Boosting VBF Reconstruction at Muon Colliders

Abstract

Forward muon detection at high-energy muon colliders is crucial for resolving the underlying electroweak process. Detecting these muons is challenging in current detector designs, limited by the shielding required to suppress the beam-induced background. This work proposes using asymmetric beam energies to boost one of the forward muons into the detector acceptance, enhancing the ability to distinguish between $W$- and $Z$-initiated vector boson fusion processes. We demonstrate the capabilities of such an asymmetric collider using VBF Higgs production at 3 and 10 TeV muon colliders with modest boost asymmetries. Asymmetric beam configurations can partially recover the physics potential lost in forward regions when detector coverage is limited.

Figures (4)

• Figure 1: Schematic illustration of the impact of an asymmetric beam configuration ($\beta = 0.8$) on particle angles in the lab frame. A forward muon pair (brown arrows) initially produced at $5^\circ$ relative to the beam axis is Lorentz-boosted such that one muon (blue arrow) enters the detector region.
• Figure 2: Left: Normalized angular distribution at $\sqrt{s} = 3$ TeV of the muon moving in the opposite direction of the boost. Right: Normalized angular distribution at $\sqrt{s} = 3$ TeV of the $b$-quark from the Higgs decay ($H\rightarrow b\bar{b}$). The different curves show $\beta = 0, 0.5, 0.8, 0.9$. The detector acceptance of 10 degrees from the beamline is shown in dashed black, where most of the muons get lost in the symmetric collider configuration. At the same time, central processes get boosted outside of the acceptance, and the balancing of the two effects is responsible for the better reach for the VBF topology.
• Figure 3: Geometric efficiency for VBF Higgs production with a detector coverage of $10^{\circ} < \theta^{\text{lab}} < 170^{\circ}$, shown as a function of the asymmetry boost. The Forward and Backward curves represent the efficiency for detecting the muons along the beamline, while the Central curve shows the efficiency for detecting the $H(b\bar{b})$$b$-jets. The combined efficiency for the full VBF process is shown in red. The bottom panel illustrates the scenario where the shielding must be extended on the side of the less energetic beam, modeled by a geometric acceptance that degrades linearly with the boost, from $10^{\circ}$ up to $30^{\circ}$.
• Figure 4: Combined $95\%$ C.L from the VBF Higgs process for the $\Delta \kappa_W$ vs $\Delta \kappa_Z$ for 3 TeV and 10 TeV asymmetric colliders with boosts $\beta = 0.5, 0.8, 0.9$. To compare with the asymmetric configuration, we consider a symmetric configuration with twice the energy of the most energetic beam, shown in dashed, given by (5.2, 9, 13) TeV respectively, for the 3 TeV configuration and (17, 30, 44) TeV respectively for the 10 TeV configuration. The reach for a symmetric collider with the same center of mass energy always has weaker disentangling power, and is similar to the symmetric configuration shown for $\beta =0.5$. In some cases, the symmetric higher energy collider can have slightly better reach for $\Delta \kappa_W$, but it is always worse in separating the $W$ and $Z$ initiated process.