They're so massive that they're hard to make in the first place, and they quickly decay.
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- Physicists thought there were only these four quarks — up, down, strange and charm. But in the early 1970s, they started to suspect otherwise by examining some rare decays involving kaons.
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- In order to explain the weird decay that produced these kaons, theorists had to guess at the existence of a new pair of quarks, which they dubbed the top and bottom. These new quarks were much, much heavier than the other four. Being heavier means it requires more energy to see them.
Once the bottom quark was discovered in 1977, the race was on to find the sixth and final top quark. But the problem was that nobody had any idea how big it was, meaning we didn't know how much energy we had to make our particle accelerators before we could see a top quark. Every year, groups around the world upgraded their accelerators, and every year they came up short, pushing the mass of the then-hypothetical particle ever upward.
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- It wasn't until February 1995 that researchers at Fermilab could finally stake a claim to a discovery of a top quark with a mass at almost 200 times heavier than a proton. That makes the top quark about 100 trillion times heavier than the up quark.
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- Why do the quarks have such an immense range in masses?
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- This is where the Higgs boson comes in. The Higgs boson is associated with a field, kind of like the electromagnetic field that permeates all of space-time. The Higgs Field is like an invisible glue filling the universe and giving everything their mass.
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- Other fundamental particles, like electrons and neutrinos and quarks, must swim through this field to go from place to place. The very fact that the fundamental particles can't ignore the Higgs field is the very reason they have mass. The Higgs gives all particles their mass.
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- If the Higgs is somehow connected to the very concept of mass, and the top quark is far and away the heaviest of the quarks, then the Higgs boson and the top quark must be somehow connected. The top quark became one gateway to our understanding of the Higgs.
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- The hope is that with further study of the Higgs itself we can get some perspectives on the mysteriously large mass of the top quark. Stay tuned, there is still more to learn.
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- Other Reviews bout Quarks:
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- 1766 - Protons contain quarks and gluon particles that have a powerful force holding the nucleus of the atom together.
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- 1502 - The Standard Model of Particle Physics. Could the quark be composed of even smaller particles?
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- 56 - The universe of fundamental particles. Richard Feymann insightful interpretation of high energy data later became known as quarks.
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- March 3, 2019
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