Recent Results from HERA

TL;DR

HERA collider experiments have provided detailed measurements of proton structure functions, leading to refined parton distribution functions and improved understanding of QCD, especially at low x and high Q^2 regimes.

Contribution

This paper compiles recent high-precision measurements from HERA, including structure functions and jet production, and updates the proton PDFs with combined data and new analyses.

Findings

Precise low-x structure function measurements constrain sea quark and gluon densities.

Combined H1 and ZEUS data achieve ultimate DIS cross section measurement precision.

H1's jet analysis enables determination of the strong coupling constant _S.

Abstract

HERA $ep$ collider provides unique information on the proton structure. High center of mass energy $s=320$ GeV gives access to both the low Bjorken-$x$ domain and regime of high momentum transfers $Q$. Recently the H1 collaboration reported a high precision measurement of the structure function $F_2$ at low $x$ leading to tight constraints on the sea quark and gluon densities. Both the H1 and ZEUS collaborations measure the structure function $F_L$ which provides an important cross check of the conventional QCD picture. This measurement is recently extended by H1 to low $Q^2$ where small $x$ corrections may play important role. An ultimate precision of the deep inelastic scattering cross section measurement is achieved by combining the measurements of the H1 and ZEUS collaborations. The combined data are used as a sole input to a QCD fit to obtained HERA PDF set. New measurements of inclusive $e^-p$ neutral and charged current scattering cross sections by the ZEUS collaboration at high $Q^2$ improve precision in this kinematic domain. H1 analysis of the DIS high $P_t$ jet production cross section is used for a determination of the strong coupling constant $\alpha_S$. Separation of the strange quark density from the total sea is obtained by the HERMES collaboration using tagged $K^{\pm}$ production.