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charm is predicted to be produced primarily in gluon fusion reactions in the early stages of a collision @xcite . if charm is indeed produced in initial hard ( high @xmath3 ) processes , one will observe that charm production scales with the number of binary ( nucleon - nucleon ) collisions . the charm production cross - section can be calculated by summing up feynman diagrams at the `` fixed - order plus next - to - leading - log ( fonll ) '' level . the total charm cross - section per binary collision as predicted by fonll for @xmath1 = 200 gev is @xmath4 @xcite . both the star and phenix experiments at rhic observe binary scaling when comparing p+p to au+au ( phenix ) and d+au to au+au ( star ) ; however , previously measured charm cross - sections in star and phenix differ above declared uncertainties @xcite . also , current fonll calculations under - predict measured star charm cross - section values @xcite . this may suggest that different physical processes are at play than are assumed by fonll calculations . this analysis uses data taken with the time projection chamber ( tpc ) at the solenoidal tracker at rhic ( star ) , one of the experiments at the relativistic heavy ion collider ( rhic ) at brookhaven national lab ( bnl ) . the tpc measures an energy loss per unit distance , de / dx , by particles ionization of the p10 gas in the detector s chamber . the momentum is measured through the particles curvature in a 0.5 t magnetic field @xcite . by using a bichsel parameterization , a particle identification ( pid ) is acquired . the @xmath5 invariant mass spectrum is reconstructed via the @xmath2 decay channel . the @xmath6 ( or @xmath7 ) invariant mass is given by @xmath8 where @xmath9 is the angle between @xmath10 and @xmath11 . the invariant mass spectrum was extracted from 28.7 million cu+cu minimum bias events at @xmath12 gev . then the uncorrelated background was subtracted via the rotational background subtraction method . to implement this method one of the daughter tracks in a two body decay is rotated in momentum space to every 5 degrees from 150 to 210 degrees in the plane transverse to the beam line . after the background is subtracted a peak with a statistical significance of @xmath13 ( @xmath14 , s = area of signal peak , b = background under peak ) is seen ( see figure [ d0]a ) .    @xmath15 % \cr . \mbox{\bf ( 1 ) } & \mbox{\bf ( 2 ) } \cr \mbox{\bf } & \mbox{\bf } % \mbox{\bf ( a ) } & \mbox{\bf ( b ) } \end{array}$ ] figure [ d0]b shows a transverse momentum spectrum for @xmath16 at mid - rapidity . efficiency and acceptance corrections , as calculated from a detailed geant simulation of the star detector , and a branching ratio correction of @xmath17 @xcite were applied . an @xmath18 exponential fit is done to the spectrum ( @xmath19 ) . by integrating over the entire @xmath20 spectra , we find that @xmath21 = @xmath22 . the @xmath21 yield is converted to a cross - section via @xmath23 here , @xmath24 is the charm cross - section per binary collision , @xmath25 mb is the proton+proton inelastic cross - section @xcite , @xmath26 is the average number of binary nucleon collisions in a cu+cu minimum bias collision found using the glauber model , @xmath27 is a normalization factor to extrapolate to full rapidity ( based on pythia simulation ) @xcite , and @xmath28 is the ratio of @xmath6 to @xmath29 , measured in @xmath30 collider events @xcite . the preliminary cu+cu charm cross - section is thus calculated to be @xmath31 mb and is shown in figure [ cucu_cross_section ] . evaluation of systematic error bars for the cu+cu measurement is in progress . this new measurement confirms previous star measurements @xcite showing that charm production follows a binary scaling from p+p to central au+au collisions . star measured @xmath5 in cu+cu collisions with a statistical significance of @xmath13 . the charm cross - section in @xmath1 = 200 gev minimum bias cu+cu collisions was measured to be @xmath31 mb . this is consistent with binary scaling when compared to other star measurements , verifying charm production via hard processes in the initial stages of the collision . z. lin and m. gyulassy , phys . c * 51 * 4 2177 ( 1995 ) . m. cacciari , p. nason , and r. vogt , phys . lett . * 95 * 122001 ( 2005 ) . s.s . adler _ et al . _ ( phenix ) , phys . lett . * 94 * 082301 ( 2005 ) . et al . _ ( phenix ) , phys . lett . * 97 * 252002 ( 2005 ) . j. adams _ et al . _ ( star ) , phys . lett . * 94 * 062301 ( 2005 ) . y. zhang ( star ) , e - print arxiv : nucl - ex/0607011 . m. anderson _ ( star tpc group ) , nucl . instr . and meth . a * 499 * 659 ( 2003 ) . w - m yao _ et al . _ ( particle data group ) , j. phys . g : nucl . part . phys . * 33 * 1 ( 2006 ) . c. adler _ et al . _ ( star ) , phys . 91 * 172302 ( 2003 ) .
we present the mid - rapidity @xmath0 yield measured in @xmath1 = 200 gev cu+cu collisions at rhic via direct reconstruction through the @xmath2 decay channel . 
 a charm cross - section is reported and compared to theoretical predictions and to previous rhic experimental results . 
 open charm , cu+cu , quark - gluon plasma , fonll , star 12.38.mh , 21.65.qr