Interface to HzTool

HzTool[6] is a package, that provides code to compare data plots published by the HERA experiments to Monte Carlo programs. Some of the plots could also be compared to next-to-leading order calculations and an interface from this library to HzTool is presented here.

Note, that several observables are not applicable in next-to-leading order programs, such as particle or track multiplicities, and others would require to add hadronisation and fragmentation effects to the calculation. Therefore the comparison is a priori limited to a few observables.

HzTool reads data from the HEPEVT common block, a standard format for high energy physics Monte Carlo programs. In addition HzTool expects, that every call contains the full information for one event with a corresponding weight. Since different contributions to one event have to use a special error treatment, a decent error calculation without changing all HzTool routines is not possible.

The restrictions implied are therefore:

• Only observables available to next-to-leading programs allow comparisons.
• Be especially aware of cuts, that spoil cancelations of divergencies[7].
• Errors calculated by HzTool are not valid.
• Differences according to non-perturbative effects can be expected.
• Some NLO programs might give unusable results, e.g. DiJet rates need calculations of $\cal {O}$(1) and $\cal {O}$($\alpha_{s}^{}$) tree level diagrams simultaneously, which is e.g. not possible in Disaster++.

To use the HzTool interface, add the file nlolib/src/hztool/hzhep.f to your source. This routine provides implementations to the standard user routines and therefore replaces the interface specified in section 3 and figure 1 by the one given in figure 2.

Figure 2: Overview of the calling tree when using HzTool.

The routines, that have to be provided by the user are hzinit(), hzterm(), and hzuser(). These routines should call the hzxxxxx routines with iflag equal to 1,3, and 2 respectively. See the HzTool manual[6] for more information.