Exotic Mesons from an experimental perspective S. Olsen 贵州大学 June

M(MeV) J PC DD  (3770)  c1  c2 ’c’c cc X(3940) X(4160) X(3872) Y(3940)  (4040)  (4415)  (4160) Y(4260) Y(4360)  c0 hchc J/  ’’  c2 ’ Z + (4440) Y(4660) Placed here by J PC The XYZ Mesons can’t all be accommodated in the charmonium spectrum

What are they? NA Tornqvist PLB 590, 209 (2004) ES Swanson PLB 598,197 (2004) E Braaten & T Kusunoki PRD (2004) CY Wong PRC 69, (2004) MB Voloshin PLB 579, 316 (2004) F Close & P Page PLB 578,119 (2004) X Liu arXiv … L Maiani et al PRD 71, (2005) T-W Chiu & TH Hsieh PRD 73, (2006) D Ebert et al PLB 634, 214 (2006) … P Lacock et al (UKQCD) PLB 401, 308 (1997) SL Zhu PLB 625, 212 (2005) FE Close, PR Page PLB 628, 215 (2005) E Kou, O Pene PLB 631, 164 (2005) …

Molecules? PDG: M D0 + M D*0 = ± 0.4 MeV MeV M(X3872) PDG: M(X3872) = M(Z4430) Belle: M(Z4430) =4433 ± 5 MeV PDG: M D* + M D1 = ± 1.4 MeV Equal to 1 part in Coincidence?

arXiv: hep-ph/ arXiv: correct predictions But not 1 +

J P of the Z(4430)? qplqpl p l+l+ l-l- y’y’ qklqkl K l+l+ l-l- y’y’ J P =1 + favored, but ~2s level 1+1+

arXiv: ” ”… arXiv: ” ”

Molecules/threshold effects should be near thresholds D S D S thresholds DD thresholds some of the states are near thresholds, but this is not a universal feature Note: there is no  - or  -exchange between D s states ??

Molecular picture may work for some XYZ states, but not all.

Diquark –antidiquark? u c c u d c c d d c c u u c c d These should come in isospin- & SU(3)-multiplets where are the “partner states”? X u (3872)X d (3872) X + (3872) X - (3872) Expect: Bf(B 0  K - X + )Bf(X +      J/  ) Bf(B -  K - X 0 )Bf(X +      J/  ) ≈ 2 B +  K - X u B 0  K 0 X d M(X d )-M(X u )= 2(m d -m u )/cos  L Maiani et al PRD 71, (20050  8 ± 3 MeV

B  K S X & B  K ± X comparison  M = 0.22 ± 0.90 ± 0.27 MeV Compared to 8±3 MeV (Maiani et al PRD ) BaBar K S mode K ± mode K S mode K ± mode  M = 2.7 ± 1.6 ± 0.4 MeV

no X ± (3872) isospin partner is seen B 0  K ± p ∓ p 0 J/y B ∓  K S p ∓ p 0 J/y Bf(B 0  K - X + )Bf(X +  p + p 0 J/y) Bf(B -  K - X 0 )Bf(X +  p + p - J/y) < 0.4 (expect  2) ??

None of the partner states required by the diquark-diantiquark picture have yet been seen.

How about cc-gluon hybrids? cc qq-gluon excitations predicted 30 yrs ago LQCD: lowest 1 -- cc-gluon mass ~4.3 GeV - QCD sum rules get lower values ~3.7 GeV relevant open charm threshold is D**D (~4.28 GeV)  (  J/  ) larger than that for normal charmonium  (e + e - ) for 1 -- states less than ordinary charmonium Horn & Mandula PRD 17, 898 (1977) Banner et al, PRD 56, 7039 (1997); Mei & Luo, IJMPA 18, (2003) Isgur, Koloski & Paton PRL 54, 869 (1985) McNeile, Michael & Pennanen PRD 65, (2002) Close & Page NP B443, 233 (1995) Kisslinger et al, arXiv (2008) Y(4260) seems to match all of these !!!

DD** thresholds in & “Y(4260)” 4.26 D** spectrum M(     J/  ) GeV No obvious distortions D1DD1D D2DD2D D D D D D D DD ( ** ) thresholds

e + e -       ’ peaks in Belle M=4324  24 MeV  = 172  33 MeV 548 fb -1 X.L. Wang et al (Belle) arXiv: PRL 99, (2007) Two peaks! M=4664  11 ± 5 MeV  = 48  15 ± 3 MeV M=4361  9 ± 9 MeV  = 74  15 ± 10 MeV Earlier BaBar values (both relatively narrow) (& both above all D**D thresh) (& neither consistent with 4260)

Y(4360) & Y(4660) are above all DD** thresholds D** spectrum D D D D D D

No signs in s(e + e -  D 0 Dp) Belle: G. Pakhlova et al, PRL 100, (2008)PRL 100, (2008) D 0 *(2400)D + D 2 *(2460)D pb

s(e + e -   +  - J/  ) ~60pb C.Z. Yuan et al, PRL 99, (2007)PRL 99, (2007) eyeball estimate

s(e + e -   +  -  ’ ) ~70pb ~40pb X.L. Wang et al, PRL 99, (2007)PRL 99, (2007) eyeball estimate

G(Y  p + p - J/y (y ’ )) are large 10x X.H. Mo et al, PLB640, 182 (2006): G (Y4260  p + p - J/ y )> 10x G ( y 3770  p + p - J/ y ) BES: PRL 88, (2006) Belle (DD + DD* + D*D* + DD p )

Data are in poor agreement with hybrid expectations Moreover, there are no charged charmonium hybrids, so these can’t account for the Z + (4430)

Are there XYZ counterparts in the ss- & bb- systems?

Belle:  (  (5S)   (nS)) 2S 3S 4S  (4S)   (1S)  +    (4S)   (1S) 477 fb -1 from Belle 44±8 evts “  (5S)”   (1S) 23.6 fb -1 from Belle (1/20 times the data & ~1/10 th the crosssection) 325±20 evts! 8 times as many events! Belle K.F. Chen et al (Belle) PRL 100, (2008) is Huge!!!

Partial Widths N.B. Resonance cross section ± nb at GeV PRD 98, (2007) [Belle] Cf  (2S)   (1S)     ~ 6 keV  (3S) 0.9 keV  (4S) 1.8 keV Assume “  (5S)” =  (5S) PDG value taken for  (nS) properties >100 times bigger!!

p + p -  (nS) Dalitz plots  (1S)  +    (2S)  +  

It looks like there is a bb version of the Y(4260), the “Y b,” lurking around the  (5S) W.-S. Hou PRD 74, (2007) Y b  p + p -  (nS)  ( 5S ) (4S)(4S)

If there are bb versions of the XYZ’s, why not ss versions as well?

1 -- Y s states around 2 GeV? Y(2175)  f 0 (980)  from BaBar e+e-   f 0 (980) Ecm ~10.6 GeV BESII M(f 0 (980)  GeV M.Ablikim et al (BES) PRL 100, (2008) ss equivalent of the J/ y

Maybe the X(1835) is one too? M. Ablikim et al (BESII), Phys.Rev.Lett.95:262001,2005 J/    X(1835) |       ’ X(1835) mostly ss

comments There is a new meson spectroscopy not well explained as qq states –Maybe more than one –Bodes well for BESIII, Super-B factories & PANDA Some states are narrow even though they are far above decay thresholds –e.g. Y(4660)   ’ & Z + (4430)     ’ have large Q but  ≈50 MeV characterized by large partial widths (or Bfs) to hadrons+J/  (or  ’)  – Br(X(3872)   J/  ) > 4.3% (Isospin=1) –  (Y(3940)   J/  ) > 7 MeV –  (Y(4260)      J/  ) > 1.6 MeV States that decay to  ’ not seen decaying to J/  (and vice-versa) –Bf(Y(4660)   ’) >> Bf(y(4660)   J/  )  same for Y(4360) & Z(4430   ’ –Y(4260) not seen in Y(4260)   ’ The new 1 -- states are not apparent in the e + e -  D ( * ) D ( * ) cross sections There are no evident changes at the D**D mass threshold None of the existing ideas for non-qq mesons, i.e. molecules, di-quarks & hybrids, provide a natural explanation for the observed properties.

Not all candidate states are close to thresholds. None of the expected Ispin- or SU(3) partners are seen No influence from DD** threshold observed No possibility to accommodate the Z + (4430) Candidate models

Implications for BES-III Search for charmonium-like states decaying to h c mesons so far only J/ y & y ’ final states have been studied At BES-III we have the possibility of clean h c signals

For example: arXiv: (last week) Accessible at BES-III?

Implications for BES-III Search for charmonium-like states decaying to h c mesons so far only J/ y & y ’ final states have been studied At BES-III we have the possibility of clean h c signals Measure “open strangeness” decay modes for X(1835), Y(2175), etc hybrid models say K 1 (1270)K &/or K 1 (1400)K should dominate Systematic studies of final states including a f or an h ’ need to find patterns

Example: p + p - h ’ spectrum with 58M J/ y ’s M(  ’  ) GeV/c 2 2 BESII X(1835) 2.5 BES-III M(  ’  ) GeV/c 2

final comments

1963 Elementary particle “zoo” mesons baryons +…

One good idea baryons sususdsd dsdsusus dududuudud mesons etc. Gell-Mann Zweig

2008: a new “zoo” X(1835) Y(4360) Y(4660) Z + (4430) Y(2175) Y(3940) X(3940) Y(4260) X(4160) We need a new idea

There is lots still to be learned about hadronic physics. BES-III is well positioned in time & energy to contribute. There are big challenges (& opportunities) for theorists. Summary

My advice to theorists present: Think out of the box. 加油

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