# What does A * Gev/c mean?

1. Nov 7, 2012

### Waxbear

I have an exam in introductory nuclear physics coming up in 2 days. I am supposed to present an article which i have already drawn. The article is about heavy ion collisions in the SPS accelerator at CERN. They keep mentioning that the experiment uses Pb + Pb collisions at 158 A*Gev/c beam momentum. Does this mean that i have to divide by the nuclear mass number A, to get the momentum of individual nucleons?

2. Nov 7, 2012

### Bill_K

It means 158 GeV/c per nucleon.

3. Nov 7, 2012

### Waxbear

Okay. But according to Cern, the SPS is capable of beam energies of 400 Gev. I guess this is also pr nucleon then?

4. Nov 7, 2012

### Bill_K

In a given magnetic field, the radius of curvature of the orbit of a singly charged particle is the same whether it's by itself or in a nucleus. So from what you say, the SPS can accelerate a single proton to 400 GeV, or a nucleus containing Z protons to 400 GeV per Z. For Pb-209, the ratio Z/A = 82/209 = 0.39, so 400 GeV per Z works out to 158 GeV per A.

5. Nov 7, 2012

### Waxbear

Ah, well that certainly explains it. Beautiful how the max energy of the sps works out to be exactly the energy mentioned in the article. Thank you for your help Bill!

6. Nov 7, 2012

### Staff: Mentor

I think your number of 400 GeV is outdated. As preaccelerator for the LHC, the SPS provides proton beams with 450 GeV.

The LHC has a similar ratio for proton proton and lead lead mode: 3.5 TeV protons and 1.38A TeV lead (corresponds to 3.517 TeV per charge) in 2011.

7. Nov 7, 2012

### Waxbear

I think you're right. But i think the SPS was upgraded from 400 Gev to 450 Gev when it was to be used as a pre-accelerator for the LHC. The experiment from my article was done way back in 2000, when the SPS was probably still operating at 400 Gev.