WHIZARD

simulate e+e- -> ttbar->wbwb

Asked by laetitia

Hi,

I wanted to simulate the process: e+e- -> ttbar->W+bW-bbar with W+,W- decay into dileptonic channel, with t,tbar and W that could be off-shell and then exported the events to an LHE file. I want to perform an analysis with ROOT to reconstruct the t,tbar and W invariant mass with the final state particles, but I’m not really sure how to simulate the process :

model=SM
me=0
mmu=0
alias lepton = E1:e1:E2:e2
alias neutrino = n1:N1:n2:N2

process eett = e1, E1 => lepton,neutrino,b,lepton,neutrino,bbar
$restrictions = "3+4~Wp && 6+7~Wm && 3+4+5~t && 6+7+8~tbar"

sqrts = 400 GeV
n_events=10000
sample_format = lhef
simulate (eett)

Does this description correct or do I miss something?
With these restrictions, whizard can automatically choose the lepton/neutrino pair that satisfy the leptonic conservation law ?

Thanks a lot!
Laetitia

Question information

Language:
English Edit question
Status:
Solved
For:
WHIZARD Edit question
Assignee:
Juergen Reuter Edit question
Solved by:
Juergen Reuter
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Last reply:
Revision history for this message
Best Juergen Reuter (j.r.reuter) said : 		#1

Dear Laetitia,
in principle you could define lepton and antilepton containers, e.g.
alias lep = e1:e2
alias alep = E1:E2
and similarly for the neutrinos. However, the b charge is sufficient to only allow one charge combination on either side.
What didn't work are your restrictions, they were ignored, as you can see from the output of the matrix element code generation:
[1/6] e- e+ -> e+ nuebar b e- nue bbar ... allowed. [time: 0.30 secs, total: 1.78 secs, remaining: 1.48 secs]
[2/6] e- e+ -> e+ numubar b mu- nue bbar ... allowed. [time: 0.29 secs, total: 1.76 secs, remaining: 1.17 secs]
[3/6] e- e+ -> e+ numubar b e- numu bbar ... allowed. [time: 0.29 secs, total: 1.76 secs, remaining: 0.88 secs]
[4/6] e- e+ -> mu+ nuebar b mu- nue bbar ... allowed. [time: 0.29 secs, total: 1.75 secs, remaining: 0.58 secs]
[5/6] e- e+ -> mu+ nuebar b e- numu bbar ... allowed. [time: 0.29 secs, total: 1.75 secs, remaining: 0.29 secs]
[6/6] e- e+ -> mu+ numubar b mu- numu bbar ... allowed. [time: 0.29 secs, total: 1.75 secs, remaining: 0.00 secs]
There should be four different combinations, all electrons, all muons, and the two charge-conjugate mixed cases. The parts [3/6] and [4/6] are a wrong flavor combination. You need to set constraints _before_ your process definition, i.e.

$restrictions = "3+4~W+ && 6+7~W- && 3+4+5~t && 6+7+8~tbar"
process eett = e1, E1 => lepton,neutrino,b,lepton,neutrino,bbar

or as an optional argument:

process eett = e1, E1 => lepton,neutrino,b,lepton,neutrino,bbar
 { $restrictions = "3+4~W+ && 6+7~W- && 3+4+5~t && 6+7+8~tbar" }

(the brackets are important here!). Also note that the particle names need to be the same as for the intrinsic matrix element generator (that is bad heirloom unfortunately), so Wp and Wm must be W+ and W-, respectively. Then Whizard tries out more combinations, but gives you only the four ones consistent with intermediate tops and Ws:
[01/24] e- e+ -> mu- numu b mu+ numubar bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 8.01 secs]
[02/24] e- e+ -> mu- nue b e+ numubar bbar ... forbidden. [time: 0.35 secs, total: 8.38 secs, remaining: 7.68 secs]
[03/24] e- e+ -> mu- nue b mu+ nuebar bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 7.31 secs]
[04/24] e- e+ -> mu- nuebar b mu+ nue bbar ... forbidden. [time: 0.35 secs, total: 8.37 secs, remaining: 6.97 secs]
[05/24] e- e+ -> mu- numubar b e+ nue bbar ... forbidden. [time: 0.35 secs, total: 8.38 secs, remaining: 6.63 secs]
[06/24] e- e+ -> mu- numubar b mu+ numu bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 6.27 secs]
[07/24] e- e+ -> e- numu b e+ numubar bbar ... forbidden. [time: 0.35 secs, total: 8.37 secs, remaining: 5.93 secs]
[08/24] e- e+ -> e- numu b mu+ nuebar bbar ... forbidden. [time: 0.35 secs, total: 8.37 secs, remaining: 5.58 secs]
[09/24] e- e+ -> e- nue b e+ nuebar bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 5.23 secs]
[10/24] e- e+ -> e- nuebar b e+ nue bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 4.88 secs]
[11/24] e- e+ -> e- nuebar b mu+ numu bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 4.53 secs]
[12/24] e- e+ -> e- numubar b e+ numu bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 4.18 secs]
[13/24] e- e+ -> e+ numu b e- numubar bbar ... forbidden. [time: 0.35 secs, total: 8.35 secs, remaining: 3.83 secs]
[14/24] e- e+ -> e+ nue b mu- numubar bbar ... allowed. [time: 0.35 secs, total: 8.35 secs, remaining: 3.48 secs]
[15/24] e- e+ -> e+ nue b e- nuebar bbar ... allowed. [time: 0.35 secs, total: 8.35 secs, remaining: 3.13 secs]
[16/24] e- e+ -> e+ nuebar b e- nue bbar ... forbidden. [time: 0.35 secs, total: 8.35 secs, remaining: 2.78 secs]
[17/24] e- e+ -> e+ numubar b mu- nue bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 2.44 secs]
[18/24] e- e+ -> e+ numubar b e- numu bbar ... forbidden. [time: 0.35 secs, total: 8.35 secs, remaining: 2.09 secs]
[19/24] e- e+ -> mu+ numu b mu- numubar bbar ... allowed. [time: 0.35 secs, total: 8.36 secs, remaining: 1.74 secs]
[20/24] e- e+ -> mu+ numu b e- nuebar bbar ... allowed. [time: 0.35 secs, total: 8.36 secs, remaining: 1.39 secs]
[21/24] e- e+ -> mu+ nue b mu- nuebar bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 1.04 secs]
[22/24] e- e+ -> mu+ nuebar b mu- nue bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 0.70 secs]
[23/24] e- e+ -> mu+ nuebar b e- numu bbar ... forbidden. [time: 0.35 secs, total: 8.35 secs, remaining: 0.35 secs]
[24/24] e- e+ -> mu+ numubar b mu- numu bbar ... forbidden. [time: 0.35 secs, total: 8.36 secs, remaining: 0.00 secs]

So, withusing charge-specific lepton containers, you get:
alias lepton = E1:e1:E2:e2
alias neutrino = n1:N1:n2:N2
alias lep = e1:e2
alias alep = E1:E2
process eett2 = e1, E1 => alep,neutrino,b,lep,neutrino,bbar
 { $restrictions = "3+4+5~t && 6+7+8~tbar" }

You do not need to specify the intermediate Ws because there is no other possibility. This gives the same four different combos:
[01/12] e- e+ -> e+ numu b e- numubar bbar ... forbidden. [time: 0.35 secs, total: 4.17 secs, remaining: 3.82 secs]
[02/12] e- e+ -> e+ nue b mu- numubar bbar ... allowed. [time: 0.35 secs, total: 4.17 secs, remaining: 3.48 secs]
[03/12] e- e+ -> e+ nue b e- nuebar bbar ... allowed. [time: 0.34 secs, total: 4.16 secs, remaining: 3.12 secs]
[04/12] e- e+ -> e+ nuebar b e- nue bbar ... forbidden. [time: 0.34 secs, total: 4.15 secs, remaining: 2.77 secs]
[05/12] e- e+ -> e+ numubar b mu- nue bbar ... forbidden. [time: 0.35 secs, total: 4.16 secs, remaining: 2.42 secs]
[06/12] e- e+ -> e+ numubar b e- numu bbar ... forbidden. [time: 0.34 secs, total: 4.15 secs, remaining: 2.08 secs]
[07/12] e- e+ -> mu+ numu b mu- numubar bbar ... allowed. [time: 0.35 secs, total: 4.16 secs, remaining: 1.73 secs]
[08/12] e- e+ -> mu+ numu b e- nuebar bbar ... allowed. [time: 0.35 secs, total: 4.16 secs, remaining: 1.39 secs]
[09/12] e- e+ -> mu+ nue b mu- nuebar bbar ... forbidden. [time: 0.35 secs, total: 4.16 secs, remaining: 1.04 secs]
[10/12] e- e+ -> mu+ nuebar b mu- nue bbar ... forbidden. [time: 0.35 secs, total: 4.16 secs, remaining: 0.69 secs]
[11/12] e- e+ -> mu+ nuebar b e- numu bbar ... forbidden. [time: 0.35 secs, total: 4.16 secs, remaining: 0.35 secs]
[12/12] e- e+ -> mu+ numubar b mu- numu bbar ... forbidden. [time: 0.35 secs, total: 4.16 secs, remaining: 0.00 secs]

Cheers,
    JRR

Revision history for this message
laetitia (laetitia38) said : 		#2

Thanks Juergen Reuter, that solved my question.