Spectroscopy of -Hypernuclei by Electroproduction HNSS/HKS Experiments at JLAB L. Tang Hampton University & JLAB SNP2006, Zhangjiajie, Sept 5-8, 2006

Introduction – YN Interaction ,0 (uds) n (udd) p+ (uud) + (uus) - (dds) - (dss) 0 (uss) S Q I S = 0 S = -1 S = -2 JP=1/2+ 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

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 ≠ 0 B-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 – Strangeness Challenges 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

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 it signifies - 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

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

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

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

Model Productions of -hypernuclei OR S P Particle hole Particle (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 due to high momentum transfer and the spin covered by the virtual photons

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

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

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)

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

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

Electroproduction of -hypernuclei in 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

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

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

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

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

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

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

Jlab HKS experiment (2005) High-resolution ~400 keV (factor of 2 improvement) High yield rates High yield Better S/A ratio ~5 times improvement Explore hadronic many-body systems with strangeness through the reaction spectroscopy by the (e,e’K+) reaction Immediate Physics goals 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….

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 in both trigger and analysis Need sophisticated calibrations and analyses

5 times Target thickness Scattered electrons (0.2 to 0.4 GeV/c) (1)from bremsstrahlung (2)associate with virtual photons (3) from Møller scattering Tilt Method (1) Brems e’ (3) Moeller scattering (2) Virtual photon Associated e’ (1/1000) 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

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

HKS: 2005 -  &  production (CH2, calibration) 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, and 10,11Be (short runs, yield test) - 51Ti and 89Sr (short runs, yield test)

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

p(e,e’K+)&0 used for kinematics and optics calibration HKS-JLAB CH2 target ~ 70 hours  15 times more yield 6 times better S/A Preliminary M = 1.43 MeV (FWHM) M = (MR - M0) = - 44 keV M = 1.47 MeV (FWHM) M = (MR - M0) = - 83 keV Counts (0.4MeV/bin) Events from C 0 Accidentals B (MeV)

12C(e,e’K+)12B used for kinematics and optics calibration Preliminary JLAB – HKS ~ 90 hrs w/ 30A s(g.s.) Ground State (2-/1-):  = 670 keV (FWHM) B = -11.383 MeV p C.E. #1 15 times more yield 4 times better S/A Counts (0.2 MeV/bin) C.E. #2 or more Accidentals B (MeV)

28Si(e,e’K+)28Al – First Spectroscopy of 28Al Preliminary JLAB – HKS ~140 hrs w/ 13A s p C.E. ? C.E. ? Ground State:  = 745 keV (FWHM) B = -17.93 MeV Yield = ~5/hr (30A) Counts (0.25 MeV/bin) Accidentals B (MeV)

7Li(e,e’K+)7He – First Observation of ½+ G.S. of 7He Preliminary JLAB – HKS ~ 30 hrs s (1/2+) Ex. state? Ground State:  = 940 keV (FWHM) B = - 5.50 MeV (Threshold: 6He+) Counts (0.4 MeV/bin)

HKS-HES (E05-115) - Heavy Hypernuclei 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

New Era of Hypernuclear Spectroscopy ! 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 !

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)

Preliminary Accidentals 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)

Preliminary Accidentals 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)

Preliminary Accidentals 7Li(e,e’K+)7He – First Observation of ½+ G.S. of 7He Preliminary JLAB – HKS ~ 30 hrs 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)