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we report measurements of strange particle momentum distributions in jets from p+p @xmath4 collisions measured by the star experiment .
these results provide additional tests to qcd inspired models of fragmentation such as pythia @xcite or the modified leading log approximation ( mlla ) @xcite , beyond the usual comparisons to charged hadron momentum distributions .
furthermore , predictions for the modification of jet chemistry in heavy - ion collisions relative to p+p have been made @xcite .
these predictions show the @xmath5 and @xmath6 ratios in jets are expected to be higher in the presence of a medium .
it is therefore essential we test theoretical descriptions of identified particle momentum distributions in p+p jets , if predictions in the modification of heavy - ion jet chemistry are to be made .
finally , since jets are from hard processes , comparisons of particles yields in jets to inclusive spectrum measurements may help elucidate the contributions from hard processes to those measurements as a function of @xmath7 .
the data presented are from @xmath8 8 million jet - patch triggered p+p @xmath9 gev events recorded in 2006 by the star experiment .
the jet - patch trigger is designed to select events with jets , and thus requires energies above 8 gev to be deposited in an area @xmath10 within the electromagnetic calorimeter @xcite .
the time projection chamber ( tpc ) is used to detect the charged particles @xcite , while the barrel electromagnetic calorimeter , bemc , is used for neutral particles .
three jet finders are employed from the fast - jet package @xcite : @xmath11 , anti-@xmath11 and sis .
we select recoil jets with respect to the triggered jets to measure fragmentation functions .
this is because the triggered jets have a bias towards the neutral jet component .
the jets are found within a resolution parameter , r @xmath12 and a jet axis @xmath13 cut @xmath14 to ensure the jet area lies within the tpc / bemc acceptance .
the resolution parameter can be thought of as an effective jet radius in the @xmath15 plane .
the minimum @xmath7 cut for a charged particle is 200 mev / c , while the minimum calorimeter tower energy is 200 mev .
towers which match charged particles are removed from the jet to avoid over counting of electrons and minimum ionising particles ( mips ) .
no corrections are applied to the jet energy scale which means the reconstructed jet @xmath16 is likely to be less than the actual jet @xmath7 due to tpc / bemc detection inefficiencies , and missing neutral energy principally from undetected @xmath17 and @xmath18 particles .
studies are underway to determine a correction for this .
finally , in order to measure the momentum distributions of the @xmath19 , @xmath20 , and @xmath21 particles , v0s are identified within the jet area from tpc tracks .
the invariant mass distributions are calculated to extract the yields of these particles via their dominant decay channels : @xmath22 , @xmath23 , @xmath24 . in conjunction with a minimum @xmath16 cut of 1 gev / c
, a series of topological cuts are placed on the v0s to minimise the relative background contribution , and ensure the signal to background ratios are approximately the same for each particle .
the residual background after all cuts is not yet removed from the fragment yields .
strange particle momentum distributions as a function of the reconstructed jet @xmath16 are shown in figure [ fig1 ] .
the momentum distribution is expressed in @xmath25 , where @xmath26 and @xmath27 are the reconstructed jet and fragment @xmath7 respectively . for a particular particle species ,
the integral of the @xmath28 function gives its mean multiplicity per jet .
the uncertainties are statistical added in quadrature to the small differences obtained by comparing the three different jet finders .
a data point is the mid point value between the lowest and highest values the three jet finders give .
the measured v0 yields are not yet corrected for acceptance and tpc tracking inefficiencies .
the pythia predictions are obtained by processing pythia events with star s detector simulation , and running the track , jet , and v0 reconstruction software on the simulated output in the same way as the real data .
this ensures the pythia events are subject to the same acceptance restrictions / detector inefficiencies as the real data .
all pythia predictions shown in these proceedings are from version 6.4 with tune a. we find that pythia gives a reasonable description of the @xmath3 data .
jetset ( the jet production scheme in pythia ) has also been shown to describe @xmath29 fragmentation functions in @xmath30 collisions well , where the jet energies range @xmath31 gev @xcite .
furthermore , pythia has been shown to describe charged hadron momentum distributions in p+p collisions at the same center of mass energy @xcite . on the other hand , we note that the pythia description of @xmath1 and @xmath2 momentum distributions are less satisfactory .
although the predictions appear to predict the correct yield over all @xmath28 , they tend to over predict the yields at low @xmath28 and under predict the yields at intermediate @xmath28 . whether this is due to a mismatch in the reconstruction of pythia events and real data , or due to physics ,
is under investigation .    in figure [ fig2 ] ,
we show ratios of integrated yields @xmath32 and @xmath33 for @xmath34 gev / c as a function of reconstructed jet @xmath16 .
the analysis shows the @xmath32 ratio is below 1 showing the baryon asymmetry in the colliding system ( p+p ) is transferred to jets over all jet energies measured .
we also find the @xmath32 ratio is consistent with the value obtained from inclusive spectra measurements @xcite .
pythia also seems to reproduce the magnitude of the ratio .
the jaggedness of the predictions is due statistical fluctuations which are @xmath35 and not shown . regarding the @xmath33 ratios in jets , these are higher than values from inclusive spectrum measurements over all @xmath7 .
the inclusive spectrum measurement will be dominated by production below 1 gev / c .
when we compare the ratios in jets to the inclusive spectrum measurement above 1 gev / c , we find they are generally consistent .
this may mean that @xmath19 and @xmath21 spectrum measurements with @xmath34 gev / c have a dominant contribution from hard processes i.e. jet production .
however , measurements of the same ratio from the underlying event are needed to further qualify this observation .
we also find pythia again reproduces the magnitude of the ratio .    in figure [ fig3 ]
, we show the position of the maximum of the @xmath28 distribution , @xmath36 , for the various particles as a function of the reconstructed jet @xmath7 .
since the @xmath7 dependent tracking inefficiency / acceptance will distort the shape of the @xmath28 distribution , we correct the distributions using embedding which determines the v0 reconstruction efficiency .
a gaussian is fitted in the peak region to extract @xmath36 .
the fit range is chosen to avoid the region in @xmath28 affected by the minimum @xmath16 cut on the fragments .
in the mlla scheme , the position of the maximum can be described by the following relation @xcite ; @xmath37 where @xmath38 is a constant and @xmath39 is : @xmath40 where @xmath41 is the jet opening angle , and @xmath42 is the effective transverse momentum ( relative to the jet axis ) where a parton ceases to branch in the parton shower .
mlla predictions for momentum distributions of hadrons with mass @xmath43 typically assume @xmath44 @xcite .
equation [ equ : mlla1 ] then implies a scaling behaviour of @xmath36 with the mass of the hadron i.e. @xmath36 should decrease for the higher mass hadrons .
the value of @xmath36 should also increase with jet energy for a given hadron which is observed in figure [ fig3 ] for all particles .
however , we find that @xmath45 which is contrary to the expected scaling . on the other hand , @xmath46 and @xmath47 which is consistent with such a scaling assuming pions dominate particle production in jets .
a similar observation was made for @xmath48 fragmentation functions for similar jet energies in @xmath30 collisions @xcite . finally , we note in interest that if we extract the mode of the transverse rapidity , @xmath49 , distribution ( motivated by this study @xcite ) , we find a mass scaling in @xmath49 space i.e @xmath50 for a given reconstructed jet @xmath7 bin . for a given particle species ,
we also find @xmath51 increases with jet energy .    in figure [ fig4 ]
we show the momentum distributions of _ non - leading _ charged hadrons for the cases where the leading particle is a charged hadron , @xmath19 , or @xmath21 .
we want to investigate whether tagging jets according to the species of the leading hadron , preferentially selects on gluon or quark jets .
both measured data @xcite and theoretical predictions show hadron multiplicities are larger in gluon jets compared to quark jets : mlla gives the ratio 9/4 for gluon / quark jet multiplicities .
thus , if tagging jets with particle a preferentially selected gluon jets , and tagging jets with particle b preferentially selected quark jets , we would expect the jets associated with particle a to have more non - leading charged hadrons compared to jets associated with particle b. however , in figure [ fig4 ] we observe at given jet energy , the charged hadron multiplicities are the same for each of the tagged jets .
this might be expected for the highest jet @xmath16 bin where jet production is expected to be dominated by hard scattering of valance quarks , however at lower jet energies there should be mixture of quark and gluon jets @xcite .
therefore , our observation suggests quark / gluon jets can not be tagged in this way .
further studies are underway to confirm this .
in summary , we have shown measurements of strange particle momentum distributions . we have found that pythia describes the @xmath21 momentum distributions well , however we observe some deviations for the @xmath19 and @xmath20 data .
we have found that @xmath32 ratios ( @xmath34 gev / c ) in jets are consistent with values obtained from inclusive spectra .
@xmath52 ratios ( @xmath34 gev / c ) in jets were found to be similar to values obtained from inclusive spectra in the same @xmath16 range .
this may suggest that @xmath53 and @xmath21 production above 1 gev / c is dominated by hard processes in p+p @xmath9 gev collisions .
we investigated a mass scaling of the peak position of @xmath28 ( inferred from mlla ) , and found although @xmath46 and @xmath47 , @xmath45 .
finally , we have found tagging jets with leading strange baryons / mesons may not preferentially select on quark / gluon jets .
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measurements of strangeness production in jets help illuminate the qcd mechanisms in fragmentation . furthermore , they provide a crucial baseline for heavy - ion studies where modifications in jet chemistry have recently been predicted . 
 we present new results on strange particle production in jets from p+p @xmath0 = 200 gev collisions measured by the star experiment . 
 the momentum distributions of the @xmath1 , @xmath2 and @xmath3 particles are obtained using various jet finding algorithms , and then compared to various models . 
 strange particle ratios in jets are obtained and compared to values obtained from the inclusive spectra . 
 finally , we show jets tagged with leading strange baryons and mesons , in order to investigate whether gluon or quark jets can be isolated in this way .