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Experiments on X -Nucleus interaction at J-PARC

Experiments on X -Nucleus interaction at J-PARC. Kiyoshi Tanida (Seoul National Univ./JAEA) 13 Dec. 2013 International Workshop on Strangeness Nuclear Physics Xiamen, China. Hyper-nuclear chart. Unexplored world of S=-2. Physics Motivation for S=-2 world.

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Experiments on X -Nucleus interaction at J-PARC

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  1. Experiments on X-Nucleusinteraction at J-PARC Kiyoshi Tanida(Seoul National Univ./JAEA) 13 Dec. 2013 International Workshop on Strangeness Nuclear Physics Xiamen, China

  2. Hyper-nuclear chart Unexplored world of S=-2

  3. Physics Motivation for S=-2 world • A doorway to the multi-strangeness system • Very dynamic system? • Large baryon mixing? Inversely proportional tomass difference. • H dibaryon as a mixed state of LL-XN-SS? • Little is known so far Main motivation of J-PARC

  4. Importance of X systems • Valuable information on XN (effective) interaction • e.g., How strong XN  LL (and thus XN-LL mixing) is? • Relevant to the existence of H dibaryon • XN component in LL-hypernuclei • How about A dependence? • One-meson exchange models predict significant A dependence. • In contrast to small A dependence in normal and L nuclei. • Impact on neutron stars • Does X- play significant role in neutron stars because of its negative charge? • Need to know the XA interaction and its A dependence. • S- was supposed to be important, but its interaction with neutron matter is found to be strongly repulsive.

  5. XN interaction model and XA optical potential (examples) • One boson exchange (NHC-D, Ehime) • strong attraction in odd states  strong A dependence • ESC04d* • strong attraction in 3S1（T=0）

  6. Quark cluster model potential • Example:Kyoto-Niigata/fss2+ G-matrix • Potential shape isnon-trivial, but overallrather weak. • Integral is almost 0

  7. Experimental information • X nuclei in emulsion • V=24±4 MeV?? [C.B. Dover, A.Gal, Ann. Phys. 146 (1989) 309.] • Formation is not guaranteed experimentally, rather doubtful • 12C(K-,K+) reactions • Two experiments, KEK-PS E224 & BNL-AGS E885 • Both shows significant events in the X bound region, after considering the effect of poor experimental resolution AGS E885

  8. Naïve Interpretation • Simple model • Rigid 11B core + X- core excitation is ignored • Woods-Saxon potential with negligible width V=-14~-16 MeV??

  9. Problems (1) • Core excitation • Cross-sections of ground/excited states depend strongly on XN interaction detail If excited states dominate, underestimation results. Sugimoto & Motoba Ehime potential(weak)

  10. Problems (1) • Core excitation • Cross-sections of ground/excited states depend strongly on XN interaction detail If excited states dominate, underestimation results. Sugimoto & Motoba ESC04d potential(strong spin-spin force)

  11. Problems (2) • XNLL conversion • LL continuum can appear at the same energy as X states • Calculation by Kohno and Hashimoto E885 spectrum can be explained with V = 0 MeV (G = 4 MeV) V~-14 MeV is anoverestimation

  12. So, what can we say? • XA potential is still quite a lot uncertain • V~-14 MeV can be underestimate or overestimate • X bound state vsLLcontinuum • Shallower real part ⇔ Larger imaginary part (actual balance is model dependent) LL continuum G (or W) both 4 MeV X bound state -V 14 MeV

  13. How can we distinguish? • If X bound states are dominant • Weak XN-LL coupling • Small imaginary part • These states must be rather narrow (G < 4 MeV) Distinct peaks may be observed • LL continuum dominant • Spectrum would be rather structureless High resolution spectroscopy

  14. E05 X-hypernuclei • Missing mass spectroscopy of 12C(K-,K+)X • 12XBe, 12LLBe 1.8 GeV/c K- beam high intensity 1.4x106 K- /spill (Phase-1) high purityK-/p- ~6.9 Proton beam 30GeV-9mA

  15. ~30msr 2.7T(395A) ~1.5T SksPlus Spectrometer PK+ ~1.3 GeV/c Dp/p=0.12% • 95°total bend • ~7m flight path • Dx=0.3 mm (RMS) high resolution：　DE~ 3 MeV

  16. Expected 12XBe Spectrum VX= -20MeV p X DE = 3 MeVFWHM 1 monthdata taking [counts/0.5MeV] s X Optical potential VX= -14MeV -BX [MeV]

  17. Even higher resolution Ex andG can be as small as 1 MeV Even higher resolution is desirable

  18. S-2S spectrometer • Under construction by grant-in-aid 2011-2015 • Large acceptance: 60 msr • Excellent resolution: Dp/p=0.05%  DM=1.5 MeV (FWHM) x2 more stat. & x2 better resolution than the originalplan! First data expected in 2016

  19. Fe target K- K+ X- X ray E03 X-ray spectroscopy of X atom • The first measurement of X rays from X-atom • Gives direct information on the XA optical potential • Produce X- by the Fe(K-,K+) reaction, make it stop in the target, and measure X rays. • Aiming at establishing the experimental method • Possibility for double-L hypernuclear g-ray

  20. Principle of the experiment • Atomic state – precisely calculable if there is no hadronic interaction • 1st order perturbation • If we assume potential shape,we can accurately determine its depth with only one data • Shape information can be obtained with many data • Even if 1st order perturbation is not good, this is still the same. • Peripheral, but direct  complementary information • Applicable regardless of potential type (repulsive, ...)

  21. X atom level scheme l=n-1 (circular state) X l=n-2 l=n-3 ... Energy (arbitrary scale) ... Z nuclear absorption ... X Z ... l (orbital angular momentum) X ray energy shift – real part Width, yield – imaginary part Successfully used for p-, K-,`p, and S-

  22. Experimental Setup • ＠K1.8 beamline • Long used at KEK-PS K2 beamline (E373, E522, ...) • Large acceptance (~0.2 sr) K- K+ 1.8 GeV/c 1.4x106/spill (4s)

  23. Choice of Target • Physics view: Batty et al. PRC59(1999)295 • For given state, there is optimal target • Nuclear absorption is reasonably small • X-ray energy shift and width are the largest (~a few keV) • They suggested 9F, 17Cl, 53I, and 82Pb for n=3,4,7,9. • The choice depends on the optical potential itself  We can’t know before the 1st experiment

  24. For the 1st experiment • We chose Fe (Iron) because of (mostly) experimental reason • Production rate: A-0.62 as cross section scales with A0.38 • Stopping probability: requires high target density (X- range: 10-20 g/cm2, bgct ~ 2cm) • X-ray absorption: significant at large Z  Small Z(A), yet high density • Koike calculated the energy shift (width) & yield of the Fe X ray (n=6  5) • Woods-Saxon potential: -24 - 3i MeV • Energy shift: 4.4 keV, width: 3.9 keV • Yield per stopped X-: 0.1 (~0.4 without absorption)

  25. X-ray detection • Hyperball-J • 32 Ge detectors • PWO anti-Compton • Detection efficiency • 16% at 286 keV • High-rate capability • < 50% deadtime • Calibration • In-beam, frequent • Accuracy ~ 0.05 keV • Resolution • ~2 keV (FWHM)

  26. Yield & sensitivity estimation • Total number of K-: 1.0x1012 for 100 shifts. • Yield of X • production:3.7×106 • stopped: 7.5×105 • X-ray yield：　2500 for n=65 transition • 7200 for n=76 • Expected sensitivity • Energy shift: ~0.05 keV (systematic dominant)  Good for expected shift (~1 keV, 4.4 keV by Koike ) < 5% accuracy for optical potential depth • Width: directly measurable down to ~ 1 keV • X-ray yield gives additional (indirect) information on absorption potential.

  27. Expected X-ray spectrum (1) n= 65 shift & width 0 keV

  28. Expected X-ray spectrum(2) n= 65 shift & width 4 keV

  29. Run Plan • Expected beam time: somewhere in 2015 after E07 • Primary beam intensity: ~ 50 kW (~20 % of design) • Present J-PARC intensity: ~ 24 kW (~9%) • Two step strategy • In the first beam time, only ~10% of statistics may be obtained. What can we do with that statistics? We can take rather good data

  30. Expectation with ~10% stat. (1) • Observation of X rays is certainly possible • 76 transition: 720 counts with 410 counts/keV BG Rather easy (but no physicsinformation)

  31. Expectation with ~10% stat. (2) • Can we see the 65 transition we are interested in? • Depends on absorption (width & yield) If the width is 0, it’s certainly possible

  32. Expectation with ~10% stat. (3) • Can we see the 65 transition we are interested in? • Depends on absorption (width & yield) If the width is 4 keV, (assumed in proposal) the peak is hardly seen

  33. Expectation with ~10% stat. (4) • Can we see the 65 transition we are interested in? • Depends on absorption (width & yield) If the width is ~1 keV, peak can be seen It may be more clearer because yield would be higher due to smaller absorption at the initial state Shift accuracy: 0.1~0.2 keV  enough for 1 keV shift

  34. Future Prospects（hope） • First experiment • Determine actual yield & background • Establish experimental method • Based on shift & width in iron, • If too small to be seen, use heavier target (Co, Ni) • If too large to be seen, use lighter target (Mn, Cr) • If we are lucky, take a few data points around, and then go to different mass region. • Final goal: a few points for each n • ~10 data points in total • Potential shape, A dependence. • At full intensity, it will take a few weeks/target • Gamma-ray spectroscopy of double L hypernuclei?

  35. Summary & perspective • S=-2 system is a main subject in J-PARC • Potential of X in nuclei is interesting with respect to XN interaction, XN-LL coupling, neutron star, etc. • However, present theories and experiments are not enough to determine the potential • Excited state  deeper potential • LL continuum  shallower potential w/ large absorption • High-resolution spectroscopy of X nuclei can distinguish those 2 scenarios  J-PARC E05 • X-ray spectroscopy of X atom provides complementary information  J-PARC E03

  36. Backup

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