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The Next Generation of Hypernucleus and Hyperatom Experiments

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  1. The Next Generation ofHypernucleus and Hyperatom Experiments GSI, 18.10.2000 Josef Pochodzalla Univ. Mainz

  2. L0 S- X- W- ... d s u d Proton Neutron s s d d s s s s u d u d d u Quark Structure of Hyperons Nucleons Hyperons

  3. su  du sd  dd W Present Status of s=-1 Nuclei • Until few years ago hypernuclear studies focused on (p+,K+) or (K-,p-) reaction • New tools • e+e- F1020  KK tagging (FINUDA @ DANE) • g-spectroscopy with Ge (BNL, KEK, GSI) • (e,e’K+)YX (TJNAF, MAMI-c) • Topics • YN interaction • non-mesonic weak decay Lp  pn Ln  nn • unique chance to study baryon-baryon weak interaction ! Weak decays...

  4. Quark configuration Baryon configuration uds p n L p s 4He p s 5He L Hypernuclei and Deconfinement • Manifestation of the Pauli priciple on the quark ? Question...

  5. Hypernucleus BLL[MeV] DBLL [MeV] LLHe 10.9  0.6 4.7  0.6 LLBe 17.7  0.4 4.3  0.4 LLB 27.6  0.7 4.8  0.7 6 10 13 Status of Multi - Hypernuclei • Multi-Hypernuclei are a terra incognita... • ...but they exist ! 6 candidates for LL-hypernuclei are observed 1963: Danysz et al. 10Be 1966: Prowse 6He 1991: KEK-E176 10Be or 13Be 1991: KEK-E176 3 non-mesonic decays LL LL LL LL (K-,K+) X-

  6. LL-Nuclei as a Laboratory • Hyperon-hyperon interaction • H-particle R.L. Jaffe (1977) Sakai et al (nucl-th/9912063)... „The situation in a finite nucleus will be that the low-lying states have the character of LL bound states, but that some of excited states may have strong admixture of the H-nuclear states.“

  7. The s=-3 Challange - • W hypernuclei by WW production • Electric quadrupole moment of the W by hyperfine splitting in W-atoms*) • tensor forces between quarks • expectation QW= (0 - 3.1) 10-2 fm2 • DE(ℓ=10 ℓ=9) ~ 515 keV • DEQ ~ few keV for Pb QW = +0.02 fm2 QW = - 0.02 fm2 spin-orbit DEℓs ~ (aZ)4ℓmW quadrupole DEQ ~ (aZ)4Q33m3W *) C.J. Batty (1995)... “…The precision measurements of X-rays from W- Pb atoms will certainly require a future generation of accelerators and probably also of physicists.“

  8. 2K 1000 1 _ X 3 GeV/c X- Production of s=-2 Hypernuclei • relativistic HI collisions • coalescence of hyperons Bodmer (1971), Rufa et al. (1989), Schaffner et al. (1991)... • X-capture: X- p  LL + 28 MeV • (K-,K+) KEK-PS E373, BNL-E906... • pp annihilation at rest K. Kilian (1987), DIANA coll. • X X threshold _ _ pp  K*K* p(K*) = 285 MeV/c  K*N  K X- p d  {KKp}+X- _ - - _ p

  9. X- capture • X-atoms: x-rays • conversion • X-(dss)p(uud)L(uds)L(uds) • DQ = 28 MeV Conversion probability... • ...approximatly 5-10%

  10. Hyperon Production • with L=2·1032 cm-2s-1  700 s-1 for a C target _ X+X- 2.6 GeV/c For example...

  11. X- Properties • X- mean life 0.164 ns Consequence... • minimize distance production – capture • initial momentum 100-500 MeV/c range ~ few g/cm2

  12. - p - X- X+ Setup • beam: 3 GeV/c,  1mm; no halo (roman pots?) • internal gas target e.g. Ne, width 1mm • Tracking detector for X- • 2-3 cm thick • diamond strip • Si strip • capillary fiber gas jet readout

  13. 20mm Capillary Detector • Glascapillaries filled with szintillator • - interaction (CHORUS) Problem... • fast readout • possible solution :Hybrid Phototube + ALICE pixel chip Needs R&D !

  14. Gamma Spectroscopy • Ge box based on VEGA type detectors • segmented Clover • 7 cm , 14 cm long • 4 seg. clover, ePH = 0.13 @ 1.33 MeV • resolution ~ 0.5 % • fast electronics under development beam - p crucial point...

  15. Count Rate • luminosity 2·1032 cm-2s-1 • X+X- cross section 2mb for pp 700 Hz • p(100-500 MeV/c) p500 0.0005 • X+ reconstruction probability 0.5 • stopping and capture probability pCAP 0.20 • total stopped X-3000 / day • X-to LL conversionprobability pLL 0.05 • total LL hyper nucleus production 4000 / month • gamma emission/event, pg  0.5 • g-ray peak efficiency pGE 0.1 - total single line g-rate • ~ 5/day „golden events“ (X+trigger) • ~ 500/day with KK trigger

  16. Competition experiment reaction device beam/ target status BNL-AGS E885 (X--,12C)  12B + n neutron detector arrays K- beam, diamond target 20000 stopped X- LL BNL-AGS E906 2p decays Cylindrical Detector System K- beam line few tens 2p decays of 4LLH KEK-PS E373 (K-,K+)X emulsion (K-,K+) several hundreds stopped X- facility reaction device beam/ target Observed captured X- per day JHF (K-,K+)X spectrometer, DW =30 msr 8·106/sec 5 cm 12C <7000 ¯ ¯ ¯ cold anti-protons p p  K*K* K*N  X K vertex detector 106 stopped p per sec 2000 ¯ ¯ ¯ GSI-HESR p p  X X vertex detector + g-spectrometer L=2·1032,thin target, production vertex  decay vertex 3000 „golden events“ ~ 300000 KK trigger

  17. Conclusion • The anti-proton storage ring HESR @ GSI can provide a unique facility to study strange hyperatoms and hypernuclei. • Key points • highest luminosity possible • moderate beam quality • micro tracking device • high rate Germanium array • Detailed spectroscopic studies of multi-strange systems will be possible. “hyperon laboratory”