- Higgs boson discovery
This one is obvious: the Higgs tops the ranking not only on Résonaances, but also on BBC and National Enquirer. So much has been said about the boson, but let me point out one amusing though rarely discussed aspect: as of this year we have one more fundamental force. The 5 currently known fundamental forces are 1) gravitational, 2) electromagnetic, 3) weak, 4) strong, and 5) Higgs interactions. The Higgs force is attractive and proportional to the masses of interacting particles (much like gravity) but manifests itself only at very short distances of order 10^-18 meters. From the microscopical point of view, the Higgs force is different from all the others in that it is mediated by a spinless particle. Résonaances offers a signed T-shirt to the first experimental group that will directly measure this new force. - The Higgs diphoton rate
Somewhat disappointingly, the Higgs boson turned out to look very much as predicted by the current theory. The only glitch so far is the rate in which it decays to photon pairs. Currently, the ATLAS experiment measures the value 80% larger than the standard model prediction, while CMS also finds it a bit too large, at least officially. If this were true, the most likely explanation would be a new charged particle with the mass of order 100 GeV and a large coupling to the Higgs. At least until the next Higgs update in March we can keep a glimmer of hope that the standard model is not a complete theory of the weak scale... - Theta-1-3
Actually, the year 2012 was so kind as to present us not with one but with two fundamental parameters. Except the Higgs boson mass, we also learned about one entry in the neutrino mixing matrix, the so-called θ_13 mixing angle. This parameter controls, among other things, how often the electron neutrino transforms into other neutrino species. It was pinpointed this year by the neutrino reactor experiment Daya Bay who measured θ_13 to be about 9 degrees - a rather uninspired value. The sign of the times: the first prize was snatched by the Chinese (Daya Bay), winning by a hair before the Koreans (RENO), and leaving far behind the Japanese (T2K), the Americans (MINOS), and the French (Double-CHOOZ). The center of gravity might be shifting... - Fermi line
Dark matter is there in our galaxy, but it's very difficult to see its manifestations other than the gravitational attraction. One smoking-gun signature would be a monochromatic gamma-ray line from the process of dark matter annihilation into photon pairs. And, lo and behold, a narrow spectral feature near 130 GeV was found in the data collected by the Fermi gamma-ray observatory. This was first pointed out by an independent analysis, and later confirmed (although using a less optimistic wording) by the collaboration itself. If this was truly a signal of dark matter, it would be even more important than the Higgs discovery. However past experience has taught us to be pessimistic, and we'd rather suspect a nasty instrumental effect to be responsible for the observed feature. Time will tell... - Bs-to-μμ
This year the LHCb experiment finally pinpointed the super-rare process of the Bs meson decaying into a muon pair. The measured branching fraction is about 3 in a billion, close to what was predicted. The impact of this result on theory was a bit overhyped, but it's anyway an impressive precision test. Even if "The standard model works, bitches" is not really the message we wanted to hear... - Pioneer anomaly
A little something for dessert: one long standing mystery was ultimately solved this year. We knew all along that the thermal emission from Pioneer's reactors could easily be responsible for the anomalous deceleration of the spacecraft, but this was cleanly demonstrated only this year. So, one less mystery, and no blatant violation of Einstein's gravity in our solar system...
Particle Physics Blog
Monday, 31 December 2012
2012 Highlights
One can safely assume nothing else important will happen this year... so let's wrap up. Here are the greatest moments of the year 2012, from the point of view of an obscure particle physics blog.
Fermi line: no mention of what the collaboration really expressed? This is most probably a systematic effect. To be forgotten in 2013.
ReplyDelete
ReplyDeleteIs the new Higgs Force a ficticious force?
Fermi said they do see it but they're not sure if it's real. So it could go either way.
ReplyDeleteof course it won't be any worse, there's no new data at all for 2013!
ReplyDeleteSo there is a "Higgs force" between two particles at close range? Is it possible to say something as simple as "it is an attractive force" or "it is a repulsive force"? Or is it too different for that kind of thinking?
ReplyDeleteIt's a legitimate attractive force. However for the particles that make matter around us (light quarks, electrons) it's much much weaker than the weak force, so probably it can never be measured.
ReplyDeleteJester, on the digamma excess rate you say:
ReplyDelete"If this were true, the most likely explanation would be a new charged particle with the mass of order 100 GeV and a large coupling to the Higgs"
Are you talking here about a doubly charged Higgs or something else? A doubly charged Higgs would have left its signature in the Bs to dimuon channel, which we know it is ruled out by the latest reports. In any event, shouldn’t a new charged particle with mass around 100 GeV and strongly coupled to the Higgs affect other decay channels?
It doesn't have to be doubly charged, anything that has charge would do (of course, the bigger the charge, the larger effect, keeping all other parameters constant). Also, it doesn't have to be a part of the Higgs sector, it doesn't even have to be a scalar. If the particle has charge but no color it won't affect other decays than to gamma-gamma (except maybe Z-gamma). In specific models, like type-II 2HDM there would indeed be strong constraints on the charged Higgs from Bs to mu-mu, and b to s gamma, but that's model dependent. Certainly, a 100+ GeV charged particle cannot be excluded in a model independent way.
ReplyDelete
ReplyDelete"It's a legitimate attractive force. However for the particles that make matter around us (light quarks, electrons) it's much much weaker than the weak force, so probably it can never be measured."
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Or it is ficticious in every sense of the word?
How could we ever know scientifically?
good comments ! Thanks !
ReplyDeleteOther than the appearance of a scalar boson resonance between 100GeV and 800 GeV, are there scientific tests of the hypothesis that the Higgs Mechanism is something real and not a just-so story?
ReplyDeleteThis is not pure facetiousness, but a serious question that I hope others will answer, or attempt to answer.
I suspect that it's only reasonable to address the question above once 1) the anonymous poster proves that he or she actually exists and isn't just a fluke, 2) once the 800 GeV second Higgs shows up. ;-)
ReplyDeleteJester,
ReplyDeleteIf the center of gravity is shifting towards Asia, does that have any implications for the Jester Exclusion Principle?
Cheers,
Steve
Hmmm, since bosons and fermions are already taken that only leaves anyons to the Asians.
ReplyDelete"It's a legitimate attractive force. However for the particles that make matter around us (light quarks, electrons) it's much much weaker than the weak force, so probably it can never be measured."
ReplyDeletewell, there are also gluons that form ordinary hadronic matter such as nucleons: since the Higgs couples to gluons (via loop of top quarks) it has a coupling to nucleons that is an order one number times the nucleon mass in units of the EW scale. Summing coherently for heavy nuclei over the nucleons, and you will end up with a sizable attractive force. The problem is instead the short range.
I think the biggest problem is not the short range but the fact that there's no particle that interacts only via the Higgs force and nothing else. The weak force is also short range but we have neutrinos as test particles - we can shoot neutrinos at a target and see that once in a while they get deflected. In your example of NR scattering on nucleons, whatever test particle we use the Higgs force will always be negligible compared to the EM, weak or strong forces involved. But if we had e.g. a dark matter particle that interacts only via the Higgs forces, that would be a different story :-)
ReplyDeleteIf there is a fifth force proportional to mass, then there are three types of masses, namely, inertial mass, gravitational mass, and Higgsian mass. What is the equivalence principle that makes Higgsian mass numerically equal to the other two?
ReplyDeleteTo the last anon: as I understood it, the "higgs charge" that a particle has gives it mass because its interaction with the higgs field gives it potential energy, and energy is equivalent to both inertial and gravitational mass according to relativity.
ReplyDelete> higgs field gives it potential
ReplyDelete> energy, and energy is equivalent
> to both inertial...
No, the existance of the higgs field explains the source of inertial mass. But it still doesn't explain why objects have gravitational mass, any why this gravitational mass is proportional to inertial mass.