J/psi Meson Detection: ΔEΔt≈h

In summary, the conversation discusses the difference between a histogram peak and standard deviation in a CMS graph. The speaker expected the peak to align with their calculation, but was confused by the 52±3 standard deviation. The teacher explains that the larger width and different shape are also differences, and there are other factors to consider in the CMS measurement. Additionally, the conversation compares this situation to measuring the length of something with a ruler, where the result may not necessarily be the exact length.
  • #1
MoAli
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Homework Statement


See Image
The bit about Spectral lines, I couldn't explain why[/B]

Homework Equations


ΔEΔt≈h

The Attempt at a Solution


I expected the histogram to peak at the given mass in question and to have a width of about 0.08 MeV calculated as ΔE from the Energy-time uncertainty, but I don't understand how the standard deviation is 52±3 in the CMS graph, this is so far away from my calculation, plus, is this the only difference? I would also suspect that i misunderstood the question maybe. I haven't dealt with such graphs before!
 

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  • #2
If you measure the length of something that is exactly 1.381352413243543 meters long with a ruler, do you expect a result of 1.381352413243543 meters? What would actually happen?

The same happens in the CMS measurement, just for different reasons because it is not a length measurement.

The larger width is not the only difference, the shape looks different as well, and there are at least two things you can find (although I'm not sure if the teacher expects those).
 

What is a J/psi meson?

A J/psi meson is a subatomic particle made up of a charm quark and its antiparticle, the charm antiquark. It was first observed in 1974 and has a mass of approximately 3097 MeV/c².

How is a J/psi meson detected?

A J/psi meson can be detected through its decay products, which typically include a muon and an antimuon. The detection process involves measuring the energy (ΔE) and time (Δt) of the decay products, and comparing it to the expected value of Planck's constant (h). If ΔEΔt≈h, it is a strong indication that a J/psi meson was present.

Why is ΔEΔt≈h used for J/psi meson detection?

ΔEΔt≈h is a characteristic signature of J/psi meson decays, as it follows from the conservation of energy and momentum in the decay process. This method of detection is also useful because it allows for the identification of J/psi mesons in the presence of background noise.

What is the significance of detecting J/psi mesons?

The detection of J/psi mesons is significant because it provides evidence for the existence of charm quarks, which were first theorized in the 1960s but not directly observed until the discovery of J/psi mesons. It also helps to further our understanding of the fundamental forces and particles that make up our universe.

What are some applications of J/psi meson detection?

J/psi meson detection has many applications in particle physics research, including the study of quark-gluon plasma and the search for new particles and interactions. It is also used in medical imaging techniques, such as PET scans, to track the decay of positron-emitting isotopes in the body.

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