HubBucket NYC | Particle Physics Research

HubBucket Inc New York City ("HUB-NYC / HubBucket NYC") is a Scientific Research, Exploration, and Discovery branch of HubBucket Inc ("HubBucket"). HubBucket NYC primarly focuses on Particle Physics, and the research done at CERN and Fermilab.

We use the research done by organizations such as CERN and Fermilab to further our knowledge about Particle Physics, and related subjects and topics, in addition to using that information to aid us in our own research and development - R&D projects.

Please Note:

1. HubBucket Inc ("HubBucket") and the HubBucket NYC branch of HubBucket are NOT affiliated with CERN and Fermilab.

2. HubBucket Inc ("HubBucket") supports and promotes Diversity, Equity, and Inclusion ("DEI") in Science, Technology, Engineering, and Mathematics ("STEM") education, fields, organizations, agencies, businesses, internships, and professions / jobs.

What is Particle Physics?

Particle Physics is the study of the fundamental constituents of matter and the forces of nature.

Science doesn’t get much bigger or more exciting than this. Particle physics research involves the biggest, most complicated experiments in the history of science, with the fastest computers, the coldest temperatures and the strongest magnets on Earth.

Particle Physics re-creates the universe just after the Big Bang and hopes to answer the questions humans have been asking for eternity:

1. where do we come from?
2. what are we made of?

Atoms and Particles

Particle Physics is a journey into the heart of matter. Everything in the universe, from stars and planets, to you and the chair that you’re sitting on, is made from the same basic building blocks, particles of matter. Some particles were last seen only billionths of a second after the Big Bang. Others form most of the matter around us today.

Particle physics studies these very small building block particles and works out how they interact to make the universe look and behave the way it does.

How small is small?

Really small. Think about the width of a human hair, one of the smallest things we can see. Twenty of them placed side by side fit across one millimeter.

If we use a microscope to look inside a hair we see cells, which are formed from molecules. Each molecule is made up of a collection of atoms.

We know that everything is formed from various types of atoms and that atoms are really small. You can fit a hundred thousand of them across a human hair.

But particle physics doesn’t stop there. We can see right inside the atom. We see that atoms consist of a nucleus, ten thousand times smaller than the atom, surrounded by a cloud of electrons. The nucleus is a collection of particles called protons and neutrons. And inside protons and neutrons we find particles called quarks.

Quarks are so small that we haven’t yet been able to measure how big they are. We just know that they are at least ten thousand times smaller than the nucleus. They are so small that we treat them like mathematical pinpoints in our theories.

Zooming down in scale from a person to a fundamental particle like a quark or an electron is like shrinking the diameter of the whole earth to the size of a 5p coin. And then shrinking the 5p by the same amount again. This is what we mean by really small.

How do we do Particle Physics?

We recreate the conditions just after the Big Bang, when particles roamed freely through the Universe.

We do this with powerful particle accelerators, which accelerate particles close to the speed of light and smash them together. Particle Physicists then look at what happens in the high energy collisions.

Particle physics is a bit like trying to find out how a watch works by bashing together two very expensive Swiss watches and then learning to rebuild them from all the bits of glass, cogs and springs.

In place of Swiss watches we use particles so small that you could fit about ten thousand million of them across a watch face and, despite their tiny size, the collisions between these particles have as much energy as a large airplane taking off!

The Universe | Matter

Matter is everything that exists in the universe, all the stuff that was created in the Big Bang. Particle physicists believe that matter is built of twelve types of ‘fundamental particle’, the building blocks of the universe. These fundamental particles cannot be broken down any further.

There are two families of fundamental particles, the quarks and the leptons. There are six sorts of quarks and six sorts of leptons. Together they make up a theory called the Standard Model.

Most matter on earth is made from a combination of two quarks, called the up and the down quarks and a lepton called the electron.

The up and down quarks form protons and neutrons inside the nucleus of the atom, and the electrons orbit the nucleus to complete the whole atom.

The rest of the twelve fundamental particles are more commonly found in high energy environments, for example in Particle Accelerator collisions, or right at the start of the universe just after the Big Bang.

Forces

We believe that there are four fundamental forces in the universe:

1. Gravity
2. Electromagnetic Force
3. The Weak Force
4. The Strong Force

We think the effect of gravity on fundamental particles is really tiny. So we do not really consider it for the moment in particle physics.

The electromagnetic force affects any electrically charged fundamental particle (that’s half of the leptons and all the quarks). It’s the same force that makes lightning strike and different poles of bar magnets attract each other.

The weak force is responsible for radioactive decay. It actually makes neutrons turn into protons, amongst other things, and every type of matter particle experiences it.

The strong force (so-called because it is stronger than the weak force) is only felt by quarks. It behaves like elastic, because the further apart you pull two quarks, the stronger the strong force gets between them.

Each force has one or more force-carrying particles associated with it. We think forces are felt by matter particles when force-carrying particles interact with them.

So what is left to find out?

Our theory of particle physics, the Standard Model, is a mathematical description of the 12 fundamental particles and three forces. We haven’t yet found any experiment that disagrees with it, however hard we try.

However, there are a lot of things that aren’t explained yet in particle physics. For example:

1. Why are there exactly twelve fundamental matter particles?
2. Are these twelve particles fundamental, or are they in turn made up of other, smaller particles?
3. What is mass? How do particles get heavy?
4. Where does gravity fit in to the Standard Model?

So our understanding is clearly incomplete. In fact, we do not know what 96% of the universe is made of, and that’s why we do research.

Particle Accelerators

What is a Particle Accelerator and why do we use them?

Just after the Big Bang, the universe was a rapidly expanding ball of fundamental particles.

As the universe expanded, it cooled and the particles decayed, changing into other fundamental particles. These particles then joined together and gradually formed the matter that we see around us today.

In particle accelerators we smash beams of particles together in head-on collisions that are energetic enough to turn the clock back to just after the Big Bang. The more energetic the collisions, the more likely we are to make fundamental particles appear again.

Once we’ve produced fundamental particles, we can study their behavior to find out why the universe is made the way it is.

What does a Particle Accelerator look like?

The biggest Particle Accelerator in the world is at CERN, the center for Particle Physics research, just outside Geneva in Switzerland.

Above ground, you wouldn’t know anything about it, but if you were to go 100 meters underground, you’d find yourself in a circular tunnel, about the size of a London underground tube tunnel. This is where the Large Hadron Collider (LHC), the world’s most powerful particle accelerator, is being built.

The LHC tunnel runs for about the same distance as the London Underground Circle Line, 27 kilometers in a ring underneath the French-Swiss border. If you were inside the accelerator tunnel you would see a tube which runs continuously in either direction. This tube is the ‘beam pipe’, so-called because inside here, two beams of particles fly round the tunnel.

The beams are accelerated to very high energies by magnets surrounding the beam pipe. These make sure that the two particle beams circulate in opposite directions without crashing into each other. When the beams of particles reach their final top energy, the magnets alter their path and bring them into collision at predetermined points around the accelerator ring.

By this time, the particle beams are traveling so close to the speed of light that they collide forty million times a second. Inside each collision we have a snapshot of the fundamental particles that last existed billionths of a second after the Big Bang. Now all we have to do is build gigantic particle detectors at each collision point to try and work out exactly what went on.

Particle Detectors

If we’ve created particles in a collision in an accelerator, we want to be able to look at them. And that’s where particle detectors come in. We build these at the collision points in an accelerator and use them to identify as much of what was produced in the collision as we can.

The principle of a particle detector is simple. It will never ‘see’ a particle directly, but it shows where it has traveled, what signature tracks it leaves behind and the effect it has on the detector when it is stopped as it flies out of the collision.

Detectors consist of layers of different types of material, which are used to either show us the path of a particle as it travels along, or absorb it to make the particle stop.

We can identify different types of particles depending on where they stop in the detector and what their path of travel looks like. It’s a bit like a police investigation after a car crash. If we know what particles were produced in the collision, in which direction they flew and how much energy they had, we can reconstruct what exactly happened in the collision.

In Particle Physics, reconstructing the particle collision means you can find new types of particles and work out how they interact with each other.

What does a Particle Detector look like?

Big! Current experiments are as big as a house. ATLAS, an experiment that will run at the LHC, will be as big as a cathedral. Detectors have to be this big to stop highly energetic particles that were traveling near the speed of light.

From the outside, detectors look like huge boxes, with literally kilometers of cables attached. These cables carry electronic signals from inside the detector to computers outside to be processed. If you could see inside, you’d see onion-like layers of materials like silicon, plastic, steel, lead glass and lots of support structure to hold the whole thing together.

The data pouring out of these detectors will be analyzed to answer fundamental questions about the way the universe works.

Elementary particle physics is the study of fundamental particles and their interactions in nature. Those who study elementary particle physics —the particle physicists—differ from other physicists in the scale of the systems that they study. A particle physicist is not content to study the microscopic world of cells, molecules, atoms, or even atomic nuclei. They are interested in physical processes that occur at scales even smaller than atomic nuclei. At the same time, they engage the most profound mysteries in nature: How did the universe begin? What explains the pattern of masses in the universe? Why is there more matter than antimatter in the universe? Why are energy and momentum conserved? How will the universe evolve?

Four Fundamental Forces

An important step to answering these questions is to understand particles and their interactions. Particle interactions are expressed in terms of four fundamental forces. In order of decreasing strength, these forces are the strong nuclear force, the electromagnetic force, the weak nuclear force, and the gravitational force.

Strong nuclear force. The strong nuclear force is a very strong attractive force that acts only over very short distances (about 10−15m). The strong nuclear force is responsible for binding protons and neutrons together in atomic nuclei. Not all particles participate in the strong nuclear force; for instance, electrons and neutrinos are not affected by it. As the name suggests, this force is much stronger than the other forces. Electromagnetic force. The electromagnetic force can act over very large distances (it has an infinite range) but is only 1/100 the strength of the strong nuclear force. Particles that interact through this force are said to have “charge.” In the classical theory of static electricity (Coulomb’s law), the electric force varies as the product of the charges of the interacting particles, and as the inverse square of the distances between them. In contrast to the strong force, the electromagnetic force can be attractive or repulsive (opposite charges attract and like charges repel). The magnetic force depends in a more complicated way on the charges and their motions. The unification of the electric and magnetic force into a single electromagnetic force (an achievement of James Clerk Maxwell) stands as one of the greatest intellectual achievements of the nineteenth century. This force is central to scientific models of atomic structure and molecular bonding.

Weak nuclear force. The weak nuclear force acts over very short distances (10−15m) and, as its name suggest, is very weak. It is roughly 10−6 the strength of the strong nuclear force. This force is manifested most notably in decays of elementary particles and neutrino interactions. For example, the neutron can decay to a proton, electron, and electron neutrino through the weak force. The weak force is vitally important because it is essential for understanding stellar nucleosynthesis —the process that creates new atomic nuclei in the cores of stars.

Gravitational force. Like the electromagnetic force, the gravitational force can act over infinitely large distances; however, it is only 10−38 as strong as the strong nuclear force. In Newton’s classical theory of gravity, the force of gravity varies as the product of the masses of the interacting particles and as the inverse square of the distance between them. This force is an attractive force that acts between all particles with mass. In modern theories of gravity, this force behavior is considered a special case for low-energy macroscopic interactions. Compared with the other forces of nature, gravity is by far the weakest.

The fundamental forces may not be truly “fundamental” but may actually be different aspects of the same force. Just as the electric and magnetic forces were unified into an electromagnetic force, physicists in the 1970s unified the electromagnetic force with the weak nuclear force into an electroweak force. Any scientific theory that attempts to unify the electroweak force and strong nuclear force is called a grand unified theory, and any theory that attempts to unify all four forces is called a theory of everything. We will return to the concept of unification later in this chapter.

Classifications of Elementary Particles

A large number of subatomic particles exist in nature. These particles can be classified in two ways: the property of spin and participation in the four fundamental forces. Recall that the spin of a particle is analogous to the rotation of a macroscopic object about its own axis. These types of classification are described separately below.

Classification by Spin

Particles of matter can be divided into fermions and bosons. Fermions have half-integral spin (12ℏ,12ℏ,...) and bosons have integral spin (0ℏ,1ℏ,2ℏ,...).

Familiar examples of fermions are electrons, protons, and neutrons. A familiar example of a boson is a photon . Fermions and bosons behave very differently in groups. For example, when electrons are confined to a small region of space, Pauli’s exclusion principle states that no two electrons can occupy the same quantum-mechanical state. However, when photons are confined to a small region of space, there is no such limitation.

The behavior of fermions and bosons in groups can be understood in terms of the property of indistinguishability. Particles are said to be “indistinguishable” if they are identical to one another. For example, electrons are indistinguishable because every electron in the universe has exactly the same mass and spin as all other electrons—“when you’ve seen one electron, you’ve seen them all.” If you switch two indistinguishable particles in the same small region of space, the square of the wave function that describes this system and can be measured (|ψ|2) is unchanged. If this were not the case, we could tell whether or not the particles had been switched and the particle would not be truly

indistinguishable. Fermions and bosons differ by whether the sign of the wave function (ψ) - not directly observable—flips:

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ψ→−ψ(indistinguishablefermions),

ψ→+ψ(indistinguishablebosons).

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Fermions are said to be “antisymmetric on exchange” and bosons are “symmetric on exchange.” Pauli’s exclusion principle is a consequence of exchange symmetry of fermions—a connection developed in a more advanced course in modern physics. The electronic structure of atoms is predicated on Pauli’s exclusion principle and is therefore directly related to the indistinguishably of electrons.

Classification by force interactions

Fermions can be further divided into quarks and leptons. The primary difference between these two types of particles is that quarks interact via the strong force and leptons do not. Quarks and leptons (as well as bosons to be discussed later) are organized in Figure 11.2.1. The upper two rows (first three columns in purple) contain six quarks. These quarks are arranged into two particle families: up, charm, and top (u, c, t), and down, strange, and bottom (d, s, b). Members of the same particle family share the same properties but differ in mass (given in MeV/c2). For example, the mass of the top quark is much greater than the charm quark, and the mass of the charm quark is much greater than the up quark. All quarks interact with one another through the strong nuclear force.

Ordinary matter consists of two types of quarks: the up quark (elementary charge, q=+2/3) and the down quark (q=−1/3). Heavier quarks are unstable and quickly decay to lighter ones via the weak force. Quarks bind together in groups of twos and threes called hadron s via the strong force. Hadrons that consist of two quarks are called mesons, and those that consist of three quarks are called baryons. Examples of mesons include the pion and kaon, and examples of baryons include the familiar proton and neutron. A proton is two up quarks and a down quark (p=uud,q=+1) and a neutron is one up quark and two down quarks (n=udd,q=0). Properties of sample mesons and baryons are given in Table 11.2.1.

Quarks participate in all four fundamental forces: strong, weak, electromagnetic, and gravitational.

The lower two rows in the figure (in green) contain six leptons arranged into two particle families: electron, muon, and tau (e,μ,τ), and electron neutrino, muon neutrino, and tau neutrino (νe,νμ,νT).

The muon is over 200 times heavier than an electron, but is otherwise similar to the electron. The tau is about 3500 times heavier than the electron, but is otherwise similar to the muon and electron. Once created, the muon and tau quickly decay to lighter particles via the weak force. Leptons do not participate in the strong force. Quarks and leptons will be discussed later in this chapter. Leptons participate in the weak, electromagnetic, and gravitational forces, but do not participate in the strong force.

Bosons (shown in red) are the force carriers of the fermions. In this model, leptons and quarks interact with each other by sending and receiving bosons. For example, Coulombic interaction occurs when two positively charged particles send and receive (exchange) photons. The photons are said to “carry” the force between charged particles. Likewise, attraction between two quarks in an atomic nucleus occurs when two quarks send and receive gluons. Additional examples include W and Z bosons (which carry weak nuclear force) and gravitons (which carry gravitational force). The Higgs bosonis a special particle: When it interacts with other particles, it endows them not with force but with mass. In other words, the Higgs boson helps to explains why particles have mass. These assertions are part of a tentative but very productive scientific model (the Standard Model) discussed later.

Particles and Antiparticles

In the late 1920s, the special theory of relativity and quantum mechanics were combined into a relativistic quantum theory of the electron. A surprising result of this theory was the prediction of two energy states for each electron: One is associated with the electron, and the other is associated with another particle with the same mass of an electron but with a charge of e+. This particle is called the antielectron or positron. The positron was discovered experimentally in the 1930s.

Soon it was discovered that for every particle in nature, there is a corresponding antiparticle. An antiparticle has the same mass and lifetime as its associated particle, and the opposite sign of electric charge. These particles are produced in high-energy reactions. Examples of high-energy particles include the antimuon (μ+), anti-up quark (u), and anti-down quark (d). (Note that antiparticles for quarks are designated with an over-bar.) Many mesons and baryons contain antiparticles. For example, the antiproton ((\overline{p}\)) is u¯¯¯u¯¯¯d¯¯¯ and the positively charged pion (π+) is ud¯¯¯. Some neutral particles, such as the photon and the π0 meson, are their own antiparticles.

Particles and their Properties

The same forces that hold ordinary matter together also hold antimatter together. Under the right conditions, it is possible to create antiatoms such as antihydrogen, antioxygen, and even antiwater. In antiatoms, positrons orbit a negatively charged nucleus of antiprotons and antineutrons.

Figure 11.2.2 compares atoms and antiatoms.

Antimatter cannot exist for long in nature because particles and antiparticles annihilate each other to produce high-energy radiation. A common example is electron-positron annihilation. This process proceeds by the reaction e−+e+→2γ.

The electron and positron vanish completely and two photons are produced in their place. (It turns out that the production of a single photon would violate conservation of energy and momentum.) This reaction can also proceed in the reverse direction: Two photons can annihilate each other to produce an electron and positron pair. Or, a single photon can produce an electron-positron pair in the field of a nucleus, a process called pair production. Reactions of this kind are measured routinely in modern particle detectors. The existence of antiparticles in nature is not science fiction.