Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Baryon Spectroscopy in Exclusive Meson Photoproduction Experiments Volker Credé Florida State University, Tallahassee, FL Int. Seminar on Electromagnetic Interactions of Nuclei Moscow, Russia 10/05/2015 V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Outline Introduction 1 The Spectrum of Hadrons: Baryons and Mesons Spectroscopy of Baryon Resonances 2 Complete Experiments Polarization Observables in γ p → N π Polarization Observables in γ p → p ω Decay Cascades of Excited Baryons 3 Summary and Outlook 4 Are we there yet? Open Issues in Light Baryon Spectrosocpy Summary and Outlook V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Outline Introduction 1 The Spectrum of Hadrons: Baryons and Mesons Spectroscopy of Baryon Resonances 2 Complete Experiments Polarization Observables in γ p → N π Polarization Observables in γ p → p ω Decay Cascades of Excited Baryons 3 Summary and Outlook 4 Are we there yet? Open Issues in Light Baryon Spectrosocpy Summary and Outlook V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Strong-Coupling Quantum Chromodynamics (QCD) QCD is the theory of the strong nuclear force q ( i γ µ D µ − m q ) q � ¯ L QCD = which describes the interactions of quarks and gluons making up hadrons. q − 1 Strong processes at larger distances and at 4 F µν F µν small (soft) momentum transfers belong to the realm of non-perturbative QCD. “pQCD” ➜ ➜ Confinement Asymptotic Freedom “Strong QCD” V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Hadrons: Baryons & Mesons The strong coupling confines quarks and breaks chiral symmetry, and so defines the world of light hadrons. Baryons are special because their structure is most obviously related to the color degree of freedom, e. g. | ∆ ++ � = | u ↑ u ↑ u ↑ � . they are the stuff of which our world is made. Baryons Mesons V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Hadrons: Baryons & Mesons The strong coupling confines quarks and breaks chiral symmetry, and so defines the world of light hadrons. Baryons are special because their structure is most obviously related to the color degree of freedom, e. g. | ∆ ++ � = | u ↑ u ↑ u ↑ � . 300 b) S (1650) D (1675) F (1680) Baryons 11 15 15 µ F (1905) ( 35 + p X σ π → P (1232) 33 250 P (1620) P (1910) D (1700) 31 31 33 - p X π → S (1535) 200 11 F (1950) 37 ➜ PDG 2010, J. Phys. GG 37. P (1720) 13 150 D (1520) H (2220) 13 19 G (2190) G (2250) 17 19 Great progress H (2420) 100 P (1440) 11 3 11 in recent years: 50 ➜ γ N & π N data 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 W (GeV) Courtesy of Michael Williams V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Hadrons: Baryons & Mesons The strong coupling confines quarks and breaks chiral symmetry, and so defines the world of light hadrons. Baryons are special because their structure is most obviously related to the color degree of freedom, e. g. | ∆ ++ � = | u ↑ u ↑ u ↑ � . 300 b) S (1650) D (1675) F (1680) 11 15 15 µ F (1905) ( 35 + p X σ π → P (1232) 33 250 P (1620) P (1910) D (1700) 31 31 33 - p X π → S (1535) 200 11 F (1950) 37 P (1720) 13 150 D (1520) H (2220) 13 19 G (2190) G (2250) 17 19 H (2420) Many Y ∗ QN not measured: 100 P (1440) 11 3 11 (Quark model assignments) 50 ➜ many Ξ ∗ and Ω ∗ , etc. 0 1 1.2 1.4 1.6 1.8 2 2.2 2.4 W (GeV) Courtesy of Michael Williams V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Spin and Parity Measurement of the Λ( 1405 ) Baryon K. Moriya et al. [CLAS Collaboration], Phys. Rev. Lett. 112 , 082004 (2014) J P = 1 − Data for γ p → K + Λ( 1405 ) support (a) (b) 2 Decay distribution of Λ( 1405 ) → Σ + π − � � consistent with J = 1 / 2. Polarization transfer, � Q , in Y ∗ → Y π : S -wave decay: � Q independent of θ Y S -wave decay P -wave decay Λ 1 ) (1405) 2 data counts /(5 MeV/c 1000 Λ * Σ (1520) + K 0.5 S -wave: J P = 1 − Σ * 0 (1385) Y (1670) 2 z Q 0 500 -0.5 P -wave: J P = 1 + (a) b 2 -1 -1 -0.5 0 0.5 1 θ 0 cos Σ 1.35 1.4 1.45 1.5 1.55 + Σ π + - 2 M( ) (GeV/c ) V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Non-Perturbative QCD How does QCD give rise to excited hadrons? What is the origin of confinement? 1 How are confinement and chiral 2 symmetry breaking connected? What role do gluonic excitations play in 3 the spectroscopy of light mesons, and can they help explain quark confinement? Baryons: What are the fundamental degrees of freedom inside a nucleon? Constituent quarks? How do the degrees change with varying quark masses? V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Non-Perturbative QCD How does QCD give rise to excited hadrons? What is the origin of confinement? 1 How are confinement and chiral 2 symmetry breaking connected? What role do gluonic excitations play in 3 the spectroscopy of light mesons, and can they help explain quark confinement? Mesons: What are the properties of the predicted states beyond simple quark-antiquark systems (hybrid mesons, glueballs, ...)? ➜ Gluonic Excitations provide a measurement of the excited QCD potential. Hybrid baryons are possible but do not carry “exotic” quantum numbers. V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Spectrum of N ∗ Resonances (PDG < 2012) —— S. Capstick and N. Isgur, Phys. Rev. D34 (1986) 2809 3000 ⋆ ** ⋆ ⋆ ⋆ ⋆ *** ⋆ 2500 ⋆ **** **** ** **** Mass [MeV] * * ** 2000 ** S ** 1. Excitation Band: ** S S ( 70 , 1 − 1 ) ✓ **** *** *** **** **** **** 1500 2. Excitation Band: **** **** **** ( 56 , 0 + 2 ) , ( 56 , 2 + 2 ) ✓ ( 70 , 0 + 2 ) , ( 70 , 2 + 2 ) ( ✓ ) Theory ( 20 , 1 + 2 ) ? Experiment 1000 **** J � 1/2+ 3/2+ 5/2+ 7/2+ 9/2+ 11/2+ 13/2+ 1/2- 3/2- 5/2- 7/2- 9/2- 11/2- 13/2- V. Credé (Highlights in) Light-Baryon Spectroscopy
Introduction Spectroscopy of Baryon Resonances The Spectrum of Hadrons: Baryons and Mesons Decay Cascades of Excited Baryons Summary and Outlook Spectrum of N ∗ Resonances J P ( L 2 I , 2 J ) N ∗ 2010 2014 1 / 2 + ( P 11 ) N ( 1440 ) ∗ ∗ ∗∗ ∗ ∗ ∗∗ 3000 3 / 2 − ( D 13 ) N ( 1520 ) ∗ ∗ ∗∗ ∗ ∗ ∗∗ 1 / 2 − ( S 11 ) N ( 1535 ) ∗ ∗ ∗∗ ∗ ∗ ∗∗ 1 / 2 − ( S 11 ) N ( 1650 ) ∗ ∗ ∗∗ ∗ ∗ ∗∗ 5 / 2 − ( D 15 ) ** N ( 1675 ) ∗ ∗ ∗∗ ∗ ∗ ∗∗ 5 / 2 + ( F 15 ) N ( 1680 ) ∗ ∗ ∗∗ ∗ ∗ ∗∗ *** 2500 N ( 1685 ) ∗ 3 / 2 − ( D 13 ) N ( 1700 ) ∗ ∗ ∗ ∗ ∗ ∗ 1 / 2 + ( P 11 ) N ( 1710 ) ∗ ∗ ∗ ∗ ∗ ∗ **** 3 / 2 + ( P 13 ) **** N ( 1720 ) ** ∗ ∗ ∗∗ **** ∗ ∗ ∗∗ 5 / 2 + Mass [MeV] * N ( 1860 ) * ∗∗ ** 2000 ** S ** N ( 1875 ) 3 / 2 − ∗ ∗ ∗ 1 / 2 + ** S S N ( 1880 ) ∗∗ 1 / 2 − N ( 1895 ) ∗∗ **** 3 / 2 + ( P 13 ) *** *** **** N ( 1900 ) ∗∗ ∗ ∗ ∗ **** **** 7 / 2 + ( F 17 ) N ( 1990 ) ∗∗ ∗∗ 1500 **** 5 / 2 + ( F 15 ) **** N ( 2000 ) ∗∗ ∗∗ **** ———— N ( 2080 ) D 13 ∗∗ ———— N ( 2090 ) S 11 ∗ 3 / 2 + N ( 2040 ) ∗ 5 / 2 − N ( 2060 ) ∗∗ 1000 1 / 2 + ( P 11 ) N ( 2100 ) ∗ ∗ **** N ( 2120 ) 3 / 2 − ∗∗ 7 / 2 − ( G 17 ) J � 1/2+ 3/2+ 5/2+ 7/2+ 9/2+ 11/2+ 13/2+ N ( 2190 ) 1/2- 3/2- 5/2- ∗ ∗ ∗∗ 7/2- 9/2- ∗ ∗ ∗∗ 11/2- 13/2- ———— N ( 2200 ) D 15 ∗∗ 9 / 2 + ( H 19 ) N ( 2220 ) ∗ ∗ ∗∗ ∗ ∗ ∗∗ V. C. & W. Roberts, Rep. Prog. Phys. 76 (2013) V. Credé (Highlights in) Light-Baryon Spectroscopy
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