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\newcommand{\pis}{\ensuremath{\pi_{\mathrm{slow}}}}
\newcommand{\dstar}{\ensuremath{D^\star}}
\newcommand{\DM}{\ensuremath{\Delta M}}

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\begin{titlepage}

\noindent
%Date:        \today       \\
%Version:     0.1          \\
%Editors:     \myref{mailto:kruegerk@mail.desy.de}{~K.~Kr\"uger}       \\
%Referees:    \myref{mailto:???@mail.desy.de}{A.~Meyer},\myref{mailto:grab@phys.ethz.ch}{~C.~Grab}  \\
      

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 \begin{small}
 \begin{tabular}{llrr}
 {\bf H1prelim-08-075} Submitted to & & &
 \epsfig{file=/h1/iww/ipublications/H1PublicationTemplates/H1logo_bw_small.epsi
 ,width=1.5cm} \\[.2em] \hline
 \multicolumn{4}{l}{{\bf
                XVI International Workshop on Deep-Inelastic Scattering, DIS2008},
                 April 7-11,~2008,~London} \\
%                  Abstract:        & {\bf }    & & \\
                  Parallel Session & {\bf Heavy Flavours}   & & \\ \hline
   \multicolumn{4}{l}{\footnotesize {\it Electronic Access:https://www-h1.desy.de/publications/H1preliminary.short\_list.html
     %www-h1.desy.de/h1/www/publications/conf/conf\_list.html
     }} \\[.2em]
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\vspace{2cm}

\begin{center}
\begin{Large}

{\bf Investigation of the $\mathbf{D^\star p}$ Resonance\\ in the 3 GeV Region
with HERAII Data }

\vspace{2cm}

H1 Collaboration

\end{Large}
\end{center}

\vspace{2cm}

\begin{abstract}
A possible resonance decaying into the \dstar-proton final state is investigated
in deep inelastic scattering at HERA. The data were taken with the H1 detector 
in the years 2004 to 2007 and correspond to an integrated luminosity 
of ~348 pb$^{-1}$ thus increasing 
the available data significantly compared to the analysis of HERAI data. 
\end{abstract}

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Event Selection}
The data sample corresponds to an integrated luminosity of 
$~348~\text{pb}^{-1}$ and was recorded with the H1 experiment in the years 
2004--2007, where either electrons or positrons at \mbox{27.6 GeV} were 
collided with protons at \mbox{920 GeV}. 


\begin{table}[htdp]
\begin{center}
\begin{tabular}{l|c |}
variable & cut \\ \hline
energy of scattered electron $E_e^\prime$  & $> 10$ GeV  \\
angle  of scattered electron $\theta_e$ & $< 3.09$ \\
photon virtuality $Q^2$ & $2<Q^2 < 100$ GeV$^2$ \\
radius cut & $(x_{Sp}+2.025 {\rm cm})^2 + y_{Sp}^2 > (12.$ cm$)^2$ \\
inelasticity $y$ & $0.05 < y < 0.7$ \\ \hline 
\end{tabular}
\end{center}
\caption{Table of electron cuts adapted to the SpaCal geometry in
HERAII.}
\label{tab_kin}
\end{table}


\dstar~me\-sons are identified in their golden decay channel
$D^{\star\pm} \rightarrow D^0 \pi_\mathrm{slow}^\pm  
\rightarrow K^\mp \pi^{\pm} \pi_\mathrm{slow}^\pm$.
The tracks of the decay particles are reconstructed by the CTD.
The kaon, the pion and the slow pion must have a transverse momentum greater 
than \mbox{0.5 GeV, 0.3 GeV} and \mbox{0.12 GeV}, respectively. A cut on the 
scalar sum of the transverse momenta of the pion and kaon above 2.0~GeV is made 
in order to suppress background from the light quarks u,d and s.  
Due to these cuts the visible region, in which \dstar~mesons are reconstructed, 
is restricted to $p_t(\dstar) > \mbox{1.5 \text{GeV}}$.
In order to suppress the non-charm background further the 
pseudo-rapidity is restricted to
$-1.5 < \eta(\dstar) < 1.0$ and the inelasticity of the \dstar\ meson, 
$z(\dstar) = \frac{(E-p_z)_{\dstar}}{2yE_e}$, to $z(\dstar) > 0.2$. 

In contrast to the published HERAI analysis, {\bf no} particle identification by
dE/dx requirements is used for the \dstar\ selection.
  

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Results}

In order to show the sensitivity of the data to the decay of heavier charmed
particles into a \dstar\ meson and an additional particle, the decay of the
$D_1(2420)^0$ and the $D^\star_2(2460)^0$ into a \dstar\ and a pion is studied.
The pion candidate is required to have the opposite charge than the \dstar\ and
a transverse momentum larger than \mbox{0.12 GeV}. The resulting mass distribution, 
reconstructed by $M(\dstar \pi) = 
M(K\pi\pis\pi) - M(K\pi\pis) + M_{\dstar}$ with $M_{\dstar} = 2.010\,{\rm GeV}$,
is shown in figure~\ref{massD2}. 

The selection of pentaquark candidates is kept close to the  "high proton
momentum" selection of the published analysis. Central tracks with opposite
charge than the \dstar\ meson and a momentum $p(p) > 2\,{\rm GeV}$ are combined
to form a pentaquark candidate. The invariant mass $M(\dstar p)$ is calculated
with the assumption of the proton mass by $M(\dstar p) = 
M(K\pi\pis p) - M(K\pi\pis) + M_{\dstar}$. The resulting mass distribution is
shown in figure~\ref{massPenta} for HERAI and for HERAII data. 

Under the assumption that a possible $\dstar p$ resonance has a Gaussian 
resolution of $12\,{\rm MeV}$ (in agreement with the resolution in 
HERAI data), {\bf the $95 \%
$ confidence limit for statistical errors only is 16.3 events (H1 preliminary), corresponding to
a ratio of $\dstar p$ to \dstar\ of 1.0 per mille (H1 preliminary)}. The
corresponding ratio in the HERAI data sample with the same kinematic cuts is
$8.1 \pm 2.1$ per mille (H1 preliminary).

The \DM\ distribution is shown in figure~\ref{backward} for events in a $\pm
15\,{\rm MeV}$ window around the HERAI $\dstar p$ signal and a
sideband region, $2.99$ to $3.07$ and $3.13$ to $3.21\,{\rm GeV}$, scaled by a
factor $3/16$ to account for the different widths. While for HERA1 the
distributions differ around the expected value for \dstar\ mesons, the signal
and sideband distributions agree for HERAII data.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Conclusion}
A study of the invariant mass spectrum of identified \dstar meson candidates
with high momentum proton candidates similar to the HERAI search for a narrow
charmed baryonic resonance has been performed with HERAII data. The selection 
is kept close to the "high proton momentum" selection of the published HERAI 
analysis to be independent from possible differences in the dE/dx calibration 
between the two datasets. The structure at $\sim 3.1\,{\rm GeV}$ in HERAI data 
is found again, also in the kinematic range accessible in HERAII. 
In the HERAII data sample, that is roughly 4 times larger, no significant 
peak structure is visible in HERAII data. The $95 \%
$ confidence limit for statistical errors only is 16.3 events for HERAII, 
corresponding to
a ratio of $\dstar p$ to \dstar\ of 1.0 per mille. In the $\DM_{\dstar}$
distribution an enrichment at the expected value for \dstar\ mesons is found in
the $\dstar p$ "signal" region relative to the sidebands also only for HERAI data,
not for HERAII.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%Figures

%%%%
\begin{figure}%[htp]
\centering
\subfigure{
\includegraphics[width=.49\textwidth]{H1prelim-08-075.fig1.eps}}
 \caption{\label{SignalDist}The distribution of $\DM = M(K\pi\pis) - M(K\pi)$ 
 in the  HERAII data sample. The signal data sample is shown as 
 black points and the wrong charged D background as yellow histogram.}
\end{figure}
%%%% 
	 
%%%%
\begin{figure}%[htp]
\centering
\subfigure{
 \includegraphics[width=.49\textwidth]{H1prelim-08-075.fig2.eps}}
 \caption{\label{massD2} The distribution of $M(\dstar \pi)= 
M(K\pi\pis\pi) - M(K\pi\pis) + M_{\dstar}$ in the 
 HERAII data sample. The data are fitted with the sum of two
Breit-Wigner functions (with masses and widths fixed to the PDG values of the
$D_1(2420)^0$ and $D^\star_2(2460)^0$) and a background function, which is
parameterised as $p0 \cdot (M(\dstar \pi) - M_{\dstar} -M_{\pi})^{p1} \cdot
(1. + p2 \cdot M(\dstar \pi) + p3 \cdot M(\dstar \pi)^2)$ with four free
parameters. }
\end{figure}
%%%% 
	 
%%%%
\begin{figure}%[htp]
\centering
\subfigure{
\includegraphics[width=.49\textwidth]{H1prelim-08-075.fig3a.eps}}
\subfigure{
\includegraphics[width=.49\textwidth]{H1prelim-08-075.fig3b.eps}}
 \caption{\label{massPenta} The distribution of $M(\dstar p) =
 M(K\pi\pis p) - M(K\pi\pis) + M_{\dstar}$ for the high proton momentum
 selection ($p(p)>2\,{\rm GeV}$) in the 
 HERAI (left) and HERAII
 (right) data samples. The right charge data sample 
 is shown as  black points, the background from a \dstar\ Monte Carlo and the 
 wrong charged \dstar\ background as orange and yellow histograms.
 The right charge data are fitted with a 3 parameter function
 $p0 \cdot ( M(\dstar p) - M_{\dstar} - M_{p})^{p1} \cdot
\exp(p2 \cdot (M(\dstar p) - M_{\dstar} - M_{p}))$ (plus a Gaussian for the HERAI
data). }
\end{figure}
%%%% 
	 
%%%%
\begin{figure}%[htp]
\centering
\subfigure{
\includegraphics[width=.49\textwidth]{H1prelim-08-075.fig4a.eps}}
\subfigure{
\includegraphics[width=.49\textwidth]{H1prelim-08-075.fig4b.eps}}
 \caption{\label{massPenta2} The distribution of $M(\dstar p)$ for the high proton momentum
 selection ($p(p)>2\,{\rm GeV}$) in the 
 HERAII (left) and the sum of HERAI and HERAII
 (right) data samples.}
\end{figure}
%%%% 
	 

%%%%
\begin{figure}%[htp]
\centering
\subfigure{
\includegraphics[width=.49\textwidth]{H1prelim-08-075.fig5a.eps}}
\subfigure{
\includegraphics[width=.49\textwidth]{H1prelim-08-075.fig5b.eps}}
 \caption{\label{backward} The $\DM$ distribution 
 in the HERAI (left) and HERAII (right) data samples for events 
 in a $30\,{\rm MeV}$ window around $3.1\,{\rm GeV}$ in $M(\dstar p)$ compared
 to the corresponding distribution from the side bands 
 ($2.99$ to $3.07$ and $3.13$ to $3.21\,{\rm GeV}$) in the $M(\dstar p)$
 distribution, normalised according to the widths of the chosen sample regions.}
\end{figure}
%%%% 
	 

\end{document}




