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Accessing CKM suppressed top decays at the LHC

by Darius A. Faroughy, Jernej F. Kamenik, Manuel Szewc, Jure Zupan

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Submission summary

Authors (as registered SciPost users): Darius Faroughy · Jure Zupan
Submission information
Preprint Link: scipost_202303_00037v1  (pdf)
Date accepted: 2023-11-07
Date submitted: 2023-03-29 23:12
Submitted by: Faroughy, Darius
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
  • High-Energy Physics - Experiment
  • High-Energy Physics - Phenomenology
Approaches: Experimental, Phenomenological


We propose an extension of the existing experimental strategy for measuring branching fractions of top quark decays, targeting specifically $t\to j_q W$, where $j_q$ is a light quark jet. The improved strategy uses orthogonal $b$- and $q$-taggers, and adds a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of $b$-tagged jets in an event. Careful inclusion of the additional complementary observable significantly increases the expected statistical power of the analysis, with the possibility of excluding $|V_{tb}|=1$ at $95\%$ C.L. at the HL-LHC, and accessing directly the standard model value of $|V_{td}|^2+|V_{ts}|^2$.

Published as SciPost Phys. 16, 131 (2024)

Reports on this Submission

Anonymous Report 2 on 2023-9-19 (Invited Report)


The authors have sufficiently addressed my comments. Therefore I recommend this manuscript for publication.

  • validity: -
  • significance: -
  • originality: -
  • clarity: -
  • formatting: -
  • grammar: -

Anonymous Report 1 on 2023-8-25 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:scipost_202303_00037v1, delivered 2023-08-25, doi: 10.21468/SciPost.Report.7711


This is an interesting paper showing that to measure Vtb different from one counting q-jets in addition to counting b-jets substantially improves the sensitivity, potentially making a measurement possible at HL-LHC. The conclusions of the paper seem sound even if the model is simplified.


The mapping of the technique to real data may not yield the same improvements, but it seems certain there will be substantial improvement, so this is really a minor weakness.


The authors' answers to my previous comments address the issues raised. I still wonder what will happen when this is applied to not-so-well-modeled real data, but this should be a second order effect, and his certainly not up to these authors to address.

Requested changes


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

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