Dear Michael and others, On Mon, 26 Nov 2001, Michael Murray wrote: > I think it is worth discussing the > change of shape with centrality even if it only reflects the > growth of hard collisions at central rapidity. What is |eta| RMS for pp and and > what is the reference? I calculated the width for pp data (UA5, pp at sqrt(s) = 200 GeV - G.J. Alner et al., Z. Phys 33, 1 (1986).) The numbers were read from their figure 1 a). Result: RMS_pp = 2.36+-0.03, which compared to our data is between the RMS values for central and peripheral collisions. The pp point is plotted as a purple circle in the upper panel of the figure: http://lynx.uio.no/trine/brahms/mult/RMS_with_pp_AMPT.gif together with our sets of RMS values for 200 (red) and 130 (blue) GeV, going from central to peripheral collisions from left to right. The error bars on the pp point includes (approximately) inaccuracy in reading from the figure. In the lowermost panel of the figure, the pp dN/dEta (purple) and our dN/dEta/(Npart/2) distribution for 0-5% (red) and 40-50% central (blue) collisions are compared. I made a similar calculation for the AMPT calculations at 200 GeV, taking the numbers from AMPT_xx_xx.dat files in the kansas account. The RMS values (calculated over the same Eta interval as for the experimental data) follow the experimental points very closely, (green points in the upper panel - on top of the red ones.) Our Figure 4 indicates that the widths as a function of centrality evolve differently from 130 to 200 GeV for experimental and theoretical results. I think the theoretical RMS values for 130 GeV will vary less with centrality than the experimental ones. Are the Kharzeev & Levin and AMPT dN/dEta numbers at 130 GeV explicitly available somewhere? It might be interesting to calculate the theoretical RMS values to find out more about possible interpretations. > We may also want to reference to SPS distributions. Do we have any good SPS references covering a large enough region in Eta and where it's possible to compare different centralities (Dieter?) Best wishes, Trine
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