# How are pions created?

I have listened to a lecture explaining the strong force which is actually nuclear force and colour force.

And the pions are the force carrier of the nuclear force. And basically pions are created from two quarks (a quark and an anti-quark). But my question is, where do these two quarks come from?

• Quantum Field Theory proposes that every particle can be viewed as an excitation of a given field, such as a quark field, or an electron field, or Higgs Field etc. If you read this it might help en.m.wikipedia.org/wiki/Quantum_field_theory – user108787 Jul 13 '16 at 19:20

## 2 Answers

We don't know where quarks come from, anymore than we know where electrons come from. They are supplied by nature, as far as we know, as the basic elementary particles that the world around us is built upon. In the same way, we don't yet know why the speed of light is 300,000 m/s or what Dark Matter or Dark Energy are.

We have a theory, called the Standard Model, which is based on experimental evidence. In turn, the Standard Model is based around Quantum Field Theory, which provides theoretical predictions that we can test using instruments such as the LHC.

However, to make the Standard Model work, we have to simply accept the properties of around 20 parameters, such as the strength of interaction of photons with electrons. We have no real idea why these parameters have the values they do, we can only measure them and use them in our predictions. An animation of the nuclear force (or residual strong force) interaction between a proton and a neutron. The small colored double circles are gluons, which can be seen binding the proton and neutron together. These gluons also hold the quark-antiquark combination called the pion together, and thus help transmit a residual part of the strong force even between colorless hadrons.

Quarks use gluons, which are massless, to exchange the color force, which keeps 3 quarks together to form neutron and protons (baryons), and pions(mesons) use gluons to keep a quark and antiquark together. BUT, the force carried by gluons has a very short range, always staying inside baryons and mesons. The force between protons and neutrons, which keeps the nucleus together, is carried by mesons. If you read the above link (slowly :) ) it will give you the full picture.

• Anomalies provide a little theoretical justification for picking the Standard Model vs some other arbitrarily chosen QFT. But things like 3 generations is a "who ordered that" puzzle. – AHusain Jul 13 '16 at 22:49
• Some Examples: Scalar Field, Yang-Mills, Einstein-Hilbert. Things like Gauge Anomaly will tell you your theory was inconsistent. – AHusain Jul 13 '16 at 23:14
• @count_to_10 thank you very much for that answer...one more thing I want to make sure of.. is every thing I wrote right or I missed something? – Talal Sharaa Jul 13 '16 at 23:31
• @count_to_10 Thank you very much sir, so I read the link twice and here is what I figured out: the net colour-charge nearly cancels out, but there is still some colour-charge left carried by gluons and this is what forms the residual neuclear force that bounds protons and neutrons together..if that's right I guess we will get back to my original question where does the two quarks forming pions come from? And I guess you answered it saying we dont know, right? – Talal Sharaa Jul 14 '16 at 1:33
• Quantum Field Theory implies that a field underlies every particle and force carrier. It then proposes that the fields act to both create and destroy particles such as quarks, gluons, in fact the whole zoo of particles. Because it is impossible for us humans to imagine 4 Dimensional spacetime, it is a better use of our time to concentrate on mathematical models and their predictions, then test them in experiments. Nobody knows where quarks come from and, to be honest, some people don't care, (not including me) because we will never be able to visualise them in our "ordinary" world. – user108787 Jul 14 '16 at 2:24

The nuclear force can be thought as the 'residual' of the strong force, just like the Van der Waals force is the residual of the electrostatic force. The carrier of the strong force are gluons and this is naively analogous to thinking of photons as being the carrier of the electromagnetic force.

Quarks are fundamental particles, just like electrons. This basically means that they cannot be broken down into pieces. Asking where do quarks come from is like asking where does matter come from, because everything around you is fundamentally made out of quarks and leptons(the class of particles to which the electron belongs). In fact, matter and energy are equivalent. Quark-antiquark pairs therefore spontaneously form (from the 'vacuum' energy) and annihilates. There are a countless number of these processes happening around you every second.

Pions are particles which consists of a quark and an anti quark. They can be formed, whenever there are the corresponding quarks and enough energy available. For example, they can be formed by colliding protons head-on at the LHC at Cern.