<p> Present WIMP Dark Matter search strategies are mainly focused on possible direct detection through elastic or inelastic scatterings on atomic nuclei, or with electrons. This approach<br>
becomes insensitive to M(DM) < 10 GeV. Indirect DM detection refers to the search for DM-DM or DM-M annihilation, decay debris from DM particles, or other particle production,<br>
resulting in detectable species. </p>
<p><br>
New physics processes, initiated by cosmic ray or dark matter interactions may be observable in underground indirect search experiments by excess high multiplicity neutron<br>
production in nuclear targets. Even for M(DM) < 10 GeV, DM-M interaction is capable of<br>
producing large signals, >200 neutrons if the energy is deposited in a Pb target.</p>
<p><br></p>
<p> The NMDS-II detector, located at an underground laboratory within the Pyhasälmi<br>
complex metal mine in central Finland, collated data for 6504 ± 1 hours at 583 m.w.e.<br>
and for 1440 ± 1 hours at 1166 m.w.e.. The detector system consists of a 30 cm cube<br>
Pb-target surrounded by 60 He-3 proportional tubes and a two layer Geiger Counter muon<br>
detection system. The lead target is used to interact with potential dark matter particles, and<br>
neutron numbers are measured with He-3 tubes. The neutron event multiplicity production is<br>
compared to Geant4 simulations, starting with the well measured absolute muon momentum<br>
and angular distribution flux rate at sea level, then propagating the muon flux through rock<br>
while preserving the momentum-angular correlation to a depth 4m above the the detector at<br>
the two depth locations. The muon flux modeling is compared to the uncorrelated Miyake<br>
model at each depth as verification of the muon propagation simulation. Finally, the Geant4<br>
fully simulates the passage of the muon and its induced showers through a model universe<br>
10000 m^2 x 12 m depth, and the simulated response of the detector to the calculated muon<br>
flux, is compared with the data. <br>
</p>
<p> The Geant4 prediction and the observed data neutron event multiplicity distributions<br>
have matching power law shapes, k × n^(-p), and do not have exponential shapes. For the<br>
data collected at 583 m.w.e., p=2.36±0.10 with χ2/DoF = 0.76 and for the simulation<br>
p=2.34±0.01 with χ2/DoF = 1.05. At 1166 m.w.e., p=2.29±0.007 for the simulation with χ2/DoF = 1.16. And for the data the collection with only 6 detected events above multiplicity 5, yields p=2.50 ± 0.35 predicted by the Maximum Likelihood Estimatation method. </p>
<p><br></p>
<p> The DM acceptance as a function of mass is found using a proton-Pb spallation model.<br>
The dark matter mass is assumed to be equal to the proton kinetic energy and to interact<br>
uniformly over the volume of the lead target. The number of excess events is found to be<br>
-6.1 ± 5.1, that is no excess events are observed. The upper limit with 90% confidence<br>
level is then found assuming 2.3 events. The Poisson estimation then yielding search limits<br>
1.1×10^(-44) cm^(-2) for 10 GeV deposited energy, 1.9×10^(-45) cm^(-2) at 1 GeV and 3.0×10^(-45) cm^(-2) for 500 MeV deposited energy and no acceptance at 100 MeV.<br>
</p>
<p> An indirect dark matter search was conducted based on DM-M interactions depositing<br>
energy in a Pb-target allowing DM masses to be probed in a region 100 MeV < M(DM) <<br>
10 GeV not accessible to direct dark matter searches. Limits are placed on DM-M energy<br>
deposition independent of the DM-M interaction. <br>
<br>
<br>
<br>
</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/22685170 |
| Date | 26 April 2023 |
| Creators | Haichuan Cao (15347563) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Thesis_HC_04242023_pdf/22685170 |
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