
CERN experiment discovers five new particles - musha68k
http://www.stfc.ac.uk/news/cern-experiment-discovers-not-one-but-five-new-particles/
======
dkural
Just to give a bit more context:

* These are not elementary particles. * It was predicted for a long time that these composite particles should exist. So it is not "new" in the sense that it was unexpected, but we finally have the resolution (energy, luminosity etc.) to detect these with statistical significance. * These belong to the same class as protons and neutrons - these are hadrons made with multiple quarks.

Here's a super simple overview of Quantum Field Theory & Particle Physics:

Everything is made of force fields and matter fields.

* We discovered that force fields (i.e. electromagnetism) is quantized, giving rise to quantum mechanics etc.

* Matter fields are also quantized, hence their excitations behave like discrete particles - the ones we observe at the atomic scale, for instance.

* In hindsight, we should've been able to predict this after E = mc^2 telling us energy <> matter, thus if energy is quantized so should matter.

~~~
wfunction
I've never heard the term "matter field"... Is that a thing?

~~~
tbrownaw
I assume you've heard of particle/wave duality, or how really tiny things are
never _exactly_ in only one place.

There are a set of wave equations that describe how this works.

There are also two kinds of things. Some things can go thru eachother, like
photons. Other things bounce off eachother, like neutrons (and other things
considered matter).

The equations for the kind of things that bounce off eachother would be a
matter field.

~~~
danbruc
_There are also two kinds of things. Some things can go thru eachother, like
photons. Other things bounce off eachother, like neutrons (and other things
considered matter)._

This is not true. The difference between bosons and fermions lies in the way
swapping two of them works. The carriers of the weak force, W and Z bosons,
are for example electrically charged and can therefore scatter off each other.
Gluons, the carriers of the strong force, also interact with each other. Even
photon photon scattering is thing. On the other hand you can try to collide
two neutrinos, which are fermions, for quite some time and not much will
happen.

~~~
tbrownaw
_The difference between bosons and fermions lies in the way swapping two of
them works._

That sounds like what Wikipedia says is the rigorous version of the Pauli
exclusion principle[1].

I was trying to get close to the not-rigorous version (1st paragraph of the
link) in terms that are easily understandable without having taken a
university QM course. I guess can/can't be in the same place at the same time
would be a better approximation of it?

[1]
[https://en.wikipedia.org/wiki/Pauli_exclusion_principle](https://en.wikipedia.org/wiki/Pauli_exclusion_principle)

~~~
danbruc
Loosely peaking the wave function of a quantum mechanical system specifies for
each possible state of the system the probability of finding the system in
that state. Actually it is not the probability but the probability amplitude,
a complex number from which you can derive the probability by squaring it.

Assume you have two identical fermions, say two electrons, the first one in
state x and the second one in state y. State means everything required to
fully describe the particle, for example position and spin. Therefore x stands
for the first electron being in a specific position and having a specific
spin, similarly for y and the second electron.

Let A(x, y) be the probability amplitude for finding the first electron in
state x and the second electron in state y, i.e. the first argument of A is
the state of the first electron, the second argument is the state of the
second electron. Now swap the two electrons, take the first and put it where
the second one is, take the second one and put it where the first one was.
Also change the spins as necessary. The probability amplitude is now A(y, x),
the first electron is now in state y, the second electron is now in state x.

The important thing is now that the two electrons are identical, you can not
tell the difference between the situations before and after swapping the two
electrons. Had you painted one electron blue and one red, then you could
easily tell the difference, but without that you can not. That was the entire
point of swapping the electrons, bringing them into exactly the state of the
other one.

But if you can not distinguish the two situations, then it better be the case,
that they have the same probability, i.e. A(x, y) = A(y, x). But that is not
quite right, A is the probability amplitude, not the probability. It turns out
that there are actually two valid possibilities, A(x, y) = A(y, x) and A(x, y)
= -A(y, x). As mentioned at the beginning, you get the probability by squaring
the probability amplitude, so that the minus sign in the second case vanishes.

The first possibility is how bosons (particles with integer spin, for example
photons and gluons) behave, the second one is how fermions (particles with
half integer spin, for example quarks and electrons but also helium-3) behave.
Now we finally arrive at the important point, what happens if both electrons
are in the same state, i.e. if the first electron is in state x and the second
electron is also in state x. Then the probability amplitude is A(x, x) and we
have to satisfy A(x, x) = -A(x, x) because electrons are fermions.

But there is only one complex number identical to its negative and that is of
course zero. Therefore the probability amplitude and in consequence the
probability obtained by squaring the probability amplitude are both zero,
which means that the probability of finding the system in the state where the
first electron is in state x and the second electron is also in state x, is
zero. The two electrons or more generally two fermions can never be in the
exact same state.

------
teddythetwig
I assume these particles were already predicted as part of the Standard Model?

~~~
brutuscat
Professor Tim Gershon, Professor of Physics at University of Warwick and UK
spokesperson for the LHCb experiment: “After the LHCb experiment is upgraded
in the next long shutdown of the LHC (during 2019-20), it will be able to move
to the next stage in the search for new particles: namely, doubly heavy
baryons. These states – which contain two charm quarks or two beauty quarks or
one of each – have long been predicted, but never yet observed. Their
discovery will help to address important unsolved questions about how hadrons
are bound together by the strong interaction.”

So I would assume that yes they have been predicted and is opening the doors
for further confirmations?

~~~
wolfgke
> Their discovery will help to address important unsolved questions about how
> hadrons are bound together by the strong interaction.

If the particles were already predicted by the standard model, what kind of
unsolved questions are to address here, besides validating the predictions of
the standard model even further? (serious question)

~~~
binarymax
Because a prediction is just an assumption (theory), and it can become a house
of cards when basing future science on that assumption. Observation is proof,
so future science can use that proof without worry.

~~~
nonbel
Can you clarify? In my mind

    
    
      "prediction" != "assumption" != "theory" 

and

    
    
      "observation" != "proof"
    

Basically I seem to disagree with everything you wrote.

~~~
herpdorplarp
By assuming validity of a theory you can make predictions. Observations
provide evidence in support of this.

~~~
iamconfused
A theory comes later. You start off with a hypothesis. You don't make any
assumptions of validity.

------
grkvlt
For more in-depth information see the CERN press release "LHCb observes an
exceptionally large group of particles" at
[https://home.cern/about/updates/2017/03/lhcb-observes-
except...](https://home.cern/about/updates/2017/03/lhcb-observes-
exceptionally-large-group-particles)

Or, the paper "Observation of five new narrow Ω0c states decaying to Ξ+cK−" is
available at
[https://arxiv.org/abs/1703.04639](https://arxiv.org/abs/1703.04639)

And finally, the LHCb web site section on "Observation of five new narrow Ωc0
excited states" at [http://lhcb-public.web.cern.ch/lhcb-
public/Welcome.html#Omeg...](http://lhcb-public.web.cern.ch/lhcb-
public/Welcome.html#Omega_c)

------
grabcocque
I have to admit, I rather admire their putting a brave face on things, with
their mildly-too-insistent claim that the LHC is vital for finding new physics
despite the increasing likelihood it's not going to find any.

In that sense the LHC is a political failure, because it has failed at its
primary political job, which is to make the argument for an even bigger
collider.

~~~
bpicolo
How'd it fail at it's primary task? Wasn't the Higgs a big part of that? Or is
the argument that is hasn't found anything outside of the standard model?

~~~
shepardrtc
It succeeded at its primary task, and the Higgs was a big part of it. Its
still doing its job, so give it time. Finding nothing can often be just as
important as finding something unexpected.

~~~
wolfgke
> Finding nothing can often be just as important as finding something
> unexpected.

From a scientific point you are right. From a political point or the point of
securing further funding this statement is (unluckily) wrong.

~~~
TheGRS
I think its a fundamental problem with teaching science history. We tend to
look at achievements in history as being inevitable, like of course we
discovered flight after the locomotive was invented, that's just how it
happened! But those discoveries were all a circumstances of chance. If we're
going to continue to make progress in science we need to accept that new,
groundbreaking discoveries don't happen inevitably, they happen from people
doing a lot of the dirty work and from imaginative people putting the puzzle
pieces together in new ways. There's no inevitability to discovery.

