1. Bottom-Tetraquarks – Current Status & Prospects
Ahmed Ali
DESY, Hamburg
April. 27, 2015
WG7: B2TiP Workshop, Krakow
Ahmed Ali (DESY, Hamburg) 1 / 33
2. An Overview of Charmonium- and Bottomonium-like states
Enigmatic Υ(5S) decays?
Spectroscopy of tetraquark states
Charged tetraquarks and heavy quark spin conservation
Dipion mass distributions in Υ(5S) → Υ(nS)ππ decays
Tetraquark model for Yb production and decays
Summary
Ahmed Ali (DESY, Hamburg) 2 / 33
9. Enigmatic Υ(5S) Decays: Is there a Yb(10890) close to Υ(5S)?
Ahmed Ali (DESY, Hamburg) 7 / 33
10. σ(e+e− → b¯b) in the Υ(10860) and Υ(11020) region [Belle 2015]
Rb data and fit
Fb¯b = |Anr|2 + |Ar + A5Seiφ5S f5S + A6Seiφ6S f6S|2
fnS = MnsΓnS/[(s − M2
ns) + iMnSΓnS] [Breit-Wigner]
Ar and Anr are coherent and incoherent continuum terms
No peaking structure seen at 10.9 GeV, hinted by the BaBar data;
Γ(e+e−) < 9 eV (@ 90% C.L.)
Ahmed Ali (DESY, Hamburg) 8 / 33
11. σ(e+e− → Υ(nS)π+π−) in the Υ(10860) and Υ(11020) region [Belle 2015]
FΥ(nS)ππ = |A5S,nf5S|2 + |A6S,nf6S|2 + 2KnA5S,nA6S,nR[eiδn f5Sf∗
6S]
Kn and δn allowed to float
Fit Values (MeV): M5S = 10891.1 ± 3.2+0.6
−1.5; Γ5S = 53.7+7.1 +0.9
−5.6 −5.4
M5S(Υ(nS)ππ) − M5S(b¯b) = 9.2 ± 3.4 ± 1.9 MeV
Ahmed Ali (DESY, Hamburg) 9 / 33
13. Branching Ratios of Υ(10860) is a Puzzle!
Rb and Rπ+π−Υ(nS) are not independent
b¯b contribution: Pb = |A5S(b¯b) × BW(5S)|2
Υ(nS)ππ contribution: P(π+π−nS) =
PHSP × |A5S(nS) × BW(5S)|2
Book-keeping of the BRs at Υ(10860)
From Rπ+π−Υ(nS): P(π+π−nS) = (17 ± 0.9)% of Pb
Adding Υ(5S) → ππhb(1P, 2P)and assuming isospin symmetry
yields P(ππb¯b) = (42 ± 4)%
Adding Zb → πB(∗) ¯B(∗)yields P(ππb¯b + πZb) = (109 ± 15)%
No, or very little, room for direct decays: Υ(5S) → B(∗) ¯B(∗), Bs
¯Bs
In particular, what is the source of the Bs
¯B
(∗)
s events? They are not
seen off-the resonance, nor in the decays of Zb!!
Ahmed Ali (DESY, Hamburg) 11 / 33
14. Spectroscopy of tetraquark states
Interpolating diquark operators (P = −1 larger energy):
“good”: 0+ Qiα = αβγ(¯b
β
c γ5q
γ
i − ¯q
β
ic
γ5bγ) α, β, γ: SU(3)C indices
“bad”: 1+ Qiα = αβγ(¯b
β
c γq
γ
i + ¯q
β
ic
γbγ)
Ahmed Ali (DESY, Hamburg) 12 / 33
15. Spectroscopy of tetraquark states
Interpolating diquark operators (P = −1 larger energy):
“good”: 0+ Qiα = αβγ(¯b
β
c γ5q
γ
i − ¯q
β
ic
γ5bγ) α, β, γ: SU(3)C indices
“bad”: 1+ Qiα = αβγ(¯b
β
c γq
γ
i + ¯q
β
ic
γbγ)
NR limit: States parametrized by Pauli matrices :
“good”: 0+ Γ0 = σ2√
2
“bad”: 1+ Γ = σ2σ√
2
Ahmed Ali (DESY, Hamburg) 12 / 33
16. Spectroscopy of tetraquark states
Interpolating diquark operators (P = −1 larger energy):
“good”: 0+ Qiα = αβγ(¯b
β
c γ5q
γ
i − ¯q
β
ic
γ5bγ) α, β, γ: SU(3)C indices
“bad”: 1+ Qiα = αβγ(¯b
β
c γq
γ
i + ¯q
β
ic
γbγ)
NR limit: States parametrized by Pauli matrices :
“good”: 0+ Γ0 = σ2√
2
“bad”: 1+ Γ = σ2σ√
2
Diquark spin sQ tetraquark total angular momentum J:
Y[bq] = sQ, s ¯Q; J
Tetraquark matrix representation:
0Q, 0 ¯Q; 0J = Γ0
⊗ Γ0
,
1Q, 1 ¯Q; 0J =
1
√
3
Γi
⊗ Γi, . . .
0 iAhmed Ali (DESY, Hamburg) 12 / 33
17. NR Hamiltonian
States need to diagonalize Hamiltonian:
H = 2mQ + H
(qq)
SS + H
(q¯q)
SS + HSL + HLL
Ahmed Ali (DESY, Hamburg) 13 / 33
18. NR Hamiltonian
States need to diagonalize Hamiltonian:
H = 2mQ + H
(qq)
SS + H
(q¯q)
SS + HSL + HLL
with constituent mass
Ahmed Ali (DESY, Hamburg) 13 / 33
19. NR Hamiltonian
States need to diagonalize Hamiltonian:
H = 2mQ + H
(qq)
SS + H
(q¯q)
SS + HSL + HLL
with
H
(qq)
SS = 2(Kbq)¯3[(Sb · Sq) + (S¯b · S¯q)]
H
(q¯q)
SS = 2(Kb¯q)(Sb · S¯q + S¯b · Sq)
+ 2Kb¯b(Sb · S¯b) + 2Kq¯q(Sq · S¯q)
qq spin coupling q¯q spin coupling
Ahmed Ali (DESY, Hamburg) 13 / 33
20. NR Hamiltonian
States need to diagonalize Hamiltonian:
H = 2mQ + H
(qq)
SS + H
(q¯q)
SS + HSL + HLL
with
H
(qq)
SS = 2(Kbq)¯3[(Sb · Sq) + (S¯b · S¯q)]
H
(q¯q)
SS = 2(Kb¯q)(Sb · S¯q + S¯b · Sq)
+ 2Kb¯b(Sb · S¯b) + 2Kq¯q(Sq · S¯q)
HSL = 2AQ(SQ · L + S ¯Q · L)
HLL = BQ
LQ ¯Q(LQ ¯Q + 1)
2
LS coupling LL coupling
Ahmed Ali (DESY, Hamburg) 13 / 33
21. NR Hamiltonian
States need to diagonalize Hamiltonian:
H = 2mQ + H
(qq)
SS + H
(q¯q)
SS + HSL + HLL
with
H
(qq)
SS = 2(Kbq)¯3[(Sb · Sq) + (S¯b · S¯q)]
H
(q¯q)
SS = 2(Kb¯q)(Sb · S¯q + S¯b · Sq)
+ 2Kb¯b(Sb · S¯b) + 2Kq¯q(Sq · S¯q)
HSL = 2AQ(SQ · L + S ¯Q · L)
HLL = BQ
LQ ¯Q(LQ ¯Q + 1)
2
fit to known hadrons Empirical observation
Spin-spin interactions scale as the inverse product of quark masses, i.e.,
(κij)¯3mimj is constant, leading to a weak spin-spin interaction in diquarks,
counter-intuitive, and in disagreement with data
Ahmed Ali (DESY, Hamburg) 13 / 33
22. New Paradigm for spin interactions in tetraquarks
L. Maiani et al., Phys. Rev. D89, 114110 (2014)
Replace the spin-spin part in the q¯q coupling in different diquarks
H ∼ 2κq¯qsq¯q(sq¯q + 1)
by the spin coupling between quarks in the same diquark
H ∼ 2κqc(sq.sc + s¯q.s¯c)
M = M00 +
BQ
2
L2
− 2a L · S + 2κqQ sq · sQ + s¯q · s ¯Q
= M00 − 3κqQ − aJ(J + 1) +
BQ
2
+ a L(L + 1) + aS(S + 1)
+ κqQ sqQ(sqQ + 1) + s¯q ¯Q(s¯q ¯Q + 1)
Q = c, b; signs of BQ, a and κqQ are positive
Ahmed Ali (DESY, Hamburg) 14 / 33
23. Low-lying S- and P-wave Tetraquark States
S-wave states
In the |sqQ, s¯q ¯Q; S, L Jand |sq¯q, sQ ¯Q; S , L J bases, the positive parity
S-wave tetraquarks are given in terms of the six states listed
below (charge conjugation is defined for neutral states)
Label JPC |sqQ, s¯q ¯Q; S, L J |sq¯q, sQ ¯Q; S , L J Mass
X0 0++ |0, 0; 0, 0 0 |0, 0; 0, 0 0 +
√
3|1, 1; 0, 0 0 /2 M00 − 3κqQ
X0
0++ |1, 1; 0, 0 0
√
3|0, 0; 0, 0 0 − |1, 1; 0, 0 0 /2 M00 + κqQ
X1 1++ |1, 0; 1, 0 1 + |0, 1; 1, 0 1 /
√
2 |1, 1; 1, L 1 M00 − κqQ
Z 1+− |1, 0; 1, 0 1 − |0, 1; 1, 0 1 /
√
2 |1, 0; 1, L 1 − |0, 1; 1, L 1 /
√
2 M00 − κqQ
Z 1+− |1, 1; 1, 0 1 |1, 0; 1, L 1 + |0, 1; 1, L 1 /
√
2 M00 + κqQ
X2 2++ |1, 1; 2, 0 2 |1, 1; 2, L 2 M00 + κqQ
P-wave (JPC = 1−−) states
Label JPC |sqQ, s¯q ¯Q; S, L J |sq¯q, sQ ¯Q; S , L J Mass
Y1 1−− |0, 0; 0, 1 1 |0, 0; 0, 1 1 +
√
3|1, 1; 0, 1 1 /2 M00 − 3κqQ + BQ
Y2 1−− |1, 0; 1, 1 1 + |0, 1; 1, 1 1 /
√
2 |1, 1; 1, L 1 M00 − κqQ + 2a + BQ
Y3 1−− |1, 1; 0, 1 1
√
3|0, 0; 0, 1 1 − |1, 1; 0, 1 1 /2 M00 + κqQ + BQ
Y4 1−− |1, 1; 2, 1 1 |1, 1; 2, L 1 M00 + κqQ + 6a + BQ
Y5 1−− |1, 1; 2, 3 1 |1, 1; 2, L 1 M00 + κqQ + 16a + 6BQ
Ahmed Ali (DESY, Hamburg) 15 / 33
24. Belle Data on (Bottomonium-like) exotic states
State JPC Mass [MeV]
Yb(10891) 1−− 10891.1 ± 3.2+0.6
−1.5
Yb(10987) 1−− 10987.5+6.4+9.0
−2.5−2.1
Z+
b
(10610) 1+ 10607.2 ± 2.0
Z0
b
(10610) 1+− 10609 ± 4 ± 4
Z+
b
(10650) 1+ 10652.2 ± 1.5
We identify Z+
b
(10610) and Z+
b
(10650) with Zand Z , respectively. Their mass
difference determines 2κqb
2κqb = M[Z+
b
(10650)] − M[Z+
b
(10610)] = 45 MeV
The parameter M00 can be calculated as
M00 = M[Z+
b
(10610)] + κqb = 10630 MeV
We identify Yb(10891) and Yb(10977) with Y1 and Y2, respectively. The
parameter a can be calculated from their mass difference:
2a = M[Yb(10987)] − M[Yb(10891)] − 2κqQ = 51 MeV
The parameter BQ is given by
BQ = M[Yb(10891)] − M00 + 3κqQ = 329 MeV
Ahmed Ali (DESY, Hamburg) 16 / 33
25. Charmonium-like and Bottomonium-like Tetraquark Spectrum
(with Satoshi Mishima)
Parameters in the Mass Formula
charmonium-like bottomonium-like
M00 [MeV] 3957 10629.7
κqQ [MeV] 67 22.5
BQ [MeV] 268 328.9
a [MeV] 52.5 25.7
charmonium-like bottomonium-like
Label JPC State Mass [MeV] State Mass [MeV]
X0 0++ — 3756 — 10562.2
X0 0++ — 4024 — 10652.2
X1 1++ X(3872) 3890 — 10607.2
Z 1+− Z+
c (3900) 3890 Z+,0
b
(10610) 10607.2
Z 1+− Z+
c (4020) 4024 Z+
b
(10650) 10652.2
X2 2++ — 4024 — 10652.2
Y1 1−− Y(4008) 4024 Yb(10891) 10891.1
Y2 1−− Y(4260) 4263 Yb(10987) 10987.5
Y3 1−− Y(4290) (or Y(4220)) 4292 — 10981.1
Y4 1−− Y(4630) 4607 — 11135.3
Y5 1−− — 6472 — 13036.8
Ahmed Ali (DESY, Hamburg) 17 / 33
26. Comparison with current data in the Charmonium-like sector
Our determination of the parameters M00, κqc, BC and a in the Charmonium-like
sector close to the one by Maiani et al. (2014). Their results are shown below
− − − − New; - - - - - Old
Quarks inside a Diquark are much more tightly bound than Diquarks in Baryons
Ahmed Ali (DESY, Hamburg) 18 / 33
27. Production and decay characteristics of Z±
b (10610) and Z±
b (10650)
Belle, PRL 108, 122001 (2012)
Z±
b
(10610) and Z±
b
(10650) are produced in the decays of Υ(10890)
Υ(10890) → Zb/Zb + π → Υ(1S, 2S, 3S)ππ
Ahmed Ali (DESY, Hamburg) 19 / 33
29. Hidden-Beauty Charged Tetraquarks and Heavy Quark Spin Conservation
A.A., L. Maiani, A.D. Polosa, V. Riquer; PR D91, 017502 (2015)
Interpret the Z±,0
b
(10610) = Zb and Z±,0
b
(10650) = Zb as S-wave
JPG = 1++ tetraquark states (in the notation |s[bq], s[¯b¯q] )
|Zb =
|1bq, 0¯b¯q − |0bq, 1¯b¯q
√
2
, |Zb = |1bq, 1¯b¯q J=1
JP = 1+ multiplet is completed by Xb, given by the C = +1 combination
|Xb =
|1bq, 0¯b¯q + |0bq, 1¯b¯q
√
2
Expect Xb and Zb to be degenerate, with Zb heavier
M(Zb) − M(Zb) = 2κb
A similar analysis for the hidden-charm charged tetraquarks Zc and Zc yields
2κc = M(Zc) − M(Zc) 120 MeV
QCD expectation: κb : κc = Mc : Mb. With Mc
Mb
1.27
4.18 = 0.30, yields
2κb 36 MeV, fits OK with the observed Zb − Zbmass difference ( 45 MeV)
Ahmed Ali (DESY, Hamburg) 21 / 33
30. Heavy-Quark-Spin Flip in Υ(10890) → Zb/Zb + π → hb(1P, 2P)ππ
In Υ(10890), Sb¯b = 1. In hb(nP), Sb¯b = 0, so the above transition involves
heavy-quark spin-flip, yet its rate is not suppressed, violating heavy-quark-spin
conservation
This contradiction is only apparent. Expressing the states Zb and Zb in the basis
of definite b¯b and light quark q¯q spins,
|Zb =
|1q¯q, 0b¯b − |0q¯q, 1b¯b
√
2
, |Zb =
|1q¯q, 0b¯b + |0q¯q, 1b¯b
√
2
More generally, admitting a subdominant spin-spin interaction, the above
composition may be written as
|Zb =
α|1q¯q, 0b¯b − β|0q¯q, 1b¯b
√
2
, |Zb =
β|1q¯q, 0b¯b + α|0q¯q, 1b¯b
√
2
Define gZ = g(Υ → Zbπ)g(Zb → hbπ) ∝ −αβ hb|Zb Zb|Υ
gZ = g(Υ → Zbπ)g(Zb → hbπ) ∝ αβ hb|Zb Zb|Υ
where g are the effective strong couplings at the vertices Υ Zb π and Zb hb π
Therefore, independently from the values of the mixing coefficients, the above
equation and heavy quark spin conservation require gZ = −gZ
Ahmed Ali (DESY, Hamburg) 22 / 33
31. Heavy-Quark-Spin Flip in Υ(10890) → Zb/Zb + π → hb(1P, 2P)ππ
Relative normalizations and phases for sb¯b: 1 → 1 and 1 → 0 transitions
Final State Υ(1S)π+π− Υ(2S)π+π− Υ(3S)π+π− hb(1P)π+π− hb(2P)π+π−
Rel. Norm. 0.57 ± 0.21+0.19
−0.04
0.86 ± 0.11+0.04
−0.10
0.96 ± 0.14+0.08
−0.05
1.39 ± 0.37+0.05
−0.15
1.6+0.6+0.4
−0.4−0.6
Rel. Phase 58 ± 43+4
−9
−13 ± 13+17
−8
−9 ± 19+11
−26
187+44+3
−57−12
181+65+74
−105−109
Within errors, Belle data is consistent with heavy quark spin conservation
To determine the coefficients α and β, one has to resort to sb¯b: 1 → 1 transitions
Υ(10890) → Zb/Zb + π → Υ(nS)ππ (n = 1, 2, 3)
The analogous effective couplings are
fZ = f(Υ → Zbπ)f(Zb → Υ(nS)π) ∝ |β|2
Υ(nS)|0q¯q, 1b¯b 0q¯q, 1b¯b|Υ
fZ = f(Υ → Zbπ)f(Zb → Υ(nS)π) ∝ |α|2
Υ(nS)|0q¯q, 1b¯b 0q¯q, 1b¯b|Υ
Ahmed Ali (DESY, Hamburg) 23 / 33
32. Determination of α/β from Υ(10890) → Zb/Zb + π → Υ(nS)ππ (n = 1, 2, 3)
Dalitz analysis indicate that
Υ(10890) → Zb/Zb + π → Υ(nS)ππ (n = 1, 2, 3) proceed mainly through the
resonances Zb and Zb, though Υ(10890) → Υ(1S)ππ has a significant direct
component, expected in tetraquark interpretation of Υ(10890)
A comprehensive analysis of the Belle data including the direct and resonant
components is required to test the underlying dynamics, yet to be carried out
Parametrizing the amplitudes in terms of two Breit-Wigners, one can determine
the ratio α/β
sb¯b : 1 → 1 transition
Rel.Norm. = 0.85 ± 0.08 = |α|2
/|β|2
Rel.Phase = (−8 ± 10)◦
sb¯b : 1 → 0 transition
Rel.Norm. = 1.4 ± 0.3
Rel.Phase = (185 ± 42)◦
Within errors, the tetraquark assignment with α = β = 1 is supported, i.e.,
|Zb =
|1bq, 0¯b¯q − |0bq, 1¯b¯q
√
2
, |Zb
= |1bq, 1¯b¯q J=1
|Zb =
|1q¯q, 0b¯b − |0q¯q, 1b¯b
√
2
, |Zb
=
|1q¯q, 0b¯b + |0q¯q, 1b¯b
√
2
Ahmed Ali (DESY, Hamburg) 24 / 33
37. Zb(10610)/Zb(10650) → B(∗) ¯B(∗) Contd.
|B and |B∗ differ in the spin alignment of the light quark. However, light quark
spin is not conserved by QCD (gluonic) interactions
Hence, predictions derived from the the representations (labels 0b¯q and 1b¯q are
viewed as B and B∗ mesons, respectively)
|Zb = |1b¯q, 1q¯b J=1
|Zb =
|1b¯q, 0q¯b + |0b¯q, 1q¯b
√
2
are not as reliable as those derived from the representation
|Zb =
|1q¯q, 0b¯b − |0q¯q, 1b¯b
√
2
, |Zb =
|1q¯q, 0b¯b + |0q¯q, 1b¯b
√
2
The issue of the unaccounted direct production of the B∗ ¯B∗, B¯B∗ etc., at and near
the Υ(10890), once satisfactorily resolved, may also reflect on the resonant
contributions Zb → B∗ ¯B∗ and Zb → B¯B∗
In view of this, Zb(10610)/Zb(10650) → B(∗) ¯B(∗) decays offer no firm distinction
between the tetraquark vs. hadron molecules scenarios at present, and we wait
for the improved Belle/Belle-2 measurements
Ahmed Ali (DESY, Hamburg) 26 / 33
45. Dipion mass distributions in Υ(5S) → Υ(nS)ππ decays?
tetraquark &
rescattering trying to explain data (unresolved so far)
Ahmed Ali (DESY, Hamburg) 27 / 33
46. Tetraquark model for Yb production and decays
Van Royen-Weisskopf formula
⇒ Γ(1−−→ e+e−)
Assumption: Point-like diquarks
[AA, Hambrock, Mishima, PRL (2010)]
Ahmed Ali (DESY, Hamburg) 28 / 33
47. Tetraquark model for Yb production and decays
Van Royen-Weisskopf formula
⇒ Γ(1−−→ e+e−)
Assumption: Point-like diquarks
[AA, Hambrock, Mishima, PRL (2010)]
Γee(Y[b,l/h]) =
24α2Q2
[b,l/h]
M4
Y[b,l/h]
κ2
R
(1)
11 (0)
2
Ahmed Ali (DESY, Hamburg) 28 / 33
48. Tetraquark model for Yb production and decays
Van Royen-Weisskopf formula
⇒ Γ(1−−→ e+e−)
Assumption: Point-like diquarks
[AA, Hambrock, Mishima, PRL (2010)]
diquark charge
Γee(Y[b,l/h]) =
24α2Q2
[b,l/h]
M4
Y[b,l/h]
κ2
R
(1)
11 (0)
2
Ahmed Ali (DESY, Hamburg) 28 / 33
49. Tetraquark model for Yb production and decays
Van Royen-Weisskopf formula
⇒ Γ(1−−→ e+e−)
Assumption: Point-like diquarks
[AA, Hambrock, Mishima, PRL (2010)]
radial tetraquark WF @ origin
Γee(Y[b,l/h]) =
24α2Q2
[b,l/h]
M4
Y[b,l/h]
κ2
R
(1)
11 (0)
2
Ahmed Ali (DESY, Hamburg) 28 / 33
50. Tetraquark model for Yb production and decays
Van Royen-Weisskopf formula
⇒ Γ(1−−→ e+e−)
Assumption: Point-like diquarks
[AA, Hambrock, Mishima, PRL (2010)]
hadronic size parameter
Γee(Y[b,l/h]) =
24α2Q2
[b,l/h]
M4
Y[b,l/h]
κ2
R
(1)
11 (0)
2
Ahmed Ali (DESY, Hamburg) 28 / 33
51. Tetraquark model for Yb production and decays
Van Royen-Weisskopf formula
⇒ Γ(1−−→ e+e−)
Assumption: Point-like diquarks
[AA, Hambrock, Mishima, PRL (2010)]
Γee(Y[b,l/h]) =
24α2Q2
[b,l/h]
M4
Y[b,l/h]
κ2
R
(1)
11 (0)
2
Suppressed O(10) vs Υ(5S)
Production ratio: ΓY[b,l]
/ ΓY[b,h]
= 1−2 tan θ
2+tan θ
2
Isospin breaking through production
e.g.
σΥ(1S)K+K−
σΥ(1S)K0 ¯K0
=
Q2
[bu]
Q2
[bd]
= 1
4
Ahmed Ali (DESY, Hamburg) 28 / 33
52. Yb decay
Continuum Resonance
+
Breit-Wigner shape for resonance:
1
(q2 − M2) + iMΓ
q2 ≡ M2
PP Resonances show in MPP spectrum
Not in MΥP spectrum since Zb negligible
Ahmed Ali (DESY, Hamburg) 29 / 33
53. Fit to σ(e+e− → Yb → Υ(1S)π+π−)
Fit results, data from [Belle, PRL 08]
χ2/d.o.f. = 21.5/15 Good agreement with data
Clear resonance dominance!
(˜σ: normalized to measurement )
0++ tetraquarks σ(500) + f0(980)
2++ meson f2(1270)
Ahmed Ali (DESY, Hamburg) 30 / 33
54. Predictions for Υ(1S)(K+K−, ηπ0)
Fit determines couplings (assume SU(3) flavor symmetry for couplings
(σ(500), f0(980), a0(980)) → PP , [’t Hooft, Isidori, Maiani, Polosa, Riquer, PLB 08] )
predictions for spectra:
Agreement with σK+K− = 0.11+0.04
−0.03 (BELLE)
1.0 σηπ0 2.0 predicted
Resonance dominance
Characteristic shape
Good tests (relying on Yb has 2 flavor states)
Ahmed Ali (DESY, Hamburg) 31 / 33
55. Central Issue: Are Yc, Zcs, Yb and Zbs related?
Ahmed Ali (DESY, Hamburg) 32 / 33
56. Summary
A new facet of QCD is opened by the discovery of the exotic X, Y, Z states
Dedicated studies required to establish the nature of exotics in experiments and QCD
Important puzzles remain in the complex:
What is the nature of Yc(4260)? A tetraquark? or a c¯cg hybrid?
What exactly is Υ(10888)? Is it a pure Υ(5S)? Does Yb(10890) still exist?
Branching ratios at Υ(5S) enigmatic
Tetraquarks tentatively provide a credible explanation for the BELLE anomaly at Υ(5S)
Need detailed Dalitz distributions of Y(11020). Do Zb, Zb (and related excited states) play
a role in the the decays of Y(11020)?
There is a good case for having dedicated runs above Υ(4S)at Belle-II
We look forward to experimental results from Belle-II and LHC
Ahmed Ali (DESY, Hamburg) 33 / 33
