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First steps towards the reconstruction of the squark flavour structure

by Jordan Bernigaud, Björn Herrmann

Submission summary

As Contributors: Jordan Bernigaud · Björn Herrmann
Arxiv Link: https://arxiv.org/abs/1809.04370v2
Date submitted: 2019-01-18
Submitted by: Herrmann, Björn
Submitted to: SciPost Physics
Domain(s): Theoretical
Subject area: High-Energy Physics - Phenomenology

Abstract

Assuming the observation of a squark at the Large Hadron Collider, we investigate methods to access its flavour content and thus gain information on the underlying flavour structure of the theory. Based on simple observables, we apply a likelihood inference method to determine the top-flavour content of the observed particle. In addition, we employ a multivariate analysis in order to classify different flavour hypotheses. Both methods are discussed within a simplified model and the more general Minimal Supersymmetric Standard Model including most general squark mixing. We conclude that the likelihood inference may provide an estimation of the top-flavour content if additional knowledge, especially on the gaugino sector is available, while the multivariate analysis identifies different flavour patterns and can accommodate a more minimalistic set of observables.

Current status:
Editor-in-charge assigned


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Anonymous Report 1 on 2019-2-14 Invited Report

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Report

The manuscript provides pioneering work for the determination of the flavour content of a squark from a set of experimental properties such as its mass and ratios of decay rates into final states with top, bottom or charm. Two complementary methods are employed, a likelihood inference method and a multivariate analysis, and their respective strengths and weaknesses are discussed. The work is original and the results are interesting and may trigger further studies. The presentation is clear and the style and length is appropriate.

I have one question to the authors to be addressed prior to publication: How would a change in the experimental uncertainties, assumed to be 25% for all observables entering the analysis, affect the results of the applied methods? Are the uncertainties in the ratios R_c/t and R_b/t the limiting factor in discriminiating between different flavour contents, as one might naively assume?

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  • validity: high
  • significance: high
  • originality: top
  • clarity: high
  • formatting: excellent
  • grammar: good

Author Björn Herrmann on 2019-03-11 (in reply to Report 1 on 2019-02-14)
Category:
remark
answer to question

We would like to thank the Referee for the evaluation of our manuscript and for her/his interest in our work.

Regarding the questions concerning the uncertainties:

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“I have one question to the authors to be addressed prior to publication: How would a change in the experimental uncertainties, assumed to be 25% for all observables entering the analysis, affect the results of the applied methods?”
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During our analysis, we had investigated the question of the impact of the uncertainties mentioned by the Referee by varying the value of $\sigma_i$ for a given reference point.

As expected, increasing the uncertainties $\sigma_i$ leads to an increase in the uncertainty $\sigma(x_{\tilde{t}})$ obtained from the Gaussian fit.

However, special care has to be taken when reducing the value of $\sigma_i$. First, the quality of the Monte Carlo sampling plays a crucial role. Indeed, if the parameter space is not populated well enough, the Gaussian fit “breaks down”, i.e. it cannot yield a meaningful result. In addition, if one considers the more general setup, e.g. without fixing the gaugino parameters, degeneracies between the observables and the top-content $x_{\tilde{t}}$ appear, as can be seen in Fig. 3 of our manuscript. This may lead to additional complications concerning the uncertainties.

This is why, in this first attempt of reconstructing the top content $x_{\tilde{t}}$, we do not perform a dedicated analysis of the impact of the uncertainties $\sigma_i$. In the present work, we focus on showing that it is possible to obtain information on the flavour content (in particular $x_{\tilde{t}}$) rather than presenting a complete analysis including the uncertainties.

However, this question will need to be addressed properly in the case of an actual observation of a squark-like state. In this situation, the analysis proposed here will become crucial, and information about the underlying uncertainties will be known.

As a last comment, let us emphasize that the observables should have different uncertainties $\sigma_i$.

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“Are the uncertainties in the ratios $R_{c/t}$ and $R_{b/t}$ the limiting factor in discriminiating between different flavour contents, as one might naively assume?”
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The Referee is right by assuming that the uncertainties on $R_{c/t}$ and $R_{b/t}$ would be the most limiting factors in the analysis. In particular, $R_{c/t}$ is the most constraining observable, since it shows a strong correlation with the parameter $x_{\tilde{t}}$, as can be seen in Fig. 3 of our manuscript.

We will be happy to update our manuscript with the above comments, should it be judged necessary by the Referee or the Editor.

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