Study of anomalous gauge boson self-couplings and the role of spin-$1$ polarizations

TL;DR

This thesis investigates anomalous gauge boson self-couplings using polarization observables at colliders, providing new methods to constrain these couplings and distinguish their CP properties.

Contribution

It introduces polarization asymmetries as tools to improve constraints on anomalous gauge boson couplings at $e^+e^-$ and LHC colliders, including their CP nature.

Findings

Polarization asymmetries help distinguish CP-even and CP-odd couplings.

Beam polarization enhances signal-to-background ratio and tightens coupling constraints.

Simultaneous limits on anomalous couplings are obtained using MCMC analysis.

Abstract

The prime goal of this thesis is to study anomalous gauge boson self couplings, triple gauge boson couplings in particular, with the help of spin polarization observables of the gauge bosons $Z$ and $W^\pm$ in the presence of beam polarizations where ever possible. The neutral triple gauge boson couplings, i.e., $ZZZ$, $ZZ\gamma$, $Z\gamma\gamma$, are studied in $ZZ/Z\gamma$ ($2lq\bar{q}/2l\gamma$) production at an $e^+e^-$ collider with and without beam polarization. Some of these anomalous couplings are also studied in $ZZ$ ($4l$) production at the LHC. In the charge sector the anomalous gauge boson couplings, i.e., $WWZ$, $WW\gamma$ have been studied at an $e^+e^-$ collider in $W^+W^-$ ($l^-\bar{\nu_l}q^\prime\bar{q}$) production. The $WWZ$ anomalous couplings are also studied in $ZW^\pm$ production at LHC in $3l$ + missing $E_T$ channel. All the analyses at an $e^+$-$e^-$ collider have been performed for center-of-mass (CM) energy of $500$ GeV and integrated luminosity of $100$ fb$^{-1}$. The analyses at the LHC are performed at $13$ TeV CM energy of $pp$ collisions. The cross sections and polarization asymmetries, along with other asymmetries (forward-backward, azimuthal), are used to obtain simultaneous limits on the anomalous couplings using Markov-Chain--Monte-Carlo (MCMC) method in each process. The polarization asymmetries can distinguish between $CP$-even and $CP$-odd couplings and help to put tighter constraints on the couplings. The polarization of the initial $e^-$ and $e^+$ beam, in case of $e^+e^-$ collider, are used to increase the signal to background ratio, putting tighter constraints on the anomalous couplings. The polarization asymmetries are instrumental in the measurement of anomalous couplings should a deviation from the SM be observed.