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https://cern.zoom.us/j/390597013?pwd=cUlSVGltUnVjd04vQjZ1bnpVVEE2UT09 meeting ID: 390-597-013 pwd:446459
报告人简介
曹海川，本科于2017年从中国科学技术大学毕业，后于2023年在美国普渡大学取得博士学位，现为普渡大学的博士后。博士、博士后期间主要在费米实验室的mu2e 项目和芬兰Pyhäsalmi地下物理研究中心的NMDS-II项目。在mu2e寻找带电轻子味破坏实验中，主导了stopping target monitor的信号系统模拟工作，参与了对extinction monitor模拟中的数字化，轨迹重建。并且在核心模拟组Geant4物理模型验证有重要贡献。在NMDS-II 实验中，分析了地下低本底实验的宇宙射线背景，且探讨可能存在的新物理。
The neutron event multiplicity data are taken from the 2002 NMDS-II data sets, consisting of 6504 hours collected at 583 m.w.e. and 1440 hours collected at 1166 m.w.e., using an identical detector system. The detector comprised a 30 cm cubic Pb target surrounded by 60 He-3 tubes. These neutron multiplicity measurements can be used to study cosmic-ray-induced backgrounds for underground rare-event experiments as well as to search for possible new physics signals, such as dark matter.
For the cosmic-ray background study, the neutron multiplicity distributions, n, are well described by a two-parameter power-law function, k*n^-p. The power-law behavior is confirmed by the sample-space-reducing (SSR) law. Both the Monte Carlo simulations and the experimental data at the two depths are consistent with a single slope parameter p. This result indicates that the power-law distribution can be attributed to an SSR process, with the index p remaining independent of nuclear structure and reaction type.
For the new physics study, two DM–M interaction models were employed to set limits. The first, a spallation model, assumes a single proton with kinetic energy equal to the DM–M interaction energy. The second, a fireball model, assumes annihilation between DM–M particles producing pions with a limiting Hagedorn temperature. Despite their different assumptions, the two models yield comparable upper limits on the DM–M cross section, across the DM mass range from 300 MeV to 100 GeV. The limits are derived under the assumption that all DM energy is deposited in the Pb target, resulting in spin-independent cross-section limits at the level of ~ 10^-45.
Qiang Li