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the determination of integrated and differential cross sections for the production of light mesons in the energy range up to 1  gev above threshold in proton - proton reactions is very important for the understanding of the underlying elementary mechanisms as well as for the interpretation of heavy ion results .
however , most of the high - precision and high - statistics experiments were performed near threshold . at higher energies ,
a large number of older data sets are available but only for integrated cross sections@xcite .    concerning the @xmath1 production at such energies ,
the disto collaboration provided a comprehensive set of measurements , including momentum and angular distributions as well as @xmath4 dalitz plots , all at three different beam energies ( 2.15 , 2.5 and 2.85 gev)@xcite . however , the provided angular distributions were integrated over the whole dalitz plot .
moreover , the disto collaboration studied the angular distribution of @xmath0 mesons in @xmath2 reactions at 2.85  gev beam kinetic energy@xcite .    in this work ,
we present new measurements of integrated and differential cross sections for the production of @xmath1 and @xmath0 mesons in @xmath2 reactions at 3.5  gev beam kinetic energy using the magnetic spectrometer hades@xcite ( * * h**igh * * a**cceptance * * d**i-**e**lectron * * s**pectrometer ) .
the reconstruction of @xmath0 and @xmath1 mesons was done via their decay into three pions ( @xmath5 ) .
the two protons and charged pions were identified using energy loss information in the drift chambers .
the @xmath6 was reconstructed via the missing mass method . to improve the momentum resolution ,
a kinematical fit was applied .
the background channels were removed by a cut on the probability of the fit .
the @xmath0 and @xmath1 mesons can be clearly identified as two peaks on top of a continous background in the two protons missing mass spectrum .
for the @xmath0 meson production , we present in fig . [ fig : omega ] the @xmath7 dalitz plot and polar angular distribution in the c.m . system .
all plots were corrected for the detector acceptance bin - by - bin using a corresponding factor extracted from a pluto@xcite + geant simulation .
we do not observe a strong contribution of resonances in the production and we find that the polar angular distribution of @xmath0 mesons is only slightly anisotropic . the determined cross section amounts to ( 137@xmath827 )  @xmath9b ( prelim . ) .
\a )   dalitz plot .
the thick line shows the phase space limit .
b ) polar angular distribution of @xmath0 emission in the c.m . system .
both plots are corrected for acceptance .
empty bins correspond to zero acceptance.,title="fig:",width=264 ] b )   dalitz plot .
the thick line shows the phase space limit .
b ) polar angular distribution of @xmath0 emission in the c.m . system .
both plots are corrected for acceptance .
empty bins correspond to zero acceptance.,title="fig:",width=264 ]      \a )   dalitz plot .
the thick line shows the phase space limit .
the data are corrected for acceptance .
empty bins correspond to zero acceptance .
b ) projection of the raw dalitz plot .
the dotted line shows the mass distribution as given by phase space .
the dashed line shows simulation of the mass distribution for production via @xmath3(1535 ) .
, title="fig:",width=264 ] b )   dalitz plot .
the thick line shows the phase space limit .
the data are corrected for acceptance .
empty bins correspond to zero acceptance .
b ) projection of the raw dalitz plot .
the dotted line shows the mass distribution as given by phase space .
the dashed line shows simulation of the mass distribution for production via @xmath3(1535 ) .
, title="fig:",height=207 ]    the @xmath4 dalitz plot ( fig .
[ fig : eta1]a ) shows a clear signal from the @xmath3(1535 ) resonance . to extract the relative contribution of the resonance to the production we simulated the @xmath10 mass distribution in two scenarios :    1 .
@xmath1 production according to phase space .
@xmath1 production via @xmath3(1535 ) resonance .
the resulting spectra were scaled to fit the measured data ( see fig . [
fig : eta1]b ) .
the relative contribution of @xmath3(1535 ) to the production was determined to be about 41% ( prelim . ) .
\a )   emission in the c.m
. system ( from resonance region ) .
b ) polar angular distribution of @xmath1 emission in the c.m . system ( from non - resonant region ) .
both spectra are corrected for acceptance .
empty bins correspond to zero acceptance.,title="fig:",width=264 ] b )   emission in the c.m .
system ( from resonance region ) .
b ) polar angular distribution of @xmath1 emission in the c.m .
system ( from non - resonant region ) .
both spectra are corrected for acceptance .
empty bins correspond to zero acceptance.,title="fig:",width=264 ]    the angular distribution of @xmath1 emission was determined for two regions of the dalitz plot :    1 .
the region where @xmath11 or @xmath12 @xmath13 2.8 gev@xmath14/c@xmath15 .
the @xmath1 production in this region is dominated by resonant production .
the region where @xmath11 and @xmath12 @xmath16 2.8 gev@xmath14/c@xmath15 .
the @xmath1 production in this region is dominated by non - resonant production .
the angular distribution for region i is clearly flat as shown in fig .
[ fig : eta]a , whereas that of region ii is strongly anisotropic ( fig . [
fig : eta]b ) .
the total production cross section was determined to be ( 211@xmath847 )  @xmath9b ( prelim . ) .
the hades collaboration gratefully acknowledges the support by bmbf grant 06mt9156 , 06gi146i , 06fy171 and 06dr5059 ( germany ) , by gsi ( tm - fr1 , gi / me3 , of / str ) , by excellence cluster universe ( germany ) , by grants ga as cr iaa100480803 and msmt lc 07050 ( czech republic ) , by grant kbn 5p03b 140 20 ( poland ) , by cnrs / in2p3 ( france ) , by grants mcyt fpa2000 - 2041-c02 - 02 and xuga pgid t02pxic20605pn ( spain ) , by infn ( italy ) , by grant ucy-10.3.11.12 ( cyprus ) , by intas grant 06 - 1000012 - 8861 and eu contract rii3-ct-506078 .
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we report on the exclusive production of @xmath0 and @xmath1 mesons in @xmath2 reactions at 3.5 gev beam kinetic energy . 
 production cross sections , angular distributions and dalitz plots of both mesons were determined . moreover , 
 the relative contribution of the @xmath3(1535 ) resonance in @xmath1 production at this energy was evaluated . 
 we conclude that @xmath1 mesons produced via @xmath3(1535 ) exihibit an isotropic angular distribution , whereas those produced directly show a strong anisotropic distribition . 
 @xmath0 mesons show a slightly anisotropic angular distribition . _ 
 keywords : _ 
 @xmath0 ; @xmath1 ; meson production ; proton - proton collisions pacs numbers : 14.40.be , 13.75.cs , 13.85.-t