Adjustable Parameters

Welcome to the slide-by-slide blog for the afternoon session of the first Monday of PASI 2010.

Anticipation is growing in the conference hall as people trickle back from lunch and sea water trickles out of my ear.

15:02 First up is the Sao Paulo potential from L.C. Chamon

15:04 The talk commences. The intro slide tells us that the potential is a model for the heavy-ion nuclear interaction with no adjustable parameters - one that uses data and predictions instead. Nice font.

15:06 The optical potential is extracted from elastic scattering analyses, and show significant energy dependence; in the Sao Paulo model this is from Pauli non-locality.

15:07 One for the students. And me. Difference between charge distribution and single proton density: the former gives the charge inside a volume V, the latter the probability of finding a proton inside a volume V. The charge distribution is exponential in radius, so we assume the matter density is too.

15:10 I want to start a band called the Adjustable Parameters.

15:12 Sao Paulo potential: zero range interaction with a non-local factor exponential in the kinetic energy. No adjustable parameters!

15:14 Apply to elastic scattering analysis: real part of optical potential > Sao Paulo potential, no adjustable parameters, imaginary part is the WS potential, which I keep wanting to call the Wigner-Seitz potential, but is not. This is adjustable.

15:17 Not only do we not like free parameters, but we actively want to kill them. This is getting bloodthirsty.

15:19 This is moving quickly. We've just raced through 12C-12C collisions.

15:20 Imaginary part of SP potential; by comparison with the Lax potential, assume imag. part is proportional to real part.

15:21 The same constant of proportionality works well for low and high energy elastic scattering.

15:22 Apparently there are no free parameters in this model.

15:23 Works well for exotic systems, too.

15:24 Heavy Ion fusion: SP potential is the bare potential. A new piece of information comes to light: the model contains no adjustable parameters.

15:25 Results: at low center of mass energies, there is a large deviation from a coupled cluster description, but at high energies the bare potential works well for tightly bound nuclei, but results in a 30% deviation for weakly bound nuclei. (We're talking about the relative cross sections of experiment versus theory).

15:31 12C + 12C Astrophysical S-Factor is another application which I missed because I got cramp in my thumb.

15:33 The level of detail in the talk is now reaching a critical point; there may be a phase transition in this blog very soon.

15:34 It's just been revealed that there are no free parameters. He should have pointed that out before now, I think.

15:35 CONCLUSION: SP potential offers a general description of heavy ion reactions over a large energy range, and acts as a standard with which to compare. Nucleus nucleus scattering and improvement coupled cluster models are in progress.

15:36 Questions. I hope someone asks how many adjustable parameters the model has.

15:38 No isospin dependence is raised. Arturo is asking me about internet connection so I miss what is said.

15:43 Just been giving my fingers a rest.

15:47 I somehow managed to miss most of the questions. Carlos makes the important announcement about lunch tickets. Also, sign up for the city tour, or no lunch tickets for you!