Hello once again and if you don't know already,
I'm Scott Florence and just now I'm
going to be giving an overview of what was
said at the 2 hour live stream from CERN
this morning about the Higgs Boson.
*intro music*
Ok that's enough of that and I'm going to
be giving an overview about what all of
you are wanting to hear about first, followed
by more detail as I go along.
And there are links in the description down
below about some videos that I recommend
you check out before you watch the more information
that I'm going to be talking
about later, I'm not going to be describing
what the Higgs Boson is in this video
either, that's in the links below as well.
Now they've been looking for the Higgs Boson
for quite some time now, but why have
they been looking? Well it's because the Higgs
Boson is predicted by the standard
model of particle physics, and if the Higgs
Boson has been found, that helps to
validate the standard model of particle physics
which means that we understand more
about the universe and how it all works.
Ok so basically what they've been doing at
CERN is they have something I'm sure
you've all heard of, the large hadron collider,
and attached to that collider there
are 2 sensors, ATLAS and CMS and these 2 gigantic
sensors monitor the collisions
that occur in the LHC and I'm going to be
referring to things as events, and these
events are basically things colliding and
forming other things, in layman's terms.
Now in their data there are many background
events, basically meaning that there are
many events that don't really matter, that
they don't want to see but they are
happening anyway, because they are stuck inside
the detector when the collision
happens, they are not the ones you are looking
for, but they are there anyway.
And these background events have been masking
the signal of the Higgs Boson,
basically meaning that it's easier to pick
out just 1 signal out of 2 say, than 1
signal out of 1000.
But at a mass of about 125.5 Giga electron
Volts, there is a peak that stands out of
the data, and when looking at this peak and
comparing it to the background events,
they can see that the probability of the background
events just by chance causing
this peak, is enough to say at a 5 sigma confidence
level that this is not just the
background events, this is a new particle,
a particle that has never been discovered
before. And when I say a 5 sigma confidence
level, I'm basically saying there is a 1
in 1 million chance that they are wrong. And
5 sigma tends to be defined as a
discovery.
And so far, the data they've collected seems
to be fairly consistent with the
standard models prediction of the Higgs Boson.
At the press conference afterwards, when Rolf
Heuer was asked if they have found the
Higgs Boson, he responded with "As a Layman,
I'd say we have it, but as a scientist,
I'd have to say we've found something, we
have a Boson"
Basically overall, it's a guarantee they've
found a new particle, and that that new
particle is a Boson, but if you watch my video
in the description down below, you'd
know that a Boson is just part of a field,
and it doesn't specifically have to be a
Higgs Boson.
But it does certainly look like it is a Higgs
Boson due to things like the decay
modes which I'm going to be talking about
shortly. But they plan to be getting more
data about this over the next few months from
the LHC, and that's in the hope they
can get as many details about the physical
properties of the Boson as they can.
And later in July, ATLAS and CMS will be releasing
papers about their findings, but
for now I'm going to be going up there to
talk about the mechanisms that they used
to work out where this Higgs Boson could be.
You can see up here that I've drawn a couple
of Feynman diagrams, and if you aren't
sure what they are, I really do suggest you
click the link down below about Feynman
diagrams, but for now lets talk about them
all individually. This top one is called
gluon pair production (gluon fusion),
and it's not the best technique for finding
the Higgs Boson, but it's a major one
never the less. Basically what happens is
these 2 gluons interact and form what's
called a top quark loop, and those 2 quarks
annihilate and form the Higgs Boson,
but since we can't observe the Higgs Boson
directly, it needs to decay, and what it
decays into is 2 W Bosons, those W Bosons
are things that are responsible for the
weak force if you don't know, and if you don't
know you should have clicked that
link down in the description. And those two
W Bosons form a lepton or it's anti-part
and a neutrino of that lepton or it's anti-part,
depending on which of these it comes
off. Whether it's the positively charged W
Boson or the negatively charged W Boson.
And you may see physicists refer to this as
H-lvlv. Basically meaning that the Higgs
Boson decays into a lepton and it's neutrino
and another lepton and it's neutrino.
This next one tends to be better at distinguishing
the Higgs Boson because it's more
clear when the decay products are produced,
and only 1 neutrino is formed as opposed
to 2 earlier, and the neutrinos can not be
measured themselves as they interact so
weakly with matter. And also some of the final
products are bottom quarks which are
much heavier than leptons so much more easily
measured. Basically what happens in
this case is a quark and it's antipart annihilate
together and form a high energy W
Boson and that then forms a W Boson and a
Higgs Boson, the W Boson forms a lepton
and it's antipart neutrino and the Higgs Boson
forms 2 bottom quarks. It's much
easier to work out the mass of the Higgs Boson
from this as the only thing that
comes out of this are the 2 bottom quarks.
And you may hear physicists talk about
this as WH-BB(bar), basically saying the Higgs
Boson and the w Boson form together,
the w Boson then decays into a lepton and
it's antipart neutrino, and the Higgs
Boson forms a bottom quark and an anti-bottom
quark.
The final one I'm going to be talking about
is when two leptons annihilate together
and form a w Boson, the w Boson then forms
a z Boson and a Higgs Boson. The Z Boson
forms a lepton antilepton pair, and the Higgs
Boson forms a bottom quark antibottom
quark pair. You may hear this one referred
to as ZH-LL(bar)bb(bar). And all of these
as well as Higgs di-photon production, basically
when two photons are produced from
the Higgs Boson when it decays, are all used
when monitoring the data measured from
the LHC. The W and Z are some of the ideal
ones to use as they don't have neutrinos
as an end product so that the mass can be
reconstructed, when they use ATLAS and CMS
to measure where the quarks and leptons are
going after the collision, and they can
trace it back to find where each of the events
came from, and from that they can
reconstruct the mass of the Higgs Boson.
For high mass the WW or ZZ higgs decay mechanisms
are the best to use, and they are
actually fairly good throughout the board
of all masses, however when it's at a
lower mass it tends to be quite good to use
bb(bar), both of these are examples of
that.
I realise I've been talking for a fairly long
time now, so I'll finish off with
this, when graphs like this came up on the
screen, there was a loud cheer and
applause from all of the people that were
watching in the room at the time, and what
this rather crude sketch of the graph represents,
at about 125 giga electron volts
there is an event, or series of events that
is very very unlikely to be caused by
the background events, to an extent of 5 sigma,
and also that it mostly agrees with
the standard model prediction.
Now if you actually want to own any of the
presentations made at the CERN
announcements, I've included links down below
to somewhere you can download them
all, so that you can have an actual flick
through, I was expecting to be able to
condense 2 hours of talking to less than this,
but apparently I was far from able to
do that. But I think I've got the basics across.
But otherwise, if you want to leave a comment
do so, if you like this video, leave a
like, if you want to see more of this sort
of stuff or "what is" videos or keep up
with the physics news that's interesting like
this click to subscribe up there, and
I will see you next time.
