Which are we most likely to observe at LHC: The Higgs Boson, The Graviton, Neutralinos, Hawking Radiation, ..?

Question

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The following is an article from The Economist print edition, entitled: "Known and unknown unknowns"; I think they have done a wonderful job of making some of these hairy issues [not to mention the reasons behind the very existence of LHC] conceptually available to the layperson. ... Enjoy!

http://www.economist.com/displayStory.cfm?story_id=11837478

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Answer 1

The LHC is intended to look for the Higg's boson and physics beyond the standard model of particle physics such as super symmetry and dark matter/energy candidates. The standard model does not predict that the LHC will produce mini-Black Holes; however, if physics beyond the standard model is found to hold, then mini-Black Holes might be possible. These mini-Black holes might be produced at a rate in the order of one per second. According to the some calculations, these ‘holes’ are harmless because they will quickly decay via ‘Hawking radiation’ and explode into a shower of particles. The problem with ‘Hawking radiation’ is that it too is unproven physics and, thus, might not be a correct explanation for the disappearance of mini-Black Holes. An unlikely, accumulation of mini-Black Holes could be a ‘small’ problem.

Below I will detail some of the physics that the LHC is attempting to explore.

The weak interaction is mediated by spin-1 bosons which act as force carriers between quarks and/or leptons. There are three of these intermediate vector bosons, which were all discovered at CERN in 1983. They are the charged bosons W+ and W- and the neutral Z0. Their masses are measured to be: -

M(W) = 80.3 Gev/c² and M(Z) = 91.2 Gev/c²

which gives their ranges as: -

R(W) ≈ R(Z) ≈ 2 x 10^-3 fm

Their decay modes are as follows: -

W+ -> l+ + vl

W- -> l- + vl'

Z0 -> l+ + l-

Where the l's stand for leptons and the v's for neutrinos with the prime ' indicating an anti-neutrino.

This introduction sets the scene for what follows!

The intermediate vector bosons gain their mass from the Higgs boson. Please allow me to explain.

During the nineteen-sixties the theoretical physicists Glashow, Salam and Weinberg developed a theory which unified the electromagnetic and the weak nuclear forces. This theory is known as the ‘electroweak’ theory, it predicted the neutral vector boson Z0, and weak nuclear force reactions arising from its exchange, in what are known as neutral current reactions. The theory also accounted for the heavy charged bosons W+ and W-, required for the mediation of all observed weak interactions, known as charged current reactions. These particles were discovered in 1983.This unified theory is a ‘gauge invariance’ theory, which means that if the components of its underlying equations are transformed, in position or potential, they still predict exactly the same physics. Because the force carrying particles (Z0, W+ and W-), of this theory, are massive spin-1 bosons a spin-0 boson is required to complete the theory. This spin-0 boson is the as yet unobserved ‘Higgs’ boson.

The masses of the force carrying bosons (Z0, W+ and W-), for the electroweak theory, are derived from their interaction with the scalar Higgs field. Unlike other physical fields, the Higgs field has a non-zero value in the vacuum state, labelled φ0, and furthermore this value is not invariant under gauge transformation. Hence, this gauge invariance is referred to as a ‘hidden’ or ‘spontaneously broken’ symmetry. The Higgs field has three main consequences’. The first, is that the electroweak force carrying bosons (Z0, W+ and W-) can acquire mass in the ratio: -

M(W) =cosθ(W)

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M(Z)

Where θ(W) Is the electroweak mixing angle. These masses arise from the interactions of the gauge fields with the non-zero vacuum expectation value of the Higgs field. Secondly, there are electrically neutral quanta H0, called Higgs bosons, associated with the Higgs field, just as photons are associated with the electromagnetic field. Thirdly, the Higgs field throws light on the origin of the quark and lepton masses. In the absence of the Higgs field the requirements of gauge invariance on the masses of spin-½ fermions (quarks and leptons etc,) would set them at zero for parity violating interactions (non-mirror image interactions). Parity is a conserved quantity in strong nuclear force and electromagnetic interactions but is violated in weak nuclear force interactions, which would make quark and lepton masses zero in this later case. However, interactions with the Higgs field can generate fermion masses due to the non-zero expectation value φ0 of this field, as well as with interactions with the Higgs bosons. These interactions have a dimensionless coupling constant g(Hff) related to the fermions mass m(f) by the expression: -

g(Hff) = √ (√2G(f)m(f) ²)

Where G(f) is the Fermi coupling constant and f is any quark or lepton flavour. However, this theory, that the fermion masses are mediated by their interaction with the Higgs field, does not predict their mass m(f). However, with the future discovery of the Higgs boson the above equation can be used to confirm the observed coupling constant g(Hff).

At CERN, the Large Hadron Collider (LHC) will search for the Higgs boson at an energy of up to 1 TeV by colliding protons in the reaction: -

p + p -> H0 + X

Where X is any state allowed by the usual conservation laws.

The upper atmosphere is a more energetic 'particle physics laboratory' than the LHC. If cosmic rays, slamming into the upper atmosphere, create mini-black holes then these decay rapidly! However, it may be that mini-black holes are not produce - at all - in high-energy particle collisions.

Answer 2

Well, I was going to guess the Higgs Boson, but not nearly as articulate as Dave. Although I had previously speculated that there would be no observation since it would end our universe. Admitiingly, I haven't worked out the details. :-)

Answer 3

the higgs boson for sure.

the problem with the graviton isnt that we dont having something strong enough to make it, its that we dont have something sensitive enough to detect it. and that it most likely doesnt exist.

hawking radiation can only be observed with a black hole were created in the LHC. and as ive stated many many times in other questions. the LHC would have to multiply its maximum power output by 10 trillion to create a black hole.

neutralinos could be created at the LHC since they would a mass of 100 GeV to 1 TeV, which is well within the energy range of the LHC. but it depends what type of neutralino is created that would determine if we discovered it. and this all depends on supersymmetry being true.

EDIT: dont put too much faith in what that article says. it says the LHC will create black holes, it will not.