1. Precision spectroscopy of Kaonic Helium 3d2p X-rays
Aug 25, FB18 (Santos)
Precision spectroscopy of Kaonic Helium 3d2p X-rays
RIKEN
Shinji Okada
for KEK-PS E570 collaboration

2. KEK-PS E570 collaboration list
G. Beer1, H. Bhang2, M. Cargnelli3, J. Chiba4, S. Choi2,
C. Curceanu5, Y. Fukuda6, T. Hanaki4, R. S. Hayano7, M. Iio8,
T. Ishikawa7, S. Ishimoto9, T. Ishiwatari3, K. Itahashi8, M. Iwai9,
M. Iwasaki8, B. Juhasz3, P. Kienle3, J. Marton3, Y. Matsuda8,
H. Ohnishi8, S. Okada8, H. Outa8, M. Sato6, P. Schmid3,
S. Suzuki9, T. Suzuki8, H. Tatsuno7, D. Tomono8,
E. Widmann3, T. Yamazaki8, H. Yim2, J. Zmeskal3
Victoria Univ.1, SNU2, SMI3, TUS4, INFN(LNF)5,
Tokyo Tech6, Univ. of Tokyo7, RIKEN8, KEK9

3. Introduction

4. Last orbit level shift of Kaonic atom
Last orbit level shift of Kaonic atom is sensitive to K-nucleus strong interaction.
Kaonic Helium atom 3d
X-ray Spectroscopy
3d-2p X-ray 2p
Width : G2p
Due to strong
interaction
Shift : DE2p 2p
(Only Coulomb)
Nuclear absorption
 last orbit = 2p
precisely determine the K-nucleus strong interaction at vanishing relative energy
 many experiments have been done (from Helium to Uranium)

5. The Kaonic Helium Puzzle
Last orbit energy level shift and width
of kaonic atoms
2p shift (keV)
Z=2
Exp.
~40eV
Very large
repulsive shift
The past three experiments
No theory can reproduce such a large shift (~40eV) !
theoretical calc.
 zero consistent
ex) chiral unitary+ optical model : ~0.2eV
fitted by optical-potential model
S.Hirenzaki, Y.Okumura,
H.Toki, E.Oset, and A.Ramos
Phys. Rev. C

6. A possible large repulsive shift !
Akaishi-Yamazaki prediction of “deeply-bound kanoic nuclei”
Strange multibaryon candidates
(KEK, DAFNE, BNL)
a bare K-N potential so as to simultaneously reproduce
G-matrix calc.
K-N scattering lengths
The binding energy and width of kaonic hydrogen atom
Treating L(1405) as a K-N bound state
Deep K-nucleus
potential
2p level shifts of the K--4He atom
Y.Akaishi, EXA05 proceedings (2005)
Repulsive
Attractive
200~300MeV
Predicted region
Large repulsive shift
is acceptable
~-10 eV at maximum
applied to kaonic atom

7. Three past experiments
2p level shifts of the K--4He atom
3d2p
C.E.Wiegand and R.Pehl,
Phys.Rev.Lett.27 (1971) 1410.
Exp.
Average eV eV
C.J.Batty et al.,
Nucl.Phys.A326 (1979) 455.
Shift Width
X-ray detector : Si(Li)
Energy resolution …
Large background
Absolute energies w/o in-beam calib.
S.Baird et al.,
Nucl.Phys.A392 (1983) 297.
Present experiment (KEK-PS E570)
measure the shift with a precision better than 2 eV
by improved experimental method.

8. Experiment

9. Experimental setup and features
K-4He X-ray 3d2p
~6.4keV
3) Fiducial volume cut
reaction vertex is within the liq. He volume
Ti Ka1
4.51keV
Ni Ka1
7.48keV
continuum background events  reduced
charged particle
Secondary
provide accurate in-situ calib!
2) In-beam energy calibration
K- beam
p -(or K-)
Characteristic X-rays from Ti and Ni foils
p/K ratio : ~ 200
X-ray
1) High resolution X-ray detector
Silicon Drift Detector “SDD” (8個)
Liq. Helium target

10. Setup pictures Target cell Cryostat SDD * 8 Calibration foils
w/ super-insulator
Calibration foils
(umbrella shape
 large acceptance)
SDD * 8

11. SDD (Silicon Drift Detector)
conventional Si(Li)  SDD
Schematic drawing of a SDD
electrical field
gradient
FET
KETEK 100mm2 SDD
anode e-
C = ε0S / d
X-ray hit
Anode size (capacitance) kept small independent of the detector area.
Good energy resolution with large effective area (100mm2)
Small anode  reduce the thickness (0.26mm<<4mm in previous exp.)
reduce continuum background caused by the soft-Compton process.

12. Typical resolution (with 55Fe source)
Same experimental setup with that of E570
SDD temperature : 85K
@5.899keV
Mn Ka and Kb  clearly observed
(past exp:
FWHM
= eV
@MnKa1=5.899keV

13. Preliminary result

14. Target image and fiducual volume cut
Carbon
degrader
Target cell
Calibration foils
& SDDs
Fiducial volume cut
Z vertex (mm)
Kaon beam
target
construction
projection of the reaction vertices

15. (half of all E570 statistics)
Preliminary spectrum
( Comparison with
a past experiment )
Present exp. (E570)
(half of all E570 statistics)
3d2p
-- improvement --
stopped kaon triggerd event
applying fiducial volume cut
4d2p
Resolution : x ~1.5
(300eV185eV) Ti Ni
5d2p
Statistics : x ~2.5
( 3d2p all statistics:
~1500 events )
S/N ratio : x ~5
( 0.8  4 )
Past exp.
most resent exp.
S.Baird et al.,
Nucl.Phys.A392 (1983) 297.

16. Energy calibration (high-statistics calib. data)
Kaonic atom x-ray spectrum
Simultaneously measured
Energy
Energy calibration
Ti Ka
Ni Ka
Channel
Ti Kb
Ni Kb
High statistics calib. spectrum
(self triggered event)
Ti Ka1: 15k events/SDD/8hours

17. -40eV shift is very clearly rejected
subtracted by
40 eV (past exp.)
3d2p energy calculated by only coulomb interaction
K-4He
3d2p peak
half of all statistics
(added all SDD)

18. Error estimations Estimated statistical error : ~2 eV
mean value of the 3d2p x-ray’s peak
Estimated statistical error : ~2 eV
Systematic errors … Now in progress
Energy calibration & gain adjustment
Not sure that pion induced (~500MeV/c) characteristic x-ray energy =~ photon induced (x-ray data booklet).
… At this moment, we are using x-ray data booklet energies as the calibration energies of Ti & Ni’s x-rays in our energy calibration.
… To be sure this matter, we have already performed a test experiment to measure the pion-induced x-ray spectra with calibration sources. (This experiment has been performed just until one week before at PSI. …This analysis is now in progress.)
SDD response function study etc.
(1500 events for 3d2p x-ray)

19. Summary Accurately measured K--4He 3d2p X-ray energy spectrum
High energy resolution : 185
Good S/N ratio : applying fiducial volume cut (~6)
Energy calibration was successfully done by using characteristic X-rays from Ti and Ni foils
Cleary rejected -40eV (repulsive) shift reported in the three past experiments.
Now we are still analyzing these data
including systematic error estimation.