Resonance--Continuum Interference in Light Higgs Boson Production at a Photon Collider

Abstract

We study the effect of interference between the Standard Model Higgs boson resonance and the continuum background in the process gamma gamma -> H -> b b-bar at a photon collider. Taking into account virtual gluon exchange between the final-state quarks, we calculate the leading corrections to the height of the resonance for the case of a light (m_H < 160 GeV) Higgs boson. We find that the interference is destructive and around 0.1--0.2% of the peak height, depending on the mass of the Higgs and the scattering angle. This suppression is smaller by an order of magnitude than the anticipated experimental accuracy at a photon collider. However, the fractional suppression can be significantly larger if the Higgs coupling to b quarks is increased by physics beyond the Standard Model.

Figures (4)

• Figure 1: Feynman diagrams contributing to the interference of $\gamma\gamma\rightarrow H\rightarrow b\bar{b}$ (upper row) with the continuum background (lower row) up to order $\mathcal{O}\left(\alpha_s\right)$. Only one diagram is shown at each loop order, for each amplitude. The blob contains $W$ and $t$ loops, and small contributions from lighter charged fermions.
• Figure 2: Feynman diagram for the calculation of the interference of $\gamma\gamma\rightarrow H\rightarrow b\bar{b}$ with the continuum background up to order $\mathcal{O}\left(\alpha_s\right)$. The unitarity cuts indicated by dashed vertical lines are used to compute the imaginary parts of the various amplitudes.
• Figure 3: The percentage reduction of the SM Higgs signal as a function of the Higgs boson mass, for center-of-mass scattering angle $\theta = 45^{\circ}$. The solid curve represents the result with all phases turned on; the dashed curves turn on different component phases each time. The effect is stronger for a higher mass Higgs boson.
• Figure 4: The percentage reduction of the SM Higgs signal as a function of the scattering angle for $m_H = 130$ GeV. The solid curve represents the result with all phases turned on; the dashed curves turn on different component phases each time. The total effect is maximized close to $\theta\simeq 35^{\circ}$.