Talk:750 GeV diphoton excess

Lemma

I don't think "digamma particle" is a common name for the potential particle. "Digamma particle" gives exactly 8 google hits (excluding this article). "Digamma excess" gives 133, "750 GeV boson" gives 2400, "750 GeV excess" gives 1000, "750 GeV diphoton excess" gives 6100. I suggest to move it to "750 GeV diphoton excess". or similar names (LHC diphoton excess, ...) --mfb (talk) 21:59, 2 June 2016 (UTC)

Multiple edits to the article, no veto: moved, Digamma particle can stay as redirect. --mfb (talk) 23:58, 3 June 2016 (UTC)

Confusing

The introduction says "The diphoton excess cannot be caused by an experimental or theoretical systematic error.[7] The data, however, are less than 5 standard deviations (sigma) different from that expected if there was no new particle,...".

If it doesn't meet the 5-sigma criteria to rule out experimental error, how can they know that it "cannot be caused by an experimental or theoretical systematic error."? Bubba73 ^{You talkin' to me?} 18:42, 11 July 2016 (UTC)

A statistical fluctuation (what the 5 sigma is referring to, as the uncertainty is dominated by statistics) is not an experimental or theoretical error. It is just bad luck. 5 sigma do not rule out experimental errors (=you forgot something in the measurement, for example), but they make statistical fluctuations extremely unlikely. --mfb (talk) 20:53, 11 July 2016 (UTC)

Back in my day we had a "standard error of measurement", meaning that each measurement has some uncertainty in it. I still don't understand those two sentences. If experimental error or theoretical systematic error have been ruled out, it seems to me that it is a new particle. Bubba73 ^{You talkin' to me?} 22:11, 11 July 2016 (UTC)

I concur with Bubba73. The meaning of reference 7 here could do with more explanation. Bondegezou (talk) 08:20, 12 July 2016 (UTC)

Maybe it is clearer with an example? You try to figure out if a die is loaded and delivers more "6" than it should. You throw it twice, it is 6 both times. You investigate video records of the throw, you check that the table is completely flat, you make really, really sure that you indeed rolled "6" both times - no measurement error. But you still don't know if the die is loaded, simply because the statistical uncertainty is too large: it is perfectly reasonable that an unloaded die can roll 6 twice in a row. --mfb (talk) 20:11, 12 July 2016 (UTC)

Maybe I can be clearer about the confusion. Either it is a new particle or it is an error. A sentence in the introduction states that it is not an error. If it is not an error then it is a new particle, right? Bubba73 ^{You talkin' to me?} 20:17, 12 July 2016 (UTC)

"Either it is a new particle or it is an error." - no it is not. A statistical fluctuation is not an error, no one did anything wrong. --mfb (talk) 20:35, 12 July 2016 (UTC)

OK, I get mfb's explanation: I think the text in the article could be made clearer to say that. What I don't understand (and maybe never will) is how reference 7 can so confidently rule out "experimental or theoretical systematic error"? Bondegezou (talk) 22:01, 12 July 2016 (UTC)

How theorists can do that is a different question. This particular search (invariant mass of diphoton system) has a really nice and easy concept, and no one has a plausible idea how you could get it wrong. Worst case you reduce your sensitivity ("die falls off the table and you don't see the result of this roll"), but there is no known way to see an excess by measurement error - but how can you fully rule it out? --mfb (talk) 22:16, 12 July 2016 (UTC)

I suggest it's an overly bold claim to make based on a single preprint. Can we soften the language? Or find more supporting literature? Bondegezou (talk) 23:02, 12 July 2016 (UTC)

This shows that the two sentences in the introduction do not accurately portray the actual situation and need to be rewritten. Which was my point. Bubba73 ^{You talkin' to me?} 02:37, 13 July 2016 (UTC)

I weakened the statement to "is not expected to be caused by". --mfb (talk) 20:48, 13 July 2016 (UTC)

Thank you, that addresses my point! Bubba73 ^{You talkin' to me?} 00:57, 19 July 2016 (UTC)

Since it was determined to be a statistical fluke, the confusing sentence has been removed. Bubba73 ^{You talkin' to me?} 02:42, 9 September 2016 (UTC)

Please stick to the facts

So far, we have a preliminary analysis by one experiment (ATLAS didn't make their results public yet). CMS released an analysis where they looked at events where at least one photon had to be in the barrel. Why didn't they include endcap/endcap events? I would expect that they add those later - and if their analysis takes more time this is a weak indication that there could be something. But all those speculations are not suitable for the article. --mfb (talk) 21:08, 4 August 2016 (UTC)

Counts

Can the article be extended to include the actual event counts, and estimated background plus associated error terms, in order to demystify the magical however-many-sigma numbers please? — Preceding unsigned comment added by 62.7.179.172 (talk) 06:49, 23 August 2016 (UTC)

You would have to choose an arbitrary mass range to do that, which distorts the analyses the experiments do. And we don't have the source data, only the binned results. --mfb (talk) 15:04, 23 August 2016 (UTC)

Then please find a way of using those binned results to partially demystify the stats. I'm thinking something like ... "The published data (ref) for experiment X showed E events in mass range M-N GeV, with the Standard Model predicting F on average. Assuming a Poisson model for event production, this equates to a P-value of 1 in 20000 or a local significance of about 3.9 sigma. Taking into account the look-elsewhere_effect of results from multiple tests, this equated to a global significance of around 2 sigma." ... If the reader can be given some appreciation that a few tens of events was sufficient to work the HEP community up into a publishing frenzy then that would be helpful. Thanks. — Preceding unsigned comment added by 62.7.179.172 (talk) 07:36, 25 August 2016 (UTC)

Sounds like you're asking for a naïve re-interpretation of the results, which doesn't really add anything to the article and strays into WP:NOR. A statement like "a few tens of events was sufficient to work the HEP community up into a publishing frenzy" would certainly be misleading. --192.41.131.250 (talk) 12:53, 25 August 2016 (UTC)

My previous comment was an attempt to explain why exactly this is not possible, and leads to unscientific results. --mfb (talk) 11:04, 27 August 2016 (UTC)

I already think the article overstates the trust physicists put in the data. As it's written right now, "Despite the initial significance being lower than the discovery threshold of five sigma, many physicists treated the initial excess as tantamount to a discovery, as evidenced by the extreme interest particularly by the theory community, leading to the authorship of over 500 articles.", the reasoning is a stretch.

You're supposed to believe that the number of articles—which, by the way, means nothing to laymen who don't know how many articles are otherwise published in that same time period—"authored" is closely linked to the trust physicists put in the anomaly?

I mean, we all know the LHC's results have been the biggest blow particle physics could have taken¹ and any new data at this point is reason to write that amount of articles. And that's not to mention that many articles attempted to explain the anomaly away.

And by the way, "authored" and "articles" are not precise words in this context. I mean, does the 500 number include preprints? Are they research articles, or magazine articles?

I'd like to see that paragraph rewritten. I could rewrite it if there's support.

― ¹ by the way, there's a funny video from the LHC's launch where several physicists are talking about what to expect and one of them says almost jokingly that the most terrible thing that could happen was finding the Higgs boson and nothing else, but I digress ~victorsouza (talk) 09:50, 12 May 2022 (UTC)

Proposal to move to Diphoton excess

The 750 GeV qualifier is unnecessary detail. The notable topic is "diphoton excess". Other such excesses have already been claimed. Johnjbarton (talk) 17:20, 17 March 2024 (UTC)

I don't oppose the title Diphoton excess. But a page move would require significant changes (new introduction, new table of content, what happens to the infobox?) --Kallichore (talk) 18:06, 17 March 2024 (UTC)

Ok I did those (within the current title). The content was a little redundant (too much in the first section that could go in to the 2015 or 2016 slots) but I did not try to fix it. Johnjbarton (talk) 19:47, 17 March 2024 (UTC)

I removed the infobox which referred to the 750 GeV excess. I think the article could be moved to "diphoton excess" now.--Kallichore (talk) 05:48, 18 March 2024 (UTC)

Strongly oppose as a particle physicist. "Diphoton excess" is not specific to this event. The Higgs was also found as a diphoton excess (among other decays). The energy of 750 GeV is a more important part than "diphoton". The 95 GeV excess doesn't belong here, and it's so tiny that I don't think it warrants coverage at all. --mfb (talk) 06:10, 18 March 2024 (UTC)

@Mfb To me, as a Wikipedia reader, learning that, as you say:

• "The Higgs was also found as a diphoton excess"

is way more interesting than an entire article about a colossal flub by hundreds of physicists. Knowing this kind of event played a role in one of the biggest recent discoveries in particle physics completely changes the nature of the topic. The puzzling and obscure "750 GeV diphoton excess" becomes "another possible diphoton excess". We understand the excitement and disappointment.

An article about "diphoton excess" could be an article that helps readers understand particle physics. This article about 750 GeV is obscure and technical, a kind of footnote for particle physicists. I hope you will reconsider. Johnjbarton (talk) 16:16, 19 March 2024 (UTC)

As seen from before the discovery, assuming the Higgs exists: We didn't know its mass, but for every possible mass value we could predict all other parameters, including how often it should get produced and how often it decays to what. That means we knew in advance that it could decay to two photons and that this decay would be important for the discovery if the mass is between 100 and 160 GeV - the most likely mass range based on some other measurements. When a small peak showed up at 125 GeV the interpretation was pretty obvious. We also knew that a decay to four leptons would be common, and that search saw a peak around 125 GeV as well. Both matched the predicted signal strength for the Higgs, and both experiments saw clear signals, so ATLAS and CMS announced the discovery of a new particle that "behaves like" the Higgs boson. That caveat was dropped over the following months as more and more parameters were measured. For the 750 GeV peak the situation was completely different. We didn't expect a particle there, so there were no clear predictions to compare with. "Diphoton excess" is a bad group because it doesn't tell you in which situation you are. It just tells you that you have more events with two photons than expected in some mass range. Do you see new decays of a particle that was already known before (this is by far the most common type of discovery)? Do you see a particle that was already expected to exist? Do you see something completely unexpected?

It's difficult to include background information like that in articles. It's something you learn from working in particle physics, it's not something you would find discussed in typical Wikipedia sources. It's not specific to any single article either. --mfb (talk) 17:10, 19 March 2024 (UTC)

I would like to point out that the discovery of the Higgs boson in the diphoton-channel and the 4-lepton-channel is described here, so there is no need for an additional article. I thought the idea for the article diphoton excess was to collect "diphoton-excesses with respect to the Standard Model" in an article. But it may be better to keep this article in its current version and wait for further LHC results and press coverage before starting an article 95 GeV diphoton excess. --Kallichore (talk) 17:36, 19 March 2024 (UTC)