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The light meson spectroscopy program

The light meson spectroscopy program . Landscape Experiments BES III (J/ y decays) COMPASS ( p − beam) CLAS ( g beam) Outlook. Elton S. Smith, Jefferson Lab 13 th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon. Light Mesons. q. q. q. q. q.

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The light meson spectroscopy program

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  1. The light meson spectroscopy program • Landscape • Experiments • BES III (J/y decays) • COMPASS (p− beam) • CLAS (g beam) • Outlook Elton S. Smith, Jefferson Lab 13th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon

  2. Light Mesons q q q q q q q q • Quark model mesons (u, d, s quarks) • Glueballs (gluons and no quarks) • Multiquarks (quark-antiquark pairs) • Hybrids (quarks and gluons, which contribute to static properties) Call these the “ABC” states KlemptZaitsev Phys Rep 454 (2007) 1

  3. Normal Mesons – qq color singlet bound states K* w r f K* K0 JPC = 0– +0++1– – 1+ –2++ … Allowed combinations JPC = 0– –0+ –1– +2+ – … Not-allowed: exotic Spin/angular momentum configurations & radial excitations generate the known spectrum of light quark mesons. Starting with u - d - s we expect to find mesons grouped in nonets - each characterized by a given J, P and C. Spin 0 Spin 1 S2 S = S1 + S2 J = L + S P = - (-1)L C = (-1)L+S K0 K+ S1 L h’ p0 p+ p− h K−

  4. Nonets of Scalar (0++) Mesons q q q q I3 Jaffe Phys Rev D15 (1977) 267 Crede Meyer Prog Part NuclPhy 63 (2009) 74

  5. BESIII: e+e- in the charmonium region Operating since 2008, √s = 2 − 4.2 GeV Wei Moriond QCD and High Energy Interactions 2013

  6. BES III: pp mass threshold enhancement M ~ 1.83-1.86 GeV Confirmation of enhancement first observed by BES II • Possible interpretations • Conventional meson • ppbar bound state / multi-quark • glueball Chinese Phys C 34 (2010) 421

  7. BES III: pp mass threshold PWA • Breit-Wigner and S-wave FSI describes structure • M = 1832 ± 19 MeV • G = 13 ± 39 MeV • Spin-parity of 0-+ strongly favored by PWA fit Ablikim PRL 108 (2012) 112003 Chinese Phys C 34 (2010) 421

  8. BES III: X(1835) structures in J/y->gh’p+p- • X(1835) • M = 1837 ± 3 MeV • G = 190 ± 9 MeV • X(2120) • M = 2122 ± 7 MeV • G = 83 ± 16 MeV • X(2370) • M = 2376 ± 9 MeV • G = 83 ± 17 MeV • Angular distribution of X(1835) consistent with 0-+ assignment • Pure glue lattice expects lowest 0-+ glueball mass ~ 2.5 GeV Ablikim PRL 106 (2011) 072002

  9. BES III: X(1870) in J/y->wX, X->hp+p- w X(1870) h(1405) f1(1285) • X(1870) • M = 1877 ± 6 MeV • G = 57 ± 12 MeV • X-> a0(980)p, a0->hp • Identification of X(1870)? • Spin-parity 0-+? • Is it the X(1835)? h2(1870)? • Need PWA! Ablikim PRL 107 (2011) 182001

  10. BES III: Summary and prospects • Huge data samples collected for charmonium decays at BES III • Data based on 200 M J/y events • Confirms of the ppbar mass threshold enhancement at 1832 MeV • Confirms of the X(1835)->h’p+p- and finds two new structures: X(2120) and X(2370) • Observes the new structure X(1870) in J/y -> wX(hp+p-) • 1.2 billion J/y and 500 million y events already collected • Expect rich physics results in the coming years from BES III

  11. Spectrum of 1−+ exotic signals q q q q Expectation from LQCD Unlikely Hybrid Dynamical origin? I3 Meyer Van Haarlem Phys Rev C82 (2010) 025208

  12. COMPASS: spectroscopy with pion beams Hadron Setup 2008/09 190 GeV 2004 Pilot Run (4 days 190 GeV, Pbtgt, p-) 2008/09 (high statistics, 190 GeV, LH2 tgt, p±, K±, p±) Courtesy of F. Nerling

  13. COMPASS: Exotic 1-+p1(1600)->p+p-p- ~0.4 M events Intensity =1.7% of total

  14. Amplitude analysis 3psystem in isobar model p (bachelor) 1 L pa Rpp spin S 2 pb The decay of the 3p system at point 1 to the di-pion resonance Rppand a bachelor pion is described in the Gottfried-Jackson frame. The decay of Rpp→ papb at point 2 is described in the helicity frame. Hybrid JPCMe g(beam) e = + natural e = − unnatural parity exchange n(recoil) p (target) Partial waves (in the reflectivity basis): JPCMe[isobar] L

  15. Toy example: resonant phases 2 waves Phase motion Black –Blue

  16. COMPASS: Diffractive dissociation into 3p 38% of 2008 data PWA ~ 1M events PWA ~ 24M events

  17. COMPASS: reproducing known resonances a1(1260)->(pp)sp Intensity Acceptance corrected 53 waves included Phase motion

  18. COMPASS: reference and exotic signals 1-+ Exotic Mass (GeV) Intensity Acceptance corrected 53 waves included Phase motion

  19. COMPASS: Primakoff production of p+p-p- 1-+ Exotic t’ < 0.001 GeV2 • No intensity exotic 1-+ wave near 1.6 GeV • Pilot run for Primakoff reaction, t’ < 0.001 GeV2 • Photoproduction in the Coulomb field of heavy nucleus Grube CLAS12 Workshop, Glasgow

  20. COMPASS: Summary and prospects • Diffractive production of 3p states • Analysis of 50x statistics of initial pilot run • Results for p1(1600)-> p-p-p+ and p1(1600)->p-p0p0 • Confirmation of exotic state • Ongoing analysis • Pilot Primakoff data sees no exotic in quasi-photoproduction • Exotic signals also seen in hp and h’p channels • Search for p1(2000) in the KKpp final state • COMPASS has acquired large statistics on many reactions • Diffractive dissociation of p, p-, K- on various targets • Central production of (pp) in pp reactions, which can be used for glueball searches. • p-g and K-gPrimakoff reactions on heavy targets

  21. CLAS: Photoproduction at 6 GeV Nozar PRL 102 (2009) 102002 • G12 Data Run Conditions • Ie = 60-65 nA • Eg = 3.584 – 5.453 GeV • 26.2 billion triggers • Integrated luminosity of 68 pb-1

  22. CLAS: PWA extraction of known resonances

  23. CLAS: Small non-resonant 1-+ exotic wave M=1+ and 1- Degenerate waves for unpolarizedg M=0 Expect Zero For pion exchange

  24. CLAS: PWA 1−+ − 2−+ Phase Motion

  25. CLAS: Summary and prospects • No evidence for 1−+exotic resonance in photoproduction • Confirmation of earlier limits with higher sensitivity • Intensity of exotic wave < 2% of total • Phase of exotic wave consistent with non-resonant signal • Other analyses • Study of exotic signal in gp->hp−D++ • Searches for strangeonium in gp->pfh [Spec1: D. Schott] [Future Facilities: R. Mckeown] [P. Eugenio] [L. Elouadrhiri] • GlueX in Hall D at 12 GeV • Commissioning Fall 2014 • Forward Tagger for CLAS12

  26. Summary • The spectrum of “ABC” mesons is being investigated in both collider and fixed target experiments • BES III has identified structures with masses ~ 1.8−2.4 GeV • Their internal structure is under study and may shed light on the nature of gluonic interactions. • The 1−+ exotic p1(1600)->3p is confirmed by COMPASS in p−interactions • Upper limits are set on the1−+ exotic wave in CLAS photoproduction, which are consistent with non-resonant background

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