CLAS12 Double-Pion (N ππ) �Electroproduction Analysis

Krishna Neupane

USC, Columbia, SC

Physics Analysis: Double-Pion Channel Cross-Section

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• Particle Identification:
• - Electron pid cuts ✅
• - Hadron pid cuts ✅
• Event Selection ✅
• Detector Inefficiency Cuts✅
• Cross-Section Calculations
• Corrections
• Simulations ☑️
• Holes Filling ✅

Exp. Data: - Using Run Group A, Fall2018 data with inbending configuration (pass2), 126 runs same as Inclusive analysis

- The beam energy is 10.6041 GeV

- 1.4 GeV < W< 2.15 GeV & 2.0 GeV² < Q² < 9.0 GeV²

Simulations: - TWOPEG event generator is used (gemc 5.4/5.10) (pass2)

Topology: missing pim topology (ep->e’p’pi+)

Done: Energy loss, Momentum, ΔP ✅

Acceptance Correction

Detector Efficiency from Experimental Data ✅

Bin centering Corrections ✅

Radiative Effects ✅

Background subtraction ✅

In Progress: Empty target subtraction

Next: Error Analysis (Systematic Uncertainties)

ep-->e’p’ π⁺π^-

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cut_mid_0.95 : {38.12, 38.12, 38.12, 38.12, 38.12, 38.12, };

cut_tight_0.9 : {41.88, 40.62, 41.88, 41.88, 41.88, 41.88, };

cut_loose_0.99 : {36.88, 33.12, 35.62, 35.62, 35.62, 35.62, };

Electron PID

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Double-Pion Channel Cross-Section

Electron Scattering Cross-Section:

Hadronic Cross-Section:

Single Differential Cross-Section:

The goal of the analysis is to extract the virtual photoproduction cross section σ_v of the reaction γ_vp → p′π+π−. This virtual photoproduction cross section σ_v is five-fold differential and in the single-photon exchange approximation connected with the seven-fold differential electron scattering cross section σ_e via :

Nine 1D experimental yields for 1.65-W-1.70 GeV 3.5-Q²-4.2 GeV²

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1) M_π-π+, M_π+p’, θ_π-, φ_π- and α _{(pπ-)(p’π+)} (ie. α_π-) [π−, π+, p′]

2) M_p’π+, M_π+π-, θ_p’ , φ_p’ and α_{(pp’)(π+π-)} (ie. α_p’ ) [p′, π−, π+]

3) M_π+π-, M_π-p’ , θ_π+, φ_π+ and α _{(pπ+)(p’π-)} (ie. α_π+) [π−, π+, p′]

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Binning:

• 50 MeV/c W bin size
• 9 Q² bins
• 7 bins for invariant masses
• 10 bins for θ
• 6 bins for φ
• 10 bins for α

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, W-Q² bins (reference 10⁸ events per bin)

gemc 5.10

2-2.4: 2.6 x10⁷

2.4-3.0: 3.8 x10⁷

3-3.5: 3.2 x10⁷

3.5-4.2: 4.3 x10⁷

4.2:5.0: 4.9 x10⁷

5.0-6.0: 6.1 x10⁷

6.0-7.0: 6.1 x10⁷

7.0-8.0: 6.0 x10⁷

8.0-9.0: 5.5 x10⁷

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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Acceptance Correction Factor A

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Background based on: MMSQ peaks for ep->e’p’pi+pi- topology

Simulations

Experiment

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Background Subtraction

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Exclusive topology

Missing pim topology

Experiment

Simulations

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Bin Centering Corrections

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Bin-Centering Corrections:1060-W-1.65 GeV, 4.2-Q²-5.0 GeV²

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CLAS6 and Twopeg cross-sections

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a and b will be calculated from the fit

Twopeg Cross-sections

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The fit gives us:

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a = 0.31660

b = 1.18085

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Extending the fit Up to Q² = 30.0 GeV²

Hole Fractions

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Efficiency cut

1.90-W-1.95 GeV 3.5-Q²-4.2 GeV²

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Preliminary Results

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Preliminary Results: Best and worse comparison

Nine 1D cross-sections yields for 1.85-W-1.90 GeV 2.0-Q²-2.4 GeV²

Nine 1D cross-sections yields for 1.60-W-1.55 GeV 2.0-Q²-2.4 GeV²

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Preliminary Results

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Preliminary Results

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Preliminary Results

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Preliminary Results

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Preliminary Results

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Preliminary Results

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Preliminary Results

Tasks to be done

• Systematic and statistical Error analysis
• 45, 50, 55 nA beam current adjustments

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Conclusions

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• Particle identification cuts have been implemented
• Based on missing π^- topology, two-pion events are selected
• Using TWOPEG event generator, acceptance correction factor are applied and remaining holes are filled
• Energy/momentum corrections, radiative effect corrections, background subtractions are applied
• Smearing MC data, Detector efficiency studies are in done
• Double-pion channel total and nine 1D preliminary Cross-sections are extracted
• Cross-sections are compared with CLAS6 analysis for overlapping regions and they are matching within the error bar limits
• Systematic studies are needed to quantify uncertainties and extract precise Cross-Sections

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Two-Pion Channel Cross-Section

Electron scattering Cross-Section:

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Total cross-section

Δ N = L σ

From

dN/dt = (dN/dt)_beamN_targetσ / A

Theta pim is angle betn

Three mom of initial

Proton and three mom

Of final pim.

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1) M_π-π+, M_π+p’, θ_π-, φ_π- and α _{(pπ-)(p’π+)} (ie. α_π-) [π−, π+, p′]

2) M_p’π+, M_π+π-, θ_p’ , φ_p’ and α_{(pp’)(π+π-)} (ie. α_p’ ) [p′, π−, π+]

3) M_π+π-, M_π-p’ , θ_π+, φ_π+ and α _{(pπ+)(p’π-)} (ie. α_π+) [π−, π+, p′]

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Binning:

• 50 MeV/c W bin size
• 8 Q² bins
• 6 bins for invariant masses
• 10 bins for θ
• 6 bins for φ
• 8 bins for α

Where:

ΔN, Q are no of two-pion events inside 7-differential bin and charge on faraday cup with full an empty target, A, E, R are correction factors, ΔW, ΔQ² are kinematical bins, L is luminosity,

∆τ = ∆M_pπ+∆M_π+π-∆(−cos(θ_π-))∆φ_π-∆α_π- is an element of the hadronic 5-dimensional phase space

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