Daily Modulation Constraints on Light Dark Matter with DAMIC-M

TL;DR

This work addresses daily modulation of light Hidden Sector DM from Earth-scattering in the Galactic halo and explores DM–electron interactions with a dark photon mediator. Using the DAMIC-M prototype Low Background Chamber, it performs a model-independent search for sidereal modulation and a model-dependent DM–electron scattering analysis in the mass range $m_ extchi\in[0.53,2]\mathrm{MeV}/c^2$ with a dark-photon mediator. No modulation is detected; the study derives 90% C.L. upper limits on $\bar{\sigma}_e$ that improve previous DAMIC-M constraints by up to two orders of magnitude for sub-MeV DM masses, for both ultralight and heavy mediators, using QCDark and QEDark models. The results demonstrate the value of time-domain analyses for sub-MeV DM searches and establish world-leading constraints on DM–electron interactions in this mass range.

Abstract

The flux of Hidden Sector particles from the Galactic halo reaching an underground detector can be significantly attenuated by interactions within the Earth for sufficiently large scattering crosssections. This attenuation gives rise to a characteristic daily modulation in the detection rate, due to Earth's rotation. We present results from a search for such a modulation using a 1.257 kg-day dataset collected with the DAMIC-M Low Background Chamber. A model-independent analysis reveals no significant modulation in the 1e- event rate over periods from 1 to 48 h, highlighting the excellent temporal stability of the detector. In a complementary model-dependent analysis, we target the expected daily modulation signature of Hidden Sector particles, with masses in the range [0.53,2] MeV/c2, interacting with electrons via a dark photon mediator. By leveraging the expected temporal evolution of the signal, we set improved constraints on Dark Matter masses below 1.2 MeV/c2, surpassing our previous limits.

Figures (5)

• Figure 1: $R_1^i$ as a function of time for CCD 1-D (middle), CCD 2-D (top) during D2. The temporal evolution of the total $R_1^i$, derived summing the contributions of all the CCDs, is also shown (bottom). The dashed lines indicate the boundaries between the different segments of the dataset, labeled D2-1, D2-2, and D2-3. To improve visibility, we averaged approximately seven consecutive values of $R_1^i$ within each portion of the dataset between the temporal gaps. The error on the mean is shown. During the temporal gap between D2-1 and D2-2, a dedicated run was acquired to characterize defects in the CCDs. The gap between D2-2 and D2-3 is due to a brief data acquisition incident, following which Module 2 was shut down. An additional smaller gap is visible for CCD 2-D during D2-2, which corresponds to the period of time when the CCD 2-C noise increased exponentially, before turning the malfunctioning CCD off.
• Figure 2: Top: the temporal evolution of the total $R_1^i$ (blue dots) together with that of the system temperature (black line), which is measured at the level of the lead shield inside the cryostat, surrounding the CCD box. Bottom: the temporal evolution of the total $R_1^i$ after subtracting $r^i(T_i)$.
• Figure 3: Lomb-Scargle periodograms calculated on the CCD 1-D, CCD 2-D, and total 1$e^{-}$ rates during D2. The continuous and dashed horizontal lines represent the $\mathrm{FAP}=0.159$ and $0.023$ levels, respectively. For clarity, we display the periodograms only over the period range of $18.5-30$ h, although they were computed over the full range of $1-48$ h.
• Figure 4: Residuals after the subtraction of the best-fit background-only model to the total rate, binned as a function of local apparent sidereal time. As a reference, the upper x-axis gives the isodetection angle $\Theta(t)$ for the first day of data taking. Each data point is obtained from the average of $~50$ images. The red line shows the expected signal (minus its time average) for a DM particle of mass $1$ MeV/c$^{2}$, $\bar{\sigma}_e=10^{-33}$cm$^{2}$ interacting via an ultralight dark photon mediator.
• Figure 5: DAMIC-M 90% C.L. upper limits (solid thick black) on DM-electron interactions through an ultralight (left) and heavy (right) dark photon mediator obtained from the daily modulation analysis. In green and yellow are the 1- and 2$\sigma$ sensitivity bands. The limits derived using the QEDark model are also reported (dashed thick black). Also shown are previous DAMIC-M limits DAMIC-M:2023FCDAMIC-M:2023DMDAMIC-M:2025 for Galactic DM, as well as results from other experiments, such as SENSEI@SNOLAB SolarReflectionSensei and XENON1T SolarReflectionXenon, for solar-reflected DM. Theoretical expectations assuming a DM relic abundance from freeze-in and freeze-out mechanisms are also shown in light blue freezein.