Probing neutral triple gauge couplings with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>Z</mml:mi></mml:mrow><mml:mrow><mml:mo>*</mml:mo></mml:mrow></mml:msup><mml:mi>γ</mml:mi></mml:mrow></mml:math> (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>ν</mml:mi><mml:mover accent="true"><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mrow></mml:mover><mml:mi>γ</mml:mi></mml:mrow></mml:math>) production at hadron colliders
John Ellis, Hong-Jian He, Rui-Qing Xiao
Abstract
We study probes of neutral triple gauge couplings (nTGCs) via ${Z}^{*}\ensuremath{\gamma}$ production with off-shell decays ${Z}^{*}\ensuremath{\rightarrow}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ at the LHC and the projected $pp$ (100 TeV) colliders, including both $CP$-conserving (CPC) and $CP$-violating (CPV) couplings. We present the dimension-8 Standard Model effective field theory (SMEFT) operators contributing to nTGCs and derive the correct form factor formulation for the doubly off-shell vertices ${Z}^{*}\ensuremath{\gamma}{V}^{*}$ ($V=Z$, $\ensuremath{\gamma}$) by matching them with the dimension-8 SMEFT operators. We include new contributions enhanced by the large off-shell momentum of ${Z}^{*}$, beyond those of the conventional $Z\ensuremath{\gamma}{V}^{*}$ vertices with on-shell $Z\ensuremath{\gamma}$. We analyze the sensitivity reaches for probing the $\mathrm{CPC}/\mathrm{CPV}$ nTGC form factors and the new physics scales of the dimension-8 nTGC operators at the LHC and future 100 TeV $pp$ colliders. We compare our new predictions with the existing LHC measurements of CPC nTGCs in the $\ensuremath{\nu}\overline{\ensuremath{\nu}}\ensuremath{\gamma}$ channel and demonstrate the importance of our new method.