Baryon spectroscopy with polarization observables from CLAS
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1 Baryon spectroscopy with polarization observables from CLAS 1. Unpolarized target 2. Polarized proton target (FROST) 3. Polarized neutron target (HDice) 4. CLAS 12 Forward Tagger Steffen Strauch for the CLAS Collaboration University of South Carolina Supported in parts by the U.S. National Science Foundation: NSF PHY Nucleon Resonances: From Photoproduction to High Photon Virtualities, ECT*, Trento, Italy, October 12-16, 215
2 Relevant degrees of freedom and missing resonance problem N Resonance Spectrum the low-energy signature of QCD 3 Degrees of freedom B M Mass [MeV] * S 19 ** ** ** *** **** **** 144 **** 222 **** 27 ** * ** S S *** **** **** **** 22 ** 1675 **** 219 **** 225 **** 26 *** Quark Models 1 J π L Constituent Quark Models predict many more of excited states than have been observed; some of the states may only couple weakly to πn. Quark-Diquark Models predict fewer states. Quark and Flux-Tube Models predict increased number of states. CQM: U. Löring, B.C. Metsch, and H.R. Petry, Eur. Phys. J. A1 395 (21) 2T 2J 939 **** 3* or 4* 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- P11 P13 F15 F17 H19 H1 11 K1 13 S11 D13 D15 G17 G19 I1 11 I1 13 2
3 Resonance spectrum in Lattice QCD Hadron spectrum collaboration N(938) Δ(1232) 1 1 m π = 396 MeV.6 LQCD predicts states with the same quantum numbers as CQMs with underlying SU(6) x O(3) symmetry; more states than have been identified experimentally. R.G. Edwards, J.J. Dudek, D.G. Richards, and S.J. Wallace, Phys. Rev. D 84, 7458 (211) 3
4 Extracting nucleon-resonance information from experimental data Extraction of physics Models Data Reaction Theory N*, Δ* QCD Cross sections and polarization observables Amplitude Analysis LQCD Coupled-channel analysis especially important Nucleon resonance information: mass, spin, parity, coupling constants, decay parameters, 4
5 What we measure with CLAS Proton target Neutron target γ p π p, π + n γ p ηp, η p γ p KY (K + Λ,K + Σ,K Σ + ) γ p π + π p, ω p, ρ p, φ p γ n π p γ n π + π n γ n Σ K +,ΛK e.g. CLAS frozen spin target (FROST) e.g. unpolarized deuterium target (g13), polarized HD-Ice target (g14) Cross section and polarization observables Unpolarized, circularly polarized, linearly polarized beam Unpolarized, longitudinally polarized, transversally polarized target Recoil polarization (asymmetry in the weak decay of the hyperon) 5
6 Observables in pseudoscalar meson photoproduction 4 complex amplitudes 16 possible (not independent) observables double pion photoproduction fills empty cells in the table Target Recoil Target + Recoil Beam x y z x x x y y y z z z x y z x y z x y z x y z unpolarized dσ T P T x L x Σ T z L z P L γ sin(2φ γ ) H G O x O z C z E F -C x - P L γ cos(2φ γ ) Σ -P -T -L x T z -dσ L x -T x circular P c γ dσ F -E C x C z -O z G -H O x coherent and incoherent Bremsstrahlung e.g, FROST and HDice e.g, Hyperon weak decay A.M. Sandorfi, S. Hoblit, H. Kamano and T.-S.H. Lee, J. Phys. G, Nucl. Part. Phys. 38, 531 (211) 6
7 CEBAF Large Acceptance Spectrometer in Hall B ( ) Polarized electron beam Energies up to E e = 6 GeV (now up to 11 GeV) CEBAF Large Acceptance Spectrometer (CLAS) Photon Tagger E γ = E e E e Target unpolarized p or d, polarized FROST, HDice B.A. Mecking et al., Nucl. Instr. and Meth. A 53, 513 (23). 7
8 Beam asymmetry Σ for π + and π photo production on the proton! γ p π p dσ dω = dσ dω ( 1 P γ L Σ cos(2ϕ γ )) high-energy π data: 194 MeV < W < 291 MeV γ p π θ cm π p Models: SAID DU13 (CM12), MAID7, BG211-2 Largest changes from previous fits are for well known Δ(17)3/2 - and Δ(195)5/2 + states. θ (deg) M. Dugger et. al (CLAS Collaboration), Phys. Rev. C88, 6523 (213) 8
9 Polarization Transfer Observables C x, C z! γ p K +! Λ C x ( ), C z ( ) for K + Λ channel with N(19)P 13 Bonn-Gatchina coupled-channel isobar model: N(19)P 13 needed in PWA of Nikonov et al. Strongest contributions to γp KΛ: S 11 -wave, P 13 (172), P 13 (19), P 11 (184) without N(19)P 13 State confirmed in more recent analyses. N(19)P 13 found in qqq models, not expected in quark-diquark models. CLAS Data: R. Bradford, et al., Phys. Rev. C 75, 3525 (27). Analysis: V.A. Nikonov et al., Phys. Lett. B 662, 245 (28) 9
10 Recoil Polarization P γ p K +! Λ Kaon-MAID model (green) Single-channel BW resonance fits No longer up-to-date F.X. Lee et al., Nucl. Phys. A695, 237 (21) Bonn-Gatchina model (blue) Multi-channel, unitary, BW resonance fit Large suite of N* contributions Was not predictive for recoil polarization BnGa: A.V. Sarantsev et al., Eur. Phys. J., A 25, 441 (25). Data: M. McCracken et al, (CLAS) Phys. Rev. C 81, 2521 (21). R. Schumacher, CIPANP Vail 215 1
11 Hyperon photoproduction with linearly polarized photons 17 MeV < W < 22 MeV Self-analyzing weak hyperon decay gives access to recoil polarization.! γ p K +! Λ dσ dω = dσ dω unpol (1 P L γ Σ cos(2ϕ γ ) +P R x' P γ L O x' sin(2ϕ γ ) +P R y' P P γ L T cos(2ϕ γ ) P R z' P γ L O z' sin(2ϕ γ ) ) W (GeV)! γ p K + Σ Simultaneous fit to five polarization observables: Σ, P, T, O x, and O z. prelim. CLAS g8 data g8 analysis: Dave Ireland (U. of Glasgow) W (GeV) 11
12 The FROST Target Target: Frozen beads of butanol (C 4 H 9 OH) at 5 mk Thermal equilibrium polarization of a spin-1/2 particle Polarization electron proton DNP P = tanh µb 2kT superconducting holding coils (.5 T) transverse polarization (g9b) longitudinal polarization (g9a) Temperature (K) B = 5 T 2 1 Through dynamic nuclear polarization the high electron polarization is transferred to the proton spin system via microwave induced transitions. FROST Target: C.D. Keith et al., Nucl. Instrum. and Methods A 684, 27 (212) 12
13 The simple idea of the experiment! γ! p π + n Measure polarized free-proton and unpolarized bound-nucleon yield off butanol. Measure simultaneously unpolarized bound-nucleon yield off 12 C target. Determine the polarized proton yield in the difference. N p N B α N C Butanol 12 C CH 2 Data analysis in 9 bins W = MeV.9 cos(θ cm π ) +.9 ΔW = 2 MeV, n cosθ = 3 γ p π + X S.S. et al. (CLAS Collaboration), PLB 75, 53 (215) 13
14 Double Polarization Observable E in π + n dσ dω = dσ dω ( 1 P z P E) W = MeV.9 cos(θ π cm ) +.9! γ! p π + n W = 1.65 GeV W = 1.92 GeV W = 2.17 GeV E E W = GeV SAID ST14 Juelich14 BnGa11E W = GeV SAID ST14E Juelich14E BnGa14E W = GeV W = GeV W = GeV W = GeV before after cm cos(θ ) π cm cos(θ ) π cm cos(θ ) Partial Wave Analyses Good overall description after fit, however, not with identical results. S.S. et al. (CLAS Collaboration), PLB 75, 53 (215) π 14
15 Is chiral symmetry effectively restored in highly excited mesons and baryons? An important consequence of the spontaneous breaking of the chiral symmetry is the large mass gap between chiral partners: a 1 (126) J p = 1 + N*(1535) J p = 1/2-5 MeV 6 MeV ρ(77) J p = 1 - N(938) J p = 1/2 + Mesons and baryons at higher masses are often observed in parity doublets. Example: four positive-parity and four negative-parity resonances at about 19 MeV Δ(191)1/ 2 + Δ(192)3 / 2 + Δ(195)5 / 2 + Δ(195)7 / 2 + (****) Δ(19)1/ 2 Δ(194)3 / 2 Δ(193)5 / 2 Δ(22)7 / 2 (*) A.V. Anisovich et al., arxiv: [nucl-ex] 15
16 New evidence forδ(22)7/2 - resonance BnGa analysis of CLAS and CBELSA/TAPS data Parity partner of Δ(195)7/2 + is poorly known. Δ(195)7/2+ **** Δ(22)7/2 - * E FROST π + data /2 + 2 total 7/2 2 p 2 + n Evidence found for (22)7/2 in a preliminary analysis of the Bonn/Gatchina group. E 2227 χ 2 increase K p M(Δ7/2 - ) 218 MeV 1 os θ cos θ 2 2 p 5 5 and not 195 MeV. Chiral symmetry is not restored in high-mass hadrons. with Δ(22)7/2 - without A.V. Anisovich et al., arxiv: [nucl-ex] M, MeV 7/2 + 7/2-16
17 All isospin channels are important to constrain coupled-channel analyses: two examples for π p! γ! p π p dσ dω = dσ dω { 1+ P y T + P x P F} y γ x z θ cm π y γ x z θ cm π T T 1. p p Polarized target (left/right) transverse polarized target F F 1. p p Polarized beam and target (up/down) W = 1.87 GeV CLAS preliminary SN11 MAID27 BG211-2 W = 1.87 GeV cosθ (π ) CLAS preliminary SN11 MAID27 BG cosθ (π ) g9 analysis: Hao Jiang (USC) 17
18 Helicity asymmetry E in eta photoproduction on the proton! γ p! ηp η photoproduction isolates N*(I=1/2) states in the resonance spectrum. E 1.5 <-.8-1.<cosθ cm 1.5 E(W) -.8<cosθ cm <-.4 Narrow structure seen in MAMI γp ηp cross section data. [predicted in πn PWA: Phys. Rev. C 69, 3528 (24)] E Juelich 214 (fit) 1.5 <. -.4<cosθ cm.<cosθ cm <.4 Present CLAS E data do not demand the presence of a narrow resonance with a width of 4 MeV or less at about 1.7 GeV W (MeV) W (MeV) I. Senderovich et al. (CLAS Collaboration), arxiv: [nucl-ex] 18
19 Hyperon photoproduction FROST data for Λ, Σ photoprouction F 1.7 < W < 1.8 GeV 1.8 < W < 1.85 GeV! γ p! K + Σ 1.85 < W < 1.9 GeV First measurement of the polarization observable F up to 2.3 GeV. 1.9 < W < 1.85 GeV 1.85 < W < 2. GeV 2. < W < 2.5 GeV γ y x z θ cm p K < W < 2.1 GeV 2.1 < W < 2.15 GeV 2.15 < W < 2.2 GeV Σ CLAS g9b preliminary RPR-Ghent KAON-MAID Bonn-Gatchina g9 analysis: Natalie Walford (CUA, now Basel) 2.2 < W < 2.3 GeV no sufficient previous constraints exist; all models fail to describe the data. 19
20 Double-pion photoproduction as a tool in the study of excited nucleons Nππ is a dominant decay channel of highly excited nucleons. Example: circularly polarized beam π + transversely polarized target Essential part in coupledchannel calculations. x φ θ θ cm z p α Allows for the study of sequential decays. k p' π γ p N * πδ γ p N * ρ p d 5 σ dm(π + π * ) dω π + d cosθ 2
21 Parity conservation yields to symmetry properties of observables γ p π + π p λ M γ λn λ N (θ,θ 1,φ 1 ) = ( 1) λ γ λ N + λ N M λn λ γ (θ,θ 1,2π φ 1 ) λ N circularly polarized photons - transversely polarized target I I φ* [degrees] odd observables: do not exist in single meson final states. even observables: P y and P x correspond to T and F, respectively. g9 analysis: Aneta Net (USC) P x P y φ* [degrees].1 P x P y φ* [degrees] P x P y φ* [degrees] P x P y φ* [degrees] 21
22 Preliminary results (g9a) for P c z γ p π + π p { I = I 1+ Λ z P z + β x k p' ( ) +δ l sin2β I s + Λ z P z s ( )} +δ l cos2β I c + Λ z P z c π + φ θ θ cm z π p Polarization Observable P c z P c z W = 1.46 MeV to W = 2.3 GeV Effective Lagrangian Model (A. Fix) Exchange mesons, π,ρ,σ, and resonances, Δ(1232), N*(144), N*(152), N*(1535), Δ(162), N*(1675), N*(168), Δ(17), N*(172), Nucleon and Delta Born terms; Resonance terms: π π A. Fix and H. Arenhövel, Eur. Phys. J. A 25, 115 (25); Preliminary data: Yuqing Mao (USC) Yuqing Mao (USC) N* N* N* ρ φ* (deg) π π σ π π 22
23 Preliminary results (g9b) for P x and P y γ p π + π p 11 MeV < Eγ < 12 MeV I = I ( 1+ Λcos(α )P x +Λsin(α )P y ) -1.< cos(θ π +) < < cos(θ π +) < < cos(θ π +) < < cos(θ π +) < < cos(θ π +) <-. π + x φ θ θ cm z p α.< cos(θ π +) <.2.2< cos(θ π +) <.4.4< cos(θ π +) <.6.6< cos(θ π +) <.8.8< cos(θ π +) <1. k p' π -1.< cos(θ π +) < < cos(θ π +) < < cos(θ π +) < < cos(θ π +) < < cos(θ π +) <-. Data binned in Eγ, Φ*, and cos θ*, fit with Fourier series. g9 analysis: Priyashree Roy (FSU).< cos(θ π +) <.2.2< cos(θ π +) <.4.4< cos(θ π +) <.6.6< cos(θ π +) <.8.8< cos(θ π +) <1. 23
24 Intermediate Δ(1232) Resonance γ p π + π p Example of sequential decays γ p N * πδ N(152) π + (1232) a Fourier coefficients of the angular distribution I = a k sin(kφ) N(152) π Δ ++ pππ N(152) π + Δ pππ.5 W = 1.52 GeV W = 1.52 GeV.25 a π.1.1 p = N(938) a 2 a M(pπ + ) (GeV) M(pπ - ) (GeV) CLAS Data: S.S. et al (CLAS Collaboration), Phys. Rev. Lett 95, 1623 (25); Model: A. Fix and H. Arenhövel, Eur. Phys. J. A 25, 115 (25) 24
25 Beam and target asymmetries in omega photoproduction (g9b) γ p ω p Σ FROST (g9b-linear) GRAAL (213) GRAAL (26) E: 115 MeV Preliminary E: 135 MeV Beam asymmetry c.m. Θ ω E: 125 MeV E: 145 MeV T.8 E γ : 125 MeV E γ : 135 MeV -.8 E γ : 165 MeV E γ : 175 MeV -.8 E γ : 25 MeV Target asymmetry E γ : 215 MeV E γ : 145 MeV E γ : 185 MeV E γ : 225 MeV E γ : 155 MeV E γ : 195 MeV E γ : 235 MeV Preliminary c.m. cos(θ ω ) g9 analysis: Priyashree Roy (FSU) 25
26 All isospin channels are important to constrain coupled-channel analyses Beam-Target helicity asymmetry (observable E) for proton and neutron targets! γ! p π + n! γ! n(p) π p(p) W = 188 MeV W = 19 MeV PWA solutions (already outdated) show need to measure all isospin channels. g14 analysis: Tsuneo Kageya (Jlab) Figs. A.M. Sandorfi, Spin 214 Symposium 26
27 Double pion beam-helicity asymmetry for proton and neutron targets γ p π + π p γ p(n) π + π p(n) γ n(p) π + π n(p) I I φ * (rad) preliminary Integrated I o asymmetries off proton and neutron targets are comparable. φ * (rad) preliminary g14 analysis: Peng Peng (UVa) 27
28 CLAS 12 Forward Tagger Small angle e- scattering (2.5o to 5o) Eγ = GeV.1 (GeV/c)2 < Q2 <.3 (GeV/c)2 virtual photon, (almost) real photon Quasi real photons are linearly polarized wrt to scattering plane High luminosity Forward Tagger Calorimeter CLAS12 e Tracker HTCC Moller cup e γ N e- beam Scintillation Hodoscope Moller Shield CAD implementation Fig. from M.Battaglieri, ECT* Workshop Lattice QCD and hadronic physics (214) 28
29 Quasi-Real Photoproduction with CLAS12 Baryon Spectroscopy E A - Cascade, γp K + K + Ξ - (millions of reconstructed Ξ) - Omega, γp K + K + K Ω - (4, reconstructed Ω) LOI Search for Hybrid Baryons (focus on lowest mass hybrid baryons) ) 2 Counts/(5 MeV/c Ξ γ p K + K + X present CLAS data Ξ (153) MM(K K ) (GeV/c ) L. Guo et al., Phys. Rev. C 76, 2528 (27) L. Guo et al., Jefferson Lab Experiment E A, Photoproduction of the Very Strangest Baryons on a Proton Target in CLAS12 V. Burkert et al., Jefferson Lab LOI , Search for Hybrid Baryons with CLAS12 in Hall B" 29
30 Summary and outlook New CLAS polarized photoproduction data off polarized and unpolarized, proton and neutron targets contribute to complete or nearly complete experiments. Evidence of new states found in coupled-channel analyses. Large impact expected as data analyses are being finalized. PDG baryon summary table for N* resonances future future updates Table adapted from: V. Crede and W. Roberts, Rep. Prog. Phys. 76 (213)
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