19 April 1999.

CCD-detectors mounted on NTP-target observed
first beam-induced x-ray energy spectrum.

Starting with the first electron and positron beams in DAFNE on March 29, the DEAR CCD-detectors mounted on the NTP-target (NTP ... Normal Temperature Pressure) have been running and have observed X rays. These X rays are mainly due to excitation of the target material by beam induced background.

These first measurements have two main tasks:

1) To show that no peaks or any other structure is visible in the most interesting  region to the experiment from 5.5 keV to 6.5 keV. (This is the region where the X rays due to transitions from level 2 to 1 in kaonic hydrogen are expected.)

2) The NTP target has been covered inside with titanium and zirconium foils to provide an online energy calibration throughout the whole data taking period. The purpose is to test the efficiency of this calibration method.

Figure 1 below shows the recorded energy spectrum.

Figure 1: CCD energy spectrum (sum of 1 to 8 half CCDs). One can clearly see the fluorescence peaks of the calibration foils inside the target (K-alpha and K-beta of titanium, and K-alpha of zirconium) and the aluminum peak of the material of the target cell and the detector housings. No structure is visible in the region of interest.