Resonant Structure around 1:8 GeV=c
2and ð1405Þ in J=
c
! !
þM. Ablikim,1M. N. Achasov,5D. Alberto,41Q. An,39Z. H. An,1J. Z. Bai,1R. Baldini,19Y. Ban,25J. Becker,2N. Berger,1 M. Bertani,19J. M. Bian,1O. Bondarenko,18I. Boyko,17R. A. Briere,3V. Bytev,17X. Cai,1A. C. Calcaterra,19G. F. Cao,1
X. X. Cao,1J. F. Chang,1G. Chelkov,17aG. Chen,1H. S. Chen,1J. C. Chen,1M. L. Chen,1S. J. Chen,23Y. Chen,1 Y. B. Chen,1H. P. Cheng,13Y. P. Chu,1D. Cronin-Hennessy,38H. L. Dai,1J. P. Dai,1D. Dedovich,17Z. Y. Deng,1 I. Denysenko,17bM. Destefanis,41Y. Ding,21L. Y. Dong,1M. Y. Dong,1S. X. Du,45R. R. Fan,1J. Fang,1S. S. Fang,1 C. Q. Feng,39C. D. Fu,1J. L. Fu,23Y. Gao,35C. Geng,39K. Goetzen,7W. X. Gong,1M. Greco,41S. Grishin,17M. H. Gu,1
Y. T. Gu,9Y. H. Guan,6A. Q. Guo,24L. B. Guo,22Y. P. Guo,24X. Q. Hao,1F. A. Harris,37K. L. He,1M. He,1Z. Y. He,24 Y. K. Heng,1Z. L. Hou,1H. M. Hu,1J. F. Hu,6T. Hu,1B. Huang,1G. M. Huang,14J. S. Huang,11X. T. Huang,27 Y. P. Huang,1T. Hussain,40C. S. Ji,39Q. Ji,1X. B. Ji,1X. L. Ji,1L. K. Jia,1L. L. Jiang,1X. S. Jiang,1J. B. Jiao,27Z. Jiao,13
D. P. Jin,1S. Jin,1F. F. Jing,35N. Kalantar-Nayestanaki,18M. Kavatsyuk,18S. Komamiya,34W. Kuehn,36J. S. Lange,36 J. K. C. Leung,33Cheng Li,39Cui Li,39D. M. Li,45F. Li,1G. Li,1H. B. Li,1J. C. Li,1K. Li,10Lei Li,1N. B. Li,22Q. J. Li,1
W. D. Li,1W. G. Li,1X. L. Li,27X. N. Li,1X. Q. Li,24X. R. Li,1Z. B. Li,31H. Liang,39Y. F. Liang,29Y. T. Liang,36 X. T. Liao,1B. J. Liu,33B. J. Liu,32C. L. Liu,3C. X. Liu,1C. Y. Liu,1F. H. Liu,28Fang Liu,1Feng Liu,14G. C. Liu,1H. Liu,1 H. B. Liu,6H. H. Liu,12H. M. Liu,1H. W. Liu,1J. P. Liu,43K. Liu,25K. Liu,6K. Y. Liu,21Q. Liu,37S. B. Liu,39X. Liu,20 X. H. Liu,1Y. B. Liu,24Y. W. Liu,39Yong Liu,1Z. A. Liu,1Z. Q. Liu,1H. Loehner,18G. R. Lu,11H. J. Lu,13J. G. Lu,1
Q. W. Lu,28X. R. Lu,6Y. P. Lu,1C. L. Luo,22M. X. Luo,44T. Luo,1X. L. Luo,1C. L. Ma,6F. C. Ma,21H. L. Ma,1 Q. M. Ma,1T. Ma,1X. Ma,1X. Y. Ma,1M. Maggiora,41Q. A. Malik,40H. Mao,1Y. J. Mao,25Z. P. Mao,1 J. G. Messchendorp,18J. Min,1R. E. Mitchell,16X. H. Mo,1N. Yu. Muchnoi,5Y. Nefedov,17I. B. Nikolaev,5Z. Ning,1 S. L. Olsen,26Q. Ouyang,1S. Pacetti,19M. Pelizaeus,37K. Peters,7J. L. Ping,22R. G. Ping,1R. Poling,38C. S. J. Pun,33 M. Qi,23S. Qian,1C. F. Qiao,6X. S. Qin,1J. F. Qiu,1K. H. Rashid,40G. Rong,1X. D. Ruan,9A. Sarantsev,17cJ. Schulze,2 M. Shao,39C. P. Shen,37dX. Y. Shen,1H. Y. Sheng,1M. R. Shepherd,16X. Y. Song,1S. Sonoda,34S. Spataro,41B. Spruck,36 D. H. Sun,1G. X. Sun,1J. F. Sun,11S. S. Sun,1X. D. Sun,1Y. J. Sun,39Y. Z. Sun,1Z. J. Sun,1Z. T. Sun,39C. J. Tang,29 X. Tang,1H. L. Tian,1D. Toth,38G. S. Varner,37X. Wan,1B. Q. Wang,25K. Wang,1L. L. Wang,4L. S. Wang,1M. Wang,27
P. Wang,1P. L. Wang,1Q. Wang,1S. G. Wang,25X. L. Wang,39Y. D. Wang,39Y. F. Wang,1Y. Q. Wang,27Z. Wang,1 Z. G. Wang,1Z. Y. Wang,1D. H. Wei,8Q. G. Wen,39S. P. Wen,1U. Wiedner,2L. H. Wu,1N. Wu,1W. Wu,21Z. Wu,1 Z. J. Xiao,22Y. G. Xie,1G. F. Xu,1G. M. Xu,25H. Xu,1Q. J. Xu,10X. P. Xu,30Y. Xu,24Z. R. Xu,39Z. Z. Xu,39Z. Xue,1 L. Yan,39W. B. Yan,39Y. H. Yan,15H. X. Yang,1M. Yang,1T. Yang,9Y. Yang,14Y. X. Yang,8M. Ye,1M. H. Ye,4B. X. Yu,1 C. X. Yu,24L. Yu,14S. P. Yu Yu,27C. Z. Yuan,1W. L. Yuan,22Y. Yuan,1A. A. Zafar,40A. Zallo,19Y. Zeng,15B. X. Zhang,1
B. Y. Zhang,1C. C. Zhang,1D. H. Zhang,1H. H. Zhang,31H. Y. Zhang,1J. Zhang,22J. W. Zhang,1J. Y. Zhang,1 J. Z. Zhang,1L. Zhang,23S. H. Zhang,1T. R. Zhang,22X. J. Zhang,1X. Y. Zhang,27Y. Zhang,1Y. H. Zhang,1Z. P. Zhang,39
Z. Y. Zhang,43G. Zhao,1H. S. Zhao,1Jiawei Zhao,39Jingwei Zhao,1Lei Zhao,39Ling Zhao,1M. G. Zhao,24Q. Zhao,1 S. J. Zhao,45T. C. Zhao,42X. H. Zhao,23Y. B. Zhao,1Z. G. Zhao,39Z. L. Zhao,9A. Zhemchugov,17aB. Zheng,1 J. P. Zheng,1Y. H. Zheng,6Z. P. Zheng,1B. Zhong,1J. Zhong,2L. Zhong,35L. Zhou,1X. K. Zhou,6X. R. Zhou,39
C. Zhu,1K. Zhu,1K. J. Zhu,1S. H. Zhu,1X. L. Zhu,35X. W. Zhu,1Y. S. Zhu,1Z. A. Zhu,1J. Zhuang,1 B. S. Zou,1J. H. Zou,1and J. X. Zuo1
(BESIII Collaboration)
1Institute of High Energy Physics, Beijing 100049, China 2Bochum Ruhr-University, 44780 Bochum, Germany 3Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA 4China Center of Advanced Science Technology, Beijing 100190, China 5G.I. Budker Institute of Nuclear Physics SB RAS (BINP), Novosibirsk 630090, Russia
6Graduate University of Chinese Academy of Sciences, Beijing 100049, China 7GSI Helmholtzcentre for Heavy Ion Research GmbH, D-64291 Darmstadt, Germany
8
Guangxi Normal University, Guilin 541004, China
9Guangxi University, Naning 530004, China
10Hangzhou Normal University, XueLin Jie 16, Xiasha Higher Education Zone, Hangzhou 310036, China 11Henan Normal University, Xinxiang 453007, China
13Huangshan College, Huangshan 245000, China 14Huazhong Normal University, Wuhan 430079, China
15Hunan University, Changsha 410082, China 16Indiana University, Bloomington, Indiana 47405, USA 17Joint Institute for Nuclear Research, 141980 Dubna, Russia 17aalso at the Moscow Institute of Physics Technology, Moscow, Russia 17bon leave from the Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine
17calso at the PNPI, Gatchina, Russia 18
KVI/University of Groningen, 9747 AA Groningen, The Netherlands
19Laboratori Nazionali di Frascati - INFN, 00044 Frascati, Italy 20Lanzhou University, Lanzhou 730000, China
21Liaoning University, Shenyang 110036, China 22Nanjing Normal University, Nanjing 210046, China
23Nanjing University, Nanjing 210093, China 24Nankai University, Tianjin 300071, China 25Peking University, Beijing 100871, China 26Seoul National University, Seoul, 151-747 Korea
27Shandong University, Jinan 250100, China 28Shanxi University, Taiyuan 030006, China 29Sichuan University, Chengdu 610064, China
30Soochow University, Suzhou 215006, China 31Sun Yat-Sen University, Guangzhou 510275, China 32The Chinese University of Hong Kong, Shatin, N. T. Hong Kong
33The University of Hong Kong, Pokfulam, Hong Kong 34
The University of Tokyo, Tokyo 113-0033 Japan
35Tsinghua University, Beijing 100084, China 36Universitaet Giessen 35392 Giessen, Germany 37University of Hawaii, Honolulu, Hawaii 96822, USA
37dnow at Nagoya University, Nagoya, Japan
38University of Minnesota, Minneapolis, Minnesota 55455, USA 39University of Science Technology of China, Hefei 230026, China
40University of the Punjab, Lahore-54590, Pakistan 41University of Turin INFN, Turin, Italy
42University of Washington, Seattle, Washington 98195, USA 43Wuhan University, Wuhan 430072, China
44Zhejiang University, Hangzhou 310027, China 45Zhengzhou University, Zhengzhou 450001, China
(Received 9 July 2011; published 25 October 2011)
We present results of a study of the decayJ=c ! !þ using a sample ofð225:2 2:8Þ 106
J=c events collected by the BESIII detector, and report the observation of a new process J=c ! !Xð1870Þ with a statistical significance of 7:2, in which Xð1870Þ decays to a
0ð980Þ. Fitting to
þ mass spectrum yields a mass M ¼ 1877:3 6:3ðstatÞþ3:4
7:4ðsystÞ MeV=c2, a width ¼ 57
12ðstatÞþ194 ðsystÞ MeV=c2, and a product branching fraction BðJ=c ! !XÞ BðX ! a0ð980ÞÞ
Bða
0ð980Þ ! Þ ¼ ½1:50 0:26ðstatÞþ0:720:36ðsystÞ 104. Signals forJ=c ! !f1ð1285Þ and J=c !
!ð1405Þ are also clearly observed and measured.
DOI:10.1103/PhysRevLett.107.182001 PACS numbers: 13.85.Hd, 13.25.Ft, 25.75.Gz
The resonance known as theXð1835Þ, was first observed in the0þ mass spectrum of J=c ! 0þ by BESII [1] and subsequently confirmed with a much higher signal significance by BESIII [2]. Several theoretical spec-ulations have been proposed to interpret the nature of Xð1835Þ, including the p p bound state [3–5] that was first observed near the same mass inJ=c ! p p at BESII [6] and confirmed by BESIII and CLEO [7], a second radial excitation of the0[8], and a pseudoscalar glueball [9–11]. In the lower mass region of theþ mass spectrum,
around 1:4 GeV=c2, extensive studies [12–14] have estab-lished the existence of the ð1405Þ, which has also been suggested as a candidate for a pseudoscalar glueball [15]. Experimentally, the study of the production mechanism of the Xð1835Þ and ð1405Þ, e.g., searches for them in þ final states with other accompanying particles (!, , etc.), are useful for clarifying their nature. In particular, the measurements of the production widths of these two states in hadronic decays of the J=c and a comparison with corresponding measurements in J=c
radiative decays would provide important information about the glueball possibility [16].
In this Letter, we present the results of a study ofJ=c ! !þ. A structure around 1:8–1:9 GeV=c2 in the þmass spectrum is observed. This analysis is based on a sample ofð225:2 2:8Þ 106 J=c events [17] ac-cumulated in the Beijing Spectrometer (BESIII) [18] op-erating at the Beijing Electron-Position Collider (BEPCII) [19] at the Beijing Institute of High Energy Physics.
BEPCII is a double-ring eþe collider designed to provide eþe beams with a peak luminosity of 1033 cm2s1at a beam current of 0.93 A. The cylindrical core of the BESIII detector consists of a helium-based main drift chamber (MDC), a plastic scintillator time-of-flight (TOF) system, and a CsI(Tl) electromagnetic calo-rimeter (EMC) that are all enclosed in a superconducting solenoidal magnet providing a 1.0 T magnetic field. The solenoid is supported by an octagonal flux-return yoke with resistive plate counter muon identifier modules interleaved with steel. The acceptance of charged particles and photons is 93% of 4 sr, and the charged-particle momentum and photon energy resolutions at 1 GeV are 0.5% and 2.5%, respectively. The BESIII detector is modeled with a Monte Carlo (MC) simulation based onGEANT4[20,21].
Charged tracks in the BESIII detector are reconstructed using track-induced signals in the MDC. To optimize the momentum measurement, we select tracks in the polar angle rangej cosj < 0:93 and require that they pass within 20 cm from the interaction point in the beam direction and within2 cm of the beam line in the plane perpen-dicular to the beam. Four tracks with net charge zero are required and all tracks are assumed to be pions.
Electromagnetic showers are reconstructed from clus-ters of energy deposits in the EMC. The energy deposited in nearby TOF counters is included to improve the recon-struction efficiency and energy resolution. Showers iden-tified as photon candidates must satisfy fiducial and shower-quality requirements, i.e., the showers in the barrel region (j cosj < 0:8) must have a minimum energy of 25 MeV, while those from the end caps (0:86 < j cosj < 0:92) must have at least 50 MeV. The showers in the angular range between the barrel and end cap are poorly reconstructed and excluded from the analysis. To suppress showers from charged particles, a photon must be sepa-rated by at least 10 from the nearest charged track. The EMC cluster timing requirements are used to suppress electronic noise and energy deposits unrelated to the event. In the reconstruction of J=c ! !þ, the ! is reconstructed via its þ0 mode, and the and 0 are reconstructed from pairs. The vertex of all final state particles must be consistent with the measured beam interaction point. The sum of the four-momenta of all particles is constrained to the known J=c mass and the initialeþethree-momentum in the lab frame. The vertex and four-momentum kinematic fits are required to satisfy
the quality requirements 2
V=d:o:f: < 100=3 and 2
4C=d:o:f: < 50=4, respectively. Further selections are based on the four-momenta from the kinematic fit. Photon pairs with an invariant mass satisfying M2 ð524; 572Þ MeV=c2 or ð122; 148Þ MeV=c2 are identified as or 0 candidates. The 04 combination with minimum 24C is selected in the cases where more than one candidate satisfies the above requirements in an event. If there is more than one four-photon combination in the mass range of the and 0, the assignment with the lowest value of0¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P2þ P2
0 q
is used, whereP=0 are the pulls defined asP=0¼
Mm=0
. Hereis the=
0 mass resolution determined from data.
After the application of the above requirements, the scatter plot of MðÞ versus M!ðþ0Þ (shown in Fig. 1) shows a clear cluster in the J=c ! !þ signal region denoted by the rectangle in the center of the plot. To determine whichþ pair originates from the!, jMþ0 m!j is minimized among the possible combinations of the selected charged pions, and required to be less than 28 MeV=c2.
With all the selection criteria applied, the mass spectrum ofþis shown in Fig.2(a). In the lower mass range, in addition to the well-known0peak, two other structures are observed; these are inferred to be the f1ð1285Þ and ð1405Þ based on the fit results discussed below. There is an additional structure located around 1:87 GeV=c2 that we denote asXð1870Þ. The mass spectrum for these events, shown in Fig.2(b), reveals a stronga0ð980Þ signal. The þ mass spectrum for events where either MðþÞ or MðÞ is in a 100 MeV=c2 mass window centered on the a0ð980Þ mass is shown in Fig. 2(c). The þmass spectrum for events with bothMðþÞ and MðÞ outside the a
0ð980Þ signal region is shown in Fig. 2(d). Comparison between Figs. 2(c) and 2(d) indi-cates that thef1ð1285Þ, ð1405Þ, and Xð1870Þ all primarily decay via thea0ð980Þ channel.
) 2 c (GeV/ 0 π -π + π M 0.65 0.70 0.75 0.80 0.85 0.90 ) 2 c (GeV/ γγ M 0.45 0.50 0.55 0.60 0.65
FIG. 1 (color online). Scatter plot of MðÞ versus M!ðþ0Þ. The rectangle in the middle shows the signal region defined as jMþ0 m!j < 28 MeV=c2 andjM mj < 24 MeV=c2.
To ensure that the observedf1ð1285Þ, ð1405Þ and the structure around 1:87 GeV=c2 originate from the process ofJ=c ! !a0ð980Þrather than peaking backgrounds, potential background channels are studied using both data and MC samples. The non-! and/or non-a0ð980Þ processes are estimated by the weighted sums of horizontal and vertical side bands, with the entries in the diagonal side bands subtracted to compensate for the double counting of background components. The definitions of the two-dimensional side bands are illustrated in Fig. 3. The weighting factors for the events in the horizontal, vertical, and the diagonal side bands are measured to be 0.48, 1.58,
and 0.76, respectively, which are determined from the results of a two-dimensional fit to the mass spectrum of M!ðþ0Þ versus M
a0ð980ÞðÞ. Here the two-dimensional probability density functions (PDFs) for J=c ! !a0ð980Þ, ! but non-a0ð980Þ, non-! but a0ð980Þ, non-! and non-a0ð980Þ processes are constructed by the product of one-dimensional functions, where the resonant peaks are parametrized by Breit-Wigner functions and the nonresonant parts are described by floating poly-nomials. To account for the difference of the background shape between the signal region and side bands due to the varying phase space, the obtained background þ mass distribution is multiplied by a correction curve de-termined from an MC sample of 2 106 events of the phase-space process J=c ! þ0þ.
The background channel J=c ! b1ð1235Þa0ð980Þ, where the b1ð1235Þ decays to ! and a0ð980Þ decays to , is studied by performing a two-dimensional fit to the Mð!Þ versus MðÞ mass distribution with two-dimensional PDFs defined in similar fashion. We also studied an inclusive MC sample of 2 108 J=c decays generated according to the Particle Data Group (PDG) decay table and Lund-charm model [22]. No background-induced peaks are observed around 1:87 GeV=c2. The inclusive MC sample is also used for the validation of the background estimation method described above, which is able to well reproduce the input background components. Figure4shows the results of a fit to theþ mass spectrum where either þ or are in the a0ð980Þ mass window. Here the three signal peaks are parametrized by Breit-Wigner functions convolved with a Gaussian resolution function and multiplied by an efficiency curve, which are both determined from signal MC samples and fixed in the fit. The background consists of three
) 2 c (GeV/ -π + π η M 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 0 200 400 600 800 1000 1200 1400 1600 (a) ) 2 c (GeV/ ± ηπ M 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 0 1000 2000 3000 4000 5000 (b) ) 2 c (GeV/ -π + π η M 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 0 100 200 300 400 500 600 700 800 900 (c) ) 2 c (GeV/ -π + ηπ M 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 0 200 400 600 800 1000 (d) Events / (20 MeV/c 2) Events / (20 MeV/c 2)
FIG. 2 (color online). Invariant-mass distributions for the se-lected events: (a) and (b) are the invariant-mass spectra of þandafter the application of all the event-selection
criteria; (c) is the þ mass spectrum for events with an a0ð980Þ in the final state; (d) is theþinvariant-mass
distribution for events with noa0ð980Þ in the system. The histograms in (a) and (c) are the phase-space MC events of J=c ! !þ after the same event selection and with
arbitrary normalization. ) 2 c (GeV/ 0 π -π + π M 0.65 0.70 0.75 0.80 0.85 0.90 ) 2c (GeV/ ηπ M 0.7 0.8 0.9 1.0 1.1 1.2 1.3
FIG. 3 (color online). Definition of the signal and two-dimensional side bands.
) 2 c (GeV/ -π + ηπ M 1.2 1.4 1.6 1.8 2.0 2.2 Events / (20 MeV/c 2) 0 100 200 300 400 500 600 700 800 900
FIG. 4 (color online). Results of the fit to the MðþÞ mass distribution for events with either theþ orin the a0ð980Þ mass window. The dotted curve shows the contribution
of non-! and/or non-a0ð980Þ background, the dashed line also
includes the contribution fromJ=c ! b1ð1235Þa0ð980Þ, and the dot-dashed curve indicates the total background with the non-resonant J=c ! !a0ð980Þ included. 2=d:o:f: is 1.27 for
components, namely, contributions from non-! and/or non-a0ð980Þ processes, J=c ! b1ð1235Þa0ð980Þ events, and nonresonant !a0ð980Þ processes. The background shapes and numbers of events for the non-! and/or non-a0ð980Þ processes are determined from the events in the two-dimensional side bands as discussed above, and fixed in the fit. For the J=c ! b1ð1235Þa0ð980Þ compo-nent of background, the background shape is fixed to that of the phase-space MC samples whereas the number of events is extracted and fixed to the result of a two-dimensional fit to the ! versus mass distributions. The contribution of the remaining nonresonant!a0ð980Þ process is described by a smooth floating polynomial function. The mass, width, and the product branching fractions obtained from the fit are summarized in TableI. For the f1ð1285Þ and ð1405Þ, the measured mass and width are in agreement with PDG values [23]. The statis-tical significance of the Xð1870Þ signal is determined by the change of the log likelihood value and the degree of freedom in the fits with and without the assumption of an Xð1870Þ. With all factors in the fit varied, the smallest change in the2 lnL is 60.1, corresponding to a signifi-cance of 7:2. The same procedure is applied to the f1ð1285Þ and ð1405Þ signals, and the significances are determined to be much higher than 10.
The systematic errors on the measurement of the mass and width parameters are primarily due to the uncertainty in the fitting of the mass spectrum. In detail, the fit range, background estimation method, number of background events, and the background parametrization are varied to decide the uncertainty from the background estimation and fitting as a whole. We also include the systematic errors determined from the input-output checks based on the analysis of fully reconstructed MC samples, in which the input parameters are set according to the final results and the background is represented by the background channels seen in the inclusive MC sample. For systematic errors originating from the potential structure around 2:2 GeV=c2 and the multiple-event candidate selection, we refit the mass spectrum of þ with the inclusion of an Xð2120Þ resonance as recently reported by BESIII [2] in the decay channel ofJ=c ! 0þ, and all the valid multiple-entry candidates kept in order to estimate the
uncertainty due to these two sources, respectively. With the numbers from all the sources above combined quadratically, the systematic errors on the mass and width parameters are determined as shown in TableI.
The systematic errors on the branching fraction mea-surements are also subject to errors of the number ofJ=c events [17], the intermediate branching fractions [23], the data-MC difference in the tracking efficiency, the photon detection efficiency, the kinematic fit, the signal-selection efficiency of =0, the simulation of the line shape of a0ð980Þ [24], and the angular distributions due to different possible spin-parity hypotheses. Combined in quadrature with the influence from the mass spectrum fitting, the systematic errors on the product branching fraction for the f1ð1285Þ, ð1405Þ and Xð1870Þ are summarized in TableI.
In summary, we present a study of the J=c ! !þ decay channel and report the first observation of the processJ=c ! !Xð1870Þ in which Xð1870Þ decays toa0ð980Þ, with the signal significance estimated to be 7:2. In the lower mass region of þmass spectrum, the f1ð1285Þ and ð1405Þ are also clearly observed with statistical significances much larger than 10. The mea-surements of the mass, width, and product branching fraction of BðJ=c ! !XÞ BðX ! a0ð980ÞÞ Bða
0ð980Þ ! Þ for the three resonant structures are summarized in Table I, wherein the product branching fractions for the f1ð1285Þ and ð1405Þ are measured for the first time. Whether the resonant structure ofXð1870Þ is due to theXð1835Þ, the 2ð1870Þ, an interference of both, or a new resonance still needs further study such as a partial wave analysis that will be possible with the larger J=c data sample that is anticipated in future runs of the BESIII experiment. For the ð1405Þ, the product branch-ing fraction for its production in the hadronic decay ofJ=c is measured to be smaller than that for its production in the radiativeJ=c decays [23].
We thank the accelerator group and computer staff of IHEP for their effort in producing beams and processing data. We are grateful for support from our institutes and universities and from these agencies: Ministry of Science and Technology of China, National Natural Science Foundation of China, Chinese Academy of Sciences, Istituto Nazionale di Fisica Nucleare, Russian Foundation for Basic Research, Russian Academy of Science (Siberian branch), U.S. Department of Energy, and National Research Foundation of Korea.
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TABLE I. Summary of measurements of the mass, width, and the product branching fraction of BðJ=c ! !XÞ BðX ! a
0ð980ÞÞ Bða0ð980Þ ! Þ where X represents
f1ð1285Þ, ð1405Þ and Xð1870Þ. Here the first errors are
statis-tical and the second ones are systematic.
Resonance Mass (MeV=c2) Width (MeV=c2) Bð104Þ
f1ð1285Þ 1285:1 1:0þ1:60:3 22:0 3:1þ2:01:5 1:25 0:10þ0:190:20
ð1405Þ 1399:8 2:2þ2:80:1 52:8 7:6þ0:17:6 1:89 0:21þ0:210:23
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