Is the 750 GeV Diphoton Excess Real? Analyzing the Moriond Results

[arivero]

What do you think of Moriond results? had they really got 5 sigma and chickened out? What could the particle be, if it is real?

 

[Buzz Bloom]

Hi arivero:

I confess my search methods may be poor, but I failed tried to find any information about the topic on the Internet. Would you please cite a reference?

Regards,
Buzz

 

[Vanadium 50]

had they really got 5 sigma and chickened out?

Do you have any evidence that the experiments indulged in the sort of scientific misconduct that you suggest?

 

[jtbell]

Would you please cite a reference?

Yes, please. Don't expect everyone here to be on top of recent developments. I have no idea what this is all about.

 

[collinsmark]

'Not sure if this is related to the OP's topic, but this link indicates that a 750 GeV signal was only 1.9 sigma significance, so far (mid March, 2016).
http://www.ibtimes.com/cern-lhc-upd...ak-physics-standard-model-resume-soon-2339001

Now, in fresh analysis disclosed Thursday at a conference in La Thuile, Italy, researchers said a recalibration of the full data set collected by the CMS detector pushed the statistical significance of the signal to 1.6 sigma from 1.2 sigma reported in December. Researchers at the ATLAS collaboration also re-analyzed their data collected during the first run, and now see a 1.9 sigma excess at 750 GeV.​

Again, though, I'm not sure if that's the OP's intended topic.

 

[mfb]

Let's start with some links:
Moriond conference timetable, the relevant talks are "jeudi 17 Mars 2016" afternoon, "Diphoton searches in ATLAS" and "Diphoton Searches in CMS".
News at Scientific American
Jester has a nice summary

Overall, the significance numbers didn't change much compared to the December announcements. Both experiments now have a spin-0 and a spin-2 analysis, which differ a bit in the selection but not much in the result. The local significance is somewhere at 3.x sigma for both experiments, depending on where exactly you look.

 

[arivero]

Do you have any evidence that the experiments indulged in the sort of scientific misconduct that you suggest?

Misconduct? I never suggested it.
Strasttler and Motl commented the friday that ATLAS was expected to claim "almost 5" in the friday conference but surely they were not still convinced of their own analysis. They explictly used "chickened out". Prudence is not misconduct.
http://motls.blogspot.com.es/2016/03/rumor-moriond-denied-new-atlas-almost-5.html#more

Please note also that I started the thread in the Lounge in order to allow for wide discussion. Of course, with more that 750 papers in the arxiv, almost everybody can quote its favorite model from some arxiv paper :-) I am particularly surprised that R-D gravitons are considered as a major possibility.

 

[mfb]

Strasttler and Motl commented the friday that ATLAS was expected to claim "almost 5" in the friday conference but surely they were not still convinced of their own analysis.

Based on rumors, not on actual physics. Even worse if you need a second rumor to explain the lack of evidence for the first rumor.

 

[Vanadium 50]

Misconduct? I never suggested it.

You suggested that the experiments see one thing and report another. What else would you call it?

If Lubos told me my mother loved me, I would check it out.

 

[arivero]

So the conclusion is that the events are so boring/irrelevant that critiquising the OP is funnier? Well, it could be so. I was not impressed during the first phase of the ambulance-chasing but post-Moriond I am curious about how the different explanations compete.

 

[nolxiii]

clear evidence of a hyper-symmetric triplet

but seriously someone tell me what this means!

 

[RGevo]

Yes, there is so much verbal diarrhoea on the diphoton excess out there. Peoples opinions and rumours should be ignored. It's important to be patient, particularly when we know the data this year will clarify this topic.

I'm waiting on the appearance of a thorough review by some serious authors - I'm sure this will come within months.

 

[mfb]

Within months, we'll have more data, making detailed reviews outdated as soon as they are there. We'll hopefully get some better theory papers in the meantime, but whatever happens, the summer conferences will change the situation.

 

[vanhees71]

Yes, I think it's good to wait and be a bit more patient than modern popular science-hype media want us to be. I think it's a great damage for the public understanding, reputation and credibility of science to bring forward vague evidences and speculate about them without the strict confirmation of the scientific method. An outstanding example are the BICEP2 "results", which where "published" prematurely although it was well known that the careful cross analysis with the PLANCK survey, which finally revealed that the supposed-to-be imprint of primordial gravitational waves on the CMBR polarization was just dust.

Another example were the faster-than-light neutrinos with a big media hype followed by a big spaming of all kinds of wanna-be-theory papers "explaining" possible "effects". For anybody a bit used to the physics underlying the Standard Model it was quite clear how extremely unlikely a tachyonic nature of neutrinos is, and it was no surprise at all that afterwards the technical problems with some glass fiber and a time-keeping oscillator was figured out.

All this is a great damage to science and its standing in the public. After all we all, who do fundamental research, rely on tax payers' money and we schould be greatful to the public in financing us. That's why the public has the right to learn about the right science, which is exciting and rewarding enough and very well justifies the "big money" invested by the public in fundamental and basic research!

So simply let's wait until there's either confirmation or disproval of the signal (maybe even at the $5\sigma$ level). I guess, with the LHC up and running it won't take too long to figure this out with some confidence!

 

[nolxiii]

so how safe is it to say at this point that, whatever does or doesn't come out of this, it will be the only really new/unexpected thing that the LHC will see?

 

[Hepth]

so how safe is it to say at this point that, whatever does or doesn't come out of this, it will be the only really new/unexpected thing that the LHC will see?

I would say it's safe to say that the LHC has already seen other interesting new/unexpected things. Lepton Universality Violation? Higgs? A slew of things still in tension with the Standard Model? Do you not consider these new/unexpected?

 

[nolxiii]

Was actually only aware of the higgs, which is awesome. Will have to go look into the lepton stuff.

Just meant it simply as, with the amount of data that has now been collected, has anything that the LHC will be able to see shown at least some signs by now, or is there still potential for the additional runs in the next few years to totally surprise us?

 

[mfb]

For heavy particles, the LHC collected about 0.1% of the collisions planned over the lifetime of the accelerator. There are tons of things that can appear in the next years, even without any hints so far.

 

[arivero]

so how safe is it to say at this point that, whatever does or doesn't come out of this, it will be the only really new/unexpected thing that the LHC will see?

Well, with so many papers, it could be a bit of shame in the hep-ph world if it were an unexpected thing.

Said that, it worries me how different the situation is respect to the days of the SU(2)xU(1) model. At that time it could be said that we had the charged currents (the W) and the debate was between a model only matching the W and a model that predicted the Z current too.

 

[nolxiii]

Right on. I actually found my way to physics forums looking for any intelligent discussion of this result since all of the news releases pretty much just left off at "something may or may not be there." Guess not too much has changed but I'll take it!

 

[mfb]

We had a longer discussion in December.

 

[Lord Crc]

In this[1] page about the Higgs, it's mentioned that the diphoton signal implies the particle is a boson and that it cannot be spin 1. Does the same apply if in this case, assuming it is a particle?

[1]: http://cms.web.cern.ch/news/observation-new-particle-mass-125-gev

 

[arivero]

If Lubos told me my mother loved me, I would check it out.

Valid enough. Let me to point out also Resonaances entry "the loose-cuts analysis was not approved in time by the collaboration",

http://resonaances.blogspot.com.es/2016/03/diphoton-update.html?m=1

which is also, IMO, a good reference for the current status.

 

[arivero]

We had a longer discussion in December.

Hmm, really, we had not. Models were not touched, and the discussion of significance can have evolved given the new analysis of ATLAS and the magic of CMS that incorporates new data from the days where the magnet was off. Model-wise, it seems that spin-2 loses weight.

I am also a bit puzzled by the debate between wide vs narrow resonance. It amuses me that both experiments can disagree on this.

 

[ChrisVer]

Another example were the faster-than-light neutrinos with a big media hype followed by a big spaming of all kinds of wanna-be-theory papers "explaining" possible "effects". For anybody a bit used to the physics underlying the Standard Model it was quite clear how extremely unlikely a tachyonic nature of neutrinos is, and it was no surprise at all that afterwards the technical problems with some glass fiber and a time-keeping oscillator was figured out.

I think not even the OPERA authors believed in that result and they made a comment about their setup before the problem was found [rumorsss]

 

[vanhees71]

Of course, nobody believed in really having found faster-than light neutrinos. It was, however, written in the popular press as if, and that's very bad for science in the sense, I've written above.

 

[mfb]

In this[1] page about the Higgs, it's mentioned that the diphoton signal implies the particle is a boson and that it cannot be spin 1. Does the same apply if in this case, assuming it is a particle?

[1]: http://cms.web.cern.ch/news/observation-new-particle-mass-125-gev

Yes, assuming it is a particle that decays to two photons. There are also models where the particle decays to a photon plus a very light pion-like particle that decays to two (very collimated) photons that appear like a single photon. In that case it could have spin 1.

Hmm, really, we had not. Models were not touched, and the discussion of significance can have evolved given the new analysis of ATLAS and the magic of CMS that incorporates new data from the days where the magnet was off. Model-wise, it seems that spin-2 loses weight.

"Spin 2" has a slightly lower significance, but the difference is small. The additional plots about jet distributions and so on are interesting, and we'll see how they get accounted for in upcoming theory papers.

I am also a bit puzzled by the debate between wide vs narrow resonance. It amuses me that both experiments can disagree on this.

I don't see disagreement. In ATLAS the peak looks a bit wider, in CMS it does not. All that is at the level of statistical fluctuations you would expect with such an excess.

Of course, nobody believed in really having found faster-than light neutrinos. It was, however, written in the popular press as if, and that's very bad for science in the sense, I've written above.

Well, the popular press uses the most dramatic headlines it can get away with. With the given status of the OPERA analysis at that time, what else would you have suggested? They did not understand the problem, even after checking everything for months, so they asked experts outside for help. In terms of science, 6 sigma slower than light neutrinos would have been equally surprising, but then the headlines would have been much weaker.

 

[Lord Crc]

Yes, assuming it is a particle that decays to two photons. There are also models where the particle decays to a photon plus a very light pion-like particle that decays to two (very collimated) photons that appear like a single photon. In that case it could have spin 1.

Thanks, that was exactly the kind of exceptions I was curious of.

In the spin 1 case, I guess one would have to look at other signals, guided by potential theories, to tease out the fact that it's spin 1?

 

[mfb]

Spin 1 with the three-photon decay would lead to interesting experimental signatures:

Neutral pion decays are the main background to photon analyses, so the experiments know very well how they look, and design the selection to remove them. So anything much heavier than a pion is ruled out already (it would produce a huge peak in the "background"), anything between 100 MeV and 1 GeV would distort the energy distributions in the showers, and should be notable, at least with more statistics. Lighter masses seem to be problematic in terms of theory, and indistinguishable with the calorimeter alone, but there is a method that would catch even those: some photons do pair production ("convert") in the tracking detectors. If the photon is actually two photons, the probability that one of them does a conversion is higher. It would also be a very odd conversion, as just a part of the total energy would appear as electron/positron energy.

 

[arivero]

I don't see disagreement. In ATLAS the peak looks a bit wider, in CMS it does not. All that is at the level of statistical fluctuations you would expect with such an excess

Hmm, actually, how wide the width can be in general, given a value of M? Is \Gamma > M possible?