The physics case of a 3 TeV muon collider stage

TL;DR

The paper advocates a staged muon collider program beginning at 3 TeV as a feasible path toward multi‑TeV energies, arguing that muon collisions enable direct high-energy exploration and precise SM measurements with unique sensitivity to muon-specific new physics, including g‑2 and B‑anomalies. It provides a comprehensive physics case across extended Higgs sectors and dark matter scenarios, detailing direct production channels, indirect EFT reaches, and unconventional signatures such as long-lived particles and disappearing tracks. By comparing with e+e− and hadron colliders, the report highlights the 3 TeV stage’s capability to probe Higgs couplings at permille levels, measure the Higgs trilinear coupling, and indirectly constrain heavy new physics up to scales of order $E_{ m cm}^2/ ext{(new physics scale)}$, while also addressing detector challenges from beam-induced backgrounds. The study furthermore frames muon-specific opportunities tied to muon anomalies, and outlines how higher-energy upgrades would extend this reach, offering a no‑lose pathway for probing muon-philic new physics and dark matter scenarios on a practical timescale.

Abstract

In the path towards a muon collider with center of mass energy of 10 TeV or more, a stage at 3 TeV emerges as an appealing option. Reviewing the physics potential of such muon collider is the main purpose of this document. In order to outline the progression of the physics performances across the stages, a few sensitivity projections for higher energy are also presented. There are many opportunities for probing new physics at a 3 TeV muon collider. Some of them are in common with the extensively documented physics case of the CLIC 3 TeV energy stage, and include measuring the Higgs trilinear coupling and testing the possible composite nature of the Higgs boson and of the top quark at the 20 TeV scale. Other opportunities are unique of a 3 TeV muon collider, and stem from the fact that muons are collided rather than electrons. This is exemplified by studying the potential to explore the microscopic origin of the current $g$-2 and $B$-physics anomalies, which are both related with muons.

Figures (28)

• Figure 1: Direct 95 % C.L. reach on heavy singlet mixed with the SM Higgs doublet at various muon colliders (adapted from Buttazzo:2018qqp). The direct and indirect reach at other future colliders EuropeanStrategyforParticlePhysicsPreparatoryGroup:2019qin is also shown for comparison.
• Figure 2: Direct (left panel) and indirect reach (right panel) on the SM plus real scalar singlet scenario for muon colliders with various center of mass energy. Dots indicate points with successful FOEWPT, while red, green and blue dots represent signal-to-noise ratio (SNR) for gravitational eave detection of $[50, +\infty)$, $[10, 50)$ and $[0, 10)$, respectively. Results are taken from Liu:2021jyc.
• Figure 3: Cross sections versus the non-SM Higgs mass for $\sqrt{s}=3$ TeV for pair production (left panel), single production with a pair of fermions and radiative return production (right panel) for $\tan\beta=1$ under the alignment limit of $\cos(\alpha-\beta)=0$. Plot is produced by authors of Ref. Han:2021udl.
• Figure 4: Signal statistical significance for various IDM benchmark points Klamka:2022ukx at high energy lepton collider for charged Higgs pair production and semi-leptonic final states.
• Figure 5: Direct reach on electroweak states in mono-$X$ signals. Left: Luminosity needed to exclude a Dirac fermion DM candidate for zero systematics Han:2020uak for $X=\gamma$ (solid), $X=\mu$ (dotted), $X=\mu\mu$ (dashed). Right: Mass reach on a fermionic DM candidate (assumed Majorana when $Y=0$, Dirac otherwise) at fixed 1 $\rm{ab}^{-1}$ luminosity for the 3 TeV muon collider for $X=\gamma$ and $X=W$ for 0.1% systematics Bottaro:2021snnBottaro:2022.