Associated production of a light pseudoscalar Higgs boson with a chargino pair in the NMSSM

TL;DR

This paper investigates the associated production of a very light pseudoscalar Higgs boson $A_1$ with a chargino pair in the NMSSM, focusing on the zero-mixing limit in which $A_1$ decouples from MSSM-like states and decays predominantly to two photons. The coupling responsible for the signal arises from the NMSSM term $λ S H_u H_d$, enabling $e^+ e^-$ or $pp$-collider production of $A_1$ with charginos, and producing a striking final state of two leptons, two photons, and missing energy. The study analyzes the mass and mixing conditions that allow an ultrasoft $A_1$ (with $ ext{sin} heta_A o 0$) and computes cross sections for ILC and LHC, showing rates that can yield observable event counts given realistic luminosities. A critical experimental challenge is resolving the two photons from $A_1 o ext{γγ}$; a photon-resolution capability similar to CMS preshower performances can render a sizable portion of the signal detectable, thereby providing a distinctive NMSSM signature that helps distinguish it from MSSM. The work concludes that the proposed channel is viable for exploring NMSSM parameter space with $M_{A_1} ext{ of order }{ m GeV}$ and above, and emphasizes the importance of photon-resolution in identifying the $A_1$ decay.

Abstract

In the next-to-minimal supersymmetric standard model (NMSSM), the unique $λS H_u H_d$ in the superpotential gives rise to a coupling involving the lighter pseudoscalar Higgs boson and a pair of charged or neutral Higgsinos, even in the limit of zero mixing between the two pseudoscalar Higgs bosons. We study the associated production of a very light pseudoscalar Higgs boson with a pair of charginos. The novel signature involves a pair of charged leptons from chargino decays and a pair of photons from the pseudoscalar Higgs boson decay, plus large missing energy at the LHC and ILC. The signal may help us to distinguish the NMSSM from MSSM, provided that the experiment can resolve the two photons from the decay of the pseudoscalar Higgs boson.

Figures (4)

• Figure 1: Decay branching ratios for the light pseudoscalar Higgs boson versus the mixing angle $\sin\theta_A$ for $\lambda=1$, $\mu=150$, $M_2=500$ GeV. (a) $m_{A_1} = 0.1$ GeV and (b) $m_{A_1}=5$ GeV.
• Figure 2: Production cross sections for $e^- e^+ \to \widetilde{\chi}^+_1 \widetilde{\chi}^-_1 A_1$ at the ILC with $\sqrt{s}=0.5,\, 1,\, 1.5$ TeV. We have chosen $\lambda=1$, $\sin\theta_A =10^{-4}$, $\mu = 150$ GeV, $M_2 = 500$ GeV, and $\tan\beta = 10$.
• Figure 3: Production cross sections for $pp \to \widetilde{\chi}^+_1 \widetilde{\chi}^-_1 A_1$ at the LHC. We have chosen $\lambda=1$, $\sin\theta_A =10^{-4}$, $\mu = 150$ GeV, $M_2 = 500$ GeV, and $\tan\beta = 10$.
• Figure 4: The differential cross section versus the sine of the opening angle between the two photons for $\lambda = 1$ and $\sin\theta_A = 10^{-4}$ at the LHC. Requirements of $p_{T\gamma} > 10$ GeV and $|y_\gamma| < 2.6$ are imposed.