Precision Studies of Light Mesons with COMPASS Bernhard
Precision Studies of Light Mesons with COMPASS Bernhard Ketzer Technische Universität München for the COMPASS Collaboration XV International Conference on Hadron Spectroscopy Nara, Japan 5 November 2013
Light Mesons Quantum numbers: • measured: IG (JPC) • quark model: 2 S+1 LJ S=S 1+S 2 , J=L+S L S 1 S 2 q q
Light Mesons Allowed combinations Quantum numbers: • measured: IG (JPC) • quark model: 2 S+1 LJ S=S 1+S 2 , J=L+S L S 1 S 2 q q
Light Mesons = + Allowed combinations + Molecule / 4 quarks + Hybrids “Forbidden” combinations +. . . Glueballs
Light Mesons
Light Mesons [R. J. Jaffe, PRD 15, 267 )1977]
The COMPASS Experiment Two-stage spectrometer • large angular acceptance • broad kinematical range • ~250000 channels • > 1000 TB/year Muon. Wall SM 2 E/HCAL Muon. Wall SM 1 Target Beam [COMPASS, P. Abbon et al. , NIM A 577, 455 (2007)] 50 m E/HCAL Dipole magnets Tracking detectors RICH El. -mag. calorimeter Hadronic calorimeter Muon identification
The COMPASS Experiment Talks by M. Krämer, S. Huber (Fri, l 8 -4) Talks by T. Schlüter S. Uhl Central production: • Scalar states • Glueballs A. Austregesilo, (Tue, l 4 -3)
3 p Final State - Kinematics
3 p Final State - Kinematics
Isobar Model
Isobar Model
2 -D Partial Wave Analysis 1. PWA of angular distributions in 20 Me. V mass bins and 11 t’ bins • • 80 waves with positive reflectivity 7 waves with negative reflectivity Flat wave added incoherently Well-known states as isobars
2 -D Partial Wave Analysis 1. PWA of angular distributions in 20 Me. V mass bins and 11 t’ bins not used
2 -D Partial Wave Analysis 1. PWA of angular distributions in 20 Me. V mass bins and 11 t’ bins 2. Mass-dependent c 2 fit to spin density matrix from step 1 • 6 waves • Parameterized by Breit-Wigner • Coherent non-resonant background • Waves included: 21 distributions x 100 mass bins x 11 t’ bins, 352 free parameters
Fit of Spin-Density Matrix Intensities
Fit of Spin-Density Matrix Intensities
1++0+ r(770)p S Incoherent sum
1++0+ r(770)p S Incoherent sum
New a 1 - 1++0+ f 0(980)p P Incoherent sum
New a 1(1420) - Phase Differences fit range
Results of Fit to Spin-Density Matrix • precise determination of resonance parameters • mass and width ranges from systematic studies with different fit models • final result and syst. error still under study
(pp)S Wave Systematic study: • New a 1(1420) couples exclusively to f 0(980) • Influence of isobar parameterization? Ambiguities? Artefact? Goal: • Determine dynamics of isobars with from data • Obtain model-independent isobar amplitude
Correlation m 3 p vs m 2 p
(pp)S Amplitude in 0 -+0+ (pp)Sp S Intens.
(pp)S Amplitude in 1++0+ (pp)Sp P Intens.
State of the Art Lattice QCD ? [J. Dudek et al. , Hadron Spectrum Collaboration, Phys. Rev. D 83, 111502 (2011)]
Primakoff Reactions ] radiative widths of resonances
Radiative Widths of a 2 and p 2 [Rosner 1981] [Aznauryan 1988] [Ishida 1989, Maeda 2013] [Maeda 2013] [E. N. May et al. , PRD 16, 1983 (1977)] [S. Cihangir et al. , PLB 117, 119 (1982)] [V. V. Molchanov et al. , PLB 521, 171 (2001)]
Extraction of Radiative Widths Primakoff production and decay of broad resonance (mass m 0, spin J): Radiative width: Integrate differential cross section: Experiment: determine Primakoff cross section
Radiative Widths COMPASS results (preliminary): First measurement!
Pion Polarizabilities Chiral PT prediction: [Gasser et al. , Nucl. Phys. B 745, 84 (2006)] LO NNLO
Pion Polarizabilities Chiral PT prediction: [Gasser et al. , Nucl. Phys. B 745, 84 (2006)] LO NNLO Experiments: p Compton scattering PLUTO DM 1 DM 2 Mark II Lebedev Mami A 2 Serpukhov
Pion Polarizabilities Chiral PT prediction: [Gasser et al. , Nucl. Phys. B 745, 84 (2006)] LO NNLO Experiments: p Compton scattering PLUTO DM 1 DM 2 Mark II Exp Lebedev Mami A 2 Serpukhov COMPASS
Measurement at COMPASS
Polarizability Results COMPASS preliminary result:
Polarizability Results COMPASS preliminary result:
Conclusions
Conclusions II
Conclusions III More results to come in the near future…
- Slides: 41