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The BICEP/Keck (BK) series of cosmic microwave background (CMB) polarization experiments has, over the past decade and a half, produced a series of field-leading constraints on cosmic inflation via measurements of the “B-mode” polarization of the CMB. Primordial B modes are directly tied to the amplitude of primordial gravitational waves (PGW), their strength parameterized by the tensor-to-scalar ratio, r, and thus the energy scale of inflation. Having set the most sensitive constraints to-date on r, σ(r) = 0.009 (r0.05 < 0.036, 95% C.L.) using data through the 2018 observing season (“BK18”), the BICEP/Keck program has continued to improve its dataset in the years since. We give a brief overview of the BK program and the “BK18” result before discussing the program’s ongoing efforts, including the deployment and performance of the Keck Array’s successor instrument, BICEP Array, improvements to data processing and internal consistency testing, new techniques such as delensing, and how those will ultimately serve to allow BK reach σ(r) ≲ 0.003 using data through the 2027 observing season.more » « lessFree, publicly-accessible full text available May 29, 2025
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Time-division multiplexing is the readout architecture of choice for many ground and space experiments, as it is a very mature technology with proven outstanding low-frequency noise stability, which represents a central challenge in multiplexing. Once fully populated, each of the two BICEP Array high-frequency receivers, observing at 150 GHz and 220/270 GHz, will have 7776 TES detectors tiled on the focal plane. The constraints set by these two receivers required a redesign of the warm readout electronics. The new version of the standard multichannel electronics, developed and built at the University of British Columbia, is presented here for the first time. BICEP Array operates time-division multiplexing readout technology to the limits of its capabilities in terms of multiplexing rate, noise and cross talk, and applies them in rigorously demanding scientific application requiring extreme noise performance and systematic error control. Future experiments like CMB-S4 plan to use TES bolometers with time-division/SQUID-based readout for an even larger number of detectors.more » « lessFree, publicly-accessible full text available April 24, 2025
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The Background Imaging of Cosmic Extragalactic Polarization (BICEP)/Keck (BK) collaboration is currently leading the quest for the highest-sensitivity measurements of the polarized cosmic microwave background (CMB) anisotropies on a degree scale with a series of cryogenic telescopes, of which BICEP Array (BA) is the latest Stage-3 upgrade with a total of ∼ 32,000 detectors. The instrument comprises 4 receivers spanning 30-270 GHz, with the low-frequency 30/40 GHz deployed to the South Pole Station in late 2019. The full complement of receivers is forecast to set the most stringent constraints on the tensor-to-scalar ratio r. Building on these advances, the overarching small-aperture telescope concept is already being used as the reference for further Stage-4 experiment design. This paper describes the development of the BICEP Array 150 GHz detector module and its fabrication requirements, with highlights on the high-density time division multiplexing (TDM) design of the cryogenic circuit boards. The low-impedance wiring required between the detectors and the first stage of superconducting quantum interference device amplifiers is crucial to maintaining a stable bias current on the detectors. A novel multi-layer FR4 Printed Circuit Board with superconducting traces, capable of reading out up to 648 detectors, is detailed along with its validation tests. An ultra-high-density TDM detector module concept we developed for a CMB-S4-like experiment that allows up to 1920 detectors to be read out is also presented. TDM has been chosen as the detector readout technology for the Cosmic Microwave Background Stage-4 (CMB-S4) experiment based on its proven low-noise performance, predictable costs, and overall maturity of the architecture. The heritage for TDM is rooted in mm- and sub-mm-wave experiments dating back 20 years and has since evolved to support a multiplexing factor of 64x in Stage-3 experiments.more » « lessFree, publicly-accessible full text available December 1, 2024
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Abstract Sparse wide‐angle seismic profiling supported by coincident reflection imaging has been instrumental for advancing our knowledge about rifted margins. Nevertheless, features of critical importance for understanding rifting processes have been poorly resolved. We derive a high‐resolution velocity model by applying full waveform inversion to the dense OETR‐2009 wide‐angle seismic profile crossing the northeastern Nova Scotian margin. We then create a coincident reflection image by prestack depth migrating the multichannel seismic data. This allows for the first detailed interpretation of the structures related to the final stages of continental breakup and incipient oceanic accretion at the Eastern North America Margin. Our interpretation includes a hyperextended continental domain overlying partially serpentinized mantle, followed by a 10‐km‐wide domain consisting of a continental block surrounded by layered and bright reflectors indicative of magmatic extrusions. A major fault, representing the continent‐ocean boundary, marks a sharp seaward transition to a 16‐km‐wide domain characterized by smoother basement with chaotic reflectors, where no continental materials are present and a 3‐km‐thick embryonic oceanic crust overlying partially serpentinized mantle is created by the breakup magmatism. Further seaward, thin oceanic crust overlies the serpentinized mantle suggesting magma‐poor oceanic spreading with variable magma supply as determined from variable basement topography, 2–4 km thick volcanic layer, and magnetic anomalies. Our results demonstrate that magmatism played an important role in the lithospheric breakup of the area crossed by the OETR‐2009 profile. Considering that the northeastern Nova Scotian margin has been classified as amagmatic, large margin‐parallel variations in magma supply likely characterize a single rift segment.
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Abstract We present estimates of line-of-sight distortion fields derived from the 95 and 150 GHz data taken by BICEP2, BICEP3, and the Keck Array up to the 2018 observing season, leading to cosmological constraints and a study of instrumental and astrophysical systematics. Cosmological constraints are derived from three of the distortion fields concerning gravitational lensing from large-scale structure, polarization rotation from magnetic fields or an axion-like field, and the screening effect of patchy reionization. We measure an amplitude of the lensing power spectrum
. We constrain polarization rotation, expressed as the coupling constant of a Chern–Simons electromagnetic termg a γ ≤ 2.6 × 10−2/H I , whereH I is the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 MpcB 1Mpc≤ 6.6 nG at 95 GHz. We constrain the rms of optical depth fluctuations in a simple “crinkly surface” model of patchy reionization, findingA τ < 0.19 (2σ ) for the coherence scale ofL c = 100. We show that all of the distortion fields of the 95 and 150 GHz polarization maps are consistent with simulations including lensed ΛCDM, dust, and noise, with no evidence for instrumental systematics. In some cases, theEB andTB quadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spuriousB -modes that might arise from instrumental effects. Finally, we verify that the standard deprojection filtering in the BICEP/Keck data processing is effective at removing temperature to polarization leakage. -
Abstract Computing demands for large scientific experiments, such as the CMS experiment at the CERN LHC, will increase dramatically in the next decades. To complement the future performance increases of software running on central processing units (CPUs), explorations of coprocessor usage in data processing hold great potential and interest. Coprocessors are a class of computer processors that supplement CPUs, often improving the execution of certain functions due to architectural design choices. We explore the approach of Services for Optimized Network Inference on Coprocessors (SONIC) and study the deployment of this as-a-service approach in large-scale data processing. In the studies, we take a data processing workflow of the CMS experiment and run the main workflow on CPUs, while offloading several machine learning (ML) inference tasks onto either remote or local coprocessors, specifically graphics processing units (GPUs). With experiments performed at Google Cloud, the Purdue Tier-2 computing center, and combinations of the two, we demonstrate the acceleration of these ML algorithms individually on coprocessors and the corresponding throughput improvement for the entire workflow. This approach can be easily generalized to different types of coprocessors and deployed on local CPUs without decreasing the throughput performance. We emphasize that the SONIC approach enables high coprocessor usage and enables the portability to run workflows on different types of coprocessors.
Free, publicly-accessible full text available December 1, 2025 -
Zmuidzinas, Jonas ; Gao, Jian-Rong (Ed.)Constraining the Galactic foregrounds with multi-frequency Cosmic Microwave Background (CMB) observations is an essential step towards ultimately reaching the sensitivity to measure primordial gravitational waves (PGWs), the sign of inflation after the Big-Bang that would be imprinted on the CMB. The BICEP Array is a set of multi-frequency cameras designed to constrain the energy scale of inflation through CMB B-mode searches while also controlling the polarized galactic foregrounds. The lowest frequency BICEP Array receiver (BA1) has been observing from the South Pole since 2020 and provides 30 GHz and 40 GHz data to characterize galactic synchrotron in our CMB maps. In this paper, we present the design of the BA1 detectors and the full optical characterization of the camera including the on-sky performance at the South Pole. The paper also introduces the design challenges during the first observing season including the effect of out-of-band photons on detectors performance. It also describes the tests done to diagnose that effect and the new upgrade to minimize these photons, as well as installing more dichroic detectors during the 2022 deployment season to improve the BA1 sensitivity. We finally report background noise measurements of the detectors with the goal of having photon-noise dominated detectors in both optical channels. BA1 achieves an improvement in mapping speed compared to the previous deployment season.more » « less
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Abstract We characterize Galactic dust filaments by correlating BICEP/Keck and Planck data with polarization templates based on neutral hydrogen (H
i ) observations. Dust polarization is important for both our understanding of astrophysical processes in the interstellar medium (ISM) and the search for primordial gravitational waves in the cosmic microwave background (CMB). In the diffuse ISM, Hi is strongly correlated with the dust and partly organized into filaments that are aligned with the local magnetic field. We analyze the deep BICEP/Keck data at 95, 150, and 220 GHz, over the low-column-density region of sky where BICEP/Keck has set the best limits on primordial gravitational waves. We separate the Hi emission into distinct velocity components and detect dust polarization correlated with the local Galactic Hi but not with the Hi associated with Magellanic Streami . We present a robust, multifrequency detection of polarized dust emission correlated with the filamentary Hi morphology template down to 95 GHz. For assessing its utility for foreground cleaning, we report that the Hi morphology template correlates inB modes at a ∼10%–65% level over the multipole range 20 <ℓ < 200 with the BICEP/Keck maps, which contain contributions from dust, CMB, and noise components. We measure the spectral index of the filamentary dust component spectral energy distribution to beβ = 1.54 ± 0.13. We find no evidence for decorrelation in this region between the filaments and the rest of the dust field or from the inclusion of dust associated with the intermediate velocity Hi . Finally, we explore the morphological parameter space in the Hi -based filamentary model.