First Definitive Higgs Result In 7 Years 197
PhysicsDavid writes "In a suite of new results about the Higgs boson, Fermilab presents the first new definitive evidence on the (lack of) existence of the Higgs boson since the Large Electron Positron collider shut down in 2000. Fermilab hasn't found the Higgs, but can rule out a certain range of masses for the particle that is believed to create mass for all the other particles of nature. Other Higgs news suggests a new likeliest mass range of 115 to 135 GeV for the Higgs. These results were among those presented at the ICHEP 2008 conference currently wrapping up in Philadelphia."
Higgs (Score:5, Informative)
Knowing the mass of the higgs is important because it tells us which of our theories is on the right track. For example, a very large higgs would rule out huge branches of string theory, almost killing it. Not finding it at all would rule super symmetry would destroy the standard model, with nothing left to stand it in place.
The 'worst' case is that we find the higgs exactly where we expect it to be, confirming what we pretty much knew already, without adding any new real information.
Re:Overheard at the LHC (Score:5, Informative)
Re:Newbie question (Score:5, Informative)
The electron volt [wikipedia.org] is a measure of energy. It is the energy gained by an electron accelerating through an electric field potential of one volt. And since energy and mass are equivalent [wikipedia.org], this miniscule measure of energy also makes for a useful miniscule measure of mass.
Re:Newbie question (Score:3, Informative)
It's a unit of energy that particle physicists use instead of mass. One eV is an electron-volt which is equal to the energy gained by an electron after being sent through a one volt potential. You can use E = m c^2 to convert between energies and masses.
Very misleading headline (Score:4, Informative)
Not to diminish the importance of the work done at Fermilab, but the headline is very misleading.
Re:Newbie question (Score:1, Informative)
Re:135 GeV seems very high... (Score:2, Informative)
Re:GeV = mass? (Score:4, Informative)
And 1 GeV = 1.783×1027 kg
Slashdot ate your formatting it looks like. I'll write it as 1.783E-27 kg to get around it.
Re:GeV = mass? (Score:3, Informative)
That would be 10^-27 kg, a very small number, not 1027 kg.
Re:135 GeV seems very high... (Score:5, Informative)
In these theories, mass arises of interactions with the Higgs boson. Thus, the Higgs being massive doesn't exclude less massive particles.
Re:135 GeV seems very high... (Score:3, Informative)
If particle masses were an additive quantity based on the mass of the Higgs, as your intuition seems to tell you, then as long as there are massless particles like the photon, then the Higgs would also have to be massless and, by induction, so would every other particle we observe.
Re:135 GeV seems very high... (Score:4, Informative)
Thanks for that hint, I've now found the Higgs mechanism [wikipedia.org] which is currently in the process of giving me a headache.
Re:135 GeV seems very high... (Score:4, Informative)
Having a degree in physics means nothing if you didn't do
anything in this branch of physics.
That seems a bit strong. A physics degree does mean that you can
reasonably expect an explanation to be understood without too much
effort on your part.
First off, the electron is not the lightest particle. Strictly
speaking, the electron neutrino weighs in at less than 2.2 eV, where the
electron weighs in at 0.511 MeV. Then you have the tau neutrino, which
weighs in at 15.5 MeV. Then you have the proton, which weighs 938 MeV.
After that we have the tauon, which has a mass of 1.7 GeV. All of which,
so far, are leptons.
I can see where you're going, but you made a careless error. The proton
is not a lepton.
In the standard model, leptons and quarks are fundamental particles.
Leptons and quarks are reflections of each other through a certain
symmetry. But a quark never appears by itself. A quark-antiquark pair
is called a meson (which is a boson because it has whole-integer quantum
spin), and a triplet of quarks, like a proton or neutron, is called a
baryon (which is a fermion because it has half-integer quantum spin). A
hadron is any particle that interacts through the strong force; this
includes mesons and baryons but not leptons.
Re:Nothing to see here... (Score:5, Informative)
Incidently, why is 115 GeV so hard for the LHC to see. Well at this point the Higgs is too light to decay to WW or ZZ (the W has mass of 80 GeV, Z 91GeV so needs Higgs mass of 160-180 GeV to open those channels). This means that a light Higgs of 115 GeV will decay into the heaviest particle availible to it (remember the more massive the particle, the strong the Higgs coupling) which is the bottom quark. At the Tevatron, the backgrounds to two bottom quarks isnt soo bad and the experimenters are all very experienced at tagging b quarks using their detectors. At the LHC you might as well give up so you have to go through the very rare vector boson fusion channel using a top quark loop to get two photons which itself has a bit of nasty background. Hence you will need 10 fb-1 of data which is *atleast* a years running at the LHC.
An update and a correction (Score:5, Informative)
At the Tevatron, the backgrounds to two bottom quarks isnt soo bad and the experimenters are all very experienced at tagging b quarks using their detectors.
Actually the background for b quarks at the Tevatron is ENORMOUS. b-quarks are produced by the strong interaction at rates far higher than they are produced from any possible Higgs decay. Identifying them is only half the problem: determining what produced them is the other half! The only way that we can see anything is via associated production of a Higgs and a W or Z boson (which are a lot easier to spot). This is a far rarer process than simple Higgs production.
At the LHC you might as well give up so you have to go through the very rare vector boson fusion channel using a top quark loop to get two photons which itself has a bit of nasty background.
You are actually a little out of date here. While the vector boson fusion channel is still used the decay is actually Higgs to two taus or VBF Higgs production with the two associated quarks being top quarks. At least in ATLAS we think that both of these channels will have a higher significance than the photon channel which was the original choice for a low mass Higgs.
Re:Horribly Inelegant (Score:2, Informative)
Occam's Razor would indeed say that, if it wasn't the case that the Standard Model is a very well tested model for particle physics.
The Higgs mechanism is part of the Standard Model. One of the predictions of this Model is that the quantum of the Higgs field, the Higgs boson, exists. Unfortunately, if it doesn't, it means something has gone seriously wrong with the model, because it's been successful in explaining a great many things.
Re:Nothing to see here... (Score:4, Informative)
FAIL.
Try again.
They filled it with a ton of European magnets (that worked), Japanese detectors (that worked), and US final focus magnets (that failed).
Sorry to burst your patriotic bubble.
Re:Horribly Inelegant (Score:3, Informative)
> Am I the only one who sees a problem with the circular logic
Apparently, yes.
For one thing, it's "extra mass", not "mass". The mass of the electron is fully accounted for by it's self-energy. If you integrate the EM field energy over the electron's field, then apply E=mc^2 to that result, you get the right answer.
Higgs is only needed for particles that do not follow this rule, like quarks. Quarks are heavier than their otherwise obvious self-energy can explain. So we postulate another form of "charge" (sort-of) that these particles interact with. "Charges" are transmitted by mediator particles, so if we postulate a new charge, we postulate a new particle to go with it. And since that guy was Higgs, we have the Higgs particle.
The fact that the Higgs itself would have mass is not at all interesting, any more than saying it's circular to suggest that electrons are effected by electric fields.
Maury
Re:Higgs (Score:3, Informative)
If so, then it could be argued that the complex Ptolemaic explanation is equally valid because it is actually equal, just expressed in a needlesly complex way...
It is a perfectly valid description of celestial motion. It fails Occam's Razor and provides no insights, but it is a perfectly valid description.
An interesting analogy (that goes fairly far): Epicycles are the digital description (sampling) of the analog ellipse. Given enough cycles (bits + sample rate), the result can reproduce the described motion to any arbitrary precision.
Epicycle description is to ellipse as digital recording is to analog waveform.