References A.Abashian et al. (Belle), Nucl. Instr. & Meth A479 , 117 (2002).

1. Observation of a new narrow charmonium state in exclusive BK p+p-J/ydecaysS.K. Choi, Gyeongsang Univ. and H.Guler & S.L. Olsen, Univ. of Hawaii(For the Belle Collaboration) • The 3Dc1 dominates the y(3770), a 3Dc1-y(2S) mixture • yDD is OK y is “wide” (Gtot24 MeV) • The 1Dc2 , 3Dc2 , & 3Dc3 have not been seen • 1,3Dc2DD. If M(1,3Dc2) < MD+MD*, they are narrow • 3Dc2ggg & 3Dc2p+p-J/y would be important • 1Dc2ggg & 1Dc2p+p-hcallowed; 1Dc2p+p-J/y • 3Dc3DD is OK; expected to be “wide.” • BK 3Dc2 K p+p-J/y is a good 3Dc2-discovery reaction. X X The Belle detector [1] runs at KEKB [2], an asymmetric energy e+e- collider operating at the (4S) (√s =10.6 GeV) with world-record-setting luminosity of L = 1034 cm-2s-1. B-meson decays are well suited for charmonium searches [3]. In 2002, Belle found the hc(2S) in BK KSKp decays [4]. Here we report the 1st observation of a narrow state in BKp+p-J/y decays. This could either be the 3Dc2,a DD* molecular state [5], or some mixture of the two. • Results • Nevts = 34 ± 7 ( >8s signif.) • (N y’ = 457 ± 22) • M = 3871.8 ± 0.7 (stat) ± 0.4 (syst) MeV • G < 3.5 MeV(90% CL) • (width consistent with resolution) • Select B+  K+p+p- J/y: • |Mbc-MB| < 9 MeV (3s) • |DE| < 30 MeV (2.5s) • M(p+p-) > 400 MeV reference the mass to the (nearby) y’ y’p+p- J/y magnify Events/0.002 GeV/c2 Events/5 MeV/c2 Events/0.010 GeV/c2 ??? fit Mbc for 5MeV Mp+p-J/y bins near 3870 MeV M(p+p-l+l-) – M(l+l-) (GeV/c2) M(p+p-J/y) (MeV/c2) Acknowledgement This research was made possible by the strong and dedicated efforts of the KEKB team and the extraordinary performance of the KEKB storage ring. What is it? We see a strong (8s)signal for a narrow charmonium state at M = 3871.8 ± 0.7 ± 0.4 MeV. This overlaps, within (~1MeV) errors, the lowest DD* mass threshold: M(D0) + M(D*0) = 3871.3 ± 0.5 MeV [6]. The narrow width and the decay to p+p-J/y correspond to expectations for the 3Dc2 ”missing” charmonium state, but the mass value is ~60 MeV above the center-of-gravity of the 13D triplet prediction by the Cornell [7] and the Buchmuller-Tye [8] potentials: both models give Mcog(13D) 3810 MeV. More-over, the lowest member of the triplet, the 13Dc1 has been identified as the dominant component of the y”: M=3770 MeV, which seems comfortably close to potential model expectations. The close correspondence with the D0D*0 mass threshold is very suggestive of a loosely bound DD* molecular-type multiquark state as proposed by De Rujula, Georgi and Glashow in 1977 [5]. The p+p- mass distribution The p+p- invariant masses from Xc(3870)p+p-J/y (Fig.a) concentrate near the upper kinematic limit, as is the case for y’p+p-J/y decays (Fig.b). (The shaded histogram in Fig.a is sideband-estimated background.) In the case of Xc (3870), however, the boundary is in the r mass region. If it is, in fact, Xc (3870)r J/y decay, this would violate isospin for the case where Xc (3870) is the 3Dc2, in which case it should be strongly suppressed. With more data, we can probably distinguish whether or not the p+p- system is coming from r meson decay. • References • A.Abashian et al. (Belle), Nucl. Instr. & Meth A479, 117 (2002). • S. Kurokawa and E.Kikutani (KEKB), Nucl. Instr. Meth. A499,1 2003) • E.J. Eichten, K. Lane and C. Quigg, Phys. Rev. Lett. 89, 162002 (2002). • S.K. Choi et al. (Belle), Phys. Rev. Lett. 89, 102001 (2002). • A. De Rujula, H. Georgi and S.L. Glashow, Phys. Rev. Lett. 38, 317 (1977). • D.E.Groom et al. (PDG), Eur. Phys. Journ. C15, 1 (2002) • E.Eichten,K.Gottfried,T.Kinoshita,K. Lane & T.M.Yan, Phys. Rev. D21, 203 (1980) • W.Buchmuller and S-H.H. Tye, Phys. Rev. D24, 132 (1981).