Search For Monopole-dipole Interactions At The Sub-millimeter Range With A Xenon Isotope Comagnetometer

Axion is a hypothetical particle proposed to solve the strong CP problem in QCD.It is also a possible candidate for cold dark matter in the Universe.In recent years,searching for exotic interactions propagated by axions using atomic physics methods has emerged as an important direction in the field of searching for new physics beyond the Standard Model.Monopole-dipole interactions involve scalar couplings between the spin of one particle and the mass of another.Such interactions violate P-and Tsymmetry,and can be transmitted by axions.In this thesis work,we use a 129Xe-131XeRb comagnetometer to measure the ratio of precession frequencies between the two Xe isotopes,and search for changes of the ratio correlated with the distance between a nonmagnetic bismuth germanate(BGO)crystal and the atomic cell.In the 129Xe-131Xe-Rb system,polarized Rb atoms are used to hyperpolarize Xe atoms and as an atomic magnetometer to probe the precession of Xe.We study the precession spectrum of 131Xe,and use an asymmetric atomic cell to amplify the quadrupole splitting of 131Xe.We calculate the effect of the asymmetry factor on the 131Xe precession spectrum,and compare the results with the measurements.Since the effective magnetic field produced by the polarized Rb atoms causes the largest systematic effect,we modulate the polarization of the optical pumping beam so that the effect of the polarized Rb atoms is time-averaged out,and the related systematic effect is suppressed by more than two orders of magnitude.The null results of this search improve the upper limit on the coupling strength |g_s~Ng_p~n| over the interaction range 0.11-0.55 mm,corresponding to the propagator mass range of 0.36-1.80 meV.The improvement factor reaches the largest value of 30 at 0.24 mm.