New observations and Multiquark Candidates at BESII
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Transcript of 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)[email protected]
QCD 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
ppppJ /
pKJ /K
p pKJ /
pp
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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 >= 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/p=1.7%(1+p2) z = 2.3 cm
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World J/ and (2S) Samples (106)
J/ (2S)
0
10
20
30
40
50
60
MarkI I I DM 2 BES I BES I I0
2
4
6
8
10
12
14
MKI MKII MKIII CBAL BESI BESII
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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
M=1859 MeV/c2
< 30 MeV/c2 (90% CL)
J/pp
M(pp)-2mp (GeV)0 0.1 0.2 0.3
3-body phase space acceptance
2/dof=56/56
acceptance weighted BW +3 +5
10 25
pp
BES II
Phys. Rev. Lett. 91, 022001 (2003)
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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:
KppB
Belle
BES II
ppJ /
The structure in B decays is much wider and is not really at threshold. It can be explained by fragmentation mechanism.
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)
5107~))1860(())1860(/( ppXBRXJBR
3102))1860(/( XJBR
%4))1860(( ppXBR
Considering that decaying into ppbar is only fromthe 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)?
+ n +
deuteron:
loosely bound 3-q 3-q color singlets with Md = 2mp-
baryonium:
loosely bound 3-q 3-q color singlets with Mb = 2mp-?
attractive nuclear force attractive force?
There is lots & lots of literature about this possibilityE. 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)…A. Datta, P.J. O’Donnell, PLB 567, 273 (2003)]M.L. Yan et al., hep-ph/0405087B. Loiseau et al., hep-ph/0411218G.J. Ding and M.L. Yan, Phys. Rev. C 72,
015208 (2005)…
Observations of this structure in other decay modes are desirable.
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New Observation of X(1835) in
J
PRL 95, 262001 (2005)
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Observation of X(1835) in J
'
'
'/J
'
' '/J
X(1835)6.0
X(1835)5.1
phase space
phase space
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Mass spectrum fitting
54264obsN
MeVM 7.21.67.1833
MeV7.73.207.67
410)4.04.02.2()()( XBXJB
7.7The +- mass spectrum for decaying into +- and
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Comparison of two decay modes
Mass and width from m=1827.48.1MeV/c2 , =54.234.5MeV/c2
Mass and width from m=1836.37.9MeV/c2 , =70.323.1MeV/c2
)( J
)( J
)( J410)7.08.1()()( XBXJB
)( J410)5.03.2()()( XBXJB
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.D71:054010, 2005 ) in the fit (I=0)
M = 1830.6 6.7 MeV
< 153 MeV @90%C.L.
ppp mM 2
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
p
pKJ /
Phys. Rev. Lett. 93, 112002 (2004)
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Observation of an anomalous enhancement near the threshold of mass spectrum at BES IIp
BES II pKJ /
3-body phase space
For a S-wave BW fit: M = 2075 12 5 MeV Γ = 90 35 9 MeV
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Possible Interpretations FSI? Theoretical calculations are needed. Conventional K* or a multiquark resonance?
• Search for its Kπ , Kππ decay modes would help to understand its nature.
• We are now studying J/ KKπ , KKππ
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K mass threshold enhancement
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)(GeV/c2ΛK
M
PS, eff. corrected
MMM KΛK
Observation of a strong enhancement near the threshold of mass spectrum at BES IIK
(Arbitrary normalization)
BES II pKJ /
NX*
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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 Λ* in the fits —— The structure Nx*has:Mass 1500~1650MeV Width 70~110MeV
JP favors 1/2-
The most important is: It has large BR(J/ψ pNX*) BR(NX* KΛ) 2 X 10-4 ,
suggesting NX* has strong coupling to KΛ.
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A ΛK resonance predicted by chiral SU(3) quark model
Based on a coupled-channel study of ΛK and ΣK states in the chiral SU(3) quark model, the phase shift shows the existence of a ΛK resonance between ΛK and ΣK mass threshold.
Phys.Rev. C71 (2005)
064001
Ecm – ( MΛ+MK ) (MeV)
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The KΛ mass threshold enhancement NX(1610) could be a KΛ 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
recoiling against
-sideband
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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++
410)65.027.061.2(
)()/(
XBrXJBr
2
21926
MeV/c 2820105
MeV/c 181812
M
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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?
hep-ph/0602172, hep-ph/0602190
Further look in , K*K*, …. are desirable !
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σ and κ observations
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The pole in at BESII
/J
M()
M(+-0)
M(+-
)
0
Averaged pole position:(541 39) (252 42)i MeV
Phys. Lett. B 598 (2004) 149
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κ
24872
8173 MeV/c )45309()30841(
i
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.
pp
ppJ /
pppp
J
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mass threshold enhancement was observed in
Evidence of NX(1610) was observed near KΛ mass threshold, suggesting a KΛ bound or resonant state.
An mass threshold enhancement f0(1810) was observed in J/
and are observed at BESII
Summary (II)
p pKJ /
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Thank You!
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KKJ /
00/ ss KKJ
)1710(0f
)1710(0fMeV 166
MeV 41740155108
1025
M
PWA analysis shows one scalar in 1.7 GeV region
Phys. Rev. D 68 (2003) 052003
f0(1710)
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Crystal Ball results on inclusive photon spectrum of J/psi decays
3109.0~)/( JBR
3103.4~)'/( JBR
3103~))1440(/(
50~
JBR
MeV
3102)/(
)18601830(
XJBR
X
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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.
310)4.03.1()(
)%9.06.2()(
ppBR
BR
c
c
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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 !
NO strong dynamical threshold enhancement in cross sections (at LEAR)
pp
pp
pmppM 2)(
|M|2 |M|2BES BES
elasticelasticM ~|| 2 annlabann PM ~|| 2
Both arbitrary normalization Both arbitrary normalization
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Any inconsistency? NO!
For example: with Mres = 1859 MeV, Γ = 30 MeV, J=0, 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.
4/)(4)(4
)12)(12()12(
22
2
22
2
21
rescm
outin
pcmres mE
BBmEc
SSJ
pp
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J/ decays do not suffer large t-channel “background” as ppbar collision.
>>
p p p p
p
p p p p
p
/J
In ppbar collision, the background is much larger (I)
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A.Sibirtsev, J. Haidenbauer, S. Krewald, Ulf-G. Meißner, A.W. Thomas, Phys.Rev.D71:054010, 2005
P-waveI=0 S-wave
I=1 S-wave
In ppbar elastic scattering, I=1 S-wave dominant,while in J/ radiative decays I=0 S-wave dominant.
ppbar elastic cross section near threshold
In ppbar collision, the background is much larger (II)
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So, the mechanism in ppbar collision is quite different from J/ decays and the background is much smaller in J/ decays
It would be very difficult to observe an I=0 S-wave ppbar bound state in ppbar collisions if it exists.
J/ decays (in e+e- collider) have much cleaner environment: “JP, I” filter
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Pure FSI disfavored (I)
1. 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.
2. The enhancement caused by Coulomb interaction is even smaller than one-pion-exchange FSI.
BES
one-pion-exchange FSI
|M|2 |M|2
Both arbitrary normalization
BES
pmppM 2)(
Both arbitrary normalization
Coulomb interaction
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FSI Factors
Most reliable full FSI factors are from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) , which fit ppbar elastic cross section near threshold quite well.
ppbar elastic cross section near threshold
I=1 S-wave
I=0 S-waveP-wave
pmppM 2)(
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Pure FSI disfavored (II)
I=0 S-wave FSI CANNOT fit the BES data.
ppp mM 2
58/192../2 fod
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So, pure FSI is disfavored.
However, we do not exclude the contribution from FSI.
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pp near threshold enhancement is very likely due to some broad sub-threshold 0-+ resonance(s) plus FSI.
From B.S. Zou, Exotics 05:
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.D71:054010, 2005 ) in the fit (I=0)
M = 1830.6 6.7 MeV
= 0 93 MeV
ppp mM 2
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What do we expect from J/psigamma 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
The +- mass spectrum for decaying into +- and
Statistical Significance 7.7
J
J
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Similar enhancement also observed in pK'
4 away from phase space.
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This enhancement is NOT observed in process at SAPHIR Kp
pKJBES/
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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 1535~1750 MeV, N*(1535) has the largest , and from previous estimation, NX would also have almost the largest BR to KΛ.
Also, the EM transition rate of NXto proton is very low.
Kp
Kp)*()*()*( KNBRpNBRKNp
)*( pNBR
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Discussion on KΛ mass threshold enhancement NX(1610)
NX(1610) has strong coupling to KΛ:• From (S&D-wave d
ecay) and is a P-wave decay, we can estimate
• From BESII,
• The phase space of NX to KΛ is very small, so such a big BR shows NX has very strong coupling to KΛ, indicating it has a big hidden ssbar component. (5-quark system)
3102)/( ppJBR )1600(/ XpNJ
3100.1)/( XpNJBR
4102~)()/( KNBRpNJBR XX
%20)( KNBR X
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0
/
J
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M(+-0)(GeV/c2) M(+-0)(GeV/c2) M(+-0)(GeV/c2)
M(
+ -
0 )(G
eV/c
2 )
sideband
BES II Preliminary
signal after best candidate selection (best masses)
signal with multiple entries
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Eff. curvePhase Space
Side-band
M()
BES II Preliminary
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(1760) f0(1710)f0(1790)f0(1810)
PWA Fit results
M()
Total
f2(1910) f2(160) BG
BES II Preliminary
Being submitted to PRD.
Using observed mass and width for f0(1810)in J/
f0(1710)
dominated by (1760) a 0++ is needed (6.5 )
f2(1910) 5.8
f2(1640) 5.5
BG
(1760) > 10
f0 6.5