Evidence of a new narrow resonance decaying to \chi_{c1}\gamma in B\to\chi_{c1}\gamma K


Evidence of a new narrow resonance decaying to in

V. Bhardwaj Nara Women’s University, Nara 630-8506    K. Miyabayashi Nara Women’s University, Nara 630-8506    I. Adachi High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    H. Aihara Department of Physics, University of Tokyo, Tokyo 113-0033    D. M. Asner Pacific Northwest National Laboratory, Richland, Washington 99352    V. Aulchenko Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    T. Aushev Institute for Theoretical and Experimental Physics, Moscow 117218    T. Aziz Tata Institute of Fundamental Research, Mumbai 400005    A. M. Bakich School of Physics, University of Sydney, NSW 2006    A. Bala Panjab University, Chandigarh 160014    B. Bhuyan Indian Institute of Technology Guwahati, Assam 781039    M. Bischofberger Nara Women’s University, Nara 630-8506    A. Bondar Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    G. Bonvicini Wayne State University, Detroit, Michigan 48202    A. Bozek H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342    M. Bračko University of Maribor, 2000 Maribor J. Stefan Institute, 1000 Ljubljana    J. Brodzicka H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342    T. E. Browder University of Hawaii, Honolulu, Hawaii 96822    V. Chekelian Max-Planck-Institut für Physik, 80805 München    A. Chen National Central University, Chung-li 32054    B. G. Cheon Hanyang University, Seoul 133-791    K. Chilikin Institute for Theoretical and Experimental Physics, Moscow 117218    R. Chistov Institute for Theoretical and Experimental Physics, Moscow 117218    K. Cho Korea Institute of Science and Technology Information, Daejeon 305-806    V. Chobanova Max-Planck-Institut für Physik, 80805 München    S.-K. Choi Gyeongsang National University, Chinju 660-701    Y. Choi Sungkyunkwan University, Suwon 440-746    D. Cinabro Wayne State University, Detroit, Michigan 48202    J. Dalseno Max-Planck-Institut für Physik, 80805 München Excellence Cluster Universe, Technische Universität München, 85748 Garching    M. Danilov Institute for Theoretical and Experimental Physics, Moscow 117218 Moscow Physical Engineering Institute, Moscow 115409    Z. Doležal Faculty of Mathematics and Physics, Charles University, 121 16 Prague    Z. Drásal Faculty of Mathematics and Physics, Charles University, 121 16 Prague    A. Drutskoy Institute for Theoretical and Experimental Physics, Moscow 117218 Moscow Physical Engineering Institute, Moscow 115409    D. Dutta Indian Institute of Technology Guwahati, Assam 781039    K. Dutta Indian Institute of Technology Guwahati, Assam 781039    S. Eidelman Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    D. Epifanov Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    H. Farhat Wayne State University, Detroit, Michigan 48202    J. E. Fast Pacific Northwest National Laboratory, Richland, Washington 99352    T. Ferber Deutsches Elektronen–Synchrotron, 22607 Hamburg    A. Frey II. Physikalisches Institut, Georg-August-Universität Göttingen, 37073 Göttingen    V. Gaur Tata Institute of Fundamental Research, Mumbai 400005    N. Gabyshev Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    S. Ganguly Wayne State University, Detroit, Michigan 48202    R. Gillard Wayne State University, Detroit, Michigan 48202    Y. M. Goh Hanyang University, Seoul 133-791    B. Golob Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana J. Stefan Institute, 1000 Ljubljana    J. Haba High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    T. Hara High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    H. Hayashii Nara Women’s University, Nara 630-8506    Y. Horii Kobayashi-Maskawa Institute, Nagoya University, Nagoya 464-8602    Y. Hoshi Tohoku Gakuin University, Tagajo 985-8537    W.-S. Hou Department of Physics, National Taiwan University, Taipei 10617    Y. B. Hsiung Department of Physics, National Taiwan University, Taipei 10617    H. J. Hyun Kyungpook National University, Daegu 702-701    T. Iijima Kobayashi-Maskawa Institute, Nagoya University, Nagoya 464-8602 Graduate School of Science, Nagoya University, Nagoya 464-8602    K. Inami Graduate School of Science, Nagoya University, Nagoya 464-8602    A. Ishikawa Tohoku University, Sendai 980-8578    R. Itoh High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    T. Iwashita Nara Women’s University, Nara 630-8506    T. Julius School of Physics, University of Melbourne, Victoria 3010    D. H. Kah Kyungpook National University, Daegu 702-701    J. H. Kang Yonsei University, Seoul 120-749    E. Kato Tohoku University, Sendai 980-8578    T. Kawasaki Niigata University, Niigata 950-2181    H. Kichimi High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    C. Kiesling Max-Planck-Institut für Physik, 80805 München    D. Y. Kim Soongsil University, Seoul 156-743    J. B. Kim Korea University, Seoul 136-713    J. H. Kim Korea Institute of Science and Technology Information, Daejeon 305-806    K. T. Kim Korea University, Seoul 136-713    M. J. Kim Kyungpook National University, Daegu 702-701    Y. J. Kim Korea Institute of Science and Technology Information, Daejeon 305-806    K. Kinoshita University of Cincinnati, Cincinnati, Ohio 45221    J. Klucar J. Stefan Institute, 1000 Ljubljana    B. R. Ko Korea University, Seoul 136-713    P. Kodyš Faculty of Mathematics and Physics, Charles University, 121 16 Prague    S. Korpar University of Maribor, 2000 Maribor J. Stefan Institute, 1000 Ljubljana    P. Križan Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana J. Stefan Institute, 1000 Ljubljana    P. Krokovny Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    R. Kumar Punjab Agricultural University, Ludhiana 141004    T. Kumita Tokyo Metropolitan University, Tokyo 192-0397    A. Kuzmin Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    Y.-J. Kwon Yonsei University, Seoul 120-749    J. S. Lange Justus-Liebig-Universität Gießen, 35392 Gießen    S.-H. Lee Korea University, Seoul 136-713    J. Li Seoul National University, Seoul 151-742    Y. Li CNP, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061    C. Liu University of Science and Technology of China, Hefei 230026    Z. Q. Liu Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049    D. Liventsev High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    P. Lukin Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    D. Matvienko Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    H. Miyata Niigata University, Niigata 950-2181    R. Mizuk Institute for Theoretical and Experimental Physics, Moscow 117218 Moscow Physical Engineering Institute, Moscow 115409    G. B. Mohanty Tata Institute of Fundamental Research, Mumbai 400005    A. Moll Max-Planck-Institut für Physik, 80805 München Excellence Cluster Universe, Technische Universität München, 85748 Garching    R. Mussa INFN - Sezione di Torino, 10125 Torino    E. Nakano Osaka City University, Osaka 558-8585    M. Nakao High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    Z. Natkaniec H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342    M. Nayak Indian Institute of Technology Madras, Chennai 600036    E. Nedelkovska Max-Planck-Institut für Physik, 80805 München    N. K. Nisar Tata Institute of Fundamental Research, Mumbai 400005    S. Nishida High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    O. Nitoh Tokyo University of Agriculture and Technology, Tokyo 184-8588    S. Ogawa Toho University, Funabashi 274-8510    S. Okuno Kanagawa University, Yokohama 221-8686    S. L. Olsen Seoul National University, Seoul 151-742    P. Pakhlov Institute for Theoretical and Experimental Physics, Moscow 117218 Moscow Physical Engineering Institute, Moscow 115409    G. Pakhlova Institute for Theoretical and Experimental Physics, Moscow 117218    E. Panzenböck II. Physikalisches Institut, Georg-August-Universität Göttingen, 37073 Göttingen Nara Women’s University, Nara 630-8506    H. Park Kyungpook National University, Daegu 702-701    H. K. Park Kyungpook National University, Daegu 702-701    T. K. Pedlar Luther College, Decorah, Iowa 52101    R. Pestotnik J. Stefan Institute, 1000 Ljubljana    M. Petrič J. Stefan Institute, 1000 Ljubljana    L. E. Piilonen CNP, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061    M. Ritter Max-Planck-Institut für Physik, 80805 München    M. Röhrken Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe    A. Rostomyan Deutsches Elektronen–Synchrotron, 22607 Hamburg    H. Sahoo University of Hawaii, Honolulu, Hawaii 96822    T. Saito Tohoku University, Sendai 980-8578    K. Sakai High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    Y. Sakai High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    S. Sandilya Tata Institute of Fundamental Research, Mumbai 400005    D. Santel University of Cincinnati, Cincinnati, Ohio 45221    L. Santelj J. Stefan Institute, 1000 Ljubljana    T. Sanuki Tohoku University, Sendai 980-8578    Y. Sato Tohoku University, Sendai 980-8578    V. Savinov University of Pittsburgh, Pittsburgh, Pennsylvania 15260    O. Schneider École Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015    G. Schnell University of the Basque Country UPV/EHU, 48080 Bilbao Ikerbasque, 48011 Bilbao    C. Schwanda Institute of High Energy Physics, Vienna 1050    R. Seidl RIKEN BNL Research Center, Upton, New York 11973    D. Semmler Justus-Liebig-Universität Gießen, 35392 Gießen    K. Senyo Yamagata University, Yamagata 990-8560    O. Seon Graduate School of Science, Nagoya University, Nagoya 464-8602    M. E. Sevior School of Physics, University of Melbourne, Victoria 3010    M. Shapkin Institute for High Energy Physics, Protvino 142281    C. P. Shen Graduate School of Science, Nagoya University, Nagoya 464-8602    T.-A. Shibata Tokyo Institute of Technology, Tokyo 152-8550    J.-G. Shiu Department of Physics, National Taiwan University, Taipei 10617    B. Shwartz Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    F. Simon Max-Planck-Institut für Physik, 80805 München Excellence Cluster Universe, Technische Universität München, 85748 Garching    J. B. Singh Panjab University, Chandigarh 160014    P. Smerkol J. Stefan Institute, 1000 Ljubljana    Y.-S. Sohn Yonsei University, Seoul 120-749    A. Sokolov Institute for High Energy Physics, Protvino 142281    E. Solovieva Institute for Theoretical and Experimental Physics, Moscow 117218    M. Starič J. Stefan Institute, 1000 Ljubljana    M. Steder Deutsches Elektronen–Synchrotron, 22607 Hamburg    M. Sumihama Gifu University, Gifu 501-1193    T. Sumiyoshi Tokyo Metropolitan University, Tokyo 192-0397    U. Tamponi INFN - Sezione di Torino, 10125 Torino    K. Tanida Seoul National University, Seoul 151-742    G. Tatishvili Pacific Northwest National Laboratory, Richland, Washington 99352    Y. Teramoto Osaka City University, Osaka 558-8585    K. Trabelsi High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    T. Tsuboyama High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    M. Uchida Tokyo Institute of Technology, Tokyo 152-8550    S. Uehara High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801    T. Uglov Institute for Theoretical and Experimental Physics, Moscow 117218 Moscow Institute of Physics and Technology, Moscow Region 141700    Y. Unno Hanyang University, Seoul 133-791    P. Urquijo University of Bonn, 53115 Bonn    Y. Usov Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    S. E. Vahsen University of Hawaii, Honolulu, Hawaii 96822    C. Van Hulse University of the Basque Country UPV/EHU, 48080 Bilbao    P. Vanhoefer Max-Planck-Institut für Physik, 80805 München    G. Varner University of Hawaii, Honolulu, Hawaii 96822    K. E. Varvell School of Physics, University of Sydney, NSW 2006    A. Vinokurova Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    M. N. Wagner Justus-Liebig-Universität Gießen, 35392 Gießen    C. H. Wang National United University, Miao Li 36003    M.-Z. Wang Department of Physics, National Taiwan University, Taipei 10617    P. Wang Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049    M. Watanabe Niigata University, Niigata 950-2181    Y. Watanabe Kanagawa University, Yokohama 221-8686    E. Won Korea University, Seoul 136-713    B. D. Yabsley School of Physics, University of Sydney, NSW 2006    J. Yamaoka University of Hawaii, Honolulu, Hawaii 96822    Y. Yamashita Nippon Dental University, Niigata 951-8580    S. Yashchenko Deutsches Elektronen–Synchrotron, 22607 Hamburg    Y. Yook Yonsei University, Seoul 120-749    C. Z. Yuan Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049    C. C. Zhang Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049    Z. P. Zhang University of Science and Technology of China, Hefei 230026    V. Zhilich Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    V. Zhulanov Budker Institute of Nuclear Physics SB RAS and Novosibirsk State University, Novosibirsk 630090    A. Zupanc Institut für Experimentelle Kernphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe
Abstract

We report measurements of and decays using events collected at the resonance with the Belle detector at the KEKB asymmetric-energy collider. Evidence of a new resonance in the final state is found with a statistical significance of . This state has a mass of MeV/, a value that is consistent with theoretical expectations for the previously unseen meson. We find no other narrow resonance and set upper limits on the branching fractions of the and decays.

pacs:
13.25.Hw, 13.20.Gd, 14.40.Pq

The Belle Collaboration

During the last decade, a number of new charmonium ()-like states were observed, many of which are candidates for exotic states brambilla (). The first of these, the , has been observed by six different experiments in the same final state belle1 (); cdf1 (); do1 (); babar1 (); lhcb (); cms (). A recent update from Belle belle_recent () and LHCb lhcb () results in a world average mass at MeV pdg () and a stringent upper bound on its width ( MeV) belle_recent (). The proximity of its mass to the threshold makes it a good candidate for a molecule swanson (). Other alternative models have been proposed, such as a tetraquark Lmaiani () or a hybrid meson Lihybrid ().

Radiative decays can illuminate clearly the nature of hadrons. For example, the observation of confirmed the -even parity assignment for the babarprl102 (); belle3 (). The and decays are forbidden by -parity conservation in electromagnetic processes. However, if the is a tetraquark or a molecular state, it may have a -odd partner, which could decay into and final states terasaki (); nieves ().

In the charmonium family, the observation of a -wave meson and its decay modes would test phenomenological models cornell (); buchmuller (). The as-yet undiscovered ) and states are expected to have significant branching fractions to and , respectively estia2002 (); cho1994 (). -wave states and their properties were predicted long ago but remain unconfirmed estia2002 (); cho1994 (). The E705 experiment reported an indication of a state in anything, with a mass of MeV e705 (); however, the statistical significance of this result was below the threshold for evidence.

In this letter, we report measurements of and decays, where the and decay to  mixchg (). These results are obtained from a data sample of events collected with the Belle detector abashian () at the KEKB asymmetric-energy collider operating at the resonance kurokawa ().

The meson is reconstructed via its decays to ( or ). To reduce the radiative tail in the mode, the four-momenta of all photons within 50 mrad with respect to the original direction of the or tracks are included in the invariant mass calculation, hereinafter denoted as . The reconstructed invariant mass of the candidates is required to satisfy 2.95 GeV GeV or 3.03 GeV GeV. For the selected candidates, a vertex-constrained fit is applied and then a mass-constrained fit is performed in order to improve the momentum resolution. The and candidates are reconstructed by combining candidates with a photon having energy () larger than 200 MeV in the laboratory frame. Photons are reconstructed from energy depositions in the electromagnetic calorimeter (ECL), which do not match any extrapolated charged track. To reduce the background from , we use a likelihood function that distinguishes an isolated photon from decays using the photon pair invariant mass, photon laboratory energy and polar angle kopenberg (). We reject both ’s in the pair if the likelihood probability is larger than 0.7. The reconstructed invariant mass of the () is required to satisfy 3.467 GeV 3.535 GeV (3.535 GeV 3.611 GeV). A mass-constrained fit is applied to the selected and candidates.

Charged kaons are identified by combining information from the central drift chamber, time-of-flight scintillation counters, and the aerogel Cherenkov counter systems. The kaon identification efficiency is while the probability of misidentifying a pion as a kaon is . mesons are reconstructed by combining two oppositely charged pions with the invariant mass lying between 482 MeV and 514 MeV. The selected candidates are required to satisfy the quality criteria described in Ref. goodks ().

To reconstruct candidates, each  CX () is combined with a kaon candidate and a photon having 100 MeV (and not used in the reconstruction of ). If the invariant mass of any photon pair that includes this photon is found to be consistent with a (i.e., 117 MeV 153 MeV), this photon is rejected. Among the events containing at least one candidate, 9.0% have multiple candidates. In such cases, the forming the candidate with mass closest to the or masses pdg () is not used as the additional photon. This treatment suppresses reflections from the daughter photons.

The candidate is identified by two kinematic variables: the beam-constrained mass () and the energy difference (). Here, is the run-dependent beam energy, and and are the reconstructed energy and momentum, respectively, of the meson candidates in the center-of-mass (CM) frame. Candidates within a window of MeV and with 5.23 GeV are selected. Of these, 9.8% (6.4%) have multiple candidates in the () mode; we select the candidate with closest to zero. In order to improve the resolution in , we scale the energy of the so that is equal to zero. This corrects for incomplete energy measurement in the ECL. To suppress continuum background, events having a ratio of the second to zeroth Fox-Wolfram moments foxwolfram () above are rejected.

The and projections for the signal candidates are shown in Fig. 1, where a signal is evident. In addition, there is a significant narrow peak at 3823 MeV/, denoted hereinafter as . No signal of is seen. We extract the signal yield from a two-dimensional unbinned extended maximum likelihood (2D UML) fit to the variables and .

The resolution in () is parameterized by a sum of two Gaussians (Gaussian and logarithmic Gaussian lg ()). MC studies show that the resolutions in both and for a narrow resonance in the mass range 3.8 GeV 4.0 GeV are in good agreement with those for . The parameters of the resolution functions are determined from the MC simulation that is calibrated using the signal. We take into account the natural width pdg () by convolving the Breit-Wigner function and the resolution function; for the and , zero natural widths are assumed. The two-dimensional probability density function (PDF) is a product of the one-dimensional distributions.

For decays, the mean and width of the core Gaussian are floated and the remaining parameters are fixed according to MC simulations. To fit the signal, we float the mean of the core Gaussian but constrain the detector resolution by using the signal results after taking into account the difference estimated from the signal MC study. For , the parameters are fixed to those found for the , in accordance with expectations based on the MC simulation. For , we fix the mass difference and the mass resolution change with respect to using the information from PDG pdg () and MC studies. To fit , , , and , we fix all the parameters obtained from the signal MC study after correcting the PDF shapes by applying MC/data calibration factors.

To study background with a real , we use large MC simulated samples corresponding to 100 times the integrated luminosity of the data. The non- (non-) background is studied using () sidebands in data. In , the background with a broad peaking structure is mostly due to the , , and decay modes. produces peaks in both distributions ( and ), while the other backgrounds are flat in but peaked in . We determine the PDFs from the large MC sample. The fractions of the PDF components are floated in the fit, except for , whose fraction is controlled by fixing its ratio to the signal yield. For the combinatorial background, a threshold function, , where GeV (3.585 GeV) for (), is used for and an ARGUS function argus () is used for . The value of is estimated from a MC study; its variation, which affects the signal yield in the fits, is incorporated in the systematic errors. The data sidebands are used to verify the background PDFs. The fractions for the signal and the background components are floated in the fit.

Figure 1: 2D UML fit projection for decays: (a) distribution for GeV, (b) distribution for 3.660 GeV GeV ( region, shown by the red dotted-dashed arrows in a), (c) distribution for 3.805 GeV GeV ( region, shown by the magenta solid arrows in a) and (d) distribution for 3.84 GeV GeV ( region). The curves used in the fits are described in CURVES ().

The results of the fits are presented in Figs. 1-3 and in Table 1. The significance is estimated using the value of where () denotes the likelihood value when the yield is allowed to vary (is set to zero). In the likelihood calculation, the statistic uses the appropriate number of degrees of freedom (two in the case of and one for the other decay modes). The systematic uncertainty, which is described below, is included in the significance calculation cousinhighland (). We find a significant signal in all considered channels. We also obtain evidence for the in the channel with a statistical significance of 3.8 standard deviations (). The signals are insignificant. We estimate the branching fractions according to the formula ; here, is the yield, is the reconstruction efficiency, is the secondary branching fraction taken from Ref. pdg () and is the number of mesons in the data sample. Equal production of neutral and charged meson pairs in the decay is assumed. Measured branching fractions for the are in agreement with the world average values for all the channels pdg (). We set 90% confidence level (C.L.) upper limits (U.L.) on the insignificant channels using frequentist methods based on an ensemble of pseudo-experiments.

Figure 2: 2D UML fit projection for decays: (a) distribution for GeV, (b) distribution for the region, (c) distribution for the region and (d) distribution for the region. The curves used in the fits are described in CURVES ().
Figure 3: 2D UML fit projection for decays: (a) distribution for GeV, (b) distribution for GeV, (c) and (d) distribution for the region, (e) and (f) distribution for the region, and (g) and (h) distribution for the region. The curves used in the fits are described in CURVES ().
Figure 4: 2D UML fit projection of distribution for the simultaneous fit of and decays for GeV. The curves used in the fits are described in CURVES ().
Decay Yield () (%) Branching fraction

14.8 8.6
7.8 6.0

7.2 5.1
2.9 3.5

3.8 10.9
0.1 8.8

1.2 6.0
2.4 5.0

11.1
1.3 9.3

1.6 6.2
1.1 5.2





Table 1: Summary of the results. Signal yield () from the fit, significance () with systematics included, corrected efficiency () and measured . For , the first (second) error is statistical (systematic). In the neutral decay, the efficiency below includes the branching fraction but does not include the factor of two for .

A correction for small differences in the signal detection efficiency between MC simulation and data has been applied for the lepton and kaon identification requirements. Uncertainties in these corrections are included in the systematic error. The ( or ) and samples are used to estimate the lepton identification correction and the kaon (pion) identification correction, respectively. To estimate the correction and residual systematic uncertainty for reconstruction, samples are used. The errors on the PDF shapes are obtained by varying all fixed parameters by and taking the change in the yield as the systematic uncertainty. The uncertainties due to the secondary branching fractions are also taken into account. The uncertainties of the tracking efficiency and are estimated to be 0.35 per track and , respectively. The uncertainty on the photon identification is estimated to be 2.0%photon. The systematic uncertainty associated with the difference of the veto between data and MC is estimated to be 1.2% from a study of the sample.

To improve the mass determination of the , a simultaneous fit to and is performed, assuming that = . The peak position and resolution are common for both charged and neutral candidates. From this fit, we estimate the significance for to be 4.0 (including systematic uncertainties). We determine the mass of the signal peak relative to the well-measured mass :

MeV.

Here, the first uncertainty is statistical and the second is systematic. Because of the mass-constrained fit to the candidate, the systematic uncertainty of is dominated by the additional photon’s energy scale. This photon energy scale uncertainty is estimated by the difference between the candidates’ mass without any constraint and the nominal mass pdg (), which results in 0.7 MeV as the systematic error. In order to estimate the width, we float this parameter and find no sensitivity with the available statistics: the width is MeV. Using pseudo-experiments generated with different width hypotheses for the , the U.L. at 90% C.L. on its width is estimated to be 24 MeV.

The mass of the is near potential model expectations for the centroid of the states: the Cornell cornell () and the Buchmüller-Tye buchmuller () potentials give 3810 MeV. Other models predict the mass of   (the state, having ) to be 3815-3840 MeV Godfrey (); Ebert (); Eichten (); blank (). The mass agrees quite well with these models. In addition, since no peak has been seen around in the final state pakhlov (), one expects that does not decay to  Eichten (). The ratio (at 90% C.L.) is consistent with the expectation () for  pyungwon (); qiao (); Ebert (). The limited statistics preclude an angular analysis to determine the of the . The product of branching fractions for the is approximately two orders of magnitude lower than for the , as shown in Table 1; it is consistent with the interpretation of the as , whose production rate is suppressed by the factorization fact () in the two-body meson decays.

In summary, we obtain the first evidence of a narrow state, , that decays to with a mass of MeV and a significance of 3.8 , including systematic uncertainties. We measure the branching fraction product . No evidence is found for and we set an U.L. on its branching fraction product as well as the ratio 0.41 at 90% C.L. The properties of the are consistent with those expected for the state. We also determine an U.L. on the product of branching fractions, at 90% C.L.; this is less than one quarter of the corresponding value in  pdg (). Our results show that the production of the ’s -odd partner in two-body decays and its decay to are considerably suppressed.

We thank the KEKB group for excellent operation of the accelerator; the KEK cryogenics group for efficient solenoid operations; and the KEK computer group, the NII, and PNNL/EMSL for valuable computing and SINET4 network support. We acknowledge support from MEXT, JSPS and Nagoya’s TLPRC (Japan); ARC and DIISR (Australia); FWF (Austria); NSFC (China); MSMT (Czechia); CZF, DFG, and VS (Germany); DST (India); INFN (Italy); MEST, NRF, GSDC of KISTI, and WCU (Korea); MNiSW and NCN (Poland); MES and RFAAE (Russia); ARRS (Slovenia); IKERBASQUE and UPV/EHU (Spain); SNSF (Switzerland); NSC and MOE (Taiwan); and DOE and NSF (USA). This work is partly supported by MEXT’s Grant-in-Aid for Scientific Research on Innovative Areas (“Elucidation of New hadrons with a Variety of Flavors”).

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