Higgs Boson – Can someone explain the Higgs-Boson particle?

I kind of know about it but want it in laymans terms.

Every object we see around us has the property we refer to as mass. We think of mass as the amount of matter in an object,and we recognise and describe its presence through observations of an object’s inertia , and the force required to accelerate it etc.We know that this mass comes from the mass of all the fundamental particles that such objects are made of and that the masses of these fundamental particles , vary enormously . But there is no obvious reason as to what mass actually is or why the fundamental particles have such a wide range of it.
The Higgs particle / field is believed to be the answer . The theory is that the universe is actually filled with Higgs particles /field and it is the varying degrees of the interaction of fundamental particles with the Higgs particles /field that gives rise to the property we call mass.

The Higgs boson is a massive scalar elementary particle predicted to exist by the Standard Model in particle physics. At present there are no other known fundamental scalar particles in nature.

The Higgs boson is the only Standard Model particle that has not been observed. Experimental detection of the Higgs boson would help explain the origin of mass in the universe. The Higgs boson would explain the difference between the massless photon, which mediates electromagnetism, and the massive W and Z bosons, which mediate the weak force. If the Higgs boson exists, it is an integral and pervasive component of the material world.

To understand the Higgs mechanism, imagine that a room full of physicists quietly chattering is like space filled only with the Higgs field
a well known scientist walks in, creating a disturbance as he moves across the room, and attracting a cluster of admirers with each step
this increases his resistance to movement, in other words, he acquires mass, just like a particle moving through the Higgs field
if a rumour crosses the room it creates the same kind of clustering, but this time among the scientists themselves. In this analogy, these clusters are the Higgs particles.

The Higg’s field interaction may be described as follows. 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)

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

Thus, the discovery of the Higg’s boson (some theories suggest that there are three such bosons) will complete the standard gauge model of elementary particles and their interactions.

There is an article about it below under “The search for God begins” – the 2nd link is a quicker one.

Its the god particle that only stays around for a few microseconds and has negligiable mass.


Tuesday, March 9th, 2010 Questions