On the nature of new baryon state X(2000) observed in the experiments with the SPHINX spectrometer

TL;DR

This paper reports the observation of a new baryon state X(2000) with unusual properties, suggesting it could be a cryptoexotic pentaquark, and proposes further experiments to clarify its structure.

Contribution

It provides new experimental data on X(2000), discusses its potential exotic nature, and proposes specific reactions to determine its quark structure.

Findings

X(2000) has a mass of 1986 MeV and a width of 98 MeV.

X(2000) exhibits a large branching ratio with strange particles.

New data supports previous observations of X(2000).

Abstract

In the experiment with the SPHINX spectrometer in 1995-99 a new baryon state X(2000) -> Sigma^0K^+ was observed in the proton diffractive reactions p + N(C) -> Sigma^0K^+ + N(C). The main parameters of X(2000)^+ baryon are M = 1986 +- 6 MeV, Gamma = 98 +- 21 MeV. Unusual features of massive X(2000) state (narrow decay width Gamma/M simeq 0.05, anomalously large branching ratio with strange particle emission) make it serious candidate for cryptoexotic pentaquark baryon with hidden strangeness. New data on the SPHINX with by an order of magnitude enlarge statistics are in agreement with previous data and are supported our conclusions. We propose further studies X(2000) baryon production in the meson reactions with baryon exchange: pi^{+-} + p -> X(2000)^+ + pi^{+-} OZI - forbidden suppressed reaction for the state |qqqsbar{s}>) and K^{+-} + p -> X(2000)^+ + K^{+-} (OZI - allowed reaction). If the value of R=BR[pi^{+-} + p -> X(2000)^+ + pi^{+-}]/BR[K^{+-}+p -> X(2000)^+ + K^{+-}]<<1 it will be the crucial argument in favor of X(2000)= |qqqsbar{s}>) structure. These experiments may be done on IHEP separated kaon beam with OKA spectrometer.