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[Aschenauer Elke-Caroline <elke AT bnl.gov>]

Dear all,

so yes there is a r dependence and we have more hits closer to the beam pipe, but a factor of 2 also keep in mind the inner sectors are much smaller in area, so effectively it is more like a factor of 4 as I assume Zhenyu your numbers are not normalized to the area between inner and outer.

Looking to the plots https://drupal.star.bnl.gov/STAR/system/files/yezhenyu_FST_20190829.pdf indeed the plateaus are very wide and for the outer sensor no real plateau is seen.

I saw you added the adc values to https://drupal.star.bnl.gov/STAR/system/files/yezhenyu_FST_20211228.pdf very nice thank you and one can nicely see a mip peak and it is pretty stable starting from 115 GeV and 135 GeV, respectively

So with respect to the HV setting I think the current ones are fine from the analysis you did.

Cheers elke

p.s. Flemming I can not follow this sentence in detail "From UA5 data at 549 GeV (p-pbar) the INL data have dN/deta ~3 out to eta of 3 and then drops to ~2 at eta=4.” I understand they measured an eta dependence with higher rate closer to the beam pipe, but the rest is unclear.

On Dec 29, 2021, at 18:17, videbaek <videbaek AT bnl.gov> wrote:

Hi

I agree with Zhenyu that the # for inner and outer is about right, but clearly the beam background were significant in the earlier scans.

From UA5 data at 549 GeV (p-pbar) the INL data have dN/deta ~3 out to eta of 3 and then drops to ~2 at eta=4.
The Si coverage for the outer is ~0.5 in delta(eta) and inner  ~1.1 so I would expect the inner to be larger than the outer. In addition there is more secondaries from the beam pipe for the higher eta aka inner, but whether this reproduces the actual hit ratios and yield depends on selectivity of the trigger and eta-dependence of background which is significant.

I think this could be answered by a rather simple Geant calculation with Pythia.

best Flemming


On 2021-12-29 15:54, Ye, Zhenyu wrote:

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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