Estimating Drell-Yan contribution from NLO calculation.

Ramona calculated the cross section for DY at NLO and sent the data points to us.  These were first shown in the RHIC II Science Workshop, April 2005, in her Quarkonium talk and her Drell-Yan (and Open heavy flavor) talk.

The total cross section (integral of all mass points in the region |y|<5) is 19.6 nb (Need to check if there is an additional normalization with Ramona, but the cross section found by PHENIX using Pythia is 42 nb with 100% error bar, so a 19.6 nb cross section is certainly consistent with this). She also gave us the data in the region |y|<1, where the cross section is 5.24 nb. The cross section as a function of invariant mass in the region |y|<1 is shown below.

The black curve includes a multiplication with an error function (as we did for the b-bbar case) and normalized such that the ratio between the blue and the black line is 8.5% at 10 GeV/c to account for the efficiency and acceptance found in embedding for the Upsilon 1s.  The expected counts in the region 8-11 are 20 +/- 3, where the error is given by varying the parameters of the error function within its uncertainty.  The actual uncertainty is likely bigger than this if we take into account the overall normalization uncertainty in the calculation.

I asked Ramona for the numbers in the region |y|<0.5, since that is what we use in STAR.  The corresponding plot is below.

 The integral of the data points gives 2.5 nb.  The integral of the data between 7.875 and 11.125 GeV/c2 is 42.30 pb.  The data is parameterized by the function shown in blue.  The integral of the function in the same region gives 42.25 pb, so it is quite close to the calculation.  In the region 8<m<11 GeV/c2, the integral of the funciton is 38.6 pb.  The expected counts with this calculation are 25 for both triggers.