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[Alexander Kiselev <kisselev AT mail.desy.de>]

  Hi Bob,

> This tells me that even if we do some running with High Acceptance (but lower 
> Luminosity) parameters, to better measure low pt tracks, we may still want 
> also to run
> with higher luminosity to give better data at higher pt.

  I find this particular suggestion very interesting. Indeed, as long 
as the rest of the physics program allows, one can think of collecting 
the particular data we are talking about in two chunks (one low lumi and 
small divergence, the other one high lumi and large divergence) and then 
glue the samples together using mid Pt range.

  Cheers,
    Alexander.



>  
>
> But now look at Richard’s earlier results. His slide 9 bottom left, is 
> disappointing, but remember that
>
> a) he does not include the forward calorimeter that will raise the efficiency 
> at the high pt end to near 100%; and
>
> b) He is using parameters with three times the luminosity assumed in the 
> later slides and my points 1-5; so
>
> c) It shows efficiencies below 0.4 GeV/c of only 7-8 %, but this corresponds 
> about 20% of luminosity times efficiency, while that at higher pt is around 
> 50% x 3 = 150%
> . With the forward spectrometer, that rises to nearer to 300%. These are both 
> well above that used  in the slide 19 example, and not obviously a disaster.
>
>  
>
> Can this be improved?
>
>  
>
> Richard is doing an analysis with half the momentum spread. I can make an 
> estimate of what he will conclude by assuming the case when dispersion x 
> momentum spread
> there dominates over the betatron size. The efficiency then is set just by 
> the area under the xl (outgoing proton moment as fraction of their incoming 
> momenta) with
> values less than (1.0 -  Disp x dp/p). using the distribution from Elke for 
> 20 x 250 GeV, I get
>
>  
>
>             dp/p               efficiency               Luminosity            
>   Product
>
> 6.5 e-4                   7%                         2.89                     
>    0.202                     1.0
>
>             3.25e-4                   17%                          1.91       
>                  0.324                     1.6
>
>             1.62e-4                   34%                          1.05       
>                  0.357                     1.76
>
>  
>
> I am taking the 7% here to be a confirmation of Richard’s 7-8%. If So, with 
> half the momentum spread (presumably with twice the bunch length) I am 
> expecting him to get
> around 17%. If I use Mike B’s code for hourglass and crab effects for twice 
> the bunch length, I get Lum=66%. We appear to win by a factor 1.6 giving Lum 
> x eff = 34%
> below 0.4 GeV/c and something approaching 200 % at the high energy end using 
> the forward spectrometer. These are only rough estimates, but are encouraging.
>
> The alternative approach would be to go back to ‘High Acceptance’ parameters. 
> This would give around 50% at low pt but only 100 % at high pt. This is not 
> obviously an
> improvement. The loss of high pt data could beat the gain at low pt. More 
> study is needed. Some ideal mix of High Acceptance and High Luminosity might 
> give the best
> overall performance. At least for the moment, the conclusion is that we have 
> more than one approach; we have the tools; and we will continue the studies.
>
>  
>
> There is a quite separate question about the relative advantages of higher 
> luminosity  using higher divergences in the y direction. The gains with 
> luminosity will have
> to be balanced by the increased errors in pt measurements with or without 
> transverse momentum dynamic fitting. Again we have the tools and will 
> continue the studies.
>
>  
>
> Bob
>
>