1 / 35

Introduction to Hypernuclear Physics

Introduction to Hypernuclear Physics. K. Tanida (RIKEN) CNS summer school, Aug. 21, 2002. Outline: What is hypernucleus? BB interaction and structure of hypernuclei Hyperons in nuclei Weak decay of hypernuclei Results from recent experiments Future prospects. 4. He. S.

zona
Download Presentation

Introduction to Hypernuclear Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to Hypernuclear Physics K. Tanida (RIKEN) CNS summer school, Aug. 21, 2002 • Outline: • What is hypernucleus? • BB interaction and structure of hypernuclei • Hyperons in nuclei • Weak decay of hypernuclei • Results from recent experiments • Future prospects

  2. 4 He S What is hypernucleus? • Normal nucleus -- composed of nucleon (proton, neutron) • At the quark level: p=(uud), n=(udd) • There are six quark flavors in nature: • L=(uds), S+(uus), X0=(uss), ... exist  Hyperons • Hypernucleus: not only nucleons but hyperons • (i.e., quarks other than u and d) • Known hypernuclei: strangeness (s) only. • L-hypernuclei (~50 species) • S-hypernucleus ( only) • LL-hypernuclei (a few events) u c t d s b

  3. 7 Li L Notation • A: Total number of baryons (nucleon & hyperon) • Z: Total charge (NOT number of protons!) • L: hyperon (other examples -- S, X, ...) • Some examples: • 1. 3p + 3n + 1L • 2. 2p + 2n + 2L  • 3. 1p + 2n + 1S+ • 2p + 1n + 1S0  • 3p + 0n + 1S- • (they are indistinguishable) 6 He LL

  4. How to produce? • Bring strangeness somehow into nuclei • Stopped K- method • - traditional method • - K-(`us)meson has strangeness • - 100% reaction, about 10% makes hypernuclei as • hyperfragments in A ~ 14 targets. Dirty. • In-flight (K-,p-), (K-,p0) reactions • - elementary process NK  Lp • - small momentum transfer (can be 0) • - large cross section • (p+,K+) reaction • - relatively new method, production of`ss pair • - large momentum transfer (q > 350 MeV/c) • - small cross section, but intense p beam available • Other methods • - (e,e'K+), heavy ion collision, ...

  5. Baryon-Baryon interaction and structure of hypernuclei • GOAL: unified understanding of NN, YN and YY interactions • Flavor SU(3) symmetry (symmetry in u, d, s quarks) • NN interaction -- experimentally well known from elastic • scattering data •  phenomenologically well reproduced by meson-exchange • and quark-cluster models. • YN, YY interaction -- poor scattering data • low yield, short lifetime (ct < 10 cm) • information from hypernculei is important • (mostly L-hypernuclei  LN interaction) • In L-hypernuclei: No Pauli effect, weak coupling •  simpler structure •  extraction of LN interation is rather straightforward

  6. Some features of LN interaction (1) • One pion exchange is forbidden N L p(I=1) L(I=0) N • Violates isospin symmetry • weakness of LN interaction e.g., no two body bound state weak tensor force • short range interaction heavier mesons (K, h, w, s, ...), quark-gluon picture

  7. Some features of LN interaction (2) • Two types of spin-orbit force • i.e., • VL(r) sL・LLN ‥‥ L-spin dependent • VN(r) sN・LLN ‥‥ N-spin dependent • or • Vs(r) (sL+sN)・LLN ‥‥ symmetric (SLS) • Va(r) (sL-sN)・LLN ‥‥ anti-symmetric (ALS) • In np, ALS breaks charge symmetry (~1/1000 of SLS) • Does not vanish even at flavor SU(3) limit • (c.f., SN(I=3/2) channel  ALS=0 at SU(3) limit) • Towards understanding of the source of LS force • -- vector meson exchange? (ALS < SLS) • -- quark-gluon picture? (ALS ~ SLS, VL ~ 0)

  8. Overall binding energy of hypernuclei • from A=3 to 208 • UL ~ 28 MeV ~ 2/3 UN • well reproduces data •  weakness of LN • interaction • Single particle picture • good (later in detail) (D. J. Millener et al., PRC38 (1988) 2700)

  9. 3 4 5 5 4 H He He H He L L L L L  overbinding problem of 5 He L Light hypernuclei (1) -- overbinding problem • Binding energy of hypernuclei, A=3~5 • : BL = 0.13 ±0.05 MeV • : BL = 2.04 ± 0.04 MeV (ground state, 0+) • 1.00 ± 0.06 MeV (excited state, 1+) • : BL = 2.39 ± 0.03 MeV (0+) • 1.24 ± 0.06 MeV (1+) • : BL = 3.12 ± 0.03 MeV • If we use LN interaction which reproduces A=3,4 binding • energies, overbinds by ~1 MeV in calculations • First pointed out by Dalitz et al. in 1972 （NPB47 109）, • but not solved for nearly 30 years.

  10. Solution to the overbinding problem? (1) • Quark Pauli effect? quark level baryon level L p n u s d ⇒ ⇒ no pauli blocking partial Pauli blocking • Is this significant?  seemingly no • Large baryon size is required to solve the problem • (H. Nemura et al., PTP 101 (1999) 981, Y. Suzuki et al., PTP 102 (1999) 203)

  11. 5 He L Solution to the overbinding problem? (2) • LNN three body force? • Similar to Fujita-Miyazawa 3NF • Maybe stronger • ML-MS ~ 80 MeV ~ 1/4(MD-MN) • L(T=0)  S(T=1) • a must excite to T=1 state (Ex > 30 MeV) • less significant in p S p NLN • Sorry, reality is not so simple, but this is promising. • For details, see recent papers, e.g., • Y. Akaishi et al., PRL84 (2000) 3539. • H. Nemura et al., nucl-th/0203013

  12. 4 4 He H L L Light hypernuclei (2) -- charge symmetry breaking • L has no charge, no isospin •  difference of Lp and Ln interaction is CSB. • L in is more strongly bound than by 0.35 ± 0.05 MeV • Coulomb force correction makes the difference larger! • After Coulomb force correction, this difference is ~5 times • larger than in 3H -- 3He case • The reason is not yet understood, possiblities include • - L/S0mixing in free space p0 exchange force (tensor) • - LN-SN coupling via mass difference of S+, S0, S- (~8 MeV) •  three-body force as well as two body force. • - K0 and K± mass difference (~1%), also in K* • - r/wmixing  spin-orbit • These are strongly spin dependent •  spin/state dependence is important

  13. Spin-dependence of LN interaction • No experimental data so far from scattering experiments • (analysis of KEK-PS E452 is ongoing) • All information is from hypernuclei • Data are mostly for light (s- and p-shell) hypernuclei • Spin dependent terms LN effective potential in hypernuclei • Vs(r) sL・sN ‥‥ spin-spin • VL(r) sL・LLN ‥‥ spin-orbit (L-spin dependent) • VN(r) sN・LLN ‥‥ spin-orbit (N-spin dependent) • VT(r){3(sL・r)(sN・r)/r2- sL・sN} ‥‥ tensor • In p-shell hypernuclei, we usually take • D = ∫f*LN(r)Vs(r)fLN(r) dr • and regard it as a paramter. (fLN is almost the same over p-shell) • Similarily, SL, SN, and T are defined from VL, VN, VT.

  14. How to get? J+1/2 DE J(=0) A Z Z J-1/2 A+1 L Z Z • L is in s state  state splits into two • Spatial wavefunctions are the same •  DE is determined only by LN spin-dependent interaction. • Examples in pure single-particle limit • p3/2-shell(7Li, 9Be, 11B+L): DE = 2/3D + 4/3SL- 8/5T • p1/2-shell(13C,15N+L): DE = -1/3D + 4/3SL + 8T • (more detailed calculation: see D. J. Millener et al. PRC31 (1985) 499) • DE is usually small -- we need high resolution measurement •  experimental data appear later in this talk.

  15. LL interaction • Unique channel in SU(3) BB interaction classification • Repulsive core may vanish in this channel •  possibile existense of H-dibaryon (uuddss, J=I=0) • Original prediction by Jaffe (PRL38 (1977) 195) • - H is 80 MeV bound from LL • No experimental evidence so far • - at least, deeply bound H is rejected • LL - XN (- SS) coupling important (DE = 28 MeV) • LL interaction study performed by • - LL hypernuclei (example later in this talk) • - LL final state interaction in (K-,K+) reaction • (J. K. Ahn et al., PLB444 (1998) 267 ) • Present data suggests LL interaction is weakly attractive

  16. 7 Li L Hyperons in nuclei • A hyperon behaves as an impurity in nuclei • May change some properties of nuclei, • - size, shape, collective motion, ... • Theoretical prediction: • - A L makes a loosely-bound light nuclei, such as 6Li, smaller • glue-like role (Motoba et al., PTP70 (1983) 189) a a + d  d L L 6Li • Recent experiment gives evidence for such shrinkage •  later in this talk • Other properties are also interesting, but no experimental data

  17. Test of single-particle states at the center of nucleus • Hyperons are free from Pauli blocking • -can stay at the center of nucleus (especially for L) • - is a good probe for depth of nucleus • KEK-PS E369 observed • clear and narrow peaks for • sL and pL states of • (H. Hotchi et al., • PRC64 (2001) 044302) •  There are single- • particle states in center • of nuclei 89 Y L pL sL

  18. magnetic moment • Good observable to see hyperon (L) property in nuclear matter. • - is it changed from free space? If so, how? • Meson current • S mixing? • partial quark deconfinment? • Everyone wants to measure, but no one ever did! • - lifetime too short (~ 200 ps) •  spin precession angle ~1degfor 1T magnetic field • Alternative (indirect) measurement: • B(M1) \ (gcore - gL)2 (planned in KEK-PS E518)

  19. Weak decay of hypernuclei • In free space... • L p + p-(63.9%, Q = 38 MeV) • n + p0 (35.8%, Q = 41 MeV) • DI=1/2 rule holds well. • - initial state: I=0, final state: I=1/2 or 3/2 • if If = 1/2, branch is 2:1 • 3/2, 1:2 • - this rule is global in strangeness decay, but no one knows why • This decay (called mesonic decay) is suppressed in hypernuclei • due to Pauli blocking for the final state nucleon. • Instead, non-mesonic decay occurs in hypernuclei, such as • p + L p + n, • n + L  n + n, ....

  20. Mesonic decay • Dominant only in very light hypernuclei (A<6) • Well described by (phase space)*(Pauli effect)*(p distortion) p- decay partial width free L • Exp. data from • H.Outa et al., NPA639 • (1998) 251c • V. J. Zeps et al., NPA639 • (1998) 261c • Y. Sato, Doctor thesis • (Tohoku Univ., 1998)

  21. Lifetime • Almost constant for A > 10 -- non-mesonic decay dominant •  short range nature of nonmesonic decay • exp. data from • H. Park et al.,PRC61 • (2000) 054004 • H. Outa et al., NPA639 • (1998) 251c • V. J. Zeps et al., NPA639 • (1998) 261c • J. J. Szymanski et al., • PRC43 (1991) 849 • R. Grace et al., PRL55 • (1985) 1055

  22. Gn/Gp puzzle • Simplest diagram for non-mesonic weak decay • -- one pion exchange • Virtual mesonic decay • + absorbsion • This model predicts • Gn (nLnn) << Gp(pLpn) • - 3S1 3D1 tensor coupling • has the largest amplitude, • but this is forbidden for • (nn) final state. N N p Weak Strong L N • However, experimental data indicate • Gn/Gp ~ 1 (e.g., H. Hashimoto et al., PRL88 (2002) 042503) •  Gn/Gppuzzle

  23. Solution? • Additional meson exchange? •  K (+ h, r, w, K*,....) meson • Improve the situation, but • still below exp. data. • (e.g., E. Oset et al., • NPA691 (2001) 146c) • Some models also incorporate • 2p exchange processes • (e.g., K. Itonaga et al., • NPA639 (1998) 329c) N N K Strong Weak L N • Direct quark mechanism? • - s-quark decays directly without meson propagation • (e.g., M. Oka, NPA691 (2001) 364c) • Two nucleon induced processes? (LNN  NNN)

  24. 4 He L Other topics in weak-decay • Does DI = 1/2 rule holds in non-mesonic decay? • - some models require DI=3/2 component to solve Gn/Gp puzzle • - nature of DI = 1/2 rule. Is it really global? • p+ decay -- observed only in • - decay via S+ component in hypernuclei? • - two step processes (L np0, p0p  p+n)? • Parity conserving/non-conserving amplitudes • - parity conserving part cannot be studied in NN system • - interferance  decay asymmetry in polarized hypernuclei • Weak production of hyperon • - pn  pL reaction using polarized protons • - parity-violation and T-violation • - experiments planned at RCNP (Osaka, Japan) and • COSY (Juelich, Germany)

  25. Results from recent experiments • Hyperball project • - High-resolution g-ray spectroscopy using Ge detectors • Motivation • - study of LN spin-dependent interaction via hypernuclear • structure •  high-resolution is required •  g-ray spectroscopy using Ge detectors • Hyperball • - 14 Ge detecotors of 60% relative efficiency • - BGO ACS • - solid angle: 15% of 4p • - photo-peak efficiency ~3% at 1 MeV

  26. 7 9 Li Be L L Experiments using hyperball • KEK-PS E419 (1998) • - spin-spin force in • - glue-like role • BNL-AGS E930 (1998) • - spin-orbit force in • BNL-AGS E930 (2001) • - tensor force in • - in analysis • KEK-PS E509 (2002) • - stopped K • - in analysis • KEK-PS E518 (2002) • - • - coming this September 16 O L 11 B L

  27. 7 Li L 7 Li Li Λ Λ KEK-PS E419(1) -- overview • The first experiment at KEK (Tsukuba, Japan) • studied hypernucleus using 7Li(p+,K+g) reaction 7/2+ 3+ 2.19 5/2+ K+ E2 E2 3/2+ M1 1+ 1/2+ p+ 0 (MeV) 6Li

  28. 7 Li L KEK-PS E419(2) -- Results • Two peaks observed • These attributed to • M1(3/2+ 1/2+) and • E2(5/2+  1/2+) • transitions in • Eg = 691.7±0.6±1.0 keV • 2050.1±0.4±0.7 keV • Peak shape analysis • (Doppler shift attenuation • method) • B(E2)=3.6±0.7 e2fm4 • For details, see • H. Tamura et al., PRL84(2000)5963 • K. Tanida et al., PRL86(2001)1982

  29. KEK-PS E419(3) -- discussion • Eg(M1) = 692 keV gives strength of LN spin-spin force • -6Li(1+) state has pure 3S1 (a+d) structure • D = 0.48 ~ 0.50 MeV • (D. J. Millener, NPA691(2001)93c, • H. Tamura et al., PRL84(2000)5963) • B(E2) is related to hypernuclear size or cluster distance • between a and d as B(E2) \ <r2>2 • (T. Motoba et al., PTP70(1983)189) • Without shrinkage effect, B(E2) is expected to be • 8.6±0.7 e2fm4 from B(E2) data of 6Li. • Present result (3.6±0.7 e2fm4) is significantly smaller •  strong evidence forglue-like role • (3.6/8.6)1/4 = 0.81±0.04 shrinkage of 19±4% • (K. Tanida et al., PRL86(2001)1982)

  30. 9 Be L 9 Be Λ Λ BNL-AGS E930(1) • Experiment performed at BNL (New York, USA) • Measured g ray from created by 9Be(K-,p-) reaction 3/2+ L=2 2+ 3.04 5/2+ • DE(5/2+,3/2+) •  LN spin-orbit force, SL • (core structure: 2a rotating • with L=2) E2 0+ 1/2+ 0 (MeV) 8Be

  31. BNL-AGS E930(2) 5/2+,3/2+ 1/2+ 2000 2500 3000 3500 Eg(keV) • Two peaks separated! • |DE| = 31±3 keV - very small indeed •  surprisingly small spin-orbit force (~ 1/100 of NN case) • (H. Akikawa et al., PRL88(2002)082501)

  32. 6 He LL 5 He L Hybrid emulsion experiment -- KEK-PS E373 • Hybrid emulsion -- C(K-,K+) reaction to produce X- • then stop it in emulsion • NAGARA event found (H. Takahashi et al., PRL87(2001)212502) • Track #1 is the • Binding energy of • is obtained to be • BLL = 7.3±0.3 MeV • (from a+2L) • In order to extract LL • interaction, we take • DBLL = BLL - 2BL( ) • = 1.0±0.3 MeV •  weakly attractive 6 He LL

  33. Future prospect • Near future (a few years) • - experimental studies continue at KEK, BNL, JLAB,... • KEK-PS • - E521: study of neutron rich hypernuclei by (p-,K+) reaction • - E518: g-ray spectroscopy of • - E522: study of LL final state interaction • BNL-AGS • - E964: study of LL hypernuclei with hybrid-emulsion method • and X-ray spectroscopy of X- atoms • CEBAF(JLAB, Virginia, USA) • - E01-011: spectroscopy of hypernuclei with (e,e'K+) reaction • - E02-017: weak decay study • - E94-107: high-resolution study with (e,e'K+) reaction • More activities expected at Frascati (Italy), Dubna (Russia), • Juelich, GSI(Germany), RCNP (Osaka, Japan). 11 B L

  34. Future prospect(cont'd) • Within 5 years... • - KEK-PS and BNL-AGS will be shut down • - JHF 50 GeV PS will come instead! • Much more intense kaon (and other) beam available at JHF. • - Systematic g-ray spectroscopy of single L hypernuclei •  not only LN force, but LNN force • - Hyperon-Nucleon scattering (LN, SN, XN) • - Spectroscopy of X hypernuclei with (K-,K+) reaction • - Production of relativistic hypernuclei using primary beams •  measurement of magnetic moment • - Study of LL hypernuclei and their weak decay • - Charmed hypernuclei (charm quark instead of strange) • Hypernucleus will be a main subject at JHF • - Rich field for both theoretical and experimental studies.

  35. At the end... (summary) • Hypernucleus is interesting! • There are more that I couldn't talk today. • I tried to include references as much as possible • - please look at them if you are interested in • Feel free to contact me at • tanida@rarfaxp.riken.go.jp • if you have questions, comments,....

More Related