New observations and Multiquark Candidates at BESII

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New observations and Multiquark Candidates at
BESII
Xu-Ai ZHUANG (for BES Collaboration) Institute of
High Energy Physics (IHEP) zhxa_at_mail.ihep.ac.cn Q
CD and Hadronic interactions La Thuile , Mar.
20, 2006
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Outline

• Multi-quark Candidates at BESII
• A possible bound state
  mass threshold enhancement in
  and new
  observation of X(1835).
• mass threshold enhancement in
• mass threshold enhancement in
• ?? mass threshold enhancement in J/? ? ???
• ? and ? observation

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Multi-quark State, Glueball and Hybrid

• Hadrons consist of 2 or 3 quarks
• Naive Quark Model
• New forms of hadrons
• Multi-quark states Number of quarks gt 4
• Hybrids qqg, qqqg
• Glueballs gg, ggg

Meson q q Baryon q q q
They have been searched for experimentally for
a very long time, but none is established.
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BESII
VC ?xy 100 ?m TOF ?T 180 ps
? counter ?r? 3 cm MDC ?xy 220 ?m
BSC ?E/?E 22
?z 5.5 cm ?dE/dx 8.5
?? 7.9 mr B field 0.4 T
?p/p1.7?(1p2) ?z 2.3 cm
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World J/? and ?(2S) Samples (106)

• Largest from BES

J/?
?(2S)

• 2002

• 2001

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A possible ppbar bound state
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Observation of an anomalous enhancement near the
threshold of mass spectrum at BES II
J/y?gpp
BES II
acceptance weighted BW
3 5 -10 -25
M1859 MeV/c2 G lt 30 MeV/c2 (90 CL)
c2/dof56/56
0
0.1
0.2
0.3
M(pp)-2mp (GeV)
3-body phase space
acceptance
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This narrow threshold enhancement is NOT observed
in B decays

• The structure in B decays is obviously different
  from the BES observation

Belle
The structure in B decays is much wider and is
not really at threshold. It can be explained by
fragmentation mechanism.
BES II
Threshold enhancement in J/? decays is obviously
much more narrow and just at threshold, and it
cannot be explained by fragmentation mechanism.
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X(1860) has large BR to ppbar

• We (BES) measured
• From Crystal Ball result, we estimate
• So we would have
  
• (This would be the largest BR to ppbar among
  all known mesons)

Considering that decaying into ppbar is only
from the tail of X(1860) and the phase space is
very small, such a BR indicates X(1860) has
large coupling to ppbar !
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pp bound state (baryonium)?
There is lots lots of literature about this
possibility

• E. Fermi, C.N. Yang, Phys. Rev. 76, 1739 (1949)
• I.S. Sharpiro, Phys. Rept. 35, 129 (1978)
• C.B. Dover, M. Goldhaber, PRD 15, 1997 (1977)
• Datta, P.J. ODonnell, PLB 567, 273 (2003)
• M.L. Yan et al., hep-ph/0405087
• B. Loiseau et al., hep-ph/0411218
• G.J. Ding and M.L. Yan, Phys. Rev. C 72, 015208
  (2005)

deuteron
baryonium
attractive nuclear force
attractive force?

n

-
loosely bound 3-q 3-q color singlets with Md
2mp- e
loosely bound 3-q 3-q color singlets with Mb
2mp-d ?
Observations of this structure in other decay
modes are desirable.
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• New Observation of X(1835) in

PRL 95, 262001 (2005)
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Observation of X(1835) in
X(1835) 5.1 ?
phase space
X(1835) 6.0 ?
phase space
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Mass spectrum fitting
The ??-?? mass spectrum for ?? decaying into
?????-? and ??? ??
7.7?


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Comparison of two decay modes

• Mass and width from
• m1827.4?8.1MeV/c2 , ?54.2?34.5MeV/c2
  
• Mass and width from
• m1836.3?7.9MeV/c2 , ?70.3?23.1MeV/c2

• The mass, width and branching fractions obtained
  from two different decay modes are consistent
  with each other.

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Re-fit to J/???p pbar including FSI
Include FSI curve from A.Sirbirtsev et al. (
Phys.Rev.D71054010, 2005 ) in the fit (I0)
M 1830.6 ? 6.7 MeV ? lt 153 MeV _at_90C.L.
In good agreement with X(1835)
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A Possible ppbar Bound State

• X(1835) could be the same structure as ppbar mass
  threshold enhancement.
• It could be a ppbar bound state since it
  dominantly decays to ppbar when its mass is above
  ppbar mass threshold.
• Its spin-parity should be 0- this would be an
  important test.

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Observation of mass
threshold enhancement in

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Observation of an anomalous enhancement near the
threshold of mass spectrum at BES II
BES II
3-body phase space
For a S-wave BW fit M 2075 ?12 ? 5 MeV
G 90 ? 35 ? 9
MeV
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Possible Interpretations

• FSI? Theoretical calculations are needed.
• Conventional K or a multiquark resonance?
• Search for its Kp , Kpp decay modes would help to
  understand its nature.
• We are now studying
• J/? ? KKp , KKpp

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K? mass threshold enhancement
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Observation of a strong enhancement near the
threshold of mass spectrum at BES II
NX
BES II
PS, eff. corrected
(Arbitrary normalization)
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• A strong enhancement is observed near the mass
  threshold of MK? at BES II.
• Preliminary PWA with various combinations of
  possible N and ? in the fits The structure
  Nxhas
• Mass 15001650MeV
• Width 70110MeV
• JP favors 1/2-
• The most important is

It has large BR(J/? ? pNX) BR(NX? K?) ?2 X 10-4
, suggesting NX has strong coupling to K?.
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A ?K resonance predicted by chiral SU(3) quark
model

• Based on a coupled-channel study of ?K and SK
  states in the chiral SU(3) quark model, the
  phase shift shows the existence of a ?K
  resonance between ?K and SK mass threshold.
• Phys.Rev. C71 (2005) 064001

Ecm ( M?MK ) (MeV)
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• The K? mass threshold enhancement NX(1610) could
  be a K? bound/resonant state.

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Observation of ?? mass threshold enhancement
Submitted to Phys. Rev. Lett., hep-ex/0602031
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• We studied DOZI process

J/ ? ? ? ? ? ?
? ??-?0 K K-
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Clear ? and ? signals
?
?
?
?-sideband
recoiling against ?
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Dalitz Plot
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A clear mass threshold enhancement is observed
Acceptance
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Side-bands do not have mass threshold enhancement
Side-bands
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Partial Wave Analysis is performed
0 is favored over 0- and 2
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• Is it the same 0 observed in KK mass of
  J/???KK? It is a multiquark state, a glueball, or
  a hybrid?

Further look in ??, KK, ?? . are desirable !
hep-ph/0602172, hep-ph/0602190
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s and ? observations
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The ? pole in at BESII

MeV
Averaged pole position
Phys. Lett. B 598 (2004) 149
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?
Phys. Lett. B 633 (2006) 681
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Summary (I)

• A very narrow and strong mass threshold
  enhancement is observed in decays
  at BES II
• It is not observed in B decays.
• Its large BR to suggests it be a
  bound state.
• X(1835) is observed in
  It could be same structure as the ppbar
  mass threshold enhancement, i.e., it could be a
  ppbar bound state.

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Summary (II)

• mass threshold enhancement was observed in
• Evidence of NX(1610) was observed near K? mass
  threshold, suggesting a K? bound or resonant
  state.
• An ?? mass threshold enhancement f0(1810) was
  observed in J/? ? ???
• ? and ? are observed at BESII

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Thank You!
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f0(1710)
PWA analysis shows one scalar in 1.7 GeV region
Phys. Rev. D 68 (2003) 052003
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Crystal Ball results on inclusive photon
spectrum of J/psi decays
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The large BR to ppbar suggest it could be an
unconventional meson

• For a conventional qqbar meson, the BRs decaying
  into mesons are usually at least one order higher
  than decaying into baryons.
• There are many examples in PDG.
• E.g.
• So the large BR to ppbar (with limited phase
  space from the tail of X(1830)) seems very hard
  to be explained by a conventional qqbar meson.

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NO strong dynamical threshold enhancement in
cross sections (at LEAR)

• With threshold kinematic contributions removed,
  there are very smooth threshold enhancements
  in elastic matrix element and very
  small enhancement in annihilation matrix
  element
• ? much weaker than what BES observed !

M2
M2
BES
BES
Both arbitrary normalization
Both arbitrary normalization
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Any inconsistency? NO!

• For example with Mres 1859 MeV, G 30 MeV,
  J0, BR(ppbar) 10, an estimation based on
• At Ecm 2mp 6 MeV ( i.e., pLab 150 MeV
  ), in elastic process, the resonant cross section
  is 0.6 mb much smaller than the continuum
  cross section 94 ? 20 mb .
• ? Difficult to observe it in cross
  sections experimentally.

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In ppbar collision, the background is much larger
(I)

• J/? decays do not suffer large t-channel
  background as ppbar collision.

gtgt
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In ppbar collision, the background is much larger
(II)
In ppbar elastic scattering, I1 S-wave
dominant, while in J/? radiative decays I0
S-wave dominant.
ppbar elastic cross section near threshold
I1 S-wave
P-wave
I0 S-wave
A.Sibirtsev, J. Haidenbauer, S. Krewald, Ulf-G.
Meißner, A.W. Thomas, Phys.Rev.D71054010, 2005
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So, the mechanism in ppbar collision is quite
different from J/? decays and the background is
much smaller in J/? decaysIt would be very
difficult to observe an I0 S-wave ppbar
bound state in ppbar collisions if it exists.

• J/? decays (in ee- collider) have much cleaner
  environment JP, I filter

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Pure FSI disfavored (I)

• Theoretical calculation (Zou and Chiang, PRD69
  034004 (2003)) shows The enhancement caused by
  one-pion-exchange (OPE) FSI is too small to
  explain the BES structure.
• The enhancement caused by Coulomb interaction is
  even smaller than one-pion-exchange FSI.

M2
M2
BES
BES
Both arbitrary normalization
Both arbitrary normalization
one-pion-exchange FSI
Coulomb interaction
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FSI Factors

• Most reliable full FSI factors are from
  A.Sirbirtsev et al. ( Phys.Rev.D71054010, 2005
  ),which fit ppbar elastic cross section near
  threshold quite well.

ppbar elastic cross section near threshold
I1 S-wave
P-wave
I0 S-wave
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Pure FSI disfavored (II)

• I0 S-wave FSI CANNOT fit the BES data.

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So, pure FSI is disfavored.However, we do not
exclude the contribution from FSI.
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From B.S. Zou, Exotics 05
pp near threshold enhancement is very likely
due to some broad sub-threshold 0- resonance(s)
plus FSI.
From A. Sirbirtsev
FSI factors should be included in BW fit.
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Re-fit to J/???p pbar including FSI
Include FSI curve from A.Sirbirtsev et al. (
Phys.Rev.D71054010, 2005 ) in the fit (I0)
M 1830.6 ? 6.7 MeV ? 0 ? 93 MeV
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What do we expect from J/psi?gamma ppbar results?

• The baryonium interpretation of the
  ppbar mass threshold enhancement predicts a new
  particle around 1.85 GeV which should be observed
  in other decay mode with full BW resonant
  structure.

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Observation of X(1835) in
Statistical Significance 7.7 ?
The ??-?? mass spectrum for ?? decaying into
?????-? and ??? ??
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Similar enhancement also observed in
4? away from phase space.
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This enhancement is NOT observed in
process at SAPHIR
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• Non-observation of NX in
  suggests an evidence of new baryon (personal
  view)
• It is unlikely to be N(1535).
• If NX were N(1535), it should be observed
  in process, since
• 
  
• From PDG, for the N in the mass range 15351750
  MeV, N(1535) has the largest
  , and from previous estimation, NX would also
  have almost the largest BR to K?.
• Also, the EM transition rate of NXto proton is
  very low.

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Discussion on K? mass threshold enhancement
NX(1610)

• NX(1610) has strong coupling to K?
• From
  (SD-wave decay) and
  is a P-wave decay, we can estimate
• From BESII,
• The phase space of NX to K? is very small, so
  such a big BR shows NX has very strong coupling
  to K?, indicating it has a big hidden ssbar
  component. (5-quark system)

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BES II Preliminary
?
?
M(??-?0)(GeV/c2)
M(??-?0)(GeV/c2)
M(??-?0)(GeV/c2)
M(??-?0)(GeV/c2)
? sideband
w signal with multiple entries
w signal after best candidate selection (best
w masses)
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BES II Preliminary
M(??)
Eff. curve
Side-band
Phase Space
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PWA Fit results
BES II Preliminary
f0(1710) f0(1790) f0(1810)
Total
?(1760) gt 10 ?
f0 6.5 ?
?(1760)
f0(1710)
Using observed mass and width for f0(1810) in
J/y ? g w?
f2(1640) 5.5 ?
f2(1910)
f2(160)
f2(1910) 5.8 ?
BG
BG
M(??)

• dominated by ?(1760)
• a 0 is needed (6.5 ?)

Being submitted to PRD.