[G14_run] Checking angle computation

[Haiyun Lu]

Hi All,
   Peng did a comparison with Tsuneo's result and found agreement. So I 
checked the comparison again and found that I made a mistake. Instead of 
comparing Peng's results without momentum correction, I compared a 
different file generated by me with a missing momentum correction to the 
neutron target. In a hurry, I forgot I replaced his file with my file. 
The updated comparison does show agreement and I attach it here.
Sorry about that.

Regards,
Haiyun
On 02/25/2015 04:58 PM, Reinhard Schumacher wrote:
> Hi All,
> 	After our discussion this morning, I took Haiyun's 100 events for gamma
> n to pi- p and computed the c.m. scattering angle of the pions.  I wrote
> a half-page stand-alone program to do the kinematics, and compared my
> computed angles with the values reported today from Dao's (and Tsuneo's)
> calculations.  They agreed with each other to machine accuracy, i.e.
> more than 6 decimal places.  Thus, I believe Peng has some small
> inconsistency and mistake in his calculation.
>
> Regards,
> Reinhard
>
> ______________________________________________________________________
> Reinhard Schumacher         Department of Physics, 5000 Forbes Ave.
> Carnegie Mellon University, Pittsburgh, PA 15213, U.S.A.
> phone: 412-268-5177         web: http://www-meg.phys.cmu.edu/~schumach
> ______________________________________________________________________
>
> On 02/14/2015 04:54 PM, daoh at andrew.cmu.edu wrote:
>> Dear all,
>>
>> As you might recall from the last meeting, Peng, Tsuneo and I were tasked
>> to compute the cos(pim) in the overall center of mass frame for a 100
>> events supplied by Haiyun. The initial goal was to let these events go
>> through momentum correction and energy correction to check for
>> inconsistency. However, I realized that with only 4-vector momentum
>> information for the proton, pim, and the photon, one can not do energy
>> correction (need to know the interaction vertex), nor momentum correction
>> (need to know the sector, the run number, etc...). As a result, I had not
>> applied any correction and computed the cos(pim) directly. I assumed the
>> neutron is at rest, then I boosted the pim into the photon and at-rest
>> neutron rest frame. I then computed the cos(pim) with respect to the beam
>> line.
>>
>> I attached a file with the computed values of cos(pim) with this email if
>> Peng and Tsuneo want to compare.
>> Sincerely,
>> Dao Ho
>>
>>
>>
>>> As discussed, I attached a 100-event text file. Each event has three
>>> particles: photon beam, scattered proton and scattered pi- in order.
>>> Each particle occupies one line with energy, momentum in x direction,
>>> momentum in y, and momentum in z. All these variables are in Lab frame.
>>> There are totally 300 lines.
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