Fabbietti, L.

Lapidus, K.

Mihaylov, D.

GSI Repository

Hunting forK∗+ in pp and pNb reactions∗D. Mihaylov†1,2, L. Fabbietti1,2, K. Lapidus1,2, and the HADES collaboration1Physik Department E12, TU Mu¨nchen, James-Franck-Str. 1, 85748 Garching, Germany; 2Excellence Cluster“Universe”, TU Mu¨nchen, Boltzmannstr. 2, 85748 Garching, GermanyIn a recent study performed by the HADES collaborationfor p + p and p + Nb collisions at 3.5 GeV, the productionof neutral kaons was investigated [1]. The high statisticsavailable for this analysis suggests that the exited states ofthe kaons can be investigated as well. One excited state thatis decaying into a neutral kaon is the K ∗+(892) (Fig. 1).Information about the production of this particle at the en-ergy of 3.5 GeV is of great interest, since no K ∗+(892)measurements at such low energy are available [2, 3].The study of the K∗+(892) resonance can be dividedinto two main steps. In the first step the total and differen-tial cross sections for K∗+(892) production in p + p reac-tions are reconstructed. The second step is to use this resultas a reference for a further investigation of K ∗+(892) pro-duction in p + Nb reactions. The latter is interesting, be-cause one can study the contribution by p + n reactions tothe total yield, scattering processes inside the nucleus, sec-ondary production processes (e.g. π + N → K ∗ + Λ) andeventual in-medium modifications of the K ∗+(892). Themost efficient way to reconstruct K ∗+(892) using HADESdata is by the decay scheme shown in Fig. 1.Figure 1: The short-lived K ∗+ decays at the primary vertexinto a K0S and a π+. The K0S decays into a pair of chargedpions after a short time.By selecting triplets of charged pions in each event andapplying geometrical cuts to constrain the decay topologyone can reconstruct the invariant mass spectrum of K 0Sπ+-pairs, showing the signal of K ∗+(892) (Fig. 2).For p+p reactions we find more than 1000 reconstructedK∗+(892). This statistics is sufficient to perform a differ-ential analysis. In order to correct the data for acceptanceand efficiency a model capable of reproducing the exper-imental data was needed. For this reason, as well as totest the efficiency of the implemented reconstruction pro-cedure, simulations of the K ∗+(892) production in p + pcollisions were performed. The two production channels,∗Work supported by BMBF and the Excellence Cluster “Universe”.† dimitar.mihaylov@mytum.deFigure 2: The invariant mass spectrum of the selectedK∗+(892) candidates. The measured values are in a fairagreement with the properties listed in PDG, which areM = 891.66 MeV/c2 and Γ = 50.8 MeV/c2.that are expected to be dominant, p + p → p + K ∗+ + Λ0and p + p → p + K∗+ + Σ0, were simulated and the datais to be modeled by determining the relative contributionof each channel, that allows to reproduce the experimentaldata. In the simulations a uniform phase space populationwas assumed. There are, however, few effects that com-plicate the analysis. One is the detector resolution, whichwas estimated from simulations to be around 12 MeV/c2.This effect can be accounted for by fitting the signal usinga Voigt function, which is a convolution of a Breit-Wignerfunction, which represents the resonance, and a Gaussianfunction, which models the resolution. A second issue isthe phase-space limitation for the production of K ∗+(892).The threshold energies for the two main production chan-nels (see above) are 2.95 and 3.02 GeV, respectively. Thismeans that the available center of mass energy of 3.18 GeVis just a bit above those values. Hence, the phase spacelimitations will be substantial, especially for particles withhigh transverse momentum. Thus, the fitting function mustbe further modified in order to account for the shape of thesignal.After the analysis of p + p data is completed, it will beextended to p+Nb data in order to study the nuclear effectsin the production of K ∗+(892).References[1] Berger-Chen et al., Hyperfine Int., 210(1-3), 111 (2013).[2] Baldini et al., “Numerical Data and Functional Relationshipsin Science and Technology”, Springer, Volume 12b (1988).[3] Bockmann et al., Nucl. Phys. B 166, 284 (1980).NQM-HADES-06 GSI SCIENTIFIC REPORT 20136 doi:10.15120/GR-2014-1-NQM-HADES-06

Hunting for $K^{*+}$ in pp and pNb reactions

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Hunting for $K^{*+}$ in pp and pNb reactions

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Hunting for K∗+K^{*+}K∗+ in pp and pNb reactions

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Hunting for $K^{*+}$ in pp and pNb reactions