Spin-Density Matrix Elements for Vector-Meson Photoproduction at - PowerPoint PPT Presentation

Spin-Density Matrix Elements for Vector-Meson Photoproduction at GlueX Alexander Austregesilo for the GlueX Collaboration 15 th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2019) Carnegie Mellon University, Pittsburgh, PA June 3 rd , 2019

Introduction Method Results Outlook Outline Introduction 1 Method 2 Extended Maximum-Likelihood Fit Fit Evaluation 3 Results ρ ( 770 ) → π + π − ω ( 782 ) → π + π − π 0 φ ( 1020 ) → K + K − Outlook 4 A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 2/19

Introduction Method Results Outlook GlueX Detector G lue X forward calorimeter Light quark meson spectroscopy barrel time-of calorimeter -flight start with full angular coverage counter � Data L Status target (pb − 1 ) 2016 1 analyzed 2017 20 analyzed 2018 ∼ 80 processing photon beam diamond forward drift wafer chambers central drift chamber electron superconducting tagger magnet beam electron magnet beam tagger to detector distance 2 T is not to scale → S. Dobbs, Searching for Exotic Hadrons at GlueX (Monday morning) A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 3/19

Introduction Method Results Outlook Photon Beam Line Photon Flux (Arb. Units) 7000 (a) Diamond: PARA 6000 9 GeV Polarized Photon Beam Diamond: PERP 5000 Aluminum Coherent Bremsstrahlung on thin diamond 4000 3000 Energy tagged by scattered electrons 2000 1000 Collimator to suppress incoherent part Polarization 7.5 8 8.5 9 9.5 10 10.5 11 11.5 Linear polarization in peak P γ ∼ 40 % , (b) 0.5 PARA measured by Triplet polarimeter: 0.4 PERP γ e − → e − e + e − 0.3 0.2 Rotate polarization into 4 different orientations 0.1 Beam intensity: 1 − 5 · 10 7 γ/ s in peak 0 3% Syst. Uncert. 7.5 8 8.5 9 9.5 10 10.5 11 11.5 Photon Beam Energy (GeV) A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 4/19

Introduction Method Results Outlook Photoproduction ( ρ, ω, φ ) γ X Exchange Exotic Final States 0 ++ b , h , h ′ 2 + − , 0 + − P π 0 0 − + b 2 , h 2 , h ′ 2 + − 2 P , π, ρ, ... π ± π ± 0 − + 1 − + 1 1 −− π 1 , η 1 , η ′ 1 − + ω 1 p p, n, ∆ , ... Complementary Production Mechanism Photon coupling via vector meson dominance Wide variety of quantum numbers I G J PC accessible Photon polarization provides constraints on produced systems Understanding of production mechanism is prerequisite for interpretation Very limited photoproduction data existing at these energies A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 5/19

Introduction Method Results Outlook Production Mechanism Spin-Density Matrix Elements y P γ Full angular distribution of vector meson production and decay is described by Φ spin-density matrix elements ρ k φ ij p ′ x Linear beam polarization provides access to γ p nine linearly independent SDMEs ρ π + Intensity W is expressed as function of angles cos ϑ, ϕ, Φ and degree of polarization P γ z π − W ( cos ϑ, ϕ, Φ) = W 0 ( cos ϑ, ϕ ) − P γ cos ( 2 Φ) W 1 ( cos ϑ, ϕ ) − P γ sin ( 2 Φ) W 2 ( cos ϑ, ϕ ) � 1 √ 3 1 � W 0 ( cos ϑ, ϕ ) = ( 1 − ρ 0 ( 3 ρ 0 00 − 1 ) cos 2 ϑ − 2Re ρ 0 10 sin 2 ϑ cos ϕ − ρ 0 1 − 1 sin 2 ϑ cos 2 ϕ 00 ) + 4 π 2 2 3 √ 11 sin 2 ϑ + ρ 1 00 cos 2 ϑ − 1 − 1 sin 2 ϑ cos 2 ϕ W 1 ( cos ϑ, ϕ ) = � ρ 1 2Re ρ 1 10 sin 2 ϑ cos ϕ − ρ 1 � 4 π 3 � √ W 2 ( cos ϑ, ϕ ) = 2Im ρ 2 10 sin 2 ϑ sin ϕ + Im ρ 2 1 − 1 sin 2 ϑ sin 2 ϕ � 4 π Schilling et al. [Nucl. Phy. B, 15 (1970) 397] A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 6/19

Introduction Method Results Outlook Previous Measurements SLAC, Ballam et al. [Phy. Rev. D, 7 (1973) 3150] ρ ( 770 ) Few thousand events, 7 bins in t s -channel helicity conservation: ρ 1 1 − 1 = − Im ρ 2 1 − 1 = 0 . 5 in helicity frame, all others = 0 Parity asymmetry: P σ = 2 ρ 1 1 − 1 − ρ 1 00 Dominated by natural parity exchange P = ( − 1 ) J ω ( 782 ) Several hundred events, 3 bins in t φ ( 1020 ) Few hundred events, not binned in t A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 7/19

Introduction Method Results Outlook JPAC Model Regge model, fit to SLAC data Detailed prediction for t -dependence of ρ , ω and φ meson production s -channel helicity conservation at t = 0 Mathieu et al. [Phy. Rev. D, 97 (2018) 094003] → Single and Double Meson Production at JLab (Tuesday) A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 8/19

Introduction Method Results Outlook Vector-Meson Photoproduction γ p → ρ ( 770 ) p × 6 10 2 Events / 2.5 MeV/c 0.7 γ 0.6 π + ρ (770) 0.5 π − 0.4 0.3 0.2 0.1 p p 0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 π + π − 2 Invariant Mass (GeV/c ) × 6 10 2 ) 2 2 Events / 0.004 (GeV/c) Events / 100 (MeV/c 4 6 10 3.5 3 5 10 2.5 2 1.5 4 10 1 0.5 3 10 − × 3 10 0 − − − − − 50 40 30 20 10 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 γ → π + π − 2 2 p p Missing Mass Squared (GeV/c ) 2 Squared 4-Momentum Transfer -t (GeV/c) Full 2017 data: > 10M signal events in each of the 4 orientations A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 9/19

Introduction Method Results Outlook Extraction of SDMEs W ( cos ϑ, ϕ, Φ) = W 0 ( cos ϑ, ϕ ) − P γ cos ( 2 Φ) W 1 ( cos ϑ, ϕ ) − P γ sin ( 2 Φ) W 2 ( cos ϑ, ϕ ) Measured Intensity I (Ω) ∝ W ( cos ϑ, ϕ, Φ) Extended Maximum-Likelihood Fit N M � � � ln L = ln I (Ω i ) − ln I (Ω j ) − d Ω I (Ω) η (Ω) i = 1 j = 1 � �� � � �� � � �� � Normalization Integral Signal Events Background Maximize by choosing SDMEs such that the intensity fits the observed N events Accidental background subtracted in likelihood Normalization integral evaluated by a phase-space Monte Carlo sample with the acceptance η (Ω) = 0 / 1 A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 10/19

Introduction Method Results Outlook Fit Evaluation γ p → ρ ( 770 ) p , − t ∈ [ 0 . 05 , 0 . 15 ] GeV 2 / c 2 π π - ψ Φ ϕ Invariant Mass of + = - 30000 45000 40000 25000 35000 20000 30000 25000 15000 20000 10000 15000 10000 5000 5000 0 0 − − − 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 3 2 1 0 1 2 3 ϕ ϑ cos 25000 30000 20000 25000 20000 15000 15000 10000 10000 5000 5000 0 0 − − − − − − − − 1 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1 3 2 1 0 1 2 3 black : measured distribution green : accepted MC, weighted with fit result red : accidental background A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 11/19

Introduction Method Results Outlook Result in Bins of Momentum Transfer t γ p → ρ ( 770 ) p ρ 1 0.05 GeV 2 / c 2 bin width in t 1-1 1 SCHC Average of 4 orientations 0.9 JPAC Model Errors dominated by systematics 0.8 GlueX 2017 SCHC valid for t → 0 GeV 2 / c 2 SLAC (Ballam et al.) 0.7 Agree with JPAC to ∼ 0 . 5 GeV 2 / c 2 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 2 2 -t (GeV /c ) A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 12/19

Introduction Method Results Outlook Result in Bins of Momentum Transfer t γ p → ρ ( 770 ) p ρ 0 ρ 0 ρ 0 Re 00 1-1 10 0.5 0.5 0.5 SCHC 0.4 0.4 0.4 0.05 GeV 2 / c 2 bin width in t JPAC Model 0.3 0.3 0.3 GlueX 2017 0.2 0.2 0.2 SLAC (Ballam et al.) 0.1 0.1 0.1 Average of 4 orientations 0 0 0 − 0.1 − 0.1 − 0.1 − − − 0.2 0.2 0.2 Errors dominated by systematics − − − 0.3 0.3 0.3 − − − 0.4 0.4 0.4 SCHC valid for t → 0 GeV 2 / c 2 − 0.5 − 0.5 − 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -t (GeV 2 /c 2 ) -t (GeV 2 /c 2 ) -t (GeV 2 /c 2 ) ρ ρ 1 1 ρ 1 Agree with JPAC to ∼ 0 . 5 GeV 2 / c 2 Re 11 00 10 0.5 0.5 0.5 0.4 0.4 0.4 0.3 0.3 0.3 0.2 0.2 0.2 0.1 0.1 0.1 0 0 0 − − − 0.1 0.1 0.1 − − − 0.2 0.2 0.2 − − − 0.3 0.3 0.3 − − − 0.4 0.4 0.4 − − − 0.5 0.5 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 2 2 2 2 2 2 -t (GeV /c ) -t (GeV /c ) -t (GeV /c ) ρ 1 Im ρ 2 Im ρ 2 1-1 10 1-1 1 0.5 0 − 0.9 0.4 0.1 − 0.8 0.3 0.2 − 0.7 0.2 0.3 − 0.6 0.1 0.4 − 0.5 0 0.5 − − 0.4 0.1 0.6 − − 0.3 0.2 0.7 − − 0.2 0.3 0.8 − − 0.1 0.4 0.9 − − 0 0.5 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 2 2 2 2 2 2 -t (GeV /c ) -t (GeV /c ) -t (GeV /c ) A. Austregesilo (aaustreg@jlab.org) — Vector Meson SDMEs 12/19