The China Jinping underground Laboratory (CJPL) is an excellent location for studying solar, terrestrial, and supernova neutrinos due to its 2400-meter vertical rock overburden. Its unparalleled depth gives an opportunity to investigate the cosmic-ray muons with exceptionally high average energy at <math><mo>∼</mo><mn>360</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. This paper details a study of muon-related backgrounds based on 1178 days of data collected by the 1-ton prototype neutrino detector used for the Jinping Neutrino Experiment (JNE) since 2017. The apparent effects for the leakage of muons’ secondary particles due to detector’s finite size on the measured neutron yield are first discussed in detail. The analysis of 493 cosmic-ray muon candidates and <math><mn>13.6</mn><mo>±</mo><mn>5.7</mn></math> cosmogenic neutron candidates, along with a thorough evaluation of detection efficiency and uncertainties, gives a muon flux of <math><mrow><mo>(</mo><mn>3.56</mn><mo>±</mo><msub><mn>0.16</mn><mrow><mrow><mi>stat</mi></mrow></mrow></msub><mo>±</mo><msub><mn>0.10</mn><mrow><mrow><mi>syst</mi></mrow></mrow></msub><mo>)</mo><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>10</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mi>cm</mi><mrow><mo>−</mo><mn>2</mn></mrow></msup><mtext> </mtext><msup><mi>s</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> and a cosmogenic neutron yield of <math><mrow><mo>(</mo><mn>3.37</mn><mo>±</mo><mn>1.4</mn><msub><mrow><mn>1</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.3</mn><msub><mrow><mn>1</mn></mrow><mrow><mi>syst</mi></mrow></msub><mo>)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>g</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mtext> </mtext><msup><mrow><mi>cm</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> in LAB-based liquid scintillator.

China

Xinshun Zhang

Jinjing Li

Shaomin Chen

Wei Dou

Haoyang Fu

Ye Liang

Qian Liu

Wentai Luo

Ming Qi

Wenhui Shao

Haozhe Sun

Jian Tang

Yuyi Wang

Zhe Wang

Changxu Wei

Jun Weng

Yiyang Wu

Benda Xu

Chuang Xu

Tong Xu

Yuzi Yang

Aiqiang Zhang

Bin Zhang

Study of neutron production for 360 GeV cosmic muons

A solar neutrino detector relying on the charged-current (CC) interaction of  $$\nu _e$$  <math> <msub> <mi>ν</mi> <mi>e</mi> </msub> </math>   on  $$\mathrm{{}^{7}Li}$$  <math> <mrow> <msup> <mrow></mrow> <mn>7</mn> </msup> <mi>Li</mi> </mrow> </math>   is attractive. The total CC interaction cross-section weighted by the solar  $$^8$$  <math> <msup> <mrow></mrow> <mn>8</mn> </msup> </math>  B electron neutrino spectrum is approximately 60 times that of the neutrino-electron elastic scattering process. The final state effective kinetic energy after the CC interaction on  $$\mathrm{{}^{7}Li}$$  <math> <mrow> <msup> <mrow></mrow> <mn>7</mn> </msup> <mi>Li</mi> </mrow> </math>   directly reflects the neutrino energy, which stands in sharp contrast to the plateau structure of recoil electrons of the elastic scattering. The recent measurement of the optical properties of saturated LiCl water solution, especially the long attenuation length, has once again aroused our interest in LiCl. In this work, with new B(GT) experimental measurements, the CC cross-section on  $$\mathrm{{}^{7}Li}$$  <math> <mrow> <msup> <mrow></mrow> <mn>7</mn> </msup> <mi>Li</mi> </mrow> </math>   is reevaluated to be  $$3.759\times 10^{-42}~\textrm{cm}^2$$  <math> <mrow> <mn>3.759</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>42</mn> </mrow> </msup> <mspace width="3.33333pt"></mspace> <msup> <mtext>cm</mtext> <mn>2</mn> </msup> </mrow> </math>  . Given the high solubility of LiCl of 74.5 g/100 g water at 10  $$^\circ $$  <math> <msup> <mrow></mrow> <mo>∘</mo> </msup> </math>  C and the high natural abundance of 92.41% of  $$\mathrm{{}^{7}Li}$$  <math> <mrow> <msup> <mrow></mrow> <mn>7</mn> </msup> <mi>Li</mi> </mrow> </math>  , a solar neutrino detection proposal is made. The detector with high concentration LiCl water solution has a comparable CC event rate of  $$\nu _e$$  <math> <msub> <mi>ν</mi> <mi>e</mi> </msub> </math>   on  $$\mathrm{{}^{7}Li}$$  <math> <mrow> <msup> <mrow></mrow> <mn>7</mn> </msup> <mi>Li</mi> </mrow> </math>   with that of neutrino-electron elastic scattering. The contained  $$\mathrm{{}^{35}Cl}$$  <math> <mrow> <msup> <mrow></mrow> <mn>35</mn> </msup> <mi>Cl</mi> </mrow> </math>  ,  $$\mathrm{{}^{6}Li}$$  <math> <mrow> <msup> <mrow></mrow> <mn>6</mn> </msup> <mi>Li</mi> </mrow> </math>  , and H also make a delayed-coincidence detection for  $${{\bar{\nu }}}_e$$  <math> <msub> <mover> <mrow> <mi>ν</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> <mi>e</mi> </msub> </math>   possible. The advantages of studying the upturn effect of solar neutrino oscillation, light sterile neutrinos, and Earth matter effect are investigated in detail. The sensitivities in discovering solar neutrino upturn and light sterile neutrinos are presented.

United States

Weiran Xu

Jialiang Zhang

The potential to probe solar neutrino physics with LiCl water solution

Solar, terrestrial, and supernova neutrino experiments are subject to muon-induced radioactive background. The China Jinping Underground Laboratory (CJPL), with its unique advantage of a 2400 m rock coverage and long distance from nuclear power plants, is ideal for MeV-scale neutrino experiments. Using a 1-ton prototype detector of the Jinping Neutrino Experiment (JNE), we detected 343 high-energy cosmic-ray muons and (7.86   $ \pm $  3.97) muon-induced neutrons from an 820.28-day dataset at the first phase of CJPL (CJPL-I). Based on the muon-induced neutrons, we measured the corresponding muon-induced neutron yield in a liquid scintillator to be   $ \pm $     $ \pm $   μ$^{−1}$g$^{−1}$cm$^{2}$ at an average muon energy of 340 GeV. We provided the first study for such neutron background at CJPL. A global fit including this measurement shows a power-law coefficient of (0.75   $ \pm $  0.02) for the dependence of the neutron yield at the liquid scintillator on muon energy.

Lin Zhao

Germany

Lars Bathe-Peters

Switzerland

Mourad Chouaki

Lei Guo

Ziyi Guo

Ghulam Hussain

Guang Luo

Linyan Wan

Minfang Yeh

Measurement of muon-induced neutron yield at the China Jinping Underground Laboratory  