Study of Excited Baryons with the Crystal-Barrel Detector at ELSA

Study of Excited Baryons with the Crystal-Barrel Detector at ELSA V. Credé FSU, Tallahassee, Florida NSF Review Florida State University, 11/15/2007

Outline 1 Introduction 2 Proposal: Determination of Beam Asymmetry in γp pη Proposal: Combined Analysis of CLAS and CBELSA/TAPS ππ Data Proposal: Study of π 0 η Photoproduction 3 Status of the Experiment and FSU Commitments Proposal: Measurement of the Helicity Difference in π 0 η Production

Outline Introduction 1 Introduction 2 Proposal: Determination of Beam Asymmetry in γp pη Proposal: Combined Analysis of CLAS and CBELSA/TAPS ππ Data Proposal: Study of π 0 η Photoproduction 3 Status of the Experiment and FSU Commitments Proposal: Measurement of the Helicity Difference in π 0 η Production

General Physical Motivation Study of baryon properties and search for new resonances **** *** ** * N Spectrum 11 3 6 2 Spectrum 7 3 6 6 according to PDG (J. Phys. G33 (2006) 1) little known (many open questions left)

General Physical Motivation Study of baryon properties and search for new resonances Quark models predict many more baryons than have been observed **** *** ** * N Spectrum 11 3 6 2 Spectrum 7 3 6 6 Possible solutions: a) Quark-diquark structure according to PDG (J. Phys. G33 (2006) 1) little known (many open questions left) b) They have not been observed, yet one of the internal degrees of freedom is frozen Nearly all existing data result from πn scattering experiments If the missing resonances did not couple to Nπ, they would not have been discovered!!

3000 Nucleon Resonances S. Capstick and N. Isgur, Phys. Rev. D34 (1986) 2809 many predicted states missing ** 2500 *** **** ** **** **** Mass [MeV] 2000 * S *** ** **** ** ** **** * **** ** S S *** **** 1500 **** **** **** 1000 OGE Model: residual short-range interaction based on one-gluon exchange **** J π 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-

What is required experimentally to study baryons? Unfortunately, N spectral lines look like Baryons are broad and overlapping Rescattering Effects Require Coupled-Channel Analysis (need to measure as many final states as possible) Polarization (need complete experiments)

E γ [GeV] Reaction Thresholds 3,0 W [GeV] 2.6 2.6 2.3 1.66 0.06 γp pηη 2,0 γp pπ 0 ω γp pπ 0 η γp KΛ KΣ γp pη γp pπππ γp pππ, π 0 π 0 γp pπ 1,0 Optimized for charged particles! 1.8 Limited in energy!! 0.00 only possible at ELSA 0,0 ELSA CLAS LEPS MAMI-C

CLAS/CB-ELSA Complementary Detectors Photoproduction at ELSA with the Crystal-Barrel Detector Great to measure neutral particles: π 0, η γγ, η π 0 π 0 π 0, etc. Photo/Electroproduction at CLAS Great for charged particles: p, π ±, etc.

All FSU Jefferson Lab efforts will be funded by DOE Collaboration with P. Eugenio (experiment, meson spectroscopy) My students involved with JLab N program: (Double-pion (FROST) proposal: A rating) C. Hanretty and S. Park (target construction, (FROST) chef) Undergraduate student E. McClellan (Drift chamber calibration) Funds requested here from NSF for N program at ELSA, Bonn Photo/Electroproduction at CLAS Great for charged particles: p, π ±, etc.

Crystal Barrel at ELSA: Bonn, Germany Collaboration Germany Russia Switzerland U. S. (Florida State)

Crystal Barrel at ELSA: Bonn, Germany Optimized for neutral-particle final states 4π Calorimeter (Crystal Barrel + TAPS) Linear/Circular Beam Polarization Frozen-Spin (Butanol) Target E γ < 3 GeV (W < 2.6 GeV) Collaboration Germany Russia Switzerland U. S. (Florida State)

: e.g. γp pπ 0 π 0 General Advantage: γ does not couple to π 0 Fewer Born-terms, t-channel exchanges

: e.g. γp pπ 0 π 0 General Advantage: γ does not couple to π 0 Fewer Born-terms, t-channel exchanges No diffractive ρ(770) production: ρ 0 π 0 π 0 No direct ++ π production (Kroll-Ruderman term) Bigger contribution of resonant amplitudes! Arbitrary Units 500 Entries 3738 Arbitrary Units 500 250 Entries 3738 m π + π m pπ + 0 0.4 0.6 0.8 1 1.2 1.92 GeV < E γ < 2.03 GeV m ππ [GeV] 0 1.2 1.4 1.6 1.8 2 1.92 GeV < E γ < 2.03 GeV m pπ [GeV] Saphir

1 CB-ELSA Collaboration Photoproduction of π 0 Mesons O. Bartholomy, V. C., H. van Pee et al., Phys. Rev. Lett. 94 (2005) 012003 Photoproduction of η Mesons V. C., O. Bartholomy et al., Phys. Rev. Lett. 94 (2005) 012004 [µb] σ tot 20 15 10 5-1/2 E γ [GeV] 1 1.5 2 2.5 CB-ELSA data CB-ELSA fit CLAS Hint for new N resonance N(2070)D 15 1 Needs confirmation! + 3/2-5/2 2 No need for third S 11 ρ-ω 1.6 1.8 2 2.2 2.4 W [GeV] Three resonances are dominantly contributing! N(1535)S 11, N(1720)P 13, N(2070)D 15

1 CB-ELSA Collaboration Photoproduction of π 0 Mesons O. Bartholomy, V. C., H. van Pee et al., Phys. Rev. Lett. 94 (2005) 012003 H. van Pee, O. Bartholomy, V. C. et al., Eur. Phys. J. A 31 (2007) 61 Photoproduction of η Mesons V. C., O. Bartholomy et al., Phys. Rev. Lett. 94 (2005) 012004 O. Bartholomy, R. Bogendörfer, V. C., I. Fabry, Eur. Phys. J. A 33 (2007) 133 [µb] σ tot 20 15 10 5-1/2 E γ [GeV] 1 1.5 2 2.5 CB-ELSA data CB-ELSA fit CLAS Hint for new N resonance N(2070)D 15 1 Needs confirmation! + 3/2-5/2 2 No need for third S 11 ρ-ω 1.6 1.8 2 2.2 2.4 W [GeV] Three resonances are dominantly contributing! N(1535)S 11, N(1720)P 13, N(2070)D 15

1 CB-ELSA Collaboration Photoproduction of π 0 Mesons Photoproduction of η Mesons 2 CBELSA/TAPS Collaboration Data Analysis at Florida State (A. McVeigh, A. Woodard) Crystal Barrel γp pπ 0, η, η (pπ 0 π 0, pπ 0 η) γp pη (Topic of Ph.D. thesis) Sep. 2002 Dec. 2003 (Un)polarized beam Liquid H 2, deuterium Solid targets TAPS 512 BaF Crystals Forward Detector High Granularity Fast Trigger

Study of γp pη with CBELSA/TAPS Invariant γγ Mass 800 3 10 Invariant πππ Mass { η γγ, 3π 0 (inset) (CBELSA/TAPS) 600 M. Dugger et al., PRL 89, 222002 (2002) 400 0 400 600 800 1000 2 MeV/c 200 0 0 200 400 600 800 2 MeV/c γ p p X (missing mass) (CLAS) }

Study of γp pη with CBELSA/TAPS Invariant γγ Mass 800 3 10 Invariant πππ Mass { η γγ, 3π 0 (inset) (CBELSA/TAPS) 600 Why is η (π 0 ) production important? 400 0 400 600 800 1000 2 MeV/c Ratio of η Decay Modes Entries 700 Mean 1.017 200 30 dσ (η 3π0 ) dω / dσ(η γγ) dω 0 0 200 400 600 800 2 MeV/c 20 10 0 0 0.5 1 1.5 2 Acceptance studies: η 2γ π 0 η, π 0 π 0 4γ η 6γ

µ Introduction Differential Cross Sections for γp pη sr b ] [ Full coverage Presented at dσ dω HADRON 07 1 DNP 07 (CEU)? 1 0.5 0.4 2 CBELSA/TAPS CB-ELSA CLAS SAID 800-850 850-900 900-950 950-1000 1000-1050 1050-1100 1100-1150 1150-1200 1200-1250 1250-1300 1300-1350 Preliminary 1350-1400 1400-1450 1450-1500 1500-1550 1550-1600 1600-1650 0.2-1 -0.5 0 0.5-0.5 0 0.5-0.5 0 0.5-0.5 0 0.5 V. C., A. McVeigh et al., CBELSA/TAPS Collaboration, in preparation V. C., O. Bartholomy et al., CB-ELSA Collaboration, PRL D94, 012004 (2005) -0.5 0 0.5-0.5 0 0.5 1 cos θ cms

Differential Cross Sections for γp pη µ sr b ] [ - CBELSA/TAPS - CB-ELSA - CLAS - SAID dσ dω 0.4 0.2 0.4 0.2 0.4 1650-1700 1700-1750 1750-1800 1800-1850 1850-1900 1900-1950 1950-2000 2000-2050 2050-2100 2100-2150 2150-2200 2200-2250 Preliminary 2250-2300 2300-2350 2350-2400 2400-2450 2450-2500 2500-2550 0.2-1 -0.5 0 0.5-0.5 0 0.5-0.5 0 0.5-0.5 0 0.5-0.5 0 0.5 V. C., A. McVeigh et al., CBELSA/TAPS Collaboration, in preparation V. C., O. Bartholomy et al., CB-ELSA Collaboration, PRL D94, 012004 (2005) -0.5 0 0.5 1 cos θ cms

Proposal: Study of γp pη with CBELSA/TAPS Isospin Filter: only N resonances can contribute 1968: 11 events from the ABBHHM bubble chamber experiment 1976: 7 events from the AHHM streamer chamber experiment 1998: 250 events from SAPHIR collaboration First differential cross sections 2006: over 2 10 5 events from CLAS (limited in angular coverage) (Contributions from N(1535)S 11, N(1710)P 11, J = 3/2 states) 2007: New data from CBELSA/TAPS over the full angular range HADRON 07, DNP/CEU Program (undergraduate student A. Woodard) No published beam-asymmetry data yet for η (linearly-polarized beam) Data available from ELSA (η π 0 π 0 η) Ph.D. thesis of A. McVeigh

[ Differential Cross Sections for γp pη µ sr b ] dσ dω 0.3 0.2 0.1 0.3 0.2 0.1 0.3 0.2 0.1 0.3 0.2 - CBELSA/TAPS - SAPHIR - CLAS - SAID 1500-1550 1550-1600 1600-1650 1650-1700 1700-1750 1750-1800 1800-1850 1850-1900 1900-1950 1950-2000 2000-2050 2050-2100 2100-2150 2150-2200 2200-2250 Preliminary 2250-2300 2300-2350 2350-2400 2400-2450 2450-2500 0.1-1 -0.5 0 0.5-0.5 0 0.5-0.5 0 0.5 cos θ cms FSU et al., CBELSA/TAPS Collaboration, in preparation -0.5 0 0.5-0.5 0 0.5 1

Proposal: Combined PWA of CLAS and CB Data γp pπ 0 π 0 and γp pπ + π from CB-ELSA and CLAS - CB-ELSA: - CLAS: 1500 1000 500 m(pπ 0 π 0 ): 2000-2200 MeV 7000 6000 5000 4000 3000 2000 1000 m(pπ + π - ): 2000-2200 MeV γp N / Xπ X = (1232) X = D 13 (1520) X = X(1660) 0 1000 1500 2000 m(pπ 0 ) 800 600 400 200 m(pπ 0 π 0 ): 2200-2400 MeV 0 1000 1500 2000 m(pπ 0 ) 1800 1600 1400 1200 1000 800 600 400 200 0 1 1.2 1.4 1.6 1.8 2 2.2 m(pπ - ) m(pπ + π - ) >2200 MeV 0 1 1.2 1.4 1.6 1.8 2 2.2 m(pπ - ) 12000 10000 8000 6000 4000 2000 Similar resonance structures in both data sets! m(pπ + π ): 2000 2200 MeV Collaboration 14000 with CLAS group at CMU Bla ρ(770) Use existing (CMU) code Add polarization γp pρdata (CLAS/ELSA) 0 0.2 0.4 0.6 0.8 1 1.2 m(π + π )

Proposal: Study of η ( p π 0 η) Events Events / ( 10 MeV ) A RooPlot of "Invariant pπ Mass for Energy Bin 20 and θ 25 20 15 10 5 Bin 14" NBack = 81.81 NPeak = 183.17 E γ [1900; 1950] MeV M pπ 0 η [2100; 2130] MeV/c 2 cos θ η [0.3; 0.4] η (η γγ) MC Distribution (Breit-Wigner Distribution) S 11 π 0 MC Distribution (Breit-Wigner Distribution) 0 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Invariant pπ Mass for Energy Bin 20 and θ Bin 14 (MeV) γ Isospin Filter for η (1232) π 0 p Study of γp pπ 0 η ( 500, 000 events, full angular range) Determination of prel. cross sections ( Honors thesis A. Woodard) Collaboration with FSU theorists S. Capstick and his graduate student A. Kiswandhi

Outline Introduction Status of the Experiment and FSU Commitments 1 Introduction 2 Proposal: Determination of Beam Asymmetry in γp pη Proposal: Combined Analysis of CLAS and CBELSA/TAPS ππ Data Proposal: Study of π 0 η Photoproduction 3 Status of the Experiment and FSU Commitments Proposal: Measurement of the Helicity Difference in π 0 η Production

Status of the Experiment and FSU Commitments 1 CB-ELSA Collaboration Photoproduction of π 0 Mesons Photoproduction of η Mesons 2 CBELSA/TAPS Collaboration 3 Proposals to MAMI/ELSA PAC in September 2005 ELSA/1-2005 G in single π 0 and η production ELSA/2-2005 Helicity dependence in π 0 and η production ELSA/3-2005 Σ and G in η photoproduction off neutron ELSA/4-2005 Beam-target asymmetry in ω production ELSA/5-2005 Meson-nucleus bound state ELSA/6-2005 Double polarisation in π 0 π 0 production ( 4000 h to measure E, G with E 0.05) ELSA/7-2005 Helicity difference in π 0 η production (FSU A proposal) ( 2000 h to measure E with E 0.06)

Status of the Experiment and FSU Commitments Data taking has started in September 2007 Several weeks of circularly-polarized beam on longitudinally-polarized target Collaboration on polarization observables with FSU theorist Winston Roberts FSU students: A. McVeigh, A. Wilson γ-intensity Monitor (γim) 4x4 array of lead glass crystals Determination of photon flux FSU student A. McVeigh redesigned/assembled detector

Summary Introduction Status of the Experiment and FSU Commitments 1 Introduction 2 Proposal: Determination of Beam Asymmetry in γp pη Proposal: Combined Analysis of CLAS and CBELSA/TAPS ππ Data Proposal: Study of π 0 η Photoproduction 3 Status of the Experiment and FSU Commitments Proposal: Measurement of the Helicity Difference in π 0 η Production