 |
| Peter Higgs |
On July 4, 2012 CERN
announced the discovery of Higgs Boson, existence of which was predicted by
Peter Higgs, Francois Englert and Robert Brout nearly fifty years ago. Higgs
presented his finding at Institute for Advanced Study in Princeton in 1964.
Brout didn’t live long enough to share the Nobel glory with Peter Higgs and Francois Englert next year in 2013; he died in 2011; he didn’t even live long enough to know the discovery of the elusive particle that is dubbed as God particle by Leon Lederman, he himself a particle physicist, a Nobel laureate and above all a good writer.
 |
| Englert & Brout |
It was Leon
Lederman (and reading his three books) got me interested in reading (reading
and understanding are different things, but one got to have some basic understanding, real or perceived, in order to write) particle physics a few years ago, but that
should be a different post.
Why is Higgs
boson such a big deal?
Why is Higgs boson such a big deal? Without it the whole universe will be
non-existent. To say all
particles have a mass is just assumed. The
universe came into being after the Big Bang nearly 14 billion years ago, evidence
of which has produced several Nobel Prizes in physics.
The origin of mass of a particle puzzled the best and the brightest of
physicists throughout the ages. Higgs boson is one that gives fundamental/elementary particles mass. Standard Model (the ultimate theories of
particle physics, a collective wisdom) postulates that the Higgs field is the
source of mass for fundamental particles.
Massive particles feel a sort of drag as they pass through Higgs field.
Why the Higgs
boson matters?
Isidor Isaac Rabi was awarded a Nobel Prize in physics (nuclear magnetic
resonance) in 1944. Shortly before his
death in 1988 he had MRI (magnetic resonance image). He said, “I saw myself in
that machine, I never thought my work would come to this,” nobody saw that
coming. It is hard to predict where the
irresistible and inexorable progress of science will lead us.
Rabi returned to the U.S. in 1929 when Columbia University offered him a lectureship, a job recommended by Werner Heinsburg, who was then on his lecture tour there. Leon Lederman (the one got me interested in reading particle physics) had high praise on Rabi in his Nobel Lecture, stating without Rabi he couldn’t have done what he did at Columbia University.
When Michael Faraday was working on electricity; he
discovered the laws of electromagnetic induction. Gladstone (then Chancellor of the Exchequer,
the future Prime Minister, a great Lincoln admirer, whose first order of
business when he retired from politics was to see Lincoln’s birthplace in Kentucky)
asked him, “
But after all,
what use is it?” Faraday’s response was, “Why, Sir, there is every
probability that
you will
soon be able to tax it.” A great man with a great vision; he saw things
beyond the ordinary mortals did.
The examples abound; let’s stop here for the interest of
the length of this post.
Even if the particle physics in general or Higgs boson in
particular won’t lead to any practical fruition in our life time. Let’s make it
“science for science’s sake”, as opposing to Oscar Wilde’s “art for art’s sake”
aesthetics.
If I still cannot convince you of the importance of Higgs boson,
I hope Carl Sagan could when he said, “everyone you love, everyone you know,
everyone you ever heard of, every human being who ever was, live out their
lives on the blue pale spot we know as Earth—and none of it would have ever
existed without the Higgs boson.”
Why the Higgs
boson matters to
physicists?
Physicists always tried to unify all the four forces (more
later) that govern the Standard Model of particle physics (more later). Steven Weinberg and others worked on
reconciling the electromagnetic and nuclear weak forces into a unified theory in
1960s.
We know the mass-less photon is the one carrying the
electromagnetic force, so they have to come up with a comparable particle to carry
the nuclear weak force, and they are W and Z bosons. But these physicists “hit a snag”, as W and Z
bosons have masses, which is incomparable to the photons that have no
mass. This is against the basic rule/law
of not being “symmetric”, thus not a unified theory.
The Higgs bosons come to the rescue. When the Higgs field interacts with W and Z
bosons, the Higgs field breaks the symmetry that would have kept W and Z
bosons massless. In other words, W and Z
bosons would have been massless had it not been exposed to Higgs field, so the fact of W and Z bosons being massless was masked by Higgs field/Higgs boson.
Without the mass, electrons wouldn’t “hook up” with the
nuclei to form the atom, the building block of life, of everything the All
Mighty created, although I think, it took more than seven days. “That would mean no valence bonding, so much
of chemistry, essentially all, would vanish.
Therefore no solid structure, no template for life.” (by a physicist at
Fermi National Accelerator Lab).
And again it is the Higgs bosons that given electron mass.
Approach the
elementary particles in a systemic and coherent way
There are many ways to look at the subatomic particles. One way is through the property of “strongly
interacting”—strongly interacting with strong nuclear force.
God created only four forces that we came to know: (1)
gravity, (2) electromagnetism, (3) strong
nuclear force (the force of interest to this post), (4) weak nuclear force, which is responsible for
radioactive decay.
All the elementary particles can be classified into three
groups:
(1) Non-strongly interacting particles
(2) Strongly interacting particles
(3) Bosons or strictly force-carrying particles
Leptons: non-strongly
interacting particles
These particles do not interact with the strong nuclear
force, thus not confined inside the nucleus.
There are lighter-in-mass, comparing to proton and neutron, which are
“strongly interacting particles”; they are dubbed with the “light ones”; thus lepton in Greek.
There are three kinds of charged leptons (electron, muon,
tau) and three kinds of neutral leptons (electron neutrino, muon neutrino, tau
neutrino).
Quarks:
strongly interacting particles
The Higgs boson was discovered in the Large Hadron Collider
(LHC) at CERN. Hadron is a composite,
not elementary, particle, such as proton and neutron. The constituents of hadron are quarks.
Gluon (a force-carrying boson) holds quarks together inside
the hadron.
Bosons:
force-carrying particles
Bosons have no mass; they create electromagnetic and
gravitational field. Examples are photon
(particle of light), gluon (holds the quarks together inside hydron), graviton
(particle of gravitation, a hypothetic one), W boson and Z boson that carry the weak nuclear force.
All bosons are force-carrying particles, except Higgs
boson, which should be placed here. As I
mention above, Higgs boson is the one that gives fermions (include leptons and
quarks) mass. But, who gives the Higgs
boson mass? That is a good question, which also means there is no good
answer. Not yet.
Another approach
to classify elementary particles
Another way to classify elemental particles is to separate
them into matter and force. Matter has mass occupies space whereas the force-carrying
particle has no mass and occupies no space.
Fermions: the subatomic particles that have mass
The subatomic particles that have mass are called fermions (after my Italian American hero,
Enrico Fermi), which include quarks (strongly interacting
with strong nuclear force) that are constituents of hadrons and leptons (not interacting
with strong nuclear force) which include charged leptons (electron, muon and
tau) and neutral leptons (electron neutrino, muon neutrino, and tau neutrino).
Bosons: the force-carrying particles
that have no mass
(see above)
Quarks are constituents of hadrons, the likes of
proton and neutron
 |
| Murray Gell-Mann |
There are so many hadrons (strongly interacting particles) that
led the particle physicists to think they couldn’t be elemental/fundamental
particles. Murray Gell-Mann first
proposed quark model in 1964 that subsequently proved quarks are indeed
constituents of hadrons. George Zweig
independently came to the same conclusion, but calls it [quark] “aces”. Zweig
somehow didn’t share the Nobel glory with Gell-Mann in 1969.
Murray Gell-Mann’s 1969 Nobel Lecture is somehow not
available in the nobel.com site, but one can listen to an interview that took
place in 2001, in which he did say the “quark” came from James Joyce’s “Finnegan’s Wake”, the book I checked out
twice and couldn’t finish the first chapter; I will not pick it up again.
Let this post serve as an introduction of particle physics
in general and Higgs boson (the God particle, if you will) in particular.