Transcript Study of New Light Hadron Spectroscopy at BESIII

Study of New
Hadron Spectroscopy at BESIII
Liu Fang (IHEP)
for BESIII Collaboration
The 9th National Workshop for Heavy Flavors
and CP Violation
2011.10.12-10.16
Hangzhou, Zhejiang, China
1
OUTLINE
Introduction
Latest results on new hadron spectroscopy
pp mass threshold enhancement in J/ and ’
radiative decays
Confirmation of X(1835) and observation of two
new structures
 Observation X(1870) in J/(+-)

Summary
2
Satellite view of BEPCII /BESIII
LINAC
South
BESIII
detector
2004: start BEPCII construction
2008: test run of BEPCII
2009-now: BECPII/BESIII
data taking
3
BEPCII storage rings
Beam energy:
1.0-2.3 GeV
Design Luminosity:
1×1033 cm-2s-1
Optimum energy:
1.89 GeV
Energy spread:
5.16 ×10-4
No. of bunches:
93
Bunch length:
1.5 cm
Total current:
0.91 A
Circumference：
237m
4
BES Detector
5
Data samples
• So far BESIII has collected :
– 2009: 225 Million J/(4 BESII)
– 2009: 106 Million ’ (4 CLEOC)
– 2010-11: 2.9 fb1 (3770)
(3.5  CLEO-c 0.818fb1)
- May 2011: 0.5fb1 @4010 MeV (one
month) for Ds and XYZ
spectroscopy
• BESIII will also collect:
– more J/, ’, (3770)
– data at higher energies （for XYZ
searches, R scan and Ds physics）
6
7
Light hadron

QCD allows different type of hadrons:
8
Observation of pp mass threshold enhancement
     J / ,J /   pp
@BESIII
J /    pp
@BESIII
    pp
@BESIII
9
Observation of
ppmass threshold enhancement
@ BESII
J /    pp
3-body phase space
X(1860)
0
BESII
0.2
0.1
acceptance
theoretical speculation:
 pp bound state (baryonium)
 FSI effect
 ……
0.3
Mpp-2mp (GeV)
M=1859 +3 +5 MeV/c2
10 25
PRL 91 (2003) 022001
G < 30 MeV/c2 (90% CL)
10
Several non-observations
(1S)   pp@CLEO
PRD 73 (2006) 032001
J /    pp@BESII
EPJ C53 (2008) 15
    pp@ BESII
PRL 99 (2007) 011802
No significant signal of X(1860)
near threshold found
(only 2 significance)
Mpp (GeV)
11
Observation of pp mass threshold enhancement
at BESIII
     J / ,J /   pp
J /    pp
BESII
0
0.1
0.2
0.3
M=1861 +6 -13+7-26 MeV/c2
M=1859 +3 +5 MeV/c2
G < 38 MeV/c2 (90% CL)
G < 30 MeV/c2 (90% CL)
10 25
PRL 91 (2003) 022001
Chinese Physics C 34, 421 (2010)
12
PWA on the pp mass threshold structure in
J /   p p
BESIII
X(pp)
Preliminary
results
ηc
 Evident narrow ppbar mass threshold enhancement
 Partial Wave Analysis (PWA):
• Concentrate on dealing with the pp mass threshold structure,
especially to determine the JPC (M(pp)<2.3GeV) .
• Convariant tensor amplitudes (S. Dulat and B. S. Zou, Eur.Phys.J A 26:125,
2005).
13
• Include the Juich-FSI effect (A. Sirbirtsen et al. Phys.Rev.D 71:054010, 2005).
13
PWA results and projections in
J /   p p
Preliminary results
14
Measurement for X(1860)
• PWA results are carefully checked from different aspects:
– Contribution of additional resonances
– Solution with different combinations
– Different background levels and fitting mass ranges
– Different BW formula
– ……
All uncertainties are considered as systematic errors
• Different FSI models Model dependent uncertainty
• Spin-parity, mass, width and B.R. of X(1860):
J pc  0 
Preliminary results
>6.8σ better than other Jpc assignments.
M  1832  5(stat) 1917 (syst)  19(mod)MeV/c 2
G  13  20(stat) 1133 (syst)  4(mod)MeV/c 2 or G  48MeV/c 2 @ 90% C .L.
5
B ( J /   X ( pp )) B ( X ( pp )  pp )  (9.0  0.7 (stat) 1.5
(syst)

2.3
（
mod
）
)

10
5.1
15
PWA on the pp mass threshold structure in
    pp
Preliminary results
BESIII
Obviously different line
shape of ppbar mass
spectrum near threshold
from that in J/ψ decays
χcJ
ηc
PWA results:
PWA Projection:
• Significance of X(pp) is larger than 6.9σ.
• The production ratio R:
B(    X ( pp))
R
B( J /   X ( pp))
first measurement
+0.72
=
(5.08

0.5
6(
stat)
(syst)  with
0.12(mod)
)%rule”.
-3.83
• It is suppressed compared
“12%
16
Confirmation of X(1835) in J      
and observation of two new structures
at BESIII
17
X(1835) at BESII
BESII result (Stat. sig. ~ 7.7 ) :
M  1833.7  6.1( stat )  2.7( syst ) MeV
G  67.7  20.3(stat)  7.7(syst)MeV
PRL 95,262001(2005)

LQCD predicts the 0-+ glueball mass is ~2.3GeV.

A 0-+ glueball may have similar property as c
(mainly decay into ).

J/+- was studied with 58M J/@BESII
Need to confirm X(1835) with BESIII ~225M J/ data !!!
18
Mass spectrum of   

  
BES III

  
X(1835)
Combination for  to +- and 
 X(1835) and c are evident.
 Two additional structures are
bserved at M~2.1GeV and 2.3GeV
BES III
X(2370)
o
X(2120)
 There maybe some f1(1510).
19
Fitting for the combined mass spectrum


Fitting with four resonances (acceptance weighted BW

Three background components:
gauss)
① Contribution from non-’ events estimated by ’ mass sideband
② Contribution from J /   0   ' with re-weighting method
③ Contribution from “PS background”
fbkg ( x)  ( x  m0 )1/ 2  a0 ( x  m0 )3/ 2  a1( x  m0 )5/ 2 , m0  2m  m
Red line: estimated contribution of ①+ ②
Black line: total background
BES III
Stat. sig. is conservatively estimated:
fit range, background shape, contribution
of extra resonances
20
X(1835) , X(2120), X(2370) at BESIII
BESIII fit results:
Resonance
M( MeV/c2)
G( MeV/c2)
Stat.Sig.
X(1835)
1836.5±3.0+5.6-2.1
190.1±9.0+38-36
>20σ
X(2120)
2122.4±6.7+4.7-2.7
83±16+31-11
7.2σ
X(2370)
2376.3±8.7+3.2-4.3
83±17+44-6
6.4σ
BESIII
For the X(1835):
BR( J /    X (1835)) BR( X (1835)    - ')
-4
 (2.87  0.09( stat )0.49
0.52 ( syst ))  10
X(1835) consistent with 0+
PWA is needed to understand
these structures.
21
21
Summary of X(1835), X(2120) & X(2370)
in J/(’+-)
• X(1835) resonance is confirmed at BESIII, but the
width is significantly larger than that measured at
BESII with one resonance in the fit.
• Two new resonances, X(2120) and X(2370), are
observed with significances larger than 7.2 and
6.4 respectively.
• PWA is needed not only to determine the spinparities of above three resonances, but also to make
more precise measurements on masses, widths and
BRs by considering possible interferences among
them.
22
Observation X(1870) in J/X,
Xa0(980)(+-)

X(1835) observed at BESII and then
confirmed at BESIII in J/→γπ+π-η´

theoretical interpretations: pseudoscalar
glueball, / excited states ..

study of its production in hadronic decays
to our surprise, we observed a new structure
around 1.87 GeV
23

X(1870) in J/X, Xa0(980)
a0(980)
M(+)
• With a0(980):
M(a0(980))
M()
• Veto a0(980):
 In addition to the well
-known ’, f1(1285) and
(1405), an unknown str
ucture (denoted as X(18
70)) around 1.87GeV/c2
is observed.
 The f1(1285), (1405)
and X(1870) primarily d
ecay via a0(980)± mode.
M(+) non-a0(980)
24
Fitting results of X(1870)


Fitting with three resonances (acceptance weighted BW
 Gauss)
Background component described by Polynomial function
f1(1285)
X(1870):
7.2
(1405)
① Contribution from non-
and/or non-a0(980) BG
events
② Contribution from
J/b1(1235)a0(980)
③ Contribution from “PS”
process of J/a0(980)
M(a0(980))
BR(J/X, X
)
25
Summary of X(1870) in J/(+-)
BESIII
arxiv :1107.1806
Accepted by PRL.
26
Summary and Prospects

Huge data samples collected for charmonium
decays at BESIII. A lot of results have been
obtained,
 The spin-parity of the pp mass threshold enhancement in
J/γ pp was first determined as 0-+
 Confirmation of X(1835) in J/  + and observation
of two new structures X(2120) and X(2370) in J/  
decays
 Observation of new structure X(1870) in J/

We expect more exciting results in the coming
years from BESIII.
27
many thanks for your attention !
28