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A century of the proton



In 1907, a New Zealander named Ernest Rutherford moved from McGill University in Canada to the University of Manchester. There he conducted a series of experiments in which he fired alpha particles at different materials. When he discovered that the beams deviated by about 2 ° when irradiating air, he assumed that the atomic components of the air must have electric fields of up to 100 million volts per cm to explain the effect. Over the next decade, Rutherford, along with Hans Geiger and Ernest Marsden, would carry out further experiments that ultimately led to a very important result in the history of physics: that the atom was not indivisible.

In the last year of the 1

9th century and in the first year of the 20th century, Rutherford and Paul Villard had independently classified radiation into three types: alpha, beta, and gamma. Their deeper components (as we know them today) were known much later, and Rutherford played an important role in determining what they were. By 1911, he had discovered that the atom had a nucleus that occupied 0.1% of the total volume but contained all the positive charge known today as the atom's famous Rutherford model. In 1914, he returned to Australia on a lecture tour and returned to the United Kingdom in 1915 after the start of the First World War. War activities would delay his studies for another two years, and he could devote his attention to the atom only in 1917.

This year he discovered that when bombarding various materials with alpha particles, certain long-range repulsive particles called "H particles" (a term coined by Marsden in 1913) were generated, even though nitrogen gas was present. This finding led him to conclude that an alpha particle might have penetrated the nucleus of a nitrogen atom and knocked out a hydrogen nucleus, which in turn supports the view that the nuclei of larger atoms also contain hydrogen nuclei. The hydrogen nucleus is nothing but the proton. Rutherford could publish his work on this result until 1919 after the war. He coined the term "proton" in 1920.

Interestingly, Rutherford had participated in a debate in 1901 in which he argued for the possibility that the atom consisted of smaller things, a controversial topic at the time. (His "adversary" was Frederick Soddy, the chemist who noted the existence of isotopes and Rutherford used a short but productive collaboration.) It is highly unlikely that he could have expected humans to be three or more Decades later, it would appear that the proton itself consisted of smaller particles.

In the early 1960s, studies of cosmic rays and their interactions with matter showed that the universe consisted of much more than just the basic subatomic parts. In fact, there were such a large number of particles that the idea that there might be a hitherto unknown organizational principle consisting of smaller particles was tempting, if only to a few. Murray Gell-Mann and George Zweig independently proposed such a system in 1964, claiming that many of the particles could actually consist of smaller units called quarks. Until 1965, with the help of Sheldon Glashow and James Bjorken, the quark model was able to explain the existence of a large number of particles as well as some other physical phenomena and reinforce their case.

Scientists at the Stanford Linear Accelerator Center (now SLAC National Accelerator Laboratory) began in the late 1960s with what Rutherford had done half a century earlier: smash a smaller particle into a larger particle whose energy was sufficient to break it down to reveal secrets. In particular, the physicists used the linear accelerator at the SLAC to excite electrons to 21 times the energy of a proton at rest and break it into protons. The results were particularly surprising.

A popular method of studying particles was then, as now, to radiate a smaller particle to a larger one and examine the collision for information about the larger particle. In this setup physicists expect that the higher the resolution at which the larger particle is probed, the greater the energy of the probing particle. However, this relationship fails with protons due to a characteristic called scaling: electrons with ever higher energies no longer give more information about the proton. This is because at energies beyond a certain threshold, the proton begins to resemble an accumulation of punctate entities, and the interaction of the electron with the proton on its interactions with these entities, independently of their own, is reduced to energy.

The SLAC experiments revealed that the proton actually consisted of smaller units called quarks, of two types – or flavors – called up and down were. Gell-Mann and Zweig had suggested the existence of Up [194559009] Down and strange Quarks and Glass Show and Bjorken's Charms . In the 1970s other physicists suggested the existence of lower and upper quarks discovered in 1977 and 1995, respectively. So the quark model was complete. Even more important to our story was that it literally completely messed up the proton.

In the 1970s, scientists used neutrinos as probing particles to obtain information about the distribution of quarks within protons, which were supported by more accurate data from other tests with electrons in the US and Germany, as well as with muons at CERN. They found that a proton actually contained three free quarks in a true lake of quark-antiquark pairs, and that the sum of all their impulses did not give the total momentum of a proton. This indicated the presence of another then unknown particle, which they called gluon (which is its own confusion).

In this decade, particle physicists began to construct the theoretical framework called quantum chromodynamics (QCD) to explain the life and functioning of the six flavors of quarks and antiquarks and eight gluons – all particles dominated by the strong nuclear force. Ninety years after Rutherford announced the discovery of the proton by launching alpha particles through mica slices and air columns, scientists announced the launch of the world's largest physical experiment – the Large Hadron Collider – to study the fundamental components of reality by using protons were smashed into other protons. They have proven that the Higgs boson is real, studied complicated processes with insights into the very early Universe, and sought answers to questions that still astonish physicists.

Scientists Have Striven to Improve our understanding of QCD by specifically examining how quarks, antiquarks, and gluons interact during a collision. This knowledge is crucial to determining the existence of new particles and deepening our understanding of the subatomic world. Physicists have also used collider experiments to study the properties of exotic matter forms such as glassma, quark-gluon plasma, and color glass condensates. narrow down the search for proposed particles to explain some fundamental variations in the Standard Model of particle physics; Perform precision measurements of the properties of the proton with respect to its effects on other particles (like this or that); and explore unresolved issues related to the proton (such as the spin crisis).

And 100 years after the initial construction of the proton, particle physics itself looks quite different from Rutherford's times, and much of the transformation can be traced back to the proton in one way or another. Today, physicists are pursuing other, very different particles, dreaming of building even larger machines for shattering protons, and dealing with theories that describe a world much smaller than that of quarks and gluons. It's another world with different secrets as it should be, but it's also great that there are secrets at all.


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