Higgs Boson Questions

So now they have the Higgs. Or do they? If so, where do they go from here? What real value does the discovery of the Higgs provide?
Don’t get me wrong, I’m all for science and research but not quiet clear on where this discovery leads.
Also, would a larger Collider than CERN do any better for research? Say some rich billionaire wanted to build a better(?) one?
Just wonderin’.

I am not going to go looking for a cite, but I have recently read that Higgs’ confirmation
so fully completes and confirms the Standard Model that there may not be enough for all the
newly-minted experimental physicists to do for a while. They are seriously worried about it.

As for building a new CERN, we are probably talking about a figure much greater than the fortune
of any one person, and probably the richest several just for construction. After the thing is built
there would be these ongoing expenses commonly known as “payroll” and “utilities.” Getting the drift?

I’m sure there’s plenty enough for experimental physicists to keep working on. Perhaps it’s going to get increasingly challenging to keep probing into higher masses/smaller scales, and accelerators bigger than the LHC aren’t on the drawing board in the near future, but finding the Higgs would give the standard model much bigger legs to keep sketching in the details on the theories; which will provide new directions and opportunities for clever physicists to set up experimentation.

As far as confirming the Higgs boson, it’s not going to be very relevant to many outside the physics world. And not applicable beyond the academic. But it’d be a huge discovery that should hopefully point fundamental physics onto a finer course.

This is all for the sake of knowledge and understanding for human posterity, of which our lives play out a very tiny part; yet we sit on the shoulders and enjoy the fruit of such experimental research of the past—and so on with our descendants.

As for a collider bigger than the LHC, hell yes… When it comes to particle physics, bigger is always better. Think of them as telescopes (or microscopes, rather). The bigger the collider, the finer becomes our resolution of the microcosm.

Similar queries from earlier in the year:
Higgs boson discovery confirmation
Higgs Boson or just a new particle?

Regarding the continuation of experimental physics: indeed, no one is worried in the slightest. The fraction of physicists working on Higgs-related topics is minuscule. The fraction of *particle *physicists working such topics is naturally higher but still small. Perhaps of interest: List of unsolved problems in physics. (This is a rather high-level list. Within each subfield one could create an equally long, more detailed list.)

Regarding the newly discovered particle: it’s very certain that a new particle has been discovered, but the properties of the particle are only known so well. So far, it’s consistent with being a minimal Standard Model Higgs, although some like to note the presence of (minor) tension between the data and expectation in certain decay channels. But these property measurements will require more data before they are convincingly precise. And, there are plenty of theoretical models out there that can put a novel species in this mass range.

To study this particle (Higgs or not) in depth, you want a lepton collider. The candidate machine with the most development behind it is the International Linear Collider (ILC), a proposed electron-positron collider that could run at a center-of-mass energy equal to the mass of this new particle (125 GeV). In contrast, the LHC is a proton-proton collider, and since protons are composite particles, the collisions are rather messy. With an electron-positron collider, there are no spectator particles around to make particle identification difficult or (quite importantly) to muck up the energy and momentum accounting. Foreshadowing what most think is likely – that this particle is indeed a (or the) Higgs – a lepton collider designed for studying its properties is sometimes colloquially termed a “Higgs factory”.

In any case, the LHC experiments have plenty of work to do even ignoring this 125-GeV boson. (Although, the existence of the Higgs itself reinforces several major unsolved questions in particle physics.) Supersymmetry, new weak currents, “dark forces”, gravitons, quark-gluon plasma, strong CP, b physics, … the list of topics under investigation at the LHC is quite long. And outside of the LHC but still within experimental particle physics, you’ve got WIMPs, axions, questions of neutrino mass and mixing, precision “flavor” physics (looking for new physics at high mass scales though loop effects in low-energy measurements), evidence for sterile species, … and many more. These lists are supposed to mean much to you besides conveying a sense of the breadth of particle physics, popular science headlines notwithstanding. (However, feel free to ask about any of the individual jargon-y items listed.) Further, theoretical (as opposed to experimental) investigations underway are similarly numerous. And further further, this is just particle physics, which is just a fraction of all of physics research.

edit: “These lists aren’t supposed to mean much to you besides…”

I like it better the other way.

Before the LHC was operational, it was said that the most boring thing it could find was the Higgs, and nothing else. So far, that appears to be what we have. But there are a whole host of other hypothetical particles which it was believed that the LHC might discover, which would have been much more interesting. And those can’t be ruled out yet. Maybe if we run the machine for longer, we’ll luck out and get some of those. Maybe we’ve already found some, and we just have to tease the data a little more to realize it. Heck, maybe this new particle that we’ve definitely seen is actually one of those, and not the Higgs at all. And if nothing else, every particle physicist who predicted one of those other particles now gets to explain why we didn’t see that one.

Thanks all, for the responses. You’ve given me a lot to think about!

Scientific American had a blurb a few days ago, speculating that the Higgs Boson found is really two different particles with similar mass:

I do wonder whether a more likely possibility is a 123.5 GeV Higgs, causing the decays via Z, and half the photon decays*, and some other particle at maybe 129 GeV which only decays via the photons. How well could they discriminate between one particle or two particles of similar mass, given the data they have so far?

ETA: based on there being roughly twice as many photon decays as expected.

If this were the case, the H–>(photon)(photon) region in red in this figure from the linked article would have a different appearance. In particular it would show a two-lobed structure indicating that a “source” of di-photon events exists at both masses, whereas it actually shows the di-photon data as supporting masses centered around a single point.

A skew in the energy calibrations for the different decay products could lead to an apparent split. Of course the ALTAS collaboration has looked carefully at the potential systematic uncertainties on the energy scales and has estimated them to be smaller than the difference seen. But, 2.7-sigma discrepancies have a way of coming and going. As an aside, the CMS results don’t show this split and actually favor the opposite conclusion (that is, the ZZ channels lead to a higher best-fit mass in the CMS data). Nonetheless, definitely worth keeping an eye on as the data sets grow and as CMS puts out their own update in the near future.

In that figure for the H–>(photon)(photon) curves, is there an apriori assumption that there is a single particle? If you go to the “finally updated the two-photon results” link, there are a bunch of plots, some like the first one, which seems to assume a single particle for doing the fit.

Also, is there even enough data to back up that assumption? In that plot, there’s only five data points in the 120 to 130 GeV range.

Looks like the LHC is shutting down for maintenance and upgrades for a couple years after Feb 2013 to bring her up for higher energies, so until then there’s plenty of work to keep everyone busy mining the existing data. Seems we won’t be able to better resolve this particle until then (further interpretation and refining of existing data notwithstanding), such as determining its actual spin?

So, how much would confirming whether or not this particle has a spin of 0 or 2 affect the standing of being a Higgs particle?

Sort of. For each point in the 2D space, it is assumed that there is a single particle with that mass and signal strength. The goodness of each hypothesized point is evaluated against the data assuming a single particle. If there were two particles producing photons in roughly equal amounts, then the goodness would have two maxima, one near each favored mass. That is, each point is evaluated as a single particle, but there is nothing that constrains that figure to have only one favored location. Another way to say this: if there were two particles producing photons at roughly equal rates, the procedure for drawing those 2D plots has no way of knowing which to prefer, and it would show “goodness” at both, with some smooth variation in between.

To imagine an extreme case, consider this figure you linked to. Imagine that there was another clear peak at, say, 118 GeV. Since the red curve is showing one particular assumed mass, it would not trace through the data near 118 GeV. But when scanning across potential masses when making the 2D plot here, one would get similarly good fit scores when testing 118 GeV at those obtained when testing 126 GeV. The red region would be resultingly double-lobed.

In such a scenario, one would have to consult the absolute goodness-of-fit values to see that the one-particle hypothesis wasn’t as good as a two-particle hypothesis, but even without that, the 2D allowed regions would still reveal two favored regions, each evaluated as if it were the single source of photons.

There are a few hundred di-photon events over background in that region. ATLAS having binned those events into a histogram as they have won’t effect the present discussion or the statistical implications much at all. (The width of the peak is driven by instrumental resolution, and any second peak hiding within this binning wouldn’t show up as visible to the experiment as a separate peak anyway.)

The Higgs must be spin-0 in order for the vacuum expectation value of the Higgs field to obey Lorentz symmetry. Less jargon-y: If it’s not spin-0, then it’s not the Higgs. As for spin-2: that would be extra exciting, as that’s the spin expected for a graviton.

Although, a spin-2 particle with significant mass would be so far from the theoretical description of the graviton that we’d have to call it something else. Pretty much the only two things we know about the graviton are that it’s spin-2, and that it’s massless (or as close to it as makes no difference).

While it couldn’t be the simplest conceivable graviton, massive graviton excitations come up in higher-dimensional theories, of note Kaluza-Klein. These are usually the sorts of gravitons discussed in the context of LHC searches.

That would be very exciting indeed.

Those massive excitations are generally given other names, though, in the same way that hyperons are given different names from nucleons.

They are usually given qualifiers (“Randall-Sundrum graviton”, “Kaluza-Klein graviton”), but “graviton” is still used regularly in the parlance for massive particles (with “massless graviton” used in contexts where that particular particle is ambiguously discussed).

A little symbol for a big question with big answers: :confused:

I know about differences, horseshoes, grenades, etc. Depending on context–eg in neutrinos I’m comfortable (hah!) with this being said–but this intrigued me, when I read it literally in a statement in physics.