Direct measurement of the break-out ^(19)F(p,γ)^(20)Ne reaction in the China Jinping underground laboratory(CJPL)

Calcium production and the stellar evolution of first-generation stars remain fascinating mysteries in astrophysics.As one possible nucleosynthesis scenario,break-out from the hot carbon–nitrogen–oxygen(HCNO)cycle was thought to be the source of the calcium observed in these oldest stars.However,according to the stellar modeling,a nearly tenfold increase in the thermonuclear rate ratio of the break-out ^(19)F(p,γ)^(20) Ne reaction with respect to the competing ^(19)F(p,α)^(16) O back-processing reaction is required to reproduce the observed calcium abundance.We performed a direct measurement of this break-out reaction at the China Jinping underground laboratory.The measurement was performed down to the low-energy limit of E_(c.m.)=186 keV in the center-of-mass frame.The key resonance was observed at 225.2 keV for the first time.At a temperature of approximately 0.1 GK,this new resonance enhanced the thermonuclear ^(19)F(p,γ)^(20) Ne rate by up to a factor of≈7.4,compared with the previously recommended NACRE rate.This is of particular interest to the study of the evolution of the first stars and implies a stronger breakdown in their“warm”CNO cycle through the ^(19)F(p,γ)^(20) Ne reaction than previously envisioned.This break-out resulted in the production of the calcium observed in the oldest stars,enhancing our understanding of the evolution of the first stars.

Preliminary research and scheme design of deep underground in situ geo-information detection experiment for Geology in Time

The deep earth,deep sea,and deep space are the main parts of the national“three deep”strategy,which is in the forefront of the strategic deployment clearly defined in China’s 14th Five-Year Plan(2021-2025)and the Long-Range Objectives Through the Year 2035.It is important to reveal the evolutionary process and mechanism of deep tectonics to understand the earth’s past,present and future.The academic con-notation of Geology in Time has been given for the first time,which refers to the multi-field evolution response process of geological bodies at different time and spatial scales caused by geological processes inside and outside the Earth.Based on the deep in situ detection space and the unique geological envi-ronment of China Jinping Underground Laboratory,the scientific issue of the correlation mechanism and law between deep internal time-varying and shallow geological response is given attention.Innovative research and frontier exploration on deep underground in situ geo-information detection experiments for Geology in Time are designed to be carried out,which will have the potential to explore the driving force of Geology in Time,reveal essential laws of deep earth science,and explore innovative technologies in deep underground engineering.

NνDEx-100 conceptual design report

Observing nuclear neutrinoless double beta (0vββ) decay would be a revolutionary result in particle physics.Observing such a decay would prove that the neutrinos are their own antiparticles,help to study the absolute mass of neutrinos,explore the origin of their mass,and may explain the matter-antimatter asymmetry in our universe by lepton number violation.We propose developing a time projection chamber (TPC) using high-pressure ^(82)SeF_(6) gas and Topmetal silicon sensors for readout in the China Jinping Underground Laboratory (CJPL) to search for neutrinoless double beta decay of82Se,called the NvDEx experiment.Besides being located at CJPL with the world’s thickest rock shielding,NvDEx combines the advantages of the high Qββ(2.996 MeV) of82Se and the TPC’s ability to distinguish signal and background events using their different topological characteristics.This makes NvDEx unique,with great potential for low-background and high-sensitivity 0 vββsearches.NvDEx-100,a NvDEx experiment phase with 100 kg of SeF_(6)gas,is being built,with plans to complete installation at CJPL by 2025.This report introduces 0 vββ physics,the NvDEx concept and its advantages,and the schematic design of NvDEx-100,its subsystems,and background and sensitivity estimation.

Introduction to the CDEX experiment

It is believed that weakly interacting massive particles （WIMPs） are candidates for dark matter （DM） in our universe which come from outer space and might interact with the standard model （SM） matter of our detectors on the earth. Many collaborations in the world are carrying out various experiments to directly detect DM particles. China Jinping underground Laboratory （CJPL） is the deepest underground laboratory in the world and provides a very promising environment for DM search. China Dark matter EXperiment （CDEX） is going to directly detect the WIMP flux with high sensitivity in the low WIMP-mass region. Both CJPL and CDEX have achieved a remarkable progress in recent three years. CDEX employs a point-contact germanium （PCGe） semi-conductor detector whose energy threshold is less than 300 eV. In this report we present the measurement results of muon flux, monitoring of radioactivity and radon concentration carried out in CJPL, as well describing the structure and performance of the 1 kg-PCGe detector in CDEX-1 and 10 kg- PCGe detector array in CDEX-10 including the detectors, electronics, shielding and cooling systems. Finally we discuss the physics goals of CDEX-1, CDEX-10 and the future CDEX-1T experiments.

A proposed direct measurement of cross section at Gamow window for key reaction 19F(p,α) 16O in Asymptotic Giant Branch stars with a planned accelerator in CJPL

In 2014, the National Natural Science Foundation of China （NSFC） approved the Jinping Underground Nuclear Astrophysics laboratory （JUNA） project, which aims at direct cross-section measurements of four key stellar nuclear reactions right down to the Gamow windows. In order to solve the observed fluorine overabundances in Asymptotic Giant Branch （AGB） stars, measuring the key 19F（p,a）16O reaction at effective burning energies （i.e., at Gamow window） is established as one of the scientific research sub-projects. The present paper describes this sub-project in details, including motivation, status, experimental setup, yield and background estimation, aboveground test, as well as other relevant reactions.