MadGraph Cross-section

Asked by ouseph cj on 2021-04-12

Dear Madgraph Experts,

I am computing the Deep inelastic neutrino nucleon scattering cross-section mediated by Z and Zprime, According to the analytical formula, the total cross-section (with z and Zprime) should overlap with the SM cross-section. But My madgraph results are not overlapping with the SM cross-section and in the Higher mass regime, the total cross-section differs by 2 to 3% from the SM one.

Is this a computation error associated with the Madgraph? How can I solve this problem? Or is it a problem with my model file

I am attaching my model file with this email, I am looking forward to hearing from you.

M$ModelName = "Tutorial";
M$Information = {
  Authors -> {"****"},
  Version -> "1.0.0",
  Date -> "15. 07. 2020",
  Institutions -> {"*****"}

};

M$InteractionOrderHierarchy = { {QCD,1}, {NP,1}, {QED,2} };
M$ClassesDescription = {
     V[6] == {
     ClassName -> Zp,
     SelfConjugate -> True,
     Indices -> {},
     Mass -> {MZp, 3000},
     Width -> {WZp, 600},
     ParticleName -> "Zp",
     PropagatorLabel -> "Zp",
     PropagatorType -> Sine,
     PropagatorArrow -> None,
     FullName -> "Zprime"
   }
};

M$Parameters = {

(* External Parameters *)

              (**** Overall Coupling****)

         gZp == {
         ParameterType -> External,
         Value -> 3.0,
         InteractionOrder -> {NP,1},
         TeX -> Subscript[g,Zp],
         BlockName -> NPZPCOUP,

         Description -> "Overall Zp coupling strength"
   },

              (***** neutrino coupling ******)

          gee == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,ee],
         BlockName -> NPZPCOUP

   },

          gem == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,em],
         BlockName -> NPZPCOUP

   },

          get == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,et],
         BlockName -> NPZPCOUP

   },

          gmm == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,mm],
         BlockName -> NPZPCOUP

   },

          gme == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,me],
         BlockName -> NPZPCOUP

   },

           gmt == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,mt],
         BlockName -> NPZPCOUP

   },

          gtt == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,tt],
         BlockName -> NPZPCOUP

   },

          gte == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,te],
         BlockName -> NPZPCOUP

   },

         gtm == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,tm],
         BlockName -> NPZPCOUP

   },

        (***** quark coupling******)

          gur == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,ur],
         BlockName -> NPZPCOUP

   },

          gul == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,ul],
         BlockName -> NPZPCOUP

   },

          gdr == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,dr],
         BlockName -> NPZPCOUP

         },

         gdl == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,dr],
         BlockName -> NPZPCOUP

         },

    (***** leptons coupling******)

       glR == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,lR],
         BlockName -> NPZPCOUP

         },

       glL == {
         ParameterType -> External,
         Value -> 1.0,
         InteractionOrder -> {NP,0},
         TeX -> Subscript[g,lR],
         BlockName -> NPZPCOUP

         }

};

Ln = gZp* (gee* (vebar.Ga[\[Mu]].left[ve]) +
    gem *(vebar.Ga[\[Mu]].left[vm]) +
    get *(vebar.Ga[\[Mu]].left[vt]) +
    gmm *(vmbar.Ga[\[Mu]].left[vm]) +
    gme *(vmbar.Ga[\[Mu]].left[ve]) + gmt *(vmbar.Ga[\[Mu]].left[vt]) +
    gte*(vtbar.Ga[\[Mu]].left[ve]) + gtt *(vtbar.Ga[\[Mu]].left[vt]) +
     gtm *(vtbar.Ga[\[Mu]].left[vm]) + gul*(ubar.Ga[\[Mu]].left[u]) +
    gur*(ubar.Ga[\[Mu]].right[u]) + gdl*(dbar.Ga[\[Mu]].left[d]) +
    gdr*(dbar.Ga[\[Mu]].right[d]) + glL*(lbar.Ga[\[Mu]].left[l]) +
    glR*(lbar.Ga[\[Mu]].right[l]))*Zp[\[Mu]]

L =Ln+LSM

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
Last reply:

Hi,

What is the theoretical uncertainty quoted? and what is the statistical uncertainty quoted?
Typically statistical uncertainty depend of the number of events requested (default is at the order of the % level)
theoretical uncertainty depends of the power of alpha_S present in your process (for the renormalization scale uncertainty which is the dominating one in general) but at LO you typically expect error of 40%. So a disagreement of 2-3% can be easyily explained with a difference in the renormalization scale. (at that level of precision, theoretical error in PDF and factorization scale can also explained such small difference.)

Can you help with this problem?

Provide an answer of your own, or ask ouseph cj for more information if necessary.

To post a message you must log in.