Manual: section on MadOnia

MadOnia is a module that is deeply integrated in MadGraph/MadEvent. It can be seen as a specific implemented Model. For this reason, the procedure that you need to follow to generate a new quarkonium production process and then quarkonium events is very similar to the standard MG/ME procedure. In the description below, points where the syntax is specific to quarkonium production have been highlighted. For the rest, the reader is invited to have a look to the MadGraph help page.

How to use the code

Just like the other processes that are tractable in MG/ME, you can decide to generate a new quarkonium prcocess and/or quarkonium events via one of the MG/ME clusters, or you can download the full or process-dependent code and run it on your computer. The inputs that should be entered for a new analysis have the same format in both cases.

Generate a new process

You need to edit the file proc_card.dat:

• Enter the name of the process using the following format:

pp>jcc~[3P12to445]

This corresponds to the production of a $\chi_{c2}$ (PID=445) via an intermediate state with $\normalsize 2S+1=3$, $\normalsize L=P$, $\normalsize J=2$, $\normalsize c=1$, i.e. a spin-1, P-wave, color-singlet intermediate state. As another example:

pp>jbb~[1S01to551]

corresponds to the production of an $\normalsize \eta_b$ via a color-singlet transition. For color-octet tranistion, the color index should be set to 8. If you have in mind to pass the events through Pythia for the showering and hadronization, you must be careful with the PI number of the state. Indeed, pythia uses a special label that contains the information on the color. For example, the PI number that should be used for the production of a J/psi via a color-octet transition is 9900443;

pp>jcc~[3S18to9900443]

Also, pay attention:

the heavy-quark pair must be placed in that order, and at the end! For example,

pp>jc~c[3P18to443]

or

pp>cc~[3P18to443]j

will not work!

For the model, select sm_onium.

• Once the file proc_card.dat has been edited, then type

./bin/newprocess

to generate the process

Generate parton-level events

You need to edit the usual files. If you edit the file param_card.dat, you will see that in addition to the sm parameters, you have a block called LDME. The parameters in this block correspond to the long distance matrix elements, expressed in the BBL normalization (see hep-ph/9407339). You can specify the value of the LDME's for each transition. The transition $\normalsize n$ is indicated at the end of the line as a comment. For example, the line

        3.      1.16E+00         # 3S11

sets

Note that only one LDME parameter is assigned to each transition $^{2S+1}L_J{[c]}$. For example, for all the following processes

pp >j cc~[3S18to443]	color-octet $\normalsize J/\psi$ production
pp > jcc~[3S18to10441]	color-octet $\normalsize \chi_{c0}$ production
pp > jbb~[3S18to100553]	color-octet $\normalsize \Upsilon(2S)$ production

the same LDME parameter will be used in the param_card.dat.

Note also that you can put cuts on the quarkonium state via the run_card.dat.

Once all the relevant cards have been edited, you can send the jobs on the server, or you can type

./bin/generate_events to generate events

on your personal computer.

Once your events have been generated, you can use the tool MadAnalysis to draw distributions of events.

Generate hadron-level events

If you have in mind to pass the events through Pythia for showering and hadronization, the procedure is exactly the same as the standard one. In particular, if you are using one of the MadGraph cluster, you just need to provide the input file pythia_card.dat when you submit a new request for event generation.

In the case of color-octet transition, you need to pay attention: Pythia has a prescription for the evolution of the heavy-quark pair only if it has a mass that is larger than the mass of the physical quarkonium state. This means that you need to set the mass of the heavy quark in the file param_card.dat to a sufficiently large value. For example, in the case of J/psi production via a color octet-transition, you need to set the mass of the charm quark to a value that is larger than m_Jpsi/2

ATTENTION: for CO transition in Pythia, PID(J/psi) = 9900443, PID(Upsilon(1S))=9900553

-- Main.PierreArtoisenet - 2011-11-10