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Broad absorption line (BAL) quasars are characterized by gas clouds that absorb flux at the wavelength of common quasar spectral features, although blueshifted by velocities that can exceed 0.1c. BAL features are interesting as signatures of significant feedback, yet they can also compromise cosmological studies with quasars by distorting the shape of the most prominent quasar emission lines, impacting redshift accuracy and measurements of the matter density distribution traced by the Lyman α forest. We present a catalogue of BAL quasars discovered in the Dark Energy Spectroscopic Instrument (DESI) survey Early Data Release, which were observed as part of DESI Survey Validation, as well as the first two months of the main survey. We describe our method to automatically identify BAL quasars in DESI data, the quantities we measure for each BAL, and investigate the completeness and purity of this method with mock DESI observations. We mask the wavelengths of the BAL features and re-evaluate each BAL quasar redshift, finding new redshifts which are 243 km s−1 smaller on average for the BAL quasar sample. These new, more accurate redshifts are important to obtain the best measurements of quasar clustering, especially at small scales. Finally, we present some spectra of rarer classes of BALs that illustrate the potential of DESI data to identify such populations for further study.

Highly multiplexed, fiber-fed spectroscopy is enabling surveys of millions of stars and galaxies. The performance of these surveys depends on accurately positioning fibers in the focal plane to capture target light. We describe a technique to measure the positioning accuracy of fibers by dithering fibers slightly around their ideal locations. This approach also enables measurement of the total system throughput and point-spread function delivered to the focal plane. We then apply this technique to observations from the Dark Energy Survey Instrument (DESI), and demonstrate that DESI positions fibers to within 0.″08 of their targets (5% of a fiber diameter) and achieves a system throughput within about 7% of expectations.

Accurate mock galaxy catalogues are crucial to validate analysis pipelines used to constrain dark energy models. We present a fast HOD-fitting method which we apply to the AbacusSummit simulations to create a set of mock catalogues for the DESI Bright Galaxy Survey, which contain r-band magnitudes and colours (g - r) The halo tabulation method fits HODs for different absolute magnitude threshold samples simultaneously, preventing unphysical HOD crossing between samples. We validate the HOD fitting procedure by fitting to real-space clustering measurements and galaxy number densities from the MXXL BGS mock, which was tuned to the SDSS and GAMA surveys. The best-fitting clustering measurements and number densities are mostly within the assumed errors, but the clustering for the faint samples is low on large scales. The best-fitting HOD parameters are robust when fitting to simulations with different realizations of the initial conditions. When varying the cosmology, trends are seen as a function of each cosmological parameter. We use the best-fitting HOD parameters to create cubic box and cut sky mocks from the AbacusSummit simulations, in a range of cosmologies. As an illustration, we compare the sample of galaxies in the mock with BGS measurements from the DESI one-percent survey. We find good agreement in the number densities, and the projected correlation function is reasonable, with differences that can be improved in the future by fitting directly to BGS clustering measurements. The cubic box and cut-sky mocks in different cosmologies are made publicly available.

We present initial results from the Dark Energy Spectroscopic Instrument (DESI) complete calibration of the colour–redshift relation (DC3R2) secondary target survey. Our analysis uses 230 k galaxies that overlap with KiDS-VIKING ugriZYJHKs photometry to calibrate the colour–redshift relation and to inform photometric redshift (photo-z) inference methods of future weak lensing surveys. Together with emission line galaxies (ELGs), luminous red galaxies (LRGs), and the Bright Galaxy Survey (BGS) that provide samples of complementary colour, the DC3R2 targets help DESI to span 56 per cent of the colour space visible to Euclid and LSST with high confidence spectroscopic redshifts. The effects of spectroscopic completeness and quality are explored, as well as systematic uncertainties introduced with the use of common Self-Organizing Maps trained on different photometry than the analysis sample. We further examine the dependence of redshift on magnitude at fixed colour, important for the use of bright galaxy spectra to calibrate redshifts in a fainter photometric galaxy sample. We find that noise in the KiDS-VIKING photometry introduces a dominant, apparent magnitude dependence of redshift at fixed colour, which indicates a need for carefully chosen deep drilling fields, and survey simulation to model this effect for future weak lensing surveys.

The 1D power spectrum P1D of the Ly α forest provides important information about cosmological and astrophysical parameters, including constraints on warm dark matter models, the sum of the masses of the three neutrino species, and the thermal state of the intergalactic medium. We present the first measurement of P1D with the quadratic maximum likelihood estimator (QMLE) from the Dark Energy Spectroscopic Instrument (DESI) survey early data sample. This early sample of 54 600 quasars is already comparable in size to the largest previous studies, and we conduct a thorough investigation of numerous instrumental and analysis systematic errors to evaluate their impact on DESI data with QMLE. We demonstrate the excellent performance of the spectroscopic pipeline noise estimation and the impressive accuracy of the spectrograph resolution matrix with 2D image simulations of raw DESI images that we processed with the DESI spectroscopic pipeline. We also study metal line contamination and noise calibration systematics with quasar spectra on the red side of the Ly α emission line. In a companion paper, we present a similar analysis based on the Fast Fourier Transform estimate of the power spectrum. We conclude with a comparison of these two approaches and discuss the key sources of systematic error that we need to address with the upcoming DESI Year 1 analysis.

We present the first eight months of data from our secondary target programme within the ongoing Dark Energy Spectroscopic Instrument (DESI) survey. Our programme uses a mid-infrared and optical colour selection to preferentially target dust-reddened quasi-stellar objects (QSOs) that would have otherwise been missed by the nominal DESI QSO selection. So far, we have obtained optical spectra for 3038 candidates, of which ∼70 per cent of the high-quality objects (those with robust redshifts) are visually confirmed to be Type 1 QSOs, consistent with the expected fraction from the main DESI QSO survey. By fitting a dust-reddened blue QSO composite to the QSO spectra, we find they are well-fitted by a normal QSO with up to AV ∼4 mag of line-of-sight dust extinction. Utilizing radio data from the LOFAR Two-metre Sky Survey (LoTSS) DR2, we identify a striking positive relationship between the amount of line-of-sight dust extinction towards a QSO and the radio detection fraction, that is not driven by radio-loud systems, redshift and/or luminosity effects. This demonstrates an intrinsic connection between dust reddening and the production of radio emission in QSOs, whereby the radio emission is most likely due to low-powered jets or winds/outflows causing shocks in a dusty environment. On the basis of this evidence, we suggest that red QSOs may represent a transitional 'blow-out' phase in the evolution of QSOs, where winds and outflows evacuate the dust and gas to reveal an unobscured blue QSO.

This paper describes the second data release (DR2) of the Beijing-Arizona Sky Survey (BASS). BASS is an imaging survey covering a 5400 deg2 footprint in the g and r bands using the 2.3 m Bok telescope. DR2 includes the observations through 2017 July obtained by BASS and by the Mayall z-band Legacy Survey (MzLS), which used the 4 m Mayall telescope to observe the same footprint. BASS and MzLS have completed 72% and 76% of their observations. The two surveys will be served for the spectroscopic targeting of the upcoming Dark Energy Spectroscopic Instrument. Both BASS and MzLS data are reduced by the same pipeline. We have updated the basic data reduction and photometric calibrations in DR2. In particular, source detections are performed on stacked images, and photometric measurements are co-added from single-epoch images based on these sources. The median 5σ point-source depths after Galactic extinction corrections are 24.05, 23.61, and 23.10 mag for the g, r, and z bands, respectively. The DR2 data products include stacked images, co-added catalogs, and single-epoch images and catalogs. The BASS website (http://batc.bao.ac.cn/BASS/) provides detailed information and links to download the data.

The Beijing-Arizona Sky Survey (BASS) is a new wide-field legacy imaging survey in the northern Galactic cap using the 2.3 m Bok telescope. The survey will cover about 5400 deg2 in the g and r bands, and the expected 5σ depths (corrected for the Galactic extinction) in these two bands are g = 24.0 and r = 23.4 mag (AB magnitude). BASS started observations in 2015 January and had completed about 41% of the area as of 2016 July. The first data release contains calibrated images obtained in 2015 and 2016 and their corresponding single-epoch and co-added catalogs. The actual depths of the single-epoch images are g ∼ 23.4 and r ∼ 22.9 mag. The full depths of the three epochs are g ∼ 24.1 and r ∼ 23.5 mag.

Radiative decays of the radially excited charmonium resonance, (Formula presented) into (Formula presented) (Formula presented) and (Formula presented) final states have been measured in a sample of (Formula presented) (Formula presented) events collected by the BES Collaboration. The branching ratios (Formula presented) and (Formula presented) are obtained. When compared to the corresponding radiative (Formula presented) decays, the observed (Formula presented) radiative decay rates into (Formula presented) and (Formula presented) are consistent with the prediction of the “12%” rule. © 2003 The American Physical Society.

Radiative decays of the radially excited charmonium resonance, (Formula presented) into (Formula presented) (Formula presented) and (Formula presented) final states have been measured in a sample of (Formula presented) (Formula presented) events collected by the BES Collaboration. The branching ratios (Formula presented) and (Formula presented) are obtained. When compared to the corresponding radiative (Formula presented) decays, the observed (Formula presented) radiative decay rates into (Formula presented) and (Formula presented) are consistent with the prediction of the “12%” rule. © 2003 The American Physical Society.

The branching fraction of the ψ(2S) decay into τ+τ - has been measured for the first time using the BES detector at the Beijing Electron-Positron Collider. The result is Bττ=(2.710. 43±0.55)× 10-3, where the first error is statistical and the second is systematic. This value, along with those for the branching fractions into e+e- and μ+ μ- of this resonance, satisfy well the relation predicted by the sequential lepton hypothesis. Combining all these values with the leptonic width of the resonance, the total width of the ψ(25) is determined to be (252±37) keV. ©2002 The American Physical Society.

The first measurement of (Formula presented) and an upper limit for (Formula presented) are determined from 22.3 (Formula presented) of (Formula presented) annihilation data at a c.m. energy of 4.03 GeV. The data were recorded by the Beijing Spectrometer (BES) at BEPC. A recoil charge method is applied to charm threshold data to determine the charge of the D meson in the recoil from (Formula presented) reconstructed (Formula presented) (Formula presented) mesons. The branching fractions (Formula presented) and (Formula presented) are determined from 10 events with a reconstructed D and a recoiling (Formula presented) In addition, a 90% C.L. upper limit of (Formula presented) is determined from a search for semileptonic decays of the (Formula presented) © 2000 The American Physical Society.

Using a sample of 3.8 M (Formula presented) events accumulated with the BES detector, the process (Formula presented) is studied. The angular distributions are compared with the general decay amplitude analysis of Cahn. We find that the dipion system requires some D wave amplitude, as well as S wave. On the other hand, the (Formula presented) relative angular momentum is consistent with being pure S wave. The decay distributions have been fit to heavy quarkonium models, including the Novikov-Shifman model. This model, which is written in terms of the parameter (Formula presented) predicts that D wave pions should be present. We determine (Formula presented) based on the joint (Formula presented) distribution. The fraction of D wave amplitude as a function of (Formula presented) is found to decrease with increasing (Formula presented) in agreement with the model. We have also fit the Mannel-Yan model, which is another model that allows D wave pions. © 2000 The American Physical Society.

The cross section for charmed meson production at √s=4.03 and 4.14 GeV has been measured with the Beijing Spectrometer. The measurement was made using 22.3 pb-1 of e+e- data collected at 4.03 GeV and 1.5 pb-1 of e+e- data collected at 4.14 GeV. Inclusive observed cross sections for the production of charged and neutral D mesons and momentum spectra are presented. Observed cross sections were radiatively corrected to obtain tree level cross sections. Measurements of the total hadronic cross section are obtained from the charmed meson cross section and an extrapolation of results from below the charm threshold. ©2000 The American Physical Society.

Using a sample of 3.8 M (Formula presented) events accumulated with the BES detector, the process (Formula presented) is studied. The angular distributions are compared with the general decay amplitude analysis of Cahn. We find that the dipion system requires some D wave amplitude, as well as S wave. On the other hand, the (Formula presented) relative angular momentum is consistent with being pure S wave. The decay distributions have been fit to heavy quarkonium models, including the Novikov-Shifman model. This model, which is written in terms of the parameter (Formula presented) predicts that D wave pions should be present. We determine (Formula presented) based on the joint (Formula presented) distribution. The fraction of D wave amplitude as a function of (Formula presented) is found to decrease with increasing (Formula presented) in agreement with the model. We have also fit the Mannel-Yan model, which is another model that allows D wave pions. © 2000 The American Physical Society.

The first measurement of (Formula presented) and an upper limit for (Formula presented) are determined from 22.3 (Formula presented) of (Formula presented) annihilation data at a c.m. energy of 4.03 GeV. The data were recorded by the Beijing Spectrometer (BES) at BEPC. A recoil charge method is applied to charm threshold data to determine the charge of the D meson in the recoil from (Formula presented) reconstructed (Formula presented) (Formula presented) mesons. The branching fractions (Formula presented) and (Formula presented) are determined from 10 events with a reconstructed D and a recoiling (Formula presented) In addition, a 90% C.L. upper limit of (Formula presented) is determined from a search for semileptonic decays of the (Formula presented) © 2000 The American Physical Society.

Hadronic decays of the P-wave spin-triplet charmonium states (Formula presented) are studied using a sample of (Formula presented) decays collected by the BES detector operating at the BEPC storage ring. Branching fractions for the decays (Formula presented) (Formula presented) (Formula presented) (Formula presented) (Formula presented) and (Formula presented) are measured for the first time, and those for (Formula presented) (Formula presented) (Formula presented) and (Formula presented) are measured with improved precision. In addition, we determine the masses of the (Formula presented) and (Formula presented) to be (Formula presented) and (Formula presented) © 1999 The American Physical Society.

Hadronic decays of the P-wave spin-triplet charmonium states (Formula presented) are studied using a sample of (Formula presented) decays collected by the BES detector operating at the BEPC storage ring. Branching fractions for the decays (Formula presented) (Formula presented) (Formula presented) (Formula presented) (Formula presented) and (Formula presented) are measured for the first time, and those for (Formula presented) (Formula presented) (Formula presented) and (Formula presented) are measured with improved precision. In addition, we determine the masses of the (Formula presented) and (Formula presented) to be (Formula presented) and (Formula presented) © 1999 The American Physical Society.

Purely leptonic decays of the charged D meson have been studied using the reaction e+e- → D*+D- at a center of mass energy of 4.03 GeV. A search was performed for D → μνμ recoiling against a D0 or D+ which had been reconstructed from its hadronic decay products. A single event candidate was found in the reaction e+e- → D*+D-, where D*+ → π+D0 with the D0 → K-π+, and the recoiling D- decaying via D- → μ-ν̄μ. This yields a branching fraction value B(D → μνμ) = 0.08+0.16+0.05-0.05-0.02%, and a corresponding value of the pseudoscalar decay constant fD = 300+180+80-150-40 MeV. © 1998 Elsevier Science B.V. All rights reserved.

Purely leptonic decays of the charged D meson have been studied using the reaction e+e- → D*+D- at a center of mass energy of 4.03 GeV. A search was performed for D → μνμ recoiling against a D0 or D+ which had been reconstructed from its hadronic decay products. A single event candidate was found in the reaction e+e- → D*+D-, where D*+ → π+D0 with the D0 → K-π+, and the recoiling D- decaying via D- → μ-ν̄μ. This yields a branching fraction value B(D → μνμ) = 0.08+0.16+0.05-0.05-0.02%, and a corresponding value of the pseudoscalar decay constant fD = 300+180+80-150-40 MeV. © 1998 Elsevier Science B.V. All rights reserved.

A search is performed for the production of the (Formula presented) in (Formula presented) annihilation at a center-of-mass energy of 4.03 GeV using the BES detector operated at the Beijing Electron Positron Collider (BEPC). The kinematic features of the reconstructed (Formula presented) signal are consistent with its being produced only in association with an energetic photon resulting from initial state radiation (ISR). Limits are placed on (Formula presented) production from the decay of unknown charmonia or metastable hybrids that might be produced in (Formula presented) annihilations at 4.03 GeV. Under the assumption that the observed cross section for (Formula presented) production is due entirely to ISR, the partial width (Formula presented) of the (Formula presented) is measured to be (Formula presented). © 1998 The American Physical Society.

The absolute inclusive branching fraction of (Formula presented) has been measured from data collected by the BES detector at a center-of-mass energy of 4.03 GeV, corresponding to an integrated luminosity of 22.3 pb(Formula presented). At this energy, direct pair production (Formula presented) has been observed. We have selected (Formula presented) candidate events by reconstructing five hadronic decay modes (Formula presented), (Formula presented), (Formula presented), (Formula presented) and (Formula presented) and have searched for inclusive (Formula presented)’s in the recoiling (Formula presented). We observed three recoiling (Formula presented)’s in the 166.4 (Formula presented) 31.8 (Formula presented) candidate events, which leads to the absolute branching fraction (Formula presented) and (Formula presented). © 1998 The American Physical Society.

The absolute inclusive branching fraction of (Formula presented) has been measured from data collected by the BES detector at a center-of-mass energy of 4.03 GeV, corresponding to an integrated luminosity of 22.3 pb(Formula presented). At this energy, direct pair production (Formula presented) has been observed. We have selected (Formula presented) candidate events by reconstructing five hadronic decay modes (Formula presented), (Formula presented), (Formula presented), (Formula presented) and (Formula presented) and have searched for inclusive (Formula presented)’s in the recoiling (Formula presented). We observed three recoiling (Formula presented)’s in the 166.4 (Formula presented) 31.8 (Formula presented) candidate events, which leads to the absolute branching fraction (Formula presented) and (Formula presented). © 1998 The American Physical Society.

A search is performed for the production of the (Formula presented) in (Formula presented) annihilation at a center-of-mass energy of 4.03 GeV using the BES detector operated at the Beijing Electron Positron Collider (BEPC). The kinematic features of the reconstructed (Formula presented) signal are consistent with its being produced only in association with an energetic photon resulting from initial state radiation (ISR). Limits are placed on (Formula presented) production from the decay of unknown charmonia or metastable hybrids that might be produced in (Formula presented) annihilations at 4.03 GeV. Under the assumption that the observed cross section for (Formula presented) production is due entirely to ISR, the partial width (Formula presented) of the (Formula presented) is measured to be (Formula presented). © 1998 The American Physical Society.

The absolute inclusive semileptonic branching fraction of the [Formula presented] meson has been measured based on [Formula presented] of [Formula presented] collision data collected with the Beijing Spectrometer at [Formula presented] At this energy, the [Formula presented] are produced in pairs: [Formula presented] We reconstructed [Formula presented] [Formula presented] events in five hadronic decay modes. In the recoil system of these events, several [Formula presented] inclusive semileptonic decays were observed and the branching fraction is estimated to be [Formula presented] © 1997 The American Physical Society.

The absolute inclusive semileptonic branching fraction of the [Formula presented] meson has been measured based on [Formula presented] of [Formula presented] collision data collected with the Beijing Spectrometer at [Formula presented] At this energy, the [Formula presented] are produced in pairs: [Formula presented] We reconstructed [Formula presented] [Formula presented] events in five hadronic decay modes. In the recoil system of these events, several [Formula presented] inclusive semileptonic decays were observed and the branching fraction is estimated to be [Formula presented] © 1997 The American Physical Society.

The cross section for e+e-→ρπ has been measured by the BES detector at BEPC at center-of-mass energies covering a 40 MeV interval spanning the J/ψresonance. The data are used to search for the vector gluonium state hypothesized by Brodsky, Lepage, and Tuan as an explanation of the ρπ puzzle in charmonium physics. The shape of the ρπ cross section is compatible with that of the total hadronic cross section. No distortions indicating the presence of a vector glueball are seen. © 1996 The American Physical Society.

A data-driven energy scan in the immediate vicinity of the τ pair production threshold has been performed using the Beijing Spectrometer at the Beijing Electron-Positron Collider. Approximately 5pb-1 of data, distributed over 12 scan points, have been collected. A previous mass value for the τ lepton, obtained using only the eµ final state, has been published. In this paper, the final BES result on the mass measurement is presented. The analysis is based on the combined data from the ee, eµ, eh, µµ, µh, and hh final states, where h denotes a charged Π or K. A maximum likelihood fit to the τ pair production cross section data yields the value mT=1776.96-0.21 -0.17+0.18+0.25. © 1995 The American Physical Society.