late decays of particles

[J Dutta]

Dear Experts,

How does delphes deal with late decays of particles within the collider?

Thanks & Regards,

Juhi Dutta

[Alexandre Mertens]

Hello,

Do you mean particles that travel partially the detector before the decay, or low energy particles that stay around the beam pipe and decay between two bunch crossing, or later?

Cheers,
Alexandre

[J Dutta]

Hello,

I am referring to the first case.

Thanks & Regards,

Juhi Dutta

[J Dutta]

Hi,

I have seen 2 tickets on this forum, namely ticket #138 and #219 dealing with long lived charged particles. It has been mentioned that if they have a vertex out of the tracker volume then such particles are ignored by delphes in the further analysis. (referring to the check if the particle is in the cylinder). I assume the cylinder is the inner detector of the collider here. For neutral long lived particles there will be no such tracks in the tracker chamber but say,decays can occur later in the calorimeters. Even long lived charged particles can decay later in colliders. Since when generating events and showering them in pythia, pythia decays these long lived particles if they are not stable, when we pass these events to delphes for detector simulation, does delphes distinguish these decay products coming from the later decays of their mother particles by reconstructing some information about secondary vertices and accept/reject them accordingly with respect to their position in the collider? Or does it just take these final state decay products and carry on with the analysis?

Apologies if the question appears too naive, I am having some trouble understanding the vertex reconstruction techniques in delphes. It would be very helpful if you help me understand this issue.

Thanks & Regards,

Juhi

[Pavel Demin]

Dear Juhi,

The particles produced outside of the inner tracking sub-detector are rejected by the code at lines 136-140 in modules/ParticlePropagator.cc:
https://cp3.irmp.ucl.ac.be/projects/delphes/browser/git/modules/ParticlePropagator.cc#L136

In our current detector module, the only detector with non-zero size in the radial and axial directions is the inner tracking sub-detector. So, the particles produced outside of the inner tracking sub-detector are basically produced outside of the whole detector and thus can't be directly detected.

To address this problem, we'll need to introduce non-zero radial and axial dimensions for the ECAL and HCAL calorimeters and propagate particles in theses detectors.

does delphes distinguish these decay products coming from the later decays of their mother particles by reconstructing some information about secondary vertices and accept/reject them accordingly with respect to their position in the collider?

Currently, Delphes doesn't have any code for the secondary vertex reconstruction.

Best regards,

Pavel

[J Dutta]

Hi,

Thank You for the reply!

So, the particles produced outside of the inner tracking sub-detector are basically produced outside of the whole detector and thus can't be directly detected.

The ECAL and HCAL are present outside the inner detector, but energy deposits in them are taken into account. The particle whose energy fractions are deposited in the calorimeters may or may not have been produced in the tracker volume. Can this situation not be true? In which case if the energy deposit is specified in the detector card, delphes should identify them?

Thanks & Regards,

Juhi

[Pavel Demin]

The problem is that the thickness of the ECAL and HCAL is zero in our current detector model.

In this detector model, there is no way to define if the particle is produced in ECAL or in HCAL or outside.

To address this problem, we'll need to introduce non-zero thickness for the ECAL and HCAL calorimeters and propagate particles in theses sub-detectors.

[J Dutta]

Ok. That solves my queries. Thank you for the help!

Regards,

Juhi