Hunting the elusive Higgs Boson

University of Pennsylvania physicist Jamie Saxon "on top" of the Atlas detector, five stories above ground level.
University of Pennsylvania physicist Jamie Saxon "on top" of the Atlas detector, five stories above ground level.
Posted: July 16, 2012

Einstein famously marveled over the idea that the universe was comprehensible. But on July 4, the universe started to sound weird and unnecessarily complicated. Physicists worldwide were celebrating an elusive thing called the Higgs boson, which had apparently made a brief appearance. They kept repeating that it was important because it gives matter mass, but they didn't say how such an important job can be done by a particle that needs an $8 billion device to coax it into existence for less than a nanosecond before it returns to oblivion.

The news sounded more like the twisted logic of credit default swaps than the rational progression of science. But now that the physicists have had time to catch up on their sleep and science reporters have recovered from their 4th of July hangovers, a more coherent, beautiful, and even comprehensible picture is emerging from the noise.

Q: If the Higgs particle is the answer, what was the question?

A: Some scientific endeavors rest on so many layers of questions that it's possible to lose track of where it all started. At bottom is usually a puzzle that even children can understand.

You can trace the search for the Higgs back 2,400 years. In ancient Athens, philosophers asked whether you could break matter into infinitely small pieces, or whether you would eventually get to a smallest possible piece that could not be divided.

One philosopher, Democritus, wondered whether such indivisible particles could possibly make up everything on heaven and earth. In his vision, the cosmos was just matter and void, and matter was just different combinations of atoms. His was a big, forward-thinking idea.

Democritus got the idea from his teacher Leucippus, according to the book The Dream of Reason by Anthony Gottlieb. The idea itself may be as old as human reason, but once Democritus articulated it and gave it a name — atomism — it took on a continuous life, threading through history for more than two millennia.

According to The Dream of Reason, Aristotle and Plato abhorred Democritus' idea. Plato was said to have wished to see all his writings burned. Atomism was subversive and equalizing. It meant that the same building blocks following the same rules made up the Earth, the heavens, emperors, peasants, men, women, plants and animals, the good and the bad, the living and the dead. It toppled hierarchies — whether theological, biological, or sociological.

Despite the weight of disapproval, the idea threaded through the centuries to be embraced by Galileo and other beyond him. By the 1800s, experimental science was starting to give substance to Democritus' dream.

That's when Madame Curie and pioneers began studying radioactive elements and realized they were seeing matter give up its secrets — components of atoms were getting dislodged. The first particle physics experiment was done in 1907 by Ernest Rutherford, who used radioactive materials to shoot particles at sheets of gold foil. He discovered that most of the particles went straight through, while a few bounced back or were deflected.

The first subatomic particles

That work combined with other experiments led to a picture even more elegant than Democritus could have dreamed. Everything from stars to rocks to the human body appeared to be made up just three types of particles — protons, neutrons and electrons — arranged in different ways.

What scientists had called atoms turned out to be divisible, but fundamental particles existed at the bottom of it all, just as Democritus had said. Democritus also wrote of something like forces ruling the behavior of his atoms. He didn't get the details but he was on the right track.

Reality turned out to be more complicated than the world of protons, neutrons and electrons. Electrons are indivisible, but the neutrons and protons appear to be made out of three component pieces called quarks. And scientist have turned up a handful of other particles that either don't participate in matter or aren't stable under earthly conditions.

Some of the weirder particles came from outer space in the form of cosmic rays. One, found in the 1940s, acted just like the electron but with 207 times the mass. Dubbed the muon, it prompted one physicist to ask, "Who ordered that?"

By the 1970s, scientists sorted this out into a picture called the standard model, which breaks down the universe into 17 types of particles that are considered fundamental and indivisible — the closest thing to Democritus' atoms.

The standard model predicted the existence of a few particles nobody had yet detected: elusive entities called the W and Z bosons, which were discovered in the 1980s; a top quark, which was recorded in the mid 1990s; and the Higgs boson, whose discovery was officially announced on July 4, 2012 — Independence day in a country whose political system — democracy — carries forth the name of our ancient Greek atomist.

Q: So how do they know they've found a Higgs?

A: Scientists spent more than a decade building a machine called the Large Hadron Collider (LHC) at a lab in Europe known as CERN. The LHC uses a 17-mile of circular tunnel to collide speeding protons, producing bursts of energy. As Einstein's E=mcsquared explains, the energy can spontaneously produce particles. The Higgs boson is unstable — it lasts a fraction of a nanosecond before ‘decaying' into more stable particles — but that debris can leave telltale tracks in layers of materials that make up to two detectors, called CMS and Atlas.

Penn professor Brig Williams explained that there are several major patterns of debris that are likely to be left behind by the Higgs. Sometimes the Higgs transforms into two photons or light particles. Other times it becomes a pair of W or Z bosons, which spontaneously disappear and become more commonplace particles that speed through the detectors. The problem is that any of these signals could show up without a Higgs ever gracing their experiment.

The more data they have, the lower the odds that they're seeing a coincidental convergence of background noise. Last December they had collected enough potential Higgs candidates to reduce their odds of a false sighting to one in a thousand. Now it's down to less than one in a million chance that they've seen a statistical fluke. There's almost definitely a particle there.

They aren't absolutely sure this particle is the Higgs but it has some key Higgs-like properties. In the coming months, the scientists plan to study how easily the new particle is made and the various ways it transforms itself into other particles. If it does anything that contradicts the predictions of the standard model, then physicists will have something new and exciting to explain.

Q: Does the Higgs boson really endow matter with mass?

A: Not exactly, said Matt Strassler, a physicist at Rutgers University. He says it's helpful to think of the Higgs bosons like light, which can act as a particle or as a wave. He thinks of the Higgs boson as a ripple in something called the Higgs field.

The Higgs field pervades space and some particles interact with it while others don't. Particles that feel the Higgs field act as if they have mass. Something similar happens in an electric field — charged objects are pulled around and neutral objects can sail through unaffected.

So you can think of the Higgs search as an attempt to make waves in the Higgs field to prove it's really there. There are still mysteries about the Higgs field, Strassler said. It might turn out to be made up of other fields, for example.

When it comes to endowing matter with mass, the Higgs field is a minor player, say the physicists. Protons and neutrons and other composite particles get most of their mass from other mechanisms, and the Higgs boson must get some of its mass from something other than the Higgs field. But electrons and other elementary particles do get their mass from the Higgs field. If the electrons had no mass, they would not keep their places in atoms, and matter would explode. Life as we know it seems to be dependent on our Higgs field.

Q: Wasn't it awfully nice of the universe to give us a Higgs field so that we could have planets and other useful forms of matter?

A: Essential as the Higgs field appears to be, we really don't know if our set of particles and fields represent the only recipe for a livable universe, said Victor Stenger, a physicist and author of a number of books including The Fallacy of Fine Tuning. Fine tuning is the notion that the constants of nature are tuned just right to make the universe nice for us, as if the hand of God were writing the parameters of physics.

Stenger said his calculations show there's some leeway in the constants of nature — they don't have to be exactly what they are. The appearance of design in physics is as much an illusion as it is in the biological world, Stenger said.

Rutgers' Strassler compares our situation to earlier generations trying to understand whether the distances between the solar system's planets and the sun were set by some kind of overarching law that made it impossible for them to be otherwise. Now we know there are millions of other solar systems, and ours is one of umpteen possibilities.

Accident or design?

Physicists, he said, don't know whether some deeper and more elegant idea will explain the properties of the 17 known particles and various forces and fields or whether we got some of our particular physical parameters by accident.

Science is by and large open to the notion that there could exist different universes, or regions of the universe with different physical constants and laws, with ours just one of many possibilities. Stenger sees this as more reasonable than the assumption that our visible corner of the universe is all there is.

He's currently working on a book that will trace the thread of atomist thought from ancient Greece to the Large Hadron Collider and the opposition the idea has faced. People have hated atomism because it's a materialist viewpoint that doesn't allow supreme beings to exist above and beyond matter and physical law — beings that some say give life purpose.

But an atomist world doesn't have to be meaningless, said Stenger. "We're free to find our own purpose."

Contact Faye Flam at 215-854-4977, fflam@phillynews.com, or @fayeflam on Twitter. Read her blog at philly.com/evolution.

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