Model-Specific Closure Test

Colibri can be used to run a model-specific closure tests. Here we show how to do so for the Les Houches parametrisation (implemented here).

Step 1: runcard

You can adapt the runcard presented here to run a closure test so that it includes the following:

# MODEL-SPECIFIC CLOSURE TEST:
closure_test_pdf: colibri_model
closure_test_model_settings:
    model: les_houches_example
    # The parameters of the model.
    parameters:
        beta_gluon: 10.9
        alpha_gluon: 0.356
        alpha_up: 0.718
        beta_up: 3.81
        epsilon_up: -1.56
        gamma_up: 3.30
        alpha_down: 1.71
        beta_down: 10.0
        epsilon_down: -3.83
        gamma_down: 4.64
        norm_sigma: 0.211
        alpha_sigma: -0.048
        beta_sigma: 2.20

And remove or comment out closure_test_pdf: LH_PARAM_20250519. Within the closure_test_model_settings, one needs to specify any of the hyperparameters relevant to build the model instance. The example model here shown does not necessitate further settings, but in principle one could have additional hyperparameters to tune.

Note that, unlike for a standard closure test, in this case we need to specify the initial values for each parameter of the PDF model. For the values above, we have taken the best-fit values, taken from Ref. [A+05].

Step 2: running the fit

You can produce the fit by running the following command from the colibri/les_houches_example directory:

les_houches_exe runcards/lh_fit_closure_test.yaml

where the runcard path or name should be changed as needed.

Running the fit will create a directory called lh_fit_closure_test, where you will find the output of the fit. You can read more about it in this tutorial.

You can evolve it by following the instructions given in this tutorial.