Delphes 3.1.2 not storing Track Dxy

[rob]

Hi,

I ran Delphes 3.1.2 over a HEPMC file produced with Pythia8, using the example delphes_card_CMS.tcl. Looking at the output ROOT file, whilst the Track collection has data members Xd, Yd, Zd populated, Dxy is always set to 0 (while Xd and Yd are non-zero).

I had a look at the file classes/ParticlePropagator.cc, in the function ParticlePropagator::Process(). Dxy is calculated for the track:

// calculate impact paramater
ang_mom = (xd*py - yd*px);
dxy = ang_mom/pt;

but further on, it is not stored:

candidate->Momentum = candidateMomentum;
candidate->Xd = xd*1.0E3; 
candidate->Yd = yd*1.0E3;
candidate->Zd = zd*1.0E3;
candidate->AddCandidate(mother);

It looks like candidate->Dxy should be set there as well?

Thanks

[rob]

Sorry, meant modules/ParticlePropagator.cc, not classes/ParticlePropagator.cc

[Michele Selvaggi]

Hi Rob,

if I remember correctly the original idea was to store, at the particle propagator level, only the information that was needed to calculate the impact parameter (x_d, y_d, p_x, p_y) and probably the part

// calculate impact paramater
ang_mom = (xd*py - yd*px);
dxy = ang_mom/pt;

is simply a left over. Instead the impact parameter was meant to be calculated when the module ImpactParameterSmearing is called.
Therefore if one needs no smearing (MC truth d_xy) then simply put

ResolutionFormula 0.0

when calling ImpactParameterSmearing.
If you need an example on how to call such module please have a look at the "delphes_card_FCC_basic.tcl"

This said, we will probably follow your advice at store by default the Dxy, SDxy value as computed by the ParticlePropagator.

Thanks,
Michele

[Pavel Demin <pavel.demin@…>]

In 764f12a080c1544be453156fbcd310236080e0e1/git:

set Dxy in ParticlePropagator (close #330)