MadGraph5_aMC@NLO

configuring MadSpin for decay of squarks

Asked by Arka Santra

Hello experts,
  I want to use MadSpin for the decays of squarks. The mass of the squark is 600 GeV and mN1 is 560 GeV (mN2 is 580 GeV). So this is the set of commands I am using:

    define all = e+ e- mu+ mu- ta+ ta- u u~ d d~ c c~ s s~ b b~ ve vm vt ve~ vm~ vt~
    decay susysq > jb n2
    decay susysq~ > jb n2
    decay n2 > all all n1

(full config file is here: https://github.com/asantra/SquarkProduction/blob/master/MadGraphControl_SimplifiedModel_onestepN2_ZN1.py)

But when I am looking at the PYTHIA Event Listing (hard process-modified) around line 6306 of the log, I do not see the n2 at all (but gravitino even though I did not want this).

21:47:19 -------- PYTHIA Event Listing (hard process-modified) --------------------------------------------------------------------------
21:47:19
21:47:19 no id name status mothers daughters colours p_x p_y p_z e m
21:47:19 0 90 (system) -11 0 0 0 0 0 0 0.000 0.000 0.000 13000.000 13000.000
21:47:19 1 2212 (p+) -12 0 0 3 0 0 0 0.000 0.000 6500.000 6500.000 0.938
21:47:19 2 2212 (p+) -12 0 0 4 0 0 0 0.000 0.000 -6500.000 6500.000 0.938
21:47:19 3 21 (g) -21 1 0 5 7 501 503 0.000 0.000 1257.669 1257.669 0.000
21:47:19 4 2 (u) -21 2 0 5 7 503 0 -0.000 -0.000 -2489.687 2489.687 0.000
21:47:19 5 1000001 (~d_L) -22 3 4 8 9 501 0 856.719 169.238 624.919 1230.094 600.000
21:47:19 6 -1000001 (~d_Lbar) -22 3 4 14 15 0 502 -264.385 -505.199 -422.338 929.244 600.000
21:47:19 7 2 u 23 3 4 0 0 502 0 -592.334 335.960 -1434.599 1588.018 0.000
21:47:19 8 1000022 (~chi_10) -22 5 0 10 11 0 0 744.009 142.115 580.143 1105.820 559.040
21:47:19 9 1 d 23 5 0 0 0 501 0 112.709 27.123 44.775 124.274 0.330
21:47:19 10 1000039 ~Gravitino 23 8 0 0 0 0 0 -80.207 12.021 -7.205 81.422 0.001
21:47:19 11 23 (Z0) -22 8 0 12 13 0 0 824.216 130.094 587.348 1024.399 90.323
21:47:19 12 4 c 23 11 0 0 0 504 0 790.346 132.017 540.546 966.576 1.500
21:47:19 13 -4 cbar 23 11 0 0 0 0 504 33.870 -1.922 46.802 57.823 1.500
21:47:19 14 1000022 (~chi_10) -22 6 0 16 17 0 0 -286.488 -476.687 -414.181 892.256 561.488
21:47:19 15 -1 dbar 23 6 0 0 0 0 502 22.103 -28.512 -8.156 36.988 0.330
21:47:19 16 1000039 ~Gravitino 23 14 0 0 0 0 0 -140.873 -200.743 -499.398 556.364 0.001
21:47:19 17 23 (Z0) -22 14 0 18 19 0 0 -145.615 -275.944 85.216 335.892 90.625
21:47:19 18 5 b 23 17 0 0 0 505 0 -70.337 -74.717 61.394 119.675 4.800
21:47:19 19 -5 bbar 23 17 0 0 0 0 505 -75.279 -201.227 23.822 216.217 4.800

This is the full log of the run:
https://drive.google.com/file/d/1FJx5JZCzzKrodamjffZOofDkmYgGQGwx/view?usp=sharing

Am I doing any mistake in configuring MadSpin squark decays? May I know what is the best way of using squark decay with MadSpin?

Thank you,
Arka

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

1) Here I have no clue of what you are doing and what you are trying to do.
In your python file, you seems to generate the following process:
 define susylqL = ul dl cl sl
    define susylqL~ = ul~ dl~ cl~ sl~
    define susylqR = ur dr cr sr
    define susylqR~ = ur~ dr~ cr~ sr~
    generate p p > susylqL susylqL~ $ go susyweak susylqR susylqR~ @1
    add process p p > susylqL susylqL~ j $ go susyweak susylqR susylqR~ @2
    add process p p > susylqL susylqL~ j j $ go susyweak susylqR susylqR~ @3

But in the log file, I see the following:
21:46:30 generate p p > go go

This does not make sense...
I think that you mix two computations here

2) Are you aware that the following line:
decay n2 > all all n1
is useless since
a) you do not have any n2 particles in your production events, (so this line is never use)
b) Three body decay (via off-shell production) can not be handle by MadSpin (at least in its regular mode)
(so if it was used, it will lead to a crash)
(as we always print on the screen for ANY run:)
13:02:15 INFO: BE AWARE OF THE CURRENT LIMITATIONS:
13:02:15 INFO: (1) Only a succession of 2 body decay are currently allowed

3) Note that MadSpin is ONLY valid in narrow-width approximation, I do not see in your code anything about the width. It is however important that you check the validity of the narrow-width approximation, otherwise MadSpin can return random result (or enter infinite loop).

4) I do not see anywhere in your log where "jb" is defined. Not sure why MadSpin does not complains about this....

Cheers,

Olivier

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