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Jet}} \newcommand{\otherjet}{Other{\rm Jet}} % Some useful tex commands \newcommand{\qsq}{\ensuremath{Q^2} } \newcommand{\gevsq}{\ensuremath{\mathrm{GeV}^2} } \newcommand{\et}{\ensuremath{E_t^*} } \newcommand{\rap}{\ensuremath{\eta^*} } \newcommand{\gp}{\ensuremath{\gamma^*}p } \newcommand{\dsiget}{\ensuremath{{\rm d}\sigma_{ep}/{\rm d}E_t^*} } \newcommand{\dsigrap}{\ensuremath{{\rm d}\sigma_{ep}/{\rm d}\eta^*} } % Journal macro \def\Journal#1#2#3#4{{#1} {\bf #2} (#3) #4} \def\NCA{\em Nuovo Cimento} \def\NIM{\em Nucl. Instrum. Methods} \def\NIMA{{\em Nucl. Instrum. Methods} {A}} \def\NPB{{\em Nucl. Phys.} {B}} \def\PLB{{\em Phys. Lett.} {B}} \def\PRL{\em Phys. Rev. Lett.} \def\PRD{{\em Phys. Rev.} {D}} \def\ZPC{{\em Z. Phys.} {C}} \def\EJC{{\em Eur. Phys. J.} {C}} \def\CPC{{\em Comp. Phys. Commun.} } \pagestyle{empty} \begin{titlepage} \noindent \begin{center} %{\it {\large version of \today}} \\[.3em] \begin{small} \begin{tabular}{llrr} %Submitted to & \multicolumn{3}{r}{\footnotesize Electronic Access: {\it http://www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em] \hline %Submitted to & \multicolumn{3}{r}{\footnotesize {\it www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em] \hline Submitted to & & & \epsfig{file=/h1/www/images/H1logo_bw_small.epsi ,width=2.cm} \\[.2em] \hline \multicolumn{4}{l}{{\bf XXII International Symposium on Lepton-Photon Interactions at High Energy}, June~30,~2005,~Uppsala} \\ & Abstract: & {\bf 401} &\\ & Sessions: & {\bf Flavor physics} and {\bf QCD and hadron structure} &\\ \hline & \multicolumn{3}{r}{\footnotesize {\it www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em] \end{tabular} \end{small} \end{center} \vspace*{2cm} \begin{center} \Large {\bf Acceptance corrected ratios of $D^*p(3100)$ and $D^*$ yields and differential cross sections of $D^*p(3100)$ production} \vspace*{1cm} {\Large H1 Collaboration} \end{center} \begin{abstract} The measurement of acceptance corrected ratios $\sigma(D^*p(3100))/\sigma(D^*)$ for electro-production of the anti-charmed baryon state $D^*p(3100)$ decaying into $D^*$ and $p$ is presented. The analysis based on the 1996-2000 data is performed in the deep inelastic scattering region $1 1.5 \ {\rm GeV}$, \item a pseudorapidity $\eta=-\log\tan(\Theta/2)$~in the laboratory frame in the range $-1.5 < \eta(D^*) < 1$ and \item a minimum inelasticity $z(D^*) = (E - p_z)_{D^*} / 2 y E_e$ of $z(D^*) > 0.2$, which account for the hard fragmentation of charmed hadrons. \end{itemize} In this kinematic region the combinatorial background to the $D^*$ signal is small. Some of the measured differential cross sections, namely the inelasticity distribution and the fragmentation function of the $D^*p(3100)$ baryon and the $D^*$ meson from $D^*p(3100)$ decay, are strongly affected by the cut in $z(D^*)$. In order to obtain reasonable acceptances in the full variable range for these quantities the cut in $z(D^*)$ is replaced by a cut in the $D^*p(3100)$ fragmentation variable \footnote{The measurement of the fragmentation function $x_{obs}$ is studied in section \ref{fragm}. } $x_{obs}(D^*p)$ %The measurement of the inelasticity distribution of the $D^*$ meson %and especially of the $D^*p(3100)$ baryon is strongly affected by the %In inclusive $D^*$ meson production the inelasticity %$z(D^*)$ is a convolution of the inelasticity $z(c)$ of the parent charm %quark and fragmentation function %\footnote{The measurement of the fragmentation function $x_{obs}(D^*)$ is %studied in section \ref{fragm}.} $x_{obs}(D^*)$ which is the momentum fraction of the charm quark carried by the $D^*p(3100)$ baryon by the following requirement \begin{itemize} \item $x_{obs}(D^*p)>min(0.5\cdot p(p),0.5)$, where $p(p)$ is the momentum of the proton. This selection cut allows to access the low $x_{obs}$ and $z$ regions with reasonable efficiency and gives the best sensitivity according to the pentaquark Monte Carlo and the non charm induced background as obtained from the data. \end{itemize} %In total $4219\pm 86$ %$D^*$ mesons are observed in the distribution of the mass difference \item $D^*$ candidates having a mass difference $\Delta M_{D^*} = m (K \pi \pi_s) - m (K \pi)$ within $\pm2.5~\rm{MeV}$ of the nominal value %\item $D^*$ candidates lying within $\pm2.5~\rm{MeV}$ of %the nominal value of $\Delta M_{D^*} = 145.4 ~\rm{MeV}$ are combined with oppositely charged proton candidates selected according to the proton likelihood based on the particles energy loss \dedx in the central trackers. The invariant mass distribution $M(D^* p) = m(K \pi \pi_s p) - m(K \pi \pi_s) + m(D^*)$ of these combinations is shown in figure~\ref{signal} \cite{h1cpq}. \end{itemize} \subsection{Monte Carlo Simulation} \label{model} Monte Carlo simulation is used to determine acceptances for the $D^*$ meson and for the $D^*p(3100)$ baryon. The acceptances were calculated using the RAPGAP 3.1 \cite{rapgap} event generator incorporating fragmentation according to the Lund string model \cite{lund} implemented in PYTHIA 6.1 \cite{pythia}. For simulation of the $D^*p(3100)$ baryon it is assumed that pentaquarks are produced by fragmentation as suggested by the observation of the $D^*p(3100)$ resonance \cite{h1cpq} in high energy $ep$ scattering. The decay of the $D^*p(3100)$ was introduced by changing the properties of the $D_1(2420)$ and $D_2^*(2460)$ such that they decay to $D^*$ meson plus proton with a natural width of zero, a mass of 3100 MeV and assuming isotropic decay. This model will be subsequently refered to as fragmentation production model. The generated events are passed through the full detector simulation using GEANT 3.15 \cite{geant} and are subsequently subjected to the same reconstruction and analysis chain as the data. \section{Results} \subsection{Total acceptance corrected \boldmath{$ D^*p(3100)/D^*$} yields ratios} The observed yields ratio $R(D^*p(3100)/D^*)=(1.46\pm0.32)\%$ has been corrected for $D^*p(3100)$ and $D^*$ acceptances with the approach described in the previous section. Because of our lack of knowledge about the $D^*p(3100)$ production mechanism and the ignorance of the angular momenta involved in its decay. The total acceptance corrected yields ratio is given for the visible range of the $D^*p(3100)$: $p_t(D^*p(3100))>1.5$ GeV, $-1.5<\eta(D^*p(3100))<1.0$ and of the $D^*$ meson: $p_t(D^*)>1.5$ GeV, $-1.5<\eta(D^*)<$1.0, $z(D^*)>$0.2. The same $D^*$ visibility requirements are applied to the $D^*$ meson originating from $D^*p(3100)$ baryon decay. %When applying the acceptance corrections to the $D^*p(3100)$ baryon %Wno extrapolation to the full decay phase space is done for the $D^*$ mesons %Woriginating from the $D^*p(3100)$ decay such that these $D^*$ mesons have %Walso to fulfill the requirements for the $D^*$ selection above. For this visible range the total acceptance corrected yields ratio is \begin{equation} R_{cor}(D^*p(3100)/D^*)=\left(1.59 ~\pm ~0.33(stat.)^{+~0.33}_{-~0.45}(syst.) \right)~\%. \label{rcor} \end{equation} The systematic error includes the following sources of uncertainties: %(relative change of $R_{cor}$): \begin{itemize} \item the dependence on the background shape used in the fit to the data shown in fig.\ref{signal}, \item the dependence on the $D^*$ selection window in the $\Delta M_{D^*}$ distribution, %\item a change of -9\% when reducing the $D^*$ selection window in the %$\Delta M_{D^*}$ distribution from 2.5~MeV to 1.5~MeV, %\item a change of -12\% events from the %the choice of the background shape in fig.\ref{signal}, \item the variation due to a cut of $z(D^*)>0.1$, \item the effect of removing possible contributions from $D_1(2420)$ and $D_2^*(2460)$~due to pions misidentified as protons by requiring $|M(D^*\pi)-2450~\rm{MeV}|~>~50$~MeV, \item uncertainties in the \dedx proton selection efficiency , \item the effect of a softer fragmentation function of the $D^*p(3100)$ baryon, \item the variation of the $D^*p(3100)$ efficiency due to reweighting the $\eta(D^*p)$ distribution to better describe the observed distribution in fig.\ref{dsp}a (see below). %\item efficiency variations due to re-weighting of the $D^*p(3100)$ %decay angle distribution. \end{itemize} The different contributions to the systematic error are summarized in table \ref{syst1}. The largest positive contribution to the systematic error on $R_{cor}$ is obtained when the $D_1(2420)$ and $D_2^*(2460)$ veto cut is applied in the $D^*p$ selection. The largest negative variation is observed when the cut against combinatorial background is reduced from $z(D^*)>0.2$ to $z(D^*)>0.1$. The acceptance corrected ratio $R_{cor}$ in the visible range (eq. \ref{rcor}) can be compared with the 95\% C.L. upper limit of $R_{cor}<0.51\%$ obtained by the ZEUS experiment in deep inelastic $ep$ scattering \cite{zeuscpq} using a different definition of the visible range. %To suppress the non-charm induced %background both analyses use a minimum requirement on observables %which are motivated by the hard %fragmentation of charmed hadrons. However, there is a substantial difference %in the choice of these observables. While the inelasticity $z(D^*)$, used for %background suppression in the analysis presented here, is a convolution of the %charm quark energy and the fragmentation/hadronization value of the %$D^*$ meson, the quantity $p_t(D^*)/\sum^{\Theta>10^o}$, used in the %ZEUS analysis, depends only %on the fragmentation/hadronization value of the %$D^*$ meson. Since $D^*$ mesons originating from $D^*p(3100)$ decay have to be %significantly softer than $D^*$ mesons directly produced in the fragmentation %of charm quarks %for simple decay kinematic reasons these cuts may act %differently on a possible $D^*p(3100)$ signal. Furthermore due to the physics %of charm production the two cuts suppress different regions in pseudorapidity %of the produced $D^*$ meson in the laboratory frame as well as in the %hadronic centre-of-mass system. In the laboratory frame the average $z(D^*)$ %is larger for $\eta(D^*)<0$ %while the mean of $p_t(D^*)/\sum^{\Theta>10^o}$ tends to be %smaller here because the hadronic final state is more completely %measured in the detector. %\Blue %{The 90\% C.L. upper limit from the BELLE experiment \cite{bellecpq} of %$Br(B^0\rightarrow\Theta_c\overline{p}\pi) %\times Br( \Theta_c\rightarrow D^{*-}p) %/Br(B^0\rightarrow D^{*-}p\overline{p}\pi)<11\% %$ shows that the analysis of exclusive $B^0$ decay %has not reached the sensitivity %obtained by the analysis presented here.} If acceptance corrections to the $D^*p(3100)$ signal are applied by extrapolating to the full $D^*$ phase space from $D^*p(3100)$ decay based on the fragmentation production model %the model assumption for pentaquark production given in section \ref{model}, %i.e. the visibility range %for the $D^*p(3100)$ sample does not include any $D^*$ visibility requirements a visible cross section ratio of \begin{equation} \sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)= \left(2.48 \pm 0.52(stat.)^{+0.85}_{-0.64}(syst.)\right)~\% \end{equation} is obtained. The contribution to the systematic uncertainties on this ratio are given in table \ref{syst2}. Due to the extrapolation to the full $D^*$ meson phase space in the $D^*p(3100)$ decay the largest positive variation of the ratio is observed when a softer fragmentation model has been used for the $D^*p(3100)$ baryon. Large negative variations are obtained when replacing the background suppression cut in the inelasticity $z$ of the $D^*$ meson by the cut in the fragmentation value of the $D^*p(3100)$ baryon, as described in section \ref{dsprec}, or when using the shape of the background model in figure \ref{signal} for the fit of the $D^*p$ mass distribution. \subsection{Differential distributions in \boldmath{$\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$}} \label{sigds} In order to explore the properties of the events contributing to the $D^*p(3100)$ signal, acceptance corrected ratios $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ have been determined from $M(D^* p)$ mass distributions in bins of a variety of phase space variables. In this section distributions related to event kinematics and to properties of the $D^*$ mesons involved in the $D^*p(3100)$ decay are studied. %Due to the small $D^*p(3100)$ data sample available in this analysis %the number of $D^*p(3100)$ events is determined from a background plus signal %fit to the $D^*p$ mass distributions with fixing the signal mass and width to %$M(D^*p(3100))=3099$~MeV and $\sigma=12$~MeV \cite{h1cpq}, respectively. %For the same reason For this preliminary analysis only statistical errors will be shown. %In this section the properties of the events contributing to the %$(D^*p(3100)$ signal is explored In figure \ref{kine} the acceptance corrected ratio $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ is shown as a function of the hadronic mass $W$, the four momentum transfer squared of the virtual photon $Q^2$, and the invariant mass of the $c\overline{c}$ system, $\hat{s}_{obs}$. In leading order the invariant mass $\hat{s}_{obs}$ is given by \begin{equation} \hat{s}_{obs}=\frac{\displaystyle p_t^{*2}(c)+m_c^2} {\displaystyle z(c)(1-z(c))}, \label{shat} \end{equation} where $p_t^*(c)$ and $z(c)$ denote the transverse momentum in the photon-gluon system and the inelasticity of the charm quark, respectively. Since the quantities related to the charm quark are not accessible the invariant mass $\hat{s}_{obs}$ has to be reconstructed from the charmed hadrons instead. The expression \ref{shat} can be rewritten as %from the $D^*p(3100)$ and $D^*$ properties, respectively, %according to \begin{equation} \hat{s}_{obs}=\frac{\displaystyle p_t^{*2}/x_{obs}+m_c^2x_{obs}} {\displaystyle z(1-z/x_{obs})}, \end{equation} with the transverse momentum $p_t^*$ in the centre-of-mass system, the fragmentation value $x_{obs}$ %, which measures the momentum fraction of the %charm quark carried by the charmed hadron, %\footnote{The fragmentation is studied in section \ref{fragm}.} and the inelasticity $z$ of the $D^*p(3100)$ and $D^*$, respectively. Figure \ref{kine} also includes the expectation for $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ using the fragmentation production model. Since the absolute normalization of the $D^*p(3100)$ rate is not fixed in the model, the $D^*p(3100)$ yield is normalized such to reproduce the ratio $R_{cor}$ in (\ref{rcor}). The expected variation of the ratio with $W$ and $\hat{s}_{obs}$ is a consequence of threshold effects due to the significantly different masses of the $D^*p(3100)$ and $D^*$. The observed dependence on $W$ and on $Q^2$ is well described by this model, while it is significantly above the data at large $\hat{s}_{obs}$. %\Blue{As can be %inferred from the errors the $D^*p(3100)$ signal is most pronounced for %$\hat{s}_{obs}>100~\gev^2$ while for $\hat{s}_{obs}<30~\gev^2$ the observed %$D^*p(3100)$ mass distribution is consistent with background only. %The FOCUS experiment which has preliminarily reported a negative result %of a $\Theta_c$ search \cite{focuscpq} %is sensitive to the low %$\hat{s}$ region only \cite{focus}.} In order to investigate the properties of the $D^*$ mesons contributing to the $D^*p(3100)$ resonance the ratio $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ is shown in figure \ref{dstar} as a function of the pseudorapidity $\eta(D^*)$ and the transverse momentum $p_t(D^*)$, both in the laboratory frame, the inelasticity $z(D^*)$ and the pseudorapidity $\eta^*(D^*)$ in the hadronic centre-of-mass system. Also shown are the expectations from the model. The most striking feature in the data is the suppression of the $D^*p(3100)$ baryon relative to $D^*$ meson production in the near to central region both in the laboratory frame and in the hadronic centre-of-mass system. Such a dependence is not predicted by the fragmentation production model. The data indicate that $D^*p(3100)$ baryon production is closer to the photon direction than normal $D^*$ meson production. %In terms of %pseudorapidities the cleanest %$D^*p(3100)$ signal-to-background ratio is observed in the very backward %$\eta(D^*)$ bin in the laboratory frame and closer to the % photon direction in the hadronic %centre-of-mass system, respectively, while in the close to central %rapidity regions the signal becomes marginal. \Blue{The main source for charm %production at HERA is the photon-gluon fusion process which is %similar to the gluon-gluon fusion process %at the Tevatron. %Preliminary result on the non-observation of pentaquarks at Tevatron %have been reported by the CDF collaboration \cite{cdfcpq}. %In contrast to the HERA experiments the experiments at Tevatron %are mainly sensitive to the central rapidity region %in the hadronic centre-of-mass system.} % while the experiments at HERA are more sensitive towardsto the %HERA experiments. % due to the symmetric machine. %in which the CDF analysis is performed \cite{cdfcpq}. Figure \ref{dstar} also shows the ratio $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ as a function of the inelasticity $z(D^*)$. The $D^*p(3100)$ baryons contribute mainly at small $z(D^*)$ as expected from the masses of the particles involved in the $D^*p(3100)$ decay\footnote{In order to access the small $z(D^*)$ region the cut in this variable is replaced by a minimum requirement in the $D^*p(3100)$ fragmentation variable given in section \ref{dsprec}.} within the framework of the fragmentation production model. %Assuming boson-gluon fusion to be responsible %also for charmed pentaquark production the $z(D^*)$ distribution %observed in $D^*p(3100)$ %decay is an indication for a soft hadronization function of $D^*$ mesons %originating from $D^*p(3100)$. The hadronization function is studied in detail %in section \ref{fragm}. \subsection{Differential \boldmath{$D^*p(3100)$} cross sections } To get information of the $D^*p(3100)$ production mechanism $D^*p(3100)$ differential cross sections in $D^*p(3100)$ quantities are presented in this section. The fragmentation production model is used for acceptance corrections. As in the previous section only statistical errors are given in the figures. In figure \ref{dsp} the differential $D^*p(3100)$ production cross section is shown as a function of the pseudorapidity $\eta(D^*p)$ and the transverse momentum $p_t(D^*p)$, both in the laboratory frame, the inelasticity $z(D^*p)$ and the pseudorapidity $\eta^*(D^*p)$ in the hadronic centre-of-mass system. The $D^*p(3100)$ production cross section shows the same features as a function of the pseudorapidities $\eta(D^*p)$ and $\eta^*(D^*p)$ than observed for the ratio $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ as a function of the $D^*$ variables. Within the quite large statistical errors the shapes of the $z(D^*p)$ and of the $p_t(D^*p)$ distributions are consistent with the fragmentation production model. %those of the $z(D^*)$ and $p_t(D^*)$ cross sections %of inclusive $D^*$ meson production as given in ref. \cite{f2c}. These two distributions are suggesting that boson gluon fusion is the source for the production of $D^*p(3100)$ baryons while the pseudorapidity distributions are not evidently supporting this picture. \subsection{Fragmentation function} \label{fragm} For the comparison of the observation of the $D^*p(3100)$ resonance in deep inelastic $ep$ scattering by H1 with results obtained in other high energy physics processes the momentum fraction from the parent charm quark carried by the $D^*p(3100)$ and the $D^*$ from $D^*p(3100)$ decay is of specific interest. %In contrast to charm production in $e^+e^-$ annihilation %where in leading order QCD the charm quarks are created back-to-back in the %laboratory frame and their energies are given %by the beam energies the %situation is not so simple in $ep$ scattering. Here the charm quarks are not % back-to-back in the laboratory frame and their %energies have to be reconstructed from the observed final state. Since in %$ep$ scattering charm quarks are mainly produced at threshold, i.e. %$\hat{s}\approx 4m_c^2$, jet methods %are not the primary choice for the reconstruction of the charm quarks %because one has to require a certain minimum transverse momentum $p_t$ %of some GeV.This cut %allows to access the low $x_{obs}(D^*p)$ region %with reasonable efficiency and gives %the best sensitivity according to the pentaquark Monte Carlo and the %non charm induced background as obtained from the data. %In this way charm quarks could only be reconstructed reliably at %$\hat{s}\approx 4p_t^2+ 4m_c^2$, significantly above %the charm production threshold. In order to measure the $D^*p(3100)$ fragmentation function and the $D^*$ hadronization function for $D^*$ mesons from $D^*p(3100)$ decay the analysis is performed in the hadronic centre-of-mass system. The method used to reconstruct the fragmentation variable $x_{obs}$ is sketched in figure \ref{fmethod}. It is similar to the method presented in reference \cite{rxobs}. In the plane perpendicular to the photon direction in this frame the charm quarks from the leading order boson gluon fusion process exhibit a back-to-back signature similar to the situation in $e^+e^-$ annihilation. In this way it becomes possible to reconstruct the visible quark energy even close to threshold from the hadronic final state. For the analysis only those particles with $\eta^*>0$ are used which belong to the photon hemisphere (fig. \ref{fmethod}a). Those particles which have angle smaller than $\pi/2$ with respect to the $D^*$ direction in the projection plane perpendicular to the photon direction are subsequently assigned to the $D^*$ hemisphere. The $D^*p(3100)$ fragmentation variable and the $D^*$ hadronization variable can then be defined as \begin{equation} x_{obs}=\frac{\displaystyle (E-p_z)}{\displaystyle \sum_{h\in hemi}(E-p_z)_h}, \end{equation} where $(E-p_z)$ denotes the value of $E-p_z$ of the hadrons in the laboratory frame. In the enumerator enter the quantities of the $D^*p(3100)$ baryon or the $D^*$ meson, respectively, while the sum in the denominator runs over all hadrons attributed to the $D^*$ hemisphere in the plane perpendicular to the photon direction. This method yields a definition of the fragmentation function similar to what is used in $e^+e^-$ annihilation. In figure \ref{xobs} the acceptance corrected cross section ratio $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ as a function of the $D^*$ hadronization value $x_{obs}(D^*)$ and the differential $D^*p(3100)$ cross section as a function of $x_{obs}(D^*p)$ are shown together with the prediction from the model. %In order to access the full range of the fragmentation/hadronization % variable, the selection %cut $z(D^*)>0.2$ was replaced by $x_{obs}(D^*p)>min(0.5\cdot p(p),0.5)$, where %$p(p)$ is the momentum of the proton. This cut %allows to access the low $x_{obs}(D^*p)$ region %with reasonable efficiency and gives %the best sensitivity according to the pentaquark Monte Carlo and the %non charm induced background as obtained from the data. The ratio $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ increases with decreasing $x_{obs}(D^*)$ value which means that $D^*$ mesons originating from $D^*p(3100)$ decay are significantly softer than inclusive $D^*$ mesons which carry most of the charm quark energy. In case of inclusive measurements of $D^*$ meson production in deep inelastic scattering at HERA the most probable fragmentation value is $x_{obs}(D^*)\approx 0.7$ \cite{rxobs}. %from $D^*$ mesons production is about 0.7 in the kinematic range %explored in deep inelastic $ep$ scattering at HERA \cite{rxobs}. The significantly softer $x_{obs}(D^*)$ distribution of $D^*$ mesons contributing to the $D^*p(3100)$ resonance is consistent with the expectation from the decay of the $D^*p(3100)$ particle. %\Blue{The ALEPH experiment has reported a negative result from the $\Theta_c$ %search \cite{alephcpq}. According to the information given in reference %\cite{alephc} the $D^*$ selection used in the analysis prefers %those $D^*$ mesons carrying a substantial fraction of the charm quark energy %both, for $e^+e^-\rightarrow c\overline{c}$ and %$e^+e^-\rightarrow b\overline{b}$ with the subsequent decay into charm. %From QCD evolution one expects a softer $D^*$ fragmentation %function at $\sqrt{s}=M_z$ %compared to the one observed in deep inelastic $ep$ scattering at HERA %\cite{rxobs}. Therefore the $D^*$ hadronization function %for $D^*$ mesons coming from $D^*p(3100)$ decay is expected to be even softer %at LEP compared to what is observed in %figure~\ref{xobs}a at HERA. The $D^*$ mesons from $D^*p(3100)$ decay should %have a hadronization function at LEP which comes close to what is expected %from gluon splitting, i.e. $g\rightarrow c\overline{c}$. It is not evident %if the ALEPH analysis is sensitive to such soft $D^*$ mesons.} In figure \ref{xobs}b the differential cross section $d\sigma_{vis}(D^*p(3100))/dx_{obs}(D^*p)$ is shown as a function of $x_{obs}(D^*p)$. The $D^*p(3100)$ fragmentation function is very hard compared to the $D^*$ hadronization function of figure~\ref{xobs}a. A hard fragmentation is expected for charmed hadrons. Within the limited statistics this differential cross section indicates a harder fragmentation function for the $D^*p(3100)$ baryon compared to that observed in inclusive $D^*$ mesons production \cite{rxobs}, which is expected due to the larger $D^*p(3100)$ mass compared to the $D^*$ mass. %\section{Discussion} \section{Conclusions} A detailed analysis of the exotic $D^*p(3100)$ baryon has been presented. An acceptance corrected yields ratio $ R_{cor}(D^*p(3100)/D^*)= \left(1.59 ~\pm ~0.33(stat.)^{+~0.33}_{-~0.45}(syst.)\right)~\%$ for the visible $D^*p(3100)$ and $D^*$ range has been observed. In the case of the $D^*p(3100)$ the visibility requirement is simultaneously imposed to the $D^*p(3100)$ as well as to its decay product, the $D^*$ meson. When extrapolating to the full phase space of the decay products one observes a ratio of the visible cross sections of $\sigma_{vis}\left(D^*p(3100)\right)/ \sigma_{vis}(D^*)= \left(2.48 \pm 0.52(stat.)^{+0.85}_{-0.64}(syst.)\right)~\%$. Differential distributions of $\sigma_{vis}(D^*p(3100))/ \sigma_{vis}(D^*)$ as a function of event kinematics and $D^*$ quantities have been presented. In general the fragmentation production model leads to a reasonable description of the distributions with some exceptions. The most striking deviation from the expectation is observed in $\eta(D^*)$ and $\eta^*(D^*)$. Compared to inclusive $D^*$ production the $D^*p(3100)$ production seems to be suppressed in the close to central rapidity regions in both frames. The differential $D^*p(3100)$ cross sections as a function of $D^*p(3100)$ variables show the same effect. The $D^*p(3100)$ fragmentation function is hard, consistent with the expectation for a charmed hadron with the given mass. The hadronization function for $D^*$ mesons contributing to the $D^*p(3100)$ resonance is much softer than observed in inclusive $D^*$ mesons production. This observation is consistent with the expectation for a particle with a mass of 3100 MeV decaying to $D^*$ meson plus proton. %%% THE PAPER DRAFTS HAVE NO AUTHORLIST %%% FOR PAPER ISSUED FOR THE FINAL READING %%% COPY THE AUTHOR AND INSTITUTE LISTS %%% INTO YOUR AREA %%% from /h1/iww/ipublications/h1auts.tex %%% AND UNCOMMENT THE NEXT THREE LINES %%%\begin{flushleft} %%% \input{h1auts} %%%\end{flushleft} %%%%%%%%%%%%%%%%%%%% ratios: electron kinematics %%%%%%%%%%%%%%%%%%%%% \begin{thebibliography}{99} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \bibitem{thetaKn} %% %LEPS Collaboration, T.~Nakano {\it et al.}, (LEPS), Phys. Rev. Lett. {\bf 91} (2003) 012002;\\ %CLAS S.~Stepanyan {\it et al.}, (CLAS), Phys. Atom. Nuclei {\bf 66} (2003) 1715;\\ %SAPHIR Collaboration, J.~Barth {\it et al.}, (SAPHIR), Phys. Lett. B {\bf 572} (2003) 127;\\ %CLAS Collaboration, V.~Kubarovsky {\it et al.}, (CLAS), Phys. Rev. Lett. {\bf 92} (2004) 03201 [erratum-ibid. 92 (2004) 049902]. \bibitem{thetaKp} %% %DIANA Collaboration, V.~V.~Barnim {\it et al.}, (DIANA), Phys. Atom. Nucl. {\bf 66} (2003) 1715 [Yad. Fiz. 66 (2003) 1763];\\ A.~E.~Asratyan, A.~G.~Dolgolenko and M.~A.~Kubantsev, Phys. Atom. Nucl. {\bf 67} (2004) 682;\\ %SVD COllaboration, A.~Aleev {\it et al.}, (SVD), hep-ex/0401024;\\ %HERMES Collaboration, A.~Airapetian {\it et al.}, (HERMES), Phys. Lett. B {\bf 585} (2004) 127;\\ %COSY-TOF Collaboration, M.~Abdel-Bary {\it et al.}, (COSY-TOF),Phys. Lett. B {\bf 595} (2004) 127. %ZEUS obs \bibitem{zeusspq} S.~Chekanov {\it et al.} [ZEUS Collaboration], Phys. Lett. {\bf 591} (2004) 7. % \bibitem{h1cpq} A.Aktas {\it et al.} [H1 Collaboration] Phys. Lett {\bf B 588} (2004) 17. % %% non obs \bibitem{zeuscpq} S.~Chekanov {\it et al.} [ZEUS Collaboration], Eur. Phys. J. {\bf C 38} (2004) 29. \bibitem{alephcpq} S.~R.~Armstrong, hep-ex/0410080; S.~Schael {\it et al.}, (ALPEH), Phys. Lett. B {\bf 599}(2004) 1. \bibitem{cdfcpq} D.~O.~Litvintsev, (CDF), hep-ex/0410024. \bibitem{focuscpq} K.~Stenson (FOCUS), hep-ex/0412021. \bibitem{bellecpq} R.~Mizuk {\it et al.}, (Belle), hep-ex/0411005. % \bibitem{steinhart} J. Steinhart, `Die Messung des totalen $c \bar{c}$-Photoproduktions-Wirkungsquerschnittes durch die Rekonstruktion von $\Lambda_c$ Baryonen unter Verwendung der verbesserten \dedx Teilchen\-identifikation am H1 Experiment bei HERA', Ph.D. thesis, 1999, Universit\"{a}t Hamburg (in German, available from \\ \verb+http://www-h1.desy.de/publications/theses_list.html+). % \bibitem{h1det} I. Abt {\it et al.} [H1 Collaboration], Nucl. Inst. Meth. {\bf A386} (1997) 310; \\ I. Abt {\it et al.} [H1 Collaboration], Nucl. Inst. Meth. {\bf A386} (1997) 348. % \bibitem{f2c} %\cite{Aid:1996hj} S.~Aid {\it et al.} [H1 Collaboration], %``Photoproduction of $D~{*\pm}$ Mesons in $ep$ Collisions at HERA,'' Nucl.\ Phys.\ {\bf B472} (1996) 32 [hep-ex/9604005]; \\ %\cite{Adloff:1998vb} C.~Adloff {\it et al.} [H1 Collaboration], %``Measurement of D* meson cross sections at HERA and determination of the %gluon density in the proton using NLO QCD,'' Nucl.\ Phys.\ {\bf B545} (1999) 21 [hep-ex/9812023]; \\ %\cite{Adloff:2001zj} C.~Adloff {\it et al.} [H1 Collaboration], %``Measurement of D*+- meson production and F2(c) in deep inelastic scattering %at HERA,'' Phys.\ Lett.\ {\bf B528} (2002) 199 [hep-ex/0108039]. % %%%%% MC models % \bibitem{rapgap} H.~Jung, Comp. Phys. Comm. {\bf 71} (1992) 15. \bibitem{lund} B. Andersson, G. Gustafson, G. Ingelman and T. Sj\"ostrand, Phys. Rept. {\bf 97} (1983) 31. \bibitem{pythia} T. Sj\"{o}strand {\it et al.}, Comp. Phys. Commun. {\bf 135} (2001) 238 [hep-ph/0010017]. \bibitem{geant} R. Brun {\it et al.}, GEANT3, Technical Report CERN-DD/EE/84-1, CERN, 1987. % %\bibitem{focus} J.M. Link {\it et al.}, Phys.Lett. {\bf B566} (2003) 51 %[hep-ex/0305018]. %\bibitem{alephc} ALEPH Collaboration, Eur. Phys. J. {\bf C16} (2000) 597. %{\it et al.} \bibitem{rxobs} H1 Collaboration, contributed paper to the Lepton-Photon Conference 2005, Abstract \# 407, Uppsala, Sweden. % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \end{thebibliography} \newpage \begin{table} \begin{tabular}{lr} Variation&$\frac{\displaystyle \Delta R_{cor}}{\displaystyle R_{cor}}$ [\%]\\ \noalign{\smallskip} \hline \noalign{\smallskip} \parbox[t]{9cm}{Background shape determined from background model in Fig. \ref{signal}}&-12\\ \noalign{\smallskip} \parbox[t]{9cm}{$\Delta M(D^*)$ window reduced to 1.5 MeV}&-9\\ \noalign{\smallskip} \parbox[t]{9cm}{Visible $D^*$ region extended down to $z(D^*)>$0.1}&-21\\ \noalign{\smallskip} \parbox[t]{9cm}{Require $|M(D^*\pi)-2450~\rm{MeV}|~>~50$~MeV for the $D^*p$ combinations}&+18\\ \noalign{\smallskip} \parbox[t]{9cm}{dE/dx calibration}&$\pm$10\\ \noalign{\smallskip} \parbox[t]{9cm}{Soft fragmentation of $D^*p(3100)$}&-5\\ \noalign{\smallskip} \parbox[t]{9cm}{Reweighting of $\eta(D^*p(3100))$}&-3\\ \noalign{\smallskip}\hline \noalign{\smallskip} \parbox[t]{9cm}{Total}&-28 + 21\\ \noalign{\smallskip}\hline \end{tabular} \caption{Relative systematic errors on the acceptance corrected yields ratio $R_{cor}$ for the visible $D*$ meson region. } \label{syst1} \end{table} \begin{table} \begin{tabular}{lr} Variation& $\frac{{\displaystyle\Delta} \textstyle \frac{\sigma_{vis}(D^*p(3100))}{\sigma_{vis}(D^*)}} {\textstyle\frac{\sigma_{vis}(D^*p(3100))}{\sigma_{vis}(D^*)}}$ [\%]\\ \noalign{\smallskip} \hline \noalign{\smallskip} \parbox[t]{9cm}{Background shape determined from background model in Fig. \ref{signal}}&-14\\ \noalign{\smallskip} \parbox[t]{9cm}{$\Delta M(D^*)$ window reduced to 1.5 MeV}&-10\\ \noalign{\smallskip} \parbox[t]{9cm}{Visible $D^*$ region extended down to $z(D^*)>$0.1}&-8\\ \noalign{\smallskip} \parbox[t]{9cm}{$z(D^*)$ replaced by cut in the $D^*p(3100)$ fragmentation variable $x_{obs}$}&-15\\ \noalign{\smallskip} \parbox[t]{9cm}{Require $|M(D^*\pi)-2450~\rm{MeV}|~>~50$~MeV for the $D^*p$ combinations}&+17\\ \noalign{\smallskip} \parbox[t]{9cm}{dE/dx calibration}&$\pm$10\\ \noalign{\smallskip} \parbox[t]{9cm}{Soft fragmentation of $D^*p(3100)$}&+28\\ \noalign{\smallskip} \parbox[t]{9cm}{Reweighting of $\eta(D^*p(3100))$}&-4\\ \noalign{\smallskip}\hline \noalign{\smallskip} \parbox[t]{9cm}{Total}&-26 + 34\\ \noalign{\smallskip}\hline \end{tabular} \caption{Relative systematic errors on the acceptance corrected visible cross section ratio $\sigma_{vis}(D^*p(3100))/\sigma_{vis}(D^*)$. } \label{syst2} \end{table} \newpage \begin{figure}[p] \unitlength 1mm \begin{center} \begin{picture}(100,100) \put(-30,-20){\epsfig{file=H1prelim-05-072.fig1.eps,width=0.95\textwidth}} % \put(13,185){{\Large {\bf \fontfamily{phv}\selectfont (a)}}} % Helvetica % \put(13,81){{\Large {\bf \fontfamily{phv}\selectfont (b)}}} \end{picture} \end{center} \caption{Distributions in $M(D^* p)$ for opposite-charge $D^* p$ combinations. The data are compared with a two-component background model in which ``wrong charge $D$'' $K^\pm \pi^\pm$ combinations are used to describe non-charm related background and the ``$D^*$ MC'' simulation describes background involving real $D^*$ mesons (from ref\cite{h1cpq}).} \label{signal} \newpage \end{figure} \begin{figure}[ht] \begin{center} \begin{picture}(120,180) \put(-20,75) {\epsfig{figure=H1prelim-05-072.fig2a.eps,width=0.5\textwidth}} \put(60,75) {\epsfig {figure=H1prelim-05-072.fig2b.eps,width=0.5\textwidth}} \put(20,-5){\epsfig{figure=H1prelim-05-072.fig2c.eps,width=0.5\textwidth}} \put(0,140){{\Large {\bf \fontfamily{phv}\selectfont (a)}}} % Helvetica \put(80,140){{\Large {\bf \fontfamily{phv}\selectfont (b)}}} \put(40,60){{\Large {\bf \fontfamily{phv}\selectfont (c)}}} \end{picture} \end{center} \caption{Acceptance corrected ratios $\sigma_{vis}(D^*p(3100))/\sigma_{vis}(D^*)$ as a function of the kinematic variables (a) $W$, (b) Q$^2$ and (c) $\hat{s}_{obs}$. Data (closed symbols) are compared with the expectation (dashed line) of RAPGAP 3.1 which assumes the same mechanism for $D^*$ and $D^*p(3100)$ production. Only statistical errors are shown. \label{kine}} \end{figure} \begin{figure}[ht] \begin{center} \begin{picture}(120,180) \put(-20,75) {\epsfig{figure=H1prelim-05-072.fig3a.eps,width=0.5\textwidth}} \put(60,75) {\epsfig{figure=H1prelim-05-072.fig3b.eps,width=0.5\textwidth}} \put(-20,-5) {\epsfig{figure=H1prelim-05-072.fig3c.eps,width=0.5\textwidth}} \put(60,-5) {\epsfig{figure=H1prelim-05-072.fig3d.eps,width=0.5\textwidth}} \put(0,140){{\Large {\bf \fontfamily{phv}\selectfont (a)}}} % Helvetica \put(80,140){{\Large {\bf \fontfamily{phv}\selectfont (b)}}} \put(0,60){{\Large {\bf \fontfamily{phv}\selectfont (c)}}} \put(80,60){{\Large {\bf \fontfamily{phv}\selectfont (d)}}} \end{picture} \end{center} \caption{Acceptance corrected ratios $\sigma_{vis}(D^*p(3100))/\sigma_{vis}(D^*)$ as a function of $D^*$ variables (a) $\eta(D^*)$ and (b) $p_t(D^*)$ both in the laboratory frame, (c) $z(D^*)$ and (d) $\eta^*(D^*)$ in the hadronic centre-of-mass system. Data (closed symbols) are compared with the expectation (dashed line) of RAPGAP 3.1 which assumes the same mechanism for $D^*$ and $D^*p(3100)$ production. Only statistical errors are shown. \label{dstar}} \end{figure} \begin{figure}[ht] \begin{center} \begin{picture}(120,180) \put(-20,75) {\epsfig{figure=H1prelim-05-072.fig4a.eps,width=0.5\textwidth}} \put(60,75) {\epsfig{figure=H1prelim-05-072.fig4b.eps,width=0.5\textwidth}} \put(-20,-5) {\epsfig{figure=H1prelim-05-072.fig4c.eps,width=0.5\textwidth}} \put(60,-5) {\epsfig{figure=H1prelim-05-072.fig4d.eps,width=0.5\textwidth}} \put(0,140){{\Large {\bf \fontfamily{phv}\selectfont (a)}}} % Helvetica \put(80,140){{\Large {\bf \fontfamily{phv}\selectfont (b)}}} \put(0,60){{\Large {\bf \fontfamily{phv}\selectfont (c)}}} \put(80,60){{\Large {\bf \fontfamily{phv}\selectfont (d)}}} \end{picture} \end{center} \caption{Differential $(D^*p(3100))$ cross sections as a function of $D^*p$ variables (a) $\eta(D^*p)$ and (b) $p_t(D^*p)$ both in the laboratory frame, (c) $z(D^*p)$ and (d) $\eta^*(D^*p)$ in the hadronic centre-of-mass system. Data (closed symbols) are compared with the expectation (dashed line) of RAPGAP 3.1 which assumes the same mechanism for $D^*$ and $D^*p(3100)$ production. Only statistical errors are shown. \label{dsp}} \end{figure} \begin{figure}[ht] \begin{center} \begin{picture}(120,180) \put(20,80) {\epsfig{figure=H1prelim-05-072.fig5a.eps,width=0.5\textwidth}} \put(20,0) {\epsfig{figure=H1prelim-05-072.fig5b.eps,width=0.5\textwidth}} \put(10,130){{\Large {\bf \fontfamily{phv}\selectfont (a)}}} % Helvetica \put(10,50){{\Large {\bf \fontfamily{phv}\selectfont (b)}}} \end{picture} \end{center} \caption{Sketch of the method to reconstruct the visible charm quark energies in $ep$ scattering close to threshold. (a) The hadrons in the photon hemisphere of the hadronic centre-of-mass system are projected to the plane perpendicular to the photon direction. (b) The hadrons in the $D*$ hemisphere are used to reconstruct the visible charm quark energy. \label{fmethod}} \end{figure} \begin{figure}[ht] \begin{center} \begin{picture}(120,180) \put(20,75) {\epsfig{figure=H1prelim-05-072.fig6a.eps,width=0.5\textwidth}} \put(20,-5) {\epsfig{figure=H1prelim-05-072.fig6b.eps,width=0.5\textwidth}} \put(45,140){{\Large {\bf \fontfamily{phv}\selectfont (a)}}} % Helvetica \put(45,60){{\Large {\bf \fontfamily{phv}\selectfont (b)}}} \end{picture} \end{center} \caption{Acceptance corrected ratio $\sigma_{vis}(D^*p(3100))/\sigma_{vis}(D^*)$ as a function of the $D^*$ hadronization fraction $x_{obs}(D^*)$ in (a) and differential cross section $d\sigma_{vis}(D^*p(3100))/dx_{obs}(D^*p)$ in (b). Data (closed symbols) are compared with the expectation (dashed line) of RAPGAP 3.1 which assumes the same mechanism for $D^*$ and $D^*p(3100)$ production. Only statistical errors are shown. \label{xobs}} \end{figure} \end{document}