[Frost] target depolarization

[Barry Ritchie]

Without the target magnetic field "swimming" corrections, there's going to be some uncertainty in the depolarization exercise anyway, even picking what are said to be the 90-degree events. And, of course, those corrections are needed to properly bin the asymmetry data, too.

Is there any forecast on when that might be available?

---BGR


Professor Barry G. Ritchie
Department of Physics
Arizona State University
Tempe, AZ　 85287-1504

Telephone: (480) 965-4707
Fax: (480) 965-7954



-----Original Message-----
From: frost-bounces at jlab.org [mailto:frost-bounces at jlab.org] On Behalf Of Eugene Pasyuk
Sent: Tuesday, March 22, 2011 3:44 PM
To: frost at jlab.org
Subject: Re: [Frost] target depolarization

Mike,

Poor z-vertex resolution contributes to this drop in downstream direction to some extent. There is also a geometrical asymmetry of the cell and its surroundings. On the upstream side it is only Al window and then vacuum. On the downstream end there is the cell cup wall, some He in mixing chamber and mixing chamber wall. Your z-bins are 2.5 mm but our resolution is not as good particularly for the shallow angles. To minimize the effect of the vertex resolution (just for this z-study) I would choose narrow angular range around 90 degrees in the lab(!) system and then do Z-slices. Say -0.1<cos(theta_lab)<0.1, or may be +/-0.2. 
This should shrink the slops of the distribution and the width of the distribution will be closer to reality.

-Eugene

On 03/22/11 18:11, Michael Dugger wrote:
> Hi,
>
> I have some results regarding the target polarization as a function of 
> z-vertex that might be of interest. In short: it looks like we can see 
> the downstream de-polarization of the target using the pi+ n reaction, 
> and this de-polarization is a large effect.
>
> Method:
> 1) Isolate regions of the gamma p ->  pi+ n reaction where the E 
> observable appears to be always less than -0.5. By looking at Brian's 
> slides 
> (http://www.jlab.org/Hall-B/secure/g9/morrison/brian_E_obs_2-10-2011.p
> df), I chose the region in cos(theta_cm) between -0.4 and +0.7 for 
> E_gamma between 1500 and 1600 MeV, and cos(theta_cm) between -0.7 and 
> +0.8 for E_gamma between 1600 MeV and 1750 MeV.
>
> 2) Slice the data into 32 z-vertex bins from z-vertex = -4.0 to +4.0 cm.
>
> 3) Find the |E| observable, with no carbon subtraction or other 
> background subtraction, for the missing mass (assumed reaction gamma p 
> ->
> pi+ X) between 0.89 and 0.99 GeV/c^2. This was performed assuming that 
> pi+ our
> current values of the beam*target polarization are correct.
>
> 4) Plotted the results.
>
> You can see the results here:
> http://www.jlab.org/‾dugger/g9/g9a/polZ1.gif
>
> Top panel is z-vertex of the denominator of E.
> Bottom panel is the absolute value of E as a function of z-vertex.
>
> This looks to be a huge effect. We need to figure out how to get an 
> average polarization.
>
> Questions: Can we quantify the region in z where the low field NMR 
> measurement took place? Is there any pictures, or diagrams the show 
> the placement of the low-field NMR coils?
>
> We can try and use the high field NMR data but there are a lot of 
> "anomalous" measurements that would leave gaps in our polarization 
> tables. See the entries (red implies anomalous measurement) in the 
> list given on 
> http://clasweb.jlab.org/rungroups/g9/wiki/images/6/66/Clf_spreadsheet3
> _landscape.jpg
> .
> Moreover, in general, the the high field NMR measurements made 
> previous to re-polarization might be questionable.
>
> When I look at the baseline subtracted high field NMR signals on the 
> FROST
> webpage:
> http://clasweb.jlab.org/rungroups/g9/wiki/images/c/c1/P4_2_areas_edite
> d.jpg
> they look bad.
>
> Question: Are these a fair representation of what the baseline 
> subtracted NMR signal looks like for the high field just previous to re-polarization?
>
> All the other baseline subtracted NMR plots look OK:
>
> High field after polarization ->
> http://clasweb.jlab.org/rungroups/g9/wiki/images/c/ca/P1_1_areas_edite
> d.jpg
>
> Low field after right after polarization -> 
> http://clasweb.jlab.org/rungroups/g9/wiki/images/d/d4/P2_1_areas_edite
> d.jpg
>
> Low field just before polarization ->
> http://clasweb.jlab.org/rungroups/g9/wiki/images/9/90/P3_2_areas_edite
> d.jpg
>
> Question:
> Could the poor quality of the baseline subtracted high-field NMR plots 
> be due to the large gradients in the butanol polarization with respect 
> to the beam?
>
> Thanks for your time.
>
> -Michael
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