Unidentified falling objects in the LHC as dark matter signals

TL;DR

The paper proposes that a subset of UFOs observed at the LHC may arise from axion quark nuggets (AQNs), macroscopic dark matter objects capable of generating underground acoustic shocks when passing near the collider. By coupling AQN-induced dust-release mechanisms to the LHC’s widespread beam-loss monitoring, the authors show how correlated UFO bursts across the ring could serve as a detectable DM signature, with an estimated rate ${\dot{N}}_\text{UFO}^{(AQN)} \approx 0.045$ h$^{-1}$ and significant signal-to-noise for masses $⟨M_\text{AQN}⟩$ in the few- to hundreds-of-grams range. Detection relies on temporal coincidence of multiple UFOs within a short window, complemented by seismic, DAS, and infrasound cross-correlations. If validated, this approach would establish the LHC as a large-scale acoustic detector for macroscopic DM and provide novel insights into DM–visible matter relationships and baryogenesis within the AQN framework.

Abstract

Unidentified Falling Objects (UFOs) refer to sporadic beam losses observed during LHC operation. The prevailing explanation is that micrometer-sized dust particles released from the beam screen produce beam losses through interactions with the protons. However, the release mechanism of these particles remains unknown. We propose that roughly $(1-10)$% of UFOs may be caused by axion quark nuggets (AQNs), macroscopic dark matter (DM) candidates with masses of order $(5-1000)\,$g. The AQN model naturally relates the dark- and visible-matter abundances ($Ω_\mathrm{DM}\simΩ_\mathrm{visible}$) and provides a mechanism for generating the baryon-antibaryon asymmetry, with DM composed of both matter and antimatter AQNs. When passing underground within approximately 100km of the LHC, an antimatter AQN generates acoustic waves strong enough to trigger multiple UFO events within $2\,$s. If three correlated UFOs (placed at different locations along the LHC ring) are detected, the signal-to-noise ratio can exceed 5 across the entire allowed AQN mass range for a measurement time of about 360 hours. Practically, the LHC can serve as a large broadband acoustic detector for AQNs.

Figures (3)

• Figure 1: UFO release mechanism in the LHC. Micrometer-sized dust particles can form on the beam screens within several minutes during the LHC operation. Typically, these particles settle on the bottom of the beam screen, although it is also possible for them to attach to the top. A dust particle is influenced by several forces: an adhesive force $\mathbf{F}_{\rm adh}$ that keeps it attached to the beam screen, a gravitational force $\mathbf{G}$ that is determined by its size $L$, and an unknown releasing force $\mathbf{F}_{\rm rel}$. When the releasing force becomes strong enough, the dust particle will be dislodged and can trigger a UFO event. Specifically, for particles that attach to the top of the beam screen, they can self-release due to gravitational forces once they reach a sufficient size of approximately $L\gtrsim50{\rm\,\mu m}$Belanger:2020ufo.
• Figure 2: A dust particle located at the bottom of the beam screen receives an instantaneous mechanical impulse from an external acoustic shock wave induced by an (antimatter) AQN. An underground-propagating AQN, within approximately $100\,$km of the LHC tunnel, generates an overpressure of a few hundred Pascals and a frequency of a few kHz. The dust particle as a whole experiences the force coherently.
• Figure 3: An AQN-induced UFO burst. This acoustic shock wave propagates throughout the entire LHC ring at a velocity $\mathbf{c}_{\rm s}$. It causes mechanical vibration of the dust within the LHC tunnel and triggers several consecutive UFO events. The time interval between two correlated UFO events is determined by the dot product of $\mathbf{c}_{\rm s}$ and the vectorized separation distance $\Delta \mathbf{D}$.