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["Visser, Gerard" <gvisser AT indiana.edu>]

hi all,

  I think as long as the mip peak is well above the threshold of what a hit is, we should not expect the efficiency to drop very much when you get below full depletion. It might be more illuminating to look at the mip peak vs. bias voltage to see when we have enough bias for a plateau in signal size, rather than hit count vs bias voltage.

  I'm not clear whether that is practical to look at though. What do you think, Zhenyu?

    Gerard

---

From: Star-fst-l <star-fst-l-bounces AT lists.bnl.gov> on behalf of Ye, Zhenyu <yezhenyu AT uic.edu>
Sent: Wednesday, December 29, 2021 3:54 PM
To: Aschenauer Elke-Caroline <elke AT bnl.gov>
Cc: Star-fst L <star-fst-l AT lists.bnl.gov>
Subject: Re: [Star-fst-l] HV Scan on 12/27

 

Dear Elke

Please see my comments below

On Dec 29, 2021, at 12:47 PM, Aschenauer Elke-Caroline <elke AT bnl.gov> wrote:

Dear Zhenyu,

I must say I’m a bit confused about the results you get.

But before asking some questions, let me first point out that Daniel found very strange results for the first HV scan we did for the sTGC and the FST.

One suspicion is that the beam was not yet colliding very well, so this could explain the difference in <# hits> you see at the same voltage.

What is wrong with the <#hits> from 12/17?

But if I look to the HV Scan from 12/27

Do we really expect such a large difference of <# hits> between inner and outer

Very good question. I am wondering what we should see. What is your expectation?

What FST see is actually consistent with sTGC. As shown by the sTGC online plots, there are clearly more hits closer to the beam. 

See e.g. page 144/145 https://online.star.bnl.gov/runPlots/22361030.shift.pdf

and also the dependence on the Voltage is super soft. 

This is consistent with what we see from cosmic ray tests on prototype modules, as shown for BNL ALD Review on Aug 27, 2020.

Page 12 shows efficiency as a function of R and a small change in the efficiency is measured from 70-140V. 

Note that the efficiency from 12/27 is integrated over R for inner and outer separately. Because there are more hits at smaller R, the numbers in my table are biased towards the efficiency at smaller R.  

Again what is the depletion HV Hamamatsu suggests. 

You can see the C-V measurements shown in 

https://drupal.star.bnl.gov/STAR/system/files/yezhenyu_FST_20190829.pdf

It is between 60-120V as reported by HPK.

I find these results very surprising, I think we really should look to the cosmic data.

These results are not very surprising to me, as explained above, but I do agree that it will be useful to study the cosmic data. 

Best,

Zhenyu

Cheers elke

On Dec 29, 2021, at 00:43, Ye, Zhenyu <yezhenyu AT uic.edu> wrote:

Preliminary HV scan results from yesterday can be found on page 3

https://drupal.star.bnl.gov/STAR/system/files/yezhenyu_FST_20211228.pdf

Zhenyu

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