W+/W- bosons ratio in proton-proton collision

  • #1
Hi guys,
I'm studying my first-year physics in college, and I'm having to write a report of some proton-proton collisions that were registered in the LHC of CERN years ago. The main goal is to identify different bosons (W and Z) that are decaying into other elemental particles. I've been asked to get the W+/W- ratio in these events and discuss the results.
I've done some research and I've found out that "it should be 1.4, according to the proton quarks model ", which is quite close to the results I've got after analyzing many collisions. I have tried so hard to understand what it means, but I can't.
Could someone explain to me the meaning of it and the explanation of the result?

Answers and Replies

  • #2
If you quote something it would be useful to give the source of that quote.

Anyway: Protons have three valence quarks: up, up, down. In addition they have sea quarks. Most W+ bosons are produced from up plus anti-down, most W- are produced from down plus anti-up. The antiquark has to be a sea quark, but the other one can be a valence quark (which tend to have more energy). There are more up than down, so you get more W+ than W-. To get the 1.4 you need some calculations, to see that the ratio is not one you do not.
  • #3
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I second the question.

If you just count valence quarks, you get 2:1. If you do a full calculation, you get 1.32:1. No idea where 1.4 comes from.
  • #4
The quote is from another college that is also conducting the same experiment, and it doesn't say anything else (it is written in Spanish, as I'm from there, so I didn't find it useful to add the source).
However, I've found and article about this in arXiv (a report of the ATLAS detector):
They get a result of approx. 1.45, as shown in page 21, so I don't know if it should be 1.32 or not. Could you please read it (if you want), and tell me what is wrong?
And thank you so much for the answers!!
  • #5
You didn't specify at which center of mass energy the data was taken (you just said "years ago at the LHC"). But the R=W+/W- ratio depends on the center of mass enery, so in order to get a precise answer you have to ask a more precise question.

This paper (https://arxiv.org/pdf/1004.3404.pdf) gives predictions for the ratio including NNLO QCD corrections, which are ##R=1.429 \pm 0.013## for ##\sqrt{s}=7\,\rm{TeV}##, and ##R=1.328 \pm 0.011## for ##\sqrt{s}=14\,\rm{TeV}##.
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  • #6
They don't have 8 TeV predictions, but they should be quite close to 1.4.