LHC Experiments See First Evidence of a Rare Higgs Boson Decay

CERN: The discovery of the Higgs boson at CERN's Large Hadron Collider (LHC) in 2012 marked a significant milestone in particle physics. Since then, the ATLAS and CMS collaborations have been diligently investigating the properties of this unique particle and searching to establish the different ways in which it is produced and decays into other particles. At the Large Hadron Collider Physics (LHCP) conference last week, ATLAS and CMS report how they teamed up to find the first evidence of the rare process in which the Higgs boson decays into a Z boson, the electrically neutral carrier of the weak force, and a photon, the carrier of the electromagnetic force. This Higgs boson decay could provide indirect evidence of the existence of particles beyond those predicted by the Standard Model of particle physics.

The decay of the Higgs boson into a Z boson and a photon is similar to that of a decay into two photons. In these processes, the Higgs boson does not decay directly into these pairs of particles. Instead, the decays proceed via an intermediate "loop" of "virtual" particles that pop in and out of existence and cannot be directly detected. These virtual particles could include new, as yet undiscovered particles that interact with the Higgs boson. The Standard Model predicts that, if the Higgs boson has a mass of around 125 billion electronvolts, approximately 0.15% of Higgs bosons will decay into a Z boson and a photon. But some theories that extend the Standard Model predict a different decay rate. Measuring the decay rate therefore provides valuable insights into both physics beyond the Standard Model and the nature of the Higgs boson.

Quantifiable?

[Turkinolith]

I'm not sure if this has already been established, but with this development and given the law of conservation of energy does this mean we can now quantify the absolute smallest units of mass and how much energy that equates to?

Re:Quantifiable?

[gtall]

Why would this decay have a bearing on the "absolute smallest units of mass"?

Re:

[gweihir]

Unlikely. Remember that "There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened." I would like to add that it looks like this has happened multiple times so far.

Re:

[blue trane]

Is the Law of Conservation of Energy not applicable to much beyond steam engines?

Re:

[John Cavendish]

Plank mass? - been known for a while, everything "plank" is the smallest unit physically meaningful and this includes: plank volume, plank mass, plank time, etc.

Re:

[bn-7bc]

I'm behind the times it seams, do we know the length of the Plank length (and by extension the volume of the plank volume) or is it still defined as "the smallest there is, we just don't know the number yet"?

Re:

[gtall]

From Wikipedia,

"In particle physics and physical cosmology, Planck units are a set of units of measurement defined exclusively in terms of four universal physical constants, in such a manner that these physical constants take on the numerical value of 1 when expressed in terms of these unit"

So, they are somewhat arbitrary except for helping to match up with physical theories, not physical experiments, to determine their value.

Re:

[bn-7bc]

Thank you, so that is why I cold not remember hearing about it being prickly determened, the exact values are yet to be nailed down, but now we at least know what parameters this number must satisfy, so well done to all involved and if I was able to afford it I'd kick several hunder million USD ( or it's eqvivalent in whatever local currency is most convenient to the people involved) their way so they could allocate a few more resources, cientific progress iss allways worth wile.

Re:

[John Cavendish]

From Google:
Planck length = 1.616255(18)×1035 m
Planck mass = 2.176434(24)×108 kg
Planck time = 5.391247(60)×1044 s
Planck temperature = 1.416784(16)×1032 K
Details: https://en.wikipedia.org/wiki/... [wikipedia.org]

Re:

[John Cavendish]

Sorry, copy-pasted and didn't notice incorrect powers:
x1035 m should be x10^{-35} m
x108 kg should be x10^{-8} kg
x1044 s -> x10^{-44} s
x1032 K -> x10^{32} K

Re:

[John Cavendish]

But it doesn't seem that the Planck mass is so small to qualify for your definition of "the smallest quantifiable mass".
Now I got interested as well. Indeed, what is the smallest quantifiable unit of energy - something equivalent in the meaning to the Planck length, i.e. the smallest recognizable energy change?

After reading TFA, this is what I came away with:

[hey!]

They pooled the data from two different instruments and after crunching the numbers they got a result which is consistent with the Standard Model but which does not rule out some hypothesized extensions to it.

Typical Rare Decay Result

[Roger W Moore]

That's pretty much the summary for any rare particle decay paper at the LHC so far. It is important to look for these types of decay to check whether the SM prediction is correct since, so far, we have no really clear ideas of what the new physics we need to explain all the stuff the SM cannot will look like. However, I do not see why this rare process should be any more likely to vary from the SM than, say, some rare B decay looked for by LHCb - I think the OP got a little carried away by the mention of th

Re:

[zeeky boogy doog]

Most of the time a rare decay is of interest, it is because there is very little background going on that generates a similar signal. This means a lot less modelling, a lot less chaff to sort through and better confidence when the events are detected.

In particular if the channel is purely leptonic (no strong force involved) it is easier, more reliable and more precise to trace single leptons and photons than it is to back-project the cones of everything-you-can-imagine that hadron decays spray out. But p

Re:

[The Evil Atheist]

We have not directly observed any particle after neutrinos.

Every particle accelerator discovery was about finding the predicted rates of decay of a hypothetical particle.

Re:

[haruchai]

I'm still trying to wrap my head around the fact that neutrinos - particle that barely interact with anything- make supernovas possible

Re:

[ceoyoyo]

We can't observe neutrinos either. We observe charged leptons doing weird things like popping into existence or suddenly accelerating to relativistic speeds.

Unification?

[bill_mcgonigle]

We get mass/gravity unification with electroweak just like that?

That would be cool but this seems too tasty to hold up for long.

Re:

[The Evil Atheist]

Mass, yes. Not gravity.

Am not a physicist. Anyone care to answer?

[Deal In One]

I thought Higgs Boson, as an elementary particle, does not consist of other particles. So can it actually decay into other particles?

As I understand, the Higgs Boson is associated with the Higgs field, and the Higgs field gives mass to other fundamental particles.

So if a Higgs Boson decays, does that mean that at that point in spacetime, any other particle there/within the radius of the field will not have mass?

Re:

[necro81]

I thought Higgs Boson, as an elementary particle, does not consist of other particles. So can it actually decay into other particles?

In short: yes, particles - including the Higgs - decay into other particles all the time.

A lot of particle physics' day-to-day work boils down to predicting what particle will decay into what products and with what probability. The predictions rely heavily on rules like conservation of mass+energy: the decay products' mass and energy ought to sum up to that of the pare