photons off transversely polarized protons (g9b-FROST) Lelia - PowerPoint PPT Presentation

Polarization observables in double charged pion photo-production with circularly polarized ¡ photons off transversely polarized protons ¡ (g9b-FROST) Lelia Aneta Net Research supported in parts by National Science Foundation NSF PHY-1505615 NSTAR 2017, Columbia, SC ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ August 22nd, 2017

Outline • The Theory and the Models • Double pion channel - Missing Resonances Problem • FROST Experiment (g9b) • Analysis: Extraction of polarization observables J J J • Results for I , P x , P y , P x , P y • Summary 2 ¡

THE THEORY AND THE MODELS ¡ • A QCD solution is not known at low energies (of the order of the nucleon mass and its excited states) • Different models predict different number of nucleon excited states (CQM) ¡ • Experimental data will help confirm the existence of these predicted resonances 3 ¡

DOUBLE PION PHOTOPRODUCTION • Biggest contribution to the photo-production cross section at higher energies • Branching ratio for N* decay via double pion channel could be greater than 70% (e.g. N(1720)) Hagiwara et al., 2002 4 ¡

POLARIZATION OBSERVABLES • Different helicity combinations of the initial nucleon, final nucleon and the photon give rise to 8 complex transition amplitudes describing the reaction: • The cross section sums up the squares of these transition amplitudes; polarization observables allows access to the amplitude’s phase; reveal more information about the reaction dynamics • This work focused on the extraction of 5 polarization J J J observables: I , P x , P y , P x , P y 5 ¡

Previous/Current Studies for Double Pion Photo-production with CLAS P C ¡ Z [Strauch, 2005] [Yuqing Mao, USC] ¡ 6 ¡

FROST Experiment (g9 run) at Thomas Jefferson National Accelerator Facility (Newport News, VA) h0p://www.phys.vt.edu/research/experiments/JLab-­‑Aerial.jpg ¡ 7 ¡

BEAMS AND TARGETS ¯ • Electron beam: - longitudinally polarized: P e = 87% - beam energy: 3081.73 MeV • Photon beam: - circularly polarized (4 E γ /E e ) − ( E γ /E e ) 2 δ J = ¯ E γ ≈ [0 . 5 − 3 . 0 GeV] P e 4 − (4 E γ /E e ) + (3 E γ /E e ) 2 • FROzen Spin Target (FROST) - transversely polarized protons (C 4 H 9 OH) • Target polarization: 76% - 86% • Carbon target: unpolarized • Polyethylene target: unpolarized 8 ¡

CLAS DETECTOR TORUS&MAGNET& • time and BEAM&LINE& momentum TARGET& measurements DRIFT& • coverage: CHAMBERS& 8 � < φ < 140 � TIME&OF& FLIGHT& PADDLES& − 25 � < θ < 25 � h0ps://www.jlab.org/Hall-­‑B/int-­‑web/clas_large1.jpg ¡ 9 ¡

PHOTON SELECTION 3 10 × Counts 6000 Raw Data Final Selection 5000 ∆ t = t CLAS,vertex − t γ ,vertex = 4000 d ST t T AGR + Z h i = t ST − 3000 − c · β calc c 2000 1000 PARTICLE ID 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 Δ t [ns] p ∆ β = β meas − β calc = β meas − p p 2 + m 2 c 2 3 3 × 10 × 10 6 10 × Counts Counts Counts 22 9000 9000 Mean = 0.002 Mean = 0.001 20 Mean = 0.002 Sigma = 0.010 8000 Sigma = 0.01 8000 Sigma = 0.010 18 Mean-3 = -0.029 Mean-3 = -0.036 σ σ Mean-3 σ = -0.029 7000 7000 Mean+3 = 0.033 Mean+3 = 0.038 σ σ 16 Mean+3 σ = 0.032 6000 6000 14 5000 12 5000 10 4000 4000 8 3000 3000 6 2000 2000 4 1000 1000 2 0 0 0 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 10 ¡ Δ β Δ β Δ β - + π π p

REACTION SELECTION ¡ γ p → p π + π − Final State Composition: 2 positive charges and 1 negative charge ¡ p → p ⇡ + ⇡ − ( X ) ~ �~ nothing missing Topology 1: p → ⇡ + ⇡ − ( X ) ~ �~ Topology 2: p missing p → p ⇡ + ( X ) ~ �~ Topology 3: π - missing Topology 4 : ¡ p → p ⇡ − ( X ) ~ �~ π + missing 11 ¡

SIGNAL BACKGROUND SEPARATION: PROBABILISTIC WEIGHTING METHOD Q value = the probability for a given event i to be a signal (Q=1) or a background event (Q= 0 ) Events 200 Seed event M 2 180 Q value = 0.65 0.02 ± 160 Scale factor= 9.79 0.72 ± 140 Signal Events ¡ 120 Carbon pre-fit Q = i ¡ 100 Butanol fit Signal + Background 80 Carbon scaled Carbon unscaled 60 40 20 0 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 2 2 M [GeV ] X 12 ¡ M 2 X [ GeV 2 ]

Polarization observables for circularly polarized photons off transversely polarized protons * ¡ Reaction plane Figure ¡adapted ¡from ¡[Strauch, ¡2005] ¡ 13 ¡

Simplified observable extraction (for illustration) P i H i cos α i = 1 1 P P x = 1 i cos α i J ¯ ¯ P i Q i cos 2 α i x ¯ ¯ ¯ P i Q i cos 2 α i Λ P δ J Λ P i H i sin α i = 1 1 P i sin α i P y = 1 J ¯ ¯ P i Q i sin 2 α i y ¯ ¯ ¯ i Q i sin 2 α i Λ δ J P Λ P All the final expressions correct for the acceptance effects and for the fact that the target polarization is slightly different for different run groups. ¡ 14 ¡

Polarization Observables: Results Observables fit functions: J I g1c, ¡g9b ¡ comparison ¡ PRELIMINARY ¡ 15 ¡

W=1450-2550 MeV 0.3 0.3 0.3 0.5 0.5 0.5 x x x y y y P P P P P P 0.4 0.4 0.4 W = 1450 - 1550 MeV W = 1550 - 1650 MeV W = 1650 - 1750 MeV W = 1450 - 1550 MeV W = 1550 - 1650 MeV W = 1650 - 1750 MeV 0.2 0.2 0.2 0.3 0.3 0.3 P 0.2 0.2 0.2 P 0.1 0.1 0.1 0.1 0.1 0.1 y x 0 0 0 0 0 0 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.2 -0.2 -0.2 Data Data Data Data Data Data -0.3 -0.3 -0.3 -0.2 -0.2 -0.2 Odd function fit Odd function fit Odd function fit Even function fit Even function fit Even function fit -0.4 -0.4 -0.4 -0.3 -0.3 -0.3 -0.5 -0.5 -0.5 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] 0.3 0.3 0.3 0.3 0.5 0.5 0.5 0.5 x x x x y y y y P P P P P P P P 0.4 0.4 0.4 0.4 W = 1750 - 1850 MeV W = 1850 - 1950 MeV W = 1950 - 2050 MeV W = 2050 - 2150 MeV W = 1750 - 1850 MeV W = 1850 - 1950 MeV W = 1950 - 2050 MeV W = 2050 - 2150 MeV 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0 0 0 0 0 0 0 0 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.2 -0.2 -0.2 -0.2 Data Data Data Data Data Data Data Data -0.3 -0.3 -0.3 -0.3 -0.2 -0.2 -0.2 -0.2 Odd function fit Odd function fit Odd function fit Odd function fit Even function fit Even function fit Even function fit Even function fit -0.4 -0.4 -0.4 -0.4 -0.3 -0.3 -0.3 -0.3 -0.5 -0.5 -0.5 -0.5 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] 0.3 0.3 0.3 0.3 0.5 0.5 0.5 0.5 x x x x y y y y P P P P P P P P 0.4 0.4 0.4 0.4 W = 2150 - 2250 MeV W = 2250 - 2350 MeV W = 2350 - 2450 MeV W = 2450 - 2550 MeV W = 2150 - 2250 MeV W = 2250 - 2350 MeV W = 2350 - 2450 MeV W = 2450 - 2550 MeV 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0 0 0 0 0 0 0 0 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.2 -0.2 -0.2 -0.2 Data Data Data Data Data Data Data Data -0.3 -0.3 -0.3 -0.3 -0.2 -0.2 -0.2 -0.2 Odd function fit Odd function fit Odd function fit Odd function fit Even function fit Even function fit Even function fit Even function fit -0.4 -0.4 -0.4 -0.4 -0.3 -0.3 -0.3 -0.3 -0.5 -0.5 -0.5 -0.5 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 0 90 180 270 360 φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] φ * [degrees] PRELIMINARY ¡ 16 ¡