Double-Pion Channel Analysis Updates

K. Neupane

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Ongoing tasks:

• Simulation with current-dependent background merging (✓)
• Overall more simulations (✓)
• Change in binning (invariant mass) (✓)
• Apply momentum corrections (in coordination with the Momentum Correction Task Force)

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Publication plan:

• Our first publication on the double-pion channel will be based on this analysis
• After completing additional simulations, revising invariant mass binning, and refining all analysis steps, we will begin writing a CLAS Analysis Note and a journal paper, with a target submission by December 2025

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Ongoing tasks and plans for publication

Tasks

1. Refined CDFD cuts (✓)

2. Refined Fiducial cuts (✓)

4. MMSQ cuts (✓) needed to apply

3. Merging two MC data sets (✓)

5. Splitting into 14 inv mass bins (✓)

7. Background study

8. QADB

9. Efficiency studies

10. Radiative/bin centering studies

11. Writing Analysis Note

12. No EB pid??

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Removal of proton tracks present in both CD and FD

if (dp > -0.25 && dp< 0.02 && dtheta> -3 && dtheta< 3 && dphi> -12.5 && dphi< 7.5)

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Systematics of this cut for proton and pip are performed at once and estimated to be 0.42 %.

Only about 1.1% data are cutoff from this cut.

Removal of pip tracks present in both CD and FD

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Removal of proton tracks present in both CD and FD

Without CDFD cuts

With CDFD cuts

~ 98.915 %

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Removal of proton tracks present in both CD and FD

if (dp > -0.4 && dp< 0.3 && dtheta> -10 && dtheta< 10 && dphi> -22 && dphi< 17.5)

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if (dp > -0.4 && dp< 0.3 && dtheta> -10 && dtheta< 10 && dphi> -22 && dphi< 17.5)

Removal of proton tracks present in both CD and FD

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Removal of proton tracks present in both CD and FD

Remove both tracks

~ 98.04 %

Without CDFD cuts

Remove CD tracks

~ 98.97 %

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Remove FD 99.08 %

Selected double-pion events (after all cuts)

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Removal of proton tracks present in both CD and FD

Remove both tracks

~ 98.14 %

Without CDFD cuts

Remove CD tracks

~ 99.06 %

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Remove FD 99.07 %

Selected double-pion events (after all cuts)

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1.45<=W<1.50 GeV, 4.2 <Q2< 5.0 GeV2

1.60<=W<1.65 GeV, 3.5 <Q2< 4.2 GeV2

Check in sim yields too

Particle Identification

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Electron pid cuts:

- Electron must have negative charge -1

- Event-builder electron pid cut

- Momentum of electron > 1.5 GeV

- The electron is detected in forward detector

- Vertex position cut around target

- 3.5 sigma cut on sampling fraction

- PCAL fiducial cuts:

- DC fiducial cuts:

- Cuts on V and W planes of the PCAL

- PCAL inefficient region cuts

- 1.4 GeV < W < 2.15 GeV

- 2.0 GeV² < Q² < 9.0 GeV²

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Electron DCR1 fiducial cuts (old)

Cut at 20% of max height

Show new cuts

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Electron DCR1 fiducial cuts (new)

Changed from 20% to 30 %

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Electron DCR2 fiducial cuts old

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Electron DCR2 fiducial cuts new

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Electron DCR3 fiducial cuts old

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Electron DCR3 fiducial cuts new

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Stefan Diehl

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Stefan Diehl

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�cut_at_0.95 : {38.12, 38.12, 38.12, 38.12, 38.12, 38.12, }; cut_at_0.9 : {41.88, 40.62, 41.88, 41.88, 41.88, 41.88, }; cut_at_0.99 : {36.88, 33.12, 35.62, 35.62, 35.62, 35.62, };

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Modified MMSQ Cuts Exp

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Modified MMSQ Cuts Sim

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Modified MMSQ Cuts Exp

All W-Q2 bins

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Modified MMSQ Cuts Sim

All W-Q2 bins

Simulations

• Twopeg event generator available on Jlab’s osg portal (Dr. Iuliia skorodumina)
• 1.35 GeV < W< 2.15 GeV & 1.95 GeV² < Q² < 9.0 GeV²
• 45nA background merging files
• (gemc 5.10) (pass2) + gemc 5.4

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Generated no of events in each 2D, bins

gemc 5.10

2.0-2.4: 3.5 x10⁷

2.4-3.0: 5.3 x10⁷

3.0-3.5: 4.8 x10⁷

3.5-4.2: 8.9 x10⁷

4.2:5.0: 1.1 x10⁸

5.0-6.0: 1.3 x10⁸

6.0-7.0: 1.3 x10⁸

7.0-8.0: 1.3 x10⁸

gemc 5.4 Q² < 3.3 to 8.5 GeV²

3.5-4.2: 2.9 x10⁷

4.2:5.0: 3.4 x10⁷

5.0-6.0: 4.2 x10⁷

6.0-7.0: 4.2 x10⁷

7.0-8.0: 3.9 x10⁷

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The systematics error for this effect is taken 5%, as it was the case for previous double-pion channel analysis.

Twopeg Radiative Corrections

Twopeg Radiative Corrections

• In order to simulate radiative effects (RE) the Mo and Tsai approach [12] was chosen. This  approach allows to calculate radiative integral cross sections from the given nonradiative ones in each (W, Q²) point. In [12] this is applied to the inclusive case, while here double pion integral cross sections are used instead.
• [12] only accounts for the change of cross section values, an additional procedure is used to generate the energy of the radiative photon and to account for the shift in W and Q² caused by RE.
• [12] assumes that radiative photons are emitted collinearly to the in and outgoing electron directions (so-called “peaking approximation”). (BH cross-sections may have the plot)….
• The minimal energy of the emitted radiative photon is a free parameter. It is denoted as ∆ and chosen to be equal to 10 MeV. In [12] it is claimed that the result was found to be insensitive to the choice of ∆ value, however this value must be smaller than the  resolution of the experiment.
• dσ_rad(W,Q²)/dΩdEe′= S1 +S2 +S3.  Three terms correspond to 3 regions of integration in figure. Contribution from region four in this figure is neglected in order to save computation time.
• The term S1 corresponds to the so-called “soft radiation”, in which the energy of the  radiated photon is less than ∆ (10 MeV).
• The two remaining terms correspond to the so-called “hard radiation”, in which the energy of the radiated photon is greater than ∆. S2 accounts for the changing initial electron energy and S3 for the changing scattered electron energy.

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Straggling

Elastic tail

Continuous spectra

Unfolding

Twopeg Radiative Corrections

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Twopeg Radiative Corrections

ϕ is the Spence function

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Twopeg Radiative Corrections

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Twopeg Radiative Corrections

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Twopeg Radiative Corrections

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However, the cross section change due to RE is not the only issue we are interested in. One also wants to simulate the radiative tail in distributions like missing masses, which appears due to the mismatch between the hadron and lepton momenta. This mismatch is the consequence of the fact that (W, Q2) values obtained from the initial and scattered electrons, which suffer from RE, are not those for which final hadrons are produced. To simulate this effect one needs to account for the shift in the (W, Q2) values due to RE, which in turn implies the generation of the radiated photon energy.

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equation 3.2

< ∆ < 10 MeV

Twopeg Radiative Corrections

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Results: Integrated Cross Sections in various W-Q² bins

Results: Nine Single Differential Cross Sections in various W-Q² bins

These Cross Sections will be fitted by JM model to extract the resonant amplitudes

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Double_t Bin_size_pPip0 = ((1.0 + 0.05 * w + 0.025 - MASS_PIM) - (0.938272 + 0.13957)) / 7.0;

Double_t Bin_size_pipPim0 = ((1.0 + 0.05 * w + 0.025 - MASS_P) - (0.13957 + 0.13957)) / 7.0;

�// // //adding extra bins in each end of invariant mass hist

Double_t xmin_5D[ndims_5D] = {((0.938272 + 0.13957) - 4 * Bin_size_pPip0), (0.13957 + 0.13957) - 4 * Bin_size_pipPim0, 0., 0.0, 0.};

Double_t xmax_5D[ndims_5D] = {((1.0 + 0.05 * w + 0.025 - MASS_PIM) + 4 * Bin_size_pPip0), ((1.0 + 0.05 * w + 0.025 - MASS_P) + 4 * Bin_size_pipPim0), 180, 360, 360};

5-D Binning

Bin size

Invariant mass Boundaries

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Conclusions and remarks

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1. CDFD cuts are modified
2. New refined Fiducial cuts are applied
3. MMSQ cuts are refined based on the background studies
4. Nine 1-D cross-sections are rebind and compared with CLAS6 cross-sections
5. Cross section results are focused on high Q² bins ( 3.5 < Q² < 8.0 GeV²)
6. Further refinement in the background studies are ongoing
7. Analysis note will be drafted soon

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Results: Integrated Cross Sections in various W-Q² bins

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Results: Integrated Cross Sections in various W-Q² bins