Parity Violating Asymmetries in Top Pair Production at Hadron Colliders

TL;DR

The paper investigates loop-induced parity-violating electroweak effects in polarized top-quark pair production at hadron colliders within the 2HDM and MSSM, addressing a calculation where SM EW corrections are small but new physics can enhance parity-violating observables. It presents a formalism for polarized $t\bar{t}$ production at ${\cal O}(\alpha\alpha_s^2)$, parameterizing corrections with form factors $F_V$, $F_M$, and $G_A$, and analyzes differential and integrated asymmetries in $M_{t\bar{t}}$ and the total rate. The results show 2HDM can yield integrated asymmetries up to about $2.5\%$ at the LHC and $1.4\%$ at the Tevatron, while MSSM can reach up to about $3.2\%$ at the LHC and $1.7\%$ at the Tevatron, with the size depending on Higgs/SUSY parameters such as $\tan\beta$, $M_A$, $M_{H^{\pm}}$, $\mu$, $M_2$, and $m_{\tilde{t}_1}$. The findings indicate that polarization observables at the LHC could provide a clean probe of parity-violating EW interactions beyond the SM, whereas Tevatron sensitivity is more limited by statistics.

Abstract

We study loop-induced parity violating asymmetries in the strong production of polarized top quark pairs at $pp$ and $p \bar p$ colliders. The electroweak ${\cal O}(α)$ corrections to the helicity amplitudes of $q \bar q \to t \bar t$ and $gg \to t \bar t$ are evaluated in a two Higgs doublet model (2HDM) and the minimal supersymmetric standard model (MSSM). While observables in top quark pair production receive little contribution from standard electroweak interactions, it is possible that they can be significantly enhanced in a 2HDM and the MSSM. We find that the one-loop MSSM electroweak corrections can generate parity violating asymmetries in the total production rate of left- and right-handed top quark pairs up to about 1.7% at the upgraded Tevatron ($\sqrt{S}=2$ TeV) and 3% at the LHC ($\sqrt{S}=14$ TeV).

Figures (6)

• Figure 1: The differential asymmetry $\delta {\cal A}_{LR}$ at the upgraded Tevatron and the LHC within the 2HDM for different values of $M_{H^{\pm}}$ and $\tan\beta$ (with $\alpha=\pi/2$, $M_H=75$ GeV, $M_h=70$ GeV, $M_A=75$ GeV).
• Figure 2: The variation of the integrated asymmetries ${\cal A}_{LR}$ and ${\cal A}$ with $M_{H^{\pm}}$ at the upgraded Tevatron and the LHC within the 2HDM for different values of $\tan\beta$ (with $\alpha=\pi/2$, $M_H=75$ GeV, $M_h=70$ GeV, $M_A=75$ GeV).
• Figure 3: The differential asymmetry $\delta {\cal A}_{LR}$ at the upgraded Tevatron and the LHC within the MSSM for $m_{\tilde{t}_1}=90$ GeV and different values of $\Phi_{\tilde{t}}$ and $m_{\tilde{b}_L}$ (with $M_{H^{\pm}}$=110 GeV, $\mu=120$ GeV and $M_2=3|\mu|$).
• Figure 4: The differential asymmetry $\delta {\cal A}_{LR}$ at the upgraded Tevatron and the LHC within the MSSM for $m_{\tilde{t}_1}=$160 GeV and different values of $\Phi_{\tilde{t}}, m_{\tilde{b}_L}$ and $M_{H^{\pm}}$ (with $\mu=120$ GeV and $M_2=3|\mu|$).
• Figure 5: The variation of the integrated asymmetries ${\cal A}_{LR}$ and ${\cal A}$ with $M_{H^{\pm}}$ at the upgraded Tevatron and the LHC within the MSSM for different values of $\tan\beta$, $\Phi_{\tilde{t}}$ (with $m_{\tilde{t}_1}$=90 GeV, $m_{\tilde{b}_L}$=150 GeV ($m_{\tilde{b}_L}$=800 GeV for $\Phi_{\tilde{t}}=\pi/8$), $\mu=120$ GeV and $M_2=3|\mu|$).