Slepton Trapping at the Large Hadron and International Linear Colliders

TL;DR

The paper analyzes a gravitino LSP framework where charged sleptons act as long-lived NLSPs with lifetimes in the range $10^4$–$10^8$ s, constrained cosmologically to avoid late, disruptive decays. It proposes trapping these sleptons in water tanks outside collider detectors and periodically transferring them to quiet environments for decay studies, and develops a geometry-optimization approach to maximize captured events. By applying this to both the LHC and ILC, the authors show that the LHC could capture tens–thousands of sleptons under favorable spectra, while the ILC—especially when beam energies are tuned to yield slow sleptons or when dense interstitial material is used—could trap significantly larger fractions, enabling precision measurements of the gravitino properties and gravitational interactions at collider scales. The work highlights profound implications for understanding dark matter, SUSY breaking, and early-universe physics, including potential laboratory tests of BBN and the CMB, and suggests practical paths toward high-precision tests of supergravity relations.

Abstract

We consider supergravity with a gravitino lightest supersymmetric particle. The next-to-lightest supersymmetric particle (NLSP) decays to the gravitino with lifetime naturally in the range 10^4 - 10^8 s. However, cosmological constraints exclude lifetimes at the upper end of this range and disfavor neutralinos as NLSPs, leaving charged sleptons with lifetimes below a year as the natural NLSP candidates. Decays to gravitinos may therefore be observed by trapping slepton NLSPs in water tanks placed outside Large Hadron Collider (LHC) and International Linear Collider (ILC) detectors and draining these tanks periodically to underground reservoirs where slepton decays may be observed in quiet environments. We consider 0.1, 1, and 10 kton traps and optimize their shape and placement. We find that the LHC may trap tens to thousands of sleptons per year. At the ILC, these results may be improved by an order of magnitude in some cases by tuning the beam energy to produce slow sleptons. Precision studies of slepton decays are therefore possible and will provide direct observations of gravitational effects at colliders; percent level measurements of the gravitino mass and Newton's constant; precise determinations of the gravitino's contribution to dark matter and supersymmetry breaking's contribution to dark energy; quantitative tests of supergravity relations; and laboratory studies of Big Bang nucleosynthesis and cosmic microwave background phenomena.

Figures (12)

• Figure 1: The range to mass ratio $R/M$ as a function of $p/M = \beta \gamma$ (left), and, for the specific case of a slepton with mass 219 GeV, the range as a function of energy (right). Results are given for water (solid) and lead (dashed).
• Figure 2: Diagram of the slepton trap geometry. The trap is assumed to be a spherical shell with inner radius $r_{\text{in}}$, and depth $d$ as shown. The angular parameters $\frac{1}{2} \Delta\left(\cos\theta\right)$ and $\Delta\phi$ of Eq. (\ref{['shape']}) are also indicated.
• Figure 3: The depth $d$ in meters of a 1 kton water trap in the $(\Delta (\cos \theta), \Delta \phi)$ plane for $r_{\text{in}} = 10~\text{m}$.
• Figure 4: Representative superpartner masses as a function of $M_{1/2}$ in minimal supergravity with fixed $m_0 = 0$, $A_0 = 0$, $\tan\beta = 10$, and $\mu>0$. The supersymmetry parameter $\mu$, which governs the Higgsino masses, is also shown.
• Figure 5: The energy distribution of NLSP staus produced at the LHC for integrated luminosity $100~\text{fb}^{-1}$ and minimal supergravity with $m_0 = 0$, $M_{1/2} = 600~\text{GeV}$, $A_0 = 0$, $\tan\beta = 10$, and $\mu>0$. The NLSP stau mass is $219~\text{GeV}$.