Showing papers by "K. L. Thompson published in 2022"

Probing Cosmic Inflation with the LiteBIRD Cosmic Microwave Background Polarization Survey

Abstract: LiteBIRD the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA’s H3 rocket. LiteBIRD is planned to orbit the Sun-Earth Lagrangian point L2, where it will map the cosmic microwave background (CMB) polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of 2.2 μK-arcmin, with a typical angular resolution of 0.5○ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions and synergies with other projects. Subject Index LiteBIRD cosmic inflation, cosmic microwave background, B-mode polarization, primordial gravitational waves, quantum gravity, space telescope

Snowmass 2021 CMB-S4 White Paper

Abstract: The CMB-S4 Collaboration: Kevork Abazajian,1 Arwa Abdulghafour,2 Graeme E. Addison,3 Peter Adshead,4 Zeeshan Ahmed,5 Marco Ajello,6 Daniel Akerib,5 Steven W. Allen,7,5 David Alonso,8 Marcelo Alvarez,9,10 Mustafa A. Amin,11 Mandana Amiri,12 Adam Anderson,13 Behzad Ansarinejad,2 Melanie Archipley,4 Kam S. Arnold,14 Matt Ashby,15 Han Aung,16 Carlo Baccigalupi,17,18 Carina Baker,4 Abhishek Bakshi,13 Debbie Bard,10 Denis Barkats,15,19 Darcy Barron,20 Peter S. Barry,21,22 James G. Bartlett,23 Paul Barton,10 Ritoban Basu Thakur,24 Nicholas Battaglia,25 Jim Beall,26 Rachel Bean,25 Dominic Beck,7 Sebastian Belkner,27 Karim Benabed,28 Amy N. Bender,21,29 Bradford A. Benson,13,30 Bobby Besuner,10 Matthieu Bethermin,31 Sanah Bhimani,16 Federico Bianchini,7,5 Simon Biquard,23,32 Ian Birdwell,20 Colin A. Bischoff,33 Lindsey Bleem,21,29 Paulina Bocaz,34 James J. Bock,24,35 Sebastian Bocquet,36 Kimberly K. Boddy,37 J. Richard Bond,38 Julian Borrill,10,9 François R. Bouchet,28 Thejs Brinckmann,39,40 Michael L. Brown,41 Sean Bryan,42 Victor Buza,30,29 Karen Byrum,21 Erminia Calabrese,22 Victoria Calafut,38 Robert Caldwell,43 John E. Carlstrom,30,21 Julien Carron,27 Thomas Cecil,21 Anthony Challinor,44 Victor Chan,45 Clarence L. Chang,21,30 Scott Chapman,12 Eric Charles,5 Eric Chauvin,46 Cheng Cheng,47 Grace Chesmore,30 Kolen Cheung,9,10 Yuji Chinone,48 Jens Chluba,41 Hsiao-Mei Sherry Cho,5 Steve Choi,25 Justin Clancy,2 Susan Clark,7,49 Asantha Cooray,1 Gabriele Coppi,50 John Corlett,10 Will Coulton,51 Thomas M. Crawford,30,29 Abigail Crites,25,24 Ari Cukierman,5,7 Francis-Yan Cyr-Racine,20 Wei-Ming Dai,47 Cail Daley,4 Eli Dart,10 Gregorg Daues,4 Tijmen de Haan,52 Cosmin Deaconu,30,29 Jacques Delabrouille,32 Greg Derylo,13 Mark Devlin,53 Eleonora Di Valentino,54 Marion Dierickx,19 Brad Dober,26 Randy Doriese,26 Shannon Duff,26 Daniel Dutcher,55 Cora Dvorkin,19 Rolando Dünner,56 Tarraneh Eftekhari,57 Joseph Eimer,3 Hamza El Bouhargani,10 Tucker Elleflot,10 Nick Emerson,58 Josquin Errard,23 Thomas Essinger-Hileman,59 Giulio Fabbian,22,51 Valentina Fanfani,50 Alessandro Fasano,31 Chang Feng,4 Simone Ferraro,10 Jeffrey P. Filippini,4 Raphael Flauger,14 Brenna Flaugher,13 Aurelien A. Fraisse,55 Josef Frisch,5 Andrei Frolov,60 Nicholas Galitzki,14 Patricio A. Gallardo,30 Silvia Galli,28 Ken Ganga,23 Martina Gerbino,40 Christos Giannakopoulos,33 Murdock Gilchriese,10 Vera Gluscevic,61 Neil GoecknerWald,7 David Goldfinger,19 Daniel Green,14 Paul Grimes,15 Daniel Grin,62 Evan Grohs,63 Riccardo Gualtieri,21 Vic Guarino,21 Jon E. Gudmundsson,64 Ian Gullett,65 Sam Guns,9 Salman Habib,21 Gunther Haller,5 Mark Halpern,12 Nils W. Halverson,66 Shaul Hanany,67 Emma Hand,33 Kathleen Harrington,30 Masaya Hasegawa,52 Matthew Hasselfield,51 Masashi Hazumi,52 Katrin Heitmann,21 Shawn Henderson,5 Brandon Hensley,55 Ryan Herbst,5 Carlos Hervias-Caimapo,68 J. Colin Hill,69,51 Richard Hills,70 Eric Hivon,28,71 Renée Hložek,45,72 Anna Ho,73,9 Gil Holder,4 Matt Hollister,13 William Holzapfel,9 John

The Latest Constraints on Inflationary B-modes from the BICEP/Keck Telescopes

Abstract: For the past decade, the Bicep / Keck collaboration has been operating a series of telescopes at the Amundsen-Scott South Pole Station measuring degree-scale B -mode polarization imprinted in the Cosmic Microwave Background (CMB) by primordial gravitational waves (PGWs). These telescopes are compact refracting polarimeters mapping about 2% of the sky, observing at a broad range of frequencies to account for the polarized foreground from Galactic synchrotron and thermal dust emission. Our latest publication “BK18” utilizes the data collected up to the 2018 observing season, in conjunction with the publicly available WMAP and Planck data, to constrain the tensor-to-scalar ratio r . It particularly includes (1) the 3-year Bicep 3 data which is the current deepest CMB polarization map at the foreground-minimum 95 GHz; and (2) the Keck 220 GHz map with a higher signal-to-noise ratio on the dust foreground than the Planck 353 GHz map. We fit the auto- and cross-spectra of these maps to a multicomponent likelihood model (ΛCDM+dust+synchrotron+noise+ r ) and find it to be an adequate description of the data at the current noise level. The likelihood analysis yields σ ( r ) = 0 . 009. The inference of r from our baseline model is tightened to r 0 . 05 = 0 . 014 +0 . 010 − 0 . 011 and r 0 . 05 < 0 . 036 at 95% confidence, meaning that the Bicep / Keck B -mode data is the most powerful existing dataset for the constraint of PGWs. The up-coming Bicep Array telescope is projected to reach σ ( r ) (cid:46) 0 . 003 using data up to 2027.

A Measurement of the CMB Temperature Power Spectrum and Constraints on Cosmology from the SPT-3G 2018 TT/TE/EE Data Set

Abstract: We present a sample-variance-limited measurement of the temperature power spectrum ($TT$) of the cosmic microwave background (CMB) using observations of a $\sim\! 1500 \,\mathrm{deg}^2$ field made by SPT-3G in 2018. We report multifrequency power spectrum measurements at 95, 150, and 220GHz covering the angular multipole range $750 \leq \ell<3000$. We combine this $TT$ measurement with the published polarization power spectrum measurements from the 2018 observing season and update their associated covariance matrix to complete the SPT-3G 2018 $TT/TE/EE$ data set. This is the first analysis to present cosmological constraints from SPT $TT$, $TE$, and $EE$ power spectrum measurements jointly. We blind the cosmological results and subject the data set to a series of consistency tests at the power spectrum and parameter level. We find excellent agreement between frequencies and spectrum types and our results are robust to the modeling of astrophysical foregrounds. We report results for $\Lambda$CDM and a series of extensions, drawing on the following parameters: the amplitude of the gravitational lensing effect on primary power spectra $A_\mathrm{L}$, the effective number of neutrino species $N_{\mathrm{eff}}$, the primordial helium abundance $Y_{\mathrm{P}}$, and the baryon clumping factor due to primordial magnetic fields $b$. We find that the SPT-3G 2018 $T/TE/EE$ data are well fit by $\Lambda$CDM with a probability-to-exceed of $15\%$. For $\Lambda$CDM, we constrain the expansion rate today to $H_0 = 68.3 \pm 1.5\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$ and the combined structure growth parameter to $S_8 = 0.797 \pm 0.042$. The SPT-based results are effectively independent of Planck, and the cosmological parameter constraints from either data set are within $<1\,\sigma$ of each other. (abridged)

Polarization angle requirements for CMB B-mode experiments. Application to the LiteBIRD satellite

Abstract: A methodology to provide the polarization angle requirements for different sets of detectors, at a given frequency of a CMB polarization experiment, is presented. The uncertainties in the polarization angle of each detector set are related to a given bias on the tensor-to-scalar ratio r parameter. The approach is grounded in using a linear combination of the detector sets to obtain the CMB polarization signal. In addition, assuming that the uncertainties on the polarization angle are in the small angle limit (lower than a few degrees), it is possible to derive analytic expressions to establish the requirements. The methodology also accounts for possible correlations among detectors, that may originate from the optics, wafers, etc. The approach is applied to the LiteBIRD space mission. We show that, for the most restrictive case (i.e., full correlation of the polarization angle systematics among detector sets), the requirements on the polarization angle uncertainties are of around 1 arcmin at the most sensitive frequency bands (i.e., ≈ 150 GHz) and of few tens of arcmin at the lowest (i.e., ≈ 40 GHz) and highest (i.e., ≈ 400 GHz) observational bands. Conversely, for the least restrictive case (i.e., no correlation of the polarization angle systematics among detector sets), the requirements are ≈ 5 times less restrictive than for the previous scenario. At the global and the telescope levels, polarization angle knowledge of a few arcmins is sufficient for correlated global systematic errors and can be relaxed by a factor of two for fully uncorrelated errors in detector polarization angle. The reported uncertainty levels are needed in order to have the bias on r due to systematics below the limit established by the LiteBIRD collaboration.

Asteroid Measurements at Millimeter Wavelengths with the South Pole Telescope

Abstract: We present the first measurements of asteroids in millimeter wavelength data from the South Pole Telescope (SPT), which is used primarily to study the cosmic microwave background (CMB). We analyze maps of two ∼270 deg2 sky regions near the ecliptic plane, each observed with the SPTpol camera ∼100 times over 1 month. We subtract the mean of all maps of a given field, removing static sky signal, and then average the mean-subtracted maps at known asteroid locations. We detect three asteroids—(324) Bamberga, (13) Egeria, and (22) Kalliope—with signal-to-noise ratios (S/N) of 11.2, 10.4, and 6.1, respectively, at 2.0 mm (150 GHz); we also detect (324) Bamberga with an S/N of 4.1 at 3.2 mm (95 GHz). We place constraints on these asteroids’ effective emissivities, brightness temperatures, and light-curve modulation amplitude. Our flux density measurements of (324) Bamberga and (13) Egeria roughly agree with predictions, while our measurements of (22) Kalliope suggest lower flux, corresponding to effective emissivities of 0.64 ± 0.11 at 2.0 and < 0.47 at 3.2 mm. We predict the asteroids detectable in other SPT data sets and find good agreement with detections of (772) Tanete and (1093) Freda in recent data from the SPT-3G camera, which has ∼10× the mapping speed of SPTpol. This work is the first focused analysis of asteroids in data from CMB surveys, and it demonstrates we can repurpose historic and future data sets for asteroid studies. Future SPT measurements can help constrain the distribution of surface properties over a larger asteroid population.

Searching for axionlike time-dependent cosmic birefringence with data from SPT-3G

Abstract: Ultralight axionlike particles (ALPs) are compelling dark matter candidates because of their potential to resolve small-scale discrepancies between ΛCDM predictions and cosmological observations. Axion-photon coupling induces a polarization rotation in linearly polarized photons traveling through an ALP field; thus, as the local ALP dark matter field oscillates in time, distant static polarized sources will appear to oscillate with a frequency proportional to the ALP mass. We use observations of the cosmic microwave background from SPT-3G, the current receiver on the South Pole Telescope, to set upper limits on the value of the axion-photon coupling constant g φγ over the approximate mass range 10 − 22 − 10 − 19 eV, corresponding to oscillation periods from 12 hours to 100 days. For periods between 1 and 100 days (4 . 7 × 10 − 22 eV ≤ m φ ≤ 4 . 7 × 10 − 20 eV), where the limit is approximately constant, we set a median 95% C.L. upper limit on the amplitude of on-sky polarization rotation of 0 . 071 deg. Assuming that dark matter comprises a single ALP species with a local dark matter density of 0 . 3 GeV/cm 3 , this corresponds to g φγ < 1 . 18 × 10 12 GeV . These new limits represent an improvement over the previous strongest limits set using the same effect by a factor of ∼ 3 . 8.

Optical Characterization of OMT-Coupled TES Bolometers for LiteBIRD

Abstract: Feedhorn- and orthomode transducer- (OMT) coupled transition edge sensor (TES) bolometers have been designed and micro-fabricated to meet the optical specifications of the LiteBIRD high frequency telescope (HFT) focal plane. We discuss the design and optical characterization of two LiteBIRD HFT detector types: dual-polarization, dual-frequency-band pixels with 195/280 GHz and 235/337 GHz band centers. Results show well-matched passbands between orthogonal polarization channels and frequency centers within 3% of the design values. The optical efficiency of each frequency channel is conservatively reported to be within the range 0.64 $$-$$ 0.72, determined from the response to a cryogenic, temperature-controlled thermal source. These values are in good agreement with expectations and either exceed or are within 10% of the values used in the LiteBIRD sensitivity forecast. Lastly, we report a measurement of loss in Nb/SiN $$_x$$ /Nb microstrip at 100 mK and over the frequency range 200–350 GHz, which is comparable to values previously reported in the literature.

BICEP/Keck. XVII. Line-of-sight Distortion Analysis: Estimates of Gravitational Lensing, Anisotropic Cosmic Birefringence, Patchy Reionization, and Systematic Errors

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 ALϕϕ=0.95±0.20 . We constrain polarization rotation, expressed as the coupling constant of a Chern–Simons electromagnetic term g a γ ≤ 2.6 × 10−2/H I , where H I is the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 Mpc B 1Mpc ≤ 6.6 nG at 95 GHz. We constrain the rms of optical depth fluctuations in a simple “crinkly surface” model of patchy reionization, finding A τ < 0.19 (2σ) for the coherence scale of L 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, the EB and TB quadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spurious B-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.

BICEP/Keck. XVI. Characterizing Dust Polarization through Correlations with Neutral Hydrogen

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, H i 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 H i emission into distinct velocity components and detect dust polarization correlated with the local Galactic H i but not with the H i associated with Magellanic Stream i. We present a robust, multifrequency detection of polarized dust emission correlated with the filamentary H i morphology template down to 95 GHz. For assessing its utility for foreground cleaning, we report that the Hi morphology template correlates in B 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 be β = 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 H i. Finally, we explore the morphological parameter space in the H i-based filamentary model.

Searching for axion-like time-dependent cosmic birefringence with SPT-3G Probing axionlike

Abstract: Ultralight axion-like particles (ALPs) are compelling dark matter candidates because of their potential to resolve small-scale discrepancies between ΛCDM predictions and cosmological observations. Axion-photon coupling induces a polarization rotation in linearly polarized photons traveling through an ALP field; thus, as the local ALP dark matter field oscillates in time, distant static polarized sources will appear to oscillate with a frequency proportional to the ALP mass. We use observations of the cosmic microwave background from SPT-3G, the current receiver on the South Pole Telescope, to set upper limits on the value of the axion-photon coupling constant g φγ over the approximate mass range 10 − 22 − 10 − 19 eV, corresponding to oscillation periods from 12 hours to 100 days. For periods between 1 and 100 days (4 . 7 × 10 − 22 eV ≤ m φ ≤ 4 . 7 × 10 − 20 eV), where the limit is approximately constant, we set a median 95% C.L. upper limit on the amplitude of on-sky polarization rotation of 0 . 071 deg. Assuming that dark matter comprises a single ALP species with a local dark matter density of 0 . 3 GeV/cm 3 , this corresponds to g φγ < 1 . 18 × 10 − 12 GeV × (cid:16) . These new limits represent an improvement over the previous strongest limits set using the same effect by a factor of ∼ 3 . 8.

A non-isothermal approach to evaluate the impact of the cooling stage on the startup flow of waxy crude oils

Abstract: Waxy crude oils submitted to low temperatures at quiescent conditions turn into a gel with a corresponding yield stress. Thus, a higher pressure drop is needed to restart, leading to a flow assurance issue. Generally, this problem is tackled by considering the material at rest, with a given state and an imposed pressure drop. In the present work, we investigate how the cooling process after a shutdown impacts the problem. We emulate a stoppage of short duration so that the cooling after the shutdown stage does not lead to a condition of uniform temperature. The temperature-dependent rheology of the material is such that the crude oil shows viscoplastic behavior only below the gelation temperature. The early stages of the process, before and during the shutdown, resulting in a heterogeneous gel, which serves as an initial condition for the restart stage. We perform 2D non-isothermal simulations in a pipe considering three stages, namely (i) normal operation conditions; (ii) cooling stage at rest after stoppage; (iii) restart by an imposed pressure drop. Particular emphasis is given to the role of the plastic number (Pl) and the duration of the cooling after the shutdown stage. A comparison with the corresponding homogeneous condition is also made. The results show that higher values of Pl and higher waiting times in the cooling after the shutdown stage lead to conditions less prone to restart. Only cooling times of short duration lead to restart in the same conditions as the normal operation ones. The pressure drop necessary for a restart is an increasing function of the cooling time.

Analysis of Carbopol And Triethanolamine Concentration in The Viscoplastic Properties of Aqueous Solution

Abstract: Materials with viscoplastic characteristics have being widely studied due to their applicability in industries, but also because of their common presence in nature. Fluids with such characteristic can be modelled by the equation known as Herschel-Bulkley. This type of fluid has a yield stress property, which is extremely important to characterize it. Carbopol solution is the most common fluid used for experimental studies involving this type of fluid. However, the Carbopol solution needs a neutralizing agent, which acts as a pH regulator, prevents the formation of fungus, but it also affects the yield stress. In the present work, measurements of the yield stress from flow curve tests, performed in a rheometer, were made for different combinations of Carbopol and Triethanolamine (neutralizing agent) concentrations. The yield stress increased with the increment in the concentration of both, Carbopol and Triethanolamine (TEA), in addition, it was observed that TEA concentrations must be greater than 500 ppm to avoid the formation of fungi and less than 700 ppm to obtain a homogeneous solution.

Sensitivity Modeling for LiteBIRD

Abstract: LiteBIRD is a future satellite mission designed to observe the polarization of the cosmic microwave background radiation in order to probe the inflationary universe. LiteBIRD is set to observe the sky using three telescopes with transition-edge sensor bolometers. In this work we estimated the LiteBIRD instrumental sensitivity using its current design. We estimated the detector noise due to the optical loadings using physical optics and ray-tracing simulations. The noise terms associated with thermal carrier and readout noise were modeled in the detector noise calculation. We calculated the observational sensitivities over fifteen bands designed for the LiteBIRD telescopes using assumed observation time efficiency.

Measurement of the mean central optical depth of galaxy clusters via the pairwise kinematic Sunyaev-Zel’dovich effect with SPT-3G and DES

Abstract: We infer the mean optical depth of a sample of optically-selected galaxy clusters from the Dark Energy Survey (DES) via the pairwise kinematic Sunyaev-Zel'dovich (kSZ) effect. The pairwise kSZ signal between pairs of clusters drawn from the DES Year-3 cluster catalog is detected at $4.1 \sigma$ in cosmic microwave background (CMB) temperature maps from two years of observations with the SPT-3G camera on the South Pole Telescope. After cuts, there are 24,580 clusters in the $\sim 1,400$ deg$^2$ of the southern sky observed by both experiments. We infer the mean optical depth of the cluster sample with two techniques. The optical depth inferred from the pairwise kSZ signal is $\bar{\tau}_e = (2.97 \pm 0.73) \times 10^{-3}$, while that inferred from the thermal SZ signal is $\bar{\tau}_e = (2.51 \pm 0.55^{\text{stat}} \pm 0.15^{\rm syst}) \times 10^{-3}$. The two measures agree at $0.6 \sigma$. We perform a suite of systematic checks to test the robustness of the analysis.

LiteBIRD low- and mid-frequency detectors: design and status

Abstract: The Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection (LiteBIRD) is a space mission to search for and characterize the signature of inflation in the polarized signal from the cosmic microwave background (CMB), and probe fundamental physics. LiteBIRD will precisely measure the polarization of the cosmic microwave background on large angular scales ≳ 1 deg. It will survey the full sky with three telescopes covering 15 frequency bands centered at frequencies from 40 to 402 GHz. The pixel design for the low- and mid-frequency telescopes features a hemispherical lenslet coupled to a broadband sinuous antenna. The radiation detected by the sinuous antenna propagates through a superconducting microstrip and on-chip bandpass filters before being detected by superconducting transition edge sensor (TES) bolometers. The TES design fulfills requirements for low saturation power of the space environment while maintaining a fast time response for use with a continuously-rotating half-wave plate. We present measurements of the electrical and thermal properties of the TES detectors with values required for the LiteBIRD mission, the design and measurements of a dual-polarization trichroic pixel at 40, 60, and 78 GHz suitable for the low-frequency telescope, and the design and preliminary measurements for a detector array at 100, 140, and 195 GHz suitable for the mid-frequency telescope.

2022 upgrade and improved low frequency camera sensitivity for CMB observation at the South Pole

Abstract: 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.