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\def\NCA{\em Nuovo Cimento}
\def\NIM{\em Nucl. Instr. Methods}
\def\NIMA{{\em Nucl. Instr. 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}}
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\begin{titlepage}

%\noindent
%Date:     22.5.03   \\
%Editors:     A.~Kropivnitskaya, A.~Nikiforov, A.~Rostovtsev  \\
%Referees:    Eddi de Wolf, Tim Greenshaw       \\
%Comments by
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%{\it {\large version of \today}} \\[.3em]
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%Submitted to & \multicolumn{3}{r}{\footnotesize Electronic Access: {\it http://www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em] \hline
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                & & & \\
\multicolumn{4}{l}{{\bf
                International Europhysics Conference
                on High Energy Physics, EPS03},
                July~17-23,~2003,~Aachen} \\
                (Abstract {\bf 107} & Parallel Session & {\bf 5}) & \\
                & & & \\
\multicolumn{4}{l}{{\bf
                XXI International Symposium on
                Lepton and Photon Interactions, LP03},
                August~11-16,~2003,~Fermilab} \\
                & & & \\
                \hline
 & \multicolumn{3}{r}{\footnotesize {\it
    www-h1.desy.de/h1/www/publications/conf/conf\_list.html}} \\[.2em]
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\end{center}
\vspace*{2cm}

\begin{center}
\begin{Large}

{\bf Measurements of the Inclusive Photoproduction of
\boldmath{$\bf\eta$}, \boldmath{$\bf\rho^0$}, \boldmath{$\bf
f_0(980)$} and \boldmath{$\bf f_2(1270)$} Mesons at HERA}

\vspace*{1cm}

H1 Collaboration

\end{Large}
\end{center}

%\vspace{2cm}


\begin{abstract}

\noindent

Measurements are presented of the inclusive photoproduction of the
neutral mesons $\eta$, $\rho^0$, $f_0(980)$ and $f_2(1270)$ in
$ep$ interactions at HERA at an average $\gamma{p}$ collision
energy  of $210\,$GeV. Inclusive cross-sections are shown
differentially as a function of various kinematic variables and a
comparison is made with measurements of the photoproduction of
other particle species at HERA.

\end{abstract}

\vspace{1.5cm}

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\newpage

\section{Introduction}
The process by which quarks and gluons convert to colourless
hadrons is one of the outstanding problems in particle physics.
The theory of perturbative quantum chromodynamics (QCD) is not
applicable and phenomenological models based on the laws of
thermodynamics are often used~\cite{Hagedorn,Tsallis,Beck}. High
energy particle collisions which give rise to large multiplicities
of particles produced with low values of transverse momentum
provide an opportunity to study hadronisation. This paper presents
precision measurements made by the H1 experiment of the inclusive
photoproduction of various species of neutral mesons in $ep$
collisions at HERA.

Although the production of long-lived hadrons and hadronic
resonances has been studied in detail at LEP in $Z$
decays~\cite{delphireview}, measurements made in high energy
hadronic collisions are sparse. In hadronic collisions it has been
found that particle production at central values of rapidity is
independent of the type of the colliding hadrons and is governed
by the fundamental properties of the QCD vacuum. In heavy ion
collisions phase transitions can take place to give states in
which quarks become free to move about within a confinement volume
much larger than the volume of a typical hadron (Quark-Gluon
Plasma). These phase transitions also result in a change in the
properties of the hadronic final state. Such measurements are
presently being carried out at RHIC in heavy ion collisions at
$\sqrt{s_{NN}}=200$~GeV. It is therefore important to study
particle production in light hadron collisions at about the same
energy. This is possible at the H1 experiment at the HERA collider
which so far has collected millions of multi-hadronic
photoproduction events. Measurements of the inclusive
photoproduction of charged particles~\cite{HERA_ch}, long-lived
hadrons like $K^0_S$ mesons, $\Lambda^0$ baryons~\cite{HERA_L0}
and charmed mesons~\cite{HERA_charmed} have already been reported
by the H1 and ZEUS collaborations. The particle spectra measured
at HERA are found to display interesting
regularities~\cite{rostov}.

In this report, the first measurements of the inclusive
photoproduction of the neutral hadronic resonances $\eta$,
$\rho^0$, $f_0(980)$ and $f_2(1270)$ at HERA are presented. The
measurements are based on about four million multihadronic events
recorded by the H1 detector at an average photon-proton
centre-of-mass energy $W=210\,$GeV in the 2000 running period
which correspond to an integrated luminosity of $38.7$~pb$^{-1}$.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{H1 detector}
\label{sec:selection}

The H1 detector is described in detail
elsewhere~\cite{Abt:1997xv}. A brief account of the components
that are most relevant to the present analysis is given here.
These are the positron tagger, the central tracker and the liquid
argon (LAr) calorimeter. The direction of the $z$-axis is chosen
to be along the proton beam direction and the polar angle $\theta$
is defined with respect to this axis.  The variables rapidity and
pseudorapidity are defined by
$y=\frac{1}{2}\ln\frac{E+p_z}{E-p_z}$ and
$\eta=-\ln(\tan(\theta/2))$, respectively.

The positron tagger, located at 33\,m from the interaction point
in the positron direction, measures the energy of the scattered
positron and, in conjunction with the photon detector, the
luminosity by exploiting the Bethe-Heitler process $ep\to
e'p'\gamma$. The photon detector is located 100\,m from the
interaction point, in the positron direction.

The central track detector consists of the central jet chamber
(CJC), multi-wire proportional chambers for triggering purposes
and two additional drift chambers which measure accurately the
$z$-coordinates of charged particle tracks. The pseudorapidity
range covered by the central track detector is $|\eta|<1.5$. The
CJC has 56 sensitive wire layers and is placed inside a uniform
magnetic field of strength 1.15\,T. The CJC measures the
transverse momentum of charged particles with a resolution of
$\sigma_{p_T}/p_T \approx 0.009 \times p_T$[GeV]$\, \oplus \,
0.015$.

The LAr calorimeter surrounds the tracking system and covers the
angular range $4^\circ < \theta < 154^\circ$. The calorimeter is
used here for photon reconstruction.

Photoproduction events are selected by requiring the presence of a
scattered positron in the small angle positron tagger. For these
events the photon virtuality is restricted to $Q^2 <
10^{-2}\,$GeV$^2$. The energy measured by the positron tagger is
used in the determination of the total $\gamma p$ collision
energy, $W$. In the main detector, $\gamma p$  events are
triggered by demanding the presence of at least three tracks in
the CJC in addition to a signal in the positron tagger.

\section{Event selection}

In order to reduce the non-$ep$ background contamination and to
ensure good reconstruction of the event kinematics, the following
selection criteria are applied in this analysis:

\begin{itemize}

\item

Photoproduction events are required to lie within the interval
$174<W<256$ GeV. This corresponds to an average photon-proton
collision energy of $W = 210\,$GeV.

\item

The trigger conditions are verified by selecting only multi-hadron
events with more than two reconstructed tracks pointing to the
common event vertex.

\item

In order to suppress random coincidences between Bethe-Heitler
events, which occur at a high rate, and beam-gas background in the
main H1 detector, events are rejected if a photon with energy
$E_\gamma>2\,$GeV is detected in the photon tagger.

\item

The event vertex reconstructed from the tracks of charged
particles is required to lie within $\pm 35\,$cm of the nominal
$z$-position of the interaction point, corresponding to about a
$3\sigma$ cut on the length of the interaction region which is
defined by the longitudinal size of the proton bunch.

\end{itemize}
In total about $3.7 \times 10^6$ events satisfy the above
selection criteria.

The extraction of cross sections from the observed event rates
requires the detailed simulation of the response of the H1
detector to photoproduction interactions. The PYTHIA~6.1 Monte
Carlo~(MC) event generator~\cite{PYTHIA} is used to simulate
multihadron events resulting from photon-proton interactions. The
hadronisation process is modelled using the LUND string
fragmentation scheme~(JETSET~\cite{JETSET}). The photoproduction
events generated by PYTHIA are passed through a simulation of the
H1 detector based on GEANT~\cite{GEANT} and then through the same
reconstruction and analysis chain as used for the data.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\section{Inclusive cross section determination}

\subsection{The $\bf \eta$ meson cross section}

The $\eta$ mesons are reconstructed via their two-photon decay
mode. The photons are identified as isolated LAr calorimeter
clusters with energy greater than $200\,$MeV and polar angle in
the range $0.5 < \theta < 2.6$. More than $90\%$ of the cluster
energy is also required to be contained in the electromagnetic
section of the LAr calorimeter. Figure 1c) shows the energy
distribution of the clusters which satisfy these requirements. It
is reasonably described by the MC simulations.

The transverse radius of an electromagnetic cluster about the axis
of the shower, $R_{tr}$, is defined using the expression:

\begin{center}
$R_{tr}=\frac
1A\sum_i\limits\frac{E_ir_i^2}{V_i},\quad\,\,\,\,\,\,\,\,\, $ with
$\quad \,\,\,\,\,\,\,\, A=\sum_i\limits\frac{E_i}{V_i}\,,$
\end{center}

\noindent where $E_i$ and $V_i$ are the energy and volume of the
$i^{\rm th}$ LAr calorimeter cell in the cluster and $r_i$ denotes
the radial distance of the cell from the shower axis. The $R_{tr}$
distribution for the selected event sample is shown in figure~1d).
The tail at large values of $R_{tr}$ is caused by hadrons absorbed
in the LAr calorimeter. To separate the genuine electromagnetic
clusters from clusters produced by hadrons, $R_{tr}$ is required
to be smaller than $8\,$cm.

In addition, clusters associated with charged tracks are rejected.
Figure~1e) shows the distribution of the distance between the
cluster centre and the closest reconstructed charged track,
$D_{CT}$. The peak at low $D_{CT}$ values corresponds to clusters
associated with charged particles. To reduce this background,
$D_{CT}$ is required to be larger than $15\,$cm.

Since $\eta$ mesons decay isotropically, the distribution of the
cosine of the angle~$\alpha$ between the photon's momentum in the
meson rest frame and the direction of the meson in the $\gamma p$
rest frame is expected to be flat. Conversely, the combinatorial
background is expected to be strongly anisotropic. The
distribution of $|\cos(\alpha)|$ is shown in figure~1f). To reduce
the combinatorial background, the requirement that $|\cos(\alpha)|
< 0.7|$ is made.

The reconstruction efficiency for $\eta$ mesons is calculated
using the Monte Carlo simulation described above. This efficiency
is about $30\%$ for $\eta$ mesons with transverse momenta below
$8$~GeV/c. Above this value, the two clusters in the LAr
calorimeter produced by the $\eta$ decay photons start to merge.
For $\eta$ mesons with transverse momentum below $3\,$GeV/c, the
large combinatorial background precludes a reliable identification
of the signal. Therefore, the kinematical interval chosen for the
$\eta$ meson cross section measurements is restricted to $3 < p_T
< 8\,$GeV/c.

In figure~2 the spectrum of the invariant mass of the photon pairs
is shown. This mass spectrum is fitted using the sum of a Gaussian
function for the $\eta$ meson signal and a polynomial to describe
the combinatorial background. In the fit, the nominal resonance
mass is fixed to the Particle Data Group~(PDG) value, while the
width is fixed to the value obtained in the MC calculation.

To obtain differential cross sections, the data sample is divided
into two intervals of rapidity and of transverse momentum. The fit
procedure is applied in each bin separately.
%The results of the fit and final differential cross sections for
%$\eta$ meson photoproduction are given in tables~1 and~2.
The first part of the uncertainty on the cross section values
represents the statistical error of the fit and is about $15\%$.
The second part represents the systematic uncertainty. The major
sources of systematic error are the variation of the assumptions
about the combinatorial background shape in the fit
procedure~($11\%$), the uncertainty in the detector acceptance and
efficiency calculations~($9\%$), and the precision of the
luminosity measurement~($2\%$).

\subsection{The \boldmath{$\bf \rho^0$}, \boldmath{$f_0(980)$} and
\boldmath{$\bf f_2(1270)$} meson cross sections}

The $\rho^0$, $f_0(980)$ and $f_2(1270)$ mesons are reconstructed
through their $\pi^\pm \pi^\mp$ decay mode. Any charged track
found in the CJC with $p_T > 0.15\,$GeV/c and polar angle $0.5 <
\theta < 2.6$ is taken as a charged pion candidate. This limits
the kinematical interval for the reconstructed neutral mesons in
rapidity space to be $|y_{lab}|<1$. The multiplicity and polar
angle distributions of the selected charged tracks are shown ion
figures~1a) and~1b), respectively. They are reasonably described
by the MC simulation.

To extract the $\rho^0$, $f_0$ and $f_2$ signals, the two-particle
invariant mass spectrum for like-sign pions $m(\pi^\pm\pi^\pm)$ is
subtracted from the spectrum of for opposite-sign pions
$m(\pi^\pm\pi^\mp)$. The resulting distribution is shown in
figure~3, where the $\rho^0$, $f_0$, and $f_2$ signals are clearly
seen above the residual combinatorial background.

In order to extract a cross section for a given meson, the
subtracted invariant mass distribution is fitted using a function
composed of three parts,
$$
Fit(m)=BG(m)+\Sigma(BW(m))+\Sigma(Ref(m))\,,
$$
corresponding to the combinatorial background, signal and
reflection contributions respectively. The combinatorial
background term, $BG(m)$, is taken to have the form
$$
BG(m)=a_1(m-2m_{\pi})^{a_2}e^{-a_3m-a_4m^2}
$$
where $m_\pi$ is the charged pion mass. The signal function
describes three resonances,
$$
\Sigma(BW(m))=BW_{\rho^0}(m)+BW_{f_0}(m)+BW_{f_2}(m)\,,
$$
where $BW(m)$ is the relativistic Breit-Wigner function,
$$
BW(m)=A\frac{m_0m\Gamma(m)}{(m^2-m_{0}^{2})^2+m_{0}^{2}\Gamma^{2}(m)}\,,
$$
with $\Gamma(m) = \Gamma_{0} \left( \frac{q}{q_0} \right)^{2l+1}
\frac{m_0}{m}\,,$ and $l=0$ for the $f_0$, $l=1$ for the $\rho^0$,
and $l=2$ for the $f_2$ meson. The momentum of the decay products
in the rest frame of their parents is $q$, and $q_0$ is the decay
momentum when $m = m_0$, the nominal resonance mass. In the fit
procedure the resonance masses remain as free parameters while
their widths are fixed to the Particle Data Group~(PDG) values.
For the $f_0(980)$, the width is only poorly known and is hence
allowed to vary from $50$ to $100\,$MeV. The results should be
taken as model-dependent measurements, which assume no
interference of the $f$-signals with the background and no
contribution to the $f$-meson peaks from $\pi^+\pi^-$ decays of
other resonances at similar masses.

The third term, $\Sigma(Ref(m))$, represents the sum of the
reflections in the two-pion mass spectrum originating from other
resonance decays. Two major reflections contribute to the mass
region of interest:

\begin{itemize}

\item a reflection from the decay $K^*(982)\rightarrow K^\pm
\pi^\mp$ when the $K^\pm$ is misidentified as a charged pion;

\item a reflection from the decay $\omega(782)\rightarrow \pi^\pm
\pi^\mp \pi^0$ when the $\pi^0$ is not observed.

\end{itemize}

The shape of the reflection contributions is taken from the MC
calculations and their normalization with respect to the $\rho^0$
signal is allowed to vary within broad intervals
$$
\frac{N_{K^{*0}+\tilde K^{*0}}Br(\pi^\pm
K^\mp)}{N_{\rho^0}}=0.35\pm0.25 \quad \quad \quad \quad
\frac{N_{\omega}}{N_{\rho^0}}=1.0\pm0.2 \,.
$$
These cover the corresponding particle production ratios measured
at hadron colliders~\cite{reflection_ISR} and in $e^+e^-$
annihilation~\cite{reflection_LEP}.

Figure~3 shows the result of the fit made in the mass range from
$0.55$ to $1.7\,$GeV/c$^2$. The contribution of the reflections is
also shown. The $\rho^0$ resonance in the data is shifted towards
low mass. A similar effect has been reported by the LEP
experiments~\cite{mass_shift}. It was conjectured that this arises
as a result of final state interactions between the resonance and
incoherently produced pions~\cite{BEpaper}.

In order to calculate the meson production cross sections,
detector acceptances and efficiencies are calculated using a Monte
Carlo simulation of $\rho^0$ mesons. The $f_0(980)$ and
$f_2(1270)$ are not generated by JETSET so the $\rho^0$ efficiency
is assumed for these with correction factors
$C~=~\varepsilon_{rec}^i/\varepsilon_{rec}^{\rho^0}$ $(i=f_0,f_2)$
being applied in the measured $p_T$ and $y$ intervals. Here,
$\varepsilon_{rec}$ is the efficiency for $\pi^+\pi^-$ pair
reconstruction in the corresponding mass region.

To obtain the differential cross sections, the data sample is
divided into 4 bins in rapidity and 7 bins in transverse momentum
and the fit procedure is applied in each bin separately. The
$\rho^0$ and $f_2(1270)$ resonance signals are clearly seen in all
$p_T$ intervals, while the $f_0(980)$ resonance is visible in the
$\pi^\pm\pi^\mp$ spectra for $p_T < 1.5\,$GeV/c only.
%The results of the fit and the differential cross sections for the inclusive
%photoproduction of $\rho^0$, $f_0$, and $f_2$ mesons are given in table~2.
The first part of the error on the cross section represents the
statistical error and is about $10\%$. The second part represents
the quadratic sum of the systematic uncertainties. The major
sources of systematic uncertainty arise from to the variation of
the assumptions about the normalisation of the contribution of
reflections in the fit procedure (up to $20\%$), the variation of
the assumption about the $f_0$-meson width (up to $40\%$ in the
case of the $f_0$), the uncertainty in the detector acceptance and
efficiency calculations (up to $13\%$) and the precision of the
luminosity measurement~($2\%$).


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Discussion of results}

In figure~4, the measured differential cross sections for
inclusive photoproduction of the light resonances $\eta$,
$\rho^0$, $f_0(980)$ and $f_2(1270)$ are presented as a function
of rapidity and transverse momentum. Within the measured rapidity
interval the resonance production rates are flat in rapidity,
whilst the transverse momentum spectra follow a power law. Similar
observations have already been made in charged particle production
at HERA energies. A change from the exponential $p_T$ spectra
observed at lower energies to a power law is generally attributed
to the onset of hard parton scattering and has been successfully
described by a thermodynamics-based approach~\cite{Hagedorn}. It
is interesting to note that both the large-$p_T$ tail, where the
hard parton scattering is expected to define the particle spectrum
shape, and the low-$p_T$ part of the spectrum, where the hadrons
predominantly originate from the cascade decays of heavier
resonances, are described with the same simple power law function.
This, in addition to the intrinsic complexity of a hadronising
partonic system, makes a thermodynamic analogy attractive also at
high energies. A recently proposed generalisation of standard
thermodynamics to non-extensive complex systems~\cite{Tsallis}
leads to the appearance of a power-law energy distribution rather
than a Boltzmann-like spectrum.

In figure~5, one of the universal features observed in the
behaviour of long-lived hadrons~\cite{rostov} is investigated with
the light resonances measured here. The double differential cross
sections for $\eta$, $\rho^0$, $f_0(980)$ and $f_2(1270)$
production are presented as a function of $m + p_T$, where $m$ is
the meson's nominal mass. The cross sections follow closely the
same power law function as that observed for pions at the same
$\gamma{p}$ collision energy, once allowance has been made for the
different isospin and spin of the various species of hadrons. Pion
production has not been measured at HERA, so the pion results are
derived from the measured charged particle spectrum by reducing
this by $40\%$ to account for the production of kaons, protons and
long-lived charged leptons. The production rates for the measured
hadrons are observed to depend primarily on variables such as the
hadron's mass and transverse momentum rather than on their
internal structure. This nontrivial fact supports a thermodynamic
picture of particle production in high energy collisions. In
addition, the observed regularity in the measured hadron spectra
suggests a similar production mechanism for light long-lived
hadrons, low mass vector mesons and orbitally excited tensor
mesons.

The significant $\rho^0$ mass shift observed in this experiment
and by the OPAL and DELPHI collaborations~\cite{mass_shift}
requires further investigation. It is important to understand the
origin of this effect in the context of the expected distortion of
the nominal mass and width of hadronic resonances in heavy ion
collisions at RHIC, where a similar effect could be attributed to
the formation of a quark gluon plasma.

\section{Summary}

The first measurements of cross section for the inclusive
photoproduction of the light resonances $\eta$, $\rho^0$,
$f_0(980)$, and $f_2(1270)$ at a $\gamma{p}$ average collision
energy of $210$~GeV are reported. The measured differential
spectra display features similar to those observed in studies of
light, long-lived hadrons.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section*{Acknowledgements}

\noindent We are grateful to the HERA machine group whose
outstanding efforts have made and continue to make this experiment
possible. We thank the engineers and technicians for their work in
constructing and now maintaining the H1 detector, our funding
agencies for financial support, the DESY technical staff for
continual assistance, and the DESY directorate for the hospitality
which they extend to the non-DESY members of the collaboration.

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\bibitem{reflection_LEP}
ALEPH Collab., D.~Busculic {\it et al.}, Z.Phys. {\bf C69}, (1996)
379.

\bibitem{mass_shift}
DELPHI Collab., P.~Abreu {\it et al.}, Z.Phys. {\bf C65}, (1995)
587.\ OPAL Collab., P.~D.~Acton {\it et al.}, Z.Phys. {\bf C56},
(1992) 521.

\bibitem{BEpaper}
G.~D.~Lafferty, Z.Phys. {\bf C60}, (1993) 659.

\end{thebibliography}

%\clearpage
%\input{Table_12.tex}
%\input{Table_34.tex}

\clearpage

\begin{figure}[ht]
    \setlength{\unitlength}{1cm}
    \begin{center}
        \begin{picture}(17.0,20.0)
            \epsfig{file=mcvsdata_color.eps,width=17.0cm}
            \put(-13.3,10.8){\Large $N_{tracks}$}
            \put(-5.3,10.8){\Large $\theta_{tracks}$}
            \put(-13.3,5.8){\Large $E_{clust},GeV$}
            \put(-5.5,5.8){\Large $R_{tr},cm$}
            \put(-13.0,0.6){\Large $D_{ct},cm$}
            \put(-5.4,0.6){\Large $|cos\alpha|$}
            \put(-16.0,15.3){\Large $N$}
            \put(-8.3,15.3){\Large $N$}
            \put(-16.0,10.3){\Large $N$}
            \put(-8.3,10.3){\Large $N$}
            \put(-16.0,5.0){\Large $N$}
            \put(-8.3,5.0){\Large $N$}
            \put(-10.2,14.5){\Large $a)$}
            \put(-2.6,14.5){\Large $b)$}
            \put(-10.2,9.4){\Large $c)$}
            \put(-2.6,9.4){\Large $d)$}
            \put(-10.2,4.4){\Large $e)$}
            \put(-7.2,4.4){\Large $f)$}
        \end{picture}
        \caption{Comparison of various data and Monte Carlo distributions
following the application of the selection criteria discussed in
the text. The data and Monte Carlo distributions are normalized to
the same area. a) Charged track multiplicity. b) Polar angle
distribution of charged tracks. c) LAr cluster energy. d)
Transverse radius of the clusters. e) Distance between cluster and
closest track. f) $|\cos(\alpha)|$ distribution for
electromagnetic cluster pairs with $p_T>2\,$GeV.}
        \label{fig:monitor}
    \end{center}
\end{figure}

\begin{figure}[ht]
\center \setlength{\unitlength}{1cm} \hspace*{1.0cm}
\begin{picture}(15.0,10.0)
\epsfig{file=Fig_eta_color.eps,width=13.0cm}
\put(-4.0,-0.1){\large\bf $M_{\gamma\gamma}~[GeV]$}
\put(-13.3,4){\begin{sideways}\Large\bf
$dN/dM~[1/GeV]$\end{sideways}} \put(-5.,10.5){\color{red}\Large\bf
H1 prelim.} \put(-6.8,9.5){\color{darkgreen}\large$3<p_T<8$ GeV,
$\;|y|<1$} \put(-9.8,9.8){\color{blue}\Large$\eta$}
\end{picture}
\caption{Two-photon mass spectrum after the application of the
selection criteria discussed in the text. The smooth curve
represents the result of a fit to the sum of a Gaussian and a
third order polynomial.} \label{fig:signaleta}
\end{figure}

\begin{figure}[ht]
\center \setlength{\unitlength}{1cm} \hspace*{1.5cm}
%\vspace*{4.0cm}
\begin{picture}(15.0,10.0)
\epsfig{file=Fig_rho_color.eps,width=15.0cm}
\put(-9.0,-0.1){\large\bf $M(\pi^+\pi^-)~[GeV]$}
\put(-15.6,5){\begin{sideways}\Large\bf
$dN/dM~[1/GeV]$\end{sideways}} \put(-8.5,14.){\color{red}\Large\bf
H1 prelim.} \put(-10.2,12.){\color{darkgreen}\Large$\;|y|<1$}
\put(-5.3,12.5){\Large\color{blue}$\rho^0$}
\put(-4.5,5.8){\Large\color{DeepPink3}$f_0$}
\put(-3.8,4.5){\Large\color{red}$f_2$}
\put(-9.5,9.2){\sl\large\color{DeepPink3} comb.}
\put(-10.6,8.6){\sl\large\color{DeepPink3} background}
\put(-9.7,7.9){\sl\large $\omega$}
\put(-10.1,6.5){\sl\large\color{red} $K^*(892)^0$}
\end{picture}
%\put(-10.4,12.8){\color{blue}\Large\underline{raw data}}
%\put(-4.,12.8){\color{blue}\Large\underline{final data}}
\caption{The $\pi^+\pi^-$ invariant mass spectrum following the
subtraction of the like-sign spectrum. The full curve shows the
results of the fit discussed in the text. In the left plot the
dashed curve corresponds to the contribution of residual
non-resonant background; the dotted and dash-dotted curves
describe the contributions from $\omega$ and $K^*$ reflections,
respectively. In the right plot the points represent the data
after subtraction of the background and the reflections.}
\label{fig:signalrho}
\end{figure}

\begin{figure}[ht]
\center \setlength{\unitlength}{1cm}
%\hspace*{1.5cm}
%\vspace*{4.0cm}
\begin{picture}(17.0,16.0)
\epsfig{file=sigma_color.eps,width=16.0cm}
\put(-16.3,8){\rotatebox[origin=c]{90}{\Large\bf
$d\sigma/dy[nb]$}} \put(-8.7,8){\rotatebox[origin=c]{90}{\Large\bf
$d\sigma/(dydp_T^2)[nb/(GeV)^2]$}} \put(-11.7,0.3){\large\bf $y$}
\put(-5.,0.3){\large\bf $p_T[GeV]$} \put(-9.9,13.5){\large\bf
$a)$} \put(-2.2,13.5){\large\bf $b)$}
\put(-5.7,5.7){\color{blue}\Large\bf $-\:\rho^0$}
\put(-5.7,4.6){\color{DeepPink3}\Large\bf $-\:f_0$}
\put(-5.7,3.6){\color{red}\Large\bf $-\:f_2$}
\put(-5.7,2.5){\Large\bf $-\:\eta$}
\put(-9.5,15.6){\color{red}\Large\bf H1 prelim.}
\end{picture}
\caption{The differential photoproduction cross sections for
$\eta$, $\rho^0$, $f_0(980)$ and $f_2(1270)$ mesons plotted as a
function of (a)~rapidity for $p_T > 0\,$GeV ($\rho^0$, $f_0$ and
$f_2$) and $3 < p_T < 8\,$GeV~($\eta$) and (b)~transverse momentum
for $y_{lab} = 0$.} \label{fig:sigma}
\end{figure}

\begin{figure}[ht]
\center \setlength{\unitlength}{1cm}
%\hspace*{1.5cm}
%\vspace*{4.0cm}
\begin{picture}(17.0,16.0)
\epsfig{file=sigmaptplusm_color.eps,width=16.0cm}
\put(-16.2,8){\rotatebox[origin=c]{90}{\Large\bf
$1/(2j+1)d\sigma/(dydp_T^2)[nb/(GeV)^2]$}}
\put(-9.0,0.1){\large\bf $m+p_T[GeV]$}
\put(-13.5,6.45){\color{blue}\Large\bf $-\:\rho^0$}
\put(-13.5,5.6){\color{DeepPink3}\Large\bf $-\:f_0$}
\put(-13.5,4.8){\color{red}\Large\bf $-\:f_2$}
\put(-13.5,3.95){\Large\bf $-\:\eta$} \put(-13.5,3.1){\Large\sl
$-\:\pi^+$ published } \put(-5.,13.){\color{red}\Large\bf H1
prelim.}
\end{picture}
\caption{The differential photoproduction cross sections for
$\eta$, $\rho^0$, $f_0(980)$ and $f_2(1270)$ mesons plotted as a
function of $(m+p_T)$, with $m$ being the nominal meson mass. The
open symbols show the $\pi^+$ production cross section calculated
from measurements of the charged particle spectrum in
photoproduction.} \label{fig:compare}
\end{figure}


\end{document}
