Evidence for an Anti-charmed Baryon State.pdf

a r X i v : h e p - e x / 0 5 0 6 0 7 7 v 1 3 0 J u n 2 0 0 5 Evidence for an Anti-charmed Baryon State ? Chr. RISLER for the H1 collaboration DESY, Notkestrasse 85,D-22607 Hamburg, Germany, email: risler@mail.desy.de We report on the observation of a narrow resonance in D??p and D?+p? invariant mass combinations in deep-inelastic ep scattering at centre-of- mass energies of 300 and 320 GeV at HERA. The mass of the resonance is measured to be 3099 ± 3(stat.) ± 5(syst.)MeV, the Gaussian width of 12±3(stat.)MeV is compatible with the experimental resolution. The state can be interpreted as an anti-charmed baryon with minimal constituent quark composition uuddc?, together with the charge conjugate. PACS numbers: 14.20.Lq,14.80.-j 1. Introduction In the last 2 years several experiments [1] have reported evidence of a narrow baryonic resonance with strangeness S = +1 in the invariant mass of K+n combinations. These resonances can be interpreted as candidates for a strange pentaquark θ+, the minimal constituent quark content being uudds?. These measurements were supported by similar observations [2] in the K0Sp(p?) spectrum, although this channel does not allow for the obser- vation of exotic quantum numbers, since the K0S is a linear combination of strangeness S = +1 and S = ?1 states. However, there are also a number of high-energy experiments that do not confirm the observation of θ+ can- didates [3]. Also evidence for the pentaquark cascade states, Ξ??5 and Ξ 0 5 with strangeness S = ?2, has been reported [4]. The observations of possi- ble θ+ candidates have motivated H1 to search for a charmed pentaquark. The possible existence of such states had been discussed before [5]. The clearest charm signal is seen in the decay of the D?±. Therefore a search ? Presented at the Cracow Ephipany Conference on Hadron Physics, Cracow, Poland, January 6-8, 2005 (1) 2 risler˙epiphany printed on February 4, 2008 for resonances in the D?p invariant mass spectrum was performed an