October 2014 Trento, Italy Measurements of kaonic 4 He and 3 He at DA  NE Achievements and Perspectives in Low-Energy QCD with Strangeness Diana Laura Sirghi INFN-LNF on behalf of SIDDHARTA collaboration

SIDDHARTA SIlicon Drift Detector for Hadronic Atom Research by Timing Applications

the determination of the isospin dependent KN scattering lengths through a ~ eV measurement of the shift and of the width of the K  line of kaonic hydrogen and first (similar) measurement the first (similar) measurement of kaonic deuterium The scientific aim

Fundamental study of strong interaction between anti-K & nucleus at low energy limit Fundamental study of strong interaction between anti-K & nucleus at low energy limit The scientific aim SIDDHARTA measures the X-ray transitions occurring in the cascade processes of kaonic atoms

In the framework of the SIDDHARTA experiment we have performed the measurements related with the Kaonic helium transition to the 2p level (L-lines): -for first time in a gaseous target for 4 He -for the first time ever for K 3 He The interest for such type of measurement was rather high due to: so-called “kaonic helium puzzle” some theoretical predictions of possible very small energy shift (if any) Kaonic Helium measurements SIDDHARTA experiment

Kaonic Helium atoms ε = E 3d  2p (exp) – E 3d  2p (e.m.) The most suitable transition to observe the strong interaction effects The absorption is too strong to observe the radiative transition to 1s state the last observable state is the 2p state The absorption is too strong to observe the radiative transition to 1s state the last observable state is the 2p state

Kaonic atom data (Z≥3) Used for studies of K bar N interaction Optical model Experimental X-ray data of shift & width: Well fitted with optical potentials Expected shift of K-4He 2p state: ΔE ~ 0 eV C.J. Batty et al., Physics Reports 287(1997) The shift and widths of kaonic atom X-ray energy have been measured using targets with atomic numbers from Z=1 to Z-92, which provide very important quantities for understanding the antiKN strong interaction. There are discrepancies for: Kaonic Hydrogen (Z=1) Kaonic Helium (Z=2)

2p level shifts for Kaonic Helium atoms

 E 2p (eV)  2p (eV) -41± ±1230±30 -50±12100±40 -43±855±34 Kaonic helium atom data (Z=2) Average of above

Kaonic helium atoms theoretical values Shift (eV)Ref ±0.02Batty, NPA508 (1990) 89c -0.14±0.02Batty, NPA508 (1990) 89c -1.5Akaishi, Proc. EXA05 There are two types of theories compared to the experimental results: Optical-potential model: (theoretical calculations based on kaonic atom data with Z> 2) Tiny shift (  E 2p  0 eV) Recent theoretical calculations: Akaishi-Yamazaki model of deeply-bound kaon-nucleus states Predicts a possible maximum shift:  E 2p of ± 10 eV

What is Kaonic helium puzzle? Need a new K- 4 He X-ray measurement! Experiment: Large shift (  E2p  40 eV) Theory:  E2p  0 eV or < ± 10 eV

New K 4 He results by KEK PS E570 PLB 653 (2007) 387  E 2p =2±2(stat.)±2(syst.) eV) K 4 He 3d→2p: 1500 events 3x higher statistics 2x better Energy resolution 6x better S/N

Solving the kaonic helium puzzle Old experiments: Large shift (-43±8 eV) E570 experiment: Small shift (+2±2±2 eV) Theory:  E2p  0 eV or < ± 10 eV Difference between the new and the old experiments Experimental confirmation need! SIDDHARTA experiment

SIDDHARTA experiment Monochromatic, low-momentum kaon beam from DA  NE (127 MeV/c) No hadronic background due to the beam line (compare with hadron beam line :e.g with KEK line ) Big advantages of the SIDDHARTA experiment: Low density gas target (higher yields of the atomic state in gaseous helium over the liquid one, due to the density dependent Stark mixing; negligible Compton scattering in helium). The availability of kaons with low energy and low momentum spread results in efficient kaon stopping in gas target. Silicon Drift Detector (SDDs) as detector

15 x y z e-e- 510 MeV/c e+e+ 127 MeV/c Δp/p=0.1% K+K+ K-K- ΦTarget Detect by SDDs Detect by two scintillators SIDDHARTA overview

1 cm 2 x 144 SDDs Silicon Drift Detector - SDD SDD Energy resolution:  150 eV (at 6 keV)

SDDs & Target (inside vacuum) Kaon detector SIDDHARTA setup

Kaonic 4 He data SIDDHARTA experiment The Kaonic 4 He X-ray data were taken for about two weeks in January In this period, an integrated luminosity of about 20pb -1 was collected. This corresponds to about 4.7 × 10 6 kaons detected by the kaon detector.

SDD spectrum of X-ray uncorrelated with kaon production. Ti and Mn X-ray peaks are produced by the 55 Fe source in normal condition of beam Energy resolution: FWHM keV): 151 ± 2 eV Energy calibration Target Ti foil Fe55 Degrader K-He data taking

Triple coincidences Background suppression more than 10 4

Energy spectrum of K- 4 He X-rays Energy of K 4 He L  (3d  2p) line: E exp = ±5.8 eV

New results of K- 4 He 2p level shift E exp = ±5.8 eVE e.m. = ±0.2 eV  E = E exp – E e.m. = 0±6(stat) ±2(syst) eV Published in PLB 681(2009) “kaonic helium puzzle” solved SIDDHARTA’s results is consistent with the results obtained by E570 experiment

Summary of the K- 4 He shifts

Data taking periods of SIDDHARTA in 2009 DA  NE shutdown in Summer New alignment of setup  Improve S/N ratio K-He3 data (~4days) 55Fe source: Good for reduce sys. error on K- 4 He Bad for “background” events on K-H,K-D Removed 55 Fe source in other data

SDDs Ti/Cu foil X-ray tube Data taking scheme at DAFNE calibration data SDDs degrader Scintillators Production data Calibration data with X-ray tube have been collected under the beam condition in regular interval of the production runs. For that purpose a remote controlled mechanism was built to move away the kaon detector and instead have the x-ray tube in place.

SDD X-ray energy spectra Calibration data with X-ray tube Calibration Ti&Cu SDDs Ti/Cu foil X-ray tube calibration data Instead of Fe source, “X-ray tube” data taken Estimated systematic error ~ 3-4 eV In-beam X ray tube Ti, Cu foils

SDD X-ray energy spectra Calibration data with X-ray tube Not correlated to Kaon signals Production data Energy scale determined by X-ray tube data Energy spectrum with uncorrected to kaon timing [Fig. (b)] Calibration Ti&Cu providing large statistics background events + X-Ray lines form the target maetrials induced by the beam background

SDD X-ray energy spectra Calibration data with X-ray tube Not correlated to Kaon signals Selected with K+K- & SDD timing Production data Kaon detector Time difference between SDD & Kaon detector providing kaonic atom X-ray energy spectra with a high background suppression.

SDD X-ray energy spectra Calibration data with X-ray tube Not correlated to Kaon signals Production data The shift is due to the instability of our electronics caused by differing conditions between the production and X-ray tube data. The largest contribution is a rate-dependent effect on the SDDs. The hit rate of the SDDs in the X-ray tube data was about 10 times higher than that in the production data, causing the observed shift. High rate Low rate High rate Low rate

The X-ray peak fit The accuracy of the energy scale was determined by using X-rays energis of the TiKa, CuKa and Au La lines. The intensities of these X-ray lines in the kaonic helium data were not high enough to observe systematic effects on the energy calibration and energy resolution of the SDDs, so the data measured with the deuterium target, which were taken for about 20 days, were also analyzed using the same method. Natural line widths taken into account X-ray peaks are fitted with Voigt function Determination of the accuracy of the energy scale of the SDDs: using production data not correlated with the kaon signal

The peak position The vertical axis gives the difference between the fit values and the reference data. Result of the fit: energy scale in the production data is shifted by −6 eV compared to the reference data. The accuracy of the energy determination was ±4 eV in the energy region from 4 keV to 10 keV. The variation of ±4 eV corresponds to the uncertainty of about ±0.2 channels in the analogue-to-digital converters (ADCs) used in the measurements. The variation could be related to the nonlinearity of ADCs. The uncertainty of ±4 eV is taken as a systematic error in the energy determination.

DAFNE shutdown in Summer Kaonic 3 Helium data SIDDHARTA experiment The Kaonic- 3 He X-ray data were taken for about 4 days in November In this period, an integrated luminosity of about 16 pb -1 was collected.

The Kaonic- 3 He case Transition Kaonic- 3 He e.m. (eV)(*) 3d->2p6224 4d->2p8399 5d->2p9406 There are NOT previous experiments done for the X-ray measurements for Kaonic- 3 He Planned experiments: SIDDHARTA (done); E17 (to be done) (*)Zeitschrift fur Physik D 15 (1990) 321

Kaonic Helium-3 energy spectrum extraction of the strong interaction shift E exp =6223.0±2.4(stat)±3.5(syst.) eV E e.m. = eV The calculation of the e.m. energies for kaonic 3 He was done using the Klein –Gordon equation and the vacuum polarization from the first order term of the Uehling potential. ε=ΔE 2p = E exp -E e.m. = -2±2(stat)±4(syst) World First ！ Observation of K- 3 He X-rays Determination of strong-interaction shift PLB 697 (2011) 199. Cited 13 times Target material: Kapton Polymide (C 22 H 10 N 2 O 5 )

DA  NE shutdown in Summer K-4He (3d-2p) More date on K- 4 He 2p level shift

2p level widths for Kaonic Helium atoms

Experimental results for the widths of kaonic helium atoms Average: Theory: Nuclear Physics A392 (1983) “The shift measurements are seen to be in good agreement. The situation for the width values is much less satisfactory and the error bars of the two measured values do not overlap. The error on the quoted average has been taken from the external variance of the measured values.” New experiment for the widths of the 2p state for kaonic helium: SIDDHARTA experiment

Uncertainty of detector resolution Due to the strong correlation between the detector resolution and line width of KHe, the detector resolution was fiexd form the production data not correlated with the kaon signal Since all the positions are located within the error curves, the error is taken as the accuracy of the determination of the dector resolution for the fit of the kaonic helium X-rays.  3d→2p = (65.4±2.3) eV K- 3 He  3d→2p = (66.4±2.3) eV K- 4 He The energy dependence of the energy resolution of the SDDs: evaluated from the widths of the peaks of Ti, Cu and Au The deviations from the fit file are plotted for each target material

Results for the widths of K-3He and K-4He The energy shift and broadening of the 3d→2p transition can be obtained from the peak fit using a Voigt Function V=V( ,  ), where  represents the strong-interaction 2p width and  was fixed using the values obtained from the energy resolution of the detector. The systematic error was evaluated from the uncertainity of the resolution . In addition, since the K-3He peak partially overlaps the K-O transition, the systematic error of the width of K-3He includes the uncertainity of its intensity.

Summary of the results ExperimentTargetShift [eV]Reference KEK E570Liquid+2±2±2PLB653(07)387 SIDDHARTA (He4 with 55Fe)Gas+0±6±2PLB681(2009)310 SIDDHARTA (He4)Gas+5±3±4arXiv: , PLB697(2011)199 SIDDHARTA (He3)Gas-2±2±4 *error bar

Results for the shifts and widths of K-3He and K-4He The large shift and width obtained by the experiments done in was not observed in kaonic 3He and 4He. The results for shift and width agree with the theoretical calculations. No abnornally large shift abd width were found.

L-series X-ray yields of Kaonic Helium atoms in gaseous targets

By using accurate Monte Carlo simulations, the absolute yields of the kaonic 3 He and 4 He X-ray transitions to the 2p state was successfully determined by the SIDDHARTA experiment. The measured yields provide information for understanding the cascade processes of kaonic helium atoms as a function of the target density. L-series X-ray yields of Kaonic Helium atoms in gaseous targets The absolute X-ray yield is defined as the X-ray intensity per stopped kaon. The X ray detection efficiency is defined as the number of measured X-rays normalized by the number of K+K− events recorded in the kaon detector : Comparing these efficiencies to those given by Monte Carlo simulations, the absolute yields of the kaonic atom X- rays can be determined.

(*) C.E. Wiegand, R. Pehl, Phys. Rev. Lett. 27, 1410 (1971). (**) S. Baird et al., Nucl. Phys. A 392, 297 (1983). The yields of the Lα lines in gas are about 2.0–2.5 times higher than in liquid The yields of the Lβ and Lγ lines are consistent. The intensities of the Lhigh lines in gas are obviously higher than those in liquid. These yield differences are related to the density dependence of the cascade processes, such as the molecular Stark effect and molecular ion formation. D (2.50 g/l) 3 He (0.96 g/l) 4 He (1.65 g/l) 4 He (2.15 g/l) The absolute X-ray yield (Y ) per stopped K−: In performing the comparison, the normalization was done using the number of K+K− events detected by the kaon detector.

Conclusions SIDDHARTA experiment measured the kaonic helium 3d  2p transitions:  for the first time ever for 3 He.  for the first time in a gaseous target for 4 He  Shift and width are founded to be few eV both in K- 3 He and K- 4 He  No abnormally large shift and width were found in K- 3 He and K- 4 He  These results agree with theoretical calculations  The kaonic helium puzzle was solved for shift and width both K- 3 He and K- 4 He.  These results agree with theoretical calculations  The absolute X-ray yields of L-series lines were determined for the first time  DA  NE proves to be a “ideal” kaonic atom “factory”.

Future plans The upgrade of the SIDDHARTA experimental setup Precise measurements for the X-ray transitions for kaonic deuterium. Measuring, with higher precision, the X-ray transitions for Kaonic 4 He and Kaonic 3 He to the 2p level and the first tempt to get the transitions to the 1s level. SIDDHARTA 2 experiment

Kaonic atoms data (Z>3) The shifts and widths for kaonic atoms with Z≥3 are systematically well understood; The optical model expressing the kaonic atom data have been used for calculation of the antiKaonN interaction. C.J. Batty et al., Physics Reports 287(1997) The shift and widths of kaonic atom X-ray energy have been measured using targets with atomic numbers from Z=1 to Z-92, which provide very important quantities for understanding the antiKN strong interaction. There are discrepancies for: Kaonic Hydrogen (Z=1) Kaonic Helium (Z=2) See talk of A. Romero Vidal

DAFNE shutdown in Summer New alignment of setup  Improve S/N ratio K-He3 data (~4days) 55Fe source: Good for reduce sys. error on K- 4 He Bad for “background” events on K-H,K-D Removed 55 Fe source in other data Data taking periods of SIDDHARTA in 2009

X ray energy (keV) Counts / bin KHe (3-2) KC (6-5) KHe (4-2) transition e.m.energy events (3-2) ± 37 (4-2) ± 21 (5-2) ± 19 (6-2) ± 25 higher < ± 41 Ti K  KHe used for gasstop optimization + physics interest 1 ) data from setup 2 (no Fe55 source) 1 ) compare KEK E570 KHe L lines in liquid He, consistent result, first measurement in gas KHe (5-2) KN (5-4) KHe L high p r e l i m i n a r y KC (5-4) KHe (6-2) KO (6-5) KO (7-6) Higher statistics of the K- 4 He L lines (L , L β, L  ) Smaller statistics in shift, determination of width X-ray yield information in gas (for the first time) Very preliminary K- 4 He spectrum

SDDs Ti/Cu foil X-ray tube Data taking at DAFNE -Calibration calibration data Estimated systematic error ~ 3-4 eV Seminar TUM, 27 June 2011

SDDs degrader Scintillators Production data Data taking at DAFNE - Production Seminar TUM, 27 June 2011

X ray energy (keV) Counts / bin KHe (3-2) KC (6-5) KHe (4-2) KC (5-4) transition e.m.energy events (3-2) ± 40 (4-2) ± 22 (5-2) ± 18 (6-2) ± 24 higher < ± 40 Ti K  KHe3 never measured before ! KHe (5-2) p r e l i m i n a r y KHe L high KHe (6-2) KO (6-5) KN (5-4)KO (7-6) Very preliminary K- 3 He spectrum The statistical error for the transition 3d  2p in K 3 He is less than 3 eV.

TargetShift [eV] KEK E570Liquid+2±2±2 eV SIDDHARTA (w/ 55Fe)Gas+0±6±2 eV SIDDHARTA (New)Gas+5±3±4 eV Comparison of results TargetShift [eV] SIDDHARTAGas-2±2±4 eV J-PARC E17Liquidplanned Kaonic 4He 2p level shift Kaonic 3He 2p level shift shift

Conclusions (2) Confirmed the small shift obtained by recent experiment E570 for Kaonic 4 Helium The “kaonic helium puzzle” for Kaonic 4 Helium is now solved The preliminary analysis of the 3d  2p transitions for Kaonic 3 Helium, indicate that the statistic error shift is less than 3 eV.

SDDs Ti/Cu foil X-ray tube Data taking scheme at DAFNE calibration data SDDs degrader Scintillators Production data Instead of Fe source, “X-ray tube” data taken Estimated systematic error ~ 5 eV

- rebuilding of the sdds mounts: gain of solid angle of X ray detectors - replacement of sdd modules: 144 cm 2 detectors operational - new upper kaon detector: less material in vicinity of target, clean trigger - improved shielding: new multimaterial and more narrow collimator Setup improvements during summer 2009 shutdown

Recent theoretical calculation for the width of kaonic helium atoms theoretical calculations of phenomenological optical potential model by Friedman Akaishi-Yamazaki model of deeply-bound kaon-nucleus states Small width (  E 2p  2 eV) Possible large width  5eV K-4He K-3He

Contamination of K-O peak Several small peaks were observed in all the spectram which originated from kaonic atom X-rays produced in the target window material (C22H10N2O5) The X-rays peaks are: (K - C) 6→5 (K - O) 7→6, (K - C) 6→5 (K - N) 6→5 (K - C) 8→6

Kaonic Helium atoms   p d f 3d  2p X ray E 2p (exp.) n Strong Interaction causes: energy shift  of the last energy levels form their purely electromagnetic values AND level width  finite lifetime of the state corresponding to an increase in the observed level width electromagnetic cascade K- stopped in He Repulsive type Attractive type Kaonic Helium atom: last orbit 2p E 2p (e.m.)

The experimental setup Target size: r = 72 mm height = 155 mm For He3: Temp. of gas: 20K Pressure: 1 bar Installed SDD: 144 cm 2 SDD operation temp: 170 K SDD Energy resolution:  150 eV (at 6 keV)