a K p = 1 2 (a 0 + a 1 ) (2) A similar relation applies to the case of kaonic deuterium and to the corresponding scattering length a K d:

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1 SIDDHARTA M. Bazzi (Ass. Ric.), M. Bragadireanu (Bors. UE), C. Curceanu Petrascu (Resp. Naz.), A. D Uffizi (Bors.), C. Guaraldo (Art. 2222), M. Iliescu (Ass.), P. Levi Sandri, V. Lucherini, F. Lucibello (Tecn.), S. Okada (Bors. PD), D. Pietreanu (Ass. Ric.), M. Poli Lener (Art. 23), A. Rizzo (Bors.), A. Romero Vidal (Bors PD), A. Scordo (Bors. PD), D. Sirghi (Art. 2222), F. Sirghi (Bors. UE), O. Vazquez Doce (Art. 23) 1 The SIDDHARTA scientific program The objective of the SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research by Timing Application) experiment is to continue, to deepen and enlarge the successful scientific line, initiated by the DEAR experiment in performing precision measurements of X-ray transitions in exotic (kaonic) atoms at DAΦNE. The precise determination of the shift and width of the 1s level with respect to the purely electromagnetic calculated values, in kaonic hydrogen and kaonic deuterium, generated by the presence of the strong interaction, through the measurement of the X-ray transitions to this level, will allow the first precise experimental determination of the isospin dependent antikaon-nucleon scattering lengths, fundamental quantities in understanding low-energy QCD in strangeness sector. The shift ǫ and the width Γ of the 1s state of kaonic hydrogen are related to the real and imaginary part of the complex s-wave scattering length, a K p, through the Deser formula (in the isospin limit): ǫ + iγ/2 = 2α 3 µ 2 a K p = (412 ev fm 1 ) a K p (1) where α is the fine structure constant and µ the reduced mass of the K p system. In the isospin limit, i.e. in the absence of the electromagnetic interaction and at m d = m u, a K p can be expressed directly in terms of the scattering lengths for isospin I=0 and I=1: a K p = 1 2 (a 0 + a 1 ) (2) A similar relation applies to the case of kaonic deuterium and to the corresponding scattering length a K d: ǫ + iγ/2 = 2α 3 µ 2 a K d = (601 ev fm 1 ) a K d (3) An accurate determination of the K N isospin dependent scattering lengths will place strong constraints on the low-energy K N dynamics, which, in turn, constraints the SU(3) description of chiral symmetry breaking in systems containing the strange quark. The DEAR measurement on kaonic hydrogen, performed in ) ǫ = 193 ± 37(stat.) ± 6 (syst.) ev (4) Γ = 249 ± 111(stat.) ± 39 (syst.) ev. (5) has already triggered an increased activity of the theoretical groups working in the low-energy kaon-nucleon interaction field, as well as in more general non-perturbative QCD.

2 The SIDDHARTA experiment aims to significatively improve the precision obtained by DEAR and to perform the first measurement ever of kaonic deuterium. SIDDHARTA performed as well accurately measurements on kaonic helium transitions to the 2p level (L-series). The kaonic helium 3 was measured for the first time (see below). 2 The SIDDHARTA setup SIDDHARTA represents a new phase in the study of kaonic atoms at DAΦNE. The DEAR precision was limited by a signal/background ratio of about 1/70. To significantly improve this ratio, a breakthrough is necessary. An accurate study of the background sources present at DAΦNE was redone. The background includes two main sources: synchronous background: coming together with the kaons related to K interactions in the setup materials and also to the φ-decay processes; it can be defined as hadronic background; asynchronous background: final products of electromagnetic showers in the machine pipe and in the setup materials originating from particles lost from primary circulating beams either due to the interaction of particles in the same bunch (Touschek effect) or due to the interaction with the residual gas. Accurate studies performed by DEAR showed that the main background source in DAΦNE is of the second type, which shows the way to reduce it. A fast trigger correlated to a kaon entering into the target would cut the main part of the asynchronous background. X rays were detected by DEAR using CCDs (Charge-Coupled Devices), which are excellent X-ray detectors, with very good energy resolution (about 140 ev FWHM at 6 kev), but having the drawback of being non-triggerable devices (since the read-out time per device is at the level of 10 s). A recently developed device, which preserves all good features of CCDs (energy resolution, stability and linearity), but additionally is triggerable - i.e. fast (at the level of 1µs), was implemented. This new detector is a large area Silicon Drift Detector (SDD), specially designed for spectroscopic application. The development of the new 1 cm 2 SDD device, together with readout electronics and very stable power supplies, was partially performed under the Joint Research Activity JRA10 of the I3 project Study of strongly interacting matter (HadronPhysics) within FP6 of the EU. The trigger in SIDDHARTA was given by a system of scintillators which recognized a kaon entering the target making use of the back-to-back production mechanism of the charged kaons at DAΦNE from φ decay: of the type: φ K + K. (6) The SIDDHARTA setup contains 144 SDD chips of 1 cm 2 each, placed around a cylindrical target, containing high density cryogenic gaseous hydrogen (deuterium). The SDDs are grouped in units of 3 detectors, read individually; bigger units of 18 SDDs are then realized, Fig. 1. The target is made of kapton, 75µm thick, reinforced with aluminium grid, see Fig SDD 18 cm 2 units were placed all around the target cell, as shown in Fig. 3. The SIDDHARTA setup was installed on DAΦNE in late summer 2008 (see Fig. 4) and the period till the end of 2008 was used to debug and optimize the setup performances (degrader optimization included). The kaonic atoms measurements were done in 2009, as described below.

3 Figure 1: An 18 cm 2 SDD unit, containing 18 SDD individual chips. Figure 2: The SIDDHARTA target cell, done in kapton, reinforced with an aluminium grid. It will contain about 3 liters of cryogenic and high density hydrogen (deuterium) gas.

4 Figure 3: The SIDDHARTA target cell surrounded by SDD units (detail). Figure 4: The SIDDHARTA full setup installed at DAΦNE.

5 Figure 5: The Kaonic Helium triggered spectrum. The Mn and Ti lines are used for calibration. The kaonic helium4 transition at 6.4 kev is clearly seen. 3 Activities in 2009 SIDDHARTA was in data taking from late January 2009 until 9 November 2009, with a break during August month, used for the setup maintenance and some improvements. In what follows, we present the measurements SIDDHARTA performed in Kaonic helium 4 measurement After having installed the SIDDHARTA setup on DAΦNE, we optimized the performances of the setup, including degrader and callibration method, by using kaonic helium 4 transitions to the 2p level (L-series), due to the fact that the yield of these transitions is at least a factor 10 higher than the one of kaonic hydrogen transitions. We have analyzed part of these data and published them in Ref. 2). It was the first measurement of kaonic helium in gas target - where the Compton scattering is neglijible (which is not the case of liquid targets, as those previously used). The obtained results (see Fig. 5 for the kaonic helium spectrum): E = E exp E e.m. = 0 ± 6 (stat.) ± 2 (syst) ev (7) definitely solves the so-called kaonic helium puzzle (see the paper for details). We are presently analyzing all the data, with the aim to get a better precision and information on the yield for a second publication. 3.2 Kaonic hydrogen measurement The kaonic hydrogen measurement was performed in the period 15 March - 31 July 2009 and during October 2009, for a total of about 400 pb 1 of integrated luminosity.

6 Figure 6: (color online). The Kaonic Hydrogen triggered spectrum. The kaonic Hydrogentransitions are clearly visible. In red the e.m. position of the lines. In Fig. 6 we present a preliminary partial statistics triggered kaonic hydrogen spectrum, where kaonic hydrogen transitions to the 1s level (K-series) are clearly seen. Data analyses are undergoing 3.3 Kaonic deuterium measurement We performed an exploratory measurement of kaonic deuterium transitions in September-October 2009, for a total integrated luminosity of about 100 pb 1, to be confrounted with an original request of about 600 pb 1. It is clear that the results of this exploratory measurement (analysis undergoing) cannot give a definitive result - however can be useful as an indication for a future measurement. 3.4 Kaonic helium 3 measurement In the last days of data taking, early November 2009, we measured for the first time ever the kaonic helium3 L-transitions. The total integrated luminosity for this measurement was about 10 pb 1 and the preliminary spectrum is shown in Fig. 7. Data analysis is undergoing SIDDHARTA was dismounted from DAΦNE in early December 2009, (see Fig. 8) a picture taken the day after datataking was ended.

7 Figure 7: (color online). The Kaonic helium3 triggered spectrum (black line)where the 6.2 kev and 8.4 kev lines of kaonic helium transitions are clearly visible. The line at about 10 kev corresponds to kaonic carbon transition. The red line corresponds to the events out of kaon gate in the trigger system - representing background. Figure 8: Part of the SIDDHARTA Collaboration in front of the SIDDHARTA setup in the day after the data taking ended (10 November 2009).

8 3.5 ECT* Workshop organization In the period October 2009 a Workshop entitled Hadronic Atoms and Kaonic Nuclei - solved puzzles, open problems and future challenges in theory and experiments was organized, having Catalina Curceanu as main Organizer, at the ECT* in Trento. The Workshop was very successful. For more details see CERN Courier, Volume 50, January/February 2010, page Activities in 2010 The LNF group main activities in SIDDHARTA for 2010 are the following ones: finalize analyses of kaonic helium 4 data and publish them; finalize analyses of kaonic hydrogen data and publish them; finalize analyses of kaonic deuterium data and publish them; finalize analyses of kaonic helium 3 data and publish them. In parallel, the SIDDHARTA Collaboration is preparing a proposal for an upgraded setup - to perform the kaonic deuterium measurement in the near future. We are as well considering heavier kaonic atoms (a list is being discussed with theoreticians working in the field) measurements. To be mentioned that the SIDDHARTA scientific program is important part of the Network LEANNIS (WP9) in the framework of the EU FP7 HadronPhysics2 program. 5 Publications 5.1 List of Conference Talks given by LNF Authors in Year 2009: 1. A. Scordo, First kaon measurement with scintillating fibers read by MPPC at the DAΦNE e+e- collider, talk at the XLVII International Winter Meeting on Nuclear Physics, Bormio, january 2009, Italy. 2. A. Romero Vidal, Measurements of kaonic atoms at DAΦNE: the SIDDHARTA experimen, talk at the XLVII International Winter Meeting on Nuclear Physics, Bormio, january 2009, Italy. 3. O. Vazquez Doce, The AMADEUS experiment and the analyses of the K Ke in the KLOE data, talk at the XLVII International Winter Meeting on Nuclear Physics, Bormio, january 2009, Italy. 4. O. Vazquez Doce, Deeply bound kaonic nuclear states at DAΦNE, talk at the Excited QCD, 8-14 February 2009, Zakopane, Poland. 5. C. Curceanu, SIDDHARTA and AMADEUS at LNF, talk at the HadronPhysics2 FP7 LEAN- NIS kick-off meeting, 27 March 2009, Vienna, Austria. 6. S. Okada, Kaonic atoms at DAΦN, talk at the LNF Spring School in Nuclear, Subnuclear and Astroparticle Physics, May 2009, Frascati, Italy. 7. M. Poli Lener, Performances of a GEM-based TPC prototype for new high-rate particle experiment, talk at the Fronteer detectors for fronteer physics, May 2009, La Biodola, Italy.

9 8. O. Vazquez Doce, Low energy kaon nuclei interaction studies at DAΦNE (AMADEUS experiment), talk at the 19th International IUPAP Conference on Few-Body Problems in Physics, 31 July - 5 September 2009, Bonn, Germany. 9. S. Okada, The SIDDHARTA experiment, talk at the 19th International IUPAP Conference on Few-Body Problems in Physics, 31 July - 5 September 2009, Bonn, Germany. 10. A. Scordo, The trigger system for the AMADEUS experiment, talk at the ECT* Workshop Hadronic Atoms and Kaonic Nuclei - solved puzzles, open problems and future challenges in theory and experiments, October 2009, Trento, Italy. 11. A. Romero Vidal, SIDDHARTA recent results, talk at the ECT* Workshop Hadronic Atoms and Kaonic Nuclei - solved puzzles, open problems and future challenges in theory and experiments, October 2009, Trento, Italy. 12. C. Curceanu, AMADEUS: As a matter of fact it is a fact of matter, talk at the ECT* Workshop Hadronic Atoms and Kaonic Nuclei - solved puzzles, open problems and future challenges in theory and experiments, October 2009, Trento, Italy. 13. O. Vazquez Doce, Analyses of the K He interaction in the KLOE Drift CHamber, talk at the ECT* Workshop Hadronic Atoms and Kaonic Nuclei - solved puzzles, open problems and future challenges in theory and experiments, October 2009, Trento, Italy. 14. O. Vazquez Doce, The AMADEUS experiment: low energy kaon nuclei interaction studies at DAΦNE, HADRON2009, 29 November - 4 December 2009, Tallahassee, USA. 15. C. Curceanu, AMADEUS - an experiment to measure properties of strange and even stranger matter, SMI - Colloquium, December 2009, Vienna. 5.2 Papers and Proceedings 1. C. Curceanu and J. Marton, The fascinating world of strangene exotic atoms, CERN Courier, Volume 50, January/February 2010, page J. Zmeskal et al., Int. J. Mod. Phys. A 24, 197 (2009). 3. M. Bazzi et al., Phys. Lett. B 681, 310 (2009). 4. J. Marton et al., IEEE TRans. Nucl. Sci. 56, 1400 (2009). 5. M. Poli Lener et al., Nucl. Instr. and Meth. A (2009) - to appear, doi: /j.nima O. Vazquez Doce et al., The AMADEUS experiment and the analyses of K-He in the KLOE data, Proceedings of the XLVII International Winter Meeting on Nuclear Physics, Bormio (Italy), January 2009, p A. Romero Vidal et al., Measurements of kaonic atoms at DAΦNE: the SIDDHARTA experiment, Proceedings of the XLVII International Winter Meeting on Nuclear Physics, Bormio (Italy), January 2009, p O. Vazquez Doce et al., Acta Phys. Polonica. Supp. 2, 399 (2009). 9. C. Curceanu et al., Nucl. Phys. Proc. Suppl. 186, 271 (2009).

10 References 1. G. Beer et al., Phys. Rev. Lett. 94, (2005). 2. M. Bazzi et al., Phys. Lett. B 681, 310 (2009).