Precision spectroscopy of kaonic atom x rays at DA$\Phi$NE with silicon drift detectors in SIDDHARTA (III)*

The SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research by Timing Application) project is currently in progress at the DA$\Phi$NE $e^{+}e^{-}$ collider in LNF (Laboratori Nazionali di Frascati), Italy. In this experiment, the $K$-series x rays of kaonic hydrogen atom will be measured to a precision below 10 eV to determine the strong-interaction shift and width of the kaonic hydrogen atom $1s$ state with the best accuracy ever, which is important for the understanding of the kaon nucleon interaction. A gaseous target is used to stop the kaons produced resonantly through $\Phi\rightarrow K^{+}K^{-}$ at DA$\Phi$NE interaction point. And the specifically designed SDDs with a time resolution at micro-second order in addition to an energy resolution of about 150 eV FWHM at 6 keV, were introduced to achieve both a good timing selection to reduce background and a high energy resolution. The array of 144 such SDDs each with 1 cm$^2$ effective surface will cover a large sensitive area, leading to a better acceptance of kaonic x rays. Preliminary results of the measurement carried out in 2009 will be discussed.