State-resolved laser spectroscopy at the 10−12 precision level recently reported in arXiv:2406.18719 determined the fractional change in nuclear quadrupole moment between the ground and isomeric state of 229Th, ΔQ0/Q0=1.791(2) %. Assuming a prolate spheroid nucleus, this allows to quantify the sensitivity of the nuclear transition frequency to variations of the fine-structure constant α to K=5900(2300), with the uncertainty dominated by the experimentally measured charge radius difference Δ⟨r2⟩ between the ground and isomeric state. This result indicates a three orders of magnitude enhancement over atomic clock schemes based on electron shell transitions. We find that ΔQ0 is highly sensitive to tiny changes in the nuclear volume, thus the constant volume approximation cannot be used to accurately relate changes in ⟨r2⟩ and Q0. The difference between the experimental and estimated values in ΔQ0/Q0 raises a further question on the octupole contribution to the alpha-sensitivity.
BT - Submitted N2 -State-resolved laser spectroscopy at the 10−12 precision level recently reported in arXiv:2406.18719 determined the fractional change in nuclear quadrupole moment between the ground and isomeric state of 229Th, ΔQ0/Q0=1.791(2) %. Assuming a prolate spheroid nucleus, this allows to quantify the sensitivity of the nuclear transition frequency to variations of the fine-structure constant α to K=5900(2300), with the uncertainty dominated by the experimentally measured charge radius difference Δ⟨r2⟩ between the ground and isomeric state. This result indicates a three orders of magnitude enhancement over atomic clock schemes based on electron shell transitions. We find that ΔQ0 is highly sensitive to tiny changes in the nuclear volume, thus the constant volume approximation cannot be used to accurately relate changes in ⟨r2⟩ and Q0. The difference between the experimental and estimated values in ΔQ0/Q0 raises a further question on the octupole contribution to the alpha-sensitivity.
PY - 2024 T2 - Submitted TI - Fine-structure constant sensitivity of the Th-229 nuclear clock transition UR - https://arxiv.org/abs/2407.17300 ER -