DESI 2024 IV: Baryon Acoustic Oscillations from the Lyman alpha forest

Abstract
We present the measurement of Baryon Acoustic Oscillations (BAO) from the Lyman-α
(Lyα) forest of high-redshift quasars with the first-year dataset of the Dark Energy
Spectroscopic Instrument (DESI). Our analysis uses over 420 000 Lyα forest spectra and their
correlation with the spatial distribution of more than 700 000 quasars. An essential facet of
this work is the development of a new analysis methodology on a blinded dataset. We conducted
rigorous tests using synthetic data to ensure the reliability of our methodology and findings
before unblinding. Additionally, we conducted multiple data splits to assess the consistency of
the results and scrutinized various analysis approaches to confirm their robustness. For a given
value of the sound horizon (rd
), we measure the expansion at z
eff = 2.33 with 2% precision,
H(z
eff) = ( 239.2 ± 4.8 ) (147.09 Mpc /rd
) km/s/Mpc. Similarly, we
present a 2.4% measurement of the transverse comoving distance to the same redshift, DM
(z
eff)
= ( 5.84 ± 0.14 ) (rd
/147.09 Mpc) Gpc. Together with other DESI BAO
measurements at lower redshifts, these results are used in a companion paper to constrain
cosmological parameters.