Single Z boson production using e+e- collision

Hi Dennis,

Your syntax
e+ e- > Z, Z > b b~
requires a ONSHELL Z.

So you have two issues:
1. You do not have the gamma* contribution
2. If your beam energy is not close of the Z peak then the onshell condition related to your syntax will not be possible leading to a 0 result. The onshell condition is that the invariant mass of the Z is on the pole mass up to a given number of times the width. (that number can be set in the run_card: bwcutoff parameter.

The syntax that you are looking for is likely
e+ e- > b b~

Cheers,

Olivier

> On 27 Apr 2020, at 06:18, Dennis Arogancia <email address hidden> wrote:
>
> New question #690230 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/690230
>
> Hi
>
> I want to generate this process e+ e- --> gamma*/Z, Z --> b b~ in Madgraph. What I did is
>
> generate e+ e- > Z, Z > b b~
>
> But it returned an error resulting to zero cross section after executing launch:
>
> The following switches determine which programs are run:
> /=================== Description ===================|================== values ===================|=== other options ===\
> | 1. Choose the shower/hadronization program | shower = Pythia8 | OFF|Pythia6 |
> | 2. Choose the detector simulation program | detector = OFF | PGS|Delphes |
> | 3. Choose an analysis package (plot/convert) | analysis = MadAnalysis5 | OFF|ExRoot |
> | 4. Decay onshell particles | madspin = OFF | ON|onshell |
> | 5. Add weights to events for new hypp. | reweight = OFF | ON |
> \=======================================================================================================================/
> Either type the switch number (1 to 5) to change its setting,
> Set any switch explicitly (e.g. type 'shower=Pythia6' at the prompt)
> Type 'help' for the list of all valid option
> Type '0', 'auto', 'done' or just press enter when you are done.
>>
> Do you want to edit a card (press enter to bypass editing)?
> /------------------------------------------------------------\
> | 1. param : param_card.dat |
> | 2. run : run_card.dat |
> | 3. pythia8 : pythia8_card.dat |
> | 4. madanalysis5_parton : madanalysis5_parton_card.dat |
> | 5. madanalysis5_hadron : madanalysis5_hadron_card.dat |
> \------------------------------------------------------------/
> you can also
> - enter the path to a valid card or banner.
> - use the 'set' command to modify a parameter directly.
> The set option works only for param_card and run_card.
> Type 'help set' for more information on this command.
> - call an external program (ASperGE/MadWidth/...).
> Type 'help' for the list of available command
> [0, done, 1, param, 2, run, 3, pythia8, 4, enter path, ... ][90s to answer]
>>
> INFO: Update the dependent parameter of the param_card.dat
> Generating 10000 events with run name run_01
> survey run_01
> INFO: compile directory
> compile Source Directory
> Using random number seed offset = 21
> INFO: Running Survey
> Creating Jobs
> Working on SubProcesses
> INFO: P1_ll_z_z_bbx
> INFO: Idle: 1, Running: 0, Completed: 0 [ current time: 12h13 ]
> INFO: Idle: 0, Running: 0, Completed: 1 [ 3.4s ]
> INFO: Idle: 0, Running: 0, Completed: 1 [ 3.4s ]
> INFO: End survey
> refine 10000
> Creating Jobs
> INFO: Refine results to 10000
> INFO: Generating 10000.0 unweighted events.
> INFO: Effective Luminosity 1.2e+103 pb^-1
> INFO: need to improve 0 channels
> Survey return zero cross section.
> Typical reasons are the following:
> 1) A massive s-channel particle has a width set to zero.
> 2) The pdf are zero for at least one of the initial state particles
> or you are using maxjetflavor=4 for initial state b:s.
> 3) The cuts are too strong.
> Please check/correct your param_card and/or your run_card.
> Zero result detected: See https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-14
>
>
> I clearly made some mistakes at this point. How do I correctly generate this process in Madgraph?
>
>
> Sincerely,
>
> Dennis
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Thank you for your reply. You were right I was looking e+ e- > b b~. I was thinking of the process syntax in Pythia for single boson production: WeakSingleBoson:ffbar2gmZ (Scattering f fbar → gamma^*/Z^0, with full interference between the gamma^* and Z^0. Code 221.) and try to replicate it in Madgraph. While running the process: e+ e- > b b~ and using MadAnalysis package, I encountered this error:

generate_events run_02
Traceback (most recent call last):
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/extended_cmd.py", line 1515, in onecmd
    return self.onecmd_orig(line, **opt)
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/extended_cmd.py", line 1464, in onecmd_orig
    return func(arg, **opt)
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/madevent_interface.py", line 2469, in do_generate_events
    self.run_generate_events(switch_mode, args)
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/common_run_interface.py", line 6963, in new_fct
    original_fct(obj, *args, **opts)
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/madevent_interface.py", line 2578, in run_generate_events
    self.exec_cmd('madanalysis5_hadron --no_default', postcmd=False, printcmd=False)
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/extended_cmd.py", line 1544, in exec_cmd
    stop = Cmd.onecmd_orig(current_interface, line, **opt)
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/extended_cmd.py", line 1464, in onecmd_orig
    return func(arg, **opt)
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/common_run_interface.py", line 2667, in do_madanalysis5_hadron
    return self.run_madanalysis5(line,mode='hadron')
  File "/home/dca/soft/HEPsoft/MG5_aMC_v2_7_2/madgraph/interface/common_run_interface.py", line 2843, in run_madanalysis5
    "reconstructed event file for reconstruction '%s'."%MA5_runtag[6:]
MadGraph5Error: MadAnalysis5 failed to produce the reconstructed event file for reconstruction 'BasicReco'.

I encountered no error during the installation of MadAnalysis package.

Sincerely,

Dennis

Thanks Olivier Mattelaer, that solved my question.