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Interfacing Herwig++ and EvtGen. M. Baehr, S. Gieseke, M. Gigg, D. Grellscheid , K. Hamilton, S. Latunde-Dada, S. Plaetzer, PR , M.H. Seymour, A. Sherstnev, J. Tully, B.R. Webber. Peter Richardson IPPP, Durham University. A. Siodmok. Outline. Introduction Changes needed To EvtGen

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interfacing herwig and evtgen

Interfacing Herwig++ and EvtGen

M. Baehr, S. Gieseke, M. Gigg, D. Grellscheid, K. Hamilton, S. Latunde-Dada, S. Plaetzer, PR, M.H. Seymour, A. Sherstnev, J. Tully, B.R. Webber

Peter Richardson

IPPP, Durham University

A. Siodmok

EvtGen Workshop 13th Jan

outline
Outline
  • Introduction
  • Changes needed To EvtGen
  • Conclusions

EvtGen Workshop 13th Jan

herwig
Herwig++
  • In Herwig++ we now use the same algorithm we used in the FORTRAN program for the decay of fundamental particles for both fundamental and hadron decays.
  • Herwig++ includes sophisticated modelling of the decays of fundamental particles, both SM and in BSM models, tau leptons, mesons and baryons.
  • The algorithm is the same as that in EvtGen, although the implementation is different.

EvtGen Workshop 13th Jan

d g k pp
DgKpp

Comparison of Herwig++ and EvtGen implementations of the fit of Phys. Rev. D63 (2001) 092001 (CLEO).

EvtGen Workshop 13th Jan

b g s g
Bgsg

Comparison of EvtGen and Herwig++ for the model of hep-ph/9805303

EvtGen Workshop 13th Jan

baryon decays
Baryon Decays

Angle of the L produced in the W decay with respect to the W direction in its rest frame compared to the theoretical result. Using the calculation of Z.Phys.C55,659 (1992) for the charm baryon decays and hep-ph/9905398 for the W decays.

EvtGen Workshop 13th Jan

tau decays
Tau Decays

Mass spectrum of pp in tgppnt for various models and example of mass distribution in tg5pnt comparing Herwig++ and TAUOLA.

EvtGen Workshop 13th Jan

herwig1
Herwig++
  • Modelling in Herwig++ at the same level of sophistication for light meson decays, more models for baryon decays.
  • Tau decays comparable to TAUOLA.
  • Still weaker for the B decays as hard to tune given lack of published data.
  • As Herwig++ and EvtGen use the same algorithm for spin correlations can interface them include correlation effects.

EvtGen Workshop 13th Jan

introduction
Introduction
  • When interfacing Herwig++ and EvtGen need to pass more information that just the momenta of the decaying particle.
  • However passing the information to get the spin correlations is more complicated and error prone than just passing the momenta.
  • Doing this will require some modifications to EvtGen.
  • So first some examples to show it works comparing the internal Herwig++ modelling and Herwig++ interfaced to EvtGen for some decays.

EvtGen Workshop 13th Jan

e e g u 4 s g b b
e+e-gU(4s)gB+B-
  • Angle of B+ meson with respect to the beam with the Y(4s) decay performed by either Herwig++ or EvtGen.
  • Tests the conversion of spin-1 particles, amplitudes and spin density matrices.

EvtGen Workshop 13th Jan

h 0 a g t t g p p n t n t
h0/Agt+t-gp+p-ntnt
  • Angle between t decay planes and between pions with t decay performed by Herwig++ or EvtGen.
  • Tests the conversion of spin-1/2 particles, amplitudes and spin density matrices

EvtGen Workshop 13th Jan

h 0 a g t t g r r n t n t
h0/Agt+t-gr+r-ntnt
  • Angle between the r decay planes for scalar and pseudoscalar Higgs decays.
  • Uses different combinations of Herwig++ and EvtGen for the t and r decays.
  • Tests the spinors/polarization vectors are calculated in the right frames for long decay chains

EvtGen Workshop 13th Jan

changes
Changes
  • In order to interface we need some changes to EvtGen in order to:
    • get access to some additional information;
    • set some variables which are currently private.
  • None of them will effect the current behaviour of EvtGen and hopefully they can be agreed.
  • I’ve attached a full diff file for the latest GENSER release to the talk

EvtGen Workshop 13th Jan

changes1
Changes
  • Some of the changes are fairly minor:
    • Accessors for the Rarita-Schwinger spinors in EvtParticle, as for other basis states;
    • Access to the EvtId object for a given member of the particle list in EvtPDL;
    • Access to the amplitude in EvtDecayAmp.
  • Some are more significant but don’t change current code:
    • New Init() members in EvtDiracParticle, EvtVectorParticle, EvtRaritaSchwingerParticle and EvtTensorParticle which set the basis states.

EvtGen Workshop 13th Jan

changes2
Changes
  • We would like the option of getting EvtGen to perform only the decay of a particle and not the subsequent decays of its decay products.
  • This needs
    • addition of a flag recursive to the makeDecay members in EvtDecayBase, EvtDecayAmp, EvtDecayIncoherent, EvtDecayProb and small changes to implementation.
    • Would default to true so no change to current behaviour and only minor changes to the code.

EvtGen Workshop 13th Jan

conclusions
Conclusions
  • Herwig++ has it’s own sophisticated hadron decay package.
  • As it is using the same algorithm as EvtGen we have been able to write an interface which gets the correlation effects right.
  • Will need some fairly minor changes to EvtGen to work.
  • Hopefully we can agree on these or something which will allow the same functionality for the next version of EvtGen.

EvtGen Workshop 13th Jan