What do these changes make possible? One can think of neugen3 as a set of models, each of which has a set of parameters. These changes allow a user to either change from one model to another, or modify the parameters used for a particular model. One application of this is in event re-weighting, where one applies a weight to an existing MC event calculated according to a change in model or model parameters.
Most of the parameters are set through a call to the routine SET_PARAMETERS, which requires a character string and a new value. The most useful parameter values are listed below. Also relevant is SET_PDFSET(IGROUP,ISET,Q2MIN) which switches the parton distribution set to a new PDFLIB set with the minimum Q2 value given. I have not included the INTRANUKE parameters yet but I will do so.
| Name | Description | Default Value | Reference |
|---|---|---|---|
| QEL_MA | Axial Vector mass for Quasi-elastic scattering | 1.032 | Llewellyn-Smith, Phys Rept. 3, 261 (1972). |
| RES_MA | Axial vector mass for resonance scattering | 1.032 | Rein and Sehgal, Ann. Phys. 133, 79 (1981). |
| COH_MA | Axial vector mass for coherent scattering | 1.00 | Rein and Sehgal, Nucl Phys. B223, 29 (1983). |
| QEL_FA0 | Value of the axial form factor at Q2=0 | -1.26 | Llewellyn-Smith, Phys Rept. 3, 261 (1972). |
| QEL_ETA | Elastic scattering parameter | 0.12 | Ahrens et al. Phys Rev. D 35, 785 (1987). |
| RES_OMEGA | Rein-Seghal model parameter | 1.05 | Rein and Sehgal, Ann. Phys. 133, 79 (1981). |
| RES_Z | Rein-Seghal model parameter | 0.75 | Rein and Sehgal, Ann. Phys. 133, 79 (1981). |
| COH_R0 | Scale parameter for nuclear size in coherent model | 1.00 | Rein and Sehgal, Nucl Phys. B223, 29 (1983). |
| COH_REI | Re/Im for pion scattering amplitude | 0.30 | Rein and Sehgal, Nucl Phys. B223, 29 (1983). |
| KNO_A1 | KNO hadronization parameter (nu+p reactions) | 0.5 | Schmitz, Norbert, Rapporteur's talk from the 1981 Lepton-Photon Conference, Bonn, 1981. |
| KNO_A2 | KNO hadronization parameter (nu+n reactions) | 0.0 | Schmitz, Norbert, Rapporteur's talk from the 1981 Lepton-Photon Conference, Bonn, 1981. |
| KNO_A3 | KNO hadronization parameter (nubar+p reactions) | 0.2 | Schmitz, Norbert, Rapporteur's talk from the 1981 Lepton-Photon Conference, Bonn, 1981. |
| KNO_A4 | KNO hadronization parameter (nubar+n reactions) | 0.2 | Schmitz, Norbert, Rapporteur's talk from the 1981 Lepton-Photon Conference, Bonn, 1981. |
| KNO_B | KNO hadronization parameter (proportionality constant in ln(W) vs. multiplicity relation) | 1.3 | Schmitz, Norbert, Rapporteur's talk from the 1981 Lepton-Photon Conference, Bonn, 1981. |
| KNO_"XYZ" | DIS / Resonance model tuning factors. Here X=(1,2) for CC, NC, Y=(1,2,3,4) for (nu-p,nu-n,nubar-p,nubar-n), and Z=(2,3) for final state multiplicity. | Gallagher, H., Proceedings of NuINT01, Nucl. Phys. Proc. Suppl v112, 188 (2002) |
neugen3 tuning. At the moment we are carrying out a full tuning of the generator to all the data that we have collected as being relevant. This includes old neutrino bubble chamber scattering data , structure function data at high energy, electron scattering data in the resonance region , as well as the recent data from the JUPITER experiment at JLab. We will probably modify some of the models, or even change models, based on this exercise. There are now new models available for the resonance production and coherent processes which *claim* to be better than the old models we are using. The DIS model will also be updated, the existing model is missing some important effects and includes at least one mistake found by Donna (using a HO parton distribution set with a LO calculation.). Donna in particular is evaluating the DIS model. I will arrange a separate series of weekly meetings over the next month as this progresses, let me know if you are interested in attending.