appeared to produce a Higgs boson and a Z boson. The two gray cones represent jets of particles that decayed from a bottom and an antibottom quark, which likely decayed from a Higgs particle. The green lines depict an electron and a positron,
which
likely decayed from a Z boson. No new particles have been found at the Large Hadron Collider since the Higgs boson in 2012, but physicists say there's much we can still learn from the Higgs itself...
A debate has ensued over
whether to build an even more enormous successor to the LHC  a
proposed machine 100 kilometers in circumference, possibly in
Switzerland
or China  to continue the search for new physics.
Its discovery won the 2013 Nobel Prize for Peter Higgs and François Englert, two of six theorists who proposed this massgenerating mechanism in the 1960s.
The mechanism involves a field permeating all of space.
The Higgs particle is a ripple, or quantum fluctuation, in this Higgs field. Because quantum mechanics tangles up the particles and fields of nature, the presence of the Higgs field spills over into other quantum fields.
It's this coupling that gives their associated particles mass.
That shift, or
"symmetrybreaking" event, instantly rendered quarks, electrons and
many other fundamental particles massive, which led them to form
atoms and all the other structures seen in the cosmos.
Physicists wonder whether the Higgs symmetrybreaking event had a role in creating the universe's matterantimatter asymmetry  the unexplained fact that so much more matter exists than antimatter.
Another question is whether the Higgs field's current value is stable or could suddenly change again  an unsettling prospect known as "vacuum decay."
The value of the Higgs field can be thought of as a ball settled at the bottom of a valley.
The question is,
If so, the ball will eventually tunnel to the lower, more stable valley, corresponding to a drop in the energy of the Higgs field.
A bubble of the more
stable "true vacuum" would grow and encompass the "false vacuum"
that we've been living in, obliterating everything.
In a particle collider, when particles smash together at nearly light speed, their kinetic energy converts into matter, occasionally forming heavy particles such as the Higgs boson...
This Higgs then quickly morphs into other particles, such as a pair of top quarks or W bosons, where the probability of each outcome depends on the strength of the Higgs' coupling to each type of particle.
Precisely measuring the probabilities of these different Higgs decays and comparing the numbers to Standard Model predictions reveal if anything is missing, since the probabilities must add up to one.
That's one reason she and many of her colleagues want to build a bigger, better machine.
The first phase of the proposed supercollider has been nicknamed the "Higgs factory," because the machine would collide electrons and positrons with energies precisely tuned to maximize their chance of yielding Higgs bosons, whose subsequent decays could be measured in detail.
In phase two, the giant machine would slam together protons, resulting in messier but much more energetic collisions.
David Kaplan explains how the search for hidden symmetries leads to
discoveries like the Higgs
boson. Editing and motion graphics by Ryan Griffin.
Music by Kevin MacLeod.
This would give physicists a much better sense of whether the probabilities add to one, or whether Higgs bosons are occasionally decaying into hidden particles.
Extra particles coupled to the Higgs appear in many theories of physics beyond the Standard Model, including the "twin Higgs" and "relaxion" models.
Perhaps the most important coupling that physicists want to nail down is called the triple Higgs coupling  essentially the strength of the Higgs boson's interaction with itself.
This number is measured by counting rare events, not yet seen at the LHC, in which a Higgs boson decays into two of itself.
The Standard Model makes
a prediction for the value of the triple Higgs coupling, so any
measured deviations from this prediction would signify the existence
of new particles not included in the Standard Model that affect the
Higgs.
If the Standard Model's prediction for the coupling is correct, then the universe is metastable, destined to decay billions or trillions of years from now.
This is nothing to worry about, but rather an important clue about the larger story of our cosmos.
The ability to reveal the universe's fate is why the triple Higgs coupling,
With a Higgs factory,
Cédric Weiland said, physicists could measure the triple Higgs
coupling with a precision of 44 percent. The secondphase
protonproton collider could nail its value to within 5 percent.
Some physicists balk at
the prospect of investing billions of dollars in a machine that
might simply add more decimal places of precision to our knowledge
of an existing set of equations.
Whether to spend 20 years and as many billions of dollars constructing a 100kilometercircumference collider hinges on its discovery potential. Past colliders struck upon the puzzle pieces of the Standard Model one by one.
But with that puzzle complete, there's no guarantee that a future machine will find anything new, leaving physicists with a dilemma:
