Abstract
We introduce a new unbinned two sample test statistic sensitive to CP violation utilizing the optimal transport plan associated with the Wasserstein (earth mover’s) distance. The efficacy of the test statistic is shown via two examples of CP asymmetric distributions with varying sample sizes: the Dalitz distributions of B0 → K+π−π0 and of D0 → π+π−π0 decays. The windowed version of the Wasserstein distance test statistic is shown to have comparable sensitivity to CP violation as the commonly used energy test statistic, but also retains information about the localized distributions of CP asymmetry over the Dalitz plot. For large statistic datasets we introduce two modified Wasserstein distance based test statistics — the binned and the sliced Wasserstein distance statistics, which show comparable sensitivity to CP violation, but improved computing time and memory scalings. Finally, general extensions and applications of the introduced statistics are discussed.
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Acknowledgments
We thank S. Bressler, J. Thaler for discussions on the two sample tests, and M. Gersabeck, D. White, G. Sarpis, S. Chen and Y. Brodzicka in particular for extended discussions on the energy test, as well as M. Szewc for comments on the manuscript. We thank T. Latham for help with the Laura++ framework, T. Evans for support using the AmpGen framework, and J. Brod for providing access to the local computing resources. AD acknowledges support from STFC grants ST/S000925 and ST/W000601/1. AY, JZ and TM acknowledge support in part by the DOE grant de-sc0011784 and NSF OAC-2103889.
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Davis, A., Menzo, T., Youssef, A. et al. Earth mover’s distance as a measure of CP violation. J. High Energ. Phys. 2023, 98 (2023). https://doi.org/10.1007/JHEP06(2023)098
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DOI: https://doi.org/10.1007/JHEP06(2023)098