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

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In summary, the results of the Moriond experiment are inconclusive and speculation about their findings is rampant. There is clear evidence of a hyper-symmetric triplet, but it is still unclear what this means.
  • #1
arivero
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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?
 
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  • #2
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
 
  • #3
arivero said:
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?
 
  • #4
Buzz Bloom said:
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.
 
  • #5
'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.
 
  • #6
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.
 
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  • #7
Vanadium 50 said:
Do you have any evidence that the experiments indulged in the sort of scientific misconduct that you suggest?
:wideeyed: 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.
 
  • #8
arivero said:
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.
 
  • #9
arivero said:
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.
 
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  • #10
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.
 
  • #11
clear evidence of a hyper-symmetric triplet

but seriously someone tell me what this means!
 
  • #12
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.
 
  • #13
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.
 
  • #14
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!
 
  • #15
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?
 
  • #16
nolxiii said:
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?
 
  • #17
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?
 
  • #18
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.
 
  • #19
nolxiii said:
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.
 
  • #20
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!
 
  • #23
Vanadium 50 said:
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.
 
  • #24
mfb said:
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.
 
  • #25
vanhees71 said:
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]
 
  • #26
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.
 
  • #27
Lord Crc said:
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.
arivero said:
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.
arivero said:
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.
vanhees71 said:
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.
 
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  • #28
mfb said:
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?
 
  • #29
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.
 
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  • #30
mfb said:
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 [itex]\Gamma > M [/itex] possible?
 
  • #31
You wouldn't call it particle then. PDG has resonances with Γ/M>0.3, e. g. h1(1170), or even resonances with no proper width estimate, e. g. a1(1260). Careful angular analysis of three-body decays or direct production is the only chance to see some order in the mess of extremely broad resonances.
 
  • #32
arivero said:
Let me to point out also Resonaances entry "the loose-cuts analysis was not approved in time by the collaboration"

And how would Adam know what the experiments have and do not have? "Not approved in time" implies "approved too late" and not simply "not approved".

One of the sadder things about this whole affair is that the experiments have been very careful in specifying what they do and they do not see, and this has been almost completely ignored by the theoretical community. Several of the 280+ preprints state the experiments claim discovery, which is simply false. ATLAS quotes 2 sigma significance, CMS less than 1 sigma. Yes these 280+ papers go on and pretend this is real. (And why this particular low significance excess is launching so many papers while other, more significant excesses don't is mystifying. Well, it would be. You explained it - you think the experiments have something more significant but have "chickened out" and are not telling the truth.

Here are the problems you have to deal with.
  • The significances are very low. One and two sigma are nowhere near five.
  • ATLAS and CMS see somewhat different masses.
  • ATLAS and CMS see somewhat different yields.
  • ATLAS and CMS see rather different widths.
  • The 8 TeV data does not confirm the 13 TeV data.
  • CMS doesn't see the signal in all parts of their detector.
If you want to explain these with statistical fluctuations, why not take the next step and explain the whole shebang as a statistical fluctuation? It's no less likely.

Finally, even if it's real, you won't settle things with twice as much data. You need ten times as much data.
 
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  • #33
Vanadium 50 said:
The significances are very low. One and two sigma are nowhere near five.
Don't take the LEE twice. This statement would be a proper description if ATLAS would have the excess at 750 GeV and CMS at 1 TeV. I don't think it would have triggered so many theory papers then. The masses are not exactly the same (how could they?), but very close and the yield comparison depends on your favorite theory model as the selection is different. CMS 8+13 TeV quotes 750 GeV, ATLAS quotes 750 GeV, CMS 13 TeV quotes 760 GeV, it looks like all values are rounded to multiples of 10.
Vanadium 50 said:
ATLAS and CMS see rather different widths.
The narrow width gives a fine fit for ATLAS, so does a slightly larger width for CMS. That difference is way less significant than the excesses.
Vanadium 50 said:
The 8 TeV data does not confirm the 13 TeV data.
There is a slight excess, not significant on its own but compatible with gg production.
Vanadium 50 said:
CMS doesn't see the signal in all parts of their detector.
The interpretation depends on your favorite theory model.
Vanadium 50 said:
Finally, even if it's real, you won't settle things with twice as much data. You need ten times as much data.
To figure out what it is (if it is real): sure. To get highly confident that something is there: I don't think so. If the ~3.5 local significance is the expected strength of an actual signal, twice that data with the same conditions will give an expected local significance of ~4.9 sigma. But you can do better. You can check the various theory papers to improve the selection, you can improve the background suppression and estimation and so on. Pileup will increase a bit, but that should be manageable.
 
  • #34
mfb said:
You wouldn't call it particle then. PDG has resonances with Γ/M>0.3, e. g. h1(1170), or even resonances with no proper width estimate, e. g. a1(1260). Careful angular analysis of three-body decays or direct production is the only chance to see some order in the mess of extremely broad resonances.
I assume there is some experimental reason, but I was also thinking that if the resonance pole is at M - i Γ with Γ = M then its square is in (M^2 - Γ^2) - 2 i M Γ the pure imaginary line, and that could be theoretically relevant. Also, perhaps the indeterminacy principle in energy-time has some say here, as Γ is inverse lifetime.
 
  • #35
arivero said:
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
Can you tell me what R-D gravitons refers to?
 
<h2>1. What is the 750 GeV diphoton excess?</h2><p>The 750 GeV diphoton excess refers to a potential signal observed in the data from the Large Hadron Collider (LHC) in 2015. This signal appeared as an excess of photon pairs with a combined energy of 750 GeV, which could potentially indicate the presence of a new particle.</p><h2>2. What could be causing the 750 GeV diphoton excess?</h2><p>There are multiple theories about what could be causing the 750 GeV diphoton excess. One possibility is the existence of a new particle, such as a heavy scalar or pseudoscalar boson. Another possibility is that the excess is a statistical fluctuation or error in the data.</p><h2>3. Has the 750 GeV diphoton excess been confirmed?</h2><p>No, the 750 GeV diphoton excess has not been confirmed. While the initial data from the LHC showed a potential signal, further analysis and experiments have not been able to reproduce the same results. This means that the existence of the excess is still uncertain.</p><h2>4. Why is the 750 GeV diphoton excess important?</h2><p>If the 750 GeV diphoton excess is confirmed, it could potentially lead to a major breakthrough in particle physics. The discovery of a new particle could help us better understand the fundamental building blocks of the universe and potentially open up new avenues for scientific research and technological advancements.</p><h2>5. What are scientists doing to investigate the 750 GeV diphoton excess?</h2><p>Scientists are conducting further experiments and analyses to try and confirm or disprove the existence of the 750 GeV diphoton excess. This includes collecting more data from the LHC and using other experiments and techniques to search for the potential new particle. Additionally, scientists are also exploring alternative explanations for the excess and working to improve our understanding of the data and potential sources of error.</p>

1. What is the 750 GeV diphoton excess?

The 750 GeV diphoton excess refers to a potential signal observed in the data from the Large Hadron Collider (LHC) in 2015. This signal appeared as an excess of photon pairs with a combined energy of 750 GeV, which could potentially indicate the presence of a new particle.

2. What could be causing the 750 GeV diphoton excess?

There are multiple theories about what could be causing the 750 GeV diphoton excess. One possibility is the existence of a new particle, such as a heavy scalar or pseudoscalar boson. Another possibility is that the excess is a statistical fluctuation or error in the data.

3. Has the 750 GeV diphoton excess been confirmed?

No, the 750 GeV diphoton excess has not been confirmed. While the initial data from the LHC showed a potential signal, further analysis and experiments have not been able to reproduce the same results. This means that the existence of the excess is still uncertain.

4. Why is the 750 GeV diphoton excess important?

If the 750 GeV diphoton excess is confirmed, it could potentially lead to a major breakthrough in particle physics. The discovery of a new particle could help us better understand the fundamental building blocks of the universe and potentially open up new avenues for scientific research and technological advancements.

5. What are scientists doing to investigate the 750 GeV diphoton excess?

Scientists are conducting further experiments and analyses to try and confirm or disprove the existence of the 750 GeV diphoton excess. This includes collecting more data from the LHC and using other experiments and techniques to search for the potential new particle. Additionally, scientists are also exploring alternative explanations for the excess and working to improve our understanding of the data and potential sources of error.

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