[Hps] HPS Meets March 13

[Marco Battaglieri]

Dear Tim,
thanks for your valuable thoughts. We did not investigate the 
possibility of measuring the scattered electron within the silicon 
detectors. The feeling we got from the very first kinematics 
considerations (probably based on not-fully applicable approximations) 
indicate that, to preserve a good A' detection efficiency, we need to 
reduce the threshold of detected electron to a lower energy (say 10-50 
MeV). If it is true, the only way is to instrument the backward side of 
the target with a new dedicated device, being the low energy/large angle 
scattered electrons, bent by the magnetic field to backward directions. 
The specs will be defined after a comprehensive understanding of the 
scattered electron kinematics. Using the SVT as a veto for bg electrons 
is sound. As soon as we will shave under control the scattering 
kinematics we can easily study the fraction of forward-going bg 
electrons (with energy > 100MeV) and chech the rejection efficiency.
Thanks again to keep the discussion on this idea alive. Any other 
idea/suggestions/comments are more than welcome!
Cheers
Marco


Nelson, Timothy Knight wrote:
> Dear Marco and Misha,
>
> I'm sorry I had an appointment and missed the meeting today: I think this is a good thing to be exploring. Perhaps this came up at the meeting, but I have been wondering what might be possible with the existing detector.  As you know, for signal events the incoming electron tends to be scattered at large angles and therefore will only rarely be observed in the tracker.  However, for the dominant background (Bethe-Heitler), the scattered electron is more forward, perhaps enough that it will often be observed as a track in our background events.  If that is the case, the measurement of a third track in our acceptance (with momentum significantly less than the beam energy) could be a useful veto against our dominant background.  Although this kinematic information is already encoded in the A' daughters, the critical variables one might use (the scalar momentum and angle of the scattered electron with respect to the beam direction) are not well determined (significantly smeared) by combining measurements of the A' daughters in the part of phase space we are already selecting with our cuts; when the A' carries away nearly all of the energy of the incoming electron (and the momentum of A' daughters is therefore large).  So, if one actually measures that third track, one should be able to make a more powerful cut than on the sum of the A' daughters.
>
> Have you thought about this at all?  I will be very interested in what the Bethe-Heitler background looks like and how many of the scattered incoming electrons in this background are observed in the tracker relative to signal.
>
> Cheers,
> Tim
>
> On Mar 13, 2013, at 6:29 AM, Marco Battaglieri <battaglieri at ge.infn.it> wrote:
>
>> Dear John,
>> a couple of weeks ago, talking with Stepan at JLab, we discussed the
>> possibility to add to  HPS experimental setup a tagger to measure the
>> scattered electron, emitted at low energy and big angle. If feasible,
>> the triple coincidence (e+e- from A' and scattered e' in the expected
>> position/energy range) could reduce the QED background (hopefully
>> produced with a different kinematics) cleaning the data sample and
>> (hopefully) increasing the sensitivity of the measurement.
>> Before to involve the full simulation of the experiment (including the
>> em background), Misha Osipenko, a staff researcher from our group, is
>> looking into the kinematics of the produced A' and correspondingly of
>> the scattered e'. He would like to share with the Collaboration his
>> study and present some issues he found to have a feedback form experts
>> (all of you!) and/or get suggestions to contact some expert in QED
>> calculations to overcome some of the simplifications and assumptions
>> usually used.
>> Could Misha present the attached slides at the  meeting today?
>> Thanks in advance
>> cheers
>> Marco
>>
>>
>> Jaros, John A. wrote:
>>> Dear HPS,
>>>
>>> We'll meet Wednesday, March 13, at 8:30 AM PST/ 11:30 EST.
>>>
>>> Agenda:
>>>
>>> 1. News?
>>>
>>> 2. Plans for Proposal Revisions                         Chapter Editors
>>>     Software Chapter
>>>
>>> 3. Progress on Muon Studies                             Yuri et al.
>>>
>>> 4. Summary HPS Backgrounds                              Takashi
>>>
>>> 5. AOB
>>>
>>> Hope to talk to you tomorrow.
>>>
>>> John
>>>
>>> WEBEX information is at -
>>> https://confluence.slac.stanford.edu/display/hpsg/WebEx+Connection+Details+-+HPS+Weekly
>>>
>>>
>>>
>>>
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