Fabbietti, L.

Lapidus, K.

Mihaylov, D.

GSI Repository

K* reconstructed in pp reactions at 3.5 GeV∗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, GermanyThe investigation of K∗+(892) production in 3.5 GeVp+ p reaction is of great interest, due to the lack of exper-imental data at energies near to the production threshold[1, 2]. In addition, the available p + Nb data will allowus to study the in-medium modifications of the K∗+(892)in the future by using the results obtained from the currentanalysis as a reference. The production of K∗+(892) canbe easily studied by reconstructing it from its decay intoa neutral kaon and a charged pion (Fig. 1). Thus we per-formed the analysis of the K∗+(892) production in p + pcollisions at 3.5 GeV.Figure 1: The short-livedK∗+ decays at the primary vertexinto a K0S and a pi+. TheK0S decays into a pair ofcharged pions after a shorttime.The reconstruction of the K∗+(892) can be summarizedas follows: (i) Following the scheme shown in Figure 1and applying appropriate topological cuts, the K0Spi+ pairsare reconstructed; (ii) the invariant mass spectrum of theK0Spi+ pairs is fitted with a modified Breit-Wigner func-tion, taking into account the background, phase space lim-itations and detector resolution. This allows to extract theyield of the K∗+(892). The total yield is well above 1000K∗s, which gives the opportunity to perform a single dif-ferential analysis by dividing the data into five transversemomentum bins; (iii) Assuming uniform phase space dis-tribution, we simulate the two dominantK∗+(892) produc-tion channels using the PLUTO event generator: p + p →p+K∗++Λ0 and p+p→ p+K∗++Σ0. Then the responseof the detector is simulated using HGeant. The result is an-alyzed in the same way as the experimental data. Thus, asthe acceptance and efficiency correction factor for the ex-perimental data, we can use the ratio between the numberof reconstructed K∗s after HGeant and the number of K∗sgenerated in PLUTO. Due to the small difference in thecorrection factor between the two simulated channels weuse only the Λ associated production channel for the cor-rection of the data; (iv) by normalizing the K∗ yield to theelastic pp scattering cross section observed in this experi-ment, we can find the differential cross section for each pTbin. The integration of the spectrum delivers the total K∗production cross section; (v) It is possible to investigate the∗Work supported by BMBF and the Excellence Cluster “Universe”.† dimitar.mihaylov@mytum.deb]µ [σ7 8 9 10 11 12 13 14 15Counts050100Median68% intervalExcludedFigure 2: Systematic result for the K∗+(892) total produc-tion cross section. Any topological cuts that did not pro-duce meaningful result (e.g. the fit of the IM spectrum didnot converge) were excluded. [MeV/c]Tp0 100 200 300 400 500 600 700-1 (MeV/c)×nb T/dpσd0102030Exp. dataSyst. err.)ΛPLUTO () = 0.9Λ (ndf2χFigure 3: Differential production cross section of theK∗+(892) as a function of pT .data for spin-alignment effects. This was performed and nohint for such effects was present within uncertainties.In order to investigate the stability of the reconstructionprocedure and to obtain information on its systematic er-ror, this analysis was performed over 1200 different cutcombinations. The distribution of the results for the totalK∗+(892) production cross section resulting from those it-erations is shown in Figure 2. The final cross section wasobtained by taking the median of this distribution, the sys-tematic error was obtained by taking the 68% central inter-val, and the statistical error was taken as the average sta-tistical error over all topological cuts. As shown in Figure3 the obtained distribution of the differential cross sectionin pT is in a good agreement with the prediction of pureΛ associated production of the K∗+(892). Because of therelatively large error it is difficult to evaluate the yield re-sulting from the Σ associated production channel.References[1] Baldini et al., “Numerical Data and Functional Relationshipsin Science and Technology”, Springer, Volume 12b, 1988.[2] Bockmann et al., “Inclusive K*+(892) production in pp andpi+p interactions”, Nucl. Phys. B 166 (1980) 284.MU-NQM-HADES-02 GSI SCIENTIFIC REPORT 20142 DOI:10.15120/GR-2015-1-MU-NQM-HADES-02

K* reconstructed in pp reactions at 3.5 GeV

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K* reconstructed in pp reactions at 3.5 GeV

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