Sixty years ago it was predicted that the α decay of nuclei just above doubly magic ¹⁰⁰Sn would be unusually fast (“superallowed” ) [1] because the emitted α particle and the ¹⁰⁰Sn core form an exceptionally favorable molecule-like configuration. The groundwork was laid by the discovery of the ¹⁰⁹Xe → ¹⁰⁵Te → ¹⁰¹Sn α-decay chain [2] and its subsequent measurement [3], and then by the first observation of the ¹⁰⁸Xe → ¹⁰⁴Te → ¹⁰⁰Sn chain feeding doubly magic ¹⁰⁰Sn [4]. The ¹⁰⁴Te itself α-decays directly into doubly magic ¹⁰⁰Sn. This nucleus is extremely difficult to synthesize, and its decay is so fast that it eluded measurement for decades. I will describe the experiment yielding the first direct measurement of the ¹⁰⁴Te lifetime [5]. A novel recoil-decay scintillation detector [6] and advances in understanding scintillator light collection [7] enabled this first direct measurement of the ¹⁰⁴Te lifetime. The decay turns out to be even more enhanced than theory predicted, raising a basic question about how and where an α particle assembles inside a nucleus before it escapes, a question that reaches from nuclear structure to the physics of clustering in dense matter.

References
[1] R. Macfarlane and A. Siivola, Physical Review Letters 14, 114 (1965).
[2] S. N. Liddick et al., Phys. Rev. Lett. 97, 082501 (2006).
[3] I. G. Darby et al., Phys. Rev. Lett. 105, 162502 (2010).
[4] K. Auranen et al., Phys. Rev. Lett. 121, 182501 (2018).
[5] I. Cox et al. Nature volume 654, 52–56 (2026).
[6] Y. Xiao et al., Phys. Rev. C 100, 034315 (2019).
[7] B. Kreider et al., Nucl. Instr. Meth. A 1085, 171298 (2026).

Global celebration greeted the 2012 discovery at CERN’s Large Hadron Collider of a particle that matches the textbook description of the Higgs boson. That achievement validated a remarkable chain of theoretical reasoning that combined the notion that symmetries dictate interactions with lessons from superconductivity. It was enabled by triumphs of accelerator art and experimental technique, and by human resourcefulness and collaboration on a global scale.

Some imagine that, once the keystone of the standard model of particle physics has been set, our subject is over. Others worry that we may be at an impasse, without sharp clues to a more complete understanding. I prefer to savor the challenge that our description of nature is incomplete, that we have so much more to learn.

This colloquium surveys themes that explore the breadth and depth of opportunities to enhance our understanding of the physical world, illustrated by examples from my research.