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Instrum. Methods} \def\NIMA{{\em Nucl. Instrum. Methods} {\bf A}} \def\NPB{{\em Nucl. Phys.} {\bf B}} \def\PLB{{\em Phys. Lett.} {\bf B}} \def\PRL{\em Phys. Rev. Lett.} \def\PRD{{\em Phys. Rev.} {\bf D}} \def\ZPC{{\em Z. Phys.} {\bf C}} \def\EJC{{\em Eur. Phys. J.} {\bf C}} \def\CPC{\em Comp. Phys. Commun.} \begin{titlepage} \noindent \begin{flushleft} {\tt DESY 13-012 \hfill ISSN 0418-9833} \\ {\tt January 2013} \\ \end{flushleft} %\noindent %Date: 14.01.2013 \\ %Version: 2.1 \\ %Editors: Anastasia Grebenyuk, Hannes Jung, Paul Laycock \\ %Referees: Michael Steder, Dietrich Wegener \\ %Comments by: 29.11.2012 \\ %\noindent %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \vspace{2cm} \begin{center} \begin{Large} {\bf Measurement of Charged Particle Spectra in Deep-Inelastic \boldmath$ep$ Scattering at HERA} \vspace{2cm} H1 Collaboration \end{Large} \end{center} \vspace{2cm} \begin{abstract} Charged particle production in deep-inelastic $ep$ scattering is measured with the H1 detector at HERA. The kinematic range of the analysis covers low photon virtualities, \mbox{$5 < Q^2 < 100$ GeV$^2$}, and small values of Bjorken-$x$, $10^{-4} < x < 10^{-2}$. The analysis is performed in the hadronic centre-of-mass system. The charged particle densities are measured as a function of pseudorapidity ($\eta^*$) and transverse momentum ($p_T^*$) in the range $0<\eta^*<5$ and $0 150$ MeV. The momentum of a combined track is required to be larger than $0.5$ GeV to ensure that the track has enough momentum to cross the endwall of the CJC. Both central and combined tracks are required to originate from the primary event vertex and to be in the pseudorapidity range $-2< \eta < 2.5$ measured in the laboratory frame. Using only tracks assigned to the event vertex, the contributions from in-flight decays of $K_S^{0}$, $\Lambda $ and from photon conversions and from other secondary decays are reduced. Further track quality cuts \cite{myThesis} are applied to ensure a high purity of the track reconstruction. %For each final state charged particle there may be two track candidates, one central track and one combined track. To avoid double counting, the central track is taken if it passes the central track selection, otherwise the combined track candidate will be used in the analysis if it fulfills the combined track selection criteria. %--------------------------------------------------------------------------------------------- \subsection{Definition of experimental observables} The results of this analysis are presented in the hadronic centre-of-mass frame (HCM), to minimise the effect of the transverse boost from the virtual photon. The transformation to the HCM frame is reconstructed with the knowledge of the kinematic variables $Q^2$ and $y$ \cite{myThesis}. The transverse momentum and pseudorapidity of charged particles in the HCM frame are labelled as $p_T^*$ and $\eta^*$. %In the HCM frame the pseudorapidity is defined as $\eta^* = - \ln (\tan(\theta^*/2))$, where $\theta^*$ is the angle with respect to the virtual photon direction, i.e. the positive $z^*$ direction. Since in this frame the positive $z^*$ axis is defined by the direction of the virtual photon, %In the HCM frame HFS particles with $\eta^* > 0$ belong to the current hemisphere and particles with $\eta^* < 0$ %are assigned to originate from the target (proton remnant) hemisphere. Charged particle densities as a function of transverse momentum and pseudorapidity are defined as $(1/N)({\rm d}n/{\rm d}p_T^*)$ and $(1/N)({\rm d}n/\rm{d}\eta^*)$, respectively. Here, ${\rm d}n$ is the total number of charged particles with transverse momentum (pseudorapidity) in the ${\rm d}p_T^*$ (${\rm d}\eta^*$) bin and $N$ denotes the number of selected DIS events. For distributions measured differentially in $x$ and $Q^2$, ${\rm d}n$ and $N$ are %restricted to the the numbers for the respective $(x,Q^2)$ bin. % in $x$ and $Q^2$. Hadronisation is expected to be more relevant at small transverse momenta, while the hard parton radiation is expected to contribute more significantly at high $p_T^*$ ($p_T^* > 1$ GeV) \cite{Kuhlen-pt}. To distinguish hadronisations effects from parton evolution signatures, %To separate the effects of hadronisation and parton evolution, the charged particle density is measured as a function of $\eta^*$ for \mbox{$0 < p_T^* < 1$ GeV} and for \mbox{$1 < p_T^* < 10$ GeV}. %, separately. The $p_T^*$ dependence of the charged particle densities is studied in two different pseudorapidity intervals, $0 < \eta^* < 1.5$ and $1.5 < \eta^* < 5$, referred to as the ``central region'' and ``current region'', respectively, as illustrated in \mbox{figure \ref{fig:eta-feydiag}}. Such division approximately defines the regions where the sensitivity to the hard scatter is largest (current region), and where the parton shower models can be tested (central region). The target region, $\eta^{*}<0$, is not accessible in this analysis. % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{figure}[!h] \begin{center} \includegraphics[height=4.5cm,width=7.cm]{d13-012f2.eps} \end{center} \caption{ The two pseudorapidity regions analysed in this paper. The region $0 < \eta^* < 1.5$ and $1.5 < \eta^* < 5$, are denoted as ``central'' and ``current'' regions, respectively.} \label{fig:eta-feydiag} \end{figure} %%%%%%%%%%%%%%%%%%%%%%%%%%%% %---------------------------------------------------------------------------------------------------- \section{Data corrections} The data are corrected to the number of stable charged particles including charged hyperons, with proper lifetime $c\tau>10$ mm, in the phase space given in \mbox{table \ref{tab:sel-genlev}}. Correction factors are calculated for each analysis bin from the ratio of the number of generated stable charged particles to the number of reconstructed tracks. The bin widths are chosen such that a purity\footnote{The purity is defined as the ratio of the number of charged particles generated and reconstructed in a given bin to the total number of charged particles in the phase space of the analysis which are reconstructed in this bin.} of more than $75 \%$ is ensured in all bins. The correction takes into account detector effects like limited resolution and losses near the phase space boundaries, as well as a small residual contamination from weak decays of neutral particles (e.g. $K^0$ and $\Lambda$). %The simulated photoproduction background is subtracted from the measurements. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \renewcommand{\arraystretch}{1.15} \begin{table}[t] \centering \begin{tabular}{l|l} \hline \hline \multicolumn{2}{c} {{ \bf DIS selection}} \\ \hline Four momentum transfers squared & $5 < Q^2 < 100$ GeV$^2$ \\ Inelasticity & $0.05 < y < 0.6$ \\ \hline %\newline \multicolumn{2}{c} {{ \bf Charged particles}} \\ \hline Pseudorapidity in the laboratory frame & $ -2< \eta < 2.5$ \\ Transverse momentum in the laboratory frame & $p_{T} > 150$ MeV \\ Pseudorapidity in the HCM frame & $ 0 < \eta^* < 5$ \\ Transverse momentum in the HCM frame & $ 0 < p_T^* < 10$ GeV \\ \hline \hline \end{tabular} \caption{Phase space for charged particles.} \label{tab:sel-genlev} \end{table} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% In addition to migrations between bins inside the measurement phase space, there are migrations from outside of the analysis phase space and there is background from photoproduction. These contributions are subtracted prior to applying the correction factors according to the procedure outlined in \cite{forw-jet-h1-zeus3}. The {\sc Djangoh} MC was used to correct the data. The differences to the correction factors obtained from {\sc Rapgap} are taken as systematic uncertainties. The correction factors strongly depend on $\eta^*$ and to a lesser extent on $p_T^*$. In the $1.5 < \eta^* < 5$ region they vary between $1$ and $1.8$ with the largest values seen at high $p_T^*$ and large $\eta^*$. In the $0 < \eta^* < 1.5$ region, the correction factors rise up to $2.6$ at high $p_T^*$, due to the limited detector acceptance in this region. The two MC models predict very similar correction factors for most of the phase space region, but differences %increases up to $5.5 \%$ are observed at small $\eta^*$ and high $p_T^*$. %---------------------------------------------------------------------------------------------------- \section{Systematic uncertainties} The following sources of systematic uncertainties are considered for all measured quantities. \begin{itemize} \item The systematic uncertainty on the SpaCal energy scale is $1 \%$ \cite{ElCalib}, which results in a systematic uncertainty of typically $0.4 \%$ for the measured single differential distributions. \item The SpaCal angular resolution of $1$ mrad leads to a systematic uncertainty of about $0.1 \%$ for the measured distributions. \item The hadronic energy scale uncertainty is known to a precision of $2\%$ \cite{HFSCalib}. The scale uncertainty enters into the uncertainty of the phase space calculations, which depend on $E-P_z$ of the HFS, and also affects the boost to the HCM frame. The systematic effect on the present measurements is about $0.3\%$. \item The systematic uncertainty arising from the model dependence of the data correction is taken as the difference of the correction factors calculated using {\sc Rapgap} and {\sc Djangoh} MC. The resulting uncertainty on the measurements varies between $0.2 \%$ and $5.5 \%$. \item The systematic uncertainty associated with the track reconstruction (e.g. track reconstruction efficiency, vertex reconstruction efficiency, weak decays and nuclear interaction uncertainties) is estimated to be: \begin{itemize} \item $1 \%$ for central tracks, determined from the analysis of curling tracks and from the analysis of secondary vertices of charged particles located in the material between the two CJCs and originating from %in-flight decays or interactions with the detector material. The nuclear interaction cross sections of pions and kaons is found to be smaller in the simulation than in data. After correcting for these deficits, the agreement in the track efficiency between data and MC is found to be better than $1\%$. \item $10 \%$ for combined tracks \cite{myThesis, FTDJINST_FromKarin}. This was checked using all selected central tracks, as well as by using pions from $K_S^0$ decays, as a function of transverse momentum and pseudorapidity. Consistent results are obtained from both samples showing agreement of data and MC within $10 \%$. \end{itemize} The systematic uncertainty associated with the track reconstruction is applied as an independent uncorrelated uncertainty on every data point. The resulting uncertainty on the measurements varies between $1 \%$ and $5.4 \%$ and is $1.6 \%$ on average. An additional systematic uncertainty of $0.2\%$ is assigned due to the different $K_S^0$ contamination seen in data and MC for both central and combined tracks. The corresponding effect arising from $\Lambda$ contamination is expected to be negligible. \item The systematic uncertainty on the remaining photoproduction background is estimated to be $30\%$. This results in an uncertainty on the measured densities up to $0.9 \%$ at small $x$ and $Q^2$. At large $x$ and $Q^2$ the contribution from photoproduction is small and its uncertainty is negligible. \end{itemize} The systematic uncertainties shown in the figures and tables are calculated by adding all contributions in quadrature. The total systematic uncertainty for the single differential measurements is below $2.5\%$ for most analysis bins. %---------------------------------------------------------------------------------------------------- \section{Results} The measurements of the charged particle densities as a function of pseudorapidity and transverse momentum in the phase space summarised in \mbox{table \ref{tab:sel-genlev}} are listed in tables \ref{tab:pt-curr} to \ref{tab:pt-curr7} and shown in figures \ref{fig:eta-PDF-RAPGAP} to \ref{fig:pt-bins-curr}. \subsection{Charged particle densities as a function of pseudorapidity} The charged particle densities as a function of $\eta^*$ were measured separately for \mbox{$p_T^* < 1$ GeV} and for \mbox{$1 < p_T^* < 10$ GeV}, as shown in \mbox{figure \ref{fig:eta-PDF-RAPGAP}}. In the soft $p_T^*$ region, the pseudorapidity distribution is almost flat in the $1.5 \lesssim \eta^* \lesssim 3$ range with about $1.7$ charged particles per unit of pseudorapidity. The distribution falls at small $\eta^{*}$ due to the cut on pseudorapidity in the laboratory frame. In the hard $p_T^*$ region the distribution becomes more peaked near $\eta^{*}=2.5$, with a maximum of $0.23$ charged particles per unit of pseudorapidity. For $1 < p_T^* < 10$ GeV the density increases rather strongly up to $\eta^{*} \approx 2.5$, a behaviour expected from the strong ordering of transverse momentum towards the hard scattering vertex. \mbox{Figure \ref{fig:eta-PDF-RAPGAP}} also shows the predictions of the DGLAP-like model {\sc Rapgap} based on different PDF sets. In the soft $p_T^*$ region all NLO PDFs (HERAPDF1.0 \cite{HERAPDF10}, CTEQ6.6 \cite{CTEQ66M}, GRV98NLO \cite{GRV98}) show similar results and predict less particles compared to calculations using the default LO PDF set CTEQ6L(LO). All predictions are close to the data. At large $p_T^*$, differences between the NLO PDF sets are observed, with CTEQ6L(LO) being closest to the data, %compared to other PDFs, although the differences to the data are still larger than the differences between the various PDF predictions. Similar PDF uncertainties are observed when %to be present using the CDM model as implemented in {\sc Djangoh}. To check the sensitivity to hadronisation effects, the {\sc Rapgap} predictions obtained with three sets of fragmentation parameters are compared to the data in \mbox{figure \ref{fig:eta-aleph-prof-def}}: parameters tuned by ALEPH \cite{ALEPH}, by the Professor tuning tool \cite{profftune} and default {\sc Pythia}6.424 fragmentation parameters. Significant differences between these three samples are seen in the soft $p_T^*$ region, where the data are best described by the ALEPH tune. At large transverse momenta they give similar results but none of them describes the data. Predictions from models with different approaches for QCD radiation (see section 2) are shown in \mbox{figure \ref{fig:eta-PS}}. The data are compared to the CDM model {\sc Djangoh}, the DGLAP-based MC {\sc Rapgap} and Herwig++ and the CCFM model {\sc Cascade}. In the soft $p_T^*$ region, {\sc Djangoh} and {\sc Rapgap} describe the data within the PDF uncertainties (figure \ref{fig:eta-PDF-RAPGAP}). Herwig++, which uses the cluster fragmentation model, provides a reasonable description of the data in the central region. The effect of not using the POWHEG option in Herwig++ also has been investigated. Only small differences were observed which are not considered further in this paper. {\sc Cascade} predicts too high multiplicities in most of the measured $\eta^*$ range. % In the region of $1< p_T^{*} <10$~GeV the best description of the data is achieved by {\sc Djangoh}. {\sc Rapgap} strongly undershoots the data in the central region. Herwig++ predicts a spectrum which is even below the prediction of {\sc Rapgap}. {\sc Cascade} is significantly above the data in a wide range of $\eta^*$. %---------------- x,Q2 bins The charged particle densities as a function of $\eta^*$ are shown in \mbox{figure \ref{fig:eta-soft}} for \mbox{$p_T^* < 1$ GeV} in eight different intervals of $x$ and $Q^{2}$ . The data are compared to predictions of the {\sc Djangoh}, {\sc Rapgap}, Herwig++ and {\sc Cascade} generators. {\sc Djangoh} provides a good description of the data over the full kinematic range. In general the description of the data by {\sc Rapgap} is somewhat worse, with overshooting the data by about %deviations from the data of order $10\%$ at low $x$. Herwig++ predicts smaller charged particle densities than observed in data in most of the phase space with differences of the order of $10\%$ at the highest $Q^2$. %provides a satisfactory description of the data at the lowest $Q^2$ only, while at higher $Q^2$ it is significantly below the measurements. {\sc Cascade} is significantly above the data for $\eta^{*} < 3$ in all $(x,Q^2)$ bins. In figure \ref{fig:eta-hard} the charged particle densities as a function of $\eta^*$ are shown in $(x,Q^{2})$ intervals for $1< p_T^* < 10$ GeV . The shape of the distributions changes with $x$ and $Q^{2}$ more strongly than what is observed for \mbox{$p_T^* < 1$ GeV} (\mbox{figure \ref{fig:eta-soft}}). At small values of $x$ and $Q^{2}$ the measured distribution is less dependent on $\eta^{*}$ compared to the region at high $x$ and $Q^{2}$. None of the models describes all aspects of the data. In general {\sc Djangoh} is closest to the data. However it fails to describe the data at low and medium $x$ in the central pseudorapidity region, with downwards deviations of the order of $20\%$. The {\sc Rapgap} prediction is below the data, with the strongest deviation observed at small $x$ and small $\eta^*$. Herwig++ significantly undershoots the data. The prediction of {\sc Cascade} agrees reasonably well with the measurement at low $x$ and $Q^2$, but overshoots the data significantly as $x$ or $Q^2$ increases. %---------------------------------------------------------------------------------------------------- \subsection{Charged particle densities as a function of transverse momentum} \label{chap-result} In \mbox{figure \ref{fig:pt-mcdata-cen-RDC}} the charged particle densities as a function of $p_T^*$ are shown for two pseudorapidity intervals, $0 < \eta^* < 1.5$ (central) and $1.5 < \eta^* < 5$ (current). The shapes of the measured $p_T^*$ distributions in the two pseudorapidity ranges are similar. The spectrum falls by more than four orders of magnitude from $p_T^* < 1$ GeV to $p_T^* \approx 8$ GeV. The measurements are compared to the predictions of the {\sc Djangoh}, {\sc Rapgap}, Herwig++ and {\sc Cascade} generators. {\sc Djangoh} provides in general a good description of the data, while only at high $p_{T}^*$ in the current region deviations from the measurement are observed. The other models fail to describe the data, with the strongest deviations being observed in the central region. The ratio of RAPGAP to data shows a sharp drop at $p_T^*\approx 1$ GeV. The $p_T^*$ spectra predicted by Herwig++ are even softer than those predicted by {\sc Rapgap}. {\sc Cascade} in general produces higher particle densities than measured. %---------------------(x,Q2)---------------------- In \mbox{figures \ref{fig:pt-bins-cen} and \ref{fig:pt-bins-curr}} the charged particle densities as a function of $p_T^*$ are shown for eight $(x,Q^{2})$ intervals for the central and the current region, respectively. In the central region the measurement shows a dependence on $x$, such that the number of soft particles is decreasing with increasing $x$ for fixed $Q^{2}$. In the current region this effect is less pronounced. The {\sc Djangoh} model provides in general a good description of the data over the full kinematic range in both pseudorapidity regions, degrading at high $p_{T}^*$ in the lowest $(x,Q^{2})$ bin. % Significant deviations of the {\sc Rapgap} predictions from data are observed in the central region at low $x $ and $Q^{2}$. The description becomes somewhat better at larger values of $x$ and $Q^{2}$. The same trend is observed for the current region, but the overall data description is better. Herwig++ fails to describe the measurements at high $p_{T}^*$ in the whole phase space. At lowest $x$ and $Q^{2}$ the spectrum is much softer than the one obtained with {\sc Rapgap}, while at high $x$ and $Q^{2}$ both predictions are similar. {\sc Cascade} describes the data in the lowest $x$ and $Q^{2}$ bin at high $p_{T}^*$ only. %---------------------------------------------------------------------------------------------------- %---------------------------------------------------------------------------------------------------- \section{Conclusion} This paper presents a study of charged particle production in $ep$ collisions at low $Q^2$ measured with the H1 detector. The kinematic range of the analysis covers low photon virtualities, \mbox{$5 < Q^2 < 100$ GeV$^2$}, and small values of $x$, $10^{-4} < x < 10^{-2}$. The analysis is performed in the hadronic centre-of-mass system. The charged particle densities as a function of pseudorapidity ($\eta^*$) and transverse momentum ($p_T^*$) are measured differentially in $x$ and $Q^2$. The charged particle densities as a function of pseudorapidity show different shapes, depending on the $p_T^*$ range. For $0$ 1 GeV $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ %________________________________________________________________________________________________ \renewcommand{\arraystretch}{1.15} % this increase the table in vertical direction, very useful! \begin{table}[p] \centering \tabcolsep 5.8pt % \footnotesize %\small \begin{tabular}{ccc} \begin{tabular}{|c|c|ccc|} \hline \multicolumn{5}{|c|} { {\bf \boldmath %$\eta^*$ spectra. $1< p_T^* <$ 10 GeV }} \\ \hline \hline \multicolumn{1}{|c|}{ $Q^2$, $x$ intervals} & \multicolumn{1}{|c|} {$\eta^*$ range} & $1\!/\!N \cdot {\rm d}n/\rm{d}\eta^*\,$ & stat. & sys. \\ \multicolumn{1}{|c|}{} & \multicolumn{1}{|c|} {} & \multicolumn{1}{c}{} &\multicolumn{1}{c}{($\%$)} & \multicolumn{1}{c|}{($\%$)} \\ \hline %%%%%%%%%%%%%%%%%%%%%%% bin 1 %%%%%%%%%%%%%%%%%%%%% \multirow{4}{*}{$5< Q^2 < 10 $ GeV$^{2}$} & $0.0 - 0.5$ & $0.1365$ &$ 0.39$ & $5.7$ \\ & $0.5 - 1.0$ & $0.1551$ & $0.29$ & $3.5$ \\ \multirow{4}{*}{$0.0001 1 ; (x,Q2)%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{figure}[p] \vspace{2cm} % \centering \unitlength1cm \hspace{-25mm} \begin{picture}(17.,18.)(0.0,0.0) % \begin{picture}(width,height) \includegraphics*[height=18.cm,width=17.cm]{d13-012f7.eps} \end{picture} \vspace{-30mm} \caption{Charged particle density as a function of $\eta^*$ for $1< p_T^*< 10$ GeV for eight intervals of $Q^{2}$ and $x$ compared to {\sc Djangoh}, {\sc Rapgap}, Herwig++ and {\sc Cascade} Monte Carlo predictions.} \label{fig:eta-hard} \end{figure} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %-------------------------------------pt---------------------- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \newpage \begin{figure}[!h] \unitlength1cm \begin{picture}(18.,10.5)(0.0,0.0) % \begin{picture}(width,height) \put(-0.3,0.){\includegraphics*[height=10.4cm,width=9.4cm]{d13-012f8a.eps}} \put(7.8,0.){\includegraphics*[height=10.4cm,width=9.4cm]{d13-012f8b.eps}} \put(0.6,9.2){{ \bf \Large{(a)} }} \put(8.7,9.2){{ \bf \Large{(b)} }} \end{picture} \vspace{-1.0cm} \caption{Charged particle density as a function of $p_T^*$ in the ranges (a) $0 <\eta^*< 1.5$ and (b) $1.5 <\eta^*< 5$ compared to {\sc Djangoh}, {\sc Rapgap}, Herwig++ and {\sc Cascade} Monte Carlo predictions. The ratios of MC predictions to the measurements are shown on the bottom of the figure.} \label{fig:pt-mcdata-cen-RDC} \end{figure} %%%%%%%%%%%%%%%%%%%%%%% pT ; 0 <\eta^*< 1.5; (x,Q2) %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{figure}[p] \vspace{2cm} % \centering \unitlength1cm \hspace{-25mm} \begin{picture}(17.,18.)(0.0,0.0) % \begin{picture}(width,height) \includegraphics*[height=18.cm,width=17.cm]{d13-012f9.eps} \end{picture} \vspace{-30mm} \caption{Charged particle density as a function of $p_T^*$ in the range $0 <\eta^*< 1.5$ for eight intervals of $Q^{2}$ and $x$ compared to {\sc Djangoh}, {\sc Rapgap}, Herwig++ and {\sc Cascade} Monte Carlo predictions.} \label{fig:pt-bins-cen} \end{figure} %%%%%%%%%%%%%%%%%%%%%%% pT ; 1.5 <\eta^*< 5; (x,Q2) %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \begin{figure}[p] \vspace{2cm} % \centering \unitlength1cm \hspace{-25mm} \begin{picture}(17.,18.)(0.0,0.0) % \begin{picture}(width,height) \includegraphics*[height=18.cm,width=17.cm]{d13-012f10.eps} \end{picture} \vspace{-30mm} \caption{Charged particle density as a function of $p_T^*$ in the range $1.5 <\eta^*< 5$ for eight intervals of $Q^{2}$ and $x$ compared to {\sc Djangoh}, {\sc Rapgap}, Herwig++ and {\sc Cascade} Monte Carlo predictions.} \label{fig:pt-bins-curr} \end{figure} \end{document}