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The Rumble in the Meson: a leptoquark versus a Z′ to fit b → sμ+μ− anomalies including 2022 LHCb $ {R}_{K^{\left(\ast \right)}} $ measurements


Allanach, Ben; Davighi, Joe (2023). The Rumble in the Meson: a leptoquark versus a Z′ to fit b → sμ+μ− anomalies including 2022 LHCb $ {R}_{K^{\left(\ast \right)}} $ measurements. Journal of High Energy Physics, 2023(4):33.

Abstract

We juxtapose global fits of two bottom-up models (an S$_{3}$ scalar leptoquark model and a B$_{3}$ – L$_{2}$Z′ model) of b → sμ$^{+}$μ$^{−}$ anomalies to flavour data in order to quantify statistical preference or lack thereof. The leptoquark model couples directly to left-handed di-muon pairs, whereas the Z′ model couples to di-muon pairs with a vector-like coupling. $$ {B}_s-\overline{B_s} $$ mixing is a focus because it is typically expected to disfavour Z′ explanations. In two-parameter fits to 247 flavour observables, including B$_{s/d}$→ μ$^{+}$μ$^{−}$ branching ratios for which we provide an updated combination and LHCb $$ {R}_{K^{\left(\ast \right)}} $$ measurements from December 2022, we show that each model provides a similar improvement in quality-of-fit of $$ \sqrt{\Delta {\chi}^2} $$ = 3.6 with respect to the Standard Model. The main effect of the $$ {B}_s-\overline{B_s} $$ mixing constraint in the Z′ model is to disfavour values of the s$_{L}$– b$_{L}$ mixing angle greater than about 5|V$_{cb}$|. This limit is rather loose, meaning that a good fit to data does not require ‘alignment’ in either quark Yukawa matrix. No curtailment of the s$_{L}$− b$_{L}$ mixing angle is evident in the S$_{3}$ model.

Abstract

We juxtapose global fits of two bottom-up models (an S$_{3}$ scalar leptoquark model and a B$_{3}$ – L$_{2}$Z′ model) of b → sμ$^{+}$μ$^{−}$ anomalies to flavour data in order to quantify statistical preference or lack thereof. The leptoquark model couples directly to left-handed di-muon pairs, whereas the Z′ model couples to di-muon pairs with a vector-like coupling. $$ {B}_s-\overline{B_s} $$ mixing is a focus because it is typically expected to disfavour Z′ explanations. In two-parameter fits to 247 flavour observables, including B$_{s/d}$→ μ$^{+}$μ$^{−}$ branching ratios for which we provide an updated combination and LHCb $$ {R}_{K^{\left(\ast \right)}} $$ measurements from December 2022, we show that each model provides a similar improvement in quality-of-fit of $$ \sqrt{\Delta {\chi}^2} $$ = 3.6 with respect to the Standard Model. The main effect of the $$ {B}_s-\overline{B_s} $$ mixing constraint in the Z′ model is to disfavour values of the s$_{L}$– b$_{L}$ mixing angle greater than about 5|V$_{cb}$|. This limit is rather loose, meaning that a good fit to data does not require ‘alignment’ in either quark Yukawa matrix. No curtailment of the s$_{L}$− b$_{L}$ mixing angle is evident in the S$_{3}$ model.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > Nuclear and High Energy Physics
Uncontrolled Keywords:Nuclear and High Energy Physics
Language:English
Date:6 April 2023
Deposited On:05 Jan 2024 13:12
Last Modified:28 Jun 2024 03:37
Publisher:Springer
ISSN:1029-8479
OA Status:Gold
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1007/jhep04(2023)033
  • Content: Published Version
  • Language: English
  • Licence: Creative Commons: Attribution 4.0 International (CC BY 4.0)