Abstract
A search for exotic Theta baryon via Theta -> proton +Ks decay mode in the NOMAD muon neutrino DIS data is reported. The special background generation procedure was developed. The proton identification criteria are tuned to maximize the sensitivity to the Theta signal as a function of xF which allows to study the Theta production mechanism. We do not observe any evidence for the Theta state in the NOMAD data. We provide an upper limit on Theta production rate at 90% CL as 2.13 per 1000 of neutrino interactions.
Highlights
In the last three years an intense experimental activity has been carried out to search for exotic baryon states with charge and flavor requiring a minimal valence quark configuration of four quarks and one antiquark
We provide an upper limit on Θ+ production rate at 90% confidence level (CL) as 2.13 × 10−3 per neutrino interaction
With help of Monte Carlo simulation (MC) we find a negligible contribution of Σ(1660) − Σ(2250) resonances to KS0 p invariant mass distribution while K → KS0 π decays increase the background by 5%–10% at small M ∼ 1500 MeV/c2
Summary
In the last three years an intense experimental activity has been carried out to search for exotic baryon states with charge and flavor requiring a minimal valence quark configuration of four quarks and one antiquark (such states are often referred to as “pentaquarks”). Searches for narrow pentaquark states were performed in almost every accelerator experiment in the world, providing evidence or hints for a variety of pentaquark candidates: Θ+, Ξ5−−, Θ++, and Θc0 After this initial flurry of positive results, negative results, in particular from high statistics experiments, started to dominate the field. As an example of a negative search we quote the HERA-B experiment at DESY [17] that observed neither the Θ+ resonance in the pKS0 invariant mass distribution nor the Ξ−−(1860) (another member of the antidecuplet of exotic baryons) decaying to Ξ−π−. Based on the background determination procedure and proton identification, we develop a strategy for a “blind” analysis of the Θ+ signal by finding the proton identification criteria which maximize the sensitivity to the expected signal
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