Pentaquarks search in NOMAD

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Existence of pentaquarks - hadrons build of 4 quarks and one anti-quark was predicted in a brilliant paper by Dmitry Diakonov, Viktor Petrov and Maxim Polyakov [1].

Penta-classics. 2006. Bochum. From left to right: Viktor Petrov, Dmitry Diakonov, Maxim Polyakov.

Many experiments looked for these new states. Some of them found, some did not.

The NOMAD experiment also took a part in this race. The road was not easy...

In 2004 our report‎ claimed for an evidence for the \Theta^+ state based on a sample with cleaner protons loosing however 6 times in the final statistics. However later we realized that in a less pure sample we must see pentaquarks even more clearly and we performed this time a blind analysis maximazing the sensitivity to the pentaquark state. The abstract of our article accepted for Eur.Phys.C reads:

A search for exotic \Theta^+ baryon via \Theta^+\to p+K^0_S decay mode in the NOMAD \nu_\mu N 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 x_F 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\cdot 10^{-3} per neutrino interaction.

The article is posted to hep-ex/0612063 archive.

The full list of our presentations on the subject can be found here:

Dmitry Naumov had a pleasure to meet all three penta-classics together in Bochum in house of Maxim Polyakov October 2006.

Penta-classics and Dmitry Naumov. 2006. Bochum. From left to right: Viktor Petrov, Dmitry Diakonov, Maxim Polyakov, Dmitry Naumov.
More photos and sound records of this meeting can be found here.