Monte Carlo mass comparisons.

The upper left histogram compares the data with loose cuts (blue), tight cuts (red) and background (black). A small peak is visible at M(&pi&pi)=M(K_s). This may be due to photoproduction of the &phi, followed by &phi --> K_sK_l. Because the Q value of the &phi decay is so low, most of the K_S still make the p_T cut; the K_L usually vanishes without decaying. The upper right plot compares the data and the Monte Carlo; except for the K_s, the agreement is very good. The lower left plot shows the efficiency; for M_&pi&pi > 550 MeV/c, the effiency is flat. The last plot shows the M_&pi&pi resolution of about 8.5 MeV.

Monte Carlo p_T comparisons.

Although the analysis will use t=p_T*p_T, these histograms give a different look at the data. The upper left histogram shows the p_T spectrum with loose (blue) and tight (red) cuts; with the tight cuts, there are very few events with p_T > 120 MeV/c. The upper right histogram compares the Monte Carlo reconstructed p_T for 'Int" (blue) and 'Noint' datasets. The middle left histogram is the same comparison, but for the MC generated p_T. The middle right histogram shows the p_T resolution. The peak is symmetric, and &sigma = 7.5 MeV. The lower left histogram shows the efficiency vs. p_T; it is flat except for the first bin, which is higher due to smearing (this is discussed in terms of 't' in the analysis section. The lower right histogram compares the data (red), 'Noint' (green) and 'Int' spectra.

Monte Carlo rapidity comparisons.

The upper left histogram compares the data with loose cuts (blue), tight cuts (red), and background (with loose cuts). The loose cut plot has a huge enhancement at |y|<0.1; some of this peak remains even with the tight cuts. This is likely due to cosmic rays, which are reconstructed as pairs with y=0, p_T=0. To remove the cosmic rays, we only consider events with |y|>0.1. The upper right histogram compares the data (red) and Monte Carlo (blue). Although there is a very slight asymmetry between y>0 and y<0 in the data, likely due to the varying CTB slat efficiencies, the overall agreement is very good. The effect of the slight mismatch will be discussed in the systematic errors section. The lower left histogram shows the rapidity resolution, 0.01. This is very adequate for the analysis. The lower right histogram shows the efficiency as a function of rapidity. It is not flat, since the probability of a daughter pion being outside the TPC acceptance rises as |y| rises, but since the data and MC agree well, this is no cause for concern.

Monte Carlo rVertex comparisons.

The upper left histogram compares the data with loose cuts. The left plot shows the data with loose cuts (blue), tight cuts (red), and the background (black). With the loose cuts, a rise is visible at R ~ 3.5 cm; the position of the beampipe. This completely disappears once tighter cuts are imposed. The background rate is so high here because there is no cut on z. The plot on the right compares the data (red) and the Monte Carlo (blue). As with the minimum bias data, the agreement is good.

Monte Carlo zVertex comparisons.

The upper left histogram compares the data with loose cuts (blue) and tight cuts (red), and the background (black). The tight cut data shows side peaks at +/- 75 cm in addition to the central peak at z=0. This is due to bunching from the 200 MHz RHIC RF system, and has been seen elsewhere (per Jamie Dunlop). The pT spectrum of data in the side peaks looks the same as the data in the central peak.

The upper right histogram compares the (red) data and Monte Carlo (blue). The Monte Carlo zVertex was generated as a Gaussian with width 80 cm. This does not reproduce the detailed structure in the data, but is a reasonably good overall fit. The lower right is the resolution estimated with the Monte Carlo (zVertex-zMC); the resolution is 1.1 cm. The lower left shows the efficiency as a function of zVertex. It is almost flat within +/- 100 cm.