Measurements of J/ψdecays into ωK \bar{K} πand φK \bar{K} π

1.4 MB·

by  BES Collaboration

Measurements of J/ψ decays into ωKK¯π, φKK¯π and ηK0K±π∓
S
M. Ablikim1, J. Z. Bai1, Y. Bai1, Y. Ban11, X. Cai1, H. F. Chen16, H. S. Chen1,
H. X. Chen1, J. C. Chen1, Jin Chen1, X. D. Chen5, Y. B. Chen1, Y. P. Chu1, Y. S. Dai18,
Z. Y. Deng1, S. X. Du1, J. Fang1, C. D. Fu14, C. S. Gao1, Y. N. Gao14, S. D. Gu1,
Y. T. Gu4, Y. N. Guo1, Z. J. Guo15a, F. A. Harris15, K. L. He1, M. He12, Y. K. Heng1,
J. Hou10, H. M. Hu1, T. Hu1, G. S. Huang1b, X. T. Huang12, Y. P. Huang1, X. B. Ji1,
X. S. Jiang1, J. B. Jiao12, D. P. Jin1, S. Jin1, Y. F. Lai1, H. B. Li1, J. Li1, R. Y. Li1,
8
W. D. Li1, W. G. Li1, X. L. Li1, X. N. Li1, X. Q. Li10, Y. F. Liang13, H. B. Liao1c,
0
0 B. J. Liu1, C. X. Liu1, Fang Liu1, Feng Liu6, H. H. Liu1d, H. M. Liu1, J. B. Liu1e,
2
J. P. Liu17, H. B. Liu4, J. Liu1, Q. Liu15, R. G. Liu1, S. Liu8, Z. A. Liu1, F. Lu1,

n
G. R. Lu5, J. G. Lu1, C. L. Luo9, F. C. Ma8, H. L. Ma2, L. L. Ma1f, Q. M. Ma1,
a
J M. Q. A. Malik1, Z. P. Mao1, X. H. Mo1, J. Nie1, S. L. Olsen15, R. G. Ping1, N. D. Qi1,

0 H. Qin1, J. F. Qiu1, G. Rong1, X. D. Ruan4, L. Y. Shan1, L. Shang1, C. P. Shen15,
1
D. L. Shen1, X. Y. Shen1, H. Y. Sheng1, H. S. Sun1, S. S. Sun1, Y. Z. Sun1, Z. J. Sun1,

x] X. Tang1, J. P. Tian14, G. L. Tong1, G. S. Varner15, X. Wan1, L. Wang1, L. L. Wang1,
e L. S. Wang1, P. Wang1, P. L. Wang1, W. F. Wang1g, Y. F. Wang1, Z. Wang1,
-
p Z. Y. Wang1, C. L. Wei1, D. H. Wei3, Y. Weng1, N. Wu1, X. M. Xia1, X. X. Xie1,
e
h G. F. Xu1, X. P. Xu6, Y. Xu10, M. L. Yan16, H. X. Yang1, M. Yang1, Y. X. Yang3,
[ M. H. Ye2, Y. X. Ye16, C. X. Yu10, G. W. Yu1, C. Z. Yuan1, Y. Yuan1, S. L. Zang1h,

2 Y. Zeng7, B. X. Zhang1, B. Y. Zhang1, C. C. Zhang1, D. H. Zhang1, H. Q. Zhang1,
v
H. Y. Zhang1, J. W. Zhang1, J. Y. Zhang1, X. Y. Zhang12, Y. Y. Zhang13, Z. X. Zhang11,
1
1 Z. P. Zhang16, D. X. Zhao1, J. W. Zhao1, M. G. Zhao1, P. P. Zhao1, Z. G. Zhao1i,
4 H. Q. Zheng11, J. P. Zheng1, Z. P. Zheng1, B. Zhong9 L. Zhou1, K. J. Zhu1, Q. M. Zhu1,
1
. X. W. Zhu1, Y. C. Zhu1, Y. S. Zhu1, Z. A. Zhu1, Z. L. Zhu3, B. A. Zhuang1, B. S. Zou1
2
1
(BES Collaboration)
7
0
1 Institute of High Energy Physics, Beijing 100049, People’s Republic of China
:
v
2 China Center for Advanced Science and Technology(CCAST),
i
X
Beijing 100080, People’s Republic of China
r
a 3 Guangxi Normal University, Guilin 541004, People’s Republic of China
4 Guangxi University, Nanning 530004, People’s Republic of China
5 Henan Normal University, Xinxiang 453002, People’s Republic of China
6 Huazhong Normal University, Wuhan 430079, People’s Republic of China
7 Hunan University, Changsha 410082, People’s Republic of China
8 Liaoning University, Shenyang 110036, People’s Republic of China
9 Nanjing Normal University, Nanjing 210097, People’s Republic of China
10 Nankai University, Tianjin 300071, People’s Republic of China
11 Peking University, Beijing 100871, People’s Republic of China
12 Shandong University, Jinan 250100, People’s Republic of China
13 Sichuan University, Chengdu 610064, People’s Republic of China
14 Tsinghua University, Beijing 100084, People’s Republic of China
15 University of Hawaii, Honolulu, HI 96822, USA
16 University of Science and Technology of China, Hefei 230026, People’s Republic of China
1
17 Wuhan University, Wuhan 430072, People’s Republic of China
18 Zhejiang University, Hangzhou 310028, People’s Republic of China
a Current address: Johns Hopkins University, Baltimore, MD 21218, USA
b Current address: University of Oklahoma, Norman, Oklahoma 73019, USA
c Current address: DAPNIA/SPP Batiment 141,
CEA Saclay, 91191, Gif sur Yvette Cedex, France
d Current address: Henan University of Science and
Technology, Luoyang 471003, People’s Republic of China
e Current address: CERN, CH-1211 Geneva 23, Switzerland
f Current address: University of Toronto, Toronto M5S 1A7, Canada
g Current address: Laboratoire de l’Acc´el´erateur Lin´eaire, Orsay, F-91898, France
h Current address: University of Colorado, Boulder, CO 80309, USA
i Current address: University of Michigan, Ann Arbor, MI 48109, USA
(Dated: February 2, 2008)
Abstract
Thedecays of J/ψ ωKK¯π andJ/ψ φKK¯π arestudiedusing5.8 107 J/ψ events collected
→ → ×
with the Beijing Spectrometer (BESII) at the Beijing Electron-Positron Collider (BEPC). The
K0K±π∓ and K+K−π0 systems, produced in J/ψ ωKK¯π, have enhancements in the invariant
S →
mass distributions at around 1.44 GeV/c2. However, there is no evidence for mass enhancements
in the KK¯π system in J/ψ φKK¯π. The branching fractions of J/ψ ωK0K±π∓, φK0K±π∓,
→ → S S
ωK∗K¯ + c.c., and φK∗K¯ + c.c. are obtained, and the J/ψ ηK0K±π∓ branching fraction is
→ S
measured for the first time.
PACS numbers: 13.20.Gd, 13.25.Gv, 13.20.-v,12.38.Qk,14.40.-n
2
I. INTRODUCTION
A pseudoscalar gluonium candidate, the so-called E/ι(1440), was observed in pp¯annihi-
lation in 1967 [1] and in J/ψ radiative decays in the 1980’s [2, 3, 4]. After 1990, more and
more observations revealed the existence of two resonant structures around 1.44 GeV/c2 in
a (980)π, KK¯π, and K∗K¯ spectra [5, 6, 7, 8, 9, 10, 11]. They showed that the lower state,
0
η(1405), has large couplings to a (980)π and KK¯π, while the high mass state, η(1475), fa-
0
vors K∗K¯. The η(1405)was also confirmed by MarkIII[12], Crystal Barrel[13], andDM2[4]
in decays into ηππ in J/ψ radiative decays and p¯p annihilations.
In contrast, although η(1475) was observed in KK¯π (K∗K¯) [5, 6, 7, 8, 9, 10, 11], it was
not seen in ηππ. Nonetheless, the study of KK¯π and ηππ channels in γγ collisions [14]
showed that η(1475) appeared in KK¯π, but not in ηππ, while η(1405) appeared in neither
channel.
The study of the decays J/ψ γ,ω,φ KK¯π is a useful tool in the investigation of
→ { }
quark and possible gluonium content of the states around 1.44 GeV/c2. In this paper,
we investigate the possible structure in the KK¯π final state in J/ψ hadronic decays at
around 1.44 GeV/c2, and measure the branching fraction of J/ψ ηK0K±π∓ for the first
time, based on 5.8 107 J/ψ events collected with the Beijing Sp→ectromSeter at the Beijing
×
Electron-Positron Collider (BEPC) .
II. THE BES DETECTOR
BESII is a large solid-angle magnetic spectrometer that is described in detail else-
where [15]. Charged particle momenta are determined with a resolution of σ /p =
p
1.78%p1+p2 (p in GeV/c2) in a 40-layer cylindrical main drift chamber (MDC). Par-
ticle identification (PID) is accomplished using specific ionization (dE/dx) measurement
in the MDC and time-of-flight (TOF) information in a barrel-like array of 48 scintillation
counters. The dE/dx resolution is σ 8.0%; the TOF resolution is σ = 180 ps for
dE/dx TOF
≃
Bhabha events. Outside of the time-of-flight counter is a 12-radiation-length barrel shower
counter (BSC) comprised of gas proportional tubes interleaved with lead sheets. The BSC
measures the energy and direction of photons with resolutions of σ /E 21%√E (E in
E
≃
GeV), σ = 7.9 mrad, and σ = 2.3 cm. The iron flux return of the magnet is instrumented
φ z
with three double layers of counters that are used to identify mouns.
A Geant3 based Monte Carlo (MC) package (SIMBES) with detailed consideration of
the detector performance is used. The consistency between data and MC has been carefully
checked in many high purity physics channels, and the agreement is reasonable [16]. The
detection efficiencies and mass resolutions for each decay mode presented in this paper are
obtained with uniform phase space MC generators.
III. ANALYSIS
In this analysis, ω mesons are observed in the ω π+π−π0 decay, φ mesons in the
φ K+K− decay, and other mesons are detected in →the decays: K0 π+π−, π0 γγ,
→ S → →
3
η π+π−π0. The final states of the analyzed decays J/ψ ω,η K0K±π∓, ωK+K−π0,
φK→0K±π∓, and φK+K−π0 are 2(π+π−)K±π∓γγ, π+π−K→+K{−γγγ}γ,SK+K−π+π−K±π∓,
S
and 2(K+K−)γγ, respectively.
Candidate events are required to satisfy the following common selection criteria:
1. The correct number of charged tracks with net charge zero is required for each event.
Each charged track should have a good helix fit in the MDC, and the polar angle θ of
each track in the MDC must satisfy cosθ < 0.8. The event must originate from the
| |
collision point; tracks except π± from K0 must satisfy px2 +y2 2 cm, z 20 cm,
S ≤ | | ≤
where x, y, and z are the space coordinates of the point of closest approach of tracks
to the beam axis.
2. Candidate events should have at least the minimum number of isolated photons asso-
ciated with the different final states. Each photon should have an energy deposit in
the BSC greater than 50 MeV, the angle between the shower development direction
and the photon emission direction less than 30◦, and the angle between the photon
and any charged track larger than 8◦.
3. For each charged track in an event, χ2 (i) is determined using both dE/dx and TOF
PID
information:
2 2 2
χ (i) = χ (i)+χ (i),
PID dE/dx TOF
where i corresponds to the particle hypothesis. A charged track is identified as a K
(π) if χ2 for the K (π) hypothesis is less than those for the π and p (K and p)
PID
hypotheses.
4. The selected events are subjected to four constraint kinematic fits (4C-fit), unless
otherwise specified. When there are more than the minimum number of photons in an
event, all combinations are tried, and the combination with the smallest χ2 is retained.
The branching fraction is calculated using
N
obs
B(J/ψ X) = , (1)
→ ǫ N B(X Y)
J/ψ→X→Y J/ψ
× × →
and the upper limit for a branching fraction is determined using
N
up
B(J/ψ X) < , (2)
→ ǫ N B(X Y) (1 σsys)
J/ψ→X→Y J/ψ
× × → × −
where, N is the number of events observed, N is the upper limit on the number of the
obs up
observed events at the 90% C.L. calculated using a Bayesian method [17], ǫ is the detection
efficiency obtainedfromMC simulation, N isthenumber ofJ/ψ events, (5.77 0.27) 107
J/ψ
± ×
[18], σsys is the corresponding systematic error, and B(X Y) is the branching fraction,
→
taken from the Particle Data Group (PDG) [17], of the X intermediate state to the Y final
state.
4
A. J/ψ ω,η K0K±π∓
→ { } S
AtleastonechargedtrackmustbeidentifiedasakaonusingTOFanddE/dxinformation.
If there is more than one kaon candidate, the assigned kaon is the one with the largest kaon
weight. Candidateevents arefittedkinematically usingenergymomentumconservation(4C-
fit) under the 2(π+π−)K±π∓γγ hypothesis, and χ2 < 25 is required. Each event is required
to contain one K0 meson with six possible π+π− combinations to test for consistency with
S
the K0. Looping over all combinations, we select the one closest to the K0 mass, denoted
S S
as m , provided it is within 15 MeV/c2 of the K0 mass. After K0 selection, the two
π+π− S S
remaining oppositely-charged pion combinations along with the two gammas are used to
calculate m . Figure 1 (a) shows the scatter plot of m versus m with two
π+π−γγ γγ π+π−γγ
possible entries per event, where clear η and ω signals are seen.
FIG. 1: (a) The scatter plot of m versus m , and (b) the π+π−γγ invariant mass for
γγ π+π−γγ
J/ψ ω,η K0K±π∓ candidate events with two possible entries per event. The curves in (b) are
→ { } S
the results of the fit described in the text, and the shaded histogram in (b) shows the normalized
background estimated from the K0-sideband region (0.025 GeV/c2 < m m < 0.055
S | π+π− − KS0|
GeV/c2).
The π+π−γγ invariant mass distribution with two possible entries per event is shown
in Fig. 1 (b), where η and ω signals are apparent. The branching fractions of J/ψ
→
ωK0K±π∓ and ηK0K±π∓ are obtained by fitting this distribution. The backgrounds for
S S
J/ψ ωK0K±π∓ which contribute to the peak in the ω signal region mainly come from
non-K→0 evenSts and events from J/ψ ωK0K0 that survive selection criteria. The number
of backSground events from J/ψ ωK→0K0 Sis eSstimated from Monte-Carlo simulation to be
less than 2 . Backgrounds for J→/ψ SηKS0K±π∓ contributing to the peak in the η signal
region mainly come from non-K0 eve→nts anSd events from J/ψ decays into K∗0K¯∗(1430)0
(K0π0)(K0η). The latter contrSibution is estimated to be less than one event2 from M→C
S S
simulation. Non-K0 events from the K0 sideband region (0.025 GeV/c2 < m m <
S S | π+π−− KS0|
0.055 GeV/c2) are shown in Fig. 1 (b) as the shaded histogram, the background events are
19.2 15.6ω and 4.1 7.0η by fitting thedistribution with possible signals andpolynomial
± − ±
background.
A fit to the m distribution is performed by using ω and η Breit-Wigner (BW)
π+π−γγ
functions folded with Gaussian resolution functions plus a quadratic polynomial, shown
5
as the curve in Fig. 1 (b). The numbers of events in the ω and η peaks are 1971.7
±
41.4 and 231.6 23.1, respectively. Here, the background events in the decays of J/ψ
ωK0K±π∓ and±J/ψ ηK0K±π∓ estimated above are not subtracted but are included→in
S → S
the background systematic error. The J/ψ ωK0K±π∓ and J/ψ ηK0K±π∓ detection
→ S → S
efficiencies are obtained from MC simulation to be 1.48% and 1.18%, respectively. The
branching fractions are then determined as:
B(J/ψ ωK0K±π∓) = (3.77 0.08) 10−3,
→ S ± ×
B(J/ψ ηK0K±π∓) = (2.18 0.22) 10−3.
→ S ± ×
Here the errors are statistical only.
1. J/ψ ωK∗K¯ +c.c. ωK0K±π∓
→ → S
To select the ω signal, the mass combination with π+π−γγ closest to the ω mass is
required to satisfy m m < 0.04 GeV/c2. Figure 2 shows the scatter plot of m
| π+π−γγ − ω| KS0π
versus m for J/ψ ωK0K±π∓ candidate events, where the events in the cross bands
corresponKdπto J/ψ →ωK∗K¯S+c.c..
→
FIG. 2: The scatter plot of m versus m for J/ψ ωK0K±π∓ candidate events.
KS0π K±π∓ → S
Figure3(a)showsthescatter plotofm versus m , andthereisanaccumulation
π+π−γγ π+π−
of events in the ω and K0 cross bands. The combined mass spectrum of K0π∓ and K±π∓
S S
in the signal region (box 1 in Fig. 3 (a)), which is defined as m m < 0.015 GeV/c2
| π+π−− KS0|
and m m < 0.04 GeV/c2, is shown in Fig. 3 (b), where a clear K∗ signal is
π+π−γγ ω
| − |
observed. The K∗ signal is fitted with a BW function folded with a Gaussian resolution
function plus a third-order polynomial, and 1208.3 93.3 K∗ events are obtained.
±
Non-ω andnon-K0 backgroundsarestudiedusing ω andK0 sidebandevents. Figure3(c)
S S
is the fitted Kπ mass spectrum in the ω sideband region ( m m < 0.015 GeV/c2,
| π+π− − KS0|
0.06 GeV/c2 < m m < 0.14 GeV/c2, shown as horizontal sideband boxes 2
π+π−γγ ω
| − |
6
in Fig. 3 (a)) and K0 sideband region (0.03 GeV/c2 < m m < 0.06 GeV/c2,
S | π+π− − KS0|
m m < 0.04 GeV/c2, shown as vertical sideband boxes 3), and the number of K∗
π+π−γγ ω
| − |
sidebandeventsN = (686.2 56.0)isobtained. Figure3(d)isbackgroundfromthecorner
sid1
region (0.03 GeV/c2 < m ± m < 0.06 GeV/c2, 0.06 GeV/c2 < m m <
| π+π− − KS0| | π+π−γγ − ω|
0.14 GeV/c2, shown as diagonal boxes 4), and the number of K∗ events N is equal to
sid2
(134.1 25.5). The number of background events inthe signal regionis half of the sum of K∗
events±in the ω sideband and K0 sideband regions (N ) minus a quarter of the K∗ events
S sid1
in the corner regions (N ). So N = (686.2 56.0)/2 (134.1 25.5)/4 = (309.6 28.8).
sid2 bg
± − ± ±
FIG. 3: (a) The scatter plot of m versus m , and the combined mass spectrum of K0π∓
π+π−γγ π+π− S
and K±π∓ with two entries per event J/ψ ωK∗K¯ + c.c. candidate events for (b) the signal
→
region (the central box 1); (c) the ω and K0 sideband regions (two horizontal boxes 2 and two
S
vertical sideband boxes 3); and for (d) the corner region (four diagonal boxes 4). The curves are
the results of the fit described in the text.
The detection efficiency is estimated to be 1.23% from MC simulation. After background
subtraction, the branching fraction is determined to be
B(J/ψ ωK∗K¯ +c.c.) = (6.20 0.68) 10−3,
→ ± ×
where the error is statistical only.
7
2. J/ψ ωX(1440) ωK0K±π∓
→ → S
Figure 4 (a) shows the scatter plot of m versus m , and Fig. 4 (b) is the
KS0K±π∓ π+π−γγ
K0K±π∓ invariant mass spectrum after ω selection ( m m < 0.04 GeV/c2). Figs.
4 (Sa) and (b) show a resonance near 1.44 GeV/c2, den| otπe+dπ−aγsγX−(14ω4|0). To ensure that this
peak is not due to background, we have made studies of potential background processes
using both data and MC simulations. Non-ω and non-K0 processes are studied with ω and
S
K0 mass sideband events, respectively. The main background channel J/ψ ω2(π+π−)
S →
and other background processes with 6-prong events are studied by MC simulation. In
addition, we also checked for possible backgrounds with a MC sample of 60 106 J/ψ
× →
anything decays generated by the LUND-charm model [19]. None of these background
sources produces a peak around 1.44 GeV/c2 in the K0K±π∓ invariant mass spectrum.
S
FIG. 4: (a) The scatter plot of m versus m and (b) the K0K±π∓ invariant mass
KS0K±π∓ π+π−γγ S
distribution for J/ψ ωK0K±π∓ candidate events. The curves in (b) are the results of the fit
→ S
described in the text.
The K0K±π∓ invariant mass distribution is fitted with a BW function convoluted with a
S
Gaussian mass resolution function (σ = 7.44 MeV/c2) to represent the X(1440) signal and
a third-order polynomial background function. The mass and width obtained from the fit
are M = 1437.6 3.2 MeV/c2 and Γ = 48.9 9.0 MeV/c2, and the fit yields 248.8 35.2
± ± ±
events.
Using the efficiency of 1.45% determined from a uniform phase space MC simulation, we
obtain the branching fraction to be
B(J/ψ ωX(1440)) B(X(1440) K0K±π∓) = (4.86 0.69) 10−4,
→ · → S ± ×
where the error is only the statistical error.
B. J/ψ ωK+K−π0
→
At least one charged track is required to be a kaon and the combined PID probability
for K+K−π+π− is required to be greater than those for the K±π∓π+π− and π+π−π+π−
8
hypotheses. A 4C kinematic fit is made under the K+K−π+π−4γ hypothesis. There are
three combinations to form two π0’s, and further a six-constraint kinematic fit (6C-fit) with
the smallest χ2 is made requiring two π0’s from four photons. Events with χ2 < 50 and
6C 4C
χ2 < 50 are selected. To reject the possible multiple photon background events, χ2 is
6C 4C
requiredtobelessthanthosefortheK+K−π+π−2γ,K+K−π+π−3γ,andK+K−π+π−5γ hy-
potheses. Background events with K0 decays, such as K∗0K¯∗(1430)0 K0K±π∓ π0,2π0 ,
and γK∗K¯∗ γK0K±π∓π0, are elimSinated by requiring m2 m→ >S 0.02 G{eV/c2 i}n
→ S | π+π− − KS0|
the π+π− invariant mass.
There are two π+π−π0 mass combinations, and the one closest to the ω mass, denoted
as m , is selected. The scatter plot of m versus m is shown in Fig. 5
π+π−π0 K+K−π0 π+π−π0
(a), where the circle indicates some enhancement from J/ψ ωX(1440) events in the
ωK+K−π0 decay. →
FIG.5: (a)Thescatterplotofm versusm ,(b)theK±π0 invariantmassdistribution
K+K−π0 π+π−π0
with two possible entries per event, and (c) the K+K−π0 invariant mass distribution for J/ψ
→
π+π−π0K+K−π0 candidate events. The curves are the results of the fit described in the text, and
the shaded histogram (b) shows the normalized background estimated from the ω-sideband region.
1. J/ψ ωK∗±K∓ ωK+K−π0
→ →
To suppress the main K∗0 backgrounds, m m > 0.05 GeV/c2 is required. In
K±π∓ K∗0
addition to the above selection, the further|requirem−ent of |m m < 0.04 GeV/c2
π+π−π0 ω
is imposed. The combined mass spectrum of K+π0 and K−π|0 is show−n in F|ig. 5 (b), where
the K∗± signal is seen, and is fitted to obtain the branching fraction of J/ψ ωK∗±K∓.
→
Background events for ωK∗±K∓ which could contribute to the peak in the K∗± signal
region mainly come from events with K∗ decays, such as J/ψ K∗0K¯∗(1430)0 into 4-prong
2
plus multiple photons, J/ψ φK∗K¯, and J/ψ γK∗K¯∗→, but their contributions can
→ →
be ignored according to MC studies. It is further confirmed that the J/ψ ωK∗±K∓
→
background is negligible using ω and π0 sideband events.
The K±π0 invariant mass distribution in Fig. 5 (b) (2 entries/event) is fitted with a
K∗± BW function with the mass and width fixed to PDG values [17] plus a third-order
polynomial. The number of K∗± events obtained is (175.6 27.4). The detection efficiency
is 0.32%, and the branching fraction of J/ψ ωK∗K¯ +c.c±. is determined to be
→
9
B(J/ψ ωK∗K¯ +c.c.) = (6.53 1.02) 10−3,
→ ± ×
where the error is statistical only.
2. J/ψ ωX(1440) ωK+K−π0
→ →
Figure 5 (c) shows the K+K−π0 invariant mass recoiling against the ω, where a X(1440)
signal is observed. We have also studied potential background processes using both data
and MC simulations. Non-ω processes are studied with the ω mass sideband events (0.06
GeV/c2 < m m < 0.10 GeV/c2). Background with ω decays is studied by MC
π+π−π0 ω
simulations|, similar t−o tho|se of J/ψ ωK∗K¯ + c.c. ωK+K−π0. In addition, we also
checked for possible backgrounds usin→g a MC sample o→f 60 106 J/ψ anything decays
generated by the LUND-charm model. In each case, the K+×K−π0 mass→distribution shows
no evidence of an enhancement near 1440 MeV/c2.
By fitting the K+K−π0 mass spectrum in Fig. 5 (c) with a BW function convoluted
with a Gaussian mass resolution function (σ = 14.2 MeV/c2) plus a third-order polynomial
background function, the mass and width of M = 1445.9 5.7 MeV/c2 and Γ = 34.2 18.5
MeV/c2 are obtained, and the number of events from the±fit is 62.1 18.3. A fit with±out a
±
BW signal function returns a value of 2lnL larger than the nominal fit by 31.7 with three
−
degrees of freedom (d.o.f.), corresponding to a statistical significance of 5.0 σ for the signal.
The efficiency is determined to be 0.64% from a phase space MC simulation, and the
branching fraction is
B(J/ψ ωX(1440)) B(X(1440) K+K−π0) = (1.92 0.57) 10−4,
→ · → ± ×
where the error is statistical.
C. J/ψ φK0K±π∓
→ S
Events with six charged tracks are selected, and at least two charged tracks must be
identified as kaons. If there are more than two kaons, the two kaons with the largest kaon
PID probabilities are regarded as the real kaons. The other charged tracks are assumed,
one at a time, to be a kaon, while the other three to be pions, and these combinations
of three kaons and three pions are kinematically fitted. The hypothesis with the smallest
χ2 is considered as the right combination, and χ2 < 20 is required. Two combinations of
oppositely charged pions are used to reconstruct the K0 signal, and the one closest to the
S
K0 mass is required to be within 15 MeV/c2.
S
The invariant mass of the two mass combinations formed with oppositely charged kaons
are shown in Fig. 6, where a clear φ signal is observed. A fit to the K+K− mass distri-
bution in Fig 6 is performed to obtain the number of J/ψ φK0K±π∓ events. Back-
→ S
grounds contributing to the φ signal peak mainly come from J/ψ into φf′(1525) φηη,
2
φη′ φηπ+π−, φK0K0, and φ2(π+π−) (excluding φK0K0). From MC simulations →of these
→ S S S S
10