2021
DOI: 10.21468/scipostphys.11.3.061
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Better latent spaces for better autoencoders

Abstract: Autoencoders as tools behind anomaly searches at the LHC have the structural problem that they only work in one direction, extracting jets with higher complexity but not the other way around. To address this, we derive classifiers from the latent space of (variational) autoencoders, specifically in Gaussian mixture and Dirichlet latent spaces. In particular, the Dirichlet setup solves the problem and improves both the performance and the interpretability of the networks.

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Cited by 52 publications
(53 citation statements)
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“…Again, VAEs have been shown to work for anomaly searches with LHC jets [6,7], and we can replace the reconstruction loss by an anomaly score defined in latent space. At this point, an interesting and relevant question becomes the choice of latent space and specific anomaly score, for instance in a Dirichlet latent space [8,9] which encourages mode separation [4].…”
Section: What Is Anomalous?mentioning
confidence: 99%
“…Again, VAEs have been shown to work for anomaly searches with LHC jets [6,7], and we can replace the reconstruction loss by an anomaly score defined in latent space. At this point, an interesting and relevant question becomes the choice of latent space and specific anomaly score, for instance in a Dirichlet latent space [8,9] which encourages mode separation [4].…”
Section: What Is Anomalous?mentioning
confidence: 99%
“…We hypothesize that this is because, unlike many experimental signatures, SUEP is less complex than its QCD background, and it has smaller values of ∆R than QCD. This complexity bias has been noted before [45,52,53]. The sigmoid function reduces sensitivity to large values of ∆R and p T by mapping them to values very close to 1, while remaining approximately linear for small input values, but offset to a minimum value of 0.5.…”
Section: Unsupervised Autoencodermentioning
confidence: 71%
“…To improve on this, we utilize supervised as well as unsupervised machine learning (ML). Unsupervised analysis concepts along the lines of autoencoder neural networks [39] have the potential to transform LHC analyses [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56], including searches for dark showers [45]. We point out how unsupervised methods are especially appealing for difficult-to-simulate signals like SUEP since they only rely on the known QCD background for training, while yielding at least several times greater SUEP sensitivity than the cut-and-count analysis.…”
Section: Introductionmentioning
confidence: 99%
“…Once a model is trained to recognize the background, one can evaluate it on unlabeled data and use the reconstruction errors as a measure of similarity of a given sample to the training data set. Typically, a model trained on QCD will return low reconstruction loss for samples similar to those it was trained on, and high loss for samples that are more complex [24,25]. In case of a search for new physics, an autoencoder would be trained and evaluated, with the largest 10%, 1%, and 0.1% of its reconstruction losses isolated and analyzed.…”
Section: Autoencodersmentioning
confidence: 99%