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[ intro ] the measurement of heavy - flavour production as a function of the multiplicity of charged particles produced in hadronic collisions is sensitive to the interplay between hard and soft contributions to particle production and could give insight into the role of multi - parton interactions ( mpis , i.e. several hard partonic interactions occuring in a single collision between two nucleons ) .
particle production at the lhc is expected to have a substantial contribution from mpis in pp ( p  pb ) collisions , where the highest multiplicity values observed are similar to the ones of peripheral cu  cu ( pb  pb ) collisions at rhic ( lhc ) . measurements by the cms collaboration of jet and underlying event properties have shown better agreement with models including mpis @xcite .
measurements by the alice collaboration of minijets point to an increase of mpis with increasing charged - particle multiplicity @xcite . in the heavy - flavour sector
several measurements have been performed @xcite .
in particular alice found an approximately linear increase of j/@xmath8 yield as a function of multiplicity in pp collisions at @xmath0 = 7 tev @xcite .
moreover it is interesting to compare heavy - flavour production in p 
pb collisions with pp results to test whether the yield and the transverse momentum distributions follow a scaling with the number of binary nucleon 
nucleon collisions in the p  pb collision .
this scaling is expected for particles produced in hard ( high virtuality ) partonic scattering processes in the absence of nuclear effects in the initial or in the final state of the p  pb collision .
this is studied by measuring the nuclear modification factor @xmath9 , defined as the ratio of the @xmath5-differential cross section measured in p 
pb collisions to that measured in pp collisions scaled by the mass number a of the pb nucleus .
the d - meson @xmath9 in minimum bias p  pb collisions was found consistent with unity for @xmath10 1 gev/@xmath11 within uncertainties of about 20% @xcite , showing that cold nuclear matter ( cnm ) effects ( nuclear modifications of the parton distribution functions ( pdf ) , @xmath12 broadening , energy loss in cold nuclear matter ) do not strongly affect charm - quark production in p
 pb collisions @xcite .
it is interesting to measure the nuclear modification factor in p 
pb collisions in classes of the event activity , because the latter is related to the collision centrality ( i.e. impact parameter as well as the number of participating nucleons and binary collisions ) of the p  pb collisions .
the measurement of the @xmath9 requires to estimate the average number of binary collisions @xmath7 for the event activity intervals used in the analysis .
alice has identified in p 
pb collisions several sources that can induce a bias in the centrality determination based on particle multiplicity measurement @xcite .
this bias have been observed in the measurement of the nuclear modification factor of charged particles in p 
pb collisions in multiplicity classes @xcite .
this work investigates whether such a bias is also present for @xmath6 mesons .
the results are presented in form of the @xmath6-meson self - normalized yield in pp and p  pb collisions , defined as @xmath13 where @xmath14 is the d - meson per - event yield in multiplicity intervals , @xmath15 the multiplicity integrated per - event yield , @xmath16 are the corresponding reconstruction and selection efficiencies and @xmath17 is the trigger efficiency ( only relevant in pp ) .
furthermore , the binary scaling is studied in several event activity classes via the @xmath18 ratio , defiled as : @xmath19 for the v0a and zna event activity estimators respectively , defined in the next section .
these two observables represent different ways to study the multiplicity dependence of @xmath6-meson production in p 
pb collisions : the self - normalized yields are more focused on the study of mpis , while @xmath18 reflects the scaling of charm production in p 
pb collisions relative to pp collisions .
the alice detector is described in @xcite .
the data samples analyzed are from the 2010 pp run ( 300 @xmath20 events at @xmath0 = 7 tev ) and the 2013 p 
pb run ( 100 @xmath20 events at @xmath1 = 5.02 tev ) .
details on the trigger and event selections can be found in @xcite .
events are divided in event activity classes .
three event activity estimators have been used :    * @xmath21 : number of track segments reconstructed in the silicon pixel detector ( spd - two innermost layers of the inner tracking system - @xmath22 ) ; * v0a : signal amplitude of the a - side vzero scintillator ( @xmath23 - pb going direction for p  pb collisions ) ; * zna : energy from nuclear fragments in the a - side zero degree neutron calorimeter ( 112.5 m from interaction point - pb going direction for p  pb collisions ) .
the self - normalized yields are obtained in @xmath21 intervals , while the @xmath18 analysis adopts v0a and zna multiplicity classes ( 0 - 20% , 20 - 40% , 40 - 60% , 60 - 100% ) .
the analysis is based on the reconstruction of @xmath6 mesons in their hadronic decay channels ( @xmath24 , @xmath25 , @xmath26 ) in the alice central barrel ( @xmath270.9 ) , exploiting the excellent vertex resolution and particle identification capabilities of the alice detector as described in @xcite .
@xmath6-meson efficiency corrections in pp and p  pb collisions are determined with monte carlo simulations based on pythia 6.4.21 and hijing event generators .
a fraction of the total @xmath6-meson yield comes from the decay of b mesons . for the @xmath18 analysis
this contribution was estimated based on fonll pqcd calculations as described in @xcite , while for the self - normalized yield analysis no subtraction has been performed , assuming that the fraction of feed - down @xmath6 mesons does not depend on multiplicity and cancels in the ratio of eq .
a deviation from this assumption has been considered to estimate the corresponding systematic uncertainty . the pp and p 
pb corrected yields have been used to compute the @xmath18 as in eq .
2 . the average values of @xmath28 in the four v0a and zna event activity classes have been evaluated as follows :    * v0a : the @xmath29 values have been obtained for each v0a multiplicity interval with the approach used for pb  pb collisions , i.e. via a fit to the v0a multiplicity distribution based on the glauber model for the collision geometry and a two - component model for particle production @xcite . *
zna : the @xmath30 values have been calculated by scaling the @xmath31 in minimum - bias p  pb collisions by the ratio between the average multiplicity density measured at mid - rapidity for a given zn energy event class and the one measured in minimum bias collisions .
@xmath32 is obtained as @xmath32 = @xmath30 - 1 .
the self - normalized yields have been measured for prompt @xmath2 , @xmath3 and @xmath4 mesons . they are shown in charged - particle multiplicity ( dn@xmath33/d@xmath34 ) intervals ( fig.1 ) , since a simulation study has shown that @xmath21/@xmath35 equals @xmath36 .
for all the @xmath6-meson species , the yield increases with charged - particle multiplicity .
no @xmath5 dependence of this trend has been observed .
the left panel of fig.1 shows @xmath2 self - normalized yields for pp and p  pb collisions .
both systems show an increase of the yield with charged - particle multiplicity .
the trend for pp collisions can be interpreted as being due to strong hadronic activity connected with charm production and to the presence of mpis affecting the hard momentum scale relevant for heavy - quark production . in the p 
pb case , it should be considered that high - multiplicity events can also originate from a higher number of nucleon - nucleon collisions in the nuclear interaction .
the right panel of fig.1 shows the average values of self - normalized yields for @xmath2 , @xmath3 and @xmath4 and j/@xmath8 in p 
pb collisions .
j/@xmath8 yields have been measured in 2.5@xmath374.0 ( p - going direction ) and @xmath38 ( pb - going direction ) and they show an increase with charged - particle multiplicity .
however a quantitative comparison of j/@xmath8 and @xmath6-meson yields has to take into account the rapidity dependence of cold nuclear matter effects such as gluon shadowing , that depends on the bjorken @xmath39 value of the parton involved in the process producing charm , and energy loss in cold nuclear matter @xcite .
the average value of @xmath18 for prompt @xmath2 and @xmath4 mesons is shown in the left panels of figs . 2 and 3 for the v0a and zna estimators , respectively .
a bias can be observed in the v0a measurement , where the low - multiplicity @xmath18 is below unity in all six @xmath5 bins , while the zna measurement is compatible with unity within systematic and statistical uncertainties at both low and high event activity .
these @xmath18 results are compared with the ones obtained for charged particles , shown in the right panels of figs . 2 and 3 .
these comparisons demonstrate that the @xmath18 of high @xmath5 ( @xmath40 8 gev/@xmath11 ) charged particles feature a similar pattern as the one of @xmath6 mesons , confirming the presence of a bias in the v0a - based determination of @xmath29 that is reduced using the zna estimator .
this indicates that the determination of @xmath7 depends on the rapidity region in which the event activity measurement is performed . with the least biased estimator ( zna )
we observe @xmath18 being compatible with unity for all multiplicites and @xmath5 .
details on the @xmath28 bias have been presented at this conference and they are described in @xcite .    in conclusion , the d - meson self - normalized yields show an increasing trend with increasing charged - particle multiplicity .
the trends observed for pp and p  pb collisions are compatible within uncertaintes .
the @xmath18 results for @xmath6 mesons are qualitatively similar to the ones obtained for high @xmath5 charged particles .
in particular the zna measurement shows no multiplicity dependence of the @xmath6-meson production in p 
pb collisions relative to binary scaling of pp production cross sections while v0a results show a similar bias as observed for high-@xmath5 charged particles .
00 v. khachatryan et al .
[ the cms collaboration ] , eur .
j. c 73 ( 2013 ) 2674 a. abelev et al .
[ alice collaboration ] , jhep 09 ( 2013 ) 049 m aguilar - benitez [ na27 collaboration ] , z.phys.c41 ( 1988 ) 191 r. aaij et al .
[ lhcb collaboration ] , j. high energy phys .
, 06 ( 2012 ) 141 a. abelev et al .
[ alice collaboration ] , phys .
lett b 712 ( 2012 ) 165 - 175 a. abelev et al .
[ alice collaboration ] , arxiv:1405.3452 s. li for the alice collaboration , these proceedings a. morsch for the alice collaboration , arxiv:1309.5525 a. toia for the alice collaboration , these proceedings a. abelev et al .
[ alice collaboration ] , jinst 3 ( 2008 ) s08002 a. abelev et al .
[ alice collaboration ] , jhep 1207 ( 2012 ) 191 r. russo for the alice collaboration , arxiv:1305.3435 a. abelev et al .
[ alice collaboration ] , phys .
c 88 ( 2013 ) 044909 j. martin blanco for the alice collaboration , these proceedings
in these proceedings results are presented from the measurement of open heavy - flavour production as a function of charged - particle multiplicity in pp collisions at @xmath0 = 7 tev and p  pb collisions at @xmath1=5.02 tev recorded with the alice detector in 2010 and 2013 , respectively . 
 @xmath2 , @xmath3 and @xmath4 mesons are reconstructed from their hadronic decay channels in the central rapidity region , and their production yields are measured in various multiplicity and @xmath5 intervals .    the per - event yields of @xmath6 mesons in the various multiplicity intervals , normalized to their multiplicity - integrated value , and their evolution with @xmath5 are measured for pp and p  pb collisions to study the contribution of multi - parton interactions ( mpis ) to open charm production in the two systems . 
 the nuclear modification factor of @xmath6 mesons in p  
 pb collisions , defined as the ratio of the @xmath6-meson yields in p  pb and pp collisions scaled by the average number of binary collisions @xmath7 , is discussed in terms of its dependence on the event activity . 
 several experimental estimators of the event activity are used in order to assess the role of kinematic biases .    
 qgp , heavy - flavour , multi - parton interaction