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Sep 4 – 5, 2025
Jefferson Lab
US/Eastern timezone

Generation and characterization of directional muon beams using Laser Plasma Acceleration at the BELLA Center

Not scheduled
20m
F113 (Jefferson Lab)

F113

Jefferson Lab

Speaker

Davide Terzani (Lawrence Berkeley National Laboratory)

Description

Muons are a powerful probe for applications like tomography of large, dense objects, with uses in geological surveying, nuclear non-proliferation, and industrial inspection. However, the field has been constrained by a reliance on cosmic rays, a source characterized by a low and non-directional flux, hence requiring long exposure times, limiting muography to static targets. Laser-Plasma Accelerators (LPAs), which use PW-class lasers to generate 10s of GV/m accelerating gradients, produce multi-GeV electron beams in plasma targets that are 10s of cm in length. When such an electron beam traverses high-Z material, it produces Bremsstrahlung radiation that generates muon pairs via the Bethe-Heitler process, resulting in a compact, high-flux muon source.

In this talk, we present results from a recent experiment at the BELLA Center at LBNL, where we generated muon beams using an LPA-driven electron beam with energies extending up to 8 GeV. The electron beam was stopped in the beam dump, and the resulting muons were detected behind a 90-cm concrete wall. Muon production was unambiguously confirmed by capturing delayed signals in plastic scintillators, corresponding to the decay of stopped muons. A fit to the decay signal timing yielded a lifetime of $\tau = 2.24 \pm 0.50\,\mu\text{s}$, in agreement with the known muon lifetime.

Muon production in this environment is driven by two primary mechanisms:
1) a forward-directed, high-energy muon beam from the Bethe-Heitler process in the main beam dump,
2) a quasi-isotropic, lower-energy flux from meson decays.
Our experiment observed both contributions by placing detectors on the primary beam axis and $\sim$1 m to the side (off-axis). Electrons within a 1.2 mrad divergence cone reach the beam dump unpertubed, producing forward directed muons. Electrons outside this divergence angle graze upstream high-Z elements, producing unshielded mesons via photoproduction that create a strong off-axis muon signal upon decay.
Geant4 simulations of the entire experimental environment quantitatively reproduced the measured detection probabilities for both on-axis ($1.9\pm0.5\%$) and off-axis ($14.4\pm1.4\%$) configurations. The model predicts an expected number of forward-directed muons $N_{\mu}^{LPA}\gtrsim 10^2\,\text{shot}^{-1}$. At a typical LPA repetition rate of $\sim 1\,\text{Hz}$, this flux is orders of magnitude more intense than the cosmic ray background for horizontal muography, paving the way for compact, transportable systems for rapid imaging.

This work was supported by DARPA and the U.S. Department of Energy Office of Science, Office of High Energy Physics under Contract No. DE-AC02-05CH11231, and used the computational facilities at NERSC.

Author

Davide Terzani (Lawrence Berkeley National Laboratory)

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