The progress of the ALETHEIA project in 2021

The ALETHEIA (A Liquid hElium Time projection cHambEr In dArk matter) aims to hunt for low-mass WIMPs with a liquid helium TPC. The temperature of liquid helium filling in the TPC is at $\sim$ 4 K. Cooling helium to 4 K is easier than doing it to superfluid helium ( below 2.17 K). There are lots of technical challenges ahead since no single LHe TPC has ever been demonstrated for DM hunting yet, though LXe (Liquid Xenon) and LAr (Liquid Argon) TPCs achieved great success in DM (Dark Matter) searches. The project was successfully reviewed by a panel composed of leading physicists in the community of DM and LHe in Oct 2019. Since then, we have built a liquid helium prototype detector successfully. We will mainly share experiences of making such a detector and present preliminary results on testing it.