[Clas12_verystrange] Very Strange Meeting May 2nd

[Derek Glazier]

Hi Michael,

    That looks approximately right. You could make a lorentz vector for 
the electron in the FT then subtract this from the electron beam lorentz 
vector. This way you also get linear polarisation plane, Q2 etc I am not 
sure if it makes a big difference on the missing mass or not, but is 
what I do.

   I just use the FT particle from the REC::Particle bank. You should be 
aware that the FT particles are already part of this array in case you 
use them twice.

If you use FT_particles it should probably look more like

TLorentzVector eBeam(0.0,0.0,6.423,6.423);

TLorentzVector FTe(ftCx*ftEnergy, ftCy*ftEnergy, ftCz*ftEnergy, ftEnergy);

TLorentzVector gamma=eBeam-FTe;


If you use REC::Particle, you also need to loop over REC::ForwardTagger 
and match the pindex to the REC::Particle array index to identify the FT 
entries.

Do you set the mass of the proton to the PDG mass or just use the energy 
and momentum from REC::Particle ? I guess this could give an offset of 
0.1 in MM^2 (if you do the latter).


Cheers

Derek


On 02/05/18 21:53, Michael Dugger wrote:
>
> Derek,
>
> Your stuff looks better than mine. I am using 6.423 GeV for the 
> electron beam energy and then subtract off the tagger energy like:
>
> TLorentzVector beam(0.0,0.0,6.423-ftEnergy,6.423-ftEnergy);
>
> with ftEnergy taken from
>
> FT_particles_energy
>
> Does that look wrong?
>
> Any help is appreciated.
>
> Take care,
> Michael
>
> On Wed, 2 May 2018, Derek Glazier wrote:
>
>> Hi Mike,
>>
>>
>>> ** There are a lot more events at large angle and low momentum. I 
>>> assume
>>> these events are coming from CTOF, but have not checked that 
>>> assumption.
>> This is possibly the new CVT tracking algorithm which seems to be 
>> much more efficient, while also introducing some extra background.
>>> The Bad and the Ugly->
>>>
>>> * I tried to do a missing mass for the reaction gamma p -> p X. Get 
>>> huge
>>> bump at massX squared = - 0.1 . Can't figure out what is going on 
>>> there.
>> For FT e- and run 3050 I would expect a large elastic peak at 
>> massX=0, this is what I get. Could some calibration be off? For run 
>> 3050 I use 6.4GeV beam energy.
>>>
>>> * The invariant mass of the proton pi^- system is just a blob at masses
>>> that look somewhat high. Just a mess really.
>>>
>>> If anyone can get any good looking physics (some sort of invariant mass
>>> peak at about the right location), please let me know. My stuff is just
>>> kind of awful :(
>> I attach a slide for eppi+pi- final state. I seem to get missing mass 
>> peaks at the right place and the 2pi invariant mass looks like a rho. 
>> The last few updates have certainly improved the cooked data quality. 
>> Although I do not see any Deltas for some reason.
>> Cheers
>> Derek
>>>
>>> Take care,
>>> Michael
>>>
>>>> We shall have meeting tomorrow, Wednesday May 2nd at 11:15 JLab time.
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