Processes

Before discussing the physics processes currently supported by Pepper, we stress that all processes are currently available at leading order only.

LHC processes

Pepper’s focus is on those physics processes at the LHC which have high cross sections and appear as backgrounds in almost all physics analyses. Therefore, on the simulation side, large high-fidelity samples are required for these processes, and their production takes up most of the event generation computing resources. Currently, Pepper can generate events for the following processes:

Process	Base specifier	Max. additional jets	\(\alpha_{\text{ew}}\) order	\(\alpha_\text{s}\) order
Drell-Yan production	ppee	5 (= ppeejjjjj)	2	0\(\ldots\)5
Top-antitop pair production	pptt	4 (= ppttjjjj)	0	2\(\ldots\)6
Dijet production	ppjj	4 (= ppjjjjjj)	0	2\(\ldots\)6

On request, we can consider to add support for additional processes. In particular W boson production is a process that we can easily add on-demand.

The “Base specifier” gives the corresponding value one can use to select the process using the [main] section of the runcard (see Main options), or by the -p|--process command line option (see Command-line interface reference).

Additional j characters can be appended to add additional final-state jets. The current maximum number of jets are given in the table above. This restriction is purely technical. Please contact us if you need to generate events with higher jet multiplicities, and we will try to add the required process data files.

Note

Jets are understood to be QCD-only jets; as Pepper is a parton-level event generator, this simply means that a jet is an (anti-)quark or a gluon which passes all the jet cuts. In particular, photons are not included in the jet definition.

As an example, to select Drell-Yan production in association with 4 additional jets, add the line process = ppeejjjj in the [main] section of the runcard, or use pepper --process ppeejjjj on the command line.

Partonic channels

All of the above assumes that you want to generate events for physical processes, for which all contributing partonic channels are summed over.

If you need to generate events for a single partonic channel instead, you can specify this by giving a whitespace-separated list of particles using -> to separate initial- and final-state particles. An example would be d db -> u ub. More than one channel can be specified by giving them as a comma-separated list, e.g. d db -> u ub, d db -> c cb, .... As whitespace is involved, you need to use quotation marks on the command line, e.g. pepper --process "d db -> u ub".

Partonic channel files

No contents yet.