Discussion Overview
The discussion revolves around the decay of the Higgs boson into Z and off-shell Z* particles at the Large Hadron Collider (LHC). Participants explore the implications of this decay, the characteristics of the Z* particle, and the experimental observations related to Higgs decay processes.
Discussion Character
- Technical explanation
- Experimental/applied
- Debate/contested
Main Points Raised
- One participant asks for clarification on what Z* is in the context of Higgs decay and why it has a different mass from the Z boson.
- Another participant explains that Z* refers to an off-shell Z particle, indicating that it is not a physical Z boson but rather a set of particles resulting from a Z-interaction, noting that the Higgs is too light to produce two on-shell Z bosons in decay.
- A participant provides a definition of on-shell conditions, referencing the energy-momentum relation and relating it to muon decay as an example.
- Experimental measurements are discussed, highlighting that four muons (two positive and two negative) are detected, and the process of selecting events with a specific invariant mass related to the Z boson is described.
- Another participant suggests that if the Higgs mass were greater than twice the Z mass, additional cuts could be made to identify pairs of muons with invariant mass equal to the Z mass.
- One participant remarks on the visibility of the ZZ* decay, questioning why this decay is significant despite the Z* being off-shell by a considerable amount, suggesting that the longitudinal component of the Z boson is associated with the Higgs.
- It is noted that the branching ratio for WW* decays is higher for a Higgs mass of 125 GeV, but these decays are more complex and challenging to measure compared to Z decays.
- A participant asserts that WW decays will always be more prominent than ZZ decays, attributing this to theoretical considerations involving Clebsch and Gordon.
Areas of Agreement / Disagreement
Participants express differing views on the significance and implications of the Z* particle in Higgs decay, as well as the comparative visibility of ZZ and WW decays. There is no consensus on the reasons behind the observed decay characteristics.
Contextual Notes
Participants reference specific experimental thresholds, decay characteristics, and theoretical models without resolving the underlying assumptions or dependencies on definitions related to off-shell particles.