Suppose I have a particle $W'$ which can decay into $\mu$ and $\nu_{\mu}$ and $e$ and $\nu_{e}$.

Suppose we know such new gauge bosons come from some additional gauge group added to the Standard Model. If such particle is discovered, and these two decays had been confirmed, what could be the first conclusion about their gauge group one can draw from this? I am wondering what one could infer about the new symmetry group from these two facts and why?

I have no clue how this is related to symmetry.

PS: My question comes from this: enter image description here

The above figures from the ATLAS experiment (ATLAS-CONF-2017-016) show results from a search for new heavy gauge bosons decaying to eν (left) and µν (right).

My professor asked me the following question:

Such new gauge bosons come from some additional gauge group added to the Standard Model. If the analysis considered here would have discovered the $W'$bosons that were searched for, what would be the first thing you would conclude about the new gauge group?

But I have no idea how this question should be answered.

  • $\begingroup$ This seems a bit confused. A gauge group is a property of a theory. You mean what representation of the gauge group $W'$ transforms in? $\endgroup$ – knzhou May 24 '19 at 18:00
  • $\begingroup$ Yes, I re-edited the problem. Hope that make my question clearer. $\endgroup$ – Universe Maintainer May 24 '19 at 18:04
  • $\begingroup$ You mean μ and $\bar{\nu}_\mu$ etc like the decay of the W, or are you going for lepton number violation? Are you stuck on gauge groups, or are simple old fashioned (50s, 60s) global conservation laws that are troubling you? Have you mastered the history of particle physics and the emergence of quantum numbers such as strangeness, and the violations of such by some interactions but not others? $\endgroup$ – Cosmas Zachos May 24 '19 at 20:54
  • $\begingroup$ @CosmasZachos Thank you for your reply! please see the PS part. $\endgroup$ – Universe Maintainer May 24 '19 at 21:08
  • $\begingroup$ Homework and "no idea"? oh... $\endgroup$ – Cosmas Zachos May 24 '19 at 21:19

I do not think this is a good question, except for the trivial answer: it fits the model with which we calculated the curves that fitted the $W'$ seen, and thus the assumed group properties.

When the Higgs search was on, the background was fitted with the standard model expectation , looking for a higher than background enhancement. After one appeared at 125 GeV the higgs was fixed at that mass in the Monte Carlo generation of the plots and the data on top,and presented to the public with the specific standard deviations:


A wide data search was on that the expected decay channels were there etc.

For this real case the answer is that we know the group property of the measured resonance because it obeys the standard model symmetry groups as checked with monte carlo events that have that specific symmetry .


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