# Relative momentum

1. Feb 10, 2014

### Hluf

When we study the bound state of quarks, i.e. mesons, the relative momentum is given as; q=1/2(p1-p2). Where p1 and 2, are momentum of quark and anti-quark, respectively.My question is, what is the value of q at center of mass frame? For example, P=(0,iM), at center of mass frame, where P is the momentum of meson.

2. Feb 10, 2014

### dauto

There isn't one single value. There is a distribution function of values.

3. Feb 11, 2014

### Hluf

Why not have a single value? For instance; q=1/2(p1-p2), if we consider at center of mass collision for equal mass particle, i.e. p1=(p,im1) and p2=-p[/B,im2] then q becomes
q=1/2((p1+p2),i(m1-m2))
but for equal mass, p1=p2)=p
where p is a vector
q=1/2(2p,0)⇔q=(p,0)→why not this, the value of q at center of mass frame?

4. Feb 11, 2014

### dauto

You're assuming that there is nothing else inside the meson besides its valence quarks. In fact the quarks are immersed in a soup of virtual quarks and gluons. The energy and momenta of these virtual particles must be included in the description of the meson.

5. Feb 26, 2014

### Hluf

Mass of pion meson

We know pion is the composite of up and down quarks. The mass of charged pion is 139.6 Mev/c and mass of u=1.7 to 3.0 Mev/c2 and mass of
d=4.1 to 5.7Mev/c2. From these we see that the mass of single quark greater than the mass of the pion. This is my question, why? Any one voluntary answer my question, Thanks!!!

6. Feb 26, 2014

### Hluf

Mass of pion meson

We know pion is the composite of up and down quarks. The mass of charged pion is 139.6 Mev/Mev/c2 and mass of u=1.7 to 3.0 Mev/c2 and mass of
d=4.1 to 5.7Mev/c2. From these we see that the mass of single quark greater than the mass of the pion. This is my question, why? Any one voluntary answer my question, Thanks!!!

7. Feb 27, 2014

### Staff: Mentor

Most of the mass of the light hadrons (and the pion is a light hadron) comes from binding energy - or, as an alternative picture, the kinetic energy of the real and virtual particles inside.
Those quarks don't have a fixed momentum, they have a very broad distribution, given by the parton distribution functions.

8. Feb 27, 2014

### Bill_K

I think you dropped a decimal point. 5 MeV plus 5 MeV is not greater than 139 MeV.