Accessing crystalball cdf parameters

Dear ROOTers,
I am trying to add a crystalball cdf to my function map, and adjust its parameters for every event. When I try accessing them, it tells me to use the parameter name instead of a number, but I still get nothing. When I call Print(), it tells me that there are no parameters. How can I access them in order to change them? I attach a simple macro that shows the above.
Thank you,
CB_cdf.C (610 Bytes)

  TF1 *cdf_test = new TF1("cdf_test", "ROOT::Math::crystalball_cdf(x, [Alpha], [N], [Sigma], [Mean])", -5., 5.);
  cdf_test->SetParameter("Alpha", 2.);
  cdf_test->SetParameter("N", 2.);
  cdf_test->SetParameter("Sigma", 2.);
  cdf_test->SetParameter("Mean", 1.);

Perfect, thank you very much!