4-fermion EFT bbll including interference with the SM

Authors:

• Yoav Afik (yoavafik@…)
• Shaouly Bar-Shalom (shaouly@…)
• Jonathan Cohen
• Yoram Rozen

Department of Physics, Technion: Israel Institute of Technology Haifa, Israel

Description of the model:

This is a Contact Interaction model with b-b-l-l terms, including interference with the SM, for all of the possible chirality combinations. The effective Lagrangian of the model is described by:

\begin{align*}
\mathcal{L}_{eff} = \frac{g^2}{\Lambda^2}\sum_{i,j=L,R} \eta_{ij}(\bar{b}_{i} \gamma_{\mu} b_{i}) (\bar{\ell}_{j} \gamma^{\mu} \ell_{j}),
\end{align*}

The behavior of the cross section can be parametrized by the contribution of three terms, which depend on the di-lepton invariant mass:

\begin{align*}
\sigma(m_{\ell \ell})=\sigma^{SM}(m_{\ell \ell}) + \sigma^{NP}(g,\Lambda,m_{\ell \ell}) ~,
\end{align*}

where the first term is the pure SM term and the second term contain only the NP contributions:

\begin{align*}
\sigma^{NP}(g,\Lambda,m_{\ell \ell})=\frac{g^2}{\Lambda^2} \cdot \sigma^{SM \times NP}(m_{\ell \ell}) + \frac{g^4}{\Lambda^4} \cdot \sigma^{NP \times NP}(m_{\ell \ell}) ~,
\end{align*}

Model Files:

• ​bbll_UFO.zip : the full model.

Commands for MadGraph5_aMC@NLO, for a production of an electron and a positron with jets:

define p = g u c d s b u~ c~ d~ s~ b~ 
define j = g u c d s b u~ c~ d~ s~ b~ 
generate p p > e+ e- NP^2>0
add process p p > e+ e- j NP^2>0
add process p p > e+ e- j j NP^2>0
...
set LambdaS ...
set Celbbll ...
set Celbblr ...
set Celbbrr ...
set Celbbrl ...

Where LambdaS is the scale of new physics in GeV, Celbbll is the bbee coupling with left-left chirality, etc. Note especially that the sign of Celbbll / Celbblr / Celbbrr / Celbbrl determines if the interference with the SM is constructive or destructive.

Similarly, commands for MadGraph5_aMC@NLO, for a production of a muon and an anti-muon with jets:

define p = g u c d s b u~ c~ d~ s~ b~ 
define j = g u c d s b u~ c~ d~ s~ b~ 
generate p p > mu+ mu- NP^2>0
add process p p > mu+ mu- j NP^2>0
add process p p > mu+ mu- j j NP^2>0
...
set LambdaS ...
set Cmubbll ...
set Cmubblr ...
set Cmubbrr ...
set Cmubbrl ...

References:

[1] Afik, Yoav and Bar-Shalom, Shaouly and Cohen, Jonathan and Rozen, Yoram. Phys. Lett. B. 807:135541, 2020, 1912.00425.

• Link to paper: ​https://www.sciencedirect.com/science/article/pii/S0370269320303452?via%3Dihub