Error propagation in Amplitude Analysis

The following is a review of error propagation needed to compute the errors on the normalization integrals and the intensity sum that is based on them. Consider the estimator for the intensity for a given PWA solution, based on a sum over a Monte Carlo sample with N_gen phase space events generated and N reconstructed and passing all cuts. Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I=\frac{1}{N_{gen}}\sum_i^N{ \sum_{\gamma,\delta}{\rho_{\gamma\delta} \sum_{\alpha,\beta}^n{ u_\alpha u_\beta^* A_\alpha^{\gamma}(x_i) A_\beta^{\delta *}(x_i) } } } }

where the PWA sum is over n coherent amplitudes, and indices γ, δ represent the spins of the external particles (incoming photon, incoming and outgoing nucleon), with ρ representing their collective spin-density matrix. When amplitude analysis fits contain amplitudes with no free parameters, it is convenient to rearrange the summations above, to pre-compute the sum over the intensities of the events:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I=\sum_{\gamma,\delta}{\rho_{\gamma\delta} \sum_{\alpha,\beta}^n{ u_\alpha u_\beta^* \left[ \frac{1}{N_{gen}}\sum_i^N{ A_\alpha^{\gamma}(x_i) A_\beta^{\delta *}(x_i) } \right] } } = \sum_{\alpha,\beta}^n{ u_\alpha u_\beta^* \left[ \sum_{\gamma,\delta}{\rho_{\gamma\delta} \frac{1}{N_{gen}}\sum_i^N{ A_\alpha^{\gamma}(x_i) A_\beta^{\delta *}(x_i) } }\right] } = \sum_{\alpha,\beta}^n{ u_\alpha u_\beta^* I_{\alpha\beta} } }

storing the term in square brackets, a matrix indexed by α,β, for contractions with varying free PWA parameters u in the course of a fit.

When considering the uncertainty on the overall integral, both the errors on u parameters and those from the finite MC set of events will contribute. A single detected event (i) can be viewed as one sample in a process of independent events, having therefore a count uncertainty of σ_i=1. An integral over such events is then a weighted sum of such samples, having resulting in a contribution to the variance:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma_{MC}^2= \sum_i^N{ \sigma_i^2 \left| \frac{1}{N_{gen}} \sum_{\gamma,\delta}{\rho_{\gamma\delta} \sum_{\alpha,\beta}^n{ u_\alpha u_\beta^* A_\alpha^{\gamma \delta}(x_i) A_\beta^{\gamma \delta *}(x_i) } } \right|^2 } }

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle = \sum_{\gamma,\delta,\gamma',\delta'}{ \rho_{\gamma\delta}\rho_{\gamma'\delta'} \sum_{\alpha,\beta,\alpha',\beta'}^n{ u_\alpha u_\beta^* u_{\alpha'} u_{\beta'}^* \left[ \frac{1}{N_{gen}^2} \sum_i^N{ A_\alpha^{\gamma \delta}(x_i) A_\beta^{\gamma \delta *}(x_i) A_{\alpha'}^{\gamma' \delta'}(x_i) A_{\beta'}^{\gamma' \delta' *}(x_i) } \right] } } }

The relevant piece to pre-compute over the event set for error calculation is shown in brackets. Turning our attention now to the contribution to error on the production parameters u:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma_{fit}^2= \left| \sum_k^n{ \sigma_{u_k} \frac{\partial}{\partial u_k}\left( \sum_{\gamma,\delta}{ \rho_{\gamma\delta} \sum_{\alpha,\beta}^n{u_\alpha u_\beta^* J_{\alpha\beta}} } \right) } \right|^2 }

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle =\left( \sum_k^n{ \sigma_{u_k} \sum_{\gamma,\delta}{ \rho_{\gamma\delta} \sum_{\alpha,\beta}^n{\delta_{k\alpha} u_\beta^* J^{\gamma\delta}_{\alpha\beta}} } }\right) \left( \sum_{k'}^n{ \sigma^*_{u_{k'}} \sum_{\gamma',\delta'}{ \rho_{\gamma'\delta'} \sum_{\alpha',\beta'}^n{\delta_{k'\alpha'} u_{\beta'} J^{\gamma'\delta'*}_{\alpha'\beta'}} } }\right) }

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle = \sum_{\gamma,\delta,\gamma',\delta'}{ \rho_{\gamma\delta} \rho_{\gamma'\delta'} \sum_{\alpha,\beta,\alpha',\beta'}^n{ \left(\sigma_{u_\alpha}\sigma^*_{u_{\alpha'}}\right) \left(u_\beta^* J^{\gamma\delta}_{\alpha\beta}\right) \left(u_{\beta'} J^{\gamma'\delta'*}_{\alpha'\beta'} \right) } } }

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle = \sum_{\gamma,\delta,\gamma',\delta'}{ \rho_{\gamma\delta} \rho_{\gamma'\delta'} \sum_{\alpha,\alpha'}^n{ \left(\sigma_{u_\alpha}\sigma^*_{u_{\alpha'}}\right) G^{\gamma\delta*}_\alpha G_{\alpha'}^{\gamma\delta} } } }

The product of σ terms in the summation is represented by the error matrix derived from the fit. G was defined as

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle G_\alpha^{\gamma\delta}=\sum_\beta{ u_\beta J_{\alpha\beta}^{\gamma\delta}} }

The overall uncertainty in the integral I defined in the beginning comes out to:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sigma_I=\sqrt{\sigma^2_{MC} + \sigma^2_{fit}} }