[clas12_rgk] exclusive neutral pion selection

[Francois-Xavier Girod]

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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