# XXIV International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS16)

Apr 11 – 15, 2016
DESY Hamburg
Europe/Berlin timezone

## An investigation of the HERA combined data at low Q^2

Apr 12, 2016, 9:40 AM
15m
Auditorium (DESY Hamburg)

### Auditorium

#### DESY Hamburg

Structure Functions and Parton Densities

### Speakers

Prof. A. Cooper-Sarkar (Oxford) Prof. Amanda Cooper-Sarkar (Oxford) Prof. Amanda Cooper-Sarkar (Oxford University)

### Description

In the HERAPDF2.0 PDF analysis it was noted that the fit $chi^2$ worsens significantly at low $Q^2$ for both NLO and NNLO fits. The turn over of the reduced cross section at low-$x$ and low $Q^2$ due to the contribution of the longitudinal cross section $F_L$ is also not very well described. In this paper the prediction for $F_L$ is highlighted and the corresponding extraction of $F_2$ from the data is further investigated, showing discrepancies with description of HERAPDF2.0 at low $x$ and $Q^2$. The effect of adding a simple higher twist term of the form ~constant/Q^2 to the description of $F_L$ is investigated. This results in a significantly better description of the reduced cross-sections, F2 and FL at low x, Q^2 and a significantly lower $\chi^2$ for the NNLO fit as compared to the NLO fit. This is not the case if the higher twist term is added to $F_2$.

### Primary authors

Prof. Amanda Cooper-Sarkar (Oxford) Prof. Brian Foster (Hamburg University, Oxford) Dr Iris Abt (MPI) Dr Katarzyna Wichmann (DESY) Prof. Matthew Wing (UCL) Mr Volodymyr Myronenko (DESY)

 Slides