What sparked the concept of baryon number in particle physics?

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Discussion Overview

The discussion centers on the historical origin and motivation behind the concept of baryon number in particle physics, particularly its introduction prior to the quark model. Participants explore its significance in explaining particle decay and conservation laws within the context of early experiments.

Discussion Character

  • Exploratory, Historical, Technical explanation

Main Points Raised

  • One participant notes that baryon number was introduced as a conserved quantity to explain the absence of certain decay processes, such as p -> e+ pi0.
  • Another participant mentions that the conservation of baryon number has been observed in all known experiments, tracing its origins back to early beta decay experiments, independent of quark theory.
  • It is suggested that baryons were documented before the quark model, leading researchers to categorize particles and assign baryon numbers based on their interactions in nuclear reactions.
  • Some participants propose that counting matter as +1 and antimatter as -1 for baryon number is a reasonable approach, while questioning how mesons should be categorized.
  • There is a discussion on how the quark model provides an explanation for why mesons have a baryon number of zero, suggesting that baryon number could be replaced with quark number, although the former remains widely used.

Areas of Agreement / Disagreement

Participants express various viewpoints on the historical context and implications of baryon number, with no consensus reached on a singular origin or interpretation of its significance.

Contextual Notes

Participants acknowledge that the discussion involves historical perspectives and interpretations that may depend on specific definitions and contexts within particle physics.

guest1234
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I'm doing a little research on quarks on stumbled upon the baryon number. Wikipedia says that the notion predates the quark model. I have no clue why particle physicists were motivated to introduce it before flavour quantum numbers came to the scene.

So... What's the (historical) origin of baryon number?
 
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Baryon number as a conserved quantity was to explain why you didn't see decays like p -> e+ pi0.
 
In all known experiments so far, the number of baryons is conserved, and the notion goes back to the early beta decay experiments. This has nothing to do with quarks, but most quark models incorporate baryon number conservation. Some extended symmetry theories predict proton decay into leptons and mesons which would violate baryon number conservation.
 
Well baryons were observed before the quark model and their behaviors documented.

One of the things researchers try is to sort things into groups and see what makes sense.

Doesn't it seem reasonable to count matter as +1 and antimatter as -1? Once you've done that for nucleons, and looked at what happens to the numbers in various nuclear reactions, what would be a sensible number to give mesons?
 
Where the quark model helps explain baryon number is motivating why baryon number of mesons is zero (quark/antiquark pair). Baryon number could be replaced with quark number, but everyone was used to baryon number.
 
Thanks everyone for your input! Got the type of answers I wanted.
 

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