Hadron Spectroscopy at GlueX and Beyond (3) Justin Stevens - PowerPoint PPT Presentation

Hadron Spectroscopy at GlueX and Beyond (3) Justin Stevens

Confined states of quarks and gluons Observed mesons and baryons well described by 1 st principles QCD q q q q q But these aren’t the only states mesons baryons permitted by QCD Λ b → J/ ψ pK − q q q q q q q q q pentaquark tetraquark PRL 115, 072001 (2015) Justin Stevens, � 2 HUGS 2018

Confined states of quarks and gluons Observed mesons and baryons well described by 1 st principles QCD q q q q q But these aren’t the only states mesons baryons permitted by QCD q q q q q q q q q pentaquark tetraquark q Do gluonic degrees of freedom g q manifest themselves in the bound g g states we observe in nature? glueball hybrid meson Justin Stevens, � 3 HUGS 2018

Classifying mesons General properties: mass, electric charge, quark flavor q q J P C Grouped by quantum numbers: J = ~ ~ L + ~ Angular momentum: S Spin 1 Parity: Invert spatial coordinates P = ( − 1) L +1 strangeness Charge conj.: particle ↔ antiparticle C = ( − 1) L + S Allowed J PC for mesons: q ¯ q electric charge J P C = 0 − + , 1 −− , 1 + − , 0 ++ , 2 ++ ... Justin Stevens, � 4 HUGS 2018

Hybrid mesons and gluonic excitations Excited gluonic field coupled to pair q ¯ q Rich spectrum of hybrid mesons predicted by Lattice QCD Gluonic field with J PC = 1 +- and mass = 1-1.5 GeV “Exotic” J PC : not simple from the non-rel. quark model q ¯ q q q g hybrid meson Justin Stevens, � 5 HUGS 2018

Hybrid mesons and gluonic excitations Excited gluonic field coupled to pair q ¯ q Rich spectrum of hybrid mesons predicted by Lattice QCD Gluonic field with J PC = 1 +- and mass = 1-1.5 GeV “Exotic” J PC : not simple from the non-rel. quark model q ¯ q J P C = 0 + − , 1 − + , 2 + − ... J = ~ ~ L + ~ q S q P = ( − 1) L +1 g C = ( − 1) L + S hybrid meson Justin Stevens, � 6 HUGS 2018

Lattice QCD PRD 88 (2013) 094505 2000 Meson Mass (MeV) u + d ¯ u ¯ d s ¯ s 1500 φ = | s ¯ s i 1000 � u + d ¯ ↵ � u ¯ d ω = 500 π 0 = � u − d ¯ ↵ � u ¯ d J P C Note: Justin Stevens, � 7 HUGS 2018

Lattice QCD PRD 88 (2013) 094505 negative parity positive parity exotics Meson Mass (MeV) J P C Justin Stevens, � 8 HUGS 2018

Lattice QCD PRD 88 (2013) 094505 negative parity positive parity exotics Meson Mass (MeV) Lightest hybrid mesons J P C q q g Justin Stevens, � 9 HUGS 2018

Lattice QCD PRD 88 (2013) 094505 negative parity positive parity exotics exotics Meson Mass (MeV) J P C J P C Lightest hybrid u + d ¯ u ¯ d mesons s ¯ s J P C q Most experimental q searches for hybrids g limited to the π 1 state Justin Stevens, � 10 CIPANP 2018

Light quark experiments Heavy quarks Light quarks e + e − γ p Electromagnetic probes ¯ ¯ π p pp pp pp Hadronic probes Justin Stevens, � 11 HUGS 2018

Compass: Diffractive π p scattering Long history of hadron spectroscopy in pion production experiments Rich structure in π - π + π - spectrum, modeled as intermediate resonances X - and π + π - Isobars Compass: PRD 95, 032004 (2017) Justin Stevens, � 12 HUGS 2018

Compass: Diffractive π p scattering Long history of hadron spectroscopy in pion production experiments Rich structure in π - π + π - spectrum, modeled as intermediate resonances X - and π + π - Isobars Compass: PRD 95, 032004 (2017) Justin Stevens, � 13 HUGS 2018

Double Slit Experiment Position (x) Physical Model: Justin Stevens, � 14 PHYS251: Tour

Particle physics “many slits” Step 2: For each collision record the mass of the abc system Intermediate Step 1: Create particles Particles a, b and c in some collision Z Mass of abc system Probe: particles a, b and c which Z can form heavier particles X, Y or Z a Y b Y c Physical Model: X X 2 � � � � X � � I ( M ) = V i A i ( M ) � � � � i = X,Y,Z � � Goal: determine properties Physical System Under Study: of X, Y, and Z Detector: Measure mass of abc intermediate particles X, Y, and Z system for each collision Justin Stevens, � 15 PHYS251: Tour

Amplitude Analysis Goal: Identify J PC of X → π + π - π + Model the intensity of events at the level of QM amplitudes (allow for interference) 5-dimensional problem: two new angles at each decay step ( X and I ) X → ρπ + ρ → π + π − Example Intensity: X (1 ++ ) → ρπ − (S wave) ρπ + (S wave) Justin Stevens, � 16 HUGS 2018

Amplitude Analysis Expand set of possible amplitudes over many X and I , and determine V α via maximum likelihood fit Good angular acceptance critical for disentangling J PC X → ρπ + ρ → π + π − Example Intensities: X (1 ++ ) → ρπ − (S wave) ρπ + (S wave) X (2 ++ ) → ρπ − (D wave) ρπ + (D wave) Justin Stevens, � 17 HUGS 2018

Resonance phase motion expectations Assuming a Breit-Wigner mass-dependent amplitude: Matt Shepherd Justin Stevens, � 18 HUGS 2018

Early evidence for 1 -+ exotics: π 1 (1600) COMPASS: π − p → π − π + π − p π 1 (1600) 1 -+ intensity Background PRL 104, 241803 (2010) t’ Justin Stevens, � 19 HUGS 2018

Compass π p amplitude analysis Compass: PRL 104, 241803 (2010) Compass: PRD 95, 032004 (2017) Unprecedented statistics: ~50M exclusive events Decompose into 88 amplitudes representing X - , Isobars , L , and M a 2 (1320) → ρπ Extract amplitude intensity and phase in bins of π - π + π - mass Justin Stevens, � 20 HUGS 2018

Compass π p amplitude analysis Compass: PRL 104, 241803 (2010) Compass: PRD 95, 032004 (2017) Unprecedented statistics: ~50M exclusive events Decompose into 88 amplitudes representing X - , Isobars , L , and M a 2 (1320) → ρπ Extract amplitude intensity and phase in bins of π - π + π - mass Justin Stevens, � 21 HUGS 2018

Compass π p: example amplitudes X (1 ++ ) → ρπ − (S wave) Interference X (2 ++ ) → ρπ − (D wave) t’ arXiv:1802.05913 Justin Stevens, � 22 HUGS 2018

Compass π p amplitude analysis Compass: PRL 104, 241803 (2010) Compass: 1509.00992 Unprecedented statistics a 2 (1320) → ρπ Justin Stevens, � 23 HUGS 2018

Compass π p amplitude analysis Compass: PRL 104, 241803 (2010) Compass: 1509.00992 Unprecedented statistics Also bin in t’ t’ a 2 (1320) → ρπ Justin Stevens, � 24 HUGS 2018

Evidence for 1 -+ π 1 (1600) in ρπ Low t’ High t’ arXiv:1802.05913 Compass: 1512.03599 Need to work with theorists on better models for resonant and non-resonant: Joint Physics Analysis Center t’ Justin Stevens, � 25 HUGS 2018

Evidence for 1 -+ exotics: π 1 (1600) COMPASS: π − p → η ( 0 ) π − p η η ’ η ( 0 ) PLB 740 (2015) 303 Justin Stevens, � 26 HUGS 2018

Evidence for 1 -+ exotics: π 1 (1600) COMPASS: π − p → η ( 0 ) π − p 1 -+ intensity η ’ η η ’ η PLB 740 (2015) 303 η ( 0 ) Need to work with theorists on better models to describe broad structures: Joint Physics Analysis Center Justin Stevens, � 27 HUGS 2018