wiki:Reweight

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Version 17 (modified by Olivier Mattelaer, 9 years ago) ( diff )
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Description of the method

The method consist to use a sample of events (weighted or unweighted events) and associate to those events a new weight corresponding to a new theoretical hypothesis. This weight can be propagate through the all simulation chain in order to avoid to have to perform the full-simulation on a huge number of sample. This methods works only if the original hypothesis and the new one are both significant in the same part of the phase-space. the new weight is given by $$W_{new} = |M_{new}|^{2 /|M_{old}|}2 * W_{old} $$

Reweighting of NLO sample

As in 2.3.3, we only offer Leading Order type reweighting of NLO sample (also call "kamikaze" reweighting). This consists to reweight the S events by the born matrix element and the H events by the real matrix element. We have shown that for EW EFT theory this is a correct approach. The way to run the code is the same as for the LO (see below)

The correct NLO reweighting is only available on alpha version so far and can be requested by email to olivier Mattelaer. This version will be available in 2.4.0 Here is the information to use it. In order to perform the correct NLO reweighting, you need to generate the original samples with the following options:

True = keep_rwgt_info ! keep the information for reweighting in the lhe file (huge impact on size file)

After the reweighting will automatically be the NLO and, for the user point of view, the interface to run the re-weighting is the same as the LO one described below. In order to run the "kamikaze" reweighting on this sample, you can include in the reweighting_card the following command (at the beginning of the file):

"""

change mode LO

"""

Technical details

Limitation

The two theoretical hypothesis should differ ONLY by difference in the model parameters. So this should be the same pdf/cut (you can change model and process definition).

Note that the functional form of the hard scale can not be changed.
In presence of decay chain the order of the particle in the events file is important. This is important if you want to use this tools with LHE events not produced by MadGraph5_aMC@NLO.

Do I need special package

Starting from MadGraph5_aMC@NLO.2.3.2, you need to have f2py on your machine. The easiest way to install f2py is to install numpy (if not already done).

How to use the code on the flight.

--> Add comment: Same for the NLO. Here some examples.

When running the generation of events (./bin/generate_events from the local directory or "launch" via the mg5 interface) you will have two questions. The first one is:

The following switches determine which programs are run:
 1 Run the pythia shower/hadronization:                   pythia=NOT INSTALLED
 2 Run PGS as detector simulator:                            pgs=NOT INSTALLED
 3 Run Delphes as detector simulator:                    delphes=NOT INSTALLED
 4 Decay particles with the MadSpin module:              madspin=OFF
 5 Add weight to events based on coupling parameters:   reweight=OFF
  Either type the switch number (1 to 5) to change its default setting,
  or set any switch explicitly (e.g. type 'madspin=ON' at the prompt)
  Type '0', 'auto', 'done' or just press enter when you are done.
 [0, 4, 5, auto, done, madspin=ON, madspin=OFF, madspin, reweight=ON, ... ][60s to answer] 
>

As you can see the reweight options is OFF by default, to set it on you can either type "5" (not adviced if you script) or "reweight=ON". Then you should have:

The following switches determine which programs are run:
 1 Run the pythia shower/hadronization:                   pythia=NOT INSTALLED
 2 Run PGS as detector simulator:                            pgs=NOT INSTALLED
 3 Run Delphes as detector simulator:                    delphes=NOT INSTALLED
 4 Decay particles with the MadSpin module:              madspin=OFF
 5 Add weight to events based on coupling parameters:   reweight=ON
  Either type the switch number (1 to 5) to change its default setting,
  or set any switch explicitly (e.g. type 'madspin=ON' at the prompt)
  Type '0', 'auto', 'done' or just press enter when you are done.
 [0, 4, 5, auto, done, madspin=ON, madspin=OFF, madspin, reweight=ON, ... ][60s to answer]

Then the second question is (after that you just press enter on that question):

Do you want to edit a card (press enter to bypass editing)?
  1 / param     : param_card.dat
  2 / run       : run_card.dat
  3 / reweight  : reweight_card.dat
 you can also
   - enter the path to a valid card or banner.
   - use the 'set' command to modify a parameter directly.
     The set option works only for param_card and run_card.
     Type 'help set' for more information on this command.
 [0, done, 1, param, 2, run, 3, reweight, enter path][60s to answer]

You HAVE TO define/edit the reweight_card.dat, the syntax is explained in the file. The default file is basically empty and will make the re-weighting to crash since both theoretical hypothesis are identical.

How to use the code after the generation of events as been completed.

--> Add for the NLO

You can also use the madevent interface as explained below:

go to the process directory.
launch the ./bin/madevent script
type reweight RUN_NAME
then you will see the following question:
```
Do you want to edit one cards (press enter to bypass editing)?
  1 / reweight  : reweight_card.dat
 you can also
   - enter the path to a valid card.
 [0, done, 1, reweight, enter path][60s to answer]
```
If you didn't define the content of reweight_card.dat already. You need to do it. The syntax is explained inside the file, and you can see example below (validation section). The important point, is that the first line should be launch, and then you specify which parameter, you want to modify. This is the exact same syntax has for scripting a scan over parameter.
exit the file and you are done (the script will run).

If the file Cards/reweight_card.dat is already defined, you can launch the script with

./bin/madevent reweight RUN_NAME -f

The -f options prevent the question to be asked.

Options

Note all the following options will be available in Madgraph5_aMC@NLO since version 2.3.2

"change model <XXX>" performed the reweighting within a new model (you then need to profide a full param_card and not a difference)
"change process <XXX>" change the process definition of the process.
"change process <XXX> --add" add one process definition of the process to the new list.
"change output <i>": Three options: 'default'(i.e. lhef version3 format), '2.0' (i.e. lhef version2 format, the main weight is replace), 'unweight' (a new unweighting is applied on the events sample.)
"change helicity <True|False>": perform reweighting for the given helicity (True --default--) or do the sum over helicity.
"change rwgt_dir <PATH>": change directory where the computation is performed. This can be use to avoid to recreate/recompile the fortran executable if pointing to a previously existing directory.
change mode LO:

Input/Output format

the output format follows the Leshouches agreement version 3 [link arxiv]

as an example the header looks like:

<initrwgt>
<weightgroup type='mg_reweighting'>
<weight id='mg_reweight_1'>set param_card dim6 1 100.0
</weight>
<weight id='mg_reweight_2'>set param_card dim6 2 100.0
</weight>
<weight id='mg_reweight_3'>set param_card dim6 3 100.0
</weight>
</weightgroup>
</initrwgt>

and one associated events:

<event>
 8      0 +7.9887000e-06 1.24664300e+02 7.95774700e-02 1.23856500e-01
        1 -1    0    0  501    0 +0.0000000e+00 +0.0000000e+00 +1.3023196e+03 1.30231957e+03 0.00000000e+00 0.0000e+00 -1.0000e+00
       -2 -1    0    0    0  501 +0.0000000e+00 +0.0000000e+00 -1.4499581e+02 1.44995814e+02 0.00000000e+00 0.0000e+00 1.0000e+00
      -24  2    1    2    0    0 -1.2793809e+01 -8.3954553e+01 -1.1792566e+02 1.65987064e+02 8.02071978e+01 0.0000e+00 0.0000e+00
       23  2    1    2    0    0 +1.2793809e+01 +8.3954553e+01 +1.2752494e+03 1.28132832e+03 9.12640692e+01 0.0000e+00 0.0000e+00
       11  1    3    3    0    0 -1.2462673e+01 +1.3647422e+01 -2.6083861e+01 3.19677669e+01 0.00000000e+00 0.0000e+00 -1.0000e+00
      -12  1    3    3    0    0 -3.3113586e-01 -9.7601975e+01 -9.1841804e+01 1.34019297e+02 0.00000000e+00 0.0000e+00 1.0000e+00
        4  1    4    4  502    0 -1.8321803e+01 +9.0929609e+01 +9.3905973e+02 9.43629724e+02 0.00000000e+00 0.0000e+00 -1.0000e+00
       -4  1    4    4    0  502 +3.1115612e+01 -6.9750557e+00 +3.3618969e+02 3.37698598e+02 0.00000000e+00 0.0000e+00 1.0000e+00
<rwgt>
<wgt id='mg_reweight_1'> 4.55278761371e-06 </wgt>
<wgt id='mg_reweight_2'> 2.65941887458e-06 </wgt>
<wgt id='mg_reweight_3'> 8.68203803896e-06 </wgt>
</rwgt>
</event>

The reweight_card in that case was:

launch
   set Dim6 1 100
   set Dim6 2 0
   set Dim6 3 0
   set Dim6 4 0
   set Dim6 5 0
launch
   set Dim6 1 0
   set Dim6 2 100
   set Dim6 3 0
   set Dim6 4 0
   set Dim6 5 0
launch
   set Dim6 1 0
   set Dim6 2 0
   set Dim6 3 100
   set Dim6 4 0
   set Dim6 5 0

Note:

The production events were in this case made via the SM where all those coefficient were in fact set to zero. Therefore all the line setting the line to zero were superfluous, and this is the reason why they didn't appear in the banner.
You can also specify a path to a param_card in the reweight_card. The content of the header being computed automatically with the difference of the two param_card.

The cross-section of the original file and those associated with the new hyppothesis are printed at the end of the script:

INFO: Original cross-section: 0.80086112072 +- 0.0025669959099 pb 
INFO: Computed cross-section: 
INFO: 119 : 5.0238030968 
INFO: 120 : 4.46724081967 
INFO: 121 : 0.790019392142

Validation

The comparison for the full cross-section are done like this:

./bin/madevent ./Cards/reweight_card.dat

p p > e+ e- cross-section

The reweight_card is the following:

launch
 set aewm1 100
launch 
 set aewm1 200
launch 
 set aewm1 300

The associated cross-section are
1. 1135.25 pb
2. 1095.28 pb
3. 1329.52 pb
The cross-section computed with MadEvent are
1. 1130 +- 2.815 pb
2. 1098 +- 2.478 pb
3. 1336 +- 2.777 pb

EWDIM6 Validation

input

The model use for this validation is the EWDIM6 (See: http://arxiv.org/abs/arXiv:1205.4231). 10k events where generated with the standard model (cross-section: 0.8008 ± 0.0026 pb)

The reweight_card was:

launch
   set Dim6 1 100
   set Dim6 2 0
   set Dim6 3 0
   set Dim6 4 0
   set Dim6 5 0
launch
   set Dim6 1 10
   set Dim6 2 0
   set Dim6 3 0
   set Dim6 4 0
   set Dim6 5 0
launch
   set Dim6 1 1
   set Dim6 2 0
   set Dim6 3 0
   set Dim6 4 0
   set Dim6 5 0
launch
   set Dim6 1 0.1
   set Dim6 2 0
   set Dim6 3 0
   set Dim6 4 0
   set Dim6 5 0
launch
   set Dim6 1 0.01
   set Dim6 2 0
   set Dim6 3 0
   set Dim6 4 0
   set Dim6 5 0

The same scan was done for the three first coupling (CWWW, CW, CB)

result:

For CWWW

Coupling value ($TeV^{-2}$) Reweight cross-section (pb) MadEvent cross-section (pb) Status
0.01 0.800810008029 0.7973 ± 0.0023 OK
0.1 0.800903791291 0.799 ± 0.0026 OK
1 0.802209013071 0.7987 ± 0.0025 OK
10 0.85200014698 0.8584 ± 0.00092 OK
100 5.0238030968 6.09 ± 0.0082 FAIL
100 5.04763 6.09 ± 0.0082 FAIL (make with a sample of 100k events)

The last entry fails since the expected distribution for such value of the coupling is too different from the distribution of the Standard Model. Such discrepancy are expected in this case. One hint is that the cross-section is an order of magnitude higher than the original one (Looking at the distribution confirm this). The inversed reweight (i.e. starting from the CWW=100 sample of events and reweight to find back the SM) is working properly. It returned: 0.803341120226

The various distribution for those generation are in attachment of this web page. The dashed blue curve is the one produced by reweighting. While the solid black is the curve generated by MadEvent. All sample are done with 100k events for the comparison of distributions.

For CW

Coupling value ($TeV^{-2}$) Reweight cross-section (pb) MadEvent cross-section (pb) Status
0.01 0.800798262059 0.7953 +- 0.002497 OK
0.1 0.801379445746 0.7988 ± 0.0023 OK
1 0.806872565125 0.8065 ± 0.0023 OK
10 0.889336417677 0.8832 ± 0.003 OK
100 4.46724081967 4.519 ± 0.015 FAIL
100 4.44273 4.519 ± 0.015 FAIL (make with a sample of 100k events)

Same comment as for the previous coupling.

For CB

Coupling value ($TeV^{-2}$) Reweight cross-section (pb) MadEvent cross-section (pb) Status
0.01 0.800798262059 0.7977 ± 0.0027 OK
0.1 0.800782626532 0.7985 ± 0.0024 OK
1 0.800626859275 0.7981 +- 0.002365 OK
10 0.799127987884 0.7971 ± 0.0024 OK
100 0.790019392142 0.7852 ± 0.0026 OK
100 0.786698206995 0.7852 ± 0.0026 OK (make with a sample of 100k events)

This operator has less impact on the cross-section/distributions, and therefore even a large value of the coupling is still working fine.

Note:

The cross-section obtained for 100k events sample is 0.7989 ± 0.00087
The statistical fluctuation of the original sample is reflected on the reweighing cross-section (as expected)

Attachments (6)

cwww_0.1.pdf (277.4 KB ) - added by Olivier Mattelaer 11 years ago.
cwww_0.01.pdf (277.4 KB ) - added by Olivier Mattelaer 11 years ago.
cwww_1.pdf (277.0 KB ) - added by Olivier Mattelaer 11 years ago.
cwww_10.pdf (280.9 KB ) - added by Olivier Mattelaer 11 years ago.
cwww_100.pdf (274.5 KB ) - added by Olivier Mattelaer 11 years ago.
15_12_11_ReWeighting_EFT.pdf (3.3 MB ) - added by Olivier Mattelaer 9 years ago.

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Coupling value ($TeV^{-2}$)	Reweight cross-section (pb)	MadEvent cross-section (pb)	Status
0.01	0.800810008029	0.7973 ± 0.0023	OK
0.1	0.800903791291	0.799 ± 0.0026	OK
1	0.802209013071	0.7987 ± 0.0025	OK
10	0.85200014698	0.8584 ± 0.00092	OK
100	5.0238030968	6.09 ± 0.0082	FAIL
100	5.04763	6.09 ± 0.0082	FAIL (make with a sample of 100k events)