Study of Light Hypernuclei by Pionic Decay at JLAB Liguang Tang Other spokespersons: A. Margaryan, L. Yuan, S.N. Nakamura, J. Reinhold Collaboration: From both Hall C and A hypernuclear programs JLAB PAC 33, January 14-18, 2008
Introduction Nuclei Baryon-Baryon Interaction Neutron Stars D.H. S.H. N.R.p S.H. N.R. n (uds) (uds) P (uud) n (udd) The single and double hypernuclei are the main sources of the strange sector of baryon-baryon interaction S=-1 S=-2 S=-0
Discovery of the first hypernucleus by pionic decay in emulsion produced by Cosmic Rays. Marian Danysz and Jerzy Pniewski, 1952 p + - (64%); n + 0 (36%) Remain effective even at medium A Access rich information about hypernuclear and nuclear physics Access rich information about hypernuclear and nuclear physics Used exclusively to determine the binding energy of light (A≤15) hypernuclei in emulsion Used exclusively to determine the binding energy of light (A≤15) hypernuclei in emulsion Precision: ~50keV Precision: ~50keV Resolution: ~0.5 – 1.0 MeV Resolution: ~0.5 – 1.0 MeV Problems: Problems: - Poor statistics - Calibrations - Cannot resolve pure 2-body decay Was not interested in the past ~20 years – low energy and low yield Was not interested in the past ~20 years – low energy and low yield
New Opportunity at JLAB Combination the CEBAF beam and the HKS system Combination the CEBAF beam and the HKS system High precision and high yield High precision and high yield Program features: Program features: Energy resolution: ~130 keV FWHMEnergy resolution: ~130 keV FWHM B precision: ~10 keVB precision: ~10 keV Simultaneous lifetime measurement (timing resolution ≤80ps)Simultaneous lifetime measurement (timing resolution ≤80ps) Wide range of physics Wide range of physics
Directly Produced Hypernuclei - Example p e’ e 12 C K+K+ 12 B 12 C g.s. - Mesonic two body decay ~150 keV Ground state doublet of 12 B B and
Indirectly Produced Hypernuclei – Example Fragmentation Process p e’ e 12 C 12 B * K+K+ 4 He - Mesonic two body decay (~ s) Access to variety of light and exotic hypernuclei, some of which cannot be produced or measured precisely by other means 4H4H Fragmentation (< s)
Physics Objectives – YN Interactions Emulsion data of light hypernuclei (primarily the ground states) were used to check theoretical models on YN interaction in the past 40 some years. Emulsion data of light hypernuclei (primarily the ground states) were used to check theoretical models on YN interaction in the past 40 some years. Problem of inconsistency and model of choice exist Problem of inconsistency and model of choice exist Recent -spectroscopy program has been successful for spin dependent interactions but unable to measure B Recent -spectroscopy program has been successful for spin dependent interactions but unable to measure B Recent successful mass spectroscopy programs cannot reach a precision on B exceeding emulsion data Recent successful mass spectroscopy programs cannot reach a precision on B exceeding emulsion data YN B ( 3 H) B ( 4 H)B ( 4 H * )B ( 4 He)B ( 4 He * )B ( 5 He) SC97d(S) SC97e(S) SC97f(S) SC89(S) Unbound2.47Unbound0.35 Experiment0.13 ± ± ± ± ± ± 0.02 The wealth of information coming from this poor statistics emulsion experiment is solely attributable to the technique's inherent good energy resolution, ~50 keV in this instance, and forcefully emphasizes the need to strive for comparable energy resolution in counter experiments. The wealth of information coming from this poor statistics emulsion experiment is solely attributable to the technique's inherent good energy resolution, ~50 keV in this instance, and forcefully emphasizes the need to strive for comparable energy resolution in counter experiments. - D. Davis, D. Davis, 1992 As it turns out, binding energies of light hypernuclei are highly correlated from calibrations to 12 C for example, and most likely incorrect. As it turns out, binding energies of light hypernuclei are highly correlated from calibrations to 12 C for example, and most likely incorrect. - D. Davis, HYP2006
Replace emulsion data with a new set of data that has a factor of 2-5 times better precision on B to check current and future theories with stringent limits Replace emulsion data with a new set of data that has a factor of 2-5 times better precision on B to check current and future theories with stringent limits Separate small ground state doublets Separate small ground state doublets Study charge symmetry breaking in YN interaction, such as B ( 4 H g.s. ) - B ( 4 He g.s. ) Study charge symmetry breaking in YN interaction, such as B ( 4 H g.s. ) - B ( 4 He g.s. ) YN Interactions – cont.
Search for and measure precisely the B of the exotic hypernuclei is another effective way for exotic nuclear physics Search for and measure precisely the B of the exotic hypernuclei is another effective way for exotic nuclear physics Many hypernuclei with unstable nuclear core exist, e.g. 6 He, 7 Be, 8 He, 9 Be. Other exotic hypernculei may exist, e.g. 6 H, 7 H, 8 H, 10 He, and 11 Li through fragmentation process Many hypernuclei with unstable nuclear core exist, e.g. 6 He, 7 Be, 8 He, 9 Be. Other exotic hypernculei may exist, e.g. 6 H, 7 H, 8 H, 10 He, and 11 Li through fragmentation process Search for Highly Exotic Hypernuclei Bound hypernucleus Search for light hypernuclei toward nucleon drip-lines: hypernuclei with extreme isospins Search for light hypernuclei toward nucleon drip-lines: hypernuclei with extreme isospins Other programs: Other programs: Heavy ion collision JINR, HypHI This program – high precision on B This program – high precision on B Hypernuclei at: * -stability line * Neutron rich * Nucleon drip-lines
Pion decays offer insights into the hypernuclear and nuclear structure, and the momentum dependence of the single particle wave functions Pion decays offer insights into the hypernuclear and nuclear structure, and the momentum dependence of the single particle wave functions Impurity Nuclear Physics Hypernuclear and nuclear structure Nucleus at g.s. -- Hypernucleus w/ hyperfine g.s. doublet E < 100 keV Decay pion can be used to determine the spin ordering of the doublet Hypernucleus at g.s. Nucleus w/ hyperfine g.s. doublet E < 100 keV
Example: 7 Li w/ g.s. doublet 1/2 + & 3/2 + Example: 7 Li w/ g.s. doublet 1/2 + & 3/2 + Impurity Nuclear Physics – cont. Probing nuclear structure with
Example: 10 B w/ g.s. doublet 1 - & 2 - Example: 10 B w/ g.s. doublet 1 - & 2 - Spin order is not known Spin order is not known transition (2 - 1 - ) was not found transition (2 - 1 - ) was not found Success competition by weak mesonic decay Success competition by weak mesonic decay Assumed order could be wrong Assumed order could be wrong Decay pion may provide clearification Decay pion may provide clearification 10 Be may be the candidate at JLAB 10 Be may be the candidate at JLAB
Impurity Nuclear Physics Role and effect of in Nucler Medium E2 Precise B allows separation of those low lying states which have sufficient long lifetime (i.e. decay competes with weak decay) Precise B allows separation of those low lying states which have sufficient long lifetime (i.e. decay competes with weak decay) Lifetime of these separable states allows to extract transition probabilities B(E2) and B(M1) which provide information about the medium effect to baryon or to the core medium Lifetime of these separable states allows to extract transition probabilities B(E2) and B(M1) which provide information about the medium effect to baryon or to the core medium 5/2 + 3/2 + 1/2 + E2 0 (MeV) ~1.7 5/2 + and 3/2 + states are from unbound 2 + state of 6 He core 7 He - 7 Li E2 1/2 + 5/2 + 7/2 + 0 (MeV) ~0.26 ~ B - 11 C
Tagged-Weak Pi-Method of B(E2) and B(M1) Measurement By measuring both of P B weak (t) and P A weak (t) and fitting them together to the equations above,, and m can be determined. If states can be separated and statistics is sufficient to measure lifetimes, then
Technique & Exp. Layout Standard Splitter and HKS for K + Standard Splitter and HKS for K + Enge & target moved upstream for decay pions Enge & target moved upstream for decay pions Tilted TGT (25mg/cm 2 ) Eff. TGT (50mg/cm 2 ) Tilted TGT (25mg/cm 2 ) Eff. TGT (50mg/cm 2 ) Standard pre-chicane beam line (E05-115) Standard pre-chicane beam line (E05-115) Local dump for photons Local dump for photons Similar luminosity as E (HKS/HES) Similar luminosity as E (HKS/HES) Need calibration for the absolute H S central momentum
ConfigurationEnge Split-Pole (or HES) spectrometer and detector package Central momentum115 MeV/c Momentum acceptance± 40% Momentum resolution (r.m.s.)10 -4 without multiple scattering Momentum resolution (r.m.s.) 4.9 with multiple scattering Dispersion1.28 cm/% Time-zero precision< 100 ps (~80 ps) Pion detection angle ~60 degree relative to the incident beam Flight path length309 cm - survival rate~ 60% Solid angle~20 msr Total efficiency of the detector package ~80% Parameters of the HS spectrometer
Example of Possible G.S. of Light Hypernuclei from 12 C Target 4H4H 8 Li 12 B 3H3H 7 Li 11 B 5 He 8 Be 9 Be Background: ~97.5% QF decay ~2.5% (K + & - ) accidentals G.S. only (doublet structures are not shown) G.S. only (doublet structures are not shown) Estimated based on emulsion data thus may under-estimated for some of the hypernuclei Estimated based on emulsion data thus may under-estimated for some of the hypernuclei Additional hypernuclei may appear Additional hypernuclei may appear
Targets: 12 C and 7 Li (Optimized combination) Targets: 12 C and 7 Li (Optimized combination) 12 C – Heaviest in p-shell; reliable yield rates on variety of light hypernuclei but not too crowded 12 C – Heaviest in p-shell; reliable yield rates on variety of light hypernuclei but not too crowded 7 Li – Best chance for the lightest and highly exotic hypernuclei, such as 6 H 7 Li – Best chance for the lightest and highly exotic hypernuclei, such as 6 H Beam energy: 1.8 – 2.2 GeV Beam energy: 1.8 – 2.2 GeV Beam current and acq. time Beam current and acq. time 12 C, 60A (100 Max.), 20 days 12 C, 60A (100 Max.), 20 days ~1000 counts for 4 H (physics w/ moderate yield)~1000 counts for 4 H (physics w/ moderate yield) ~6000 counts for 5 He (physics and calibration)~6000 counts for 5 He (physics and calibration) 7 Li, 30A (50 Max.), 20 days 7 Li, 30A (50 Max.), 20 days Primary: 7 He, 6 He, 5 He; Questionable: 4 He, 6 H, 5 H, 4 H Primary: 7 He, 6 He, 5 He; Questionable: 4 He, 6 H, 5 H, 4 H Trigger rate: ~ few hundred Hz Trigger rate: ~ few hundred Hz Beam Parameters and Beam Time
Summary CEBAF beam and HKS provide unique opportunity for a new counter type high precision decay pion program – Producing data that replaces emulsion data in the role of checking theories CEBAF beam and HKS provide unique opportunity for a new counter type high precision decay pion program – Producing data that replaces emulsion data in the role of checking theories It can study a wide range of physics that either not accessible by other means or complementary to other programs It can study a wide range of physics that either not accessible by other means or complementary to other programs
International Hypernuclear Network PANDA at FAIR 2012~ Anti-proton beam Double -hypernuclei -ray spectroscopy MAMI C 2007~ Electro-production Single -hypernuclei -wavefunction JLab 2000~ Electro-production Single -hypernuclei -wavefunction FINUDA at DA NE e + e - collider Stopped-K - reaction Single -hypernuclei -ray spectroscopy (2012~) J-PARC 2009~ Intense K - beam Single and double -hypernuclei -ray spectroscopy for single HypHI at GSI/FAIR Heavy ion beams Single -hypernuclei at extreme isospins Magnetic moments SPHERE at JINR Heavy ion beams Single -hypernuclei JLab, HπS Electro-production Single -hypernuclei at normal and extreme isospins Binding energies π - decay spectroscopy Impurity nuclear physics Basic map from Saito, HYP06
Introduction – cont. Example H. Outa et al., “Lifetime measurement of 4 H hypernucleus”, INS-Rep.-914 (1992) Decay - is used even in modern studies Decay - is used even in modern studies In the last 20 years or so, mesonic decay has not been really interested in study of the hypernuclear/nuclear structure, because of its low momentum and the difficulty to reach high precision with unavoidable thick targets using msonic beams In the last 20 years or so, mesonic decay has not been really interested in study of the hypernuclear/nuclear structure, because of its low momentum and the difficulty to reach high precision with unavoidable thick targets using msonic beams Emulsion: cannot resolve two body decay and typical resolution is 0.5 – 1.0 MeV Emulsion: cannot resolve two body decay and typical resolution is 0.5 – 1.0 MeV Counter type: resolution is 1.0 – 2.0 MeV Counter type: resolution is 1.0 – 2.0 MeV Time delayed
The proposed project capable to provide precise binding values of known hypernuclei and have a great potential to extend this landscape
Exotic Hypernuclei Different decay channels of excited 7 He * hypernucleus (Majling, 2006).