%================================================================ % LaTeX file with prefered layout for H1 paper drafts % use: dvips -D600 file-name %================================================================ \documentclass[12pt]{article} \usepackage{epsfig} \usepackage{amsmath} \usepackage{hhline} \usepackage{amssymb} \usepackage{times} \usepackage{cite} %%%%%%%%%%%% Comment the next two lines to remove the line numbering %\usepackage[]{lineno} %\linenumbers %\usepackage{hyperref} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \renewcommand{\topfraction}{1.0} \renewcommand{\bottomfraction}{1.0} \renewcommand{\textfraction}{0.0} \newlength{\dinwidth} \newlength{\dinmargin} \setlength{\dinwidth}{21.0cm} \textheight23.5cm \textwidth16.0cm \setlength{\dinmargin}{\dinwidth} \setlength{\unitlength}{1mm} \addtolength{\dinmargin}{-\textwidth} \setlength{\dinmargin}{0.5\dinmargin} \oddsidemargin -1.0in \addtolength{\oddsidemargin}{\dinmargin} \setlength{\evensidemargin}{\oddsidemargin} \setlength{\marginparwidth}{0.9\dinmargin} \marginparsep 8pt \marginparpush 5pt \topmargin -42pt \headheight 12pt \headsep 30pt \footskip 24pt \parskip 3mm plus 2mm minus 2mm %===============================title page============================= \begin{document} % The rest \newcommand{\pom}{{I\!\!P}} \newcommand{\reg}{{I\!\!R}} \def\gsim{\,\lower.25ex\hbox{$\scriptstyle\sim$}\kern-1.30ex% \raise 0.55ex\hbox{$\scriptstyle >$}\,} \def\lsim{\,\lower.25ex\hbox{$\scriptstyle\sim$}\kern-1.30ex% \raise 0.55ex\hbox{$\scriptstyle <$}\,} \newcommand{\PO}{I\!\!P} \newcommand{\xbj}{x} \newcommand{\xpom}{x_{\PO}} \newcommand{\dgr}{^\circ} \newcommand{\GeV}{\mathrm{GeV}} \newcommand{\cm}{\mathrm{cm}} \newcommand{\mm}{\mathrm{mm}} \renewcommand{\deg}{^\circ} \newcommand{\qsq}{\ensuremath{Q^2} } \newcommand{\gevsq}{\ensuremath{\mathrm{GeV}^2} } \newcommand{\der}{{\mathrm d}} \begin{titlepage} \begin{flushleft} {\tt DESY 09-185 \hfill ISSN 0418-9833} \\ {\tt October 2009} \\ \end{flushleft} \vspace{36mm} \begin{center} \begin{Large} {\boldmath \bf Measurement of Leading Neutron Production in Deep-Inelastic Scattering at HERA } \vspace{2cm} \rm H1 Collaboration \end{Large} \end{center} \vspace{2cm} % \begin{abstract} \noindent \rm The production of leading neutrons, where the neutron carries a large fraction $x_L$ of the incoming proton's longitudinal momentum, is studied in deep-inelastic positron-proton scattering at HERA. The data were taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of $122~\mathrm{pb}^{-1}$. The semi-inclusive cross section is measured in the phase space defined by the photon virtuality $611~\GeV$ and a polar angle $156\deg<\theta_e'<175\deg$. % The energy weighted cluster radius is required to be less than $4~\cm$, as expected for an electromagnetic shower~\cite{Aaron:2009kv}. % The $z$-coordinate of the primary event vertex is required to be within $\pm 35~\cm$ of the nominal position of the interaction point. % The remaining clusters in the calorimeters and the charged tracks are combined to reconstruct the hadronic final state. % , using an algorithm % which avoids double counting of energy \cite{Peez:2003zd}. % To suppress events with initial state hard photon radiation, as well as events originating from non-$ep$ interactions, the quantity $E - p_z$, summed over all reconstructed particles including the positron, is required to lie between $35~\GeV$ and $70~\GeV$. This quantity is expected to be twice the electron beam energy for DIS events without QED radiation. Furthermore, events are selected within the kinematic range $60.7$. It is included in the cross section definition. %-------------------------------------------------------------------------------------- \subsection{Systematic uncertainties} The effects of various systematic uncertainties on the cross section measurements are determined using Monte Carlo simulations, by propagating the corresponding estimated measurement uncertainty through the full analysis chain. The acceptance of the FNC is defined by the interaction point and the geometry of the HERA magnets and is determined using Monte Carlo simulations. The angular distribution of the neutrons studied in this analysis is sharply peaked in the forward direction. Therefore the acceptance depends critically on small inclinations of the incoming proton beam with respect to its nominal direction. The uncertainty on the position of the neutron impact point is estimated to be $5~\mm$, which results in a $4.4\%$ uncertainty in the FNC acceptance. The uncertainty in the neutron detection efficiency and the uncertainty of $2\%$ on the absolute energy scale of the FNC lead to a systematic error on the cross section of $2\%$ and $6\%$, respectively. An additional $0.5\%$ uncertainty is attributed to the trigger efficiency. These effects are strongly correlated between measurement intervals and mainly contribute to the overall normalisation uncertainty. The uncertainties on the measurements of the scattered positron energy ($1\%$) and angle ($1~\mathrm{mrad}$) in the SpaCal lead to a combined systematic uncertainty of typically $1.9\%$ on the cross section. The uncertainty of the energy measurement of the hadronic final state in the central detectors affect the reconstruction of the kinematic variables $y$, $Q^2$ and $x$. This hadronic energy scale uncertainty is estimated to be $4\%$ for this measurement, leading to an uncertainty on the cross section of $0.4\%$ on average. The systematic error on the efficiency to reconstruct the event vertex is determined by comparing the reconstruction efficiencies for the data and the Monte Carlo simulation. The discrepancy is less than $1\%$. % in the analysed $y$-range. % The QED radiative corrections amount to less than $10\%$, as evaluated % using both RAPGAP and DJANGO interfaced to the HERACLES program. The systematic uncertainty arising from the radiative corrections and the model dependence of the data correction are estimated by varying the DJANGO and RAPGAP-$\pi$ scaling factors described in Sect.~\ref{sec:mc} within values permitted by the data. The resulting uncertainty on the cross section is below $5\%$ in most of the bins and typically $2\%$. The luminosity measurement uncertainty for the selected run period leads to an overall normalisation uncertainty of $5\%$. The total systematic error in each bin is calculated as the quadratic sum of all contributions. Systematic errors are typically $10\%$ for $F_2^{LN(3)}$ and $14\%$ for $\der\sigma/\der x_L$ measurements. %-------------------------------------------------------------------------------------- \section{Results} \label{sec:result} The single differential leading neutron DIS cross sections as a function of $x_L$ are presented in Fig.~\ref{fig:EnCrsec} and Table~\ref{tab:dsdxl1}. In Fig.~\ref{fig:EnCrsec}b the differential cross section in $x_L$ is shown for $p_T<0.2~\GeV$. The difference between the shapes of distributions in Fig.~\ref{fig:EnCrsec}a and Fig.~\ref{fig:EnCrsec}b, in particular a steep fall at low $x_L$ in Fig.~\ref{fig:EnCrsec}a, is due to the geometrical acceptance of the FNC which restricts the accessible $p_T$ range to $p_T0.5$ is still too low. Figure~\ref{FNC-F2-MC} and Tables~\ref{tab:f2ln3p1}-\ref{tab:f2ln3p4} present the measurement of the semi-inclusive structure function $F_2^{LN(3)}(Q^2,x,x_L)$ in the range $6