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[videbaek <videbaek AT bnl.gov>]

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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--
Flemming Videbaek
senior scientist
videbaek @ bnl.gov
Brookhaven National Lab
Physics Department
Bldg 510D
Upton, NY 11973

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