Viktor Ananiev

• Ananiev, Viktor & Read, Alexander Lincoln (2023). SigCorr: A Python package for studies of trials factors. Journal of Open Source Software (JOSS). ISSN 2475-9066. 8(87), p. 4989–4989. doi: 10.21105/joss.04989. Full text in Research Archive Show summary

  Up-crossings, Euler characteristic and Gaussian processes are commonly relied on for the estimation of trials factors. SigCorr is the first project that assembles all of these into one Python package, that also includes the tools for parallel analysis of the Monte Carlo "toy" experiments and Gaussian process "toys" in a unified fashion. Together with the fitting framework it allows the path from the statistical model definition to a TF estimate to be travelled. It also implements validated approximations and asymptotics for fast computations of the TF and its upper bound based on classical papers in the field. The possibility of doing this in a modular but consistent fashion makes SigCorr unique in the field, and will allow users to try different methods (Figure 1), cross-validate and choose or construct the most suitable approach to their analysis. (copied and slightly modified from the publication)

• Ananiev, Viktor & Read, Alexander Lincoln (2023). Linear approximation to the statistical significance autocovariance matrix in the asymptotic regime. Journal of Instrumentation (JINST). ISSN 1748-0221. 18(P10018). doi: 10.1088/1748-0221/18/10/P10018. Full text in Research Archive Show summary

  Approximating significance scans of searches for new particles in high-energy physics experiments as Gaussian fields is a well-established way to estimate the trials factors required to quantify global significances. We propose a novel, highly efficient method to estimate the covariance matrix of such a Gaussian field. The method is based on the linear approximation of statistical fluctuations of the signal amplitude. For one-dimensional searches the upper bound on the trials factor can then be calculated directly from the covariance matrix. For higher dimensions, the Gaussian process described by this covariance matrix may be sampled to calculate the trials factor directly. This method also serves as the theoretical basis for a recent study of the trials factor with an empirically constructed set of Asmiov-like background datasets. We illustrate the method with studies of a H → γγ inspired model that was used in the empirical paper.

• Ananiev, Viktor & Read, Alexander Lincoln (2023). Gaussian Process-based calculation of look-elsewhere trials factor. Journal of Instrumentation (JINST). ISSN 1748-0221. 18(P05041). doi: 10.1088/1748-0221/18/05/P05041. Full text in Research Archive Show summary

  In high-energy physics it is a recurring challenge to efficiently and precisely (enough) calculate the global significance of, e.g., a potential new resonance. We propose a new method that models the significance in the search region as a Gaussian Process. The kernel of the Gaussian Process is approximated with a covariance matrix and is calculated with a carefully designed set of background-only data sets, comparable in number to the random background-only data sets used in a typical analysis that relies on the average upcrossings of the significance. The trials factor for both low and moderate significances can subsequently be calculated to the desired precision with a computationally inexpensive random sampling of the Gaussian Process. In addition, once the covariance of the Gaussian Process is determined, the average number of upcrossings can be computed analytically. In our work we give some highlights of the analytic calculation and also discuss some peculiarities of the trials factor estimation on a finite grid. We illustrate the method with studies of three complementary statistical models.

• Ananiev, Viktor; Balázs, Csaba; Beniwal, Ankit; Braseth, Lasse Lorentz; Buckley, Andy & Butterworth, Jonathan [Show all 21 contributors for this article] (2023). Collider constraints on electroweakinos in the presence of a light gravitino. European Physical Journal C. ISSN 1434-6044. 83(6). doi: 10.1140/epjc/s10052-023-11574-z. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Measurements of Higgs boson production cross-sections in the H → τ+τ− decay channel in pp collisions at √s = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2022(8), p. 1–81. doi: 10.1007/JHEP08(2022)175. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Modelling and computational improvements to the simulation of single vector-boson plus jet processes for the ATLAS experiment. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2022(8), p. 1–61. doi: 10.1007/JHEP08(2022)089. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Study of B+c→J/ψD+s and B+c→J/ψD∗+s decays in pp collisions at √s = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2022(8), p. 1–42. doi: 10.1007/JHEP08(2022)087. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Measurements of the Higgs boson inclusive and differential fiducial cross-sections in the diphoton decay channel with pp collisions at √S = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 27(8), p. 1–96. doi: 10.1007/JHEP08(2022)027. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Observation of WWW production in pp collisions at √s=13 TeV with the ATLAS detector. Physical Review Letters. ISSN 0031-9007. 129(6), p. 1–20. doi: 10.1103/PhysRevLett.129.061803. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Measurement of Higgs boson decay into b-quarks in associated production with a top-quark pair in pp collisions at √S = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2022:97(6), p. 1–63. doi: 10.1007/JHEP06(2022)097. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Direct constraint on the Higgs–charm coupling from a search for Higgs boson decays into charm quarks with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 82:717(8), p. 1–42. doi: 10.1140/epjc/s10052-022-10588-3. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Search for invisible Higgs-boson decays in events with vector-boson fusion signatures using 139 fb−1 of proton-proton data recorded by the ATLAS experiment. Journal of High Energy Physics (JHEP). ISSN 1126-6708. 2022:104(8), p. 1–66. doi: 10.1007/JHEP08(2022)104. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 51 contributors for this article] (2022). Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in pp collisions at √s=13 TeV. Physical Review D. ISSN 2470-0010. 106:032005(3), p. 1–28. doi: 10.1103/PhysRevD.106.032005. Full text in Research Archive
• Ananiev, Viktor & Read, Alexander Lincoln (2022). Approximating the Mode of the Non-Central Chi-Squared Distribution. International Journal of Analysis and Applications. ISSN 2291-8639. doi: 10.28924/2291-8639-20-2022-19.
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). Search for flavour-changing neutral-current interactions of a top quark and a gluon in pp collisions at √s=13 TeV with the ATLAS detector. European Physical Journal C. ISSN 1434-6044. 82:334, p. 1–35. doi: 10.1140/epjc/s10052-022-10182-7. Full text in Research Archive
• Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira & Abhayasinghe, Deshan Kavishka [Show all 50 contributors for this article] (2022). AtlFast3: The Next Generation of Fast Simulation in ATLAS. Computing and Software for Big Science. ISSN 2510-2036. 6:7, p. 1–54. doi: 10.1007/s41781-021-00079-7. Full text in Research Archive

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• Ananiev, Viktor & Read, Alexander Lincoln (2023). SigCorr. Show summary

  SigCorr is a framework that implements a wide range of tools to conduct studies of the trials factor, which is an important parameter in the statistical characterization of searches for new phenonema, such as a hypothetical elementary particle or astrophysical source. Such searches are commonly carried out for a range of possible signal hypotheses. The statistical significance of the most significant observation (generally a localized excess of data in a broad background distribution) must take into account the possibility that the background could have fluctuated anywhere in the search region, not just at the point of maximum interest. Taking into account this so-called «look-elsewhere effect» is performed by correcting the corresponding p-value from its local to a global value. The ratio of the former to the latter is known in the statistical literature as the trials factor.

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