What is bigger a quark or an atom?

During the Science Picnic, our visitors could pass their questions to scientists. Now we ask researchers some of these questions.

With the question "What is smaller than a quark?" we turned to elementary particle physicist Prof. Grzegorz Wrochna from the National Centre for Nuclear Research in Świerk.

"A piece of a quark could be smaller than a quark" - jokes Prof. Grzegorz Wrochna. But he adds: "We do not have a theory that would predict that there are any constituents of quarks. There was no need to create such a theory, because so far no physical phenomena have suggested the existence of such constituents" - says the physicist.

According to Prof. Wrochna, a quark can not exist individually. "They must immediately connect with other quarks or with an antiquark" - he points out.

He says that quarks are pieces of a proton or neutron. In turn, neutrons and protons are components of atomic nuclei. The nuclei are components of atoms, which are components of chemical molecules... "We already know this hierarchy upward. Starting downward from a quark is harder" - he admits.

"So far we have not been able to produce enough energy to look inside a quark or break it down" - says the scientist.

Even the world`s largest particle accelerator, the Large Hadron Collider (LHC) near Geneva is not capable of breaking a quark. In the LHC, particles accelerated in a tunnel with a circumference of 27 km to speeds close to the speed of light collide with each other, and during these collisions, huge energy is released (13.5 TeV). But so far, splitting a quark has not been observed at this energy. "There are plans to build even larger accelerators, with a circumference of 100 km, but whether the energy they will produce will be enough to break quarks - that is not known" - adds Wrochna.

He says that it is difficult to tell how strongly the quark components could be bound. "Because we do not know this, we can only produce higher energies and hope that we will see something" - he says.

But maybe you do not have to break a quark, and instead look for smaller particles among the particles we already know? Maybe, for example, electrons or neutrinos are smaller than quarks? Professor Wrochna says that it is not that simple. "Quantum mechanics does not allow to accurately determine that a given particle is in a given a place and has a given momentum. There is some uncertainty, which does not result from the inaccuracy of our devices, but from the theory itself" - he says.

And that - the physicist continues - is why it does make much sense to talk about the sizes of elementary particles. "Until we see that an object has components, we talk about it as a point object, and the point has no dimensions. So for now that is how we have to talk about an electron or quark" - he explains.

Thanks to the fact that quarks have been discovered, we can determine the size of the proton. The diameter of the proton is about as much as a millimetre divided by a thousand billion (10^-15m).

Physicists can not yet compare what`s larger: a quark, Higgs boson or an electron. But they can compare their masses. For example, electron neutrino has a mass below 22 keV/c2, electron - 0.51 MeV/c2, a top quark - 2.3 MeV/c2, and Higgs boson about 126 GeV/c2. "So we can say that an electron is lighter than a quark, but we can not say that it is smaller than quark" - concludes Prof. Wrochna.

PAP - Science in Poland, Ludwika Tomala

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atom: The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

carbon: The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

electric charge: The physical property responsible for electric force; it can be negative or positive.

electron: A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids. element: A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

hadron: One of a group of particles that are made up of other, smaller particles — quarks — held together by a particular kind of force. The protons and neutrons found in the nucleus of atoms are hadrons.

hydrogen: The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues. It’s made of a single proton (which serves as its nucleus) orbited by a single electron.

matter: Something that occupies space and has mass. Anything on Earth with matter will have a property described as "weight."

mean: One of several measures of the “average size” of a data set. Most commonly used is the arithmetic mean, obtained by adding the data and dividing by the number of data points.

neutron: A subatomic particle carrying no electric charge that is one of the basic pieces of matter. Neutrons belong to the family of particles known as hadrons.

particle: A minute amount of something. physicist: A scientist who studies the nature and properties of matter and energy. proton: A subatomic particle that is one of the basic building blocks of the atoms that make up matter. Protons belong to the family of particles known as hadrons.

quarks: A family of subatomic particles that each carries a fractional electric charge. Quarks are building blocks of particles called hadrons. Quarks come in types, or “flavors,” known as: up, down, strange, charm, top and bottom.

subatomic: Anything smaller than an atom, which is the smallest bit of matter that has all the properties of whatever chemical element it is (like hydrogen, iron or calcium).

The universe is a big place, but it's made out of small pieces. The periodic table includes elements such as oxygen, carbon and other building blocks that make up stars, cats or cups of coffee. But since the turn of the 20th century, scientists have been thinking about and finding smaller and smaller fundamental particles — those tinier than atoms that fill up the universe. So which of these fundamental particles is the smallest? And, conversely, which is the largest?

Don Lincoln, a senior scientist at Fermi National Accelerator Laboratory (Fermilab), near Chicago, is one of the scientists trying to answer this question. At Fermilab, scientists use a particle accelerator to smash individual particles together and look at the debris — or possible new fundamental particles — that come out. Lincoln said there are two ways to measure the size of particles: investigating their mass and measuring their physical size, like calculating the diameter of a ball.

Related: How do you weigh an atom?

In terms of mass, these questions are relatively simple to answer. The lowest nonzero-mass particle we know of is the neutrino, Lincoln said. He pointed out, however, that we don't have the exact measurement of a neutrino's mass because the instruments used to calculate mass of fundamental particles aren't sensitive enough.

"A neutrino is a particle, sort of the ghost of the subatomic world," Lincoln said. Neutrinos interact very weakly with matter and are the second most abundant particle after photons (which behave more like waves than actual particles). In fact, there are trillions of neutrinos passing through you at this very second. Neutrinos weigh nearly nothing and travel close to the speed of light.

An atomic nucleus is made up of neutrons, protons and electrons. Protons and neutrons themselves are about one-tenth the size of the nucleus as a whole, Lincoln said. An electron has near-zero mass, but it actually weighs 500,000 times more than a neutrino (again, whose exact measurement is impossible to make at this point).

Physicists use electron volts (eV) to measure the mass of subatomic particles, Lincoln said. Technically, the unit is eV/c^2, in which c is the speed of light. One electron volt is equivalent to about 1.6x10^-19 joules. To simplify things, physicists use a set of units whereby the speed of light is 1. To figure out the mass of a subatomic particle, then, you'd use Albert Einstein's famous equation E=mc^2 to get the mass (m) in kilograms.

An electron weighs 511,000 electron volts, which is equivalent to 9.11 x 10^-31 kilograms, according to Lincoln. For comparison, a typical proton in the nucleus of a typical atom weighs 938 million electron volts, or 1.67 × 10^-27 kg, he said.

Conversely, the largest (in terms of mass) fundamental particle we know of is a particle called a top quark, measuring a whopping 172.5 billion electron volts, according to Lincoln. Quarks are another fundamental particle that, as far as we know, cannot be broken down into more parts. Scientists have found six types of quarks: up, down, strange, charm, bottom and top. Up and down quarks make up protons and neutrons, and they weigh 3 million and 5 million electron volts, respectively. In comparison, the top quark weighs 57,500 times more than the up quark.

The question of physical size is harder to answer. We know the physical size of some particles, but not the smallest ones. Some "tiny" particles that people hear about in daily life, such as virus particles, are actually quite large.

Lincoln offered this sense of scale: A typical virus particle is about 250 to 400 nanometers long (a nanometer is a billionth of a meter, or 10^-9 m), and the typical atomic nucleus measures about 10^-14 m (0.00000000000001 m). That means an atomic nucleus is as small to a virus as a virus is to us. 

Currently, the smallest physical size scientists can measure with a particle accelerator is 2,000 times smaller than a proton, or 5 x 10^-20 m. So far, scientists have been able to determine that quarks are smaller than that, but not by how much.

Originally published on Live Science.