Experimental Studies on Kaonic Atoms at DA  NE

1. Experimental Studies on Kaonic Atoms at DANE LNF - Italy SMI - Austria INFN Trieste - Italy IPNE - Romania Univ. Fribourg - Switzerland Univ. Neuchâtel - Switzerland RIKEN - Japan Univ. Tokyo - Japan Univ. Victoria - Canada UCB - USA Johann Zmeskal Stefan Meyer Institute for subatomic Physics Austrian Academy of Sciences, Vienna, Austria for the DEAR/SIDDHARTA Collaborations 18th International IUPAP Conference on Few-Body Problems in Physics Aug. 21 – 26, 2006 - Santos, Brazil

2. Content • Motivation • The DEAR experimental set-up • Kaonic atom measurements with DEAR  Results on kaonic nitrogen  Results on kaonic hydrogen • The SIDDHARTA project  New X-ray detectors  New setup  Physics goals • Summary & Outlook

3. Experiments with exotic atoms,a broad research field K-p, K-d -p, -d ….

4. Motivations • K-p simplest exotic atom with strangeness • strong interaction shift ε1s and width Γ1s directly observable by X-ray spectroscopy • K-p: Information on Λ(1405) antikaon bound nuclear clusters  (A. Gal P24, Theory overview of antikaon bound state N.V. Shevchenko R1-26, Search for a K-pp bound state) • kaonic hydrogen, precision data missing • kaonic deuterium never measured before

5. Kaonic Hydrogen - Goals • Measurement of strong interaction shift and width of kaonic hydrogen and kaonic deuteriumwith an accuracy of a few eV • Determination of the isospin dependent scattering lengths near threshold • no extrapolation to zero energy • Testing chiral symmetry breaking in systems with strangeness

6. Review – results before DEAR 1000 800 600 Izycki et al, 1980 400 200 Bird et al, 1983 Davies et al, 1979 0 -500 0 500 shifte1s[eV] • K-p interaction attractive/repulsive ? • Solution by KEK experiment attractive repulsive KpX (KEK) M. Iwasaki et al, 1997 KpX widthG1s[eV] • = - 323 ± 63 ± 11 eV G = 407 ± 208 ± 100 eV

7. Strong Interaction in K-p n 4 s p d f 3 2 Shift and width of states n>1 negligible E2p Kg G1s 1 E1s e1s } Due to the strong interaction kaon-protonthe 1s level is shifted and broadened Ka ~ 6.3 keV ε1s = E2p-1s(meas.) – E2p-1s(e.m.)

8. Scattering Lengths Relation of strong interaction shift and width to the complex Kp scattering length aK-p For the determination of the isospin dependent scattering lengths a0 and a1 the hadronic shift and width of kaonic hydrogen and kaonic deuterium are necessary

9. Requirements • Kaon Beam at DANE with unique performance • Slow, nearly monochromatic kaons (E~16 MeV) • Kaon pair emitted back-to-back • Low hadronic background • Target System • Cryogenic gas target, pure hydrogen gas • Thin windows, light-weight construction • X-ray Detector • Large active area • Superior energy resolution • Background suppression capability • Calibration • “online“ calbration – fluorescence lines

10. DANE (LNFrascati) electron – positron collider collision energy tuned to the Φresonance at 1.02 GeV c.m. DEAR

11. DEAR Setup at DAΦNE APD Cryo-Cooler TMP CCD electronics CCD cooling Vacuum chamber CCD pre-amplifier Target Cell CCD55-chips K- e+ e-

12. CCD X-ray Detection • Array of 16 CCD55-30 • 1242 x 1152 pixels / chip • pixel size 22.5 x 22.5 µm • total area per chip 7.24 cm2 • depletion depth ~30 µm • read-out time per CCD 2 min. • energy resolution ~150 eV @ 6keV • temperature stabilized at 165 K

13. DEAR Target Light-weight cylindrical target structure Diameter: 12.5 cm Height: 14 cm Volume: 1150 ccm Side wall: 75 µm Hostaphan Entrance window: 125 µm Hostaphan Grid structure: glass fiber reinforced epoxy Hydrogen filling: Temperature: 25 K (hydrogen) Pressure: 2 bar Density: 2.1 g/l (3 % LHD) kaon

14. Kaonic nitrogen published in : Phys. Lett. B 593 (2004) 48-54

15. Resulting K-p X-ray Spectrum X-ray energy spectrum with all background fit-components subtracted 1s = - 193 ± 37 (stat.) ± 6 (syst.) eV 1s = 249 ± 111 (stat.) ± 30 (syst.) eV At lowest order: aK-p= (-0.468 ± 0.090stat± 0.015syst) + i(0.302± 0.135stat± 0.036syst) fm

16. DEAR Results 1000 800 600 DEAR Izycki et al, 1980 400 200 Bird et al, 1983 Davies et al, 1979 0 -500 0 500 shifte1s[eV] attractive repulsive KpX (KEK) M. Iwasaki et al, 1997 KpX widthG1s[eV] • = - 323 ± 63 ± 11 eV G = 407 ± 208 ± 100 eV

17. From DEAR to SIDDHARTA • Precision of the DEAR result limited by high X-ray background (S/N~1:70) • Next step: background reduction by using kaon – X-ray time correlation (expected background suppression ~ 3 orders of magnitude  S/N ~ 10:1 for kaonic hydrogen) • New X-ray detectors  SDDs • New dedicated target-detector set-up

18. New X-ray Detector - SDD New X-ray detectors with • timing capability  background suppression by using the kaon - X ray time correlation • excellent energy resolution • high intrinsic efficiency, large area  Development of large area SDD detectors JRA10 in I3HP (EU FP6)

19. Silicon Drift Detector SDD SDD with JFET • SDD has small capacitance  low noise • Good energy resolution, comparable with CCD • But: timing capability (t < 0.5 µs) Large area SDD with 1 cm2 active area 3 SDD on 1 chip

20. Performance of Large SDDs First application of large (1 cm2) SDDs in K-He experiment at KEK (see talk by S. Okada at this Workshop)

21. Background suppression e+ Triple coincidence: SDDX * ScintK * ScintK K+ F K- Scintillator X-ray SDD hydrogen gas Scintillator e-

22. Kaonic Deuterium (MC) Background suppression to < 10-3 Kaonic deuterium Ag K fluorescence lines (calibration) Ka Kb,g No timing SDD ‚single‘ coinc. SDD * Scint * Scint Energy (keV) Energy (keV)

23. SIDDHARTA Setup Cryogenic setup SDD array (~200 cm2 SDDs)

24. SDD unit (2x3x3 SDDs)

25. SIDDHARTA Setup cont‘d Cryogenic target cell 75 µm Kapton within a pure aluminum grid Pmax. ~ 5 bar Target cell – SDD array assembly Cryogenic target cell

26. SIDDHARTA Setup – side view SDD Array Gas target Kaon Detector Beam pipe

27. Material Analysis by PIXE Carefully selected structure materials analyzed by PIXE@VERA: Avoiding iron content

28. Monte Carlo Results K-p K-d Counts Kβ Kα Kγ Khigh Energy [keV] Energy [keV] Monte Carlo simulated X-ray spectra (data taking 30 days). Measurement with SDD array and kaon trigger. K-p:ε1s = 193 eV, Γ1s = 249 eV, Y(Kα)=2% ε1s= 2eV, Γ1s= 4eV K-d:ε1s = 325 eV, Γ1s = 630 eV, Y(Kα)=0.2% ε1s= 18eV, Γ1s= 45eV

29. SIDDHARTA - Outlook 1000 800 600 SIDDHARTA Izycki et al, 1980 400 200 Bird et al, 1983 Davies et al, 1979 0 -500 0 500 shifte1s[eV] KpX (KEK) M. Iwasaki et al, 1997 KpX widthG1s[eV] • = - 323 ± 63 ± 11 eV G = 407 ± 208 ± 100 eV DEAR

30. Outlook Future physics program at DAΦNE • Measurement of kaonic deuterium (first measurement ever) • Precision measurement of kaonic hydrogen (at the percent level). • Further perspectives: Kaonic helium studies with 3He and 4He targets Precision measurement of charged kaon mass

31. SUMMARY • First production of exotic atoms at DAΦNE, • Successful measurements on kaonic hydrogen • New X-ray detector (SDD array) and setup in preparation, • Installation at DAΦNE 2007 • repulsive shift in K-p verified • smaller shift and width values, higher precision

32. Spare

33. Results on kaonic nitrogen 3X-ray transitions - first measured extraction of the transition yields for 7-6, 6-5, 5-4

34. K-p and K-d Atoms K-p (K-d) e.m. bound kaonic atoms, Bohr radius ~80 fm *) new studies: c.f. A.N. Ivanov et al., Eur.Phys.J. A 23 (2005) 79, U.-G. Meißner, U. Raha and A. Rusetsky, arXiv:nucl-th/0603029, 2006