ePIC pfRICH mailing list

["Kiselev, Alexander" <ayk AT bnl.gov>]

  Dear Mikhail,

  answering to some of your questions:

  (1) sure plastics can be damaged by ionizing radiation. I remember well the PVC water cooling pipes used in our detector in the first year of HERMES. Anyway, in the meantime we realized with Prakhar and Alex that PEEK may be a better option overall. Its material budget is yet smaller than the one of delrin, and it definitely has radiation hard varieties. Implemented now in the GEANT model.

  (2) I'd probably prefer a 2mm thick window too, also to provide a reasonable complementary point for track seeding if needed, but the sensor would collapse under the atmospheric pressure with a window  thinner than anything below ~4mm.

  (3) The machinery to analyze both timing provided by the photons from gas radiator and window is actually in place, including some digitization, clever enough to produce a single hit if ten photons hit the same pad. We just had no time to look into this beyond the obvious need to suppress the window photons for ring imaging purposes (this works well). You are more than welcome to contribute, also for CDR purposes. Anyway, as you pointed out, nitrogen is almost certainly hopeless as a threshold Cherenkov radiator in our case, even that the DC-coupled HRPPD has very limited charge spread in the anode plane. Yet one can consider some fluorocarbon, as was also pointed out by Henry back in ATHENA proposal times, and even that it is probably a no go option these days, it may still be wise to show in the CDR that it was considered.

  Regards,

    Alexander.

---

From: osipenko <Mikhail.Osipenko AT ge.infn.it>
Sent: Thursday, March 2, 2023 10:44 AM
To: Kiselev, Alexander <ayk AT bnl.gov>; eic-projdet-pfrich-l AT lists.bnl.gov <eic-projdet-pfrich-l AT lists.bnl.gov>
Subject: Re: [Eic-projdet-pfrich-l] Aluminum -> Delrin for the honeycomb reinforcement rings

 

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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