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Hadron Spectroscopy at COMPASS

Hadron Spectroscopy at COMPASS. Stephan Paul Technische Universit ät München Hadron09. Overview. Introduction Physics COMPASS Analysis Diffraction from pions 3 p 5 p hp Central production from pions KK hh 4 p Diffraction from protons Baryon spectroscopy

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Hadron Spectroscopy at COMPASS

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  1. Hadron Spectroscopyat COMPASS Stephan Paul Technische Universität München Hadron09

  2. Overview • Introduction • Physics • COMPASS • Analysis • Diffractionfrom pions • 3 p • 5 p • hp • Central production from pions • KK • hh • 4 p • Diffractionfrom protons • Baryon spectroscopy • Central production from protons • Meson spectroscopy • Primakoff • p- Polarizability, -anomaly, p0 lifetime, radiative width Parallel sessions M. Neubert, F. Nerling M. Neubert T. Schlüter T. Schlüter T. Schlüter J. Bernhard T. Nagel

  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 • > 800 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. 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 + ... Dynamics

  9. 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)]

  10. 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

  11. 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

  12. Diffractive Reactions at COMPASS ‘04 Example: • 4p vertex in Pb target • Exclusivity  target stays intact • Momentum transfer pa pc Diffraction on nucleons Diffraction on Pb nuclei

  13. Invariant Mass of 3p System ‘04 • 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)

  14. 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)

  15. 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

  16. p1(1600) • BW parameters for p1(1600) • Leakage negligible arXiv:0910.5842 p2(1670) see talk by S. Neubert

  17. p1(1600) • BW parameters for p1(1600) • Leakage negligible a1(1260) see talk by S. Neubert

  18. COMPASS in 2008

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

  20. COMPASS in 2008

  21. p-p+p- in 2008 • 190 GeV/c hadron beam • Target: 40cm liquid hydrogen p-p p-p+p- p • Diffractive dissociation: 96% p-, 3.5% K-, 0.5% p • p-p  p1(1600) p, p1(1600)  3p: 200000 events exp. • >200 times statistics of 2004 data • PWA has started • ! High statistics requires perfect understanding of physics • Deck effect (under study) • Up to date parametrization of pp scattering • First result: compare production on proton and lead • ! m-population is different: Pb prefers higher m values  Very Preliminary Dalitz plot around p2(1670) see talk by S. Neubert

  22. 3p final state p-p p-p0p0p • Isospin partner to p-p p-p+p-p • Consistency check • Different isobars in decay chain • Isospin information • Use a2 : normalization • Example: a1 • For further examples see talk by F. Nerling a2r a1r see talk by F. Nerling

  23. (Central) production p-p p-hhp • Search for exotics - e.g. p(1400)  p-h • Seen by E852 exp. in 1997 p-pp-hpat 18 GeV/c • Confirmed by CBAR exp. in 1998 in pd → p-hp0pspectator. • Questioned by Dzierba et al.in 2003in p-pp0h n at18GeV/c • Diffractive production: _

  24. (Central) production p-p p-hhp • Search for glueballs - e.g. f0(1500)  hh • So far: h  gg • Central Production assumed: • Structure consistent with f0(1500) observed • > 10 times statistics of WA102 WA102 common h-decays Entries/40 [MeV]

  25. Multi p final states p-p p-p+p-p+p-p • Access mX > 2 GeV/c2 • Understand mass range mX [1.6-2] GeV/c2 • Start with existing observations • Study p1 (1600) • Study p(1800) • Use high mass isobars • b1, f1, h´, r(1450)….. • Combinatorics is huge • Model dependence to be investigated • PWA being started – high statistics see talk by S. Neubert

  26. Central production p-p p-p+p-p+p-p Search for scalar and tensorglueballs (f0 and f2family) • WA102: f0(1370), f0 (1500), f0 (2000) and f2(1950) • Complete exclusive kinematics selected • Select (p-)fastp+p-p+p-(pslow) • Compass has ~100 times stastistics of WA102 • WA102: pp collisions only • COMPASS : pp and pp collisions fast p- central p-p+p-p+ ~10% of pp data WA102 see talk by J. Bernhard

  27. Strangeness in final states pp pKKp • Search for hidden strangeness • Neutral and charged kaon channels • High mass isobars observed cleanly • Glueball search decaying into KK • Hybrids decaying into KKp • Information on nature of states • branching fraction • decay chain • PWA being prepared K+K-p vs K+K- K+K-p vs K+p- see talk by T. Schlüter

  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 (DPE) not clearly separable from simple Reggeon exchange • 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. 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 Analysis formalism being developed

  31. Conclusions • COMPASS hasstartedspectroscopyprogram • Tools developed • More refined PWA analysisunderway : • larger waveset, Deck effect, parallelization • VERY highstatistics (partly > 200 timespreviouswork) • Results: • Observeconsistentsignal on exoticp1(1600) using large waveset in diffraction (3p) • Nucleardependenceofproductioncharacteristics (moredata 2009) • Neutral channelsshowconsistentsignals (nofull PWA yet) p-p0p0 • 5panalysisongoing(complexanalysis) • Central productionanalysis in 4punderway • Central productionanalysis in kaonicchannelsunderwayf0(1500) • Rich structureobservedathighmasses (M> 2 GeV) in many FS • Baryon spectroscopymaybeadd on • Analysis future:adresshighmassregion

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