E-rhic-ir-l mailing list

["Palmer, Robert" <palmer AT bnl.gov>]

These are my "work in progress" dry run slides for Wednesday. Take a look at 
slides 15-17. It is not coming out as I had expected. As Alexander suggests, 
I had expected a clear gain by running in a mix of HA and HL modes. Yet it 
still seems to favor all HL. If we could push the dp/p up a little it might 
favor HL even more. What is clear to me is that we need a "standard file" for 
the HA and have a GEANT simulation of it before the revue.

Bob

-----Original Message-----
From: Alexander Kiselev [mailto:kisselev AT mail.desy.de] 
Sent: Friday, March 10, 2017 3:12 PM
To: Palmer, Robert <palmer AT bnl.gov>
Cc: Petti, Richard <rpetti AT bnl.gov>; Aschenauer, Elke <elke AT bnl.gov>; 
E-rhic-ir-l AT lists.bnl.gov
Subject: Re: [E-rhic-ir-l] Discussion of parameter choices

   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
> 
>  
> 
> 
>

Attachment: 1703-IR-talk-v1.pdf
Description: 1703-IR-talk-v1.pdf