# A Detection of CMB-Cluster Lensing using Polarization Data from SPTpol

## TL;DR

This paper presents the first detection of galaxy cluster lensing using only CMB polarization data, employing a novel estimator and data from the SPTpol survey, achieving a significant 4.8 sigma detection.

## Contribution

The study introduces a new polarization-based estimator for detecting cluster lensing and demonstrates its effectiveness with real data, aligning with other measurement methods.

## Key findings

- Detected cluster lensing at 4.8 sigma significance
- Estimated mean cluster mass consistent with other methods
- Paves the way for future polarization-based cluster cosmology

## Abstract

We report the first detection of gravitational lensing due to galaxy clusters using only the polarization of the cosmic microwave background (CMB). The lensing signal is obtained using a new estimator that extracts the lensing dipole signature from stacked images formed by rotating the cluster-centered Stokes $Q/U$ map cutouts along the direction of the locally measured background CMB polarization gradient. Using data from the SPTpol 500 deg$^{2}$ survey at the locations of roughly 18,000 clusters with richness $\lambda \ge 10$ from the Dark Energy Survey (DES) Year-3 full galaxy cluster catalog, we detect lensing at $4.8\sigma$. The mean stacked mass of the selected sample is found to be $(1.43 \pm 0.4)\ \times 10^{14}\ {\rm M_{\odot}}$ which is in good agreement with optical weak lensing based estimates using DES data and CMB-lensing based estimates using SPTpol temperature data. This measurement is a key first step for cluster cosmology with future low-noise CMB surveys, like CMB-S4, for which CMB polarization will be the primary channel for cluster lensing measurements.