ePIC pfRICH mailing list

[osipenko <Mikhail.Osipenko AT ge.infn.it>]

Hi Alexander,

indeed Delrin looks significantly better. I am not sure in what property you want to consider rad.hardness of Delrin? In structural hardness? It is a polymer, not a crystal...

Instead I made few "back of the envelop estimates" of electron Cherenkov radiation in pfRICH gas volume:

The number of Cherenkov photons can be estimated as:

dN/dx=458.6*sin^2(theta_C)*[1 um/lambda_1-1 um/lambda_2] photons/cm

for HRPPD photocathode range: 160-400 nm (mean QE~30%):

dN/dx=1719.85*(1-1/n^2) photons/cm

assuming C4F10 gas (pion threshold 2.7 GeV/c)
https://www.fisgeo.unipg.it/~fiandrin/didattica_fisica/rivelatori1516/riv_lez07_300316.pdf

- transparent down to 180 nm (thus, perhaps the real number of photons on HRPPD is somewhat less)
https://twiki.cern.ch/twiki/bin/view/LHCb/C4F10

n(300 nm)=1.00135

we get Cherenkov photon yield of:

dN/dx=4.6 photons/cm

assuming QE~30% and filling factor 70% we obtain:

dN/dx=1 p.e./cm

for 40 cm pfRICH depth we would expect 40 p.e. with mean angle of 3 deg. Should be easily visible.

assuming N2 gas (pion threshold 5.5 GeV/c) - transparent down to 120 nm
https://refractiveindex.info/?shelf=main&book=N2&page=Griesmann

n(270 nm)=1.00031757

dN/dx=1.1 photons/cm

dN/dx=0.2 p.e./cm

for 40 cm pfRICH depth we would expect 8 p.e. with mean angle of 1.44 deg. This perhaps is the main problem L*tan(theta_C)=0-1 cm, very close to the primary particle ring in quartz window R=4 mm*tan(49.5 deg)=4.7 mm, for 2 mm quartz window would be better R=2.3 mm.

In the Aerogel some e/pi separation is also available at momenta below 2.5 GeV/c.

By the way what type of calorimeter we will have behind pfRICH (how does it separate e/pi? by longitudinal sampling? Or we have momenta from tracking also at these small eta=-3.5?). Is there e/pi-separation plot as a function of momentum in the calorimeter?

Best Regards,

                         Mikhail.

On 3/2/23 11:37 AM, Kiselev, Alexander via Eic-projdet-pfrich-l wrote:

           Good morning colleagues,
      
        
      
      
          I believe a good fraction of our material budget problems
        close to the beam pipe can be fixed if one simply uses something
        like delrin instead of aluminum for the honeycomb sandwich
        reinforcement. See the comparison scans attached, where even
        without any further optimizations we are getting close to the
        ~15% rad length ballpark  numbers. Ignore the hot spot, it can
        obviously be optimized out.
      
      
        
      
      
          I don't see why would not it work for such small shapes,
        unless there are radiation hardness issues. Prakhar, Alex: I was
        wondering, can we commit to this option?
        
      
      
        
      
      
          One may ask a question why there is now no hot spot at theta
        angles, where a particle would cross either the inner vessel
        wall or the inner mirror wall in a "projective" way. The answer
        is illustrated in the attached sketch. Somewhat by accident, we
        tilted the inner mirror in such a way that such situations do
        not happen. Besides this, as also follows from the sketch, the
        wall and the mirror will never be crossed at the same time by
        any straight line originating from the IP. Therefore, for
        instance, it probably does not make much sense to try unifying
        the wall and the mirror into one layer.
      
        
      
      
          Regards,
      
            Alexander.
      
         
      
      
      
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