Gerald Gabrielse

Gabrielse was a pioneer in the field of low energy antiproton and antihydrogen physics by proposing the trapping of antiprotons from a storage ring, cooling them in collisions with trapped electrons,[8] and the use of these to form low energy antihydrogen atoms.[9] He led the TRAP team that realized the first antiproton trapping,[10] the first electron cooling of trapped antiprotons, and the accumulation of antiprotons in a 4 Kelvin apparatus.[11] The demonstrations and methods made possible an effort that grew to involve 4 international collaborations of physicists working at CERN's Antiproton Decelerator. In 1999, Gabrielse's TRAP team made the most precise test of the Standard Model's fundamental CPT theorem by comparing the charge-to-mass ratio of a single trapped antiproton with that of a proton to a precision of 9 parts in 10¹¹.[12] The precision of the resulting confirmation of the Standard Model prediction exceeded that of earlier comparisons by nearly a factor of 10⁶.

Gabrielse now leads the ATRAP team at CERN, one of the two teams that first produced slow antihydrogen atoms and suspended them in a magnetic trap.[13][14] Both TRAP and ATRAP teams used trapped antiprotons within a nested Penning trap device to produce antihydrogen atoms slow enough to be trapped in a magnetic trap. The team made the first one-particle comparison of the magnetic moments of a single proton and a single antiproton.[15][16] Their comparison, to a precision of 5 parts per million, was 680 times more precision than previous measurements.[17]

Gabrielse's group has been known to perform the most precise measurements of the electron magnetic moment by using a single trapped electron. These measurements are the most precise measurements of any single particle and are among the most stringent tests of the Standard Model.[18] Using the theory of quantum electrodynamics, a measurement of the electron magnetic moment can also be interpreted as a measurement of the fine structure constant.[19] In 2006, the group made its first measurement with an uncertainty of 0.76 parts per trillion,[20] which was 15 times more precise than a measurement that had stood for about 20 years.[21] This measurement was improved two years later by a factor of 2.[22] In 2023, the team improved upon the 2008 uncertainty by another factor of 2.[1]

In 2014, Gabrielse, as part of the ACME collaboration with John Doyle at Harvard and David DeMille at Yale, measured the electron electric dipole moment to over an order of magnitude over the previous measurement using a beam of thorium monoxide,[23] a result which had implications for the viability of supersymmetry.[24] In 2018, the ACME collaboration improved upon this upper limit by another order of magnitude.[25]

Gabrielse was also one of the discoverers of the Brown-Gabrielse invariance theorem,[26] relating the free space cyclotron frequency to the measureable eigenfrequencies of an imperfect Penning trap. The theorem's applications include precise measurements of magnetic moments and precise mass spectrometry.[27] It also makes sideband mass spectrometry possible, a standard tool of nuclear physics.[28]

Gabrielse has also invented a self-shielding superconducting solenoid that uses flux conservation and a carefully chosen geometry of coupled coils to cancel strong field fluctuations due to external sources. The device was responsible for the success of the precise comparison of antiproton and proton, and also enables magnetic resonance imaging (MRI) systems to locate changing magnetic fields from external sources, such as elevators.[29]