# B Quark Energies

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1. Aug 8, 2017

### mpolo

I am using a program that requires the energy of the up quark and down quark be given in Joules. I tried to find these values on the internet but could not find these values. Can someone please tell me what is the energy of the Up and Down Quark in Joules?

2. Aug 8, 2017

### Staff: Mentor

That's like asking for the speed of a car. What is the speed of a car?

It depends on where these quarks are, and (unlike for cars) often the energy is not even a well-defined number. Do you mean the mass (or the mass-energy equivalent) of the quarks? The Particle Data Group has numbers.

3. Aug 8, 2017

### Dr.AbeNikIanEdL

What do you mean by "Energy of the up/down quark"? If you want to convert energies from electronvolt to joules, https://en.wikipedia.org/wiki/Electronvolt should be an obvious starting point.

4. Aug 8, 2017

### mpolo

okay here's what I have. Check my math. I simply averaged the min max values for mass in Electron volts for the Up Quark and the Down quark then I converted to Joules.

Up Quark = 2.01 Mev = Average value from standard Model
Up Quark = 3.36457079e-13 Joules Converted to Joules
.000000000000336457079 Joules = Input into Program

Down Quark = 4.79 Mev = Average value from standard Model
Down Quark = 7.67442575e-13 Joules Converted to Joules
.000000000000767442575 Joules = Input into Program

5. Aug 8, 2017

### Staff: Mentor

These are estimates for the quark masses. There is no theoretical prediction for them and experimental measurements are very challenging as the quarks cannot occur as isolated particles.

The conversion from MeV to J is right. You can easily round the numbers to 2 significant digits, even the second digit is not very meaningful.

6. Aug 14, 2017

### mpolo

Thanks for the confirmation of my calculations. I did not know that there was no theoretical prediction for them. That is interesting. So the estimation that we have are vague. How do we determine the masses of particles that we can isolate? I would be very interested to know that.

7. Aug 14, 2017

### Staff: Mentor

It depends on the particle. If it lives long enough and has an electric charge, put it in a Penning trap. If it decays, measure the energies of the decay products. The only neutral long-living/stable objects known are atoms, and you can ionize them to put them to give them a charge.

If we can produce it in electron/positron collision, measure the energy where it gets produced.

Neutrino masses are much more complicated.

8. Aug 14, 2017

### mpolo

This all seems so indirect. Thanks for the additional info. I will give this information some more thought.

9. Aug 14, 2017

### Drakkith

Staff Emeritus
Indeed. Quarks can't occur as isolated particles, so we can't just put them on a scale or something. We have to resort to complicated, indirect methods to measure their masses.