Can There Be a Fourth Generation of Charged Leptons in the Standard Model?

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In summary, The Standard Model deals with three generations of particles consisting of a charged lepton, a neutrino, and two quarks. This is based on experimental evidence and the model itself does not specify the number of generations. However, there have been theories proposing additional particles, such as non-generational neutrinos, which could potentially exist.
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wedge
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here I come with a question, maybe stupid.
everyone knows about electrons, muons, taus. Is a heavier charged lepton impossible to exist? why does SM deal with three generation of particles (each consisting in a charged lepton, a neutrino plus two quarks), and not more?

thanks everyone.
 
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  • #2
wedge said:
here I come with a question, maybe stupid.
everyone knows about electrons, muons, taus. Is a heavier charged lepton impossible to exist? why does SM deal with three generation of particles (each consisting in a charged lepton, a neutrino plus two quarks), and not more?

thanks everyone.

Hi Wedge,

There are strong experimental evidences against a fourth generation of (rather light) fermions :
- the Z cross-section measured at LEP prooves there are only 3 light neutrinos. Of course, it is still possible to have a fourth neutrino much more heavier or non-interacting with Z (but is it still a similar generation ?).
- the so-called "unitarity triangle" mainly cronstrained by B physics measurements is a triangle...
But, of course, nothing prooves there are 3 and only 3 generations. The SM tells nothing about the number of generations, this is an input of the model.
 
  • #3
Giving that the number of states is N*32, four generations is a kind of paradise for model builders: you have 128 states, a exact power of 2, and then Clifford algebras have a big role.

But there are only 3 light neutrinos.
 
  • #4
hello,
thank you so much for your answers :cool:
 
  • #5
There's still the neutrino 'puzzle' - to which there have been numerous rather outlandish suggestions; check the latest (I think) Scientific American for the details. Among the proto-theories are additional, non-generational and even more weakly-interacting neutrinos. So, you're unlikely to come up with another complete generation, but it's not out of the question for particles that don't belong in any generation to come up.
 

What is Generation 4 in particle physics?

Generation 4 in particle physics refers to the fourth generation of elementary particles, specifically the leptons: electron neutrino (νe), muon neutrino (νμ), tau neutrino (ντ), and their respective charged leptons: electron (e), muon (μ), and tau (τ). These particles are fundamental building blocks of matter and are currently being studied and researched by scientists in the field of particle physics.

What are the properties of Generation 4 particles?

Generation 4 particles have similar properties to their respective particles in previous generations, such as mass, charge, and spin. However, they are heavier and less stable than their predecessors, which makes them more difficult to study and detect. They also interact with other particles through the weak nuclear force, but their interactions with other particles are still being researched and studied.

How were Generation 4 particles discovered?

Generation 4 particles were first theorized by physicists in the 1970s as a possible extension of the Standard Model of particle physics. However, it wasn't until 2010 that the existence of the top quark, the last missing piece of the Standard Model, was confirmed through experiments at the Large Hadron Collider (LHC) in CERN. This discovery provided strong evidence for the existence of Generation 4 particles.

What is the significance of Generation 4 particles?

The study of Generation 4 particles can provide a deeper understanding of the fundamental laws of nature and the building blocks of the universe. It can also help explain why there is a difference in the masses of the elementary particles and the role of symmetry breaking in the universe. Additionally, the discovery of Generation 4 particles could potentially lead to new technologies and applications in fields such as medicine and energy.

Are there other generations of particles besides 4?

Currently, the Standard Model predicts the existence of only four generations of particles. However, some theories suggest the possibility of additional generations, which could potentially lead to the discovery of new particles and a better understanding of the universe. This is an area of active research and remains to be confirmed by future experiments and observations.

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