Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I LHC Diphoton excess: CMS sees nothing in 2016 data, ATLAS nothing in spin 0 analysis

  1. Aug 4, 2016 #1

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    https://www.physicsforums.com/threads/new-lhc-results-2015-tuesday-dec-15-interesting-diphoton-excess.84798 [Broken] and status from Monday

    CMS released their conference note a bit earlier. They see absolutely nothing at the mass range where the excess appeared in 2015.

    It is a bit curious that they removed events where both photons were detected in the endcap. This was shown in earlier analyses - why not this year?

    Nothing public from ATLAS so far.


    Summary plot, a peak in the data corresponds to a downwards spike (lower = more significant):

    CpCXCqDXgAAVvNG.jpg
     
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Aug 4, 2016 #2

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    ATLAS will be showing their results Friday morning.
     
  4. Aug 4, 2016 #3

    ohwilleke

    User Avatar
    Gold Member

    It is worth noting that the naive expectation, if the bump had been real, would be for the 2016 data set (which is much bigger than the 2015 data set in which the 750 GeV bump was seen) to increase the significance of that resonance by about 2.5 sigma. Anything less than that increase in significance would have cast doubt on the 750 GeV bump being real.

    Recall that the significance of the 2015 bump was as follows: The local significances were given as 3.9 sigma (ATLAS) and 2.6 sigma (CMS). The global significances were just 2.0 (ATLAS) and less than 1.2 (CMS) – but the excess was observed at the same place, so we cannot “look elsewhere” for both experiments separately.

    The significance of the original 2015 bump at CMS increased by the 2.5 sigma that should have been expected with more data would have pushed the resonance to a local significance of 5.1 sigma or so with the new data if it was real, which would have been unmistakable. Instead, the bump is pretty much completely gone entirely from CMS, as expected if the bump in the 2015 data was almost entirely a statistical fluke.

    The rumor mill claims that ATLAS will see basically the same thing, but will know for sure a little more than twelve hours from now.
     
  5. Aug 5, 2016 #4

    vanhees71

    User Avatar
    Science Advisor
    2016 Award

    Which talk was it? Is the presentation online at Indico?
     
  6. Aug 5, 2016 #5

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The talks are this morning (Chicago time) as I understand. This is a pre-release of the CMS conference note.

    A student I co-supervise has the (ungrateful) task of giving a talk in a parallel session at the same time ...
     
  7. Aug 5, 2016 #6

    vanhees71

    User Avatar
    Science Advisor
    2016 Award

    Well, that may feel bad, but also ruling out things is important work. I remember the poor CLAS people who had to present the non-confirmation of the pentaquark...
     
  8. Aug 5, 2016 #7

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    You misread me, the student is giving a talk in a session parallel to the ATLAS and CMS results (it has nothing to do with the diphoton resonance), with the implication that basically nobody will go to that session. This would be true regardless of what ATLAS and CMS present.
     
  9. Aug 5, 2016 #8

    vanhees71

    User Avatar
    Science Advisor
    2016 Award

    Ah, I see. Yes, that's really bad. As interesting as big conferences with parallel sessions can be, I prefer smaller workshops.
     
  10. Aug 5, 2016 #9

    ohwilleke

    User Avatar
    Gold Member

    Depending on the student, it could still be O.K. Some people, even professionals with elite educations, have terrible stage fright and can be a bit more relaxed knowing that fewer people are in the audience and that the only people who are there are people who are really deeply interested in what you have to say.
     
  11. Aug 5, 2016 #10

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    If it is three people staring at their laptops it is even more depressing, but let us get back on-topic.
     
  12. Aug 5, 2016 #11

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    CMS took down their conference note again (well, replaced it by a 2-page PDF with a meaningless abstract and no content).

    The talks start at 16:00 CERN time, this post was posted 11:54 CERN time, so add 4 hours to whatever the forum shows for this post if you set the time zone correctly.

    @ohwilleke: CMS had updated their result and got a higher significance for Moriond. The 8 TeV data indicated that the 2015 excess was on the high side even if there was a new particle.
     
  13. Aug 5, 2016 #12

    1oldman2

    User Avatar
    Gold Member

  14. Aug 5, 2016 #13

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

  15. Aug 6, 2016 #14

    ChrisVer

    User Avatar
    Gold Member

    http://backreaction.blogspot.de/2016/08/the-lhc-nightmare-scenario-has-come-true.html

    What do you think about Sabine Hossenfelder's article here?
    Especially about this:
    I don't know, I found this declaration depressing and a little bit rushed for now... nothing is over yet and nothing is in vain. Also the comments get more depressing [for collider physics etc]
     
  16. Aug 6, 2016 #15

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    The Tevatron found the top-quark nine years after it reached its maximal energy. The LHC has not even reached its design energy yet, and has been close to it only for a bit more than a year.

    The data analyzed so far is not even 1% of the total planned integrated luminosity. Let's check again with the ~30-50/fb at the end of the year, with ~300/fb in ~2025, and with ~3000/fb in ~2035.
    Also, various analyses didn't get updates with 2016 data yet, or did not even start with 13 TeV data.
     
  17. Aug 6, 2016 #16

    Haelfix

    User Avatar
    Science Advisor

    I completely disagree with Sabines analysis for many reasons and I suspect most particle physicists do as well. Having said that, the nightmare scenario is a little closer than it used to be.

    She casts a lot of dispersions at certain theoretical ideas, which I think are unjustified but look there was always the possibility that one day due to technical/financial limitations the methods we have used to discover and probe the high energy frontier would hit diminishing returns. That there might be a limit to human ingenuity and to experimental guidance. Fortunately I don't think we are anywhere near that point, so all of this boils down to certain hypotheticals and extrapolations concerning human behavior. In short yet another storm in a teacup!
     
  18. Aug 7, 2016 #17

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    To be clear to non-experts, the Spin-0 and Spin-2 analyses have a very high degree of overlap: each is optimized for a particular spin hypothesis, but fundamentally they are looking at the same data. It's possible that one sees a 4 sigma excess and the other a 5 sigma excess, but it's not possible that one sees a five sigma excess and the other nothing.

    There are unhappy theorists out there, but it's not like the experiments didn't warn them that the significances were weak. They didn't want to hear about trials factors or partonic luminosity ratios or anything. We can see where that line of thinking leads.
     
  19. Aug 7, 2016 #18

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Just to be clear, there are also many theorists who did not jump to premature conclusions and rode the citation wave and actually took the hint for what it was.
     
  20. Aug 7, 2016 #19
    If anything, spending 9 months working on BSM theories for a deviation of global significance of 2.0 is questionable.

    There are many outstanding and difficult problems which need further assessment in theoretical physics.

    (Edit: the 750 GeV was never, and never will be one of these)
     
  21. Aug 8, 2016 #20
    I was actually wondering about this. What was it that allowed them to see the top quark after 9 years when they hadn't before? Just more data to get 5 sigma? Or new analysis/detectors?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: LHC Diphoton excess: CMS sees nothing in 2016 data, ATLAS nothing in spin 0 analysis
  1. LHC preprint from CMS (Replies: 6)

  2. 750 GeV diphoton excess (Replies: 36)

Loading...