Observation of a baryon resonance with positive strangeness in K + collisions with Xe nuclei

Abstract

The status of our investigation of low-energy K + Xe collisions in the Xenon bubble chamber DIANA is reported. In the charge-exchange reaction K + Xe →

Coalescence model for Θc pentaquark formation

“…The only limitation, as in DIS, is that HERWIG is able to model only hard processes. 2 In heavy quark hadroproduction the quark mass provides a hard scale, but in the case of charm this is not large enough to ensure perturbative reliability. We therefore set a minimum transverse momentum for the hard subprocess, setting the HERWIG parameter PTMIN to 5 GeV.…”

“…During the last year, many experiments have reported the observation of an exotic uudds pentaquark baryon Θ + [1,2]. Shortly after the initial experimental reports, Ref.…”

The pentaquark Θ+ in nK+ and pK0S, and its Σ+5 partner

“…1. It shows that the Θ + observed in nK + invariant mass is slightly higher than signals seen in pK 0 S , except for those two [5,10], in which the strangeness of the pK 0 S is well-defined. While the unambiguous positive strangeness of the nK + channel makes it superficially clean, Rosner has noted [11] that the diffractive background process γn → nφ → nK + K − can be a source of kinematic enhancement in the K + n channel on nuclei and thereby questions some claims for a Θ + (1540).…”

“…Several experimental groups reported to have seen the same narrow state in pK 0 S [5,6,7,8,9,10]. The importance of devising further tests for the existence of the Θ + and other predicted pentaquark baryons, B 5 , is highlighted by concerns that have been raised about the interpretation of some of the current signals [11,12,13] and also the lack of a signal for such a narrow state in other reactions, e.g.…”

“…However, for those signals seen in pK 0 S , the sign of the strangeness cannot be determined, except when an accompanying hadron with known strangeness is also detected [5,10]. In such experiments to date the narrow state has been assumed to be Θ + on the grounds that "no narrow Σ * + is known" at such masses [6,7,8].…”