SIPM efficiency and rate

[mriosmar]

Hi.

I would like to share my data and a comment about the rate.

With my two detectors (one on top of the other) in coincidence mode I get 0.21 cps. (450m above sea level)

I have made the following calculation:

Expected flow 0.4 cm^-2min^-1sr^-1 (Axani paper)

Considering 25cm^2 and estimating the solid angle of pi rad (for that configuration), I should get 0.52 cps. I have read that SIMP datasheet and the efficiency detecting 420nm photons is about 40%. So 0.52x0.4 -> 0.21 cps, which is what I get.

Is my interpretation correct?

I ask about this because I have not seen any reference to the efficiency of the SIMP in the papers..

Best regards.

[NuclearPhoenixx]

As far as I know, the efficiency of a SiPM "only" changes the number of photons it detects. So it should not affect the count rate too much, but the resulting signal height if you get a pulse. Of course a better efficiency will probably still get you more counts because you can then detect even faint signals. Maybe that's what's happening here?

Intriguing question, though! I'm excited to see what Spencer thinks of this.

[spenceraxani]

Hi,

NuclearPhoenix is correct. The SiPM efficiency would affect the number of photons detected, with a small impact on the number of muons. If you look at Fig. 13 of the PhysicsPaper.pdf, you’ll see the measured signal height (or pulse amplitude). A lower SiPM efficiency would shift the measured curves to the left. But as you can see from the red histogram (the muons), you’d have to have a pretty large change in efficiency before you start cutting away at muons (that is, parts of the red histogram fall below the threshold). I would estimate if your efficiency was 1/2 as good as it is with a generic detector, you would loose ~50% of the background events and ~5% of the muons.

The calculation you provided is a coincidence. There are other effects here as well, the 0.4 cm^-2min^-1sr^-1 is an approximation, and the detectors are not fully efficient. One study in Peru found that we likely are only triggering on ~80% of the events that pass through the detector, due to the sensitivity near the edge of the detector. I haven’t verified this. The estimate of the solid angle may need careful consideration as well.

When you say that the detectors are one-on-top of the other, which configuration of Fig. 12 are you referring too? 0.21 cps seems reasonable for (c).

Best,

Spencer ─ Dr. Spencer N. Axani @. @.>

Assistant Professor The University of Delaware 203 Sharp Lab 104 The Green, Newark, DE 19716 (608) 572-8426

On Jan 18, 2023, at 2:53 PM, NuclearPhoenix @.***> wrote:

As far as I know, the efficiency of a SiPM "only" changes the number of photons it detects. So it should not affect the count rate too much, but the resulting signal height if you get a pulse. Of course a better efficiency will probably still get you more counts because you can then detect even faint signals. Maybe that's what's happening here?

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[mriosmar]

Hi

Thanks so much for the explanation.

The detectors are set to position (c) and I get 0.21 cps.

I think the calculation I have taken is too simple because 0.4 cm^-2min^-1sr^-1 is the vertical flux and it changes with angle as cos^2. Also, as you say, I must carefully calculate the solid angle (a better approximation would be to integrate over the solid angle to include the angular variation of the flux and obtain the number of muons per unit area and unit time).

On the other hand, considering the fact that the total flux on a horizontal surface is 1 muon cm^-2min^-1, my data is compatible, estimating a solid angle with a 60º opening (3 cm separation between the scintillators).

With the detectors in position (d) and without an aluminum case I get 0.41 cps. I think it is also a reasonable value.

Best regards.