[clas12_rgk] exclusive neutral pion selection

Sat Jul 6 16:02:47 EDT 2019

Dear Viktor

Here is the complete list of exclusivity cuts I used

IM( gg ) < 0.8 GeV (two photon invariant mass cut)
MM( ep -> eggX) < 1.75 GeV (proton missing mass cut)
Angle( gg , ep->epX ) < 5 degrees (angle between pi0 direction and missing
pi0 direction)
Angle( g* ^ gg , g* ^ p ) < 3 degrees (angle between the g* pi0 scattering
plane and g* proton scattering plane, coplanarity of the final state,
resolution in phi Trento)
missing momentum transverse to the beam ep -> epggX pT < 0.25 GeV
-0.05 < missing mass squared ep -> epggX < 0.05 GeV^2
missing energy ep -> epggX < 1.5 GeV

also I imposed a cut on the angle between the scattered electron and the
photon direction to be more than 5 degrees

This set of cuts should produce a clean sample, although the angular cuts
might be tight even for the signal and reduce the yield somewhat

Best regards
FX

On Sat, Jul 6, 2019 at 9:55 PM Francois-Xavier Girod <fxgirod at jlab.org>
wrote:

> Dear Viktor
>
> Here is the complete list of exclusivity cuts I used
>
> IM( gg ) < 0.8 GeV (two photon invariant mass cut)
> MM( ep -> eggX) < 1.75 GeV (proton missing mass cut)
> Angle( gg , ep->epX ) < 5 degrees (angle between pi0 direction and missing
> pi0 direction)
> Angle( g* ^ gg , g* ^ p ) < 3 degrees (angle between the g* pi0 scattering
> plane and g* proton scattering plane, coplanarity of the final state,
> resolution in phi Trento)
> missing momentum transverse to the beam ep -> epggX pT < 0.25 GeV
> -0.05 < missing mass squared ep -> epggX < 0.05 GeV^2
> missing energy ep -> epggX < 1.5 GeV
>
> also I imposed a cut on the angle between the scattered electron and the
> photon direction to be more than 5 degrees
>
> This set of cuts should produce a clean sample, although the angular cuts
> might be tight even for the signal and reduce the yield somewhat
>
> Best regards
> FX
>
> On Sat, Jul 6, 2019 at 9:24 PM Viktor Mokeev <mokeev at jlab.org> wrote:
>
>> Dear All,
>>
>>
>> There are few differences in selection of gamma_{v}  p--> pi^0 p events
>> by Anna and FX:
>>
>>
>>
>>    1. Anna is using
>>    Cook: 5.7.4
>>    Data: skim4_5990.root (12M events)
>>    2. Anna got the photon energy from the sum ECAL+PCAL converted to the
>>    photon physical energy, while FX took them directly from EB.
>>    3. Anna selected events with a scattered electron, proton, and
>>    exactly two neutral which are not necessarily photons. FX selected
>>    scattered electron, proton, and > 2 gammas from EB.
>>
>>
>> I propose after completion of the simulation discussed at the July 5 RG-K
>> Meeting, Anna repeats the selection of  gv p--> pi^0 p events from the
>> same data set and with exactly the same selections as FX successfully
>> accomplished. For me, FX 2gamma inv masses looks great!
>>
>>
>>  Best Regards,
>>
>>                                  Victor
>> ------------------------------
>> *From:* clas12_rgk <clas12_rgk-bounces at jlab.org> on behalf of L Smith <
>> lcs1956 at me.com>
>> *Sent:* Friday, July 5, 2019 8:57:48 PM
>> *To:* Francois-Xavier Girod-Gard
>> *Cc:* clas12 rgk
>> *Subject:* Re: [clas12_rgk] exclusive neutral pion selection
>>
>> Dear FX,
>>
>> It may be the invariant mass dependence on pi0 energy is more related to
>> opening angle. For symmetric decays the two are directly related.  There is
>> persistent evidence of a theta,phi error in cluster angle reconstruction
>> for PCAL which you originally noticed (it goes through zero at the
>> mid-plane and theta=25) which would cause an accumulative error as opening
>> angle increased.
>>
>> Your study of DVCS photons in ECAL in
>> https://logbooks.jlab.org/entry/3698803 shows tails and shoulders in the
>> missing energy/mass distributions.  Of course there is considerable energy
>> loss from both transverse and longitudinal leakage at small angles (bottom
>> two plots) so a comparison with GEMC would be instructive.
>>
>> Best regards,
>> Cole
>>
>>
>> TWO PHOTON INVARIANT MASS ERROR vs OPENING ANGLE
>>
>> TOP theta_gamma=15.5  BOTTOM theta_gamma=5.5  P_gamma=5 GeV
>>
>>
>> On Jul 5, 2019, at 7:44 PM, Francois-Xavier Girod <fxgirod at jlab.org>
>> wrote:
>>
>> Dear all
>>
>> I posted some plots for my selection of exclusive neutral pion events
>> from run 5700 here
>>
>> https://logbooks.jlab.org/entry/3698969
>>
>> I get only few statistics with two photons in the FTCal but I get a
>> decent sample (10k events) with the two photons in the ECal. Checking the
>> pi0 mass dependence I did not find a polar angle or much azimuthal angle
>> dependence, but I do see a bit of dependence on the pi0 energy
>>
>> Best regards
>> FX
>> _______________________________________________
>> clas12_rgk mailing list
>> clas12_rgk at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/clas12_rgk
>>
>>
>>
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