How Many Particles Have Been Discovered At CERN?

Question

I need to find uot for my homework for A Level Physics, but cannot find it anywhere on the internet. This is my last resort!

I am not a slakcer as I have already written over 1 and a half pages about the detectors at CERN and the experiments they did.

A list of the particles would be most helpful

Thanks in advance

Tom G

Answer 1

According to Wikipedia, '

Several important achievements in particle physics have been made during experiments at CERN. These include, but are not limited to, the following.

1973: The discovery of neutral currents in the Gargamelle bubble chamber.



1983: The discovery of W and Z bosons in the UA1 and UA2 experiments.



1989: The determination of the number of neutrino families at the Large Electron Positron Collider (LEP) operating on the Z boson peak.

1995: The first creation of antihydrogen atoms in the PS210 experiment.



1999: The discovery of the direct CP-violation in the NA48 experiment.



The 1984 Nobel Prize in physics was awarded to Carlo Rubbia and Simon van der Meer for the developments that led to the discoveries of the W and Z bosons.'

Turning to the future: -

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, as you know, 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)

_____

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 t