Having completed the first part of my series on the Large Hadron Collider (LHC) -- pertaining to the workings of particle colliders -- it's time to move on to the second part, dealing with new particles (or types of particles) physicists will be looking out for.
The first priority would appear to be discovery of something called a Higgs boson. A New York Times article on the LHC from May 15, 2007 notes that: “The new collider was specifically designed to hunt for the Higgs particle, which is key both to the Standard Model and to any greater theory that would supersede it.”
Tonight's entry will first detail what a field of Higgs particles is hypothesized to embody, drawing from Brian Greene's (2004) book The Fabric of the Cosmos. How a Higgs boson is likely to be detected -- which was already touched upon in my previous, July 14, 2007, entry on particle detection in connection with an online interactive activity called “The Hunt for Higgs” -- will next be addressed briefly. Finally, the implications of various potential findings at LHC regarding the Higgs will be addressed.
Envisioning what a Higgs field is
What I grasped about Higgs fields from Greene's book is that two key areas of theoretical interest they address are: differential masses of different types of particles; and unification of different forces of nature.
Higgs fields create barriers to the movement of other kinds of particles, with different types of particles encountering different degrees of resistance. The more resistance a type of particle encounters, the more mass it is said to have. Higgs fields have been analogized to molasses or a bunch of paparazzi photographers. As Greene explains:
If we liken a particle's mass to a person's fame, then the Higgs ocean is like the paparazzi: those who are unknown pass through the swarming photographers with ease, but famous politicians and movie stars have to push much harder to reach their destination (p. 263).
Greene also notes that:
Photons pass completely unhindered through the Higgs ocean and so have no mass at all. If, to the contrary, a particle interacts significantly with the Higgs ocean, it will have a higher mass. The heaviest quark (it's called the top quark), with a mass that's about 350,000 times an electron's, interacts 350,000 times more strongly with the Higgs ocean than does an electron; it has greater difficulty accelerating through the Higgs ocean, and that's why it has a greater mass (p. 263).
In terms of unifying the different forces, Greene discusses how photons ("messenger particles" of the electromagnetic force) and W and Z particles (particles of the weak nuclear force) were indistinguishable at one point (known as "electroweak unification"), but are now considered to be different, due to the influence of the Higgs field.
Glashow, Salam, and Weinberg:
...realized that before the Higgs ocean formed, not only did all the force particles have identical masses -- zero -- but the photons and W and Z particles were identical in essentially every other way as well... At high enough temperatures, therefore, temperatures that would vaporize today's Higgs-filled vacuum, there is no distinction between the weak nuclear force and the electromagnetic force... The symmetry between the electromagnetic and weak forces is not apparent today because as the universe cooled, the Higgs ocean formed, and -- this is vital -- photons and W and Z particles interact with the condensed Higgs field differently. Photons zip through the Higgs ocean... and therefore remain massless. W and Z particles... have to slog their way through, acquiring masses that are 86 and 97 times that of a proton, respectively (excerpts from pp. 264-265).
A common term used to describe this phenomenon is "symmetry breaking."
Detecting the Higgs
The Higgs boson is posited to decay into other particles, thus forcing scientists to look for a "signature" indicative of the Higgs. This Physics World article (especially the section entitled, "Getting to know the Higgs") goes into further detail, such as in the following excerpt:
The Higgs signature depends on its mass. A relatively light Higgs with a mass of about 120 GeV will decay into pairs of B-mesons, tau leptons or photons, which will be easy to produce but hard to detect among the background of other processes and particles. If the Higgs is heavy, about 160 GeV, it will decay to pairs of W or Z bosons. These will be harder to produce, says [CERN's Jos] Engelen, but easier to spot. If there is no Higgs mechanism, the LHC will see scattering events between pairs of W bosons that would otherwise be "absorbed" by the standard Higgs mechanism.
Implications of possible Higgs-related findings
The March 23, 2007 issue of Science ran a spread of articles on the LHC, including one entitled "Physicists' Nightmare Scenario: The Higgs and Nothing Else." Probably the most succinct summary of the situation is revealed in the following quote:
Discovering the Higgs would complete the standard model. But finding only the Higgs would give physicists little to go on in their quest to answer deeper questions, such as whether the four forces of nature are somehow different aspects of the same thing... (pp. 1657-1658).
Were the LHC to find additional types of new particles, such as supersymmetric superpartners, or evidence of extra dimensions, for example, these would provide strong stimuli for further theorizing and discovery. Or, as the Science article notes:
If, on the other hand, the LHC sees no new particles at all, then the very rules of quantum mechanics and even Einstein's special theory of relativity must be wrong... (p. 1657).
For background on the Standard Model of particle physics, which the Higgs boson would round out, see this review I wrote of a book on the topic.