SciPost Submission Page
Status of leptoquark models after LHC Run-2 and discovery prospects at future colliders
by Dr. Nishita Desai, Amartya Sengupta
Submission summary
| Authors (as registered SciPost users): | Amartya Sengupta |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202406_00034v1 (pdf) |
| Date submitted: | 2024-06-15 14:54 |
| Submitted by: | Sengupta, Amartya |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Computational, Phenomenological |
Abstract
We study limits from dilepton searches on leptoquark completions to the Stan- dard Model in the parameter space motivated by anomalies in the b → s sector. After a full Run-2 analysis by LHCb, the disparity in lepton flavour universality violation has disappeared. However, the mismatch in angular distributions as well as in Bs → μ+μ− partial width is still unresolved and still implies a possible new physics contribution. We probe three models of leptoquarks — scalar models S3 and R2 as well as vector leptoquark model U1 using non-resonant dilepton searches to place limit on both the mass and couplings to SM fermions. Current limits on lepto- quarks with both non-uniform or uniform coupling to lepton flavours are calculated. Interestingly, if leptoquark couplings to electrons and muons are indeed universal, then the U1 model parameter space that corresponds to the anomalous contribution should already be accessible with Run-2 data in the non-resonant eμ channel. In the non-universal case, there is a significant exclusion in couplings, but not enough to reach regions that explain observed anomalies. We, therefore, examine the prospec- tive sensitivity at the HL-LHC as well as of a 3 TeV future muon collider. For the vector leptoquark model, we find that a muon collider can probe all of the relevant parameter space at 95% confidence with just 1 fb^{-1} data whereas R2 and S3 models can be excluded at 95% with 5 fb^{−1} and 6.5 fb^{−1} luminosity respectively.
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Report
The paper aims to study bounds on LQ models on the basis of the still surviving anomalies in the B-sector. In doing so, the presented studies rely on the limits on the relevant Wilson coefficient of a low-energy weak Hamiltonian, derived in the literature at the end of 2022. However, it needs to be reiterated that it is questionable to what extent these exact limits are still valid. The CMS results (2401.07090) have been available as a PAS note for quite some time and it is not acceptable to entirely ignore them. In this context, the title “Status of leptoquark models after LHC Run2”, implying that all relevant Run2 results are taken into consideration, is simply misleading.
Furthermore, there is no discussion provided of what is already known in the literature regarding the impact of the 2022 LHCb measurement on the validity of leptoquark models and the values of the relevant Wilson coefficients. Such analysis have been done by multiple groups, not only Ref.7, but also e.g. 2212.10497, 2304.07330, 2310.05585. Given the amount of information available, the authors should justify why they pick a result from just one paper and how the results of other analyses might impact they conclusions.
Also, as the idea behind the presented studies is not very original (similar ideas, just differently realised, have been explored), I would expect that the authors would make an effort to make detailed studies, taking into account how the end results can be affected. In contrast, the presented analysis is very arbitrary: assumptions are made without discussing their validity or their effects on the conclusions, higher-order effects are only sometimes included, sometimes not, the limitations of or uncertainties on the derived bounds are not discussed, etc.
Altogether, the paper gives an impression of an outdated draft (also manifesting through the lack of any references to 2023 or 2024 papers), instead of a high-quality final product.
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Strengths
The complete multiplet structure of the leptoquarks is taken into account whenver applicable.
Weaknesses
The results are results are not as general as indicated by the abstract and the conclusion but depend on the chosen coupling structures. No NLO corrections for the cross sections are taken into account.
Report
This paper does not meet at the current stage the expection requirements. Further details are required.
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Report
The paper provides a status of leptoquark models which is not up to date in two respects: first the motivations from B physics should be updated as they seem more than a year old. Indeed for example the Bs -> mu mu is indicated as not consistent with the SM, but taking both CMS and LHCb data into account it is in overall agreement with the SM at present. I suggest the authors update this part using recent fits. Second the choice of models for the leptoquarks is also obsolete and largely incomplete in many respects as still referring to papers mainly from 2016-2018. I suggest the authors to have a look for example to the recent papers of the Isidori group on leptoquark models consistent with flavour constraints and which also include an interesting UV completion.
Another main point concerns the bounds themselves: the analysis is a simple leading order comparison with data. More refined analyses exist in the literature. As an example see the NLO one for scalar leptoquarks at LHC in 2108.11404
In my opinion the paper does not provide an accurate present status of leptoquark models and misses existing work in the field which is more advanced and more up to date.
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