Critical view of the claimed $\Theta^+$ pentaquark

TL;DR

This paper critically examines the claimed observation of the $ heta^+$ pentaquark, demonstrating that experimental methods and data fitting procedures can artificially produce a peak, questioning the validity of the original claim.

Contribution

It provides a theoretical analysis showing that the observed peak can be an artifact of data analysis, challenging the claimed existence of the $ heta^+$ pentaquark.

Findings

The peak is likely an artifact of the analysis method.

The original background fitting distorts the data.

Alternative analysis shows no significant signal.

Abstract

We use a theoretical model of the $\gamma ~d \to ~K^+ K^- ~n ~p $ reaction adapted to the experiment done at LEPS where a peak was observed and associated to the $\Theta^{+}(1540)$ pentaquark. The study shows that the method used in the experiment to associate momenta to the undetected proton and neutron, together with the chosen cuts, necessarily creates an artificial broad peak in the assumed $K^+ n$ invariant mass in the region of the claimed $\Theta^{+}(1540)$. It is shown that the LEPS fit to the data, used to make the claim of the $\Theta^{+}(1540)$, grossly distorts the background. An alternative fit, assuming a background plus a fluctuation, returns a background practically equal to the theoretical one and a fluctuation identical to the one seen in the experimental $K^- p$ spectrum of 2$\sigma$ significance.