Re: Systematics of humidity captures

[Bernhard Lauss <lauss@berkeley.edu>]

Dear Claude,

I am just this time working on the requested
impurity note for run9,  which
exactly deals with this problem, too.

Your numbers are correct but .....

I think the factor of 2 comes finally tracked down from
the question what is the PURA humidity sensor measuring.

It is measuring the dew point, which we then
translate into relative humidity of
water molecules with respect to hydrogen molecules
by some tables (from our PNPI colleques, or less
exact in the "Handbook of chemistry ofr physics"),
if my understanding is correct.

Now all our and your caculations about the transfer rate
are taking into account atomic concentrations.
Therfore we have to recalculate the
measured humidity from the PURA device
with an extra factor of 2 due to
molecular versus atomic concentration
and then the reading is
35/2 ppb humidity,
which is a factor of 2 off from your correct calculation.


 I'll send you my suggestions for the solution to this
factor 2 as son as I have written it up nicely, today or tomorrow.



		best regards

			Bernhard





*******************************************************************
Bernhard Lauss                 E-Mail: lauss@socrates.berkeley.edu
Physics Department
366 LeConte Hall
University of California @ Berkeley
Berkeley, CA 94720                             Tel: (510)-642 4057
United States                                  Fax: (510)-642 9811
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On Mon, 6 Feb 2006, Claude Petitjean wrote:

> Dear friends,
>
> I reevalulated the systematics of muon captures on
> water (in fact, oxygen) in our tpc as follows:
>
> Our humidity sensors measured 35 ppb in eqilibrium
> state (c_O = 3.5 10^-8). The normalized density
> in 10 bar protium is phi = 0.0116 and the reduced
> transfer rate to O is lambda_Tr_O = 0.85 10^11/s
> (Schellenberg et al.).
>
> The effective muon transfer rate to Oxygen is then:
> lambda_tr_O * phi * c_O =
> 0.85 10^11/s * 0.0116 * 3.5 10^-8  = 34.5/s
>
> and the transfer probability per muon ~34.5/l_mu
> = 34.5 / 455700 = 7.6 10^-5
>
> The muon capture rate in Oxygen is l_c_O = 97400/s
> (Eckhause), the probability l_c_O/(l_c_O + l_o) =
> = 0.176.
>
> We expect thus in 35 ppb H2O 0.176 * 7.6 10^-5 =
> = 1.34 10^-05 Oxygen captures per muon.
>
> In reality we saw (background deducted)
> ~ 1.1 10^-05. Thus if we assume an overall
> detection efficiency epsilon_O = 0.82 for
> observing in the tpc the mu-O captures, then our
> impurity measurements agree exactly with the
> theoretical expectation from the humidity measurement!
>
> Question to Peter, Francoise and other experts:
>
> - Do you see anything wrong with my numbers?
>
> - Where is the factor 2 of too many impurity captures
>    which was repeatedly claimed during the last run?
>
> - Is my conclusion correct, that the impurity events
>    of our last 2 runs were clearly dominated by the
>    humidity?
>
> Lets discuss this on tomorrows teleconf.
>
> With best regards
>
> Claude
>
>