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Spectroscopy of  -Hypernuclei by Electroproduction HNSS/HKS Experiments at JLAB L. Tang Hampton University & JLAB

Spectroscopy of  -Hypernuclei by Electroproduction HNSS/HKS Experiments at JLAB L. Tang Hampton University & JLAB. FB18, Brazil, August 21-26, 2006. J P =1/2 +. S = 0. S = -1. S. Q. S = -2. n (udd). p + (uud).  + (uus).  - (dds).  - (dss).  0 (uss). , 0 (uds). I.

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Spectroscopy of  -Hypernuclei by Electroproduction HNSS/HKS Experiments at JLAB L. Tang Hampton University & JLAB

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  1. Spectroscopy of -Hypernuclei by ElectroproductionHNSS/HKS Experiments at JLABL. TangHampton University& JLAB FB18, Brazil, August 21-26, 2006

  2. JP=1/2+ S = 0 S = -1 S Q S = -2 n (udd) p+ (uud) + (uus) - (dds) - (dss) 0 (uss) ,0 (uds) I Introduction – YN Interaction • B-B interactions are fundamental in our understanding on the formation of the world – Nuclear Matter, Neutron Stars, … • Our current knowledge is basically limited at the level of S = 0 (n and p) • Study S ≠ 0 B-B interactions (YN and YY) is a MUST in order to extend our knowledge to include as well as reach beyond strangeness and seek an unified description of B-B interaction • Due to the short lifetime of Y, direct study of YN interactions is almost impossible

  3. Introduction – Hypernuclei • Hypernucleus–A nucleus with one or more nucleons replaced by hyperon, Λ, Σ, …,through elementary production process • Unique gate way to study S ≠ 0B-B interaction: YN interaction embedded in a nuclear mean field, a rich laboratory to study YN interactions with the method of NUCLEAR PHYSICS • New degree of freedom in nucleus –StrangenessChallenges the limit of conventional nuclear models of hadronic many-body system but also open doors to new or hidden aspects in the “traditional” nuclear physics

  4. Introduction – -Hypernuclei • -hypernuclei are the most stable ones(S = -1) • Novel features of -hypernucleus –N Interaction Absence of long range OPE between Λ and N due to conservaison of isospin in strong interaction, thus itsignifies - Higher mass meson exchanges that are over shadowed by the dominant OPE force in N-N interactions in the traditional nuclear nuclear physics - Sizable charge asymmetry (p and n) - Intermediate Λ-Σ coupling and significant three-body forces (ΛNN) with two-pions exchange

  5. Understanding the N-N Force In terms of mesons and nucleons: Or in terms of quarks and gluons: V =

  6. -Hypernuclei Provide Essential Clues For the N-N System: For the L-N System: Long Range Terms Suppressed (by Isospin)

  7. Introduction – -Hypernuclei • Absence of Pauli Blocking–, like an “impurity”, has full access to all levels of nuclear interior structures, thus a better illumination to explore the nuclear interior • Stabilized states with narrow width– decays weakly, thus allowing precision spectroscopy and theory descriptions • Opening issues: - Precise description of -Nucleus potential (spin dependent interactions) VΛN(r) = Vc(r) + Vs(r)(SΛ*SN) + VΛ(r)(lΛN*SΛ) + VN(r)(lΛN*SN) + VT(r)S12 - To what extend the  remains as a single particle, effective vs exact models - Short range nature of N interaction and density dependency

  8. Particle Particle hole  P-  OR P OR   S OR Model Productions of -hypernuclei • (K-, -) –Nature parity, low spin substitutional states due to low momentum transfer, high yield • (+, K+) –Nature parity, high spin stretched states due to high momentum transfer • (e, e’K+) –Unnature parity, high spin stretched states dueto high momentum transfer and the spin covered by the virtual photons

  9. Spectroscopy – Low lying A=12 system ( in s shell) (e,e’K+) Reaction (π+, K+) Reaction 1- 1- 3/2- 5.02 3/2- 4.80 2- 2- 5/2- 4.45 2- 2- 4.32 5/2- 0- 0- 1/2- 2.12 2.00 1/2- 1- 1- ~0.1 ~0.1 2- 2- 0.00 3/2- 0.00 3/2- 1- 1- 0.0 0.0 JP JP MeV MeV 12B 12C   11B 11C Complementary and charge symmetry breaking

  10. KEK E140a Hasegawa et. al., PRC 53 (1996)1210 L single particle potential Energy resolution is very limited by using hadronic beam – 1.5 MeV FWHM Hotchi et al., PRC 64 (2001) 044302 Textbook example of Single-particle orbits in nucleus L Single particle states →L-nuclear potential depth = -30 MeV →VLN < VNN

  11. Existing 12C(p+,K+)12LC spectra BNL 3 MeV(FWHM) KEK E369 1.45 MeV(FWHM) High resolution, high yield, and systematic study is essential and is the key to unlock the “gate” KEK336 2 MeV(FWHM)

  12. Thomas Jefferson National Accelerator Facility (TJNAF or JLAB) www.jlab.org Virginia Location in U.S.A.

  13. East Arc FEL South Linac +400MeV North Linac +400MeV Continuous Electron Beam Accelerator Facility (CEBAF) MCC West Arc Injector A CH C B

  14. Electroproduction of -hypernucleiin Hall C at JLAB • High precision beam → high resolution spectroscopy • High intensity and 100% duty factor → Overcome low cross section for high yield which is essential to study heavy hypernuclei • Advantage: High resolution and high yield • Challenges: Extremely high particle rates

  15. e e’  K+  N A A → Coincidence of e’ and K+ → Keep ω=E-E’ low (K+ background) → Maximize Γ –- e’ at forward angle → Maximize yield –- K+ at forward angle Key Considerations in Electroproduction d2σ/dΩk is completely transverse as Q2 → 0

  16. Side View Q K+ Target _ D D Splitter Magnet SOS Spectrometer(QDD) Electron Beam _ Q 1.864 GeV K+ 1.2GeV/c D D Target Local Beam Dump e’ Enge 0.3GeV/c Split-Pole Focal Plane Spectrometer ( SSD + Hodoscope ) Beam Dump 1m 0 First Pioneer Experiment - HNSS Year 2000 Tagged e’ at 0o!

  17. HNSS: A Great Challenge • Low resolution of the existing SOS spectrometer (p/p ~7x10-4 FWHM only) • Small solid angle acceptance (SOS has 4.5 msr) • Extremely high electron rate (200 MHz) at 0o • Can only use extremely low luminosity (20mg/cm2 target and 0.6A beam current) • High accidental coincidence background rate Goal: Aim to the future and learn experiences

  18. Λ (Σ0) Spectrum for Energy Calibration p(e,e’K+)Λ p(e,e’K+)Σ0 12C(e,e’K+)(Q.F.) Accidentals Beam time: 170 hours

  19. Achievement: 12C(e,eK+)12LB (HNSS) 11B(gs)×L(0s) 11B(gs)×L(0p) Resolution 1.5 MeV FWHM by (p+,K+) 750 keV FWHM by (e,e’K+) a month data Beam time: 450 hrs Calc. by Motoba & Miliner

  20. Spectroscopy of A=7 Systems – 7LHe (neutron rich) ~240 hrs test Bound g.s. !?

  21. Jlab HKS experiment (2005) High-resolution ~400 keV (factor of 2 improvement) High yield rates High yield Better S/A ratio ~5 times improvement • 12C(e,eK+)12LB • demonstrate the mass resolution & hypernuclear yield. • core excited states and splitting of the pL-state of 12LB…. • Mirror symmetric L hypernuclei 12LC vs. 12LB • 28Si(e,e’K+)28LAl • Prove the (e,e’K+) spectroscopy is possible for the medium-heavy target possible. • precision 28LAl hypernuclear structure and ls splitting of p-state…. Explore hadronic many-body systems with strangeness through the reaction spectroscopy by the (e,e’K+) reaction Immediate Physics goals

  22. Key Technical Approaches of HKS • Electron arm • Tilt method for the electron arm • Suppress Brems electrons by 104 times • Need higher order terms of the transfer matrix • Kaon arm (Replace SOS by HKS) • High Resolution Kaon Spectrometer (HKS) • High resolution (2 times) & Large solid angle (3 times) • Good particle ID both in the trigger and analysis Need sophisticated calibrations and analyses

  23. Tilt Method (1) Brems e’ (2) Virtual photon Associated e’ (1/1000) (3) Moeller scattering • Scattered electrons (0.2 to 0.4 GeV/c) • (1)from bremsstrahlung • (2)associate with virtual photons • (3) from Møller scattering Tilt e-arm by 7.75 deg. vertically with respect to splitter & K-arm • Singles rate of e-arm • 200 MHz → 3 MHz • with • 5 times Target thickness • 50 times Beam intensity Compared to E89-009 Better Yield and S/A Medium-heavy hypernuclei can be studied

  24. Layout of the HKS setup 2005 2 x 10-4(FWHM) 16 msr with splitter 4 x 10-4(FWHM) Tilt 7.75 degrees

  25. HKS: 2005 • Installed in 4 months (Feb. to May) • Commissioning in 1.5 months • Data taking in 2 months (near end of Sept) • Data taken for -  &  production (CH2, calibration) - 12B spectroscopy (C, calibration and physics) - 28Al spectroscopy (28Si, primary physics) - 6,7He, 9Li, and10,11Be (short runs, yield test) - 51Ti and 89Sr (short runs, yield test)

  26. HKS: Analysis • Still very preliminary • Current stage focuses on calibration and optimization of common kinematics and optics • Future stages include (1) target straggling loss for individual targets and fine optical tune and (2) beam energy and on target position studies and possible corrections

  27. p(e,e’K+)&0 used for kinematics and optics calibration HKS-JLAB CH2 target ~ 70 hours  Preliminary Counts (0.4MeV/bin) B < 150keV/77 MeV 0 Events from C Accidentals B (MeV)

  28. 12C(e,e’K+)12B used for kinematics and optics calibration JLAB – HKS ~ 90 hrs w/ 30A s Preliminary p C.E. #1 C.E. #2 Counts (0.2 MeV/bin) Current width: 670 keV FWHM Accidentals B- Binding Energy (MeV)

  29. 28Si(e,e’K+)28Al – First Spectroscopy of 28Al Preliminary JLAB – HKS ~ 140 hrs w/ 13A s d ? p C.E. ? Counts (0.25 MeV/bin) Accidentals B- Binding Energy (MeV)

  30. 7Li(e,e’K+)7He – First Observation of ½+ G.S. of 7He JLAB – HKS ~ 30 hrs Preliminary B (g.s.) = -4 MeV 1 to 1.4 MeV less bound than theory prediction! s (1/2+) Counts (0.4 MeV/bin) Accidentals B- Binding Energy (MeV)

  31. NEXT & FUTURE HKS-HES (E05-115) - Heavy Hypernuclei • Replace Enge by new HES spectrometer with larger acceptance • Use higher beam energy (> 2.1 GeV) • Obtain 30 times more yield gain over HKS experiment but the same background rate • Improve another 5 times better S/A ratio for clean spectroscopy • Study 51Ti and 89Sr in detail • Study p-shell systems with high statistics in very short running time • Current schedule: installation starts in summer of 2008 all equipment will be ready by the end of 2007

  32. Summary • The first experiment HNSS proved the potential to study hypernuclear spectroscopy with high precision using the CEBAF beam and (e,e’K+) reaction at JLAB • The HKS experiment has successfully demonstrated that such a high precision study can be carried out with high yield and heavy systems can be studied with an optimized experiment design • The next phase experiment HKS/HES will be carried out in the period of 2008-2009 • The new system and the hypernuclear program will continue after the 12 GeV upgrade in Hall A New Era of Hypernuclear Spectroscopy !

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