Abstract
Spin correlations are an important, but often neglected, effect in modern Monte Carlo event generators. We show that they can be fully incorporated in Herwig7 using the algorithm originally proposed by Collins and Knowles in all stages of the event generation process and between the different stages of the event generation. In this paper we present the final missing ingredient, correlations in both the angular-ordered and dipole shower algorithms and between the parton shower and hard production and decay processes.
Highlights
Monte Carlo event generators are essential in modern particle physics as they provide state-of-the-art theoretical calculations which can be directly compared to experimental results
In order to fully include these correlations, such that the complexity of the calculation only grows linearly with the number of final-state particles, the algorithm of Refs. [14,15,16,17,18] can be used. This algorithm was used in Herwig6 [19] to implement the correlations in the parton shower, between the hard process and the parton shower emissions [15,16,17] and between the production and decay of heavy particles, in both the Standard Model, the MSSM and its R-parity violating extension
We choose to calculate the branchings in a frame where the branching particle is along the z-axis, which is the choice made in the angular-ordered parton shower algorithm [25] in Herwig7
Summary
Monte Carlo event generators are essential in modern particle physics as they provide state-of-the-art theoretical calculations which can be directly compared to experimental results. In recent years most of the developments in these programs have focused on improving the accuracy of the hard perturbative calculation by matching with higher order and higher multiplicity matrix elements. Spin correlations give rise to correlations between the emissions in the parton shower and the hard process, and between the production and decay of heavy particles, such as the top quark. [14,15,16,17,18] can be used This algorithm was used in Herwig6 [19] to implement the correlations in the parton shower, between the hard process and the parton shower emissions [15,16,17] and between the production and decay of heavy particles, in both the Standard Model, the MSSM and its R-parity violating extension.. In this paper we will present the necessary calculations in order to implement these correlations in both parton shower algorithms available in Herwig and results from their implementation which will be available in Herwig7.2. We present some results from the implementation in Herwig followed by our conclusions
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