1. First measurement of kaonic hydrogen and nitrogen X-rays at DA  NE J. Zmeskal Institute for Medium Energy Physics, Vienna for the DEAR Collaboration LNF – IMEP - INFN Trieste - Univ. Fribourg - Univ. Neuchâtel – RIKEN – Hokkaido Univ. - Univ. Tokyo - Univ. Victoria DA  NE 04 / JZ

2. Content Motivation of DEAR Experimental set-up Features of the experiment Data analysis Kaonic nitrogen measurement Results on kaonic hydrogen Summary DA  NE 04 / JZ

3. Exotic (kaonic) atoms – probes for strong interaction  hadronic shift ε 1s and width Γ 1s directly observable  experimental study of low energy QCD Kaonic hydrogen  K - p simplest exotic atom with strangeness  kaonic hydrogen „puzzle“ solved – but still: precision data missing  kaonic deuterium never measured before  atomic physics: new cascade calculations (to be tested !) Information on  (1405) sub-threshold resonance  important for research on deeply bound kaonic states Determination of the isospin dependent KN scattering lengths  no extrapolation to zero energyMotivation DA  NE 04 / JZ

4. Kaonic Hydrogen Negative kaons stopped in H 2  initial atomic capture   electromagnetic cascade  X-ray transitions  1s  1s s p d f E 1s } E 2p n 4 3 2 1 K   keV ε 1s = E 2p-1s (meas.) – E 2p-1s (e.m.) KK As the kaon interacts strongly with the nucleus the 1s energy level is shifted and broadened Shift and width of states n>1 are negligible DA  NE 04 / JZ

5. Experimental Set-up TMP CCD Electronics Vacuum Chamber APD Cryo-Cooler Target Cell CryoTiger CCD Cooling CCD Pre-Amplifier CCD55-Chips e + e - volume: 1150 cm 3 cryogenic H 2 gas filling side wall: 75 µm Kapton entrance window: 125 µm Kapton grid structure: glass fiber reinforced epoxy Energy measurement of kaonic K lines with an array of 16 CCD X-ray detectors DA  NE 04 / JZ

6. CCD Detector Array Array of 16 CCD-55 chips - pixels format 1242 x 1152 - pixel size 22.5x22.5 µm - total area per chip 7.24 cm 2 - depletion depth ~30 µm - read-out time per CCD ~ 90 s - energy resolution ~140 eV (5.9 keV Mn-55 K  line) DA  NE 04 / JZ

7. Setup at DAΦNE DA  NE 04 / JZ

8. Features of the Experiment Nearly mono-energetic kaons from  decay (pion-induced background largely suppressed compared to proton accelerator) Light weight target for low X-ray background Carefully chosen structure materials (checked by different analysis methods) Optimized gas density for high X-ray yield (cryogenic gas target) CCD array for X-ray detection (16 CCD-55, large area 116 cm 2, pixel analysis for background reduction, excellent resolution) Multilayer shielding for background reduction DA  NE 04 / JZ

9. Experimental Data Kaonic Nitrogen 3.-29.04.2002 ca. 9000 × 16 files (160GB) 14.2 pb -1 => 20.5 × 10 6 K - Kaonic Nitrogen 6.-28.10.2002 ca. 7000 × 16 files (112GB) 17.4 pb -1 => 25.1 × 10 6 K - Kaonic Hydrogen: 30.10.-16.12.2002 ca. 18000 × 16 files (288GB) 58.4 pb -1 => 84.1 × 10 6 K - Hydrogen, 16.-23.12.2002 ca. 2600 × 16 files (42GB) no collisions DA  NE 04 / JZ

10. Results on Kaonic Nitrogen Thesis T. Ishiwatari (IMEP), Phys. Lett. B in press  3 X-ray transitions  Extraction of the transition yields  Impact on cascade calculations  Kaonic nitrogen high precision measurement of the charged kaon mass DA  NE 04 / JZ

11. Kaonic Hydrogen Data Analysis Components of the X-ray spectra: Continuous background due to bremsstrahlung Fluorescence lines from structure materials Kaonic X-ray lines (only in H) Procedure: Fit of the continuous background Disentangling of the kaonic K α line from the K α fluorescence iron line Testing the sensitivity of different input for the K(n>4) lines DA  NE 04 / JZ

12. Kaonic Hydrogen X-ray spectrum Raw spectrum – bremsstrahlung background fitted with cubic function DA  NE 04 / JZ

13. Resulting K - p Spectrum (all background fit-components subtracted) DA  NE 04 / JZ

14. Results on the Shift and Width Shift:  1s = - 194 ± 37 (stat.) ± 6 (syst.) eV Width:  1s = 249 ± 111 (stat.) ± 30 (syst.) eV a K - p = – 0.466 (± 0.104) + i 0.299 (± 0.174) fm Combined results => preliminary DEAR average to be published in Phys.Rev.Lett. 2 independent analyses starting from the raw data giving consistant results DA  NE 04 / JZ

15. DEAR Results (preliminary) width  1s  [eV] KpX -5005000 0 200 400 600 800 1000 shift  1s [eV] Davies et al, 1979 Izycki et al, 1980 Bird et al, 1983 repulsive attractive KpX (KEK) M. Iwasaki et al, 1997  = - 323 ± 63 ± 11 eV  = 407 ± 208 ± 100 eV New theoretical studies: Ivanov et al. 2003 / 2004 Meißner, Raha, Rusetsky 2004 DEAR prelim. DA  NE 04 / JZ

16. Summary Preliminary results on strong interaction shift and width: repulsive shift in K - p verified smaller values and better precision for shift and width K β, K γ resolved for the first time  future high precision measurements on kaonic atoms are feasible DEAR one of the first experiments at DAΦNE First production of exotic atoms at DAΦNE Measurements on kaonic nitrogen and kaonic hydrogen DA  NE 04 / JZ