# A Measurement of the Cosmic Microwave Background $B$-Mode Polarization Power Spectrum at Sub-Degree Scales from 2 years of POLARBEAR Data

## TL;DR

This paper presents an improved measurement of the CMB B-mode polarization power spectrum at sub-degree scales using two years of POLARBEAR data, providing evidence for lensing-induced B-modes and testing consistency with the DM model.

## Contribution

The study combines two seasons of POLARBEAR data to significantly reduce uncertainties in the B-mode power spectrum measurement and tests its consistency with DM predictions.

## Key findings

- Rejects the null hypothesis of no B-mode polarization at 3.1C3
- Measures a lensing amplitude parameter A_L = 0.60^{+0.26}_{-0.24} (stat+inst+foreground+multi)
- Provides evidence for lensing-induced B-modes in the CMB

## Abstract

We report an improved measurement of the cosmic microwave background (CMB) $B$-mode polarization power spectrum with the POLARBEAR experiment at 150 GHz. By adding new data collected during the second season of observations (2013-2014) to re-analyzed data from the first season (2012-2013), we have reduced twofold the band-power uncertainties. The band powers are reported over angular multipoles $500 \leq \ell \leq 2100$, where the dominant $B$-mode signal is expected to be due to the gravitational lensing of $E$-modes. We reject the null hypothesis of no $B$-mode polarization at a confidence of 3.1$\sigma$ including both statistical and systematic uncertainties. We test the consistency of the measured $B$-modes with the $\Lambda$ Cold Dark Matter ($\Lambda$CDM) framework by fitting for a single lensing amplitude parameter $A_L$ relative to the Planck best-fit model prediction. We obtain $A_L = 0.60 ^{+0.26} _{-0.24} ({\rm stat}) ^{+0.00} _{-0.04}({\rm inst}) \pm 0.14 ({\rm foreground}) \pm 0.04 ({\rm multi})$, where $A_{L}=1$ is the fiducial $\Lambda$CDM value, and the details of the reported uncertainties are explained later in the manuscript.