Spectroscopy of  -Hypernuclei by Electroproduction HNSS/HKS Experiments at JLAB L. Tang Hampton University & JLAB FB18, Brazil, August 21-26, 2006

Introduction – YN Interaction ,  0 (uds) n(udd) p + (uud)  + (uus)  - (dds)  - (dss)  0 (uss) S Q I S = 0 S = -1 S = -2 J P =1/2 + Nuclear Matter, Neutron Stars, …B-B interactions are fundamental in our understanding on the formation of the world – Nuclear Matter, Neutron Stars, … S = 0Our current knowledge is basically limited at the level of S = 0 (n and p) S ≠ 0Study 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 A nucleus with one or more nucleons replaced by hyperon, Λ, Σ, …,Hypernucleus – A nucleus with one or more nucleons replaced by hyperon, Λ, Σ, …, through elementary production process S ≠ 0 the method of NUCLEAR PHYSICSUnique 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 StrangenessNew 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 S = -1)  -hypernuclei are the most stable ones (S = -1)  N InteractionNovel features of  -hypernucleus –  N Interaction signifies 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

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  -N System: Long Range Terms Suppressed (by Isospin)

Introduction –  -Hypernuclei , like an “impurity”, has full access to all levels of nuclear interior structures, thus a better illumination to explore the nuclear interiorAbsence 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  decays weakly, thus allowing precision spectroscopy and theory descriptionsStabilized states with narrow width –  decays weakly, thus allowing precision spectroscopy and theory descriptions Opening issues: - Precise description of  -Nucleus potential (spin dependent interactions) interactions) V ΛN (r) = V c (r) + V s (r)(S Λ *S N ) + V Λ (r)(l ΛN *S Λ ) + V N (r)(l ΛN *S N ) + V T (r)S 12 - To what extend the  remains as a single particle, effective vs exact models exact models - Short range nature of  N interaction and density dependency

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

Spectroscopy – Low lying A=12 system (  in s shell) Complementary and charge symmetry breaking ~ /2 - 1/2 - 5/2 - 3/2 - 1/2 - 5/2 - 3/2 -  C MeV 12  C ~ MeV  11 B 12  B (π +, K + ) Reaction (e,e’K + ) Reaction JPJP JPJP

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

Existing 12 C(  +,K + ) 12  C spectra KEK336 2 MeV(FWHM) KEK E MeV(FWHM) High resolution, high yield, and systematic study is essential and is the key to unlock the “gate” BNL 3 MeV(FWHM)

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

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

Electroproduction of  -hypernuclei in Hall C at JLAB 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

Key Considerations in Electroproduction A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+K+ d 2 σ/dΩ k is completely transverse as Q 2 → 0

First Pioneer Experiment - HNSS First Pioneer Experiment - HNSS Year 2000 Year 2000 Tagged e’ at 0 o !

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 0 o Can only use extremely low luminosity (20mg/cm 2 target and 0.6  A beam current) High accidental coincidence background rate Goal: Aim to the future and learn experiences

Λ (Σ 0 ) Spectrum for Energy Calibration p(e,e’K+)Λ p(e,e’K+)Σ 0 12 C(e,e’K+)(Q.F.) Accidentals Beam time: 170 hours

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

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

Jlab HKS experiment (2005) Explore hadronic many-body systems with strangeness through the reaction spectroscopy by the (e,e’K + ) reaction High-resolution~400 keV (factor of 2 improvement) High yield ratesHigh yield Better S/A ratio~5 times improvement Immediate Physics goals 12 C(e,eK + ) 12  B –demonstrate the mass resolution & hypernuclear yield. –core excited states and splitting of the p  -state of 12  B…. Mirror symmetric  hypernuclei 12  C vs. 12  B 28 Si(e,e’K + ) 28  Al –Prove the (e,e’K + ) spectroscopy is possible for the medium-heavy target possible. –precision 28  Al 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 10 4 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

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 Better Yield and S/A Medium-heavy hypernuclei can be studied Singles rate of e-arm 200 MHz → 3 MHz with 5 times Target thickness 50 times Beam intensity Compared to E Tilt Method

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

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 (CH 2, calibration) 12  B - 12  B spectroscopy (C, calibration and physics) 28  Al - 28  Al spectroscopy ( 28 Si, primary physics) 6,7  He, 9  Li, and 10,11  Be - 6,7  He, 9  Li, and 10,11  Be (short runs, yield test) 51  Ti and 89  Sr - 51  Ti and 89  Sr (short runs, yield test) HKS: 2005

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

B  (MeV) Counts (0.4MeV/bin)  00 Accidentals Events from C p(e,e’K + )  &  0 used for kinematics and optics calibration HKS-JLAB CH 2 target ~ 70 hours Preliminary  B < 150keV/77 MeV

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

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

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

HKS-HES ( E ) - 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

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 The new system and the hypernuclear program will continue after the 12 GeV upgrade in Hall A New Era of Hypernuclear Spectroscopy !