Increasing Antihydrogen Trapping Rates by Sympathetically Cooling Positrons with Laser-Cooled Beryllium Ions*

The ALPHA collaboration studies symmetries between matter and antimatter by performing high-precision measurements of the fundamental properties of antihydrogen.These studies are accomplished by performing spectroscopic measurements of antihydrogen using laser and microwave radiation and measuring the gravitational acceleration of antihydrogen. Antihydrogen is created by slowly mixing antiproton and positron plasmas that are confined and manipulated in Penning-Malmberg traps. Since only a few antihydrogen atoms are formed from each mixing, we rely on the ability to accumulate antihydrogen over numerous repeated mixing attempts to capture the thousands of atoms necessary for precision measurements. Previous experiments and theory have demonstrated that reducing the positron temperature before mixing increases the quantity of trappable antihydrogen. Therefore, we have developed and incorporated a technique that reduces positron temperatures by sympathetically cooling the positron plasma with a spatially overlapped laser-cooled beryllium ion plasma. Using this method, we have significantly reduced positron temperatures compared to what can be achieved through cooling from cyclotron radiation alone. In this work, we will discuss the substantial improvements made in the trapping rate of antihydrogen in the ALPHA-2 spectroscopy trap by using sympathetically cooled positrons. Additionally, the ALPHA collaboration has recently finished the construction and initial commissioning of the ALPHA-g apparatus, which is vertically aligned with the Earth's gravitational field to enable novel measurements of the gravitational acceleration of antihydrogen. We will present the results from our first attempts at measuring the gravitational acceleration of antihydrogen in the ALPHA-g apparatus.