[EvtGen] S-wave with EvtGen

[John Back]

Hi Giacomo,

> On 16/07/18 10:12, Giacomo Fedi wrote:
> Hi EvtGen authors,
>
> I was wondering if it is now possible to produce samples of P+S wave
> in the JpsiPhi decay. In principle we would need an improved PVV_CPLH
> model which right now is simulating only the P-wave.
>

After carefully rechecking the LHCb EvtGen repository, we have found 
that there is in fact a model that generates Bs -> J/psi (mu mu) K K 
decays which includes the phi and f0 resonances as well as a 
non-resonant S-wave component, with decay time dependence.

It it called EvtBsMuMuKK and uses the amplitude formulae from PRD 87, 
072004 (2013), although the model imposes an ad-hoc K+K- kinematic upper 
mass limit of 1.2 GeV (specified via a decay file parameter) since there 
are issues extending it up to 2.3 GeV or so.

We will try to make this model available, along with the useful ones 
currently in the LHCb EvtGenExtras package, in our HepForge repository 
and release it around the timescale of September/October, owing to the 
summer holiday period.

Regards,
	John.