Exotic Mesons Status and Future Eberhard Klempt HelmholtzInstitut
Exotic Mesons Status and Future Eberhard Klempt Helmholtz-Institut für Strahlen- und Kernphysik Universität Bonn
• Spectroscopy of exotic mesons is at a turning point: • Data analysis of past experiments is completed (E 852 @ BNL, VES @ Protvino, Crystal Barrel/Obelix @LEAR, Ba. Bar, Belle, Cleo, . . ) • New experiments are ahead of us (Compass, Jlab, Panda, …)
• QCD predicts the existence of glueballs and hybrids • It is the task of experiments to identify them and to determine their properties • The existence of glueballs and hybrids is pre – dicted by QCD inspired models and lattice QCD • It is the task of experiments to test if these predictions find their correspondence in Nature
Outline: • • Exotics The p 1(1400) The p 1(1600) The p 1(2000) Nonexotic hybrid candidates Is Y(4260) a hybrid ? Is there a y(2 S)p+ resonance ?
Exotics: -+ : 1 Quantum numbers Exotic quantum numbers of fermion-antifermion 2 s+1 L 1 S 3 S 1 P 3 P 3 P 3 P 0 1 1 0 1 2 J ph (s-wave) JPC ph (p-wave) 0 -+ ph (d-wave) 1 -- a 0 Meson p 1 p a 2 r 1+pr (p-wave) 0++ pf 1 (s-wave) 1++ 2++ pb 1 (s-wave) b 1 p 1 a 0 pa 1 1 p 1 a 2 JPC 0+0 -1 -+ 2+3 -+
Exotics: • Meson-meson scattering: gg + qqg + qqqq + m 1 m 2 + … resonant and non-resonant interactions Exotic waves allowed Example: p p- h p- f 1, … p
p 1(1400) : BNL, VES Resonance fit c 2 = 187 / 147 p p h Background c 2 = 244 / 149
p 1(1400) : Confirmed by Crystal Barrel (LEAR) in pn p-p 0 h Triangle singularity from FSI ?
p 1(1400) : • SU(3): p 1 ph , ph´ Problem: if p 1 member of an octet if p 1 member of a decuplet K + p+ which has no phase motion There must be something wrong ! • This decuplet includes
p 1(1400) : BNL, Crystal Barrel: resonance approach VES: phen. background Indiana: chiral Lagrangian pp ~ ph interactions Crystal Barrel and Obelix found p 1 rp but in a different production reaction. Would need to be an extra state: two mass-degenerate p 1(1400) in 8 and 10.
p 1(1600) : h´p • Observed in h´p, f 1 p, rp, b 1 p • In natural and natural + unnatural parity exchange
p 1(1600) : rp • Controversial results (E 852, Indiana, VES) • Leakage leads to equal-size background for +parity and -parity exchange.
p 1(2000) 1++ 2 -+ 1 -+ Phase (1 -+ - 2 -+) Phase (1 -+ - 1++) Phase (1++ - 2 -+) • 1 -+ wave resonant, if 1++ wave is dominated by resonances: strong model assumption
Exotics • There is evidence that mesons with exotic quantum numbers have been observed. • The evidence is controversial. • The best candidate is p 1(1600) in its h´p and f 1 p decay modes. • Are there non-exotic hybrids ? (2 -+ , 1++)
Non-exotics Parity partners No parity partners for J=L+S
Two h 2 No parity partners Two p 2 for J=L+S One expected One a 1
Non-exotics • Hybrid candidates p 2(1880) and h 2(1870) strong S-wave couplings to a 2 h and f 2 h • No hybrid candidates in 1++ wave In this wave, no strong S-wave couplings. • We need better understanding of S-wave couplings.
Y(4260) • Several surprisingly narrow resonances were discovered in b-factories (Babar, Belle): • X(3872), X(3940), Y(3940), Z(3930) Are they four-quark resonances or cc 1 (2 P), hc (3 S), cc 0 (2 P), cc 2 (2 P) • Y(4260) Ba. Bar Y(4430) Belle ?
• Observed in initial state radiation: e+e- J/y pp hence JPC=1 --. • Large decay to J/y pp • Not seen in e+e- hadrons: small coupling to open charm • Must be exotic (also due to its mass) Y(4260) J/ y y (2 S) X y (1 D) X X y (4040) Y(4260) y(4415) y (2 D) y(3 D)=Y(4340)
Y(4430) • Observed in B > K p+y´ not in K p+y • Contains cc and has I=1 • Must be four-quark • Rosner: rescattering D*(2010) y(2 S) p D 1(2420)
• The new charmonium states may have exotic properties but conventional interpretations are not ruled out.
• QCD on the lattice and QCD inspired models have promissed us that we should find glueballs and hybrids. • In my view, there is no convincing evidence for their existence. • Fresh look: Compass: Pomeron-Regge fusion Jlab: Photoproduction of mesons with linearly polarised photons Panda: Hybrids in D, Ds, cc spectrum ? BES: Glueballs Thank you
Y(3940), X(3872), Z(3930) Y(3940) > J/y w like f 0(1810) > f w
X(3940) 1. 18 Ge. V/c 2 X(4156)
Y(4260) • Decay width for Y(4260) decays into J/y p+p- is much larger than for y(2 S)
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