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Register a new userThe magnetic moments of the proton and the antiproton
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Recent exciting progress in the preparation and manipulation of the motional quantum states of a single trapped proton enabled the first direct detection of the particles spin state. Based on this success the proton magnetic moment $mu_p$ was measured with ppm precision in a Penning trap with a superimposed magnetic field inhomogeneity. An improvement by an additional factor of 1000 in precision is possible by application of the so-called double Penning trap technique. In a recent paper we reported the first demonstration of this method with a single trapped proton, which is a major step towards the first direct high-precision measurement of $mu_p$. The techniques required for the proton can be directly applied to measure the antiproton magnetic moment $mu_{bar{p}}$. An improvement in precision of $mu_{bar{p}}$ by more than three orders of magnitude becomes possible, which will provide one of the most sensitive tests of CPT invariance. To achieve this research goal we are currently setting up the Baryon Antibaryon Symmetry Experiment (BASE) at the antiproton decelerator (AD) of CERN.
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The spin-magnetic moment of the proton $mu_p$ is a fundamental property of this particle. So far $mu_p$ has only been measured indirectly, analysing the spectrum of an atomic hydrogen maser in a magnetic field. Here, we report the direct high-precision measurement of the magnetic moment of a single proton using the double Penning-trap technique. We drive proton-spin quantum jumps by a magnetic radio-frequency field in a Penning trap with a homogeneous magnetic field. The induced spin-transitions are detected in a second trap with a strong superimposed magnetic inhomogeneity. This enables the measurement of the spin-flip probability as a function of the drive frequency. In each measurement the protons cyclotron frequency is used to determine the magnetic field of the trap. From the normalized resonance curve, we extract the particles magnetic moment in units of the nuclear magneton $mu_p=2.792847350(9)mu_N$. This measurement outperforms previous Penning trap measurements in terms of precision by a factor of about 760. It improves the precision of the forty year old indirect measurement, in which significant theoretical bound state corrections were required to obtain $mu_p$, by a factor of 3. By application of this method to the antiproton magnetic moment $mu_{bar{p}}$ the fractional precision of the recently reported value can be improved by a factor of at least 1000. Combined with the present result, this will provide a stringent test of matter/antimatter symmetry with baryons.
We present a fully {it ab initio}, non-perturbative, time-dependent approach to describe single and double ionization of helium by proton and antiproton impact. A flexible and accurate finite-element discrete-variable-representation is applied to discretize the problem on the radial grid in spherical coordinates. Good agreement with the most recent experimental data for absolute angle-integrated cross sections is obtained over a wide range of incident projectile energies between 3 keV and 6 MeV. Furthermore, angle-differential cross sections for two-electron ejection are predicted for a proton impact energy of 6 MeV. Finally, the time evaluation of the ionization process is portrayed by displaying the electron density as a function of the projectile location.
DeclareRobustCommand{pbar}{HepAntiParticle{p}{}{}xspace} DeclareRobustCommand{p}{HepParticle{p}{}{}xspace} DeclareRobustCommand{mup}{$mu_{p}${}{}xspace} DeclareRobustCommand{mupbar}{$mu_{pbar}${}{}xspace} DeclareRobustCommand{muN}{$mu_N${}{}xspace For the first time a single trapped pbar is used to measure the pbar magnetic moment ${bmmu}_{pbar}$. The moment ${bmmu}_{pbar} = mu_{pbar} {bm S}/(hbar/2)$ is given in terms of its spin ${bm S}$ and the nuclear magneton (muN) by $mu_{pbar}/mu_N = -2.792,845 pm 0.000,012$. The 4.4 parts per million (ppm) uncertainty is 680 times smaller than previously realized. Comparing to the proton moment measured using the same method and trap electrodes gives $mu_{pbar}/mu_p = -1.000,000 pm 0.000,005$ to 5 ppm, for a proton moment ${bm{mu}}_{p} = mu_{p} {bm S}/(hbar/2)$, consistent with the prediction of the CPT theorem.
Precision measurements of the Lu$^+$ $^3D_1$ and $^3D_2$ quadrupole moments have been carried out giving $Theta(^3D_1)=0.63862(74),e a_0^2$ and $Theta(^3D_2)=0.8602(14),e a_0^2$, respectively. The measurements utilize the differential shift between ions in a multi-ion crystal so that effects of external field gradients do not contribute leaving only the well defined Coulomb interaction. At this level of precision, hyperfine-mediated corrections will likely be important.
The recent observation of single spins flips with a single proton in a Penning trap opens the way to measure the proton magnetic moment with high precision. Based on this success, which has been achieved with our apparatus at the University of Mainz, we demonstrated recently the first application of the so called double Penning-trap method with a single proton. This is a major step towards a measurement of the proton magnetic moment with ppb precision. To apply this method to a single trapped antiproton our collaboration is currently setting up a companion experiment at the antiproton decelerator of CERN. This effort is recognized as the Baryon Antibaryon Symmetry Experiment (BASE). A comparison of both magnetic moment values will provide a stringent test of CPT invariance with baryons.
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