arXiv subjects

I. F. Larin

Publications and source records attributed to I. F. Larin.

6 recordsLinked to original sources

arXiv2016

Angular distribution in s-channel formation of the pentaquark $Θ^+$ baryon

Using the DIANA data on the charge-exchange reaction $K^+n \rightarrow pK^0$ on a bound neutron, in which the s-channel formation of the pentaquark baryon $Θ^+(1538)$ has been observed, we analyze the dependence of the background-subtracted $Θ^+ \rightarrow pK^0$ signal on the $K^0$ emission angle in the $pK^0$ rest frame. In order to describe the observed $\cosΘ_K^\mathrm{cms}$ distribution, invoking the interference between the nonresonant s-wave and the $Θ^+$-mediated higher-wave contributions to the amplitude of the charge-exchange reaction is required at a 2.8$σ$ level. The spin--parity assignment of 1/2$^-$ for the $Θ^+$ baryon is ruled out at a statistical level of 2.9 standard deviations. A physically-meaningful selection in $\cosΘ_K^\mathrm{cms}$ based on the observed angular dependence of the $Θ^+ \rightarrow pK^0$ signal allows to boost the statistical significance of the signal up to 7.1 standard deviations. This is far in excess of previously reported signals and renders the $Θ^+$ existence more credible.

hep-ex↗

arXiv2014

Observation of a narrow baryon resonance with positive strangeness formed in $K^+$Xe collisions

The charge-exchange reaction K^+ Xe --> K^0 p Xe' is investigated using the data of the DIANA experiment. The distribution of the pK^0 effective mass shows a prominent enhancement near 1538 MeV formed by \sim 80 events above the background, whose width is consistent with being entirely due to the experimental resolution. Under the selections based on a simulation of K^+Xe collisions, the statistical significance of the signal reaches 5.5σ. We interpret this observation as strong evidence for formation of a pentaquark baryon with positive strangeness, Θ^+(uudd\bar{s}), in the charge-exchange reaction K^+ n --> K^0 p on a bound neutron. The mass of the Θ^+ baryon is measured as m(Θ^+) = 1538+-2 MeV. Using the ratio between the numbers of resonant and non-resonant charge-exchange events in the peak region, the intrinsic width of this baryon resonance is determined as Γ(Θ^+) = 0.34+-0.10 MeV.

nucl-ex↗

arXiv2009

Experimental search for radiative decays of the pentaquark baryon Θ^+(1540)

The data on the reactions K^+Xe --> K^0 γX and K^+Xe --> K^+ γX, obtained with the bubble chamber DIANA, have been analyzed for possible radiative decays of the Θ^+(1540) baryon: Θ^+ --> K^0 p γand Θ^+ --> K^+ n γ. No signals have been observed, and we derive the upper limits Γ(Θ^+ --> K^0 p γ) / Γ(Θ^+ --> K^0 p) < 0.032 and Γ(Θ^+ --> K^+ n γ) / Γ(Θ^+ --> K^+ n) < 0.041 which, using our previous measurement of Γ(Θ^+ --> KN) = (0.39+-0.10) MeV, translate to Γ(Θ^+ --> K^0 p γ) < 8 keV and Γ(Θ^+ --> K^+ n γ) < 11 keV at 90% confidence level. We have also measured the cross sections of K^+ -induced reactions involving emission of a neutral pion: σ(K^+n --> K^0 p π^0) = (68+-18) \mub and σ(K^+N --> K^+ N π^0) = (30+-8) \mub for incident K^+ momentum of 640 MeV.

hep-ex↗

arXiv2009

Formation of a narrow baryon resonance with positive strangeness in K^+ collisions with Xe nuclei

The data on the charge-exchange reaction K^+Xe --> K^0 p Xe, obtained with the bubble chamber DIANA, are reanalyzed using increased statistics and updated selections. Our previous evidence for formation of a narrow pK^0 resonance with mass near 1538 MeV is confirmed and reinforced. The statistical significance of the signal reaches some 8σ(6σ) when estimated as S/\sqrt{B} (S/\sqrt{B+S}). The mass and intrinsic width of the Θ^+ baryon are measured as m = (1538+-2) MeV and Γ= (0.39+-0.10) MeV.

hep-ex↗

arXiv2006

Further evidence for formation of a narrow baryon resonance with positive strangeness in K+ collisions with Xe nuclei

We have continued our investigation of the charge-exchange reaction K^+ Xe --> K^0 p Xe' in the bubble chamber DIANA. In agreement with our previous results based on part of the present statistics, formation of a narrow p K^0 resonance with mass of 1537+-2 MeV/c^2 is observed in the elementary transition K^+ n --> K^0 p on a neutron bound in the Xenon nucleus. Visible width of the peak is consistent with being entirely due to instrumental resolution and allows to place an upper limit on its intrinsic width: Γ< 9 MeV/c^2. A more precise estimate of the resonance intrinsic width, Γ= 0.36+-0.11 MeV/c^2, is obtained from the ratio between the numbers of resonant and non-resonant charge-exchange events. The signal is observed in a restricted interval of incident K^+ momentum, that is consistent with smearing of a narrow p K^0 resonance by Fermi motion of the target neutron. Statistical significance of the signal is some 7.3, 5.3, and 4.3 standard deviations for the estimators S/sqrt{B}, S/sqrt{S+B}, and S/sqrt{S+2B}, respectively. This observation confirms and reinforces our earlier results, and offers strong evidence for formation of a pentaquark baryon with positive strangeness in the charge-exchange reaction K^+ n --> K^0 p on a bound neutron.

hep-ex↗

arXiv2003

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

The status of our investigation of low-energy $K^+$Xe collisions in the Xenon bubble chamber DIANA is reported. In the charge-exchange reaction $K^+Xe \to K^0 p Xe'$ the spectrum of $K^0 p$ effective mass shows a resonant enhancement with $M = 1539 \pm 2$ MeV/c$^2$ and $Γ\le 9 MeV/c$^2$. The statistical significance of the enhancement is near $4.4σ$. The mass and width of the observed resonance are consistent with expectations for the lightest member of the anti-decuplet of exotic pentaquark baryons, as predicted in the framework of the chiral soliton model.

hep-ex↗