BGV x CRMC meeting minutes 17/11/20

Present: Ralf, James, Helene, Bernadette

Summary of actions: 
 - Setting of impact parameter.
 - Try EPOS.
 - Investigate using CRMC with Geant4 directly.
 - Send Timepix3 info to Ralf.
 - Brainstorm which measurements could be useful for a potential contribution to model tuning.
 

• Presentation: Introduction and status of the BGV (Bernadette)

  • Notes are on the slides where some additional discussions resulted, for the content of the other slides, see the pdf of the presentation.
     

  • Slide 6 (Pipeline):
    Ralf: The way we call crmc is correct.
    Bernadette: Should we update to new version? Ralf: Will not make a big difference, update was more on models you do not use, but of course it's always good to be up to date.
     

  • Slide 7 (crmc parameter file):
    @impact parameter:
    Bernadette: I set it to 0 (= head on collisions).
    Ralf: Has no influence on hijing, but on dpmjet - he will ask Tanguy what settings he would recommend.
     

  • Slide 11/12 (PDG ID histograms):
    Ralf Comment: Are you interested in the gammas for tracking?
    Bernadette: they come from the pi0 decay, not from the primary vertex.
    Ralf: pi0 decays almost immediately.
    Q: Do we see those gammas in the detectors?
     

    Ralf: Hijing might not be a good model to use in our case - it is better for heavy ions, it is very tuned to specific collision data (e.g. Lead), different version of it exist, with different tuning.
    He recommends to try EPOS which is, similar to dpmjet, a general purpose model and tuned to several data sets.
    
    Ralf: There is also the possibility to use crmc directly with Geant4 (no reading in of the hepmc files). It is not part of the official Geant4 distribution. He can give us the contact of the people who wrote the code.
     

  • Slide 16:
    No big difference between multiplicity distributions for different gas types .
    Ralf: Could be due to the impact parameter settings! Head-on or not head-on collisions - makes a bigger difference for bigger atoms. Check the setting of the impact parameter with Tanguy.
     

• Discussion afterwards (not in chronological order):
   

  • Ralf: Coverage of our setup?
    Bernadette: see bottom plots of slide 14 for the setup used for the generator comparison. Will depend on final design of future setup however.
     

  • Ralf: what read-out system would we use for the BGV? One of the experiment ones, depending on the detector choice?
    James: No, it should be experiment independent and based on what is used in BE-BI.
     

  • Ralf: What is the difference between BGV and the LHCb SMOG?
    James: BGV was inspired by SMOG, main difference is that the SMOG cannot run continuously through the cycle, the BGV can.
     

  • Ralf: @demonstrator: did we see any degradation of the scintillating fibres with time?
    We don't think so, not that we know of the previous BGV members at least.
     

  • Ralf: Would you be interested in producing/contributing to physics results?
    Everyone: Yes.
    The BGV setup is in terms of physics very similar to cosmic rays interacting with the atmosphere. Some interesting results could be produced to contribute to the tuning of models.
     

  • There could be some things like the multiplicity distribution etc. that are interesting for validation of the models. They would be interested for example, in the ratio of pi0 to charged pions (which are hard to obtain), and therefore it would be interesting to them to measure the gammas.
    Could the Timepix3 setup we had in mind (Slide 17) be used?
    Can the Timepix3 see the gammas?
    James (after meeting): No, see the Mass Attenuation Coefficent (MAC) of silicon as a function of gamma energy: https://physics.nist.gov/PhysRefData/XrayMassCoef/ElemTab/z14.html
    e.g. for a 1 MeV gamma -> MAC = 6.631e-2 cm^2 / g
    length after which intensity reduced by e^1 = 1 / ( silicon density * MAC )
    -> length = 1 / ( 2.23 g / cm^3 * 6.631e-2 cm^2 / g ) = 6.7 cm
    So there will be very little energy deposited in a say 300um thick silicon sensor.
     

  • Ralf: How far away are the magnets downstream, what magnet is it?
    Bernadette: Around 40 m downstream, first one is a quadrupole, but there are also dipoles downstream of it.
    Idea by Ralf: There could be a possibility to measure the secondaries that go down the beampipe further downstream, e.g. at a magnet where the secondaries would come out.
     

  • Ralf will discuss with his colleagues and brainstorm for further ideas, and we stay in touch. KIT could contribute and provide some detectors.