Upgrade of Neutron Lifetime Measurement at J-PARC*

Neutron lifetime is an important parameter, and it has been precisely measured with two methods. However, there is 8.4 sec difference between these two methods. In Japan, we are measuring the neutron lifetime using new method. This experiment is using a polarized neutron beam branch of BL05, MLF, J-PARC.  A Time Projection Chamber (TPC) is used for counting both the beta-decay product and neutron flux, and it is operated using a mixture of He and CO_2 gas with 100 kPa total pressure. We are planning 2 updates in order to reduce the uncertainty. One is spin flip chopper update, and the other is taking data with a low gas pressure condition. The most significant background is gas scattering event, and it can be reduced by lowering the TPC gas pressure. We have carried out the first physics run of the low gas pressure measurement in 2017. We also have developed a new amplifier for further lower pressure operation. Details of the data analysis and new amplifier will be presented in this talk.