BGV Simulation

Overview

The following operations can be performed within the simulation application (Gauss):

• Generation of the primary beam-gas interaction
  • A third-party generator (e.g. Hijing) is used
• Propagation and interaction of the beam-gas collision products with the material defined in the BGV geometry
  • A dedicated geometry is developed that defines the relevant infrastructure, vacuum chambers and BGV detector components
  • The MCHits, i.e. the particles' energy deposit inside the sensitive detector elements, can be stored in the produced .sim file
  • The "digitization" step converts the MCHits into a pair <SciFiChannelID, Energy>, allowing the simulated data to be represented in a way identical to the raw data coming from the SciFi detectors. The MC information (e.g. particles and vertices) can be kept or not in the produced simulated files.

Usage examples

TODO: provide examples:

• Read a simulated file
• Visualize the BGV geometry and events with Panoramix
• Generate and simulate beam-gas events with Gauss
• Run a material scan job

Material budget

Introduction

• An LHCb ParticleGun tool is used to generate particles (instead of a pp generator like Hijing)
  • The particles should be "non-interacting", e.g. neutrinos, to avoid interactions and multiple scattering
  • An origin point is chosen (e.g. (0,0,0)) and many particles are generated with specific directions in order to cover the area of interest. The ParticleGun tool MaterialEval is designed for this purpose: one can generate particles in an x-y or eta-phi grid, with range and step size specified by the user
• Scoring planes are introduced in the detector description geometry (DDDB)
• The tool RadLengthColl looks when a Scoring plane is traversed and collects the information of interest
  • Scoring plane ID, x-y and eta-phi coordinates of the particles, accumulated interaction and radiation lengths, ...
  • The tool creates a ROOT NTuple containing these variables

Running a Gauss material scan job

1. Obtain a local copy of the BGV XmlDDDB which you want to scan
   • E.g. /afs/cern.ch/project/lhcbgv/sw/releases/bgv_v1r0/XmlDDDB
   • This package contains both the geometry (DDDB) and the option file needed to run the material scan job
2. Enable the Scoring planes in the XmlDDDB which you want to scan
   • By default, the Scoring planes are there, but are commented-out
   • Need to uncomment the relevant lines in 3 files: DDDB/structure.xml, DDDB/geometry.xml and DDDB/BGV/geometry.xml
   • An example with enabled Scoring planes can be found in /afs/cern.ch/project/lhcbgv/sw/releases/bgv_v1r0/XmlDDDB/DDDB_MatScan
3. Run the Gauss job
   • gaudirun.py XmlDDDB/options/MaterialScanJob.py
   • The main switches are:
     • nEvts: number of events. By default 1 particle is generated per event, so 62800 events are needed to scan the full plane (in the option file you can see the various settings for the grid and the step size)
     • MCP_ORIGIN_Z: z coordinate of the origin point of the generated particles (neutrinos) (a recent version of Sim/GaussTools is needed in order to use this feature; otherwise, only z=0 can be used; the feature is added in Gauss >v48r2?)
4. Analyze the produced ROOT NTuple

• A separate Gauss job must be run for each origin point. E.g. for the BGV one can study (0,0,0), (0,0,500), (0,0,1000), and (0,0,1500) -- see results below

Results (BGV XmlDDDB svn Rev. 92)

In total, 8 scoring planes are added in the BGV DDDB. See the Panoramix view on the right. Of biggest interest is Plane 7 which sits right behind the far station. The Eta-Phi and X-Y maps shown below refer to this plane.

Plot Type	z_origin = 0 mm	z_origin = 500 mm	z_origin = 1000 mm	z_origin = 1500 mm
		Wide Eta range
Rad_Len vs Eta_averaged_over_phi
Rad_Len Eta - Phi Map
Rad_Len X - Y Map
		Zoomed Eta range
Rad_Len vs Eta_averaged_over_phi
Rad_Len Eta - Phi Map
Rad_Len X - Y Map