Development #241


Making a smeared target the standard behaviour?

Added by Sascha Reinecke about 7 years ago. Updated almost 7 years ago.

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10.00 h
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I made some simulations directly comparing the actual behaviour (i.e. interaction point exactly at 0) with a smeared target (interaction point homogeneously smeared in z-direction).
The results for the pi0 and also for direct photons show an increase of (possible) reconstructed pi0/direct photons (plots like on the collaboration meeting, i.e. particle ID with MC-true and reconstruction with refitted momentum; need signal in STS and RICH).

Therefore I suggest to make a smeared target the standard behaviour for the simulations, at least as it doesn't influence simulation time and also is more realistic than the fixed interaction point.
Especially for all analyses which make use of conversions this might be an important aspect.

Attached plots show comparison of the results for both behaviours.

(Simulations were done for 18k UrQMD events, 25AGeV, central collisions, with 100 pi0 embedded per event with the boxgenerator)


fhGlobalNofDirectPhotons.png (59.7 KB) fhGlobalNofDirectPhotons.png Number of reconstructed direct photons Sascha Reinecke, 05/13/2015 12:25 PM
fhEFG_startvertex_allSameG.png (69.3 KB) fhEFG_startvertex_allSameG.png Conversions inside the target Sascha Reinecke, 05/13/2015 12:26 PM
fhEPEM_invmass_all_refitted.png (78.3 KB) fhEPEM_invmass_all_refitted.png Reconstructed pi0 (with signal in STS and RICH) Sascha Reinecke, 05/13/2015 12:26 PM
Actions #1

Updated by Volker Friese about 7 years ago

  • Tracker changed from Feature to Development
  • Due date set to 07/31/2015
  • Status changed from New to Scheduled
  • Assignee set to Volker Friese
  • Target version set to NOV15
  • Start date changed from 05/13/2015 to 07/01/2015
  • Estimated time set to 5.00 h

Dear Sascha,

I agree that sampling the interaction point from the target extension (in z) and from the beam profile (in x and y) should be the default in our simulations.

There are two reasons why this is not yet so:

1. In FairPrimaryGenerator, where this functionality is to be applied through the methods SetTarget, SetBeam, SmearVertexZ and SmearVertexXY, the target position and thickness have to be specified. If this is done in the run macro, there is no guarantee that these values are consistent with the actual target geometry used in the simulation. I will look for a possibility to get position and thickness of the target from the geometry and set them automatically to the FairPrimaryGenerator instance, somewhere at the intialisation stage.

2. We do not have firm information on the transverse beam profile to be expected from SIS-100, so everything we put here is something between a wish and a guess. But maybe it is better than nothing.

Actions #2

Updated by Volker Friese about 7 years ago

  • Estimated time changed from 5.00 h to 10.00 h
Actions #3

Updated by Volker Friese almost 7 years ago

  • Status changed from Scheduled to Resolved

The required functionality was implemented in the macro run_sim.C. The interaction point is now, by default, sampled flatly in z over the target extension and Gaussian-like in x and y over the beam profile. The smearing can be de-activated at the top of the macro without having to interfere with the main macro body.

The following default parameters were set:
target material: Gold
target position: (0., 0., 0.)
target thickness: 250 mum
target diameter: 2.5 cm
beam width: 1 cm

This change is on the macro level only, and it is only implemented in run_sim.C, so it has to be propagated into other macros, in particular those used in the regular tests.

Actions #4

Updated by Volker Friese almost 7 years ago

  • % Done changed from 0 to 100
Actions #5

Updated by Sascha Reinecke almost 7 years ago

  • Status changed from Resolved to Closed

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