Indirect Detection Search for Dark Matter

Haichuan Cao, Purdue University

Abstract

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 becomes insensitive to MDM < 10 GeV. Indirect DM detection refers to the search for DMDM or DM-M annihilation, decay debris from DM particles, or other particle production, resulting in detectable species. New physics processes, initiated by cosmic ray or dark matter interactions may be observable in underground indirect search experiments by excess high multiplicity neutron production in nuclear targets. Even for MDM < 10 GeV, DM-M interaction is capable of producing large signals, >200 neutrons if the energy is deposited in a Pb target. The NMDS-II detector, located at an underground laboratory within the Pyhasälmi complex metal mine in central Finland, collated data for 6504 ± 1 hours at 583 m.w.e. and for 1440 ± 1 hours at 1166 m.w.e.. The detector system consists of a 30 cm cube Pb-target surrounded by 60 3He proportional tubes and a two layer Geiger Counter muon detection system. The lead target is used to interact with potential dark matter particles, and neutron numbers are measured with 3He tubes. The neutron event multiplicity production is compared to Geant4 simulations, starting with the well measured absolute muon momentum and angular distribution flux rate at sea level, then propagating the muon flux through rock while preserving the momentum-angular correlation to a depth 4m above the the detector at the two depth locations. The muon flux modeling is compared to the uncorrelated Miyake model at each depth as verification of the muon propagation simulation. Finally, the Geant4 fully simulates the passage of the muon and its induced showers through a model universe 10000 m2 x 12 m depth, and the simulated response of the detector to the calculated muon flux, is compared with the data. The Geant4 prediction and the observed data neutron event multiplicity distributions have matching power law shapes, k × n −p , and do not have exponential shapes. For the data collected at 583 m.w.e., p=2.36±0.10 with χ 2/DoF = 0.76 and for the simulation p=2.34±0.01 with χ 2/DoF = 1.05. At 1166 m.w.e., p=2.29±0.007 for the simulation with χ 2/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. The DM acceptance as a function of mass is found using a proton-Pb spallation model. The dark matter mass is assumed to be equal to the proton kinetic energy and to interact uniformly over the volume of the lead target. The number of excess events is found to be −6.1 ± 5.1, that is no excess events are observed. The upper limit with 90% confidence level is then found assuming 2.3 events. The Poisson estimation then yielding search limits 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. An indirect dark matter search was conducted based on DM-M interactions depositing energy in a Pb-target allowing DM masses to be probed in a region 100 MeV < MDM < 10 GeV not accessible to direct dark matter searches. Limits are placed on DM-M energy deposition independent of the DM-M interaction.

Degree

Ph.D.

Advisors

Koltick, Purdue University.

Subject Area

Energy|Astronomy|Astrophysics|Atomic physics|Physics|Theoretical physics

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