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NY Times, Oct. 18 2016
Physicists Recover From a Summer’s Particle ‘Hangover’
by George Johnson
As I sat last month in the cafeteria at CERN, the nuclear research
center near Geneva that is home to the Large Hadron Collider, I looked
out at the expanse of tables and wondered what all those young
physicists were talking about.
Judging from their enthusiasm, they had recovered from the summer’s
“diphoton hangover,” the nickname given to the disappointment that
followed the coming apart, weeks earlier, of a striking observation — an
excess number of photons hinting that some exotic new particle might be
lurking behind the scenes, an encore to the Higgs boson.
Could it be a cousin of the Higgs, or a long sought particle of dark
matter? The excitement led to a speculative bubble of papers seeking to
explain what turned out to be a nonevent. What had jumped out as a
pattern in the data was apparently a mirage, like seeing a pyramid on Mars.
A victim of its own success, particle physics has come to a turning
point. For decades, the theorists have been calling the shots,
predicting particles like the Higgs for the experimenters to find,
plugging the holes in the cosmic puzzle. Now, with the pieces in place,
in the form of the Standard Model, the theorists are hoping to push
further, looking again to the experimenters to confront them with new
things to theorize about — clues, perhaps, to an even deeper order.
As plates and utensils clattered around me, I thought of an earlier
changing of the guard. In 1962 in this same cafeteria, a 32-year-old
theorist named Murray Gell-Mann wrote a prediction on a napkin that
helped set the course for the next half-century of research.
During the early decades of the 1900s, swashbuckling experimenters had
run the show. Launching their instruments in balloons and carrying them
to mountaintops, they brought back snapshots of cosmic ray particles
that made no sense.
“Who ordered that?” Isidor I. Rabi, a renowned theorist, famously said
after he learned of the muon — a fat, short-lived cousin of the
electron. Then came interlopers called pions, kaons, lambdas, sigmas and
Just three particles — electrons, protons and neutrons — seemed like
enough to make the world. What were all of these extras? They didn’t fit
into any existing scheme.
With pencil and paper, Dr. Gell-Mann devised one, doing for physics what
Mendeleev, with his periodic table of the elements, had done for
chemistry. Sorting the particles into clusters of eight and 10, Dr.
Gell-Mann came up with a framework he called the Eightfold Way. It had
nothing to do with Buddhism. He just liked the name.
Among the rows and columns of Mendeleev’s table there had been empty
spaces — place holders for elements like germanium (a kin to carbon,
silicon, tin and lead) that would not be discovered for years. And so it
was with the gaps in the Eightfold Way.
If Dr. Gell-Mann’s math was right — a pretty good bet — there had to be
a particle he called the omega minus. He described what to look for on a
cafeteria napkin and handed it to a colleague, Nicholas Samios.
Two years later, Dr. Samios, one of the great experimenters of his
generation, discovered the particle at Brookhaven National Laboratory on
Long Island. (It had also been predicted by the Israeli physicist Yuval
Ne’eman, who was sitting at lunch that day with Dr. Gell-Mann at CERN.)
From then on, the theorists were ascendant. With its bona fides
established, the Eightfold Way led to quarks, gluons and ultimately the
Standard Model, a chart with its own holes to fill. One by one, the
experimenters obliged until the keystone, the Higgs, was put in place,
discovered with the Large Hadron Collider in 2012.
And that, for the theorists, led to a postpartum depression. Though now
complete, the Standard Model (available on a T-shirt at the CERN gift
shop) lacks the elegance one might like in a well-made universe.
There are matter particles and force particles with masses ranging from
zero (photons and gluons) and near zero (neutrinos) to the top quark,
which is as hefty as an entire atom of tungsten — an element whose name,
in Swedish, means “heavy stone.”
The Higgs explains how particles acquired mass, but not why they were
spit forth with such a hodgepodge of different values. Least satisfying
of all, the Standard Model leaves out the most salient of forces,
gravity, which is described by an entirely different theory.
Is this how the universe just happens to be? Or is there a grander
theory that would demand that things be precisely this way? And so the
search goes on.
There is no reason other than sheer stubbornness for human brains to
assume that they are neurologically equipped to understand the finest
details of creation. But those vibrant physicists in the CERN cafeteria
didn’t seem burdened with existential angst.
As they lined up to bus their lunch trays, placing the dishes on a
conveyor belt, I wondered for a moment about the fate of all those
discarded napkins. All it might take is one, marked in pencil or ink
with a unique scribble, to set particle physics off on its next adventure.
Beneath our feet, particles collided silently in the tunnels, striking
more sparks to puzzle over.
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