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Title: Electron Ionization via Dark Matter-Electron Scattering and the Migdal Effect

Abstract

There are currently several existing and proposed experiments designed to probe sub-GeV dark matter (DM) using electron ionization in various materials. The projected signal rates for these experiments assume that this ionization yield arises only from DM scattering directly off electron targets, ignoring secondary ionization contributions from DM scattering off nuclear targets. In this work we investigate the validity of this assumption and show that if sub-GeV DM couples with comparable strength to both protons and electrons, as would be the case for a dark photon mediator, the ionization signal from atomic scattering via the Migdal effect scales with $$Z^2 (m_e/m_N)^2 \mathbf{q}^2$$ where $$m_N$$ is the mass of the target nucleus and $$\mathbf{q}$$ is the 3-momentum transferred to the atom. The result is that the Migdal effect is always subdominant to electron scattering when the mediator is light, but that Migdal-induced ionization can dominate over electron scattering for heavy mediators and DM masses in the hundreds of MeV range. We put these two ionization processes on identical theoretical footing, address some theoretical uncertainties in the choice of atomic wavefunctions used to compute rates, and discuss the implications for DM scenarios where the Migdal process dominates, including for XENON10, XENON100, and the recent XENON1T results on light DM scattering.

Authors:
 [1];  [2];  [3]
  1. Chicago U., EFI
  2. Illinois U., Urbana
  3. Fermilab
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1561549
Report Number(s):
arXiv:1908.00012; FERMILAB-PUB-19-257-A
oai:inspirehep.net:1747539
DOE Contract Number:  
AC02-07CH11359
Resource Type:
Journal Article
Journal Name:
TBD
Additional Journal Information:
Journal Name: TBD
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Baxter, Daniel, Kahn, Yonatan, and Krnjaic, Gordan. Electron Ionization via Dark Matter-Electron Scattering and the Migdal Effect. United States: N. p., 2019. Web.
Baxter, Daniel, Kahn, Yonatan, & Krnjaic, Gordan. Electron Ionization via Dark Matter-Electron Scattering and the Migdal Effect. United States.
Baxter, Daniel, Kahn, Yonatan, and Krnjaic, Gordan. Wed . "Electron Ionization via Dark Matter-Electron Scattering and the Migdal Effect". United States. https://www.osti.gov/servlets/purl/1561549.
@article{osti_1561549,
title = {Electron Ionization via Dark Matter-Electron Scattering and the Migdal Effect},
author = {Baxter, Daniel and Kahn, Yonatan and Krnjaic, Gordan},
abstractNote = {There are currently several existing and proposed experiments designed to probe sub-GeV dark matter (DM) using electron ionization in various materials. The projected signal rates for these experiments assume that this ionization yield arises only from DM scattering directly off electron targets, ignoring secondary ionization contributions from DM scattering off nuclear targets. In this work we investigate the validity of this assumption and show that if sub-GeV DM couples with comparable strength to both protons and electrons, as would be the case for a dark photon mediator, the ionization signal from atomic scattering via the Migdal effect scales with $Z^2 (m_e/m_N)^2 \mathbf{q}^2$ where $m_N$ is the mass of the target nucleus and $\mathbf{q}$ is the 3-momentum transferred to the atom. The result is that the Migdal effect is always subdominant to electron scattering when the mediator is light, but that Migdal-induced ionization can dominate over electron scattering for heavy mediators and DM masses in the hundreds of MeV range. We put these two ionization processes on identical theoretical footing, address some theoretical uncertainties in the choice of atomic wavefunctions used to compute rates, and discuss the implications for DM scenarios where the Migdal process dominates, including for XENON10, XENON100, and the recent XENON1T results on light DM scattering.},
doi = {},
journal = {TBD},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {7}
}