You’ve probably heard that the Higgs boson has been discovered – and it’s probably
true.
I’ve described the situation in another video, but the bottom line is that the particle
we found looks very much like the Higgs boson.
We’ll need to look at the data when the LHC turns back on in 2015 to be completely
sure.
However, let’s assume that we really did find the Higgs boson predicted back in 1964.
What does this mean?
Does this make us happy, or does it make us confused?
Well, actually the answer is both.
We’re happy to have confirmed the theory, as it means we’re on the right track.
However we’re also confused as even though it appears that the energy field predicted
by Peter Higgs and others really exists, we don’t know why it exists.
Now, this isn’t a problem really.
Physicists are used to understanding only a bit of the problem.
It gives us something to work on.
However, there is a real problem, buried deep inside the theory, with how the Higgs boson
ties into Standard Model.
This idea is a little complicated, but since it’s probably the leading research topic
that LHC physicists will attack when the accelerator resumes operations, it’s worth understanding
it.
The problem originates in the principles of quantum mechanics.
Here’s how it goes.
If the Higgs boson were just a simple particle, it would get its mass by interacting with
the Higgs field, just like all the particles.
One particle with one mass.
However things aren’t that simple in the quantum world.
Particles are constantly changing their identity.
A Higgs boson might fluctuate briefly into a top quark/antiquark pair before turning
back into a Higgs boson.
It might then turn into a pair of W bosons or a pair of Z bosons.
Even weirder, it might even turn into a pair of Higgs bosons.
This weird changing of identity is not unique to Higgs bosons.
All subatomic particles are quantum chameleons.
But we’ll just talk about the Higgs boson for now.
Remember that the Higgs field interacts more with some particles than others.
That’s why some particles have more mass than others.
This means that it has favorites when it fluctuates.
While it can transform into all particles, the top quark (which is a particle of the
class called fermions) and W, Z and Higgs particles (which are all bosons) are the ones
that matter the most.
Okay, so here’s where things get a little complicated.
But hang in there- I’m certain it will all make sense.
This really isn’t that hard to understand.
When physicists try to predict the mass of the Higgs boson, there are two things that
matter.
They are the mass they calculate when the Higgs hasn’t undergone a change and the
mass when it has.
These two masses are added together and that’s the mass we expect to measure.
The mass that has been measured is about 125 times heavier than a proton.
So that sets some limits on what the two components can be.
They have to add to 125.
They could be 15 & 110 or 50 & 75.
But they can’t be huge.
By the way, you should know that the real equation is more complex than I’ve described
here.
An expert will certainly turn their nose up at it, but that’s okay… this gives you
the big picture and illustrates all the important points.
If you look in the text posted with this video, you can read the technical details.
So now we get to the meat of the problem.
The contribution to mass of the Higgs boson from quantum effects comes from two terms
multiplied together.
The first term involves the maximum energy at which the Standard Model should apply and
the second term depends on the mass of all the important bosons minus the mass of all
the important fermions.
We remember that this means the W, Z and Higgs bosons and the top quarks, but we just write
it as bosons minus fermions.
So this simple equation tells us everything.
Multiply these two numbers together and the result should be small, meaning a number somewhere
between zero and a hundred or so.
So let’s think for a minute.
If I have to multiply two numbers together and they have to equal a small number, if
one number is big, the other will be small.
We can illustrate this in these examples, in which the two numbers multiplied together
equal one.
If one number is 10, the other is 0.1.
If one is 1,000, the other is 0.001.
If one is a million, the other is 0.000001.
If one number gets very big, the other number gets closer and closer to zero.
So what are the numbers involved in these quantum additions to the Higgs mass?
Well, the first number is related to the maximum energy for which the Higgs theory is expected
to apply.
This energy is the Planck energy, which is a quadrillion or so times higher than the
LHC energy.
Because of that complicated equation that I alluded to earlier, this makes the first
number 10 to the 38, which is a one, followed by 38 zeros.
This means that the other number has to be very, very, very near zero.
It doesn’t have to be exactly zero, but it must be extremely close.
So now we are at the core of the whole thing.
This number that has to be near zero comes from the bosons minus the fermions.
There’s a minus sign, which is good, because that means it’s possible.
It’s just extremely hard to believe that the effects of the W, Z and Higgs bosons are
somehow magically identical to the effects of the top quarks.
Physicists have a word for a coincidence like this.
We call it… unnatural.
Coincidences like this don’t just happen by chance.
It’s like having a billionaire’s annual income and expenses equal to the penny.
This means that there must be some sort of new physics that ensures this term in the
equation is near zero.
There are a couple of possibilities.
The most popular one involves an idea called supersymmetry, which I described in another
video.
If supersymmetry is true, for every known fermion, there is a corresponding boson that
we haven’t discovered yet.
This new boson would cancel out the known fermion.
The converse is true, with a new fermion for every known boson, with similar cancelling
properties.
The cancellation of the terms to zero would then be natural, simple, easy as pie and physicists
would be very happy indeed.
The only problem is that the data taken at the LHC so far really doesn’t favor this
particular explanation.
It’s not that the idea is dead yet, but many scientists are starting to look around
for alternate solutions.
I don’t know what the answer will be, but I do know that there must be an answer.
The low mass of the Higgs boson requires some new physics that naturally tames that troublesome
quantum term and there is only one facility that can shed light on it.
This accelerator is the Large Hadron Collider and scientists are looking forward to 2015,
when the machine resumes operations.
Finding the solution to this question is the next big problem for particle physicists and
the answer absolutely requires a discovery will be made.
Stay tuned.