Changes between Initial Version and Version 1 of Manual


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Timestamp:
03/20/12 16:19:20 (7 years ago)
Author:
trac
Comment:

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  • Manual

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     3=== Short description of the tool ===
     4
     5The aim is to build an event generator for quarkonium physics. Production rates are computed within the NRQCD theory (Non-Relativistic QCD, Bodwin, Braaten and Lepage, see hep-ph/9407339), where cross sections are expanded in %$\alpha_s$% and %$\normalsize v$%, the relative velocity in the heavy quarkonium state. As a result, cross sections read
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     9where  the creation of a heavy-quark pair is described by the short-distance coefficients %$\hat \sigma(Q\bar Q(n))$%, whereas the non-perturbative evolution of this heavy-quark pair into a quarkonium state is encoded into the long-distance matrix elements  %$<O^{\mathcal Q}(n)>$%. The label %$\normalsize n $% stands for the intermediate state of the heavy quark pair, which is usually expressed in the spectroscopic notation:
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     13with %$\normalsize S $% the spin of the heavy quark pair, %$ \normalsize L $% its orbital angular momentum, %$ \normalsize J $% its total angular momentum, and %$ \normalsize c $% its color state.
     14 
     15MadOnia automatically generates any tree-level amplitude for an arbitrary transition %$\normalsize n$% (up to P-wave state) required for the computation of the short-distance coefficients. The amplitude generator is interfaced with MadEvent to produce unweighted events. These events are written in the same format in the  lhe format and can be passed through Pythia for the showering and hadronization.
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     17
     18=== How to use the code ===
     19
     20==== Edit the proc_card.dat and generate the process ====
     21
     22   * Enter the processus name in the proc_card.dat in the following format:
     23
     24{{{
     25pp>jcc~[3P18to443]
     26}}}
     27
     28This corresponds to the production of a %$\normalsize J/\psi$% (PID=443) via an intermediate state %$\normalsize 2S+1=3$%, %$\normalsize L=P$%, %$\normalsize J=1$%, %$\normalsize c=8$%, i.e. a spin-1,  P-wave, color-octet intermediate state. As another example:
     29
     30{{{
     31pp>jbb~[1S01to551]
     32}}}
     33
     34corresponds to the production of an %$\normalsize \eta_b$% via a color-singlet transition.
     35
     36'''Pay attention'''
     37
     38the heavy-quark pair must be placed in that order, and at the end! For example,
     39
     40{{{
     41pp>jc~c[3P18to443]
     42}}}
     43
     44or
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     46{{{
     47pp>cc~[3P18to443]j
     48}}}
     49
     50will not work!
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     52For the model, select sm_onium.
     53
     54   * Then type
     55
     56./bin/newprocess           
     57
     58to generate the process
     59
     60==== Edit the param_card.dat ====
     61
     62If you edit the file param_card.dat, you will see that in addition to the sm parameters, you
     63have a block called LDME. The parameters in this block
     64correspond to the long distance matrix element, expressed in the BBL normalization (see hep-ph/9407339).
     65You can specify the value of the LDME's for each transition. The transition %$\normalsize n$% is indicated at the end of the line
     66as a comment. For example, the line
     67
     68{{{
     69        3.      1.16E+00         # 3S11
     70}}}
     71
     72sets
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     76Note that only one LDME parameter is assigned to each transition %$^{2S+1}L_J^{[c]}$%. For example, for all the  following processes
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     78   || pp >j cc~[3S18to443]    ||               color-octet  %$\normalsize J/\psi$% production ||
     79   || pp > jcc~[3S18to10441]  ||             color-octet  %$\normalsize \chi_{c0}$% production ||
     80   || pp > jbb~[3S18to100553]    ||       color-octet  %$\normalsize \Upsilon(2S)$% production ||
     81
     82the same LDME parameter will be used in the param_card.dat.
     83
     84
     85==== For the rest... ====
     86
     87Just proceed as for a usual generation of events:
     88
     89./bin/generate_events   to generate events
     90
     91Note that you can put cuts on the quarkonium state via the run_card.dat.
     92
     93Once your events have been generated, you can use the tool MadAnalysis to draw distributions of events.
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     99-- Main.PierreArtoisenet - 02 Mar 2009
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