Source: National Natural Science Foundation of China

Grant No:91636216

Project: Determination the Proton-Electron Mass Ratio Based on High Precision Measurement of Rovibrational Spectroscopy of HD+

Chief Specialist: Prof.Xin Tong

Abstract:

The proton-electron mass ratio is a dimensionless fundamental physical constant. To determine this constant with high precision is of great importance both for the verifications and predictions of the basic physical theories. HD+ consists of one proton, one deuterium nucleus and one electron. And it is the simplest molecule, whose rovibrational transition frequencies strongly depend on the proton-electron mass ratio. Combining the precision measurements of the rovibrational spectroscopy and the quantum electrodynamics (QED) calculations, the proton-electron mass ration can be determined with high precision. In this project, the HD+ ions generated by the threshold photoionization method will be sympathetically cooled by the laser-cooled atomic ions to realize the accurate controlling of the internal and external degrees of freedom. Then, the HD+ ions, with the transitional kinetic energy around mK and in the ground state of the rovibration, can be obtained. The 991 nm overtone transition frequency from the rovibrational ground state to the 6th vibrational excited state will be measured by the precision spectroscopy method with the relative accuracy about 0.4 ppb, two to three times better than current measurements. Meanwhile, using QED theory, we will derive rigorously the equivalent operators for the high-order relativistic and radiation corrections, perform the high-precision numerical calculations for the expectation values of the operators. Together with the results of low-order QED corrections which have been finished by the applicant, the theoretical prediction of the rovibrational transition frequency is expected with the relative accuracy 0.1 ppb. Comparing the results from our experimental spectroscopy and theoretical prediction, the proton-electron mass ratio is expected to be determined with the relative accuracy better than 1ppb, to be accepted as reference data for CODATA.