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Register a new userExperimental study of the $gamma prightarrow K^0Sigma^+$, $gamma nrightarrow K^0Lambda$, and $gamma nrightarrow K^0 Sigma^0$ reactions at the Mainz Microtron
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Publication date
2018
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English
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This work measured $dsigma/dOmega$ for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the $gamma prightarrow K^0Sigma^+$, $gamma nrightarrow K^0Lambda$, and $gamma nrightarrow K^0 Sigma^0$ reactions. Our results for $gamma nrightarrow K^0 Sigma^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^*$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $pi N$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.
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The differential cross section for the quasi-free photoproduction reaction $gamma nrightarrow K^0Sigma^0$ was measured at BGOOD at ELSA from threshold to a center-of-mass energy of SI{2400}{MeV}. A peak is observed at SI{2050}{MeV} where the cross section rises by approximately a factor of four. The available statistics prevent an accurate description of this structure, however it appears consistent with models describing a resonance driven by the constructive interference of dynamically generated vector meson-baryon states, where an equivalent model predicted the $P_C$ states observed at LHCb. If proven correct, this could indicate parallels between the strange and charmed quark sectors.
We report measurements of the photon beam asymmetry $Sigma$ for the reaction $vec{gamma} pto K^+Sigma^0$(1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected using a linearly polarized photon beam in the energy range of 8.2-8.8 GeV incident on a liquid hydrogen target. The beam asymmetry $Sigma$ was measured as a function of the Mandelstam variable $t$, and a single value of $Sigma$ was extracted for events produced in the $u$-channel. These are the first exclusive measurements of the photon beam asymmetry $Sigma$ for the reaction in this energy range. For the $t$-channel, the measured beam asymmetry is close to unity over the $t$-range studied, $-t=(0.1-1.4)~$(GeV/$c$)$^{2}$, with an average value of $Sigma = 1.00pm 0.05$. This agrees with theoretical models that describe the reaction via the natural-parity exchange of the $K^{*}$(892) Regge trajectory. A value of $Sigma = 0.41 pm 0.09$ is obtained for the $u$-channel integrated up to $-u=2.0$~(GeV/$c$)$^{2}$.
The Dalitz decay pi^0 -> e^+e^-gamma has been measured in the gamma p -> pi^0 p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the pi^0 electromagnetic transition form factor, a_pi = 0.030+/-0.010_tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of a_pi is lower than in previous results based on the pi^0 -> e^+e^-gamma decay.
Differential cross sections for the reaction $gamma p to K^{*0} Sigma^+$ are presented at nine bins in photon energy in the range from 1.7 to 3.0 GeV. The kstar was detected by its decay products, $K^+pi^-$, in the CLAS detector at Jefferson Lab. These data are the first kstar photoproduction cross sections ever published over a broad range of angles. Comparison with a theoretical model based on the vector and tensor $K^*$-quark couplings shows good agreement with the data in general, after adjusting the models two parameters in a fit to our data. Disagreement between the data at forward angles and the global angle-energy fit to the model suggests that the role of scalar $kappa$ meson exchange in $t$-channel diagrams should be investigated.
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 phi gamma has been measured using an integrated luminosity of 1.0 fb-1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of sqrt(s)=7 TeV. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.23 +/- 0.06(stat.) +/- 0.04(syst.) +/- 0.10(fs/fd), where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for BR(B0 -> K*0 gamma), the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.5 +/- 0.4) x 10^{-5}. The direct CP asymmetry in B0 -> K*0 gamma decays has also been measured with the same data and found to be A(CP)(B0 -> K*0 gamma) = (0.8 +/- 1.7(stat.) +/- 0.9(syst.))%. Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations.
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