Baryon Spectroscopy in Exclusive Meson Photoproduction Experiments - - PowerPoint PPT Presentation

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

1

Introduction The Spectrum of Hadrons: Baryons and Mesons

2

Spectroscopy of Baryon Resonances Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

3

Decay Cascades of Excited Baryons

4

Summary and Outlook 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 Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Outline

1

Introduction The Spectrum of Hadrons: Baryons and Mesons

2

Spectroscopy of Baryon Resonances Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

3

Decay Cascades of Excited Baryons

4

Summary and Outlook 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 Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Strong-Coupling Quantum Chromodynamics (QCD)

QCD is the theory of the strong nuclear force which describes the interactions of quarks and gluons making up hadrons. Strong processes at larger distances and at small (soft) momentum transfers belong to the realm of non-perturbative QCD.

Asymptotic Freedom “pQCD” Confinement “Strong QCD”

LQCD =

• q

¯ q (iγµDµ − mq) q −1 4F µνFµν

➜ ➜

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Hadrons: Baryons & Mesons

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.

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Hadrons: Baryons & Mesons

Baryons

W (GeV) 1 1.2 1.4 1.6 1.8 2 2.2 2.4 b) µ ( σ 50 100 150 200 250 300

X → p

+

π X → p

• π

(1440)

P (1520)

D (1535)

S (1650)

S (1675)

D (1680)

F (1720)

P (2190)

G (2220)

H (2250)

G (1232)

P (1620)

P (1700)

D (1905)

F (1910)

P (1950)

F (2420)

H

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↑.

Courtesy of Michael Williams

➜ PDG 2010, J. Phys. GG 37.

Great progress in recent years: ➜ γN & πN data

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Hadrons: Baryons & Mesons

W (GeV) 1 1.2 1.4 1.6 1.8 2 2.2 2.4 b) µ ( σ 50 100 150 200 250 300

X → p

+

π X → p

• π

(1440)

P (1520)

D (1535)

S (1650)

S (1675)

D (1680)

F (1720)

P (2190)

G (2220)

H (2250)

G (1232)

P (1620)

P (1700)

D (1905)

F (1910)

P (1950)

F (2420)

H

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↑.

Courtesy of Michael Williams

Many Y ∗ QN not measured:

(Quark model assignments)

➜ many Ξ∗ and Ω∗, etc.

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Spin and Parity Measurement of the Λ(1405) Baryon

Data for γp → K +Λ(1405) support JP = 1

2 −

Decay distribution of Λ(1405) → Σ+π− consistent with J = 1/2. Polarization transfer, Q, in Y ∗ → Yπ: S-wave decay: Q independent of θY

)

2

) (GeV/c

• π

+

Σ M(

1.35 1.4 1.45 1.5 1.55

)

2

counts /(5 MeV/c

500 1000 data (1405) Λ (1520) Λ

+

Σ

*

K (1385) Σ (1670)

*

Y

(a)



(a)



(b)

S-wave decay P-wave decay

Σ

θ cos

• 1
• 0.5

0.5 1

z

Q

• 1
• 0.5

0.5 1

• K. Moriya et al. [CLAS Collaboration], Phys. Rev. Lett. 112, 082004 (2014)

b

S-wave: JP = 1

2 −

P-wave: JP = 1

2 +

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Non-Perturbative QCD

How does QCD give rise to excited hadrons?

1

What is the origin of confinement?

2

How are confinement and chiral symmetry breaking connected?

3

What role do gluonic excitations play in 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 Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

Non-Perturbative QCD

How does QCD give rise to excited hadrons?

1

What is the origin of confinement?

2

How are confinement and chiral symmetry breaking connected?

3

What role do gluonic excitations play in 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 Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

• 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- J

Mass [MeV] 1000 1500 2000 2500 3000

**** **** * **** ** **** ** ** **** ** **** **** * **** *** ** **** ** **** **** *** S S S ***

—— S. Capstick and N. Isgur, Phys. Rev. D34 (1986) 2809

⋆ ⋆ ⋆ ⋆ ⋆ ⋆

⋆

• 1. Excitation Band:

(70, 1−

1 ) ✓

• 2. Excitation Band:

(56, 0+

2 ), (56, 2+ 2 ) ✓

(70, 0+

2 ), (70, 2+ 2 ) (✓)

(20, 1+

2 ) ?

Spectrum of N∗ Resonances (PDG < 2012)

Theory Experiment

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook The Spectrum of Hadrons: Baryons and Mesons

• 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- J

Mass [MeV] 1000 1500 2000 2500 3000

**** **** * **** ** **** ** ** **** ** **** **** * **** *** ** **** ** **** **** *** S S S ***

Spectrum of N∗ Resonances

N∗ JP (L2I,2J ) 2010 2014 N(1440) 1/2+ (P11) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1520) 3/2− (D13) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1535) 1/2− (S11) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1650) 1/2− (S11) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1675) 5/2− (D15) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1680) 5/2+ (F15) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1685) ∗ N(1700) 3/2− (D13) ∗ ∗ ∗ ∗ ∗ ∗ N(1710) 1/2+ (P11) ∗ ∗ ∗ ∗ ∗ ∗ N(1720) 3/2+ (P13) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1860) 5/2+ ∗∗ N(1875) 3/2− ∗ ∗ ∗ N(1880) 1/2+ ∗∗ N(1895) 1/2− ∗∗ N(1900) 3/2+ (P13) ∗∗ ∗ ∗ ∗ N(1990) 7/2+ (F17) ∗∗ ∗∗ N(2000) 5/2+ (F15) ∗∗ ∗∗ ———— N(2080) D13 ∗∗ ———— N(2090) S11 ∗ N(2040) 3/2+ ∗ N(2060) 5/2− ∗∗ N(2100) 1/2+ (P11) ∗ ∗ N(2120) 3/2− ∗∗ N(2190) 7/2− (G17) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ———— N(2200) D15 ∗∗ N(2220) 9/2+ (H19) ∗ ∗ ∗∗ ∗ ∗ ∗∗

• V. C. & W. Roberts, Rep. Prog. Phys. 76 (2013)
• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Outline

1

Introduction The Spectrum of Hadrons: Baryons and Mesons

2

Spectroscopy of Baryon Resonances Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

3

Decay Cascades of Excited Baryons

4

Summary and Outlook 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 Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

• 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- J

Mass [MeV] 1000 1500 2000 2500 3000

**** **** * **** ** **** ** ** **** ** **** **** * **** *** ** **** ** **** **** *** S S S ***

Spectrum of N∗ Resonances

N∗ JP (L2I,2J ) 2010 2014 N(1440) 1/2+ (P11) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1520) 3/2− (D13) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1535) 1/2− (S11) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1650) 1/2− (S11) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1675) 5/2− (D15) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1680) 5/2+ (F15) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1685) ∗ N(1700) 3/2− (D13) ∗ ∗ ∗ ∗ ∗ ∗ N(1710) 1/2+ (P11) ∗ ∗ ∗ ∗ ∗ ∗ N(1720) 3/2+ (P13) ∗ ∗ ∗∗ ∗ ∗ ∗∗ N(1860) 5/2+ ∗∗ N(1875) 3/2− ∗ ∗ ∗ N(1880) 1/2+ ∗∗ N(1895) 1/2− ∗∗ N(1900) 3/2+ (P13) ∗∗ ∗ ∗ ∗ N(1990) 7/2+ (F17) ∗∗ ∗∗ N(2000) 5/2+ (F15) ∗∗ ∗∗ ———— N(2080) D13 ∗∗ ———— N(2090) S11 ∗ N(2040) 3/2+ ∗ N(2060) 5/2− ∗∗ N(2100) 1/2+ (P11) ∗ ∗ N(2120) 3/2− ∗∗ N(2190) 7/2− (G17) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ———— N(2200) D15 ∗∗ N(2220) 9/2+ (H19) ∗ ∗ ∗∗ ∗ ∗ ∗∗

• V. C. & W. Roberts, Rep. Prog. Phys. 76 (2013)
• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Polarization Transfer in γp → K + Λ : Cx, Cz

without N(1900)P13 with N(1900)P13

• R. Bradford et al. [CLAS Collab.], PRC 75, 035205 (2007)

Fits: BoGa-Model, V. A. Nikonov et al., Phys. Lett. B 662, 245 (2008)

∗ ∗ N(1900)P13, N(2000)F15, N(1990)F17 Bonn-Gatchina PWA requires N(1900)P13 No quark-diquark oscillations! ➜ Both oscillators need to be excited.

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

• 1/2+

3/2+ 5/2+ 7/2+ 9/2+ 11/2+ 13/2+ 15/2+ 1/2- 3/2- 5/2- 7/2- 9/2- 11/2- 13/2- 15/2- J

Mass [MeV] 1000 1500 2000 2500 3000

* **** **** *** *** **** ** **** * ** **** ** **** ** * **** * *** * * ** **

Reactions can serve as isospin filter: γp → ∆η → p π0η γp → ∆ω → p π0ω

∆∗ JP (L2I,2J ) 2010 2014 ∆(1232) 3/2+ (P33) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ∆(1600) 3/2+ (P33) ∗ ∗ ∗ ∗ ∗ ∗ ∆(1620) 1/2− (S31) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ∆(1700) 3/2− (D33) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ∆(1750) 1/2+ (P31) ∗ ∗ ∆(1900) 1/2− (S31) ∗∗ ∗∗ ∆(1905) 5/2+ (F35) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ∆(1910) 1/2+ (P31) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ∆(1920) 3/2+ (P33) ∗ ∗ ∗ ∗ ∗ ∗ ∆(1930) 5/2− (D35) ∗ ∗ ∗ ∗ ∗ ∗ ∆(1940) 3/2− (D33) ∗ ∗∗ ∆(1950) 7/2+ (F37) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ∆(2000) 5/2+ (F35) ∗∗ ∗∗ ∆(2150) 1/2− (S31) ∗ ∗ ∆(2200) 7/2− (G37) ∗ ∗ ∆(2300) 9/2+ (H39) ∗∗ ∗∗ ∆(2350) 5/2− (D35) ∗ ∗ ∆(2390) 7/2+ (F37) ∗ ∗ ∆(2400) 9/2− (G39) ∗∗ ∗∗ ∆(2420) 11/2+ (H3,11) ∗ ∗ ∗∗ ∗ ∗ ∗∗ ∆(2750) 13/2− (I3,13) ∗∗ ∗∗ ∆(2950) 15/2+ (K3,15) ∗∗ ∗∗

Spectrum of ∆∗ Resonances

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

High Statistics Study of the Reaction γp → p π0η

• E. Gutz, V. C. et al. [CBELSA/TAPS Collaboration], Eur. Phys. J. A 50, 74 (2014)
• V. L. Kashevarov et al., EPJ A 42, 141 (2009) @MAMI

0.5 1 1.5 2 2.5 3 3.5 1000 1200 1400 1600 1800 2000 2200 2400

∆η N(1535)π a0(980)p

Eγ , MeV σtot , µb

0.2 0.4 0.6 0.8

1050 dσ/d cos θ(ηp), µb/0.1

0.2 0.4 0.6 0.8

1150

0.2 0.4 0.6 0.8

1250

0.2 0.4 0.6 0.8

• 1
• 0.5

0.5 1

1350 cos θ(ηp) (hel)

0.2 0.4 0.6 0.8

1050 dσ/d cos θ(π), µb/0.1

0.2 0.4 0.6 0.8

1150

0.2 0.4 0.6 0.8

1250

0.2 0.4 0.6 0.8

• 1
• 0.5

0.5 1

1350 cos θ(π)

helicity center-of-mass

Dominant Isobars ∆(1232)η, N(1535) 1

2 −π, pa0(980)

Observation of some ∆∗ → N(1535) 1

2 −π → p πη

Bonn-Gatchina ∆(1700) 3

2 −

∆(1600) 3

2 +

∆(1920) 3

2 +

∆(1940) 3

2 −

∆(1905) 5

2 +

∆(2360) 3

2 −

N(1880) 1

2 +

N(2200) 3

2 +

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Baryon Spectroscopy from Lattice QCD

mπ = 396 MeV ∆(1700) ∆(1620) N(938) ∆(1232)

Missing states?

• R. Edwards et al., Phys. Rev. D 84, 074508 (2011)

Exhibits broad features expected of SU(6) ⊗ O(3) symmetry ➜ Counting of levels consistent with non-rel. quark model, no parity doubling

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Quark-Model Classification: Ordinary & Exotic Mesons

Quantum Numbers [q¯ q] (JPC ≡ 2S+1LJ) Parity: P = (−1)L+1 Charge Conjugation: C = (−1)L+S (defined for neutral mesons) G parity: G = C (−1)I

12 GeV CEBAF upgrade has high priority (DOE Office of Science, Long Range Plan) “[key area] is experimental verification of the powerful force fields (flux tubes) believed to be responsible for quark confinement.”

L = 0, S = 0 : e.g. π, η (JPC = 0−+) L = 0, S = 1 : e.g. ρ, ω, φ (JPC = 1−−)

Forbidden States (Exotics): JPC = 0+−, 0−−, 1−+, 2+− · ··

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Gluonic Excitations on the Lattice

500 1000 1500 2000

The mass scale is m − mρ for mesons and m−mN for baryons. Common scale of ∼ 1.3 GeV for gluonic excitation, but hybrid baryons are difficult to identify experimentally.

• J. J. Dudek and R. G. Edwards, Phys. Rev. D 85, 054016 (2012)

mu = md = ms mπ = 702 MeV mπ = 524 MeV mπ = 396 MeV

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Helicity Amplitudes for the “Roper” Resonance

Q 2 (GeV 2) A1/2 (103 GeV 1/2)

• 80
• 60
• 40
• 20

20 40 60 80 1 2 3 4

Consistency between both channels (Nππ, Nπ): sign change, magnitude, ... At short distances (high Q2), Roper behaves like radial excitation. Low Q2 behavior not well described by LF quark models: e.g. meson-baryon interactions missing ➜ Gluonic excitation likely ruled out!

➜ E. Golovach, R. Gothe

Data from CLAS

A1/2 and S1/2 amplitudes: e.g. V. Mokeev et al., PRC 86, 035203 (2012); PRC 80, 045212 (2009). Quark-model calculations: —- q3 radial excitation

• - -

—- q3G hybrid state

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Why are Polarization Observables Important?

Atomic Spectrum of Hydrogen Eγ [MeV] γp → p π0

CLAS@JLab

ELSA MAMI GRAAL SPring-8 ...

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Why are Polarization Observables Important?

For single-meson production: d σ d Ω = σ0 { 1 − δ l Σ cos 2φ + Λ x ( −δ l H sin 2φ + δ ⊙ F ) − Λ y ( −T + δ l P cos 2φ) − Λ z ( − δ l G sin 2φ + δ ⊙ E)}

Box Box

Chiang & Tabakin, Phys. Rev. C55, 2054 (1997) In order to determine the full scattering amplitude without ambiguities, one has to carry out eight carefully selected measurements: four double-spin

• bservables along with four single-spin observables.

Eight well-chosen measurements are needed to fully determine production amplitudes F1, F2, F3, and F4.

Eγ [MeV] γp → p π0

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Example: Ambiguities in γ p → p π0

Bonn-Gatchina (2011-02) SAID (SN11, CM12) MAID

Helicity Difference:

E = − 1 2 Λz δ⊙ N→⇒ − N→⇐ N→⇒ + N→⇐

σ1/2 σ3/2

2. 3. 4.

➜ ➜

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Helicity Asymmetry E in γ p → p π0 @ ELSA

• M. Gottschall et al., PRL 112, 012003 (2014)

cos θπ0 E

E = σ1/2 − σ3/2 σ1/2 + σ3/2

Eγ ∈ [0.6, 2.2] GeV

• CBELSA/TAPS

— Maid — Said (CM12) — BoGa (2011_2) Angular distributions sensitive to interference between resonances.

• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Asymmetry G in γ p → p π0 @ ELSA

cos θπ

Surprisingly, π production also not well understood at lower energies: — BoGa

• -

SAID

.... MAID

d σ d Ω = σ0 { 1 − δ l Σ cos 2φ + Λ x ( −δ l H sin 2φ + δ ⊙ F ) − Λ y ( −T + δ l P cos 2φ) − Λ z ( − δ l G sin 2φ + δ ⊙ E)}

• A. Thiel et al., PRL 109, 102001 (2012)
• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Asymmetry G in γ p → p π0 @ ELSA

θπ = 90 ± 5◦ θπ = 130 ± 5◦ Surprisingly, π production also not well understood at lower energies. Below 1 GeV, discrepancies can be traced to the E0+ and E2− multipoles, which are related to certain resonances:

E0+: N(1535) 1

2 −, N(1650) 1 2 −, ∆(1620) 1 2 −

E2−: N(1520) 3

2 −, ∆(1700) 3 2 −

d σ d Ω = σ0 { 1 − δ l Σ cos 2φ + Λ x ( −δ l H sin 2φ + δ ⊙ F ) − Λ y ( −T + δ l P cos 2φ) − Λ z ( − δ l G sin 2φ + δ ⊙ E)}

• A. Thiel et al., PRL 109, 102001 (2012)
• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Beam Asymmetry Σ in γ p → p π0 @ CLAS (g8b)

— — SAID DU13 – . – SAID CM12 – – MAID 07

......

BoGa 2011-02 Largest changes in SAID DU13 Improved mapping

• f dip near 60◦

Couplings of ∆(1700) 3

2 −

∆(1905) 5

2 +

• M. Dugger et al. [CLAS Collaboration], PRC 88, 065203 (2013)
• V. Credé

(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Helicity Difference E in γ p → n π+ @ CLAS (FROST)

∆+ N∗

p π0 :

• 2

3 |I = 3 2, I3 = 1 2 −

• 1

3 |I = 1 2, I3 = 1 2 n π+ :

• 1

3 |I = 3 2, I3 = 1 2 +

• 2

3 |I = 1 2, I3 = 1 2

— — SAID ST14 – . – MAID 07 – – BoGa 2011-02

......

Jülich 14

• S. Strauch et al., Phys. Lett. B 750, 53 (2015)
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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Target Asymmetry T in γ p → n π+ (CLAS FROST)

– MAID 07 – SAID – BoGA 12

cos Θc.m. cos Θc.m.

• M. Dugger (ASU), CLAS g9b run group

Early-stage results (g9b) Transverse Target Polarization

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Observable F in γ p → n π+ (CLAS FROST-g9b)

Box

– MAID 07 – SAID 12 BoGa not shown

• M. Dugger (ASU), CLAS g9b run group

cos Θc.m. d σ d Ω = σ0 { 1 − δ l Σ cos 2φ + Λ x ( −δ l H sin 2φ + δ ⊙ F ) − Λ y ( −T + δ l P cos 2φ) − Λ z ( − δ l G sin 2φ + δ ⊙ E)}

• Transv. target pol. & circ. beam pol.

Early-stage analysis Reasonable agreement among predictions for W < 1.7 GeV ➜ Much to learn at the higher energies

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Baryon Resonances in the Reaction γ p → p ω

Spin Observable E ELSA [4] E Beam Asym. Σ GRAAL [5], [6] ELSA [7] Polarized SDMEs ELSA [1]

• Unpol. SDMEs

ELSA [1], CLAS [2] Spin Observable G ELSA [4] Cross Section CLAS [2],ELSA [1] LEPS [3]

➜ Vector Meson Photoproduction (ω, ρ, φ) is still underexplored.

PWA Results [1], [2]: N(1720) 3/2+ N(1875) 3/2− N(1895) 1/2− N(2000) 5/2+ N(2120) 3/2− N(> 2100) 7/2− ?

[1] Wilson et al., arXiv:1508.01483 (2015) [2] Williams et al., PRC 80, 065208 (2009) [3] Sumihama et al., PRC 80, 052201 (2009) [4] Eberhardt et al., arXiv:1504.02221 (2015) [5] Vegna et al., PRC 91, 065207 (2015) [6] Ajaka et al., PRL 96, 132003 (2006) [7] Klein et al., PRD 78, 117101 (2008)

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Complete Experiments in γ p → p ω (& γ p → p π+π−)

γp → p ω → p π+π−π0

miss

➜ same final state as γp → p π+π− Analysis in basically three steps: Kinematics & Event Selection (p π+π−)

• lin. pol.
• circ. pol.

g9a USC (✓) FSU ✓, CU (✓) g9b FSU ✓ USC (✓) Event-based background subtraction ➜ p π+(π−), p (π+)π−, p π+π− ✓ p π+π−(π0) ✓ p π+π−(η)? Physics:

published (+ SDME’s) in progress d σ d Ω = σ0 { 1 − δ l Σ cos 2φ + Λ x ( −δ l H sin 2φ + δ ⊙ F ) − Λ y ( −T + δ l P cos 2φ) − Λ z ( − δ l G sin 2φ + δ ⊙ E)}

➜ ➜

g9b: ω ← ⇑

Eγ ∈ [1.4, 1.5] GeV

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Beam- & Target-Asymmetry in γ p → p ω (CLAS-g9b)

Preliminary

• 1
• 0.8
• 0.6
• 0.4
• 0.2

FROST (g9b-linear) GRAAL (2013) GRAAL (2006) FROST (g9b-linear) GRAAL (2013) GRAAL (2006)

• 1
• 0.8
• 0.6
• 0.4
• 0.2

FROST (g9b-linear)

c.m. ω

Θ

FROST (g9b-linear)

E : 1350 MeV E : 1450 MeV E : 1550 MeV E : 1650 MeV

P r e l i m i n a r y

E : 1350 MeV E : 1550 MeV

c.m.

cos

• 0.8
• 0.6
• 0.4
• 0.2

• 1
• 0.8 -0.6 -0.4 -0.2

E : 1750 MeV E : 1950 MeV

• 0.8 -0.6 -0.4 -0.2

• 0.6
• 0.4
• 0.2

Target-Asymmetry, T (first-time measurement)

• lin. pol. beam
• circ. pol. beam

We are close to a complete experiment in γ p → p ω: Event-based dilution factors (➜ frozen-spin butanol target) Extraction of observables in event-based likelihood fits

Σ

Priyashree Roy (Florida State), to be published

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

Beam-Target Asymmetry F in γ p → p ω (CLAS-g9b)

• 0.8
• 0.6
• 0.4
• 0.2
• 0.8
• 0.6
• 0.4
• 0.2
• 0.8
• 0.6
• 0.4
• 0.2
• 0.4
• 0.2

Preliminary

: 1250 MeV

E : 1650 MeV

E : 2050 MeV

E : 1350 MeV

E : 1750 MeV

E : 2150 MeV

E : 1450 MeV

E : 1850 MeV

E : 2250 MeV

E : 1550 MeV

E : 1950 MeV

E : 2350 MeV

E

• 0.8

0.8

• 0.8

0.8

• 0.8

0.8

• 1 -0.5 0

0.5 1

• 1 -0.5

0.5 1

• 1 -0.5

0.5 1

• 1
• 0.5

0.5 1 c.m.

)

ω

Θ cos( F

Priyashree Roy (Florida State), to be published

d σ d Ω = σ0 { 1 − δ l Σ cos 2φ + Λ x ( −δ l H sin 2φ + δ ⊙ F ) − Λ y ( −T + δ l P cos 2φ) − Λ z ( − δ l G sin 2φ + δ ⊙ E)}

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook

Outline

1

Introduction The Spectrum of Hadrons: Baryons and Mesons

2

Spectroscopy of Baryon Resonances Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

3

Decay Cascades of Excited Baryons

4

Summary and Outlook 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 Decay Cascades of Excited Baryons Summary and Outlook

Observation of Decay Cascades in γ p → p π0π0

2 4 6 8 10 12 500 1000 1500 2000 2500

Eγ , MeV σtot , µb

CBELSA pπ0 / 3

2.5 5 7.5 10 300 400 500 600 700 800

E[MeV] [µb]

[o]

• 10

10

• 10

10 100 200 300 100 200 300

XXXXXX

➜ Search for states in decay cascades!

Preliminary ➜

• F. Zehr et al., Eur. Phys. J. A 48, 98 (2012) @MAMI

Observation of new decay modes in the decay of N∗ resonances; weak at most in ∆∗ decays. Bonn-Gatchina PWA

• V. Sokhoyan, E. Gutz, V. C. et al. @ELSA

Cross Sections Beam Asymmetry, I⊙

γp → p π0

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook

Observation of Decay Cascades in γ p → p π0π0

2 4 6 8 10 12 500 1000 1500 2000 2500

Eγ , MeV σtot , µb

CBELSA pπ0 / 3

XXXXXX Preliminary ➜

Nucleon states with S = 3

2 require spatial

wave functions of mixed symmetry. For L = 2 the wave functions do have equal admixtures of MS and MA = [ φ0p( ρ ) × φ0p( λ ) ](L = 2) , a component in which both the ρ and the λ oscillator are excited simultaneously. Observation of new decay modes in the decay of N∗ resonances; weak at most in ∆∗ decays. Bonn-Gatchina PWA

Sokhoyan, Gutz, V. C. et al., EPJ A 51, no. 8, 95 (2015)

γp → p π0 λ∗ ρ∗ ρ∗ + λ∗

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook

Observation of Decay Cascades in γ p → p π0π0

XXXXXX

Nucleon states with S = 3

2 require spatial

wave functions of mixed symmetry. For L = 2 the wave functions do have equal admixtures of MS and MA = [ φ0p( ρ ) × φ0p( λ ) ](L = 2) , a component in which both the ρ and the λ oscillator are excited simultaneously. Observation of new decay modes in the decay of N∗ resonances; weak at most in ∆∗ decays. Bonn-Gatchina PWA

Sokhoyan, Gutz, V. C. et al., EPJ A 51, no. 8, 95 (2015)

λ∗ ρ∗ ρ∗ + λ∗

N(1880) 1/2+ N(1900) 3/2+ N(2000) 5/2+ N(1990) 7/2+            N(1520)π N(1535)π N(1680)π Nσ (l = 1) ➜ Quartet of (70, 2+

2 ) with S = 3 2.

Decays observed in PWA into, e. g.

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Are we there yet? Open Issues in Light Baryon Spectrosocpy Summary and Outlook

Outline

1

Introduction The Spectrum of Hadrons: Baryons and Mesons

2

Spectroscopy of Baryon Resonances Complete Experiments Polarization Observables in γp → N π Polarization Observables in γp → p ω

3

Decay Cascades of Excited Baryons

4

Summary and Outlook 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 Decay Cascades of Excited Baryons Summary and Outlook Are we there yet? Open Issues in Light Baryon Spectrosocpy Summary and Outlook

➜ E. Pasyuk: “Complete Experiments in Kaon Photoproduction”

Table representing CLAS@JLab measurements.

Need more observables on: γp → p ππ, p πη γp → p πω, ...

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Are we there yet? Open Issues in Light Baryon Spectrosocpy Summary and Outlook

Open Issues in Light Baryon Spectroscopy

Some questions need to be addressed in light baryon spectroscopy:

1

What are the relevant degrees of freedom in (excited) baryons? Can the high-mass states be described by the dynamics of three flavored quarks?

2

Can we identify the leading interactions between the constituents?

3

Do we understand the decay of high-mass baryon resonances?

4

Do hybrid baryons exist? What is the role

• f glue in excited baryons?

5

Do we observe states beyond the ➜ simple |qqq picture, e.g. in γn → n η?

6

What are the missing resonances and why are so many still missing?

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Are we there yet? Open Issues in Light Baryon Spectrosocpy Summary and Outlook

Summary and Outlook

Our understanding of baryon resonances has made great leaps forward. There is good evidence that most of the known states (listed in the PDG) will also be confirmed in photoproduction and that new states will be revealed: Goal of performing (almost) complete experiments has been (almost) achieved; significant contributions from (double-)polarization experiments. Still too early to nail down degrees of freedom in excited baryons? Well, is any of the different approaches THE correct one? Or, do they just represent different legitimate views? I think we are moving toward a new exciting era in hadron spectroscopy (COMPASS@CERN, BES III, PANDA, etc.): GlueX in Hall-D at JLab will start to take physics data this year. Advances in both theory and experiment will allow us to finally understand QCD and confinement.

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(Highlights in) Light-Baryon Spectroscopy

Introduction Spectroscopy of Baryon Resonances Decay Cascades of Excited Baryons Summary and Outlook Are we there yet? Open Issues in Light Baryon Spectrosocpy Summary and Outlook

Baryons 2016 Conference: May 16 - 20, 2016

➜ baryons2016@hadron.physics.fsu.edu

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(Highlights in) Light-Baryon Spectroscopy