Person: Buder, I
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Publication Inflation Physics from the Cosmic Microwave Background and Large Scale Structure(The Division of Particles and Fields of the American Physical Society, 2013) Abazajian, K. N.; Arnold, K.; Austermann, J.; Benson, B. A.; Bischoff, Colin; Bock, J.; Bond, J. R.; Borrill, J.; Buder, I; Burke, D. L.; Calabrese, E.; Carlstrom, J. E.; Carvalho, C. S.; Chang, C. L.; Chiang, H. C.; Church, S.; Cooray, A.; Crawford, T. M.; Crill, B. P.; Dawson, K. S.; Das, S.; Devlin, M. J.; Dobbs, M.; Dodelson, S.; Doré, O.; Dunkley, J.; Feng, J. L.; Fraisse, A.; Gallicchio, J.; Giddings, S. B.; Green, D.; Halverson, N. W.; Hanany, S.; Hanson, D.; Hildebrandt, S. R.; Hincks, A.; Hlozek, R.; Holder, G.; Holzapfel, W. L.; Honscheid, K.; Horowitz, G.; Hu, W.; Hubmayr, J.; Irwin, K.; Jackson, M.; Jones, W. C.; Kallosh, R.; Kamionkowski, M.; Keating, B.; Keisler, R.; Kinney, W.; Knox, L.; Komatsu, E.; Kovac, John; Kuo, C.-L.; Kusaka, A.; Lawrence, C.; Lee, A. T.; Leitch, E.; Linde, A.; Linder, E.; Lubin, P.; Maldacena, J.; Martinec, E.; McMahon, J.; Miller, A.; Mukhanov, V.; Newburgh, L.; Niemack, M. D.; Nguyen, H.; Nguyen, H. T.; Page, L.; Pryke, C.; Reichardt, C. L.; Ruhl, J. E.; Sehgal, N.; Seljak, U.; Senatore, L.; Sievers, J.; Silverstein, E.; Slosar, A.; Smith, K. M.; Spergel, D.; Staggs, S. T.; Stark, Antony; Stompor, R.; Vieregg, A. G.; Wang, G.; Watson, S.; Wollack, E. J.; Wu, W. L. K.; Yoon, K. W.; Zahn, O.; Zaldarriaga, M.Fluctuations in the intensity and polarization of the cosmic microwave background (CMB) and the large-scale distribution of matter in the universe each contain clues about the nature of the earliest moments of time. The next generation of CMB and large-scale structure (LSS) experiments are poised to test the leading paradigm for these earliest moments---the theory of cosmic inflation---and to detect the imprints of the inflationary epoch, thereby dramatically increasing our understanding of fundamental physics and the early universe. A future CMB experiment with sufficient angular resolution and frequency coverage that surveys at least 1% of the sky to a depth of 1 uK-arcmin can deliver a constraint on the tensor-to-scalar ratio that will either result in a 5-sigma measurement of the energy scale of inflation or rule out all large-field inflation models, even in the presence of foregrounds and the gravitational lensing B-mode signal. LSS experiments, particularly spectroscopic surveys such as the Dark Energy Spectroscopic Instrument, will complement the CMB effort by improving current constraints on running of the spectral index by up to a factor of four, improving constraints on curvature by a factor of ten, and providing non-Gaussianity constraints that are competitive with the current CMB bounds.Publication Degree-Scale Cosmic Microwave Background Polarization Measurements From Three Years of BICEP1 Data(American Astronomical Society, 2014) Barkats, D.; Aikin, R.; Bischoff, Colin; Buder, I; Kaufman, J. P.; Keating, B. G.; Kovac, John; Su, Meng; Ade, P. A. R.; Battle, J. O.; Bierman, E. M.; Bock, J. J.; Chiang, H. C.; Dowell, C. D.; Duband, L.; Filippini, J.; Hivon, E. F.; Holzapfel, W. L.; Hristov, V. V.; Jones, W. C.; Kuo, C. L.; Leitch, E. M.; Mason, P. V.; Matsumura, T.; Nguyen, H. T.; Ponthieu, N.; Pryke, C.; Richter, S.; Rocha, G.; Sheehy, C.; Kernasovskiy, S. S.; Takahashi, Y. D.; Tolan, J. E.; Yoon, K. W.BICEP1 is a millimeter-wavelength telescope designed specifically to measure the inflationary B-mode polarization of the cosmic microwave background at degree angular scales. We present results from an analysis of the data acquired during three seasons of observations at the South Pole (2006-2008). This work extends the two-year result published in Chiang et al., with additional data from the third season and relaxed detector-selection criteria. This analysis also introduces a more comprehensive estimation of band power window functions, improved likelihood estimation methods, and a new technique for deprojecting monopole temperature-to-polarization leakage that reduces this class of systematic uncertainty to a negligible level. We present maps of temperature, E- and B-mode polarization, and their associated angular power spectra. The improvement in the map noise level and polarization spectra error bars are consistent with the 52% increase in integration time relative to Chiang et al. We confirm both self-consistency of the polarization data and consistency with the two-year results. We measure the angular power spectra at \(21 \leq l \leq 335\) and find that the EE spectrum is consistent with Lambda cold dark matter cosmology, with the first acoustic peak of the EE spectrum now detected at \(15\sigma\). The BB spectrum remains consistent with zero. From B-modes only, we constrain the tensor-to-scalar ratio to \(r = 0.03^{+0.27}_{-0.23}\), or \(r < 0.70\) at 95% confidence level.Publication BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array(IOP Publishing, 2015) Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.; Alexander, Kate; Barkats, D.; Benton, S. J.; Bischoff, Colin; Bock, J. J.; Brevik, J. A.; Buder, I; Bullock, E.; Buza, Victor; Connors, Jake Anthony; Crill, B. P.; Dowell, C. D.; Dvorkin, Cora; Duband, L.; Filippini, J. P.; Fliescher, S.; Golwala, S. R.; Halpern, M.; Harrison, S.; Hasselfield, M.; Hildebrandt, S. R.; Hilton, G. C.; Hristov, V. V.; Hui, H.; Irwin, K. D.; Karkare, Kirit Sukrit; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, John; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Mason, P.; Megerian, K. G.; Netterfield, C. B.; Nguyen, H. T.; O’Brient, R.; Ogburn IV, R. W.; Orlando, A.; Pryke, C.; Reintsema, C. D.; Richter, Sonja Valeska; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Sudiwala, R. V.; Teply, G. P.; Thompson, K. L.; Tolan, J. E.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Willmert, J.; Wong, C. L.; Yoon, K. W.The Keck Array is a system of cosmic microwave background polarimeters, each similar to the Bicep2 experiment. In this paper we report results from the 2012 to 2013 observing seasons, during which the Keck Array consisted of five receivers all operating in the same (150 GHz) frequency band and observing field as Bicep2. We again find an excess of B-mode power over the lensed-ΛCDM expectation of >5σ in the range 30 < ℓ < 150 and confirm that this is not due to systematics using jackknife tests and simulations based on detailed calibration measurements. In map difference and spectral difference tests these new data are shown to be consistent with Bicep2. Finally, we combine the maps from the two experiments to produce final Q and U maps which have a depth of 57 nK deg (3.4 μK arcmin) over an effective area of 400 deg(2) for an equivalent survey weight of 250,000 μK(−)(2). The final BB band powers have noise uncertainty a factor of 2.3 times better than the previous results, and a significance of detection of excess power of >6σ.Publication Improved Constraints on Cosmology and Foregrounds from BICEP2 and Keck Array Cosmic Microwave Background Data with Inclusion of 95 GHz Band(American Physical Society (APS), 2016) Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.; Alexander, K. D.; Barkats, D.; Benton, S. J.; Bischoff, Colin; Bock, J. J.; Bowens-Rubin, Rachel; Brevik, J. A.; Buder, I; Bullock, E.; Buza, Victor; Connors, Jake Anthony; Crill, B. P.; Duband, L.; Dvorkin, Cora; Filippini, J. P.; Fliescher, S.; Grayson, J.; Halpern, M.; Harrison, Sarah; Hilton, G. C.; Hui, H.; Irwin, K. D.; Karkare, Kirit Sukrit; Karpel, E.; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, John; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Megerian, K. G.; Netterfield, C. B.; Nguyen, H. T.; O’Brient, R.; Ogburn, R. W.; Orlando, A.; Pryke, C; Richter, Sonja Valeska; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Steinbach, B.; Sudiwala, R. V.; Teply, G. P.; Thompson, K. L.; Tolan, J. E.; Tucker, C.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wiebe, D. V.; Willmert, J.; Wong, C; Wu, W. L. K.; Yoon, K. W.We present results from an analysis of all data taken by the BICEP2 and Keck Array cosmic microwave background (CMB) polarization experiments up to and including the 2014 observing season. This includes the first Keck Array observations at 95 GHz. The maps reach a depth of 50 nK deg in Stokes Q and U in the 150 GHz band and 127 nK deg in the 95 GHz band. We take auto- and cross-spectra between these maps and publicly available maps from WMAP and Planck at frequencies from 23 to 353 GHz. An excess over lensed ΛCDM is detected at modest significance in the 95 × 150 BB spectrum, and is consistent with the dust contribution expected from our previous work. No significant evidence for synchrotron emission is found in spectra such as 23 × 95, or for correlation between the dust and synchrotron sky patterns in spectra such as 23 × 353. We take the likelihood of all the spectra for a multicomponent model including lensed ΛCDM, dust, synchrotron, and a possible contribution from inflationary gravitational waves (as parametrized by the tensor-to-scalar ratio r) using priors on the frequency spectral behaviors of dust and synchrotron emission from previous analyses of WMAP and Planck data in other regions of the sky. This analysis yields an upper limit r0.05 < 0.09 at 95% confidence, which is robust to variations explored in analysis and priors. Combining these B-mode results with the (more model-dependent) constraints from Planck analysis of CMB temperature plus baryon acoustic oscillations and other data yields a combined limit r0.05 < 0.07 at 95% confidence. These are the strongest constraints to date on inflationary gravitational waves.Publication Detection of B-Mode Polarization at Degree Angular Scales by BICEP2(American Physical Society (APS), 2014) Ade, P. A. R.; Aikin, R. W.; Barkats, Denis; Benton, S. J.; Bischoff, Colin; Bock, J. J.; Brevik, J. A.; Buder, I; Bullock, E.; Dowell, C. D.; Duband, L.; Filippini, J. P.; Fliescher, S.; Golwala, S. R.; Halpern, M.; Hasselfield, M.; Hildebrandt, S. R.; Hilton, G. C.; Hristov, V. V.; Irwin, K. D.; Karkare, Kirit; Kaufman, J. P.; Keating, B. G.; Kernasovskiy, S. A.; Kovac, John; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Mason, P.; Netterfield, C. B.; Nguyen, H. T.; O’Brient, R.; Ogburn, R. W.; Orlando, Abigail; Pryke, C; Reintsema, C. D.; Richter, Sonja Valeska; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Sudiwala, R. V.; Teply, G. P.; Tolan, J. E.; Turner, A. D.; Vieregg, A. G.; Wong, C; Yoon, K. W.We report results from the BICEP2 experiment, a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around ℓ∼80. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor 150 GHz bolometers each with temperature sensitivity of ≈300 μK(CMB)√s. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square deg was observed to a depth of 87 nK deg in Stokes Q and U. In this paper we describe the observations, data reduction, maps, simulations, and results. We find an excess of B-mode power over the base lensed-ΛCDM expectation in the range 30 < ℓ < 150, inconsistent with the null hypothesis at a significance of >5σ. Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. Cross correlating against WMAP 23 GHz maps we find that Galactic synchrotron makes a negligible contribution to the observed signal. We also examine a number of available models of polarized dust emission and find that at their default parameter values they predict power ∼(5-10)× smaller than the observed excess signal (with no significant cross-correlation with our maps). However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal. Cross correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with 3σ significance and its spectral index is found to be consistent with that of the CMB, disfavoring dust at 1.7σ. The observed B-mode power spectrum is well fit by a lensed-ΛCDM+tensor theoretical model with tensor-to-scalar ratio r = 0.20_(-0.05)(+0.07), with r = 0 disfavored at 7.0σ. Accounting for the contribution of foreground, dust will shift this value downward by an amount which will be better constrained with upcoming data sets.Publication bicep2/Keck Array. IV. Optical Characterization and Performance of the Bicep2 and Keck Array Experiments(IOP Publishing, 2015) Ade, P. A. R.; Aikin, R. W.; Barkats, Denis; Benton, S. J.; Bischoff, Colin; Bock, J. J.; Bradford, K. J.; Brevik, J. A.; Buder, I; Bullock, E.; Dowell, C. D.; Duband, L.; Filippini, J. P.; Fliescher, S.; Golwala, S. R.; Halpern, M.; Hasselfield, M.; Hildebrandt, S. R.; Hilton, G. C.; Hui, H.; Irwin, K. D.; Kang, J. H.; Karkare, Kirit Sukrit; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, John; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Megerian, K. G.; Netterfield, C. B.; Nguyen, H. T.; O’Brient, R.; IV, R. W. Ogburn; Orlando, A.; Pryke, C; Richter, Sonja Valeska; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Sudiwala, R. V.; Teply, G. P.; Thompson, K.; Tolan, J. E.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wong, C; Yoon, K. W.bicep2 and the Keck Array are polarization-sensitive microwave telescopes that observe the cosmic microwave background (CMB) from the South Pole at degree angular scales in search of a signature of inflation imprinted as B-mode polarization in the CMB. bicep2 was deployed in late 2009, observed for three years until the end of 2012 at 150 GHz with 512 antenna-coupled transition edge sensor bolometers, and has reported a detection of B-mode polarization on degree angular scales. The Keck Array was first deployed in late 2010 and will observe through 2016 with five receivers at several frequencies (95, 150, and 220 GHz). bicep2 and the Keck Array share a common optical design and employ the field-proven bicep1 strategy of using small-aperture, cold, on-axis refractive optics, providing excellent control of systematics while maintaining a large field of view. This design allows for full characterization of far-field optical performance using microwave sources on the ground. Here we describe the optical design of both instruments and report a full characterization of the optical performance and beams of bicep2 and the Keck Array at 150 GHz.Publication Antenna-coupled TES Bolometers used in BICEP2, Keck Array, and SPIDER(IOP Publishing, 2015) Ade, P. A. R.; Aikin, R. W.; Amiri, M.; Barkats, D.; Benton, S. J.; Bischoff, Colin; Bock, J. J.; Bonetti, J. A.; Brevik, J. A.; Buder, I; Bullock, E.; Chattopadhyay, G.; Davis, G.; Day, P. K.; Dowell, C. D.; Duband, L.; Filippini, J. P.; Fliescher, S.; Golwala, S. R.; Halpern, M.; Hasselfield, M.; Hildebrandt, S. R.; Hilton, G. C.; Hristov, V.; Hui, H.; Irwin, K. D.; Jones, W. C.; Karkare, Kirit Sukrit; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, John; Kuo, C. L.; LeDuc, H. G.; Leitch, E. M.; Llombart, N.; Lueker, M.; Mason, P.; Megerian, K.; Moncelsi, L.; Netterfield, C. B.; Nguyen, H. T.; O’Brient, R.; IV, R. W. Ogburn; Orlando, A.; Pryke, C; Rahlin, A. S.; Reintsema, C. D.; Richter, S.; Runyan, M. C.; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Sudiwala, R. V.; Teply, G. P.; Tolan, J. E.; Trangsrud, A.; Tucker, R. S.; Turner, A. D.; Vieregg, A. G.; Weber, A.; Wiebe, D. V.; Wilson, P.; Wong, C; Yoon, K. W.; Zmuidzinas, J.; undefined, undefinedWe have developed antenna-coupled transition-edge sensor (TES) bolometers for a wide range of cosmic microwave background (CMB) polarimetry experiments, including BICEP2, Keck Array, and the balloon borne SPIDER. These detectors have reached maturity and this paper reports on their design principles, overall performance, and key challenges associated with design and production. Our detector arrays repeatedly produce spectral bands with 20%-30% bandwidth at 95, 150, or 220~GHz. The integrated antenna arrays synthesize symmetric co-aligned beams with controlled side-lobe levels. Cross-polarized response on boresight is typically ~0.5%, consistent with cross-talk in our multiplexed readout system. End-to-end optical efficiencies in our cameras are routinely 35% or higher, with per detector sensitivities of NET~300 uKrts. Thanks to the scalability of this design, we have deployed 2560 detectors as 1280 matched pairs in Keck Array with a combined instantaneous sensitivity of ~9 uKrts, as measured directly from CMB maps in the 2013 season. Similar arrays have recently flown in the SPIDER instrument, and development of this technology is ongoing.Publication Bicep2/keck Array. Vii. Matrix Basede/bseparation Applied to Bicep2 and the Keck Array(American Astronomical Society, 2016) Ade, P. A. R.; Ahmed, Z.; Aikin, R. W.; Alexander, Kate; Barkats, Denis; Benton, S. J.; Bischoff, Colin; Bock, J. J.; Bowens-Rubin, Rachel; Brevik, J. A.; Buder, I; Bullock, E.; Buza, Victor; Connors, Jake Anthony; Crill, B. P.; Duband, L.; Dvorkin, Cora; Filippini, J. P.; Fliescher, S.; Grayson, J.; Halpern, M.; Harrison, Sarah; Hildebrandt, S. R.; Hilton, G. C.; Hui, H.; Irwin, K. D.; Kang, J.; Karkare, Kirit Sukrit; Karpel, E.; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, John; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Megerian, K. G.; Namikawa, T.; Netterfield, C. B.; Nguyen, H. T.; O’Brient, R.; IV, R. W. Ogburn; Orlando, A.; Pryke, C.; Richter, S.; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Steinbach, B.; Sudiwala, R. V.; Teply, G. P.; Thompson, K. L.; Tolan, J. E.; Tucker, C.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wiebe, D. V.; Willmert, J.; Wong, C; Wu, W. L. K.; Yoon, K. W.A linear polarization field on the sphere can be uniquely decomposed into an E-mode and a B-mode component. These two components are analytically defined in terms of spin-2 spherical harmonics. Maps that contain filtered modes on a partial sky can also be decomposed into E-mode and B-mode components. However, the lack of full sky information prevents orthogonally separating these components using spherical harmonics. In this paper, we present a technique for decomposing an incomplete map into E and B-mode components using E and B eigenmodes of the pixel covariance in the observed map. This method is found to orthogonally define E and B in the presence of both partial sky coverage and spatial filtering. This method has been applied to the Bicep2 and the Keck Array maps and results in reducing E to B leakage from ΛCDM E-modes to a level corresponding to a tensor-to-scalar ratio ofPublication BICEP2 III: Instrumental Systematics(IOP Publishing, 2015) Ade, P. A. R.; Aikin, R. W.; Barkats, Denis; Benton, S. J.; Bischoff, Colin; Bock, J. J.; Brevik, J. A.; Buder, I; Bullock, E.; Dowell, C. D.; Duband, L.; Filippini, J. P.; Fliescher, S.; Golwala, S. R.; Halpern, M.; Hasselfield, M.; Hildebrandt, S. R.; Hilton, G. C.; Irwin, K. D.; Karkare, Kirit Sukrit; Kaufman, J. P.; Keating, B. G.; Kernasovskiy, S. A.; Kovac, John; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Netterfield, C. B.; Nguyen, H. T.; O’Brient, R.; IV, R. W. Ogburn; Orlando, Abigail; Pryke, C; Richter, Sonja Valeska; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Sudiwala, R. V.; Teply, G. P.; Tolan, J. E.; Turner, A. D.; Vieregg, A. G.; Wong, C; Yoon, K. W.In a companion paper, we have reported a >5σ detection of degree scale B-mode polarization at 150 GHz by the Bicep2 experiment. Here we provide a detailed study of potential instrumental systematic contamination to that measurement. We focus extensively on spurious polarization that can potentially arise from beam imperfections. We present a heuristic classification of beam imperfections according to their symmetries and uniformities, and discuss how resulting contamination adds or cancels in maps that combine observations made at multiple orientations of the telescope about its boresight axis. We introduce a technique, which we call "deprojection," for filtering the leading order beam-induced contamination from time-ordered data, and show that it reduces power in Bicep2's actual and null-test BB spectra consistent with predictions using high signal-to-noise beam shape measurements. We detail the simulation pipeline that we use to directly simulate instrumental systematics and the calibration data used as input to that pipeline. Finally, we present the constraints on BB contamination from individual sources of potential systematics. We find that systematics contribute BB power that is a factor of ~10× below Bicep2's three-year statistical uncertainty, and negligible compared to the observed BB signal. The contribution to the best-fit tensor/scalar ratio is at a level equivalent to r = (3–6) × 10−3.Publication BICEP2/Keck Array VIII: Measurement of Gravitational Lensing from Large-scale B-Mode Polarization.(American Astronomical Society, 2016) Array, The Keck; Ade, BICEP2; Ahmed, Z.; Aikin, R.; Alexander, Kate; Barkats, Denis; Benton, S.; Bischoff, Colin; Bock, J.; Bowens-Rubin, Rachel; Brevik, J.; Buder, I; Bullock, E.; Buza, Victor; Connors, Jake Anthony; Crill, B.; Duband, L.; Dvorkin, Cora; Filippin, J.; Fliescher, S.; Grayson, J.; Halpern, M.; Harrison, Sarah; Hildebrandt, S.; Hilton, G.; Hui, H.; Irwin, K.; Kang, J.; Karkare, Kirit Sukrit; Karpel, E.; Kaufman, J.; Keating, B.; Kefeli, S.; Kernasovskiy, S.; Kovac, John; Kuo, C.; Leitch, E.; Lueker, M.; Megerian, K.; Namikawa, T.; Netterfield, C.; Nguyen, H.; O'Brient, R.; Ogburn, R.; Orlando, A.; Pryke, C.; Richter, Sonja Valeska; Schwarz, R.; Sheehy, C.; Staniszewski, Z.; Steinbach, B.; Sudiwala, R.; Teply, G.; Thompson, K.; Tolan, J.; Tucker, C.; Turner, A.; Vieregg, A.We present measurements of polarization lensing using the 150 GHz maps, which include all data taken by the BICEP2 and Keck Array Cosmic Microwave Background polarization experiments up to and including the 2014 observing season (BK14). Despite their modest angular resolution ($\sim 0\buildrel{\circ}\over{.} 5$), the excellent sensitivity (~3μK-arcmin) of these maps makes it possible to directly reconstruct the lensing potential using only information at larger angular scales (${\ell }\leqslant 700$). From the auto-spectrum of the reconstructed potential, we measure an amplitude of the spectrum to be ${A}_{{\rm{L}}}^{\phi \phi }=1.15\pm 0.36$ (Planck ΛCDM prediction corresponds to ${A}_{{\rm{L}}}^{\phi \phi }=1$) and reject the no-lensing hypothesis at $5.8\sigma $, which is the highest significance achieved to date using an EB lensing estimator. Taking the cross-spectrum of the reconstructed potential with the Planck 2015 lensing map yields ${A}_{{\rm{L}}}^{\phi \phi }=1.13\pm 0.20$. These direct measurements of ${A}_{{\rm{L}}}^{\phi \phi }$ are consistent with the ΛCDM cosmology and with that derived from the previously reported BK14 B-mode auto-spectrum (${A}_{{\rm{L}}}^{\mathrm{BB}}=1.20\pm 0.17$). We perform a series of null tests and consistency checks to show that these results are robust against systematics and are insensitive to analysis choices. These results unambiguously demonstrate that the B modes previously reported by BICEP/Keck at intermediate angular scales ($150\lesssim {\ell }\lesssim 350$) are dominated by gravitational lensing. The good agreement between the lensing amplitudes obtained from the lensing reconstruction and B-mode spectrum starts to place constraints on any alternative cosmological sources of B modes at these angular scales.