NLO production of W' bosons at hadron colliders using the MC@NLO and POWHEG methods

TL;DR

The paper develops a comprehensive NLO treatment of W' production at hadron colliders, incorporating full W–W' interference and arbitrary chiral couplings. It implements MC@NLO/Herwig++ and POWHEG matching within the Wpnlo generator to produce fully exclusive, positive- or near-positive-weight events, enabling detailed phenomenology at the LHC and Tevatron. Key findings include a consistent NLO K-factor around 1.3, enhanced high-p_T tails, and interference-driven modifications to cross sections and distributions, especially for left-handed W'. The study also provides mass–width observation curves and demonstrates the stability of NLO results against factorization-scale variations, highlighting the practical impact for interpreting searches for W' bosons.

Abstract

We present a next-to-leading order (NLO) treatment of the production of a new charged heavy vector boson, generically called W', at hadron colliders via the Drell-Yan process. We fully consider the interference effects with the Standard Model W boson and allow for arbitrary chiral couplings to quarks and leptons. We present results at both leading order (LO) and NLO in QCD using the MC@NLO/Herwig++ and POWHEG methods. We derive theoretical observation curves on the mass-width plane for both the LO and NLO cases at different collider luminosities. The event generator used, Wpnlo, is fully customisable and publicly available.

Figures (18)

• Figure 1: Feynman diagram for $pp \rightarrow W/W' \rightarrow \ell \nu X$.
• Figure 2: The interference term $S_{int}$ in the case where $h_{W'} = 1$, $M_{W'} = 1 ~{\rm TeV}$, plotted against $\hat{s}$, for different widths: $\Gamma_{W'} = 1, 35, 100 ~{\rm GeV}$ (green, blue, purple respectively). The terms $S_{W,W}$ (red) and $S_{W',W'}$ (black) are shown for comparison. It is evident that $S_{int}$ is negative in the intermediate region $(M_W^2,M_{W'}^2)$. It is also clear that the magnitude of the interference term is comparable to $S_{W,W}$ and $S_{W',W'}$. As the width decreases the negative peak becomes narrower, but there always exists a portion of the curve which is independent of the width.
• Figure 3: Transverse momentum distribution at the Tevatron obtained for MC@NLO/Herwig++ in the DIS and MSbar factorisation schemes (PDFs: cteq5d and cteq5m Lai:1999wy respectively), POWHEG MSbar (cteq5m) and LO (PDF: MRST2001LO Martin:2001es), in the mass range $(70-90)~{\rm GeV}$.
• Figure 4: The normalised variation with scale of the cross section calculations at NLO (red crosses) and LO (black circles) are shown for a proton-proton collider at 14 TeV, $M_{W'} = 1~{\rm TeV}$, $\Gamma_{W'} = 36~{\rm GeV}$ and left-handed chirality in the invariant mass range [400,5000] GeV.
• Figure 5: Transverse mass distributions at the LHC obtained using the MC@NLO/Herwig++ and POWHEG methods (cteq5m/MSbar) and LO (MRST2001LO) for a purely left-handed $W'$. The plots correspond to masses/widths equal to $[1~{\rm TeV},36~{\rm GeV}]$ (left) and $[2~{\rm TeV},72~{\rm GeV}]$ (right). The invariant mass range was taken to be $(0.4-3.0)~{\rm TeV}$ for the $1~{\rm TeV}$ case and $(0.4-5.0)~{\rm TeV}$ for the $2~{\rm TeV}$ case. The effect of the destructive interference can be observed in both cases. Note that the plots have been normalised to unity.