Change Details

**Static variable** The `m_bbprod` variable is `static` and alters behaviour for signal decays when there is a general decay definition (in general table), as reported by Belle II. https://gitlab.cern.ch/evtgen/evtgen/-/blob/R03-00-00-beta1/EvtGenModels/EvtBtoXsgammaKagan.hh#L145 **Documentation** Reported to EvtGen dev mailing list: Dear EvtGen developers, I am working with the Belle 2 experiment and I have recently been using it to generate B->Xs gamma events using the BTOXSGAMMA model, documented in https://evtgen.hepforge.org/doc/EvtGenGuide.pdf, page 76. In there you list the default parameters which describe the default behaviour of the model. If the inputs are not given, a precomputed, hardcoded set of hadronic masses is used. If the inputs are given this triggers the calculation of the hadronic masses. In the default parameters that the documentation states were used to precompute hadronic masses, `λ_1 = 0.3` is listed. However, this cannot be true, because the lambda parameter is defined as negative, see e.g. https://arxiv.org/pdf/hep-ph/9805303.pdf, page 24, right after equation 24; What I think was the original default parameter is `λ_1 = -0.3`. In fact, when I tried to reproduce the spectrum with `λ_1 = 0.3` given explicitly, this had very long integration times and the integrals for the hadronic mass computation did not converge. Switching to `λ_1 = -0.3` I was able to reproduce the "default" behaviour of the BTOXSGAMMA model. I think the lambda value should be corrected to avoid any confusion for those using the model in the future. Let me know if case you need more information, Kind Regards, Henrikas

**Static variable** The `m_bbprod` variable is `static` and alters behaviour for signal decays when there is a general decay definition (in general table), as reported by Belle II. https://gitlab.cern.ch/evtgen/evtgen/-/blob/R03-00-00-beta1/EvtGenModels/EvtBtoXsgammaKagan.hh#L145 The issue has been studied and summarised here. https://gitlab.desy.de/ana.luisa.mc/evtgen_issue **Documentation** Reported to EvtGen dev mailing list: Dear EvtGen developers, I am working with the Belle 2 experiment and I have recently been using it to generate B->Xs gamma events using the BTOXSGAMMA model, documented in https://evtgen.hepforge.org/doc/EvtGenGuide.pdf, page 76. In there you list the default parameters which describe the default behaviour of the model. If the inputs are not given, a precomputed, hardcoded set of hadronic masses is used. If the inputs are given this triggers the calculation of the hadronic masses. In the default parameters that the documentation states were used to precompute hadronic masses, `λ_1 = 0.3` is listed. However, this cannot be true, because the lambda parameter is defined as negative, see e.g. https://arxiv.org/pdf/hep-ph/9805303.pdf, page 24, right after equation 24; What I think was the original default parameter is `λ_1 = -0.3`. In fact, when I tried to reproduce the spectrum with `λ_1 = 0.3` given explicitly, this had very long integration times and the integrals for the hadronic mass computation did not converge. Switching to `λ_1 = -0.3` I was able to reproduce the "default" behaviour of the BTOXSGAMMA model. I think the lambda value should be corrected to avoid any confusion for those using the model in the future. Let me know if case you need more information, Kind Regards, Henrikas

**Static variable** The `m_bbprod` variable is `static` and alters behaviour for signal decays when there is a general decay definition (in general table), as reported by Belle II. https://gitlab.cern.ch/evtgen/evtgen/-/blob/R03-00-00-beta1/EvtGenModels/EvtBtoXsgammaKagan.hh#L145 The issue has been studied and summarised here. https://gitlab.desy.de/ana.luisa.mc/evtgen_issue **Documentation** Reported to EvtGen dev mailing list: Dear EvtGen developers, I am working with the Belle 2 experiment and I have recently been using it to generate B->Xs gamma events using the BTOXSGAMMA model, documented in https://evtgen.hepforge.org/doc/EvtGenGuide.pdf, page 76. In there you list the default parameters which describe the default behaviour of the model. If the inputs are not given, a precomputed, hardcoded set of hadronic masses is used. If the inputs are given this triggers the calculation of the hadronic masses. In the default parameters that the documentation states were used to precompute hadronic masses, `λ_1 = 0.3` is listed. However, this cannot be true, because the lambda parameter is defined as negative, see e.g. https://arxiv.org/pdf/hep-ph/9805303.pdf, page 24, right after equation 24; What I think was the original default parameter is `λ_1 = -0.3`. In fact, when I tried to reproduce the spectrum with `λ_1 = 0.3` given explicitly, this had very long integration times and the integrals for the hadronic mass computation did not converge. Switching to `λ_1 = -0.3` I was able to reproduce the "default" behaviour of the BTOXSGAMMA model. I think the lambda value should be corrected to avoid any confusion for those using the model in the future. Let me know if case you need more information, Kind Regards, Henrikas