Can Z decay into a neutral pion?

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    Decay Neutral Pion
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Discussion Overview

The discussion centers around the possibility of the decay process \(\Xi^0 \to \Lambda + \pi^0\), exploring the mechanisms involved, particularly the role of the Z boson in quark flavor transitions. Participants examine theoretical aspects of particle decay, including the interactions of quarks and the constraints of the Standard Model.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes that a strange quark in the Lambda particle could emit a Z boson, transitioning to a down quark, which would then create an up-antiup pair through the Z boson.
  • Another participant asserts that the decay mode \(\Xi^0 \to \Lambda + \pi^0\) is dominant with a branching fraction greater than 99.5%, suggesting a different decay mechanism involving a W boson instead of a Z boson.
  • It is noted that while the Z boson can interact with quarks, flavor changes via Z emission require loop processes, not direct transitions.
  • A later reply clarifies that Z bosons cannot change quark flavor at tree level, and flavor-changing neutral currents (FCNC) are not permitted without loop corrections.
  • Confusion arises regarding the ability of the Z boson to change quark flavor, with references to external sources that claim Z bosons cannot change flavor.

Areas of Agreement / Disagreement

Participants express disagreement regarding the role of the Z boson in flavor-changing processes, with some asserting that it cannot change flavor while others suggest that it can under certain conditions. The discussion remains unresolved on the specifics of quark transitions involving Z bosons.

Contextual Notes

Participants reference the Standard Model's constraints on flavor-changing processes and the necessity of loop corrections for certain interactions, indicating a complex interplay of theoretical principles that are not fully settled in the discussion.

center o bass
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I wondered if the following decay was possible:
[tex]\Xi^0 \to \Lambda + \pi^0[/tex]

The only mechanism I can think of is that a strange quark of the Lambda particle emits a Z and becomes a down quark followed by the Z creating a up-antiup pair. But I'm not sure whether the strange to up transition (by emission of Z) is allowed. Neither am I sure about the Z to u-antiu pair is allowed. I know that W can decay into an up and a down quark, but do the Z only interact with neutrinos?
 
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http://pdglive.lbl.gov/Rsummary.brl?nodein=S023&sub=Yr&return=BXXX030 , this is the dominant decay mode with >99,5% branching fraction.

s->u+W, W->anti-u+d, combine the d with the existing u+s to form the lambda, and use the u anti-u for the pion.

The Z can interact with quarks, but in order to change their flavor with Z emission you need loop processes.
 
Last edited by a moderator:
mfb said:
http://pdglive.lbl.gov/Rsummary.brl?nodein=S023&sub=Yr&return=BXXX030 , this is the dominant decay mode with >99,5% branching fraction.

s->u+W, W->anti-u+d, combine the d with the existing u+s to form the lambda, and use the u anti-u for the pion.

The Z can interact with quarks, but in order to change their flavor with Z emission you need loop processes.

Thank you for the reply! So the Z can change flavour anyway? I did some research and found this page on hyperphysics which claimed that a Z boson could not change the flavour of quarks.

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neucur.html#c1
 
Last edited by a moderator:
It is true that a Z cannot change flavour - there are no so called Flavour Changing Neutral Currents (FCNC) - at tree level (i.e. without loops). A source of confusion might be that FCNC processes are permitted at higher order, that is, when loops are included. See the picture at Wikipedia: http://en.wikipedia.org/wiki/Flavor-changing_neutral_current

A Z boson will however, never be able to change the flavour of a quark "on its own". So decays of the type s->Z+d are not permitted in the Standard Model.
 

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