ttbar generation problem
Hi everyone
I don't know where to ask a question about a generation problem. Please direct me to the right place if this is not.
I want to generate a ttbar process decaying hadronically, lepton+jets and dilepton. For this I wrote:
generate p p > t t~, (t~ > W- b~, W- > l- vl~), (t > W+ b, W+ > l+ vl)
add process p p > t t~, (t~ > W- b~, W- > j j), (t > W+ b, W+ > j j) @2
add process p p > t t~, (t~ > W- b~, W- > l- vl~), (t > W+ b, W+ > j j) @3
add process p p > t t~, (t~ > W- b~, W- > j j), (t > W+ b, W+ > l+ vl) @4
I am not if this is correct, because I am analysing the branching ratio of this process and it doesn't fit. I want to be sure if I am doing the right thing.
Thanks for your help.
Alejandro
Question information
- Language:
- English Edit question
- Status:
- Solved
- Assignee:
- No assignee Edit question
- Solved by:
- Johan Alwall
- Solved:
- 2011-09-15
- Last query:
- 2011-09-15
- Last reply:
- 2011-09-14
Johan Alwall (johan-alwall) said : | #1 |
Hi Alejandro,
Did you include the tau in the definition for leptons?
define l = l ta+ ta-
If not, that might explain your branching ratio disagreement.
Johan
Johan Alwall (johan-alwall) said : | #2 |
Sorry, I meant
define l+ = l+ ta+
define l- = l- ta-
of course.
alefisico (alefisico) said : | #3 |
Thanks Johan for your answer.
It doesn't seem to change anything. So, in principle it is correct the way I am generating this process?? Because it also could be a problem of my analyser, but before start to change my analyser I want to know if I am doing the right think.
Thanks!!!!
Alejandro
|
#4 |
Hi Alejandro,
Using your process generation, I get results in perfect agreement with
BR(t->b e/mu/ta nu)= 0.33, BR(t->bjj)=0.67. Note that you need to run
without cuts on the decay products (e.g. by setting cut_decays=F) to
get the expected cross section ratios.
Cheers,
Johan
alefisico (alefisico) said : | #5 |
Hi Johan and thanks for your help.
I didn't change cut_decays to false but instead I changed the minimum and maximum values of standard cuts, it is not the same?
If yes, this is what I was afraid, that perhaps the generation is correct but my analyser is wrong. It is an easy way to calculate the BR in MG5 or I should create an "external" analyser (like a python script or something like that) to do this?
Best,
Alejandro
Johan Alwall (johan-alwall) said : | #6 |
Hello Alejandro,
You get the cross sections for the different process groups (specified by
the process identifier @N) directly in the generation html page. It's
trivial to calculate the BRs directly from the different cross sections:
2l: BR(t->lnu)
0l: BR(t->jj)
1l: xsec(1l)
Cheers,
Johan
alefisico (alefisico) said : | #7 |
Hi Johan
Thanks for your help and patience. That is what I needed. I really appreciate it.
Cheers,
Alejandro
alefisico (alefisico) said : | #8 |
Thanks Johan Alwall, that solved my question.