If my layperson's understanding is correct (probably vastly generalized), this should be considered exciting news. A few years ago the existence of the Higgs Boson was confirmed with some degree of confidence. These Higgs Bosons are produced when particles interact with the Higgs Field giving them mass.
The next question from that was - is that really the Higgs Boson, does it behave the way we expect it to (according to standard model)? I believe this is a test to verify that it does and they measured the coupling constant and it matched up. Neat. This could help with a much deeper understanding of why particles have mass.
ATLAS physicist here -- you're mostly right! The existence of a Higgs boson has been confirmed with extremely high confidence. And this news... it's exciting in the sense that it's an important result, but it's a bit of a damper on those of us who were hoping to discover new secrets about the universe.
Interestingly, the primary production mechanism for the Higgs boson at the LHC proceeds via the fusion of gluon particles from the colliding protons. This seems strange at first glance, since the Higgs interacts with particles proportionally to their mass, while the gluons are massless. In the standard model, there is a higher-order process wherein the gluons annihilate into a virtual "loop" of top quarks (which are very massive), which then "lend" their mass to produce the Higgs.
Because previous measurements have been consistent with the Standard Model prediction, we already had some evidence that the coupling to top quarks was nominal. However, there are other possible scenarios involving exotic physics that could mimic this production mechanism, which could imply the existence of new forces/particles, and that the Higgs boson does not couple to "normal" particles in the predicted fashion. Because of the nature of these heavy virtual loop processes, it turns out that it's pretty hard to distinguish between different such scenarios by examining the kinematic properties of the events. Hence, the main observable is the rate, and even that can be made to match a wide range of values with or without standard couplings, given a clever enough theory.
This recent result demonstrates directly that the Higgs boson does indeed couple to the top quark in a matter roughly consistent with the Standard Model expectation (the CMS measurement shows an upward fluctuation, indicating even stronger coupling than expected, although this is probably just a statistical fluctuation). Therefore, no fancy/exotic physics (such as string theory, strong gravity, etc) are required to explain the observed production of Higgs bosons so far at the LHC.
As a layperson, this is so confusing. On one hand, we have Higgs Bosons "giving" particles mass, presumably in a nondeterministic quantum manner, on the other hand we have relativity theory that says mass "warps" space-time itself. What is the relation between the two theories?!
Yeah, they are spectacular. And then you look at the green parts on the side and realize that thing is 4 stories high.
As an aside, I like the understated way the description is written:
The extraction of these events from the LHC data is challenging as there are many mundane type of events that can mimic them. Identifying these events requires measurements from all CMS subdetectors, which makes the reconstruction quite complex.
I can only imagine what the value of "many" and the amount of effort behind "challenging"and "quite complex" really is.
To some, further confirmation of the standard model is a disappointment because it doesn't tell us anything we didn't already know or point to some exciting new physics.
CMS physicist here! As our ATLAS colleagues, we also use boosted decision trees extensively in our analysis, as well as the so-called Matrix Element Method -- a way to combine the knowledge of the differential theoretical cross-sections for the signal and background processes with our knowledge of the experimental resolution of our detectors. More details are available in [1].
However, in CMS we have recently started using Deep Neural Networks. These are used for the separation of signal and background events in the "single-lepton channel" of the search, i.e., the search where the Higgs boson decays to two bottom quarks and the top quarks decay in such a way that at least one electron or muon is present in the final state. Again, more details here: [2]
I was a bit involved in the ATLAS result. IMHO, it's not really that fancy. Basically, there's a boosted decision tree that is used to select signal-like events, and it was re-optimized some new features and a larger training set. Also, they dropped a statistical categorization that was of interest for a related process in favor maximizing sensitivity to this ttH production mechanism specifically.
I haven't looked too carefully at the CMS result, so no comment there.
[+] [-] politelemon|7 years ago|reply
The next question from that was - is that really the Higgs Boson, does it behave the way we expect it to (according to standard model)? I believe this is a test to verify that it does and they measured the coupling constant and it matched up. Neat. This could help with a much deeper understanding of why particles have mass.
[+] [-] cshimmin|7 years ago|reply
Interestingly, the primary production mechanism for the Higgs boson at the LHC proceeds via the fusion of gluon particles from the colliding protons. This seems strange at first glance, since the Higgs interacts with particles proportionally to their mass, while the gluons are massless. In the standard model, there is a higher-order process wherein the gluons annihilate into a virtual "loop" of top quarks (which are very massive), which then "lend" their mass to produce the Higgs.
Because previous measurements have been consistent with the Standard Model prediction, we already had some evidence that the coupling to top quarks was nominal. However, there are other possible scenarios involving exotic physics that could mimic this production mechanism, which could imply the existence of new forces/particles, and that the Higgs boson does not couple to "normal" particles in the predicted fashion. Because of the nature of these heavy virtual loop processes, it turns out that it's pretty hard to distinguish between different such scenarios by examining the kinematic properties of the events. Hence, the main observable is the rate, and even that can be made to match a wide range of values with or without standard couplings, given a clever enough theory.
This recent result demonstrates directly that the Higgs boson does indeed couple to the top quark in a matter roughly consistent with the Standard Model expectation (the CMS measurement shows an upward fluctuation, indicating even stronger coupling than expected, although this is probably just a statistical fluctuation). Therefore, no fancy/exotic physics (such as string theory, strong gravity, etc) are required to explain the observed production of Higgs bosons so far at the LHC.
[+] [-] pacala|7 years ago|reply
[+] [-] mullikine|7 years ago|reply
[+] [-] martinpw|7 years ago|reply
As an aside, I like the understated way the description is written:
The extraction of these events from the LHC data is challenging as there are many mundane type of events that can mimic them. Identifying these events requires measurements from all CMS subdetectors, which makes the reconstruction quite complex.
I can only imagine what the value of "many" and the amount of effort behind "challenging"and "quite complex" really is.
[+] [-] spullara|7 years ago|reply
[+] [-] c12|7 years ago|reply
[+] [-] unknown|7 years ago|reply
[deleted]
[+] [-] eric-hu|7 years ago|reply
[+] [-] thiagotomei|7 years ago|reply
However, in CMS we have recently started using Deep Neural Networks. These are used for the separation of signal and background events in the "single-lepton channel" of the search, i.e., the search where the Higgs boson decays to two bottom quarks and the top quarks decay in such a way that at least one electron or muon is present in the final state. Again, more details here: [2]
[1] http://arxiv.org/abs/1803.05485
[2] http://cms-results.web.cern.ch/cms-results/public-results/pr...
[+] [-] cshimmin|7 years ago|reply
I haven't looked too carefully at the CMS result, so no comment there.