New Spectroscopy with Charm and Beauty Multiquark States

Luciano MAIANI CERN and Università di Roma “La Sapienza” EMFCSC, Erice, June 30, 2013

Luciano Maiani Erice 2013. Multiquark Mesons 1 Erice 1967: making the Standard Model...

Luciano Maiani Erice 2013. Multiquark Mesons 2 Foreword from my Erice lectures 2007

• For long, we lived very well with the Gell-Mann from the summary of the 1967 Zweig paradigm: Erice School - mesons = - baryons = • Paradigm rested on: absence of I=2, ππ resonances and of S>0 baryons. • The case had to be revisited, because: - the lowest lying, scalar mesons do not fit in the picture - the f0(980), and a0(980); - it was also found, much later, that new “charmonium” states seen by Belle and BaBar, do not fit the charmonium picture at all. • The discovery of Θ+, S=+1 baryon (“pentaquark”), seemed to make the case...but the first observations have not been confirmed. WORK IN PROGRESS

Luciano Maiani Erice 2013. Multiquark Mesons 3 1.The light scalar mesons octet

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Antisymmetric tetraquarks work better

Luciano Maiani Erice 2013. Multiquark Mesons 4 Diquark [qq] in color = 3bar, spin=0, SU3 flavour = 3bar makes a simple unit to form color singlets (Jaffe, Jaffe & Wilcezck) Diquark needs to combine with other colored objects q → baryon (e.g. Λ), Y-shape [qq] → scalar meson, H-shape

radial and orbital excitations, many states string topology is more related to Baryon-antiBaryon: if you break the string,

[qq][¯qq¯] [qq][¯qq¯] + meson !

Meson-meson molecules have a different string topology: - are they bound? - very few states

Luciano Maiani Erice 2013. Multiquark Mesons 5 Instantons solve two scalar meson puzzles

• (a) Mixing of tetraquarks with q-qbar mesons, identified with the multiplet made by a0(1474) (I=1), K0(1412), (I=1/2), and three isosinglets: f0(1370), f0(1507) and f0(1714) (one could be a glueball);

• (b) the decay f0(980) ➔ 2π

Luciano Maiani Erice 2013. Multiquark Mesons 6 2. Conventional and less conventional Quarkonia • The accuracy with which the spectra of Q Qbar states (Q=c, b) are predicted and measured makes it possible to discover new states “by difference” • Terminology of Q-Qbar states in S and P wave:

2S+1 spin = S, orb. ang. mom. = L, tot. ang. mom. = J : LJ radial excitation = n 1 3 ⌘c(1S)= S0; J/ (1S)= S1 1 3 hc(1P )= P1, c(1P )= PJ

Particle Data Group: S. Eidelman et al., Developments in Heavy Quarkonium Spectroscopy, 2012;

Quarkonium Working Group: N. Brambilla et al., Heavy quarkonium: progress, puzzles, and opportunities, 2011.

Luciano Maiani Erice 2013. Multiquark Mesons 7 Latest conventional Quarkonia (PdG)

Luciano Maiani Erice 2013. Multiquark Mesons 8 PDG: Unanticipated “Quarkonia”

Luciano Maiani Erice 2013. Multiquark Mesons 9 A LOOSELY BOUND MOLECULE? WHERE ARE THE OTHERS LBM’S? Yet a remarkable(!) amount of ‘unoccupied’ thresholds courtesy of A. Polosa

Y 4660 1-- y'f0 1+- y'h' Y 4630 -+ 0 hc'f0 ++ 0 hc'h' -- H L J cc2f -+ ++ H L J hcf - 2 cc2f0 -+ +- 2 cc2h'- 1 hcf0 ++ -- 1 cc1f0 - 1 hch' - * ++ -+ J D D2 J y'w r- 1 cc1h'

-- J- D*D 1 cc0f 1 1+- h 'w-h 'r c ê c ++ 0 cc0f0 -+ 1 cc0h' H L X 4350 Y 4350 J-- c w-c r - c2 c2 2 DD2 +- J hcw-hc r - 1 DD1 H L YH4274 L H L Y 4260 H L +- + * * 1 y'h J Ds Ds 1-- c w-c r H L c0 c0 H L X 4160 H L ++ J-+ yf 2 cc2h + * -- 1 DsDs 1 yf0-hch H L -+ +- 1 cc1 h - 1 yh'

J+ D*D* H < +- Y 4008 1 hc f

-+ 0 cc0 h - hc f0 + ++ 0 DsDs X 3940 G 3900 0 hc h' H L Y 3915 H L J++ yw-yr 1+ DD* X 3872 H L H L H L 1+- Hy'p L

H L ++ 0 hc'p-110.hcw

0+ DD Luciano Maiani Erice 2013. Multiquark Mesons 10 X AS A COMPACT TETRAQUARK?

8c courtesy of A. Polosa 3¯c ...less bound (R=1 fm) 6c

3c 6¯c a compact `tetraquark’ 8c 8c the ‘hybrid’ option 1c 8c X: a loosely bound molecule (R ~10 fm) 1 R ⇡ p2M E D bind 1c

quark (heavy or light) antiquark

gluon

Luciano Maiani Erice 2013. Multiquark Mesons 11 X(3872) production @ LHC

4 part $1 • Production at Colliders speaks against Pythia 2!2 :: y "2 :: !#100 nb extended objects; 3 ! " "

• using Pythia to estimate the probability to nb ! 2 find a D-Dbar pair in the relevant phase Σ space, factors of 10-2 with respect to the 1 X(3872) cross section measured by CDF 0 (~ 30 nb) are found. 0.0 0.2 0.4 0.6 0.8 1.0

krel GeV C. Bignamini, B. Grinstein, F. Piccinini, A. Polosa, C. Sabelli, Phys Rev Lett, 103, 162001 (2009) Luciano Maiani Erice 2013. Multiquark Mesons ! " 12 Heavy Quark Spin Symmetry

• one could have also excited charmonium, which could explain decay of Z(4630) into ψ(2S): • the wave function depends from the separation, R, of c and cbar; for R large, light quarks/antiquarks may neutralize color and mimic a molecular state • relation to D-D* masses is dubious unless large R really dominates • what does stabilize the light quark/antiquark cloud?

Luciano Maiani Erice 2013. Multiquark Mesons 13 3. Tetraquark picture of unexpected quarkonia

• I=1, 0 L.Maiani, F.Piccinini, A.D.Polosa and V.Riquer, Phys. Rev. D 71 (2005) 014028 • S-wave: positive parity • total spin of each diquark, S=1, 0 • neutral states may be mixtures of isotriplet and isosinglet • mass splitting due to spin-spin interactions (e.g. the non-relativistic costituent quark model A A H =2M 2  (~s ~s ) i j diquark ij i · j 2 2 i

Luciano Maiani Erice 2013. Multiquark Mesons 14 Mass spectrum of X and Z particles from spin-spin interactions

L.Maiani, F.Piccinini, A.D.Polosa and V.Riquer, Phys. Rev. D 71 (2005) 014028

2m[cq] +

The JPG=1 +, ± charmonium tetraquarks • consider isotriplets only: S ,S >, S =0, 1 | cq c¯q¯ cq • three states with different charge conjugation properties • states labeled by diquark spin: 1, 0 + 0, 1 X(3872),G= 1: | i | i; (3872 MeV, input) ¯ p2 X(3872) : J/ + ⇢/!,DD⇤ 1, 0 0, 1 Zc,G=+1: | i| i; (3882 MeV, computed) Zc : J/ ⇡,J/ ⌘ ?, ⌘c ⇢? p2 Z0 ,G=+1: 1, 1 ; (3755 MeV, computed) c | iJ=1 Luciano Maiani Erice 2013. Multiquark Mesons 15 (cq) (¯cq¯0)¯ Tetraquark picture (cont’d) 3col 3col q, q0 = u, d

• neutral states may be mixtures of isotriplet and isosinglet • predicted multiplets (in bold the states identified with observed states):

- JPC=2++(2 multiplets) - JPC=1++(1 multiplet): X(3872); PC +- - J =1 (2 multiplets): Zc (3900), Z’c or Z b(10610), Z’b(10650) - JPC=0++(2 multiplets) BELLE 2011

Zb , Z’b as Tetraquark: Ali, Hambrock, Wang, Phys. Rev. D 85 (2012) 054011 as Molecule: A.Bondar et al.,Phys.Rev.D 84(2011)054010

Mass difference agrees with M(B*)-M(B) Tetraquark tends to predict larger splitting, depending on the value of the poorly known qq¯

Luciano Maiani Erice 2013. Multiquark Mesons 16 The unexpected JPC= 1-- resonance, Y(4260) BABAR, 2006 B.Aubert et al.[BaBar + + Collaboration]Phys.Rev.Lett.95(2005) 142001 e e (ISR)+J/ ⇡ ⇡ ! •seen by Babar in processes with Initial State Radiation:

•the Dalitz plot shows the f0 band, which lead us to assume the quark composition: [cs][¯cs¯] L. Maiani et al Phys.Rev.D 72 (2005) 031502

•however, after discovery of the instanton effect, one realizes that the composition [ cq ][¯ cq¯] gives the same result and fits better the mass of this orbital excitation

c¯ f q¯ J/ 0 q { c time

is there a J/ ⇡ ± line? Luciano Maiani Erice 2013. Multiquark Mesons 17 4. The unexpected JPC= 1-- resonance, Y(4260), and its unexpected JPG= 1++ descendants Observed by BES III, BELLE and CLEO : + f0 J/ J/ ⇡ ⇡ Y (4260) ! + ! Zc ⇡ J/ ⇡ ⇡ tetraquark de-excitation ? ⇢ ! CLEO

± ± Zc ? Zc ?

± Zc ? 0 Zc ?

18 Luciano Maiani Erice 2013. Multiquark Mesons our fit with two Zc lines

data, our fit R. Faccini et al., arXiv:1303.6857 [hep-ph] DD* D*D* 90 ABES 0.92 0.07 80 ±

2 BBES 61 18 •tetraquark predicts a second 70 ± 60 ABelle 0.98 0.09 resonance some 100 MeV below 50 ± BBelle 49 15 the peak, which could even be 40 ± 30 M1 (MeV) 3890 6 there! see fit

Events/0.01 GeV/c ± 20 1 (MeV) 63 12 •molecules would correlate the 10 ± M2 (MeV) 3836 13 second peak to D* (Dbar)* 0 ± 3.65 3.70 3.75 3.80 3.85 3.90 3.95 4.00 4.05 (MeV) 30 18 ± 2 2 threshold, some 100 MeV above Mmax( J/) (GeV/c ) ± C 0.30 0.25 2 ± data, our fit 2 (DEG) 109 33 DD* D*D* ± •two peaks, Zb and Zb’, are 70 2 /DOF 41/65 clearly seen in the b case: why 60 CL 99% 2 this difference? 50 •Zb and Zb’ are observed in the 40 Result of the combined fit. CL is the confidence level. 30 decay of Y(5S), namely a bona fide bottomonium: is it relevant?

Events/0.02 GeV/c 20

10

0 more precise expts are called for 3.7 3.8 3.9 4.0 4.1 4.2 ± 2 Mmax( J/) (GeV/c ) a clear discrimination.

Luciano Maiani Erice 2013. Multiquark Mesons 19 Decay modes and widths of Zc(3900)

• Zc much broader than X(3872), but: • many open decay channels: J/ ⇡± • larger phase space (2S) ⇡± + ¯ 0 + ¯ 0 • our estimate about 60 MeV D D⇤ ,D⇤ D • loosely bound molecule should ⌘c ⇢± decay like its components: hc ⇡± Z DD¯⇡,DD¯ radiative decays c ! • for molecules, see

Qian Wang, Christoph Hanhart, Qiang Zhao. Thomas Gutsche, Valery E. Lyubovitskij. arXiv:1303.6355 [hep-ph] arXiv:1306.0824 [hep-ph] | Yubing Dong Amand Faessler, Thomas Gutsche, Valery E. Lyubovitskij J.Phys. G40 (2013) 015002 Luciano Maiani Erice 2013. Multiquark Mesons 20 other critical issues of molecule vs color bound system

• are isospin multiplets complete? • lack of isospin partners would be in favor of molecular picture • missing: - Z’s neutral partners, I=1 and 0 - charged X and Y partners 0 • is there isospin conservation in neutral Z particles decays, e.g. Zc ➝J/Ψ η • is there conservation of the total heavy spin Sc-cbar ? • the observation of decay modes with Sc-cbar=0 (e.g involving ηc or hc) would be very informative

A vast experimental programme for BES, BELLE, LHCb and the other collider experiments

Luciano Maiani Erice 2013. Multiquark Mesons 21 Conclusions

• exotic, hidden charm and beauty ARE there, although their nature is still unclear; • production at colliders disfavors extended structures vs. compact structures bound by color forces, of which tetraquark is a working example; • search of one additional peak in Ψ(4260) decays, below or above the Zc(3900) mass, may be crucial to tell molecules from tetraquarks; • search for missing partners is called for, in all channels; • checking the selection rules (isospin, heavy quark spin...) involves control 0 of decay modes with π , η , ηc, which may be quite a formidable challenge... • ... and a lot of work at flavor factories and LHC, to keep us busy for a while.

Luciano Maiani Erice 2013. Multiquark Mesons 22