Transcript New Results from BES

New Observations and
Multiquark Candidates
at BESII
HongXun Yang
(for BES Collaboration)
Institute of High Energy Physics (IHEP)
[email protected]
CPS2006
BEIJING, Sept. 16, 2006
J/ decays are an ideal factory to search for
and study light exotic hadrons:
 The production cross section of J/ is high.
 The production BR of hadrons in J/ decays are
one order higher than ’ decays (“12% rule”).
 The phase space to 1-3 GeV hadrons in J/
decays are larger than  decays.
 Exotic hadrons are naively expected to have
larger or similar production BR to conventional
hadrons in J/ decays.
 Clean background environment compared with
hadron collision experiments, e.g., “JP, I” filter.
World J/ Sample (106)
2001
60
50
40
30
20
10
0
MarkIII
DM2
BESI
BESII
Outline
 A possible p p bound state:
pp
threshold enhancement in J /  p p
new observation of X(1835).
mass
and

J
/


pK

p


mass threshold enhancement in
 K   mass threshold enhancement in J /  pK  
  mass threshold enhancement in J/  
 New observation of a broad 1- - resonance in
J/  K+K- 0
A possible ppbar bound state
Observation of an anomalous enhancement near
the threshold of pp mass spectrum at BES II
BES II J/pp
acceptance
weighted BW
M=1859 +3 +5 MeV/c2
10 25
G < 30 MeV/c2 (90% CL)
c2/dof=56/56
0
Phys. Rev. Lett. 91, 022001 (2003)
3-body phase space
0.1
0.2
M(pp)-2mp (GeV)
acceptance
0.3
This narrow threshold enhancement is
NOT observed in pp   ) S1(  at CLEO
Br ( (1S )   X) / Br ( J /    X)
 0.7% @ 90% CL
 This result cannot be
explained by pure FSI effect,
since FSI is a universal effect.
FSI interpretation of the
narrow and strong ppbar
threshold enhancement is
disfavored.
 This indicates that X(1860)
has a production property
similar to ’ meson.
c.f.:
Br ( (1S )    ' ) / Br ( J /     ' )
No enhancement
near threshold
 0.4% @ 90% CL
This narrow threshold enhancement is
NOT observed in pp   / J at BESII
Br ( J /   X) / Br ( J /    X)
 0.5
@ 95% CL
No narrow strong
enhancement
near threshold
 This again disfavors FSI
and indicates that X(1860)
has a production
property similar to ’
meson.
c.f.:
Br ( J /     ' ) / Br ( J /     ' )
 0.04
 This also indicates
X(1860) may have strong
coupling to gluons as ’
meson.
Pure FSI disfavored
I=0 S-wave FSI CANNOT fit the BES data.
FSI curve from A.Sirbirtsev
et al. ( Phys.Rev.D71:054010,
2005 ) in the fit (I=0)
c 2 / d .o. f  192/ 58
FSI * PS * eff + bck
M pp  2mp
X(1860) has large BR to ppbar
 We (BES) measured:
BR( J /  X (1860))  BR( X (1860)  pp) ~ 7 105
 From Crystal Ball result, we etimate:
BR( J /  X (1860))  2 103
 So we would have:
BR( X (1860)  pp)  4%
(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 !
Summary of the properties of the strong ppbar
mass threshold enhancement X(1860)
 So far, it is only observed in J/ radiative
decays:
• It has production properties similar to ’ meson.
• It could have strong coupling to gluons as ’ meson.
 It could have the largest decay BR to ppbar
among all PDG particles:
• It has strong coupling to ppbar.
New Observation of X(1835) in
J      


PRL 95, 262001 (2005)
Observation of X(1835) in
J       
Statistical Significance 7.7 
J       
The +- mass spectrum for  decaying into
+- and  
Mass spectrum fitting
The +- mass spectrum
for  decaying into
+- and  
7.7
N obs  264  54
m  1833.7  6.1  2.7MeV
BESII Preliminary
G  67.7  20.3  7.7MeV
B( J   X ) B( X    )  (2.2  0.4  0.4)  104
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
G < 153 MeV @90%C.L.
In good agreement with X(1835)
M pp  2mp
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.
Observation of p  mass
threshold enhancement in

J /  pK 
Observation of an anomalous enhancement near
the threshold of p mass spectrum at BES II
BES II
J /  pK
3-body phase space
Phys. Rev. Lett. 93, 112002 (2004)
For a S-wave BW fit: M = 2075 12  5 MeV
Γ = 90  35  9 MeV
K mass threshold enhancement
Observation of a strong enhancement near the
threshold of K   mass spectrum at BES II
NX*
BES II
J /  pK
M K  Λ (GeV/c 2 )
PS, eff. corrected
(Arbitrary normalization)
MKΛ  MK  M
 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.
A ΛK resonance predicted by
chiral SU(3) quark model
 Based on a coupledchannel 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.
( F. Huang, Z.Y. Zhang et al.
Phys. Rev. C71: 064001, 2005 )
Ecm – ( MΛ+MK ) (MeV)
 The KΛ mass threshold enhancement
NX(1610) could be a KΛ
bound/resonant state
(5-quark system with hidden ssbar
components).
Observation of  mass
threshold enhancement
 We studied DOZI process:
J/    +

+

+-0


K+ K-
Clear  and  signals



recoiling against 
Dalitz Plot
A clear mass threshold enhancement is observed

Acceptance
Phys. Rev. Lett. 96, 162002 (2006)
 The radiative decay of J/ has been
observed in the 58M J/ data.
 A significant structure of  has been found
near the mass threshold.
 PWA shows the structure favors 0++, with a
mass 181219
, width 1052028 MeV,
26  18MeV
and the corresponding branch ration is
(2.610.270.65)x10-4.
 It could be a multiquark/hybrid/glueball state.
 Its relation with f0(1710),f0(1790)?
Is the STRONG threshold enhancement
universal/naïve in J/ decays ? —— NO !
 Actually in many other cases we do NOT see STRONG
threshold enhancements !
 For example: In J/ decays at BES II
J /  K  K 
J /  pp 0
M ( pp)  2mp
M (KK )
J /  pK 
J /  pn 
M ( pK )
M ( p )
New observation of a broad
1- - resonance in J/  K+K- 0
hep-ex/0606047, Submitted to Phys. Rev. Lett.
J/  K+K- 0
very clean 0 signal
0

J/  K+K- 0
X (1580)
0
X (1580)
K * (1410) 
K * (890) 
Background
PID and kinematic fit can significantly reduce
the dominant background from J/  + - 0.
Partial Wave Analysis of J/  K+K- 0 events
Parity conservations in J/  K+K- 0 requires that
spin-parity of K+K- should be 1--,3--,…
X ,  (1700), K * (890), K * (1410)
PWA fit with
and
phase space (PS) gives ( preliminary ):

J
PC

1
( 3  can be ruled out by much worse likelihood )
 98
11 32
2
(157649
)

i
(409
)
MeV
/
c
5591
1267
 X pole position
 Br ( J /  X )  Br ( X  K K )  (8.5  0.6 3.6 ) 10
0


2.7
4
 big destructive interference among X ,  (1700) and PS
Broad X cannot be fit with known mesons
or their interference
 It is unlikely to be (1450), because:
• The parameters of the X is incompatible with (1450).
• (1450) has very small fraction to KK. From PDG:
Br (  (1450)  K  K  )  1.6 103 (95%C.L.)
 It cannot be fit with the interference of (770) ,
(1900) and (2150):
• The log-likelihood value worsens by 85 (c2=170).
How to understand broad X(1580)?
 Search of a similar structure in J/  KSK  will
help to determine its isospin.
 X(1580) could have different nature from
conventional mesons:
• There are already many 1- - mesons nearby.
• Width is much broader than other mesons.
• Broad width is expected for a multiquark state.
Summary (I)
 BES II has observed several strong mass threshold
enhancements in J/ decays.
 Why strong mass threshold structures are important?
Multiquark states may be only observable near mass
thresholds with limited decay phase space.
 Otherwise, it might be too wide to be observed as a resonance
since it can easily fall apart into two or more mesons.
I can see
f0(980)
I can see
broad 
under
other
peaks
broad
resonance or
phase space?
any broad
resonance
under other
peaks?
Summary (II)
 A very narrow and strong pp mass
threshold enhancement is uniquely
observed in J /  pp decays at BES II:
• It is NOT observed in Y(1S) decays, nor in J/psi
hadronic decays. FSI is strongly disfavored.
• Its large BR to pp suggests it be a pp bound
state.
 
J




 
 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.
Summary (III)
 p  mass threshold enhancement was observed
in J /   pK  
 Evidence of NX(1610) was observed near KΛ mass
threshold, suggesting a KΛ bound or resonant
state.
 An  mass threshold enhancement was
observed in J/  .
 A very broad 1- - resonance X(1580) is observed in
J/  K+K- 0 .
J/ψ decay is an ideal place to study
exotic structures.
谢
Thank
谢！
You!
Multi-quark State, Glueball and Hybrid

Hadrons consist of 2 or 3 quarks：
Naive Quark Model：
Meson（ q q ）
Baryon（q q q）

New forms of hadrons:
•
Multi-quark states ：Number of quarks >＝ 4
•
Hybrids ： qqg，qqqg …
•
Glueballs ： gg， ggg …
How quarks/gluons form a hadron is far from being well understood.
Multi-quark states, glueballs and hybrids have
been searched for experimentally for a very long
time, but none is established.
However, during the past two years, a lot of
surprising experimental evidences showed the
existence of hadrons that cannot (easily) be
explained in the conventional quark model.
Most of them are multi-quark candidates.
Searching for multi-quark states becomes one of
the hottest topics in the hadron spectroscopy.
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.
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
NO strong dynamical threshold enhancement in
pp
cross sections (at LEAR)
 With threshold kinematic contributions removed,
there are very smooth threshold enhancements in pp
elastic “matrix element” and very small enhancement in
annihilation “matrix element”:
 much weaker than what BES observed !
|M|2
|M|2
BES
Both arbitrary normalization
BES
Both arbitrary normalization
| M elastic |  ~  elastic
2
M ( pp)  2mp
| M ann |2  ~ Plab ann
Any inconsistency? NO!
 For example: with
Mres = 1859 MeV, Γ = 30 MeV,
J=0, BR(ppbar) ~ 10%, an estimation based on:
 res
(2 J  1)
4 (c)2
Bin Bout G2

2
(2S1  1)(2S2  1) Ecm
 4m2p ( Ecm  mres )2  G2 / 4
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
experimentally.
pp cross sections
This narrow threshold enhancement is
NOT observed in B decays
 The structure in B decays is obviously
different from the BES observation:
Belle
B   ppK 
BES II
J /  pp
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.
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.
|M|2
BES
|M|2
BES
Both arbitrary normalization
Both arbitrary normalization
one-pion-exchange FSI
M ( pp)  2mp
Coulomb interaction
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
P-wave
I=0 S-wave
M ( pp)  2mp
In ppbar collision, the background is much lager (I)
p
p
p
p
>>
p
p
p
p

J /
p
p
 J/ decays do not suffer large t-channel
“background” as ppbar collision.
In ppbar collision, the background is much lager (II)
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
I=1 S-wave
P-wave
I=0 S-wave
A.Sibirtsev, J. Haidenbauer, S. Krewald, Ulf-G. Meißner, A.W. Thomas,
Phys.Rev.D71:054010, 2005
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
So, pure FSI is strongly disfavored.
However, we do not exclude the
contribution from FSI.
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.
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
G = 0  93 MeV
FSI * BW * PS * eff + bck
M pp  2mp
Crystal Ball results on
inclusive photon spectrum of J/psi decays
G ~ 50MeV
BR( J /  (1440)) ~ 3  103
BR( J /  ' ) ~ 4.3 103
BR( J /  ) ~ 0.9 103
X (1830 1860)
BR( J /  X )  2  103
Discussion on I=1 S-wave FSI
Pure FSI disfavored (III) — I = 1
Pure I=1 S-wave FSI is disfavored by more than 3 .
FSI + BW
Pure FSI
M = 1773  21 MeV
G = 0  191 MeV
 2 ln L  85 .3
 2 ln L  65 .8
M pp  2mp
I=0 dominant in J/  radiative decays
 Most I = 0 states have been observed in J/  radiative
decays with big production rate ( especially for 0-+
mesons ) such as , ’, (1440), (1760), f2(1270),
f2(1525), f0(1500), f0(1710).
 The only observed I=1 meson in J/  radiative decays
is 0 with low production rate 4*10– 5, e.g., no evidence
for (1800) in J/   3  process.
It is unlikely to be from (1800) .
I=1 S-wave FSI seems unlikely.
ppbar bound state in NNbar potential
 Paris NNbar potential:
( Paris 93, B. Loiseau et al., hep-ph/0411218, 0501112 )
• For 11S0 , there is a bound state:
E = - 4.8 - i 26.3 MeV
quite close to the BES observation.
 However, Julich NNbar model:
( A. Sibirtsev et al., hep-ph/0411386 )
• For 11S0 :
E = - 104 - i 413 MeV
seems quite far away from BES observation.
They both predict an 11S0 ppbar bound state,
although they are quantitatively different.
BES II Preliminary
J /  
0
J /    


0
No (1800)
J /  
J /  '   ()
NO strong dynamical threshold enhancement in
pp cross sections (at LEAR)
 With threshold kinematic contributions removed, there
are very smooth threshold enhancements in pp elastic
“matrix element” and very small enhancement in
annihilation “matrix element”:
 much weaker than what BES observed !
|M|2
|M|2
BES
Both arbitrary normalization
BES
Both arbitrary normalization
| M elastic |  ~  elastic
2
M ( pp)  2mp
| M ann |2  ~ Plab ann
The large BR to ppbar suggest it could
be an unconventional meson
 For a conventional qqbar meson, the BRs
decaying into baryons are usually at least one
order lower than decaying into mesons.
• There are many examples in PDG.
E.g.
BR(c  )  (2.6  0.9)%
BR(c  pp)  (1.3  0.4)  103
 So the large BR to ppbar (with limited phase
space from the tail of X(1860)) seems very hard to
be explained by a conventional qqbar meson.
pp bound state (baryonium)?
There is lots & lots of literature about this possibility
E. Fermi, C.N. Yang, Phys. Rev. 76, 1739 (1949)
…
deuteron:
baryonium:
I.S. Sharpiro, Phys. Rept. 35, 129 (1978)
C.B. Dover,
M. Goldhaber,attractive
PRD 15, 1997force?
(1977)
attractive nuclear
force
…
A. Datta, P.J. O’Donnell, PLB 567, 273 (2003)]
M.L. Yan et al., hep-ph/0405087
B. Loiseau et al., hep-ph/0411218
…
+
n
+

loosely bound
loosely bound
3-qObservations
3-q color
3-q color
of this3-q
structure
in
singlets with
singlets with
other decay modes are desirable.
Md = 2mp- e
Mb = 2mp-d ?
Analysis of
'
 


J       (     )


X(1835)
5.1 
Analysis of
'
J       (   )


X(1835)
6.0 
Comparison of two decay modes
 Mass and width from J       (      )
m=1827.48.1MeV/c2 , G=54.234.5MeV/c2
 
 Mass and width from J       (    )
m=1836.37.9MeV/c2 , G=70.323.1MeV/c2
J      (     )
B( J   X ) B( X    )  (1.8  0.7)  104
 
 J       (    )
B( J   X ) B( X    )  (2.3  0.5) 104

 The mass, width and branching fractions obtained
from two different decay modes are consistent with
each other.
Similar enhancement also observed in
 '  pK
4 away from phase space.
This enhancement is NOT observed
in p  K process at SAPHIR
BES
J /  pK
Discussion on KΛ mass threshold
enhancement NX(1610)
 NX(1610) has strong coupling to KΛ:
• From BR( J /  pp)  2 103
(S&D-wave
decay) and J /  pNX (1600) is a P-wave
decay, we can estimate
BR( J /  pNX )  1.0 103
• From BESII,
BR( J /  pNX ) BR( N X  K) ~ 2 104
BR( N X  K)  20%
• 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)
Non-observation of NX in p  K
suggests an evidence of new baryon :
 It is unlikely to be N*(1535).
If NX were N*(1535), it should be observed
in p  K
process, since:
•  (p  N *  K)  BR( N *  p) BR( N *  K)
• From PDG, for the N* in the mass range
1535~1750 MeV, N*(1535) has the
largest BR( N *  p) , 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.
Side-bands do not have mass threshold enhancement

Side-bands
Partial Wave Analysis of J/  K+K- 0 events
Four decay modes are included :
1 component :
J /  ( X ,  (1700)) 0 , ( X ,  )  K  K 
K * (890)   K  0
J /   ( K * )  K  , ( K * )   K  0
where K *  K * (890), K * (1410)
Amplitudes are defined by
Covariant tensor formalism
K * (1410)   K  0
points : data
hist : PWA fit
B.S. Zhou and D.V. Bugg, Eur. Phys. J. A16, 537(2003)
 BW with energy-dependent width
1
BW ( s ) 
;
2
s  M R  i s GR ( s )
M R2 p( s ) 2l 1
GR ( s )  GR ( M )
(
)
2
s p( M R )
2
R
J.H. Kuhn, A. Satamaria, Z. Phys. C48, 445 (1990).
1  component :
X  K K 
 (1700)  K  K 
PS
Angular distributions for events with M K
from PWA fit
points : data,
Figures on the right:
 (a),(c),(e) are polar angles
in lab. reference frame
 (b),(d),(f) are polar angles
in CM frames of
K  0 and K  K  respectively

K

 1.7 GeV / c 2
hist : PWA fit
Features of the enhancement near the threshold
of pp mass spectrum at BES II
BES II J/pp
 Peak position:
~ 0 MeV above threshold
 “Width”:
~ 60M eV
 Strong (“Height”):
(S+B)/B ~ 2
0
0.1
0.2
M(pp)-2mp (GeV)
0.3
The above features may
help us easily to judge
whether it is observed in
other processes.