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Event generation

In the past, an empirical formula used to describe the distribution of the collision energy at next-generation linear colliders has been presented by Yokoya and Chen[14]. In addition, recently developed software, called CAIN[13], is capable of simulating detailed beam-beam interactions at tex2html_wrap_inline1195, tex2html_wrap_inline1389 and tex2html_wrap_inline1391 linear colliders. The function in [14] has been found to give a good approximation to the CAIN calculation, as shown in Figure 14.17 at tex2html_wrap_inline1393=250GeV. Table 14.1 summarizes the relevant parameters for the calculations.

Figure 14.17 shows that the function reasonably reproduce the CAIN result at tex2html_wrap_inline1395GeV, where a small difference seen in the figure is due to a beam disruption included in the CAIN.

Figure 14.18: Luminosity spectra calculated by the generator (histogram) and the function (solid circles).
Figure 14.17: Luminosity spectra calculated by the empirical function (histogram) and CAIN (solid circles).

Table 14.1: Major parameters of JLC.

To improve the efficiency of calculations, a luminosity-spectrum generator code has been created[15]. The generator code precisely reproduces the empirical function as shown in Figure 14.18.

It should be noted that besides the beam-beam interactions, the beam-energy spread also affects the luminosity-spectrum. Its effects were simulated, and the results are shown in Figure 14.19. In these calculations a uniform energy spread of tex2html_wrap_inline14271% was assumed for the original beams. It can be seen that the luminosity peaks are smeared at around tex2html_wrap_inline1429=500GeV.

Figure 14.19: (a) The luminosity-spectra weighted by the Bhabha cross section, without (with) the tex2html_wrap_inline14271% uniform beam-energy spread, which is shown by the solid (dashed) histogram. (b) The spectra calculated by the acollinearity angles of the Bhabha events, where no entry above tex2html_wrap_inline1429=500GeV exists by definition.

The differential cross section of the Bhabha scattering process was calculated using the program GRACE[16]. This is a program package for automatic amplitude calculations. The numerical integration and unweighted event generation were performed by two programs, BASES and SPRING[17], respectively. In this study, the lowest order Feynman diagrams of this process were taken into account, since the effect of the initial state radiation can be precisely estimated[18].

next up previous contents
Next: Measurement of the Luminosity Up: Luminosity Spectrum Previous: Luminosity Spectrum

Toshiaki Tauchi
Thu, May 29, 1997 04:47:48 PM