A Classic Thesis Style - Johannes Gutenberg-Universität Mainz

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84 conclusions cm [nb/sr] dσ v / dΩ K cm [nb/sr] dσ v / dΩ K 600 500 400 300 200 100 0 600 500 400 300 200 100 0 p(e,e’K + cm )Λ cos θ = 0.35 K MAMI SAPHIR CLAS K-Maid original K-Maid reduced Saclay-Lyon K-Maid extended 0 0.05 0.1 0.15 0.2 Q 2 [(GeV/c) 2 ] p(e,e’K + )Σ o MAMI SAPHIR CLAS K-Maid original K-Maid reduced Saclay-Lyon K-Maid extended cm cosθ = 0.35 K 0 0.05 0.1 0.15 0.2 Q 2 [(GeV/c) 2 ] Figure 52: Dependence of the kaon electroproduction cross sections on the virtual photon’s four-momentum Q 2 . Model predictions and data points are the same as in Fig. 50. From [71]. well with the data. Results for the Λ channel differential cross section, obtained from the lower statistics 2008 data are shown in Fig. 51 together with model predictions. In the reduced version of Kaon-Maid (K-Maid orig.G3P13=0 in the figure), only the longitudinal coupling for the N*(1720) resonance was switched off. It can be seen that this makes the main effect of the longitudinal reduction. SAPHIR and CLAS data are shown for two energies: 1.665 and 1.675 GeV. An energy dependence is apparent from their relative systematical shift. Both data sets confirm that the transition from photoproduction to electroproduction proceeds in both channels smoothly in sharp contrast with the predictions of the original K-Maid model, as can be seen in Figs. 52 and 53, where electroproduction and photoproduction data are shown for a representative angular bin at cos θ ∗ = 0.35.
cm [nb/sr] dσ / dΩ K 500 400 300 200 100 0 K-Maid original p(e,e’K + )Λ cm cos θ = 0.35 K MAMI SAPHIR CLAS σ total σ T ε σ L ε σ TT (2ε (ε+1)) 1/2 σ TL 0 0.05 0.1 0.15 0.2 Q 2 [(GeV/c) 2 ] conclusions 85 Figure 53: Predictions for the separated and total cross sections in the Λ electroproduction channel from the original K-Maid model for the kinematics probed at MAMI. A strong contribution of longitudinal, σL, and transverse-longitudinal interference, σT L, cross sections is noted. The transverse contribution, σT , is slowly decreasing with Q 2 . From [71] In the original Kaon-Maid model, the step rise of the cross-section as a function of Q 2 is specially apparent in Fig.53 at W = 1.67 GeV. This is the result of the strong longitudinal coupling to the resonance P13(1720). The data shows that the actual cross section does indeed decrease when entering the virtual photon region. This behavior has been also been documented by CLAS results on the unpolarized cross-section in the K + Λ channel (measured for 0.65 < Q 2 < 2.5 (Gev/c) 2 )(see Fig. 54). It is interesting to see that the Q 2 fits to a dipole form C/(Q 2 + M 2 ) 2 (where C is an arbitrary constant) for the K + data, significantly overshoot the photon point specially at forwardangles. This can not be explained by a significant contribution to the cross section from σL, since CLAS could also measure the separated contributions from σL and σT , proving that σL contribution is rather small. According to Janssen et al. [72], a Q 2 dependence of the kaon and proton form factors might explain the observed behavior. On the other hand, Bydžovský and Mart [36] have demonstrated that the behavior of forward-angle cross sections as a function of the energy for models that include the hadronic form factors is far from realistic. Although no data are available for direct comparison, such a strong damping has not been observed in the experimental data near forward angles. Clearly low Q 2 data is of relevance to clarify this problem.
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M E A S U R E M E N T O F T H E U N
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A B S T R A C T The new stage of th
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C O N T E N T S i kaon electroprodu
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Part I K A O N E L E C T R O P R O
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4 introduction Lorentz invariance.
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6 introduction appear in the K + Λ
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8 introduction there was almost no
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10 introduction This allows us to w
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12 introduction K ¡p γ ∗ Λ(Σ
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14 introduction means of the isobar
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16 introduction amount of resonance
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18 introduction photo and electropr
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20 introduction 1.6 previous experi
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22 introduction Figure 9: Total cro
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E X P E R I M E N TA L S E T U P A
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2.3 target 27 Figure 11: Schematic
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2.4 kaos spectrometer 2.4 kaos spec
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M MWPC L F 2.4 kaos spectrometer 31
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134 theoretical background by showi
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136 theoretical background With thi
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138 bibliography [16] J. C. David,
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140 bibliography [44] M. Bockhorst
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142 bibliography [71] P. Achenbach
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144 bibliography [98] S. Nozawa and
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146 bibliography Figure 24 Spek B d
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Figure 73 Annealing at 80° of the
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A Classic Thesis Style - Johannes Gutenberg-Universität Mainz

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