Wednesday, December 14, 2011

"The God Particle": How Big a Deal?

Well, the latest news (e.g. WSJ, today, 'Physicists Close in on a Universal Puzzle', p. A6) is that the particle colliders at CERN (using the LHC or 'large hadron collider;') are "closing in" on the fulsome-named "God particle" (actually the Higgs boson). This is based on claims that the last few weeks have seen "an excess of events around 125 GeV" - that is, giga-electron volts of energy where 1 eV = 1.6 x 10^-19 J so that 1 GeV = 10^9(1.6 x 10^-19 eV) = 1.6 x 10^-10 J.

But when all is said and done, how big a deal is finally detecting the Higgs, really? Well, we are told that the Higgs us the only particle that the Standard Model of cosmology (and indeed, physics) says should be there in exist...because it "ties together all others" and describes (or would using the Standard Model basis) how all other particle interact.

Elaborating - this so-called 'Standard Model' is generally defined as the symmetry:

SU(3) x SU(2) X U(1)

where each of the above denotes a specific matrix, or more exactly a group. See, e.g.

In the case of SU(2) we describe it as the "special unitary group" which has the form:

S =


where a*, b* are complex conjugates and we have (aa* + b*b) = 1. Thus the elements of SU(2) are the unitary 2 x 2 matrices with DET (determinant) = 1. These groups thus define the behavior of a specific class of subatomic particles.

Spontaneous symmetry breaking would therefore resolve this combination into constituent parts, e.g.: SU(3) associated with the 'color force' of quarks, SU(2) x U(1) associated with the electro-weak force.

One possible symmetry breaking (quark -boson format) is:

SU(3) x SU(2) X U(1) -> SU(3) + SU(2) x U(1)

which would occur at a particular ambient temperature (T_qb) for the universe at some epoch (E_qb) in the past. In the foregoing, the synthesis of SU(2) and U(1) into the locally gauge invariant electro-weak theory requires a mechanism which confers mass to three vector bosons while leaving the photon massless. This 'mass-giving' mechanism is called the Higgs Field or Higgs mechanism, and it demands the existence of one or more massive, spin-0 bosons otherwise called Higgs bosons.

The problem is, of course, that the Higgs boson remains hypothetical until formally detected (and confirmed!). Because it is hypothetical only, the Standard Model cannot be said to be complete. Therein lies the hype and the hoopla. Obviously also, since no one knows a priori what the mass of the Higgs might be, it must be hunted indirectly with ginormous collision machines such as the LHC.

But to show how commentators and even physicists can be led astray, one need only read from the WSJ piece (in synch with the earlier noted "mechanism" to leave the photon massless, that if the Higgs was found it would:

"help explain why some objects in the universe - such as the quark- have mass,.....while other objects - such as photons, the constituent of light, have only energy."

But is this really true? Consider that from very early in the last century the phenomenon of "radiation pressure" was known to exist, and it had to arise as a result of some finite (albeit tiny) mass of the individual photons. The very first experiment to detect radiation pressure was performed by the Russian physicist P. Lebedev in 1901, but the real effect was smothered by the '"radiometer effect". (This is the one associated with toy radiometers which possess one side of their rotating vanes black, which absorbs incident radiation and thereby experiences a slight push from the adjacent air-gas.) Unless a vacuum is quite good, it can swamp the real radiation pressure effect. Moreover, such specious radiometers always revolve the wrong way from what a genuine radiation force would produce.

By 1923, Gerlach and Golsen ('Zeitschrift fur Physik', Vol. 15, pp. 1-7) produced the first "clean" measurement of radiation pressure using a vacuum better than 10^-6 torr (where 1 torr = 1mm of mercury at 0 Celsius, and standard atmospheric pressure is 760mm of Hg). Their experiment was basically a test of the relationship:

c = W(1 + rho)/ F

where c was the (already established speed of light, or c = 2.998 x 10^8 m/s, W is the incident power in hundredths of a watt, rho is the reflection coefficient for the material used for the vanes (e.g. rho = 0.60 for platinum, 0.43 for nickel, 0.81 for aluminum), and F is the measured force on the vanes in 10^-10 newtons.

Gerlach and Golsen in five trials obtained an average for c of 2.98 x 10^8 m/s and to produce this generated incident power ranging from 2.78 to 6.39 x 10^-2 watts, and a measured force from 1.74 x 10^10 N to 3.14 x 10^-10 N. These results directly led to the momentum relation for photons of E = pc, where p is the momentum. Hence, if the photon has momentum - and it must to produce the force for radiation pressure, then it must have mass.

How much? Fortunately, many more refinements of differing measurement methods have enabled us to at least put a good estimate on the photon mass.

In the reference 'Gravitation and Spacetime', 2nd ed., Ruffini and O'Hanian give the UPPER limit of the photon's mass as:

m_ph < 10^-59 g

This is based on possible deviations from Maxwell's equations. Readers can see other limits - derived from experimental and galactic magnetic data here:

The limit of (7 x 10^-17 eV) cited in one experiment (by Roderic Lakes in 1998) is actually about 7 orders of magnitude larger than the limit set by Ruffini and O'Hanian. However, it is much smaller than the 3 x 10^-27 eV limit..So it seems that the Ruffini & O'Hanian value is probably a reasonable limit from a number of perspectives.

Given this, we hope the CERN collision specialists appreciate the context here. And also, are able to address the question: what constraints are to be placed on the Higgs if the photon is not absolutely massless? The words of one physicist, Dr. Soldner-Rembold of the University of Manchester, echo loudly here (ibid.):

"It would perhaps be even more exciting if it (Higgs) isn't where it's supposed to be. Then we'd have to come up with something else."

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