Report on NSTAR 2005 Workshop

Transcription

1 Report on NSTAR 2005 Workshop V. Credé 1 1 Florida State University Tallahassee, FL Cascade Workshop at JLab, 12/03/2005

2 Outline Introduction 1 Introduction 2 What are the problems? The NSTAR 2005 Workshop 3 4

3 Outline Introduction What are the problems? The NSTAR 2005 Workshop 1 Introduction 2 What are the problems? The NSTAR 2005 Workshop 3 4

4 What are the problems? The NSTAR 2005 Workshop Search for missing resonances Quark models predict many more baryons than have been observed * * N spectrum spectrum according to PDG (Phys. Rev. D66 (2002) ) little known (many open questions left) Possible solutions: a) Quark-Diquark Structure b) They have not been observed, yet Nearly all existing data result from πn scattering experiments If the missing states did not couple to Nπ, they would not have been discovered!!

5 Parity Doublets Introduction What are the problems? The NSTAR 2005 Workshop 3000 Nucleons * 2700 Mass [MeV] * 1986 S 1710 * 2090 * S S * J π 1/2+ 1/2-3/2+ 3/2-5/2+ 5/2-7/2+ 7/2-9/2+ 9/2-11/2+ 11/2-13/2+ 13/2-

6 Parity Doublets Introduction What are the problems? The NSTAR 2005 Workshop 3000 Nucleons * Mass [MeV] * 1986 S 1710 * 2090 * S S * Is this compelling empirical data? J π 1/2+ 1/2-3/2+ 3/2-5/2+ 5/2-7/2+ 7/2-9/2+ 9/2-11/2+ 11/2-13/2+ 13/2-

7 Parity Doublets Introduction What are the problems? The NSTAR 2005 Workshop 3000 Nucleons * Mass [MeV] * 1986 S 1710 * * S S * Is this compelling empirical data? Glozman: "... and thus we have a complete and total, 100 % ironclad proof that..." (according to T. Cohen) J π 1/2+ 1/2-3/2+ 3/2-5/2+ 5/2-7/2+ 7/2-9/2+ 9/2-11/2+ 11/2-13/2+ 13/2-

8 Parity Doublets Introduction What are the problems? The NSTAR 2005 Workshop 3000 Nucleons * Mass [MeV] * 1986 S 1710 * * S S * Is this compelling empirical data? Glozman: "... and thus we have a complete and total, 100 % ironclad proof that..." (according to T. Cohen) Cohen: "... and thus we have a faint hint of a whisper of the suggestion of the possibility that perhaps..." J π 1/2+ 1/2-3/2+ 3/2-5/2+ 5/2-7/2+ 7/2-9/2+ 9/2-11/2+ 11/2-13/2+ 13/2-

9 Let s look for them... What are the problems? The NSTAR 2005 Workshop Atomic Spectra Discrete spectrum of absorption and emission lines Excitation spectrum of nucleon offers access to QCD

10 However,... Introduction What are the problems? The NSTAR 2005 Workshop N spectral lines look more like Baryons are broad and overlapping Rescattering Coupled-channel effects Polarization (need complete experiment)

11 Outline Introduction What are the problems? The NSTAR 2005 Workshop 1 Introduction 2 What are the problems? The NSTAR 2005 Workshop 3 4

12 What are the problems? The NSTAR 2005 Workshop Tallahasse, Florida

13 Program of the Workshop What are the problems? The NSTAR 2005 Workshop Focus session on coupled-channel analysis Recent experimental results, including Pentaquarks, and strangeness production Cascades Focus session on polarization Focus session on developments in theoretical description of baryon spectrum, including lattice QCD and coupled-channel unitarised chiral models

14 Coupled-Channel Analyses What are the problems? The NSTAR 2005 Workshop Important in 2nd and 3rd resonance region Amplitude analysis of data Extract N parameters Interpretations in terms of QCD

15 Coupled-Channel Analyses What are the problems? The NSTAR 2005 Workshop Unitary Isobar Models MAID JLab/Yerevan UIM Multi-Channel K-Matrix Models SAID Giessen Model, KVI Model Kent State University (KSU) Carnegie-Mellon-Berkeley (CMB) Model Recent applications: Zagreb, PITT-ANL, FSU-PITT Dynamical Reaction Models Jülich, SL, DMT, Ohio-Utrecht,... Important in 2nd and 3rd resonance region Amplitude analysis of data Extract N parameters Interpretations in terms of QCD

16 Coupled-Channel Analyses What are the problems? The NSTAR 2005 Workshop Unitary Isobar Models MAID JLab/Yerevan UIM Multi-Channel K-Matrix Models SAID Giessen Model, KVI Model Kent State University (KSU) Carnegie-Mellon-Berkeley (CMB) Model Recent applications: Zagreb, PITT-ANL, FSU-PITT Dynamical Reaction Models Jülich, SL, DMT, Ohio-Utrecht,... Coordinating efforts by BRAG (Baryon Resonance Analysis Group)

17 Outline Introduction 1 Introduction 2 What are the problems? The NSTAR 2005 Workshop 3 4

18 Baryon Spectroscopy at BES: J/ψ pπ n ( pπ + n ) N (1440)? N (1520) N (1535) N (1650) N (1675) N (1680)? Possible new state M = 2065 ± MeV/c2 Γ = 175 ± 12 ± 40 MeV/c 2 Prel. PWA favors (hep-ex/ )

19 Strangeness Production K + Λ K + Σ 0 Models developed from fits to Bonn data (SAPHIR) Only reproduce the threshold region

20 Induced Polarization of the Λ and Σ 0 Hyperon CLAS results consistent with some older data from Bonn

21 Strangeness Production Neither hadrodynamic nor Regge calculations reproduce the magnitudes or the trends seen in the hyperon polarization data Data included in recent coupled-channel analysis (Sarantsev et al.): SAPHIR and CLAS Beam asymmetry data from SPring-8/LEPS for K + Λ Recent π 0 / η data from CB-ELSA New P 11 at 1840 MeV Two D 13 : at 1870 MeV and 2130 MeV (1940)D 33 only contributing to K + Σ 0

22 Recent Results from the CB-ELSA Experiment dσ/dω [µb/sr] CB-ELSA CB-ELSA fit GRAAL CLAS TAPS cosθ cm

23 dσ/dω [µb/sr] CB-ELSA CB-ELSA fit GRAAL CLAS TAPS V. Credé, O. Bartholomy, and The CB-ELSA Collaboration Phys. Rev. Lett. D94, (2005) cosθ cm

24 [µb] σ tot /2 E γ [GeV] /2-5/2 CB ELSA data CB ELSA fit GRAAL CLAS TAPS ρ-ω W [GeV] Hint for N resonance (2070)D 15 (Phys. Rev. Lett. D94, (2005)) Needs confirmation! No need for third S 11 The angular coverage of new data allows determination of the total cross section CB-ELSA Isobar-Model Fit: (Data included) γp pη, γp pπ 0 (CB-ELSA) γp pη (TAPS, low energies) Σ ( γp pη), Σ ( γp pπ 0 ) (GRAAL) Σ ( γp pπ 0 ), σ (γp nπ + ) (SAID)

25 Outline Introduction 1 Introduction 2 What are the problems? The NSTAR 2005 Workshop 3 4

26 Polarization: Single-Meson Production d σ d Ω = σ 0 { 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)} Single-Meson Final States (7 Observables) δ l, δ : Beam Polarization Λ x, Λ y, Λ z : Target Polarization

27 Polarization: 2-Meson Production (π + π, π 0 π 0, π 0 η,...) γn Nππ = γn π Nππ + γn Nρ Nππ, etc. Many possibilities to be included Polarization treated in terms of density matrix for each quasi two-body (QTB) state C est pas très efficace! (W. Roberts) In addition: QTB treatment neglects contributions that are not QTB Interferences may be (largely) ignored Treating process as Nρ, for example, will lead to results (of some kind) Interpretation may not be convincing

28 Polarization: 2-Meson Production (π + π, π 0 π 0, π 0 η,...) γn Nππ = γn π Nππ + γn Nρ Nππ, etc. Many possibilities to be included Polarization treated in terms of density matrix for each quasi two-body (QTB) state C est pas très efficace! (W. Roberts) Direct Calculation (W. Roberts and T. Oed, Phys. Rev. C71, (2005)): I = I 0 { ( 1 + Λ i P ) + δ (I + Λ i P ) + δ l [ sin 2β ( I s + Λ i P s ) cos 2β ( I c + Λ i P c ) ] } Double-Meson Final States (15 Observables)

29 Measurement of I at CLAS 0.3 W = 1.40 GeV W = 1.45 GeV W = 1.50 GeV I I I 0 W = 1.55 GeV W = 1.70 GeV W = 1.60 GeV W = 1.75 GeV W = 1.65 GeV W = 1.80 GeV Only one observable in ππ, I, measured and published (S. Strauch et. al., PRL 95, (2005)) Circularly-polarized beam on unpolarized target Mokeev et al. (solid, dotted) Fix and Arenhövel (dashed) W = 1.90 GeV W = 2.10 GeV W = 2.30 GeV I φ (deg) φ (deg) φ (deg)

30 Polarization Experiments in 2006 CLAS, JLab GRAAL Crystal Barrel, Bonn Crystal Ball, Mainz

31 The FROST Program at CLAS Search for Missing Nucleon Resonances in the Photoproduction of Hyperons using Polarized Photon Beam and Polarized Target Pion Production From a Polarized Target Helicity Structure of Pion Photoproduction Measurement of Polarization Observables in η Photoproduction + Measurement of π + π Photoproduction in Double-Polarization Experiments (to be submitted to PAC 29 next Monday)

32 Model Calculations of P y (new) by W. Roberts 0.3 φ 0, φ = 0.56 rad, φ = 2.09 rad, φ π γ p p π + π W = 2 GeV Invariant pπ + mass [GeV/c 2 ] Circ. Beam Trans. Target (target pol. reaction plane) D 13 (1520) π g 1 = (solid) g 2 = g 1 = 0 (dot-dashed) g 2 = 0 (dashed)

33 Model Calculations of P s z (known as G) by W. Roberts φ 0, φ = 0.56 rad, φ = 2.09 rad, φ π γ p p π + π W = 2 GeV Lin. Beam Long. Target D 13 (1520) π g 1 = (solid) g 2 = g 1 = 0 (dot-dashed) g 2 = 0 (dashed) Invariant pπ + mass [GeV/c 2 ]

34 Model Calculations of P c z (new) by W. Roberts φ 0, φ = 0.56 rad, φ = 2.09 rad, φ π γ p p π + π Lin. Beam Long. Target W = 2 GeV D 13 (1520) π g 1 = (solid) g 2 = g 1 = 0 (dot-dashed) g 2 = 0 (dashed) Invariant pπ + mass [GeV/c 2 ]

35 The CB-ELSA Polarization Program

36 The CB-ELSA Polarization Program (E γ 3.0 GeV) Advantage: Very good Neutral-Particle Detection Proposals submitted to ELSA/MAMI PAC-05/September ELSA/ G in single π 0 and η production 2. ELSA/ Helicity Dependence in Single π 0 /η Production 3. ELSA/ Σ and G in η photoproduction off Neutron 4. ELSA/ Beam-Target Asymmetries in ω Photoproduction 5. ELSA/ Meson-Nucleus Bound States 6. ELSA/ Double Polarization in 2π 0 Photoproduction 7. ELSA/ Helicity Difference in π 0 η Photoproduction

37 Sensitivity of Observable P z (or E) to Resonances Best Solution No N(2100)P Mηp (GeV) Mπp (GeV) Mηπ (GeV) No (1940)D Mass Region: MeV/c CosΘ(π) CosΘ(η) CosΘ(p) Effects are big...

38 3000 U. Löhring, B.C. Metsch and H.R. Petry, Eur. Phys. J. A10, (2001) Mass [MeV] * 1920 * * * * too low in mass 2350 * * * * Bonn model: residual short-range interaction based on instanton-induced forces J π 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- P31 P 33 F 35 F 37 H 39 H 3 11 K 3 13 K 3 15 S 31 D 33 D 35 G 37 G 39 I 3 11 I 3 13 L 2T 2J

39 Combined Analysis: CLAS and Crystal Barrel For example: γ p p π + π at CLAS Not Competitors Complementary γ p p π 0 π 0 at CB-ELSA

40 Fruitful Discussions at NSTAR 2005 in Tallahassee!

41 Next NSTAR Workshop: Bonn, Germany in 2007!