[Tpe] tpe meeting minutes

[Andrei Afanasev]

Thanks. I have to clarify that the figure I sent shows the calculated 
deviation from unity for the ratio of cross sections of e^+ to e^-.
The asymmetry would be twice smaller.
-Andrei

On 4/9/2010 2:14 PM, John R. Arrington wrote:
>
> The 6% comes from the raw ratio, without correcting for the 
> electron-proton interference.
>
> On Fri, 9 Apr 2010, Andrei Afanasev wrote:
>
>> Hello,
>>
>> The attached figure demonstrates the e+/e- asymmetry that comes from 
>> soft TPE combined with brem -VCS
>> interference. This is a standard correction previously included in 
>> SLAC Rosenbluth analysis. The formulas used are from the original 
>> Tsai's paper. I calculated the asymmetry here for a fixed beam energy 
>> of 1.6 GeV, while Q^2 is variable. VEPP3 kinematics corresponds to 
>> epsilon=0.4. You can see that the `soft' asymmetry is about 3% for 
>> their kinematics. A new effect, if found, would correspond to a 
>> difference between this `soft' asymmetry and the measurement. I do 
>> not know if the preliminary 6% from VEPP
>> include the soft term or not.
>>
>> -Andrei
>>
>> On 4/8/2010 2:27 PM, Larry Weinstein wrote:
>>> Dear TPE folks,
>>>
>>> Here is a summary of what we discussed at our meeting last Friday:
>>>    1) Whether we should have 0.25" lead on the vacuum box or a hut 
>>> around
>>> the box.
>>>       - needs simulation.  Lead is a feasible solution.
>>>    2) Engineered vs stacked chicane shielding.  Engineered is better 
>>> but
>>> stacked worked well.  We will look into how to make the shielding more
>>> hermetic between the first Italian Dipole and the pair spectrometer.
>>> Rob will post  pictures of that area.
>>>    3) Sparse fiber detector as a beam monitor.  This will be placed 
>>> right
>>> before the downstream collimator, as it was in the test run.  We will
>>> simulate the background effects of placing it there to double check it
>>> is OK.
>>>    4) Optimize Moller catcher geometry.  This was well studied by Megh.
>>> The current shape is good.  We do not need to adjust the jaw opening.
>>>    5) calorimeter location.  Downstream of CLAS, probably on the 
>>> catwalk
>>> between the forward carriage and the alcove.  The existing photon beam
>>> profiler will be placed on the front face of the calorimeter.
>>>     - Valparaiso has already received the 30 Shashlik calorimeter 
>>> modules
>>> and is starting to build the bases and order the PMTs.
>>>    6) RadPhi wall collimator.  It was lead with a 2-cm brass insert
>>> during the test run.  We would like it to be 2-cm tungsten (preferably)
>>> or lead for the actual run.
>>>    7) Are the TOF TDCs running in multi-hit mode?
>>>    8) Novosibirsk finished their run in January at Q^2=1.5 and
>>> epsilon=0.4 (one data point).  They see a measurable effect (~6% from
>>> the online results).  This is pre-preliminary.
>>>
>>> - Larry
>>>
>>>
>>
>>