Beyond the God Particle (40 page)

Dark matter therefore remains a mysterious quarry of the two conjoined sciences of cosmology and particle physics of our present day. So, these two sciences—particle physics, the ultimate microscopy, and cosmology, the ultimate “telescopy”—very much overlap, as they did in the era of Hans and Zacharias Jannsen and of Galileo, as the optical microscope and telescope were developed side-by-side. These sciences are intimately connected and symbiotically benefit from one another. Dark matter definitely informs us that there are things out there that we do not yet understand and that go beyond the philosophy contained in our Standard Model. There definitely is something beyond the Standard Model and beyond the Higgs boson. And there are so many unanswered questions within the Standard Model that clearly some deeper organizing principle(s) lie beyond it.

In many ways, cosmology is like studying the fossil record of dinosaurs, learning what once existed and what questions such things may pose for the overall structure of particle physics. Cosmology is an essential subdiscipline of modern physics. However, if you want to study the detailed processes that define what we call active “life,” you need to go into the biology lab and use electron microscopes. Likewise, to understand what the basic constituents of matter are, and what the forces that control them are, you need to build a powerful particle accelerator, like the LHC or Project X, eventually, perhaps, a Muon Collider.

THE UNHEALTHY WEALTHY STATE

The health and wealth of nations critically depends upon the activity of basic research, including the seemingly more abstract construction of powerful particle accelerators. It is a no-brainer that powerful and able governments should fund it, even at the seemingly enormous costs it demands. The fact is that a world-class particle collider, nowadays, will cost some multiple of $10 billion. That multiple may be 1 ×, or 1.5 ×, or even 3 ×. But on the scale of government spending, and of the scale of the wealth of nations, this is
almost a trivial expenditure. Yet the US Congress is showing little interest in healthy science funding. Europe, Japan, and China are forging on.

To get a sense of scale, the US Navy's new
Gerald R. Ford
–class (CVN-21) aircraft carriers cost about $15 billion for R&D and construction. These will replace the 10
Nimitz
-class nuclear aircraft carriers the US Navy currently operates and that cost about $50 billion just for construction (nuclear reactors, operations, etc., drive the cost up a lot more).
²
Moreover, the US sits on top of an
estimated
total $200 trillion—that's $200,000 billion—of coal, gas, and oil.
³
The total assets of households and businesses in the US is about $200,000 billion = $200 trillion,
⁴
while the top 100 richest US citizens have a combined wealth of about $1,000 billion = $1 trillion.
⁵
Particle physics gave us the World Wide Web, which creates an annual revenue stream globally measured in tens of trillions of US dollars. Yet endless squabbles persist in Congress over a national debt of $17 trillion (at this writing) and a deficit of less than $1 trillion. Meanwhile, the economy and the American standard of living falters, and science wilts on the vine.

HOW DOES THE HIGGS BOSON GET ITS MASS?

The Higgs boson of the Standard Model does explain (though some may prefer to say “accommodate”) the masses of quarks, the charged leptons, the neutrinos, and the W and Z bosons. But it
does not explain its own mass
, about 126 GeV. It is the Higgs boson mass that determines Fermi's scale in the Standard Model. But we're still in the dark about the origin of the Higgs boson mass.

Where does the Higgs boson mass itself come from? That question has now moved to the forefront of the unanswered questions we have “beyond the Higgs boson.”

This is rather frustrating for a significant reason: our very successful theory of quarks and gluons and the strong interactions, known as “quantum chromodynamics” (QCD), emerged from a series of breakthroughs in 1974. Once it was understood, and the quarks and gluons were confirmed, the theory neatly explained where the
strong masses
come from (see the
Appendix
). These are the masses of a long list of particles found in the 1950s and 1960s, and most of the masses of the proton and neutron.
In fact, we should apologize for not telling you this fact earlier, but strong mass, through the proton and neutron masses, actually makes up most of the visible mass in the universe—the masses of stars, planets, and large clouds of dust and debris of supernovas seen through telescopes. Very little of this actually comes from the fundamental and relatively tiny masses of the up quark, down quark, and electron. Strong mass comes from the inherent mass scale found in QCD, and not from the Higgs boson!

But QCD explains the strong mass scale in a remarkable and beautiful way—
it is due to quantum mechanics itself
. QCD starts out at extremely short distances (high energy) as a
scale-invariant
theory—that means it has no inherent mass scale at the outset—and the coupling of gluons to quarks is very feeble. However, due to quantum effects, the coupling of gluons to quarks becomes stronger and stronger as we descend to lower energies, or to larger distances. Finally, at a certain energy scale, about 100 MeV, or equivalently, a distance scale of about 0.0000000000001 centimeters (that's 10
^-13
cm), this coupling strength becomes virtually infinite. This causes the quarks and gluons to form composite states—the protons, the neutrons, the pions, and all the other strongly interacting particles. The quarks and gluons are then “confined” and are never observable outside of a composite state in the laboratory. This mass scale of 100 MeV is determined by the quantum interactions themselves—nature creates strong mass through its own dynamics, essentially out of no mass! It has nothing to do with any other scale of the onion of physics.

This leads to a beautiful conjecture about mass:
all masses in nature are generated by quantum effects
.
⁶
That is, if we could somehow “turn off” quantum theory, somehow make Planck's constant go to zero, we would live in a world with no mass—the particle utopia we described in earlier chapters. This is exactly how the strong interactions, as described by QCD, work. It is a natural idea to extend this hypothesis, and it immediately implies that the weak interactions would work the same way.

Unfortunately, the discovery of a Standard Model Higgs boson seems to have no obvious correlation with this hypothesis. We see no clue, at the moment, as to how to solve the riddle of the Higgs boson mass itself in a manner such as QCD generates strong mass. Nature has consolidated all of the quark and lepton and W and Z boson masses into the Higgs boson field, but the Higgs boson remains a black box—it does not yet tell us anything
deeper about the origin of the electroweak mass scale, or equivalently, about its own mass.

FINALE

The most important next step for our science is the LHC run, scheduled to begin sometime around January 1, 2015, yielding possible major and dramatic new physics results in 2017 or so. Hopefully the LHC, when it comes back online, will reveal new particles and new phenomena, and the next layer of the onion will finally come into view.

Without such a revelation, without new targets for future colliders, can we rationally ask our government for a multi-billion-dollar high-energy particle collider at this time? The answer may be: we shouldn't.
⁷
It may be irrational and irresponsible to do so given that we have no indications of what new physics to pursue with such a machine. It would be a costly shot in the dark. Rather, we must wait until 2017 and continue reliably slugging it out at the LHC, participating actively in future machine and detector upgrades. There's still lots to learn from the LHC.

However, here in the US, we have a golden opportunity to penetrate deeply into the fog of the highest energies with a different, cost-effective approach, the approach of Becquerel, the Curies, and Rutherford, back in the earliest era of our science. We can now roll up our sleeves and build a smaller, few-billion-dollar machine, called Project X. With Project X, as we have seen, we could simultaneously probe nature for indirect hints as to what lies at energy scales 100 to 1,000 times beyond the LHC, while also collaborating actively in the energy frontier effort at the LHC. Project X could help to solve major global challenges, such as ridding the world of plutonium and providing clean nuclear power, as well as yielding rich scientific discoveries. It may ultimately lead us to the next-generation particle collider, first with a relatively small Muon Collider Higgs factory, using the powerful Project X beam to provide the requisite muon source. Later we could upgrade to a multi-TeV Muon Collider to provide point-like probes of any interesting new targets at the highest energies. This approach is staged, economical, and sensible. This is a most sensible evolutionary program that would allow the full benefit of advanced-technology R&D
to provide much-needed “exogenous inputs” into our economy This, we believe, is our best pathway forward, beyond the Higgs boson.

Experiment will always be the ultimate arbiter, so long as it's science we're doing. So far, regarding the Higgs boson there's not a hint of new dynamics. While we all expected that a major revolution was coming to the science of elementary particle physics, immediately with the discoveries at the LHC few expected a single Standard Model Higgs boson. So far the major revolution hasn't happened.

So what does this imply for the future? What else remains to be understood that can be understood? What, perchance, is not dreamt of in our philosophies? What generates the Higgs boson mass? Has the LHC missed something? Surely, there have to be some clues somewhere. Or maybe we're just not being clever enough? Are we misunderstanding what nature is telling us? We're working on it.

Please stay tuned for the all-important LHC results in 2017 or so. And let's roll up our sleeves and get started on Project X!

THE STRONG INTERACTIONS

By the mid-1960s, a vast array of
strongly interacting
particles was produced in many experiments at the many new accelerator labs. The number of new particles surpassed the number of atomic elements. Almost all of these various new particles were cousins of the proton, the neutron, and the pion—the components of the atomic nucleus. These particles were unstable, some having comparatively “long lifetimes” of a hundredth of a millionth to a tenth of a millionth of a billionth of a second (10
^-8
to 10
^-16
seconds), while others had ridiculously short lifetimes, about 10
^-23
seconds, not much longer than the transit time of light across their diameters. As these new strongly interacting particles proliferated, only one tool could be brought to bear to try to make sense of them—symmetry.

TOO MANY FUNDAMENTAL PARTICLES

The first order of business in any science, such as zoology or botany or epidemiology, is to classify things. This means that you make lists of everything you have observed and then try to put these items into general related categories. For example, we might list animals according to whether or not they have backbones (vertebrates and invertebrates). Within this category we make a sub-list according to whether they have scales, feathers, fur, etc. Then we look for patterns among the lists. Eventually we discover relationships, and we can then formulate theories of their origins and try to explain the myriad patterns.

By the end of the 1950s there were three broad categories of “elementary” particles. First, there were a few
non–strongly interacting
matter particles (particles that don't participate in the strong interactions, that is, they do not interact with Yukawa's pions or any of their relatives). These were
initially seen to be comparatively lighter-in-mass particles compared to the proton and neutron, so they were dubbed the “light ones,” which in Greek is
leptons
. The class of leptons contained the electron, the muon, and two very hard-to-observe particles called the electron neutrino,
v
_e
, and the muon neutrino,
v
_μ
. Much later, in the mid 1970s, another pair joined and completed this class of leptons, called the “tau,”
τ
, and the “tau” neutrino,
v
_τ
. Even though the tau is heavier, it shares the non–strongly interacting behavior of the electron and muon, and it fits into the lepton family.

By the 1970s accelerator experiments had confirmed that leptons were point-like, or structureless, objects down to the smallest accessible distance scales, about a hundredth of a millionth of a billionth of a centimeter (10
^-17
cm). In addition to the leptons there were two other particles that are strictly force carriers and that fall into a special class we call “gauge bosons.” These include the well-known photon, the particle of light, and a hypothetical “graviton”—the particle of gravity.