Inadequacy of zero-width approximation for a light Higgs boson signal

Understand

The zero-width approximation (ZWA) restricts the intermediate unstable particle state to the mass shell and, when combined with the decorrelation approximation, fully factorizes the production and decay of unstable particles.

• The ZWA uncertainty is expected to be of O(Gamma/M), where M and Gamma are the mass and width of the unstable particle.
• We review the ZWA and demonstrate that errors can be much larger than expected if a significant modification of the Breit-Wigner lineshape occurs.
• A thorough examination of the recently discovered candidate Standard Model Higgs boson is in progress.