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Mesons Spectroscopy at COMPASS

Mesons Spectroscopy at COMPASS. Stephan Paul Technische Universit ät München EINN09 Milos. Overview. Introduction Physics COMPASS Analysis Diffraction from pions 3 p 5 p Central production from pions KK hh Diffraction from protons Baryon spectroscopy

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Mesons Spectroscopy at COMPASS

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  1. Mesons Spectroscopyat COMPASS Stephan Paul Technische Universität München EINN09 Milos

  2. Overview • Introduction • Physics • COMPASS • Analysis • Diffractionfrom pions • 3 p • 5 p • Central production from pions • KK • hh • Diffractionfrom protons • Baryon spectroscopy • Central production from protons • Meson spectroscopy • Primakoff • Radiative width

  3. Experimental Tools Deep Inelastic Lepton Scattering and related hard e.m. processes Spectroscopy Processes at low Q2 • Hadron Structure at • Low Energies • Polarizabilities • Chiral anomaly • QCD Bound States • Mass spectrum • Gluonic excitations • Multi-quark systems • Nucleon Structure • Helicity • Transversity • GPDs

  4. Experimental Tools Deep Inelastic Lepton Scattering and related hard e.m. processes Spectroscopy Processes at low Q2 • Hadron Structure at • Low Energies • Polarizabilities • Chiral anomaly • QCD Bound States • Mass spectrum • Gluonic excitations • Multi-quark systems • Nucleon Structure • Helicity • Transversity • GPDs

  5. COMPASS at CERN COmmonMuon and Proton Apparatus for Structure and Spectroscopy LHC SPS • p up to 400 GeV • secondary hadrons (p, K, ...): 2·107/s • tertiary m (polarized): 4·107/s

  6. The COMPASS Experiment MuonWall SM2 E/HCAL E/HCAL SM1 Dipole magnets Tracking detectors RICH El.-mag. calorimeter Hadronic calorimeter Muon identification MuonWall Target RICH Beam • Two-stage spectrometer • large angular acceptance • broad kinematical range • ~250000 channels • > 600 TB/year 50 m [hep-ex/0703049, NIM A 577, 455 (2007)]

  7. The COMPASS Experiment MuonWall SM2 E/HCAL E/HCAL SM1 MuonWall Target RICH Beam • Two-stage spectrometer • large angular acceptance • broad kinematical range • ~250000 channels • > 800 TB/year 50 m • Data taking periods: • 2002-2004: 160 GeV/c m+ • 2004: 2 weeks 190 GeV/c p- • 2006-2007: 160 GeV/c m+ • 2008-2009: 190 GeV/c p,p- [hep-ex/0703049, NIM A 577, 455 (2007)]

  8. The COMPASS Experiment MuonWall SM2 E/HCAL E/HCAL SM1 MuonWall Target RICH Beam • Two-stage spectrometer • large angular acceptance • broad kinematical range • ~250000 channels • > 600 TB/year 50 m • Data taking periods: • 2002-2004: 160 GeV/c m+ • 2004: 2 weeks 190 GeV/c p- • 2006-2007: 160 GeV/c m+ • 2008-2009: 190 GeV/c p,p- [hep-ex/0703049, NIM A 577, 455 (2007)]

  9. Meson Spectroscopy Quark model: bound state of qq Quantum numbers: IG (JPC) P=(-1)l+1, C=(-1)l+s, G=(-1)I+l+s = QCD: other color-neutral configurations with same quantum numbers  mixing + + • Decoupling only possible for • narrow states • vanishing leading qq term • exotic JPC: + Hybrids Glueballs + ...

  10. Glueballs Events / 0.08 GeV M(hh) (GeV) • Lightest glueballs: Quenched L-QCD prediction • Experimental candidate: • f0(1500) (Crystal Barrel, WA102) • JPC = 0++ mixing with isoscalar • mesons! [WA102, Phys. Lett. B479, 59 (2000)  COMPASS [Y. Chen et al., Phys. Rev. D 73, 014516 (2006)]

  11. Hybrids Events / 0.04 GeV/c2 M(3p) (GeV/c2) • Light meson sector exotics JPC=1-+: • p1(1400) (VES, E852, Crystal Barrel) • p1(1600) (E852, VES) • p1(2000) • still controversial... 35 waves 20 waves [S.U. Chung et al., PRD 65, 072001 (2002)] [A.R. Dzierba et al., PRD 73, 072001 (2006)]  COMPASS

  12. Hadron Reactions at COMPASS Two production mechanisms studied in parallel usingproton, pionandkaonprojectiles Central production Diffractive dissociation • Rapidity gap between pslow, hfast, X • Beam particle looses ~10% of its energy • Particles at large angles from X decays • Possible source of glueballs (DPE) • Forward kinematics • Need to separate particles at • very small angles • Study of JPC-exotic mesons

  13. Diffractive Reactions at COMPASS Example: • 4p vertex in Pb target • Exclusivity  target stays intact • Momentum transfer pa pc Diffraction on nucleons Diffraction on Pb nuclei

  14. Invariant Mass of 3p System • COMPASS: pp=190 GeV/c • 4M events in 3 days (full t range) • 450k events in 0.1<t’<1.0 GeV2/c2 • BNL852: pp=18 GeV/c • 250k events  p1(1600)

  15. Invariant Mass of 3p System Acceptance

  16. PWA Technique • high s: t-channel Reggeon exchange • Reflectivity basis in G-J frame • e = h of Regge trajectory • Isobar model 1. Mass-independent PWA of angular distributions in 40 MeV mass bins • Tire production amplitudes - determined by fit • 42 partial wavesi = JPCMe[...]L • [...] = isobar: (pp)S, f0(980), r(770), f2(1270), r3(1690)

  17. Wave Set Included into Fit (Mass independent)

  18. PWA Technique • high s: t-channel Reggeon exchange • Reflectivity basis in G-J frame • e = h of Regge trajectory • Isobar model 1. Mass-independent PWA of angular distributions in 40 MeV mass bins • 2. Mass-dependent c2 fit to results of step 1 • 6 waves • Parameterized by BW (incl. barrier factors and G(m) ) • Coherent background for some waves

  19. Major Waves a1(1260) p2(1670) a2(1320)

  20. p1(1600) • BW parameters for p1(1600) • Leakage negligible

  21. p1(1600) • BW parameters for p1(1600) • Leakage negligible

  22. Summary of Waves Publication submitted to CERN (preprint)and to PRL

  23. COMPASS in 2008

  24. COMPASS in 2008 RPD Ring A RPD Ring B b b

  25. COMPASS in 2008

  26. Statistics in 2008 • 190 GeV/c hadron beam • Target: 40cm liquid hydrogen • Diffractive dissociation: 96% p-, 3.5% K-, 0.5% p • p-p  p1(1600)p, p1(1600)  3p: 120000 events exp.  Very Preliminary

  27. Analysis of 5p • Need to extend study to high masses • Decay of heavy resonances into high mass isobars • Multi pion final states • Complex analysis (106 waves) 5p mass 4p submass

  28. Central Production (KK) • Central production used to search for glue-rich states • WA102 was successful studying f0 mixing scheme • Study central production with mesons and protons • In ideal world: production very similar (except for spin effects) • At COMPASS: Pomeron-Pomeron not clearly separable from Reggeon excange • Mixture of diffraction and central production • Kaons are promising selective final states

  29. Central Production (KK) with 190 GeV/c p K0sK0s K+K-

  30. Central Production (KK) with 190 GeV/c p (part II)

  31. Central production (hh) Glue-rich states expected to couple tohh f0(1500): pp, 4p - hh, hh‘, KK (small) f0(1710): pp - hh, hh‘, KK (large)

  32. Diffractive Baryon Production (pp+p-) • Baryon spectroscopy studied in • pN scattering • gN scattering polarized) • Limitations: • Coupling to photons • Mass range (MN < 2.5 GeV) p p p p Impressions from an analysis COMPASS can reach very high masses About 15% of full statistics Have to acquire expertise for analysis

  33. Conclusions • COMPASS has started spectroscopy program • Tools developed • More refined PWA analysis underway • Deck effect • Unitarity constraints • Results: • Observe consistent signal on exotic p(1600) using large wave set in diffraction • 5p analysis ongoing (complexe analysis) • Central production analysis in kaonic channels underway f0(1500) • Neutral channels show consistent signals (no PWA yet) p-p0p0 • Rich structure observed at high masses (M> 2 GeV) in many FS • Baryon spectroscopymay be add on

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