Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Facilities and Detectors for Baryon Physics

Volker Credé

Florida State UniversityTallahassee, FL

APS-DNP Town MeetingRutgers University, 01/14/2007

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Outline

1 Introduction

2 (Photoproduction) Facilities

3 Advantages of Neutral Final States

4 Summary

“Crystal Ball”

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Outline

1 Introduction

2 (Photoproduction) Facilities

3 Advantages of Neutral Final States

4 Summary

“Crystal Ball”

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

0,0

1,0

2,0

3,02.6

ELSA

2.6

CLAS

2.3

LEPS

1.9

MAMI-C

E γ [GeV]

0.00

0.06

1.66

Reaction Thresholds

γp→ pπγp→ pππγp→ pπππγp→ pηγp→ pπ0η

γp→ pπ0ω

γp→ pηη

γp→ KΛ KΣ

W [GeV]*

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

0,0

1,0

2,0

3,02.6

ELSA

2.6

CLAS

2.3

LEPS

1.9

MAMI-C

E γ [GeV]

0.00

0.06

1.66

Reaction Thresholds

γp→ pπγp→ pππγp→ pπππγp→ pηγp→ pπ0η

γp→ pπ0ω

γp→ pηη

γp→ KΛ KΣ

W [GeV]*

1 Facilities are all complementary2 International collaborations crucial

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Outline

1 Introduction

2 (Photoproduction) Facilities

3 Advantages of Neutral Final States

4 Summary

“Crystal Ball”

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

LEPS at SPring-8: Hyogo, Japan

LEPS (international) CollaborationJapanSouth KoreaTaiwanCanadaU. S. (Ohio University)

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

LEPS at SPring-8: Hyogo, Japan

Detector optimized for charged-particle final statesLinear Polarization (Compton Backscattering)Eγ < 2.4 GeV (new laser will allow Eγ < 3 GeV)LEPS covers very forward angles (θlab > 1)

LEPS (international) CollaborationJapanSouth KoreaTaiwanCanadaU. S. (Ohio University)

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

LEPS at SPring-8: Hyogo, Japan

0

1

2

2 3 4 5 6Eγ (GeV)

dσ/d

t(t=-

|t|m

in) (

µb/G

eV2 )

SLAC(1973)

BONN(1974)

DESY(1978)

DARESBURY(1982)

SAPHIR(2003)

This work

0

0.2

0.4

0.6

0.8

-1 -0.5 0 0.5 1

0

0.5

1

1.5

0 100 200 300

0

0.2

0.4

0.6

0.8

-1 -0.5 0 0.5 10

0.5

1

1.5

0 100 200 300

W 2πW

(a) (b)

1.97< Eγ< 2.17 1.97< Eγ< 2.17

cosθ

2.17< Eγ< 2.37

φ-Φ

2.17< Eγ< 2.37

0 π 2π

Original detector optimized for K detectionDiffractive φ-Meson Photoproduction on the Proton near Threshold

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

LEPS at SPring-8: Hyogo, Japan

Original detector optimized for K detectionDiffractive φ-Meson Photoproduction on the Proton near Threshold~γn→ K+Σ−: Differential Cross Section/Photon Beam Asymmetry

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

LEPS at SPring-8: Hyogo, Japan

-0.4

-0.2

0

0.2

0.4

0 2 4 6φK

+ (rad)

(kN

v-N

h)/(k

Nv+

Nh)

-0.4

-0.2

0

0.2

0.4

0 2 4 6φK

+ (rad)

(kN

v-N

h)/(k

Nv+

Nh)

Original detector optimized for K detectionDiffractive φ-Meson Photoproduction on the Proton near Threshold~γn→ K+Σ−: Differential Cross Section/Photon Beam AsymmetryBeam Polarization Asymmetries for ~γp→ K+Λ and ~γp→ K+Σ0

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Crystal Ball at MAMI-C: Mainz, Germany

A2 (international) CollaborationGermanyGreat BritainItalyRussiaSwitzerland

U. S. (GWU, UCLA, Kent State)BelgiumSwedenCroatiaCanada

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Crystal Ball at MAMI-C: Mainz, Germany

Optimized for neutral-particle final states4π Calorimeter (Crystal Ball + TAPS)⇒ First-Level Trigger

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Crystal Ball at MAMI-C: Mainz, Germany

Optimized for neutral-particle final states4π Calorimeter (Crystal Ball + TAPS)⇒ First-Level TriggerCharged-Particle Detection (MWPC)

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Crystal Ball at MAMI-C: Mainz, Germany

Optimized for neutral-particle final states4π Calorimeter (Crystal Ball + TAPS)⇒ First-Level TriggerCharged-Particle Detection (MWPC)Polarized Beam and TargetEγ < 1.5 GeV (W < 1.9 GeV)

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Crystal Ball at MAMI-C: Physics Goals

Focus on

Measurements of total (σ) and differential crosssections ( dσ

dΩ) using unpolarized neutrons (LD2):γn→ nπ0

γn→ n ηγn→ n η

′

γn→ KΛ

Single- and double-polarization measurementswith polarized deuterium target

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Crystal Barrel at ELSA: Bonn, Germany

CB-ELSA CollaborationGermanyRussiaSwitzerlandU. S. (Florida State)

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Crystal Barrel at ELSA: Bonn, GermanyOptimized for neutral-particle final states

4π Calorimeter (Crystal Barrel + TAPS)Linear/Circular Beam PolarizationFrozen-Spin (Butanol) TargetEγ < 3 GeV (W < 2.6 GeV)

CB-ELSA CollaborationGermanyRussiaSwitzerlandU. S. (Florida State)

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Neutral-Meson Final States: Available Data from ELSA

Crystal Barrel @ ELSA (2000/2001)γp→ pπ0 (PRL D94, 012003 (2005))

γp→ pη (PRL D94, 012004 (2005))

1.4 1.6 1.8 2 2.2 2.4

1

10

100

200

400 0.5 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

1.6 1.8 2 2.2 2.4

5

10

1520 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

-1/2

+3/2

-5/2

ω-ρ

γp→ pπ0

γp→ pη

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Neutral-Meson Final States: Available Data from ELSA

)0πm(p1 1.11.21.31.41.51.61.71.81.9 2

0

2000

4000

6000

8000

10000 Baryon Decays into pπ0π0

Ü N∗/∆∗ resonances notcoupling to Nπ or γNcould be produced insuch decay cascades

Crystal Barrel @ ELSA (2000/2001)γp→ pπ0 (PRL D94, 012003 (2005))

γp→ pη (PRL D94, 012004 (2005))

γp→ pπ0η (π0π0)Ü Strong indication for new states

1.4 1.6 1.8 2 2.2 2.4

1

10

100

200

400 0.5 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

1.6 1.8 2 2.2 2.4

5

10

1520 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

-1/2

+3/2

-5/2

ω-ρ

Preliminary

γp→ pπ0

γp→ pη

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Neutral-Meson Final States: Available Data from ELSA

Crystal Barrel @ ELSA (2000/2001)γp→ pπ0 (PRL D94, 012003 (2005))

γp→ pη (PRL D94, 012004 (2005))

γp→ pπ0η (π0π0)Ü Strong indication for new states

1.4 1.6 1.8 2 2.2 2.4

1

10

100

200

400 0.5 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

1.6 1.8 2 2.2 2.4

5

10

1520 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

-1/2

+3/2

-5/2

ω-ρ [ MeV ]s

1600 1800 2000 2200

b ]

µ [σ

2

4

6

8

10

12

14

Total cross sections with 20 MeV bin size

(exp)η0π p→p γ

(pwa)η0π p→p γ0π0π p→p γ

(GRAAL)0π0π p→p γ

Total cross sections with 20 MeV bin size

Preliminary

γp→ pπ0

γp→ pησπ0π0 ≈ σπ0η

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Neutral-Meson Final States: Available Data from ELSA

Crystal Barrel @ ELSA (2000/2001)γp→ pπ0 (PRL D94, 012003 (2005))

γp→ pη (PRL D94, 012004 (2005))

γp→ pπ0η (π0π0)Ü Strong indication for new states

CB/TAPS @ ELSA (2002/2003)Factor of 10 more unpolarized data and(almost) full angular coverageLinear photon polarization

Ü Cross sections, asymmetries, PWA

Double-Polarization (2007 –)Longitudinal Target Polarization

1.4 1.6 1.8 2 2.2 2.4

1

10

100

200

400 0.5 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

1.6 1.8 2 2.2 2.4

5

10

1520 1 1.5 2 2.5

W [GeV]

[GeV]γ Eb]µ [ totσ

-1/2

+3/2

-5/2

ω-ρ

γp→ pπ0

γp→ pη

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Outline

1 Introduction

2 (Photoproduction) Facilities

3 Advantages of Neutral Final States

4 Summary

“Crystal Ball”

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Photoproduction of Neutral Mesons: e.g. γp→ pπ0π0

General Advantage: γ does not couple to π0

Fewer Born-terms, t-channel exchanges

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Photoproduction of Neutral Mesons: e.g. γp→ pπ0π0

General Advantage: γ does not couple to π0

Fewer Born-terms, t-channel exchangesNo diffractive ρ(770) production: ρ0 9 π0π0

No direct ∆++π− production (Kroll-Ruderman term)

0

1000

2000

0.4 0.6 0.8 1 1.2

Entries 7937

1.19 GeV < Eγ < 1.26 GeV mππ [GeV]

Arb

itrar

y U

nits

0

2000

1.2 1.4 1.6 1.8 2

Entries 7937

1.19 GeV < Eγ < 1.26 GeV mpπ [GeV]

Arb

itrar

y U

nits

Saphir

mπ+π− mpπ+

1.19 GeV < Eγ < 1.26 GeV

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Photoproduction of Neutral Mesons: e.g. γp→ pπ0π0

General Advantage: γ does not couple to π0

Fewer Born-terms, t-channel exchangesNo diffractive ρ(770) production: ρ0 9 π0π0

No direct ∆++π− production (Kroll-Ruderman term)

0

500

0.4 0.6 0.8 1 1.2

Entries 3738

1.92 GeV < Eγ < 2.03 GeV mππ [GeV]

Arb

itrar

y U

nits

0

250

500

1.2 1.4 1.6 1.8 2

Entries 3738

1.92 GeV < Eγ < 2.03 GeV mpπ [GeV]

Arb

itrar

y U

nits

Saphir

mπ+π− mpπ+

1.92 GeV < Eγ < 2.03 GeV

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Photoproduction of Neutral Mesons: e.g. γp→ pπ0π0

General Advantage: γ does not couple to π0

Fewer Born-terms, t-channel exchangesNo diffractive ρ(770) production: ρ0 9 π0π0

No direct ∆++π− production (Kroll-Ruderman term)Ü Bigger contribution of resonant amplitudes!

0

500

0.4 0.6 0.8 1 1.2

Entries 3738

1.92 GeV < Eγ < 2.03 GeV mππ [GeV]

Arb

itrar

y U

nits

0

250

500

1.2 1.4 1.6 1.8 2

Entries 3738

1.92 GeV < Eγ < 2.03 GeV mpπ [GeV]

Arb

itrar

y U

nits

Saphir

mπ+π− mpπ+

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

γp → pπ0π0 and γp → pπ+π− from CB-ELSA and CLAS

- CB-ELSA: - CLAS:

) 0πm(p1000 1500 20000

500

1000

1500): 2000-2200 MeV0π0πm(p

) -πm(p1 1.2 1.4 1.6 1.8 2 2.2

0

1000

2000

3000

4000

5000

6000

7000

): 2000-2200 MeV-π+πm(p

) 0πm(p1000 1500 20000

200

400

600

800

): 2200-2400 MeV0π0πm(p

) -πm(p1 1.2 1.4 1.6 1.8 2 2.2

0

200

400

600

800

1000

1200

1400

1600

1800

) >2200 MeV-π+πm(p

γp → N∗/∆∗ → Xπ

X = ∆(1232)

X = D13(1520)

X = X(1660)

⇒ Similar resonancestructures in bothdata sets !

) −π+πm(0.2 0.4 0.6 0.8 1 1.20

2000

4000

6000

8000

10000

12000

14000

): 2000−2200 MeV−π+πm(p

ρ(770)

γp → pρ

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Baryon Spectroscopy at BES: J/ψ → pπ− n ( pπ+ n )

N∗(1440) ?

N∗(1520)N∗(1535)

N∗(1650)N∗(1675)N∗(1680)

ÜÜ

Ü

?

Possible new stateM = 2065± 3+15

−30 MeV/c2

Γ = 175± 12± 40 MeV/c2

⇒ Prel. PWA favors 32

+(hep-ex/0405030)

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Outline

1 Introduction

2 (Photoproduction) Facilities

3 Advantages of Neutral Final States

4 Summary

“Crystal Ball”

V. Credé Facilities and Detectors for Baryon Physics

Introduction(Photoproduction) Facilities

Advantages of Neutral Final StatesSummary

Summary

European and Asian facilities/detectors important(complementary to CLAS)

Crystal Ball (A2 Collaboration)Crystal Barrel (CB-ELSA Collaboration)

1 Neutral final states

2 Beam/target polarization

SPring-8 (LEPS Collaboration)Charged-particle final states (very forward direction)

Polarized photon beam (Compton Backscattering)

V. Credé Facilities and Detectors for Baryon Physics