EBEX

EBEX
Name	EBEX
Operator	University of Minnesota, California Institute of Technology, Jet Propulsion Laboratory, Columbia University
Mission type	Balloon-borne cosmic microwave background polarimeter
Launch site	McMurdo Station, Long Duration Ballooning facilities

EBEX

EBEX was a balloon-borne polarimeter designed to measure the polarization of the cosmic microwave background (CMB) and search for signatures of primordial gravitational waves and interstellar dust polarization. The project was led by a consortium of institutions from the United States and Canada and combined technology development for superconducting detectors, cryogenics, and balloon-borne optics. EBEX operated in the tradition of high-altitude experiments such as BOOMERanG and SPIDER (balloon-borne instrument), and contributed to the experimental lineage that includes Planck (spacecraft), BICEP2, and ACT (Atacama Cosmology Telescope).

Overview

EBEX was conceived to probe B-mode polarization patterns in the CMB that could provide evidence for inflationary models associated with the early Universe, linking to theoretical frameworks developed by figures connected to Alan Guth, Andrei Linde, and Paul Steinhardt. The instrument emphasized multi-frequency observations to separate cosmological signals from polarized foregrounds like Galactic dust traced by surveys from IRAS, Planck Collaboration, and WISE. The collaboration incorporated expertise from institutions such as University of Minnesota, University of California, Berkeley, California Institute of Technology, Columbia University, and Jet Propulsion Laboratory.

Instrumentation and Design

EBEX employed a refracting/telescope optical system with a cryogenic receiver housing transition-edge sensor (TES) bolometer arrays developed with technology influenced by work at NASA centers and university labs. The focal plane used frequency multiplexed superconducting detectors similar in heritage to arrays used on SPT (South Pole Telescope) and ACTPol, read out with superconducting quantum interference device (SQUID) amplifiers pioneered in programs at NIST and Caltech. Polarimetry was achieved using a continuously rotating achromatic half-wave plate (AHWP), an approach related to modulation techniques used by experiments like POLARBEAR and ABS (Atacama B-mode Search). The payload integrated a gondola and attitude control systems inspired by designs developed for BOOMERanG and MAXIMA, with motors and star cameras for pointing tied to engineering practices at Ball Aerospace and JPL.

Cryogenics for EBEX relied on liquid helium and sub-Kelvin refrigerators, including adiabatic demagnetization refrigeration (ADR) or dilution technologies tested in lab settings at University of Chicago and NIST. The instrument observed in multiple bands centered near 150 GHz, 250 GHz, and 410 GHz to enable component separation of CMB and foregrounds, paralleling band strategies used by Planck (spacecraft) and ground-based arrays.

Science Objectives and Results

Primary science objectives were to detect or constrain primordial B-mode polarization generated by tensor perturbations during inflation, quantify lensing B-modes caused by large-scale structure associated with surveys like SDSS and DES (Dark Energy Survey), and characterize polarized Galactic dust emission mapped previously by Planck Collaboration. EBEX measured polarized dust properties and provided upper limits on inflationary tensor-to-scalar ratio parameters that complemented constraints from BICEP/Keck and WMAP. Ancillary goals included characterization of instrument systematics, polarization modulation efficacy, and demonstration of TES/SQUID performance in a stratospheric environment, informing subsequent missions and instruments such as LiteBIRD proposals and advancements at NASA Goddard Space Flight Center.

Flight Campaigns and Operations

The EBEX program flew a long-duration balloon mission launched from Antarctic or other high-latitude facilities employing resources coordinated with Columbia Scientific Balloon Facility and logistics associated with McMurdo Station. Flight operations followed protocols similar to those used by BOOMERanG and SPIDER, with telemetric links and recovery plans coordinated with agencies including NASA and national polar logistics units. The campaign included instrument integration and ground testing at partner institutions such as University of Minnesota and Caltech, pre-flight calibrations using polarized sources and beam mapping in facilities employed by JPL and university laboratories. The flights provided several weeks of stratospheric observing time, subject to environmental constraints and flight termination recovery operations managed with collaboration from NSF-supported Antarctic programs.

Data Analysis and Processing

EBEX data processing involved time-ordered data (TOD) reduction, instrumental transfer function deconvolution, map-making using maximum-likelihood and pseudo-Cl estimators similar to pipelines developed for Planck (spacecraft), ACT, and SPT, and component separation leveraging methods used by Commander and internal linear combination (ILC) implementations. Systematics mitigation addressed beam asymmetries, polarization angle calibration using astronomical sources like the Crab Nebula (linked to Maxwell Lyapunov-era polarimetry heritage) and instrument-induced polarization from the AHWP. The collaboration released data products and likelihoods used in joint analyses with datasets from BICEP/Keck, Planck Collaboration, and WMAP, contributing to combined cosmological parameter constraints.

Collaborations and Funding

The EBEX collaboration comprised researchers from universities and national laboratories including University of Minnesota, California Institute of Technology, Columbia University, University of Pennsylvania, University of British Columbia, and Jet Propulsion Laboratory. Funding and logistical support were provided by agencies such as NASA, the National Science Foundation, and institutional grants from participating universities, with in-kind contributions from partner laboratories including JPL and NIST. The project exemplified interdisciplinary cooperation among experimental cosmology groups, detector development teams, and ballooning operations units common to high-altitude observational programs.

Category:Suborbital astronomy projects