Hadrons

By -

 Table of contents 

HADRONS


View my previous article here -

View the next article here -

-----------------------------------------

(In this article, and in furthermore, u means up quark and d means down quark. Similarly, u with a bar on top means anti-up quark and d with a bar on top means anti-down quark.)

As well as the leptons and quarks, there is another quite different group in the mix - hadrons!

A hadron is a particle that is composed of two or more quarks, a composite particle of which protons and neutrons are examples. The quarks are held together by the ‘strong force’, much in the same way that the electromagnetic force holds molecules together. This helps explain the name- the word hadron comes from the Greek hadros, meaning ‘strong’ or ‘robust’.

Although the only hadrons existing in the everyday world are protons and neutrons, many more types of hadron can be created in high-energy particle collisions. Such reactions are common in the upper atmosphere where high-energy protons from outer space (known as cosmic rays) collide with nuclei of nitrogen and oxygen, smashing them apart and creating new hadrons. Since the 1960s, such reactions have been closely studied in laboratories such as CERN (the European Organization for Nuclear Research), where high-energy beams of particles are smashed together.

Although many dozens of different types of hadron may be created in this way, all of the new ones are unstable and rapidly decay into other, long-lived particles, such as leptons, protons and neutrons. Fortunately, it’s not necessary to dwell on the names and properties of all the types of hadron, because there is a straightforward description for building them from particles that are believed to be fundamental, namely from quarks and antiquarks.

Quarks and antiquarks only occur bound together inside hadrons; they have never been observed in isolation. While it may seem like the process of ‘building’ a hadron would be something very complicated, there are in fact 3 simple ‘recipes’ to remember.

A hadron can consist of either:
  • Three quarks (in which case it is called a baryon).
  • Three antiquarks (in which case it is called an antibaryon).
  • One quark and one antiquark (in which case it is called a meson).








Any combination of quarks and antiquarks that obeys one of the three recipes above is a valid hadron. The net electric charge of a hadron is simply the sum of the electric charges of the quarks or antiquarks of which it is composed. The net charge of a hadron is therefore always a whole number, even though the quarks themselves have a non-whole number electric charge.

As a specific example of the hadron-building recipe, the proton is a baryon, so it is composed of three quarks, and as mentioned above, it is composed of up and down quarks only.

The proton has a charge of +e. The only way that three up or down quarks can be combined to make this net charge is by combining two up quarks with a down quark. So the quark content of a proton is (uud), giving a net charge of +(2/3) e + (2/3) e - (1/3) e = + e.

The tally of six leptons and six quarks, each with their own antiparticles, may seem like a huge number of fundamental particles, but virtually everything in the Universe is made up of merely the first generation of each type of particle namely:
  • electrons
  • up quarks, and
  • down quarks,
with electron neutrinos being created in radioactive decays.

As for the other generations:
  • the second generation of leptons (muon and muon neutrino)
  • the second generation of quarks (charm and strange)
  • the third generation of leptons (tauon and tauon neutrino), and
  • the third generation of quarks (top and bottom)

all have exactly the same properties as their first-generation counterparts except that they are more massive.

Quite why nature decided to repeat this invention three times over is not currently understood!

-----------------------------------------

View the next article here -

View my previous article here -

View a more structured order of the articles here -

-----------------------------------------

Feel free to ask/share anything additional in the comments section!

I am still learning Particle physics, but will try my best to answer your questions :)

Kindly let me know about any errors here.

You can also share anything additional for this article here.

View my previous article here -

View the next article here -

View a more structured order of the articles here -

See more articles here -

Solve brain teasers! View my other blog here-

With Warm Wishes,
Lavanya

Comments

Post a Comment

Popular posts from this blog

What are Quarks, Leptons and Bosons?

By -
    Table of contents  WHAT ARE  QUARKS, LEPTONS  AND  BOSONS? View my previous article here - How were Neutrinos Discovered? View the next article here - The Fundamental Forces ----------------------------------------- Here is a brief overview of what are quarks, leptons and bosons - families of particles that make up the Standard Model! (Based on what has been discussed so far).  * ADDITIONAL * -  A fermion is any particle that has an odd half-integer (like 1/2, 3/2, and so forth) spin.  Quarks  and  leptons , as well as most composite particles, like  protons  and  neutrons , are fermions. QUARKS: Quarks are subatomic particles that are found in protons and neutrons in the atomic nucleus. There are 6 quarks .  Up quark and Down quark belong to the first generation. Charm quark and Strange quark belong to the second generation. Top quark and Bottom quark belong to the third generation. The second and thi...
Read more

Particle Physics - Introduction

By -
Table of contents   PARTICLE PHYSICS - INTRODUCTION View the next article here - More on Particle Physics and Why it matters? ----------------------------------------- What is Particle physics? Let me give a hint by telling you what particles are? Everything in our universe is made up of extremely small components known as particles. Now did you get it? Particle Physics is nothing but the study of how our universe was made and what our universe is constituted of. To prove their existence and see how they behave, scientists observe them until the particles leave a sign. Often, instead of waiting for the particles to leave a sign, they make particles by colliding known particles. How? Well, the accelerators speed up the known particles almost to the speed of light. The particles collide and release massive energy, which results in the creation of new particles. This is why Particle physics is also known as High Energy Physics . At present, there are 17 particles that have been ident...
Read more

Gluons

By -
Image
    Table of contents  GLUONS View my previous article here - Introduction to Quantum Electrodynamics and Quantum Chromodynamics View the next article here - Introduction to Feynman Diagrams ----------------------------------------- Just like how electrons carry the electric charge, the quarks also carry the electric charge, but this electric charge is weaker in quarks. Quarks additionally carry a coloured charge , as discussed in the previous article . This coloured charge generates a gluon force field. An accelerating quark creates a vibrating ripple in the gluon field, which is known as gluons. Just like how a photon can create an electron and positron (anti-electron) pair - energetic gluon can create a quark and antiquark pair - While the electromagnetic charge has only one version, the colour charge has 3. But the colour charge never shows up in the hadron quark combinations. (Keep reading to find out about hadrons.) This led to the idea that the three colour charges...
Read more