The EvtGen Project has been in development and use for over a decade and with the growing popularity of B physics, we feel that it is ever as important to have a high quality Monte Carlo data generation. The EvtGen package provides a versatile B decay functionality which is why a team was formed at the University of Warwick, sheltered by CERN, to take up the development of this package so that a stable release is available to all the particle physics experiments. If you wish to know more about us, please feel free to read this website or contact us.

Recent News items

New version 1.6.0

EvtGen version 1.6.0 (R01-06-00) is now available. Recommended external packages are HepMC 2.06.09, pythia 8.186, Photos++ 3.61 and Tauola++ 1.1.5. The main changes with respect to version 1.5.0 are:

  • Added DECAY.DEC/XML, which contain updated semileptonic charm and beauty branching fractions using the 2014 PDG, tuned to minimize disagreements between measurements and EvtGen for both inclusive and exclusive decays. For Ds+ → 2pi+ pi- there was double counting of branching fractions resulting in the total branching fraction being 1.5 times larger than the measured one. Fixed by revisiting submodes, which now fill total Ds → 3pi.
  • Updated the evt.pdl particle properties file to the PDG 2014 edition.
  • Added EvtKStopizmumu model for KS → pi0 mu mu decays based on JHEP08 004, 1998.
  • Added extensions to the EvtHQET2(FF) model for semitauonic decays.
  • Implemented new LQCD form factors for Lb → L mu mu from arXiv paper 1602.01399 (EvtRareLbToLllFFlQCD); old LQCD form factors are removed.
  • Fixed incorrect spinor algebra used in S1 → 1/2 S2, 1/2 → S3 S4 decays in EvtDiracParticle::rotateToHelicityBasis() functions.
  • Fixed bug in the definition of the initial spinor term Sinit in EvtRareLbToLll::HadronicAmpRS().


New version 1.5.0

EvtGen version 1.5.0 (R01-05-00) is now available. Recommended external packages are HepMC 2.06.09, pythia 8.186, Photos++ 3.61 and Tauola++ 1.1.5. The main changes with respect to version 1.4.0 are:

  • Physics model updates and additions:

    1. Bc → scalar ell nu (EvtBcSMuNu) and Bc → tensor ell nu (EvtBcTMuNu) decays

    2. EvtbsToLLLLAmp and EvtbsToLLLLHyperCP for B0_q → l+ l- l+ l- decays

    3. Modified EvtSVPHelAmp and added a new EvtSVPHelCPMix model, implementing the complete mixing phenomenology of Bs to vector gamma decays

    4. Added the EvtB2MuMuMuNu model for simulating the very rare four-leptonic decays B- → mu+ mu- anti-nu_mu mu-

    5. Fixed form-factor calculations for the BTOSLLBALL model 6 used to generate b → sll decays. Affects B → K*ll, B → rho ll and B → omega ll, particularly the electron modes

    6. EvtD0mixDalitz code cleanup, inverted q/p for decays of D0bar (simplifies user decay files) and fixed y parameter bug.

  • Changed the installation and set-up script name to be just; it uses the VERSION variable to specify the required tag. List of tags are available using either “svn ls -v”
    or by going to tags.
    Modified the configure and scripts to work on Mac; needed Mac compilation patch files added to the new “platform” subdirectory.
  • Updated EvtGenExternal/EvtPhotosEngine to check that additional particles from the outgoing vertex are indeed (FSR) photons, since later versions of PHOTOS introduce pair emission, where particles may not always be photons.
    Updated the configure script to automatically select the library names for PHOTOS++; version 3.56 and below
    uses Fortran, version 3.61 and above uses C++ only (default). Avoid using v3.60, since it does not work. This needs the PHOTOS libraries built before EvtGen is configured.
    Changed the initialisation order of the infrared cut-off in EvtPhotosEngine. This actually has no effect, since the exponentiation function sets it to the same 1e-7 value, but it’s now in the correct order if we need to update it.
  • Added Mersenne-Twister random number generator (RNG) EvtMTRandomEngine. It requires c++11 compiler features (>= gcc 4.7), which should automatically be enabled by the configure script. Introduced the preprocessor environment variable EVTGEN_CPP11 for c++11 features. EvtMTRandomEngine is the default RNG for the validation and test examples
    if c++11 features are enabled.

  • Fixed accessed uninitialised memory in EvtPDL.cpp, line 213.
  • Reimplemented the real Spence function in C++ and removed its fortran implementation.
  • Added the validation program to create ROOT files containing information about the complete decay tree.
    Added a phase-space test validation/ and PhaseSpacePlots.C to visually check the flatness of Dalitz plots in order to ensure that the RNG is not producing biased results that depend on particle ordering.

  • Changed the width of chi_b1 in evt.pdl from 9.8928 GeV to zero.


New version 1.4.0

EvtGen version 1.4.0 (R01-04-00) is now available. The main changes with respect to version 1.3.0 are:

  • The removal of the EvtStdlibRandomEngine class since this can produce biases to kinematic distributions when one or more of the daughters is a resonance, such as B0 —> K pi psi. All example and validation codes now use the
    EvtSimpleRandomEngine, which does not show biases. We are in the process of adding at least one other random number engine (Mersenne twister) to the package, but further tests are needed.

  • Added the ability to store named attributes for EvtParticles in the form of an STL map<string, int>. The setAttribute(name, value) stores the required value, while getAttribute(name) retrieves the integer value. This is used in EvtPhotosEngine to specify the final-state radiation “FSR” attribute to 1 for any additional photons (EvtPhotonParticles) created by Photos++. It also stores the “ISR” attribute, but this is always set to zero, since only FSR photons are created. If the named attribute doesn’t exist, then getAttribute() returns zero.

  • To avoid clashes with other namespaces, EvtReport has been modified to use logging output severity status flags with the “EVTGEN_” prefix, e.g. INFO becomes EVTGEN_INFO. The global report() function has been also been renamed to EvtGenReport().

  • Added rare Lambda B to Lambda* l l models described in arXiv:1108.6129, with various form factors from Gutsche et al. (arXiv:1301.3737) and lattice QCD (arXiv:1212.4827).

  • For EvtbTosllBallFF: implementation of Bs —> K* form factors from Ball-Zwicky and z-parametrization form factors from
    arXiv:1006.4945; fixed Bs —> phi l l form factors, since T3 showed a non-physical pole at very low q2 which significantly affected the electron mode.

  • Changed to in the setup script; the CERN svn access address has changed since last time.


New version 1.3.0

EvtGen version 1.3.0 (R01-03-00) is now available. The main changes with respect to version 1.2.0 are fixes to compilation warnings provided by gcc >= 4.6, the requirement of using the latest version of Pythia 8 (8.180) for changes to the Pythia source code header files (not backwards compatible), as well as updates to the generic Dalitz plot model.


Site up again

The EvtGen website is back up again.


Page undergoing emergency maintenance

Due to server problems, the website is undergoing some emergency maintenance. We apologize for inconvenience.