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The effects of a scalar singlet Leptoquark at the $Z$ factory

Dazhuang He, Yu Zhang, Hao Sun

Abstract

We evaluate the observability of the effects of a scalar singlet leptoquark (LQ) in $μ$ and $τ$-pair productions at the $Z$ factory. In the scenario addressing the charged-current anomalies, the LQ contributions to $μ$-pair final state are negligible. In contrast, a sizable contribution arises in the $τ$-pair production, which is identical in both $Z$ decay and $e^+e^-$ collider at $Z$ pole. These effects are mainly sensitive to left-handed interaction, showing a maximum deviation of about $-0.7\%$ for both 1\,TeV and 2\,TeV LQ. The suppression of new physics effects from the heavy LQ can be compensated by the enlarged couplings parameter space. For the $τ$-pair production channel, we further specify the coupling constraints corresponding to the expected measurement precision at the future $Z$ factory. Moreover, we provide an analytic function in terms of the LQ mass and couplings to quantify the LQ effects. The differential distributions in the collision process indicate that the LQ effects remain stable throughout the kinematic region. Meanwhile, the measurement sensitivity of the $τ$-pair final state at the future $Z$ factory is expected to impose further constraints on the LQ theory.

The effects of a scalar singlet Leptoquark at the $Z$ factory

Abstract

We evaluate the observability of the effects of a scalar singlet leptoquark (LQ) in and -pair productions at the factory. In the scenario addressing the charged-current anomalies, the LQ contributions to -pair final state are negligible. In contrast, a sizable contribution arises in the -pair production, which is identical in both decay and collider at pole. These effects are mainly sensitive to left-handed interaction, showing a maximum deviation of about for both 1\,TeV and 2\,TeV LQ. The suppression of new physics effects from the heavy LQ can be compensated by the enlarged couplings parameter space. For the -pair production channel, we further specify the coupling constraints corresponding to the expected measurement precision at the future factory. Moreover, we provide an analytic function in terms of the LQ mass and couplings to quantify the LQ effects. The differential distributions in the collision process indicate that the LQ effects remain stable throughout the kinematic region. Meanwhile, the measurement sensitivity of the -pair final state at the future factory is expected to impose further constraints on the LQ theory.

Paper Structure

This paper contains 5 sections, 6 equations, 8 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Model
  3. The $\tau$ and $\mu$-pair productions in $Z$ decay
  4. The $\tau$ and $\mu$-pair productions at $e^+ e^-$ collider
  5. Summary

Figures (8)

  • Figure 1: The contribution of single scalar LQ $S_1$ to semi-leptonic B-meson decay is shown.
  • Figure 2: The contributions of $S_1$ to V-bosons self-energy functions, $\tau$ lepton self-energy function and $Z\tau \tau$ vertex, where $V=Z$ and $\gamma$.
  • Figure 3: The contributions of $S_1$ to $Z \to \tau^+ \tau^-$ decay. The left and right panels are the results of $M_{S_1}=1,2$ TeV, respectively.
  • Figure 4: The dependence of NP effects on $M_{S_1}$ for $Z \to \tau^+ \tau^-$ and $Z \to \mu^+ \mu^-$ decays are shown in left and right panels. The couplings in the left panel fixed to the values of BP0 and BP1.
  • Figure 5: The left panel shows the dependence of NP effects on the right-hand coupling by fixing the $\lambda_{b\tau}^{1L}=$ 0.5, 0.8, 1 and $M_{S_1}=$ 1 TeV. The right panel shows the dependence of the NP effects on the left-handed coupling $\lambda_{b\tau}^{1L}$, with $\lambda_{c\tau}^{1R}$ fixed to zero. The numerical results we calculated are indicated by the dots, while the curves correspond to the results obtained from function Eq. \ref{['eq:fitted']}.
  • ...and 3 more figures