I have to admit that this post is really only important for experimentalists interested in searching for non-Standard Model decays of the Higgs particle. I try to keep these technical posts very rare, but this time I do need to slightly amend a technical point that I made in an article a few weeks ago.
Recently I wrote an article on this website, which I briefly described in this post, about the possibility that the Higgs particle might decay to two new spin-one particles (which I called a “ZD“), each of which could then decay to a lepton-antilepton pair. Based on my recent paper with twelve other authors about the possibility of unexpected (“exotic”) decays of the Higgs particle, I argued that this could be discovered with existing LHC data from 2011-2012, even if it only happens in one in every 100,000 Higgs particles.
All of that is correct. But in the second-to-last paragraph of that article, I also briefly noted a different variant of this possibility: that the Higgs might occasionally decay to a (known) Z particle plus an (unknown) ZD particle. For this possibility, I said something which my co-authors and I now think is not correct — and once corrected, a search for this process becomes even more pressing and interesting.
I said: “However, there are indirect limits on h → Z ZD from electroweak precision measurements, and these are still a few times stronger than any limits that likely can be obtained from measurements using current LHC data. Only with future data will such a search become competitive with the indirect limits.” But while we were soliciting comments before submitting our paper, one of our colleagues pointed out an issue with one of the articles on which we relied in determining the electroweak precision-based limits. Revisiting these limits, we now find the true electroweak precision limits are somewhat weaker than we had inferred, which is relevant for a ZD with mass above about 10 GeV/c². As a result, it is in fact possible, contrary to what I said last month, for measurements on the 2011-2012 LHC data looking for Higgs decaying to Z + ZD to show a signal, or to put stronger limits than any existing precision measurements. So please go make the measurement on current data!
I’ve adjusted the wording of my website article accordingly, and version 2 of our paper, with this adjustment, will be on the arXiv within a few days.