B Meson Lifetime: Exploring B-Tagging & Decay

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In summary: Yes, charm tagging is done when it is possible to do so. Charm is a harder particle to tag than b, so it is less common.
  • #1
Malamala
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Hello! I read about a technique called b-tagging in which one can check if a b meson was produced in a collision by looking for a jet which has a secondary vertex within it. The reason is that b mesons are long lived, so that meson would travel a bit before decaying, hence the secondary vertex. Why are b meson long lived? And why can't we do this with other kind of quarks, like strange or charm? Thank you!
 
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  • #2
Beautiful quark is noted for having a combination of long lifetime and large decay energy.
Strange quark is even longer lived but has a small decay energy.
Charmed quark has larger decay energy than strange, but shorter lifetime than beauty.
Strangeness:
lowest mesons are charged K, lifetime 12380 ps, energy 493 MeV, and long neutral K, lifetime 51660 ps, energy 497 MeV, lowest hyperon Λ, lifetime 263 ps, energy 1115 MeV
Charm:
lowest meson charged D, lifetime 1,04 ps, energy 1869 MeV, lowest hyperon charmed Λ, lifetime 0,2 ps, energy 2286 MeV
Beauty:
lowest meson charged B, lifetime 1,64 ps, energy, 5279 MeV, lowest hyperon beautiful Λ, lifetime 1,41 ps, energy 5620 MeV.
 
  • #3
snorkack said:
Beautiful quark is noted for having a combination of long lifetime and large decay energy.
Strange quark is even longer lived but has a small decay energy.
Charmed quark has larger decay energy than strange, but shorter lifetime than beauty.
Strangeness:
lowest mesons are charged K, lifetime 12380 ps, energy 493 MeV, and long neutral K, lifetime 51660 ps, energy 497 MeV, lowest hyperon Λ, lifetime 263 ps, energy 1115 MeV
Charm:
lowest meson charged D, lifetime 1,04 ps, energy 1869 MeV, lowest hyperon charmed Λ, lifetime 0,2 ps, energy 2286 MeV
Beauty:
lowest meson charged B, lifetime 1,64 ps, energy, 5279 MeV, lowest hyperon beautiful Λ, lifetime 1,41 ps, energy 5620 MeV.
Thank you for the reply! My confusion is, why there is a 4 order of magnitude difference between the b mesons lifetime and the charm mesons lifetime. They both decay by strong interaction and I would imagine a more massive particle to decay faster
 
  • #4
Malamala said:
why there is a 4 order of magnitude difference between the b mesons lifetime and the charm mesons lifetime.

No there isn't. They are comparable.

Malamala said:
They both decay by strong interaction

No they don't. They decay by the weak interaction.
 
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  • #5
B-tagging is more general, it's including all methods to detect that there was a B meson (and often it's also detecting the type, i.e. bottom or anti-bottom quark).
Collisions often produce pairs of b quarks which then fly away individually. Isolated b quarks can only decay via the weak interaction, that gives the lightest B hadrons a relatively long lifetime.

You can do the same with charm. It can decay within its generation (to strange), so the lifetime is a bit shorter but still comparable.
Particles with a strange quark live much longer, that leads to different approaches to study them.
 
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  • #6
Vanadium 50 said:
No there isn't. They are comparable.
No they don't. They decay by the weak interaction.
Sorry I meant why are they 4 orders of magnitude between strange and bottom mesons lifetime? Also, if charm and bottom have the same lifetime, why is there no such a thing as charm tagging, too? Thank you!
 
  • #7
mfb said:
B-tagging is more general, it's including all methods to detect that there was a B meson (and often it's also detecting the type, i.e. bottom or anti-bottom quark).
Collisions often produce pairs of b quarks which then fly away individually. Isolated b quarks can only decay via the weak interaction, that gives the lightest B hadrons a relatively long lifetime.

You can do the same with charm. It can decay within its generation (to strange), so the lifetime is a bit shorter but still comparable.
Particles with a strange quark live much longer, that leads to different approaches to study them.
Thanks a lot for this! I haven't actually heard of charm tagging anywhere before. Is that really done?
 
  • #8
Malamala said:
I meant why are they 4 orders of magnitude between strange and bottom mesons lifetime

Do you understand the lifetime calculation? The rate goes as Q5 which is much larger for b than s. So much larger that other factors have to come into play to keep the lifetime only four orders of magnitude less.

If you don't understand the lifetime calculation, I don't see how I can say much beyond "that's what comes out of the calculation".

Malamala said:
I haven't actually heard of charm tagging anywhere before. Is that really done?

Sure. It doesn't work well since you need to reject light quarks and b-quarks so are squeezed at both ends. Also, charm decays have fewer charged particles than b decays, so your tagger has less to work with.
 
  • #9

1. What is a B meson and why is its lifetime important in scientific research?

A B meson is a subatomic particle that is made up of a bottom quark and an anti-up quark. Its lifetime is important in scientific research because it can provide insights into the fundamental forces and interactions of the universe, specifically the weak force. By studying the lifetime of B mesons, scientists can better understand the behavior and decay of these particles, which can lead to a deeper understanding of the underlying laws of nature.

2. How do scientists measure the lifetime of B mesons?

Scientists use a technique called B-tagging, which involves identifying and tracking the decay products of B mesons. By measuring the time it takes for the B meson to decay, scientists can determine its lifetime. This is typically done in high-energy particle colliders, such as the Large Hadron Collider (LHC), where B mesons are produced in large quantities.

3. What is the current understanding of the B meson lifetime?

The current understanding of the B meson lifetime is based on experimental data and theoretical calculations. The most recent measurements from the LHC show that the B meson has a lifetime of approximately 1.5 trillionths of a second. This value is consistent with the predictions of the Standard Model of particle physics.

4. How does B-tagging help in studying B meson decay?

B-tagging allows scientists to identify and track the decay products of B mesons, which can provide valuable information about the decay process. By studying the decay products, scientists can determine the lifetime of the B meson and also gain insights into the interactions and forces involved in the decay process. B-tagging also helps in distinguishing B meson decays from other particles, which is crucial in accurately measuring its lifetime.

5. What are the potential implications of further research on B meson lifetime?

Further research on B meson lifetime could lead to a better understanding of the fundamental forces and interactions of the universe, which could have implications in various fields of science, including particle physics, cosmology, and astrophysics. It could also help in testing and refining the predictions of the Standard Model, and potentially lead to the discovery of new particles or phenomena that could challenge our current understanding of the universe.

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