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in heavy - ion (  ) as well as in proton - proton ( ) collisions , the measurements related to strange hadrons constitute unique tools to study the physics of the strong interaction . in this respect , given their strangeness content , the charged multi - strange baryons ( @xmath3 ) , ( @xmath4 ) , ( @xmath5 ) , ( @xmath6 )  are of certain importance . the interest in strangeness and specifically in and can be explained mainly by two reasons :    * the initial system formed by the projectiles is free from strange valence quarks , thus the strange quarks that compose the strange hadrons of the final state have to be produced during the process of the collisions ; * due to the identification via weak - decay topology reconstruction , the multi - strange baryons can be studied over a large momentum range , typically from @xmath7  @xmath8 up to @xmath9 . the resulting @xmath7 spectra then cover the region dominated by the soft processes and reach the energy scale where hard scattering mechanisms may prevail . a significant part of the investigation in  physics depends on our understanding of the production mechanisms ( soft and hard ) in the system , meaning as they occur in the benchmark system . the measurement of multi - strange particle spectra in collisions is the topic of this report . the data presented here are from a minimum bias ( mb ) sample of collisions at @xmath0 = 7 , collected at the lhc @xcite with the alice experiment @xcite during summer 2010 . the entire statistics presently analysed stands for about @xmath10 mb interactions . the study makes use of the two alice main tracking detectors placed at mid - rapidity , covering the full azimuth : the inner tracking system , composed of 6 cylindrical layers of high - resolution silicon detectors  @xcite , and the cylindrical time projection chamber ( tpc )  @xcite . the multi - strange hadron identification is performed using a combination of displaced - vertex finding , invariant mass analysis and particle identification ( pid ) method at the single track level ( in this analysis , compatibility selection based on the energy loss measurements from the tpc ) . the reconstruction of the , , , particles hinges on their respective charged weak decays , the so - called _ cascade _ structures . for each species of interest , the main characteristics and utilized decay channels are listed in table [ tab : maire - cascdecaychannel ] . the anti - baryons are similarly reconstructed via the decay channel involving the charge conjugates . lccccc particles & mass ( @xmath11 ) & @xmath12 ( ) & charged decay channel & b.r . + @xmath13 ( @xmath14 ) & @xmath15 & @xmath16 & @xmath17 & 63.9% + @xmath18 ( @xmath3 ) & @xmath19 & @xmath20 & @xmath21 & 99.9% + @xmath22 ( @xmath5 ) & @xmath23 & @xmath24 & @xmath25 & 67.8% +    the guidelines of the reconstruction algorithm , consisting of pairing a  or  baryon with an additional particle ( _ v0 _ structure combined with a so - called _ bachelor _ track ) , are sketched in @xcite and detailed in @xcite . the protocol to extract the signal counts per @xmath7 interval ( bin ) is also presented in @xcite . due to the large statistics available for the 7  data sample , and but also and can be studied distinctively . at central rapidity ( ) , the overall raw signal amounts to about @xmath26 counts for , as well as for , and about @xmath27 counts for as well as for its anti - particle . the upper part of the figure [ fig : maire - fig1-correctedspectra ] shows the four corrected spectra . they are normalised to the number of inelastic events ( inel ) . both spectra range from @xmath7 = 0.6 to 8.5 , while the spectra are measured between 0.8 and 5.0 . in order to extract the integrated yields , the data points are fitted with a tsallis function @xcite . the fits result in a good description of data ( @xmath28 close to unity ) and are further used to extrapolate the spectra in the non - measured low @xmath7 region ( @xmath29 of the total @xmath30 for or , @xmath31 for or ) .     as a function of transverse momentum , for , , , measured at central rapidity ( @xmath32 ) in inelastic events at @xmath0 = 7 . the upper panel shows the corrected spectra for the four different species together with their fits by a tsallis function . the lower panel presents the ratio between the measured data and the predictions returned by the tune perugia 2011 ( p2011 ) of pythia . ]    note that , provided the difference in the normalisation scheme chosen by alice ( inel ) and cms ( non - single diffractive , nsd ) @xcite , the ( ) spectra by both experiments are found to be in agreement within the limit of uncertainties . a significant part of our understanding of collisions is based on description by the monte carlo models ( mc ) . this is especially the case in the _ soft _ regime ( @xmath7@xmath33 2 - 3 ) . the confrontation with experimental measurements is necessary , as it spurs further improvements of such phenomenological approaches . the lower part of the figure [ fig : maire - fig1-correctedspectra ] shows the ratio between data and mc predictions . the data are here compared to the tune perugia 2011 ( tune s350 @xcite ) of the pythia model @xcite . although this specific tune provides an improved description of data with respect to earlier tunes ( tunes z2 and perugia 0 ) @xcite , it can still be seen that mc underestimates the measured spectra , up to a factor @xmath34 2 for the charged , @xmath34 5 for the . however it should be noted for ( ) that there is an agreement between mc and data at @xmath7 @xmath35 6 , where the fragmentation regime may already be reached . the figure [ fig : maire - fig2-ratioomegaoverxi - pt ] provides another viewpoint on the comparison of data to mc . it computes the ratio of ( ) to ( ) as a function of @xmath7 . as before , it can be noted the model tends to underpredict the particle ratio , by a factor @xmath342 . regarding the data ratio itself , it turns out the ratio first rises with @xmath7 , before seemingly saturating at a value of 0.15 , which could suggest that the hierarchy between and production becomes constant at high @xmath7 .     between ( + ) and ( + ) as a function of transverse momentum , for collisions at @xmath0 = 7 . the ratio is given for alice data as well as pythia perugia 2011 ( p2011 ) . as a consistency check , the ratio of the tsallis functions fitted to the data or to the model predictions is also shown . ] values ( @xmath36 ) for different species identified by the alice experiment in collisions , at @xmath0 = 0.9 @xcite and 7 . these values are compared to the isr parametrisation ( performed from the @xmath37 , k , p species in collisions at ) and star measurements in central @xmath38 collisions at @xcite . ]      the figure [ fig : maire - fig3-alicemeanpt - ppcollisions ] presents the alice preliminary values obtained for the mean @xmath7 ( @xmath36 ) of various identified particles , as measured in collisions at 7 . for comparison , the data are plotted together with results published by alice for data at @xmath0 = 0.9 @xcite as well as by star for the central @xmath38 collisions at @xmath39 = 0.2 @xcite . for a given particle studied in collisions , it appears that the @xmath36 rises with @xmath0 . at , the data come to reach the values obtained in the most central  collisions at rhic , raising the question of the physical similarities between these different systems at different energies . with the results presented in this report , the alice experiment provides the first lhc measurement of and at central rapidity . together with and results , it actually enables an extension of the excitation function in a system . this is of importance to define the baseline necessary for the studies related to the so - called _ strangeness enhancement _ besides , although the tune perugia 2011 is a priori the current most suitable pythia tune for the description of hyperons in collisions at lhc energies , it is observed that it underestimates the data at intermediate @xmath7 .
in the perspective of comparisons between proton - proton and heavy - ion physics , understanding the production mechanisms ( soft and hard ) in that lead to strange particles is of importance . 
 measurements of charged multi - strange ( anti-)baryons ( and ) are presented for collisions at @xmath0 = 7 . 
 this report is based on results obtained by alice ( a large ion collider experiment ) from the 2010 data - taking . 
 + taking advantage of the characteristic cascade - decay topology , the identification of , , and can be performed , over a wide range of momenta ( e.g. from 0.6 to 8.5 for , with the present statistics analysed ) . 
 the production at central rapidity ( @xmath1 ) as a function of transverse momentum , @xmath2 , is presented . 
 these results are compared to pythia perugia 2011 predictions .