[Halla_pi0] pi0 meeting

[richard lindgren]

Cole,

Our ellipses are pretty close for the ones I checked.

I guess the point is that the left side of my ellipse is pion phi =180 deg (BB=43.5 deg) and the right side is pion phi=0 deg (BB=0 deg). We see very little data (MM peak) at low W and phi=0 deg ( BB=-54 deg) These correspond to kin A,B, C, and D, D is the worst. My question is where is phi = 0 deg? I don't have a feeling why we are missing that part of the cone.
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Dr. Richard A Lindgren
Research Professor of Physics 
Department of Physics
University of Virginia
382 McCormick Rd
Charlottesville, VA 22904
ral5q at virginia.edu







On Jun 26, 2012, at 1:17 PM, Cole Smith wrote:

> 
> Whatever you sent was corrupted and full of security certificates
> that I had to trust or reject, etc.
> 
> Can you verify that your ellipses agree with mine:
> 
> http://galileo.phys.virginia.edu/~lcs1h/halla/cm.html
> 
>> From what I plot, 54 deg gets a much smaller piece of
> the ellipse at these kinematics.  Also the cross section
> is smaller by an order of magnitude at  phi*=0 compared
> to phi*=180, according to the models (and our data).
> Finally I'm not sure that Khem uses the full horizontal
> acceptance of BigBite.
> 
> Just to be sure...Khem, does the lowest summed W histogram
> in your file correspond to W=1.07375 ?
> 
> Cole
> 
> 
> 
> On Tue, 26 Jun 2012, richard lindgren wrote:
> 
>> Hi,
>> 
>> There is still something that doesn't look right about Coles plots for D1 kinematics at low W. I agree with your comments about the cone fitting into BigBite and if you don't have the cone, then you won't see anything.
>> 
>> However, it appears to me that you do have the cone. If you look at the plot of thee ellipses which I have attached, you will see that -54 degrees BitBite 2 setting contains half of the cone at low Q2 and low W . In fact it is centered at W=3.77 MeV and Q^2 =0.058, but when you look at the plots for D1 kinematics which is -54 degrees, you do not see much of a missing mass peak until about 5.5 MeV. Below 5.5 MeV there is no missing mass peak and you should see something.
>> 
>> If you make the same comparison with BigBite 3 kinematics which is -43.5 degrees (The ellipse plot shows it for -42 degrees), you see a beautiful missing mass peak all the way down to threshold. BigBite is centered at about 1.687 MeV. The position of BigBite 3 and BigBite 2 are basically similar in terms of proton momentum except one is on the right side of the ellipse, which  is phi=0 deg pion cm, and one is on the left side, which is phi=180 degree pion cm angle.  How can the missing mass peak be so clear on one side all the way down to threshold and not even visible on the other side. It is not kinematics or the cone because in both case at least half of the cone is in BigBite based on the ellipse figure.
>> 
>> Please take a look at this.
>> 
>> Richard
>> 
>> Dr. Richard A Lindgren
>> Research Professor of Physics
>> Department of Physics
>> University of Virginia
>> 382 McCormick Rd
>> Charlottesville, VA 22904
>> ral5q at virginia.edu
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 

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