F2F, a model-independent method to determine the mass and width of a particle in the presence of interference

TL;DR

The paper introduces F2F, a model-independent Fourier-based method to detect and measure the mass and width of particles, accounting for interference effects, without relying on specific signal models.

Contribution

F2F is a novel, model-independent approach that uses Fourier series to determine particle properties amidst interference, applicable to Higgs and new resonance searches.

Findings

F2F accurately recovers input mass and width in toy experiments.

The method effectively measures the Standard-Model Higgs width.

F2F enables statistical interpretation in resonance searches with interference.

Abstract

It is generally believed that any particle to be discovered will have a TeV-order mass. Given its great mass, it must have a large decay width. Therefore, the interference effect will be very common if they and the Standard-Model (SM) particles contribute to the same final state.However, the interference effect could make a new particle show up not like a resonance, and it is difficult to search and measure its properties. In this work, a model-independent method, F2F (Fit To Fourier coefficients), is proposed to search for an unknown resonance and to determine its mass ($M$) and width ($\Gamma$) in the presence of interference. Basically we express the sum of reosnant signal and the interference as a cosine Fourier series and relate the Fourier coefficients with the mass and width. The relation is based on the general propagator form, $1/(x^2-M^2+iM\Gamma)$. Thus it does not need any signal model. Toy experiments show that the obtained mass and width agree well with the inputs with a similar precision as using an explicit signal model. We also show that we can apply this method to measure the Stardard-Model Higgs width and to make statistic interpretation in searching for new resonance allowing for interference.