[Paper Review] The FUNK search for Hidden Photon Dark Matter in the eV range

Babette Döbrich, K. Daumiller+10 more|arXiv (Cornell University)|Oct 20, 2015

CCD and CMOS Imaging Sensors7 citations

TL;DR

The FUNK experiment searches for hidden photon dark matter in the eV mass range by detecting optical signals generated via kinetic mixing between photons and hidden photons in a large spherical mirror. Using a 14 m² mirror array, the experiment aims to concentrate signals at the mirror's radius point; a low-noise PMT is being prepared to achieve sensitivity in unexplored parameter space, with characterization and installation ongoing for improved single-photon detection capabilities.

ABSTRACT

We give a brief update on the search for Hidden Photon Dark Matter with FUNK. The experiment uses a large spherical mirror, which, if Hidden Photon Dark Matter exists in the accessible mass and coupling parameter range, would yield an optical signal in the mirror's center in an otherwise dark environment. After a test run with a CCD, preparations for a run with a low-noise PMT are under way and described in this proceedings.

Motivation & Objective

• To search for hidden photon dark matter in the eV mass range using a novel optical detection technique.
• To overcome limitations of previous CCD-based measurements by deploying a low-noise photomultiplier tube (PMT) for improved sensitivity.
• To test and optimize PMT performance at cryogenic temperatures to minimize dark counts and enhance single-photon detection.
• To characterize the signal spot size and motion due to dark matter velocity distribution and Earth's motion, ensuring optimal detector placement.
• To prepare for a new data run with enhanced sensitivity in previously untested parameter space for hidden photon dark matter.

Proposed method

• Utilizes a 14 m² spherical mirror array composed of 6×6 elements from the Pierre Auger Observatory, designed to focus radiation from hidden photon dark matter at the radius point.
• Relies on kinetic mixing between visible photons and hidden photons, with coupling strength parameterized by χ, to induce detectable optical signals in the mirror's center.
• Employs a photomultiplier tube (PMT) model 9107QB with 25 mm active diameter, selected for its low dark count rate and suitability for single-photon counting.
• Mounts the PMT in a FACT50 housing capable of cooling to −50 °C to reduce noise, with the PMT tested under light-tight conditions.
• Performs high-voltage characterization to identify the plateau region and optimize trigger thresholds, minimizing non-single-photon signals.
• Uses a linear translation stage to enable lateral movement of the PMT for signal and background measurements in the mirror's focal region.

Experimental results

Research questions

• RQ1 Can a large spherical mirror effectively concentrate optical signals from hidden photon dark matter at its radius point rather than the focal point?
• RQ2 What is the optimal PMT configuration and operating point for detecting weak optical signals from hidden photon dark matter with minimal noise?
• RQ3 How does the velocity distribution of dark matter affect the size and motion of the signal spot on the mirror's center?
• RQ4 What is the achievable sensitivity of the FUNK experiment with a low-noise PMT in the eV mass range for hidden photon dark matter?
• RQ5 Can cryogenic cooling significantly reduce dark count rates in the PMT to enable single-photon detection in a dark environment?

Key findings

• The FUNK mirror's 90% spot radius was reduced to approximately 2 mm through careful alignment, improving signal localization.
• The expected signal spot size due to dark matter velocity dispersion and Earth's motion is estimated at ∆d ∼ 3.4 mm for a mirror radius of 3.4 m.
• The PMT model 9107QB exhibits a dark count rate of 0.35 ± 0.02 Hz at −20 °C, indicating low noise performance suitable for single-photon detection.
• The plateau region of the PMT's response was identified at high voltage, enabling optimization of trigger thresholds to suppress non-single-photon signals.
• The PMT is being mounted on a linear stage to allow lateral positioning for distinguishing signal from background.
• The experiment is preparing for a new data run with a low-noise PMT, aiming to access previously unexplored parameter space for hidden photon dark matter in the eV range.