# transverse mass in Madanalysis

Asked by GuojinTseng on 2019-07-18

I generated a process p p > w+ w- by Madgraph. And then I used MadAnalysis to produce MT(w+ w-). Why does the diagram show that all MT(w+ w-) are zero?

If I use this definition:
MT_{w+ w-}^2 = (ET_{w+} + ET{w-})^2 - (PT_{w+}+PT_{w-})^2
, where ET_{w+} = Sqrt(m^2+PT_{w+}^2), PT = (p_x, p_y) and m is invariant mass, to calculate MT(w+ w-), I cannot get the zero results.

In my situation, PT_(w+) + PT_(w-) = 0. MT_{w+ w-}^2 should be (ET_{w+} + ET{w-})^2 and it is must greater than zero. This result disagree with MadAnalysis' result.

So, how does MadAnalysis deal with the MT? Am I misunderstand the definition about MT(w+ w-)

Guojin Tseng

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2019-07-18
2019-07-18
 Benjamin Fuks (fuks) said on 2019-07-18: #1

Hi,

In your syntax, you ask madanalysis 5 to first sum the four momenta of the two w-bosons (so that the summed vector has only a non-vanishing energy and pz componet), and then compute the transverse mass of the resulting four-vector. In this case, the transverse mass equals the transverse energy (since the combined pt vanishes). There are several definitions of the transverse energy and the one we use is
Et = E pt^2/(pt^2+pz^2)
i.e. this corresponds to the fraction of the energy in the transverse direction which is thus 0.

Regards,

Benjamin

> On 18 Jul 2019, at 05:02 , GuojinTseng <email address hidden> wrote:
>
> New question #682128 on MadAnalysis 5:
>
> Dear MadAnalysis team:
>
> I generated a process p p > w+ w- by Madgraph. And then I used MadAnalysis to produce MT(w+ w-). Why does the diagram show that all MT(w+ w-) are zero?
>
> If I use this definition:
> MT_{w+ w-}^2 = (ET_{w+} + ET{w-})^2 - (PT_{w+}+PT_{w-})^2
> , where ET_{w+} = Sqrt(m^2+PT_{w+}^2), PT = (p_x, p_y) and m is invariant mass, to calculate MT(w+ w-), I cannot get the zero results.
>
> In my situation, PT_(w+) + PT_(w-) = 0. MT_{w+ w-}^2 should be (ET_{w+} + ET{w-})^2 and it is must greater than zero. This result disagree with MadAnalysis' result.
>
> So, how does MadAnalysis deal with the MT? Am I misunderstand the definition about MT(w+ w-)
>
>
> Guojin Tseng
>
> --
> You received this question notification because you are an answer
> contact for MadAnalysis 5.