TEST Event Mixing Method on GEN events

Here photon i from event1 is mixed with photon j=1,2... of event2 if E(j-1)>E(i).

Fig.1 Invariant mass of MC mixed photons (aka mixed background). Distribution binned in pT2, z, Q2, Nu bins






Figures to follow are: 1. Number of GEN pi0 (identified by ID) in pT2, z, Q2, Nu bins (selected events contain Npi0 < = 5)
2.Invariant mass of 2photons in the same pT2, z, Q2, Nu bins (selected events contain Ngamma<=10). Fitted with POL4 in range:
0.1-0.17 excluding (0.132,1385). Fit parameters are fixed as determined from Fig.1, free parameter is normalization p0 ;
Fit range is drawn in red, in black - function from this fit drawn in the full range of the histogramm, distribution in blue - 2photon inv.mass from MC.
Number on hists is Delta_N = N_hist-N_back. Printed in red this number is extracted in the fit range 0.1-0.17, in black - 0-0;3

Fig.2a Pi0 in pT2 bins. TOP - Generated Npi0 by ID; BOTTOM - Invariant mass of 2photons fitted with mixed background
Discrepancy between N Gen and Delta_N(red) are: 0.72, 0.86, 0.93, 1.14, 1.05,1.09, 1.17, 1.19, 1.19 % in each pT2 bins corresp.


Fig.2b Pi0 in Z bins. TOP - Generated Npi0 by ID; BOTTOM - Invariant mass of 2photons fitted with mixed background


Fig.2c Pi0 in Q2 bins. TOP - Generated Npi0 by ID; BOTTOM - Invariant mass of 2photons fitted with mixed background


Fig.2d Pi0 in V bins. TOP - Generated Npi0 by ID; BOTTOM - Invariant mass of 2photons fitted with mixed background




Here photon i from event1 is mixed with each photon j=1,2...

Fig.3 Invariant mass of MC mixed photons (aka mixed background). Distribution binned in pT2, z, Q2, Nu bins





Fig.4 Invariant mass of 2photons fitted with mixed background(from Fig.3) in pT, z, v, q bins







Energy and Position of Photons are SDMEARED acc. to CLAS >esolution

Testing Mixing methods. Illustrated particular example of z-bin and Pol4 fit to background.

Npi0 extracted after mixed background subtraction are to be compared with a actual generated Npi0 from a sample of 10M generated events where the photons were
meared according to EC energy and position resolution + and constrained in this example in Egamma>0.15 and 8 Fig.0 Sample of generated events in z- bins and to compare further plots with:


e 1. All uncorrelated photons (order and mixed by decreasing energy) are mixed in a elementary (Q2,Nu) bins.
Fig.1a Mixed bakcground fitted with pol4. Egamma>0.15, 8 < theta < 45

Fig.1biInvariant Mass with background fitted [0]*pol4.Egamma>0.15, 8 < theta < 45

Deviation from generated events (Fig.0) in each bin of z are as follows: 9.1%, 6.6%, 5.2%, 4.2%, ..., ..., ..., 0.5%, -0.7%.
Fig.1a Here photons are unconstrained in E, Theta and background comes from unconstrained dist as well


2. Photons are mixed in a rotated frame such that one virtual photon is rotated by deltaPhi (difference in Phi of virtual photons from one event and from the other ), real photons belonging to this virtual photons are rotated by deltaPhi and boosted. Events are mixed in bins of Q2, Nu. Also, backgr distribution were checked for the case of E,P of the virtual photons coinciding in range 10,50,..200 MeV which affected poorly the shapes. Egamma>0.15 and 8 Fig.2a Mixed bakcground fitted with pol4. Egamma>0.15, 8 < theta < 45

Fig.2biInvariant Mass with background fitted [0]*pol4.Egamma>0.15, 8 < theta < 45

Deviation from generated events in each bin of z are as follows: 6.0%, 5.0%, 4.6%, 3.9%, ..., ..., ..., 0.0%, -0.1%.
Fig.2c Here photons are unconstrained in E, Theta and background comes from unconstrained dist as well


3. Virtual photons are mixed in a frame where one virtual photon is rotated on phi to coincide to go along z, its photon is also rotated on the same angle and boosted as if the virtual photons of another event had been directed along z as well. Events are mixed in elementary bins and were also tested in the coincidence of their virtual photon in E, P. Here Egamma>0.15 and 8 Fig.3a Mixed bakcground fitted with pol4. Egamma>0.15, 8 < theta < 45

Fig.3biInvariant Mass with background fitted [0]*pol4.Egamma>0.15, 8 < theta < 45




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