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New (e,e ’ K+) hypernuclear spectroscopy with a high-resolution kaon spectrometer

New (e,e ’ K+) hypernuclear spectroscopy with a high-resolution kaon spectrometer. Significance of the (e,e’K+) hypernuclear spectroscopy Lessons from the previous E89-009 (e,e’K+) experiment Optimization of the experimental condition

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New (e,e ’ K+) hypernuclear spectroscopy with a high-resolution kaon spectrometer

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  1. New (e,e’K+) hypernuclear spectroscopywith a high-resolution kaon spectrometer • Significance of the (e,e’K+) hypernuclear spectroscopy • Lessons from the previous E89-009 (e,e’K+) experiment • Optimization of the experimental condition • New high-resolution kaon spectrometer for (e,e’K+) spectroscopy Osamu Hashimoto Department of Physics, Tohoku University December 4-7 EMI2001 at RCNP, Osaka

  2. Current issues of hypernuclear physics • A new degrees of freedom • can examine deeply bound states • baryon structure in nuclear medium • New nuclear structure with strangeness • nucleus with a new quantum number • electromagnetic properties • Hyperon-nucleon, hyperon-hyperon interaction • Hyperon scattering and hypernuclear structure • S=-2 system and beyond • Weak interaction in nuclear medium • decay widths, polarization high quality(high resolution & high statistics) spectroscopy plays a significant role Reaction spectroscopy : From MeV to sub-MeV resolution g-ray spectroscopy

  3. １２Ｃ（p＋，Ｋ＋）12LC spectra by the SKS spectrometer at KEK 12 GeV PS 2 MeV(FWHM) E336 1.45 MeV(FWHM) E369

  4. Hypernuclear mass spectra of 89LY, 139LLa and 208LPbby the (p+,K+) reaction KEK SKS E140a

  5. A L Hyperon in nuclear medium

  6. The (e,e’K+) reaction for hypernuclear spectroscopy • Proton to L – Neutron rich L hypernculei • Large angular momentum transfer • Spin-flip amplitude • Higher energy resolution L Hyperon production reactions for spectroscopy DZ = 0 DZ = -1 comment neutron to L proton to L (p+,K+) ( p-,K0) stretched, high-spin large momentum transfer In-flight (K-,p-) in-flight (K-,p0) substitutional stopped (K-,p-) stopped (K-,p0) large momentum transfer (e,e'K0) (e,e'K+) spin-flip (g,K0) (g,K+) & large momentum transfer

  7. Comparison of the (K-,p-),(p+,K+), (e,e’K+) reactions 0+ q~100MeV/c Dl=0  substitutional states DS=0  J=0+ L 12C(K-,p-)12C FWHM 2MeV 1- Relative Strength 12 0 6 L 12C(p+,K+)12C q~300MeV/c Dl=1,2  stretched states DS=0  J=1-,2+ FWHM 2MeV 2+ 1- 6 0 12 L 12C(e,e’K+)12B q~300MeV/c  Dl=1,2  stretched states DS=0,1  J=2-,3+ 3++2+ FWHM 0.6MeV 1-+2- 1- 2+ 3+ 2- 12 0 6 Ex(MeV)

  8. Physics goals of Jlab E01-011 Explore hadronic many-body systems with strangeness through the reaction spectroscopy by the (e,e’K+) reaction Immediate goals • Hypernuclear structure up to medium-heavy mass region • 28LSi(e,e’K+) 28LAl reaction and beyond • LN interaction in the p-shell region • 12C(e,e’K+)12LB reaction • Mirror symmetric L hypernuclei 12LC vs. 12LB High-resolution and high hypernuclear yield rates are keys of the experiment High-resolution 3-400 keV High yield rates > a few 100/day for 12LB ground state (comparable to the (p+,K+) spectroscopy) New experiment designed based on the E89-009 experience

  9. The E89-009 experiment SOS Spectrometer • The first successful (e,e’K+) hypernuclear spectroscopy • 0 degree tagging method employed • Low luminosity Resolution 5 x 10-4 Solid angle 4 msr(with splitter) Side View + K Target _ D D Q Splitter Top View Magnet Electron beam _ Q + K (0.66 mA@ 1.645 GeV/c) D D Target Focal Plane ( SSD + Hodoscope ) Beam Dump 0 1m ENGE Spectrometer -4 Resolution 2x10-4

  10. E89-009 kinematics K+ arm At very forward angle (2 degrees) Maximum hypernuclear production cross section K+ Target nucleus pK=1.2 GeV/c Eg=1.5 GeV Beam e- e’ Ee=1.8 GeV pe=0.3GeV/c e’ arm At exactly zero degree Advantage : Maximum virtual photon flux Disadvantage : Huge backgrounds from Bremsstrahlung

  11. E89-009 results 12C(e,e’K+)12LB • Clean observation of 12LB ground state by the (e,e’K+) reaction • About 600 keV(FWHM) resolution • 0 degree tagging method employed pL sL p(e,e’K+)L p(e,e’K+)S0 12C(e,e’K+) quasi-free Accidental

  12. What limited the E89-009 hypernuclear physics experiment ? • Energy resolution • Momentum resolution of the kaon spectrometer limited hypernuclear mass resolution • Hypernuclear yield rates • Kaon spectrometer solid angle limited detection efficiency • High count rates at the focal plane of the Enge spectrometer set the limit of maximum beam intensity • High accidental background rate A high-resolution large-solid-angle kaon spectrometer designed “Tilt method” proposed

  13. E01-011 design principle • Optimize the experimental kinematics : Similar to E89-009 • Avoid 0 degree Brems associated electrons in ENGE • Avoid 0 degree positrons in the kaon arm • Maximize acceptance of the kaon spectrometer • Higher energy resolution(down to a few 100 keV) Matching the momentum acceptances etc. Tilt method High resolution kaon spectrometer

  14. HKS overview 1.0 GeV/c 1.4 GeV/c 1.2 GeV/c New QQD Spectrometer -4 Resolution 2 x 10 （ Solid angle 30 msr ） TOF Side View + K CHAMBER 0 1m B E A M D Q1 Q2 SOS Spectrometer Resolution 5 x 10-4 - Solid angle 6 msr(with splitter) Side View + K Target _ D D Q Top View Splitter Electron _ Q + Beam K D D (1.645 GeV/c) Target Focal Plane ( SSD + Hodoscope ) Beam Dump 0 1m ENGE Spectrometer Resolution 2x10-4

  15. Basic parameters of the E01-011 experiment Beam conditionBeam energy 1.8 GeV, Beam momentum stability < 1 x 10-4 Beam current 30 mA General configurationSplitter+Kaon spectrometer+Enge spectrometer • Kaon spectrometer • Configuration QQD and horizontal bend • Central momentum 1.2 GeV/c • Momentum acceptance 12.5 % • Momentum resolution(Dp/p) 2 x 10-4(FWHM) • (Beam spot size 0.1mm assumed) • Solid angle 18 msr with the splitter • (30 msr without the splitter) • Kaon detection angle Horizontal: 7 degrees • Enge split-pole spectrometer • Central momentum 0.3 GeV/c • Momentum acceptance  30 % • Momentum resolution(Dp/p) 5 x 10-4(FWHM) • Electron detection angle Horizontal: 0 degrees • Vertical : 4.5 degrees

  16. General experimental condition Phys. Lett. B 445, 20 (1998) M. Q. Tran et al. 2.0 σtotal(mb) 1.0 1.2 1.4 1.6 1.8 2 1 Eγ(GeV) p(g,K+)L Total cross section • Virtual Photon energy Eg ~1.5 GeV • Elementary cross section: • constant from 1.1 to 1.5 GeV • Higher Eg: Smaller momentum transfer  Lower hypernuclear cross section • Beam energy Ee ~ 1.8 GeV • Higher Ee: • Opens other kaon production channels • e’ momentumEe’~Ee-Eg = 0.21 ~ 0.39 GeV • Lower pe’: Better resolution • Kaon momentum pK • Eg determines pK = 1.2 GeV/c ± 12.5 % • Lower pK : • Better resolution, particle ID • Smaller K survival factor Reaction Threshold(MeV) gp  KL 911 KS 1046 KL(1405) 1452 K*(892)L 1679

  17. Hypernuclear yield vs. electron energy Flight path 5-10m 7m 6m 5m Survival rate of kaons 8m 9m 10m Kaon momentum ( MeV/c ) K+ Angular distribution Ee’ = 0.285 GeV/c, qe’ = 0, qK = 0, DWK = 30 msr Decay in flight

  18. Correlation of kaon and electron momenta,and hypernuclear mass

  19. What is “Tilt method” ? Scattered electrons in the Enge acceptance • Avoid Brems electron tail • The tail extends due to multiple scattering in the target • Avoid Moeller scattering electrons • Peak around 2.5 degrees for the beam energy around 1.8 GeV and momentum acceptance of 300 MeV+-30% Moeller ring Brems electron Allows us to run at 250 time higher luminocity compared to E89-009. 1.8 GeV electron beam on a 100mg/cm212C target

  20. Optimization of the tilt angle Virtual photon flux • Very forward peaked • Long tail at the larger angle • Brems electron angular distribution is more forward peaked(dominated by multiple scattering in the target)

  21. Optimization of “tilt” geometry Full tracking of scattered electrons at the focal plane of the Enge spectrometer New tracking chamber Careful study of optics and momentum reconstruction method Simulation and calibration methods Handling of higher singles rates Pions, protons Higher rejection efficiency against pions and protons Cerenkov counters Better time resolution The “Tilt method” requires For the scattered electron arm For the kaon arm

  22. Optics of Electron Arm (Splitter + Split-Pole) Tilt 4.5o with respect to a virtual source point. Optimize the figure of merit for S/A (e ~3o) Maximize the average virtual photon acceptance (~1.5%) (HNSS ~ 35%) Minimize the scattered electron rate (~3MHz) (HNSS ~ 200MHz) Clean separation/blocking of the bremsstrahlung electrons Improve momentum acceptance (~180 MeV/c) (HNSS ~ 120 MeV/c) Full measurement of X, X’, Y and Y’ is needed (HNSS – X only)

  23. Splitter + Enge energy resolutiondE/E ~5x10-4 (FWHM)

  24. The HKS spectrometer system under construction Configuration Q + Q + D Maximum momentum 1.2 GeV/c Dispersion 4.7 cm/% -4 2 10 (FWHM) Momentum resolution 30 msr w/o splitter 18 msr w splitter Solid angle Flight path length 10 m Angular acceptance 170 mrad vertical 180 mrad horizontal Momentum acceptance ±12.5 % Maximum dipole field 1.5 T Conductor normal Design specification of HKS

  25. Transport Study (R12=R34=0) Horizontal Focusing & Vertical Focusing (R12=R44=0) Horizontal Focusing & Vertical Parallel

  26. Momentum resolution of HKS • Chamber position • Two DCs • 50cm from 1st order focal plane • (235cm downstream from D exit) Momentum resolution s = 270mm  dp/p 210-4 FWHM (SOS DC =160~180mm)

  27. QQD configuration flexible to adjust vertical and horizontal focusing Horizontally thin Q1, Q2 design allows to minimize distance from the target without bumping to Enge magnet Solid angle of HKS

  28. Expected performance • Resolution • 300 – 400 keV(FWHM) depending on target mass • Yield • More than factor of 50 gain over E89-009 • Comparable to the present (p+,K+) spectroscopy • Accidental background • 8 x 10-4/sec vs. 1.3 x 10-2/(100nb/sr)/sec per 100 keV bin ( an order of magnitude better than E89-009) • Can be further improved with the lower beam intensity

  29. Singles rates Ie = 30 mA, 100 mg/cm2 • Scattered electron rate is considerably lower than E89-009 • Pion and proton rates of the kaon arm are high High rejection efficiencies of Cerenkov counters against pions and protons required

  30. A comparison of the (p+,K+) reaction and the (e,e’K+) reactions for the hypernuclear physics (p+,K+) (e,e’K+) (e,e’K+)/(p+,K+) SKS E89-009 RATIO E01-011/E89-009 Cross sections (12LCgr or 12LBgr)10 0.05 5x10-3 (mb/sr) (g,K+) Target thickness 1 0.01 10-2 ~ 4.5 (g/cm2) Beam intensity 106 109-10 103-4 ~ 45 (particle/sec) (virtual photon) K+ momentum 0.72 1.2 (GeV/c) K+ solid angle ~ 60 % ~ 10 % 0.18 ~ 3 coverage (%) (100 msr) (4 msr) K+ survival rate(%) ~ 0.4 ~ 0.4 1 ~ 0.8 (Flight path) (5 m) (8 m) Overall ~1 x 10-1~-2~ 100 SKS at KEK vs HNSS at Jlab

  31. Yield comparison of E01-011 and E89-009

  32. Expected hypernuclear production ratesin the (e,e’K+) reaction Hypernuclear production rates Calculated hypernuclear cross sections (Target thickness 100 mg/cm2 with HKS) Motoba

  33. Expected energy resolution 2001.12.05.

  34. Expected hypernuclear spectra

  35. An installation plan of the new spectrometer system in Hall C

  36. Summary • New (e,e’K+) hypernuclear spectroscopy, E01-011, was proposed based on the experience of the pioneering E89-009 experiment at Jlab. • With the new “Tilt method” and with a new high-resolution kaon spectrometer(HKS), twice better resolution, more than an order of magnitude higher yield rates and an order of magnitude better signal to accidental ratios will be realized. • Design of the high-resolution kaon spectrometer (HKS) has been completed and construction of the spectrometer magnets and detector systems is under way supported by Monkasho. • The spectrometer system will be ready for installation by the beginning of 2003, although it is subject to Jlab scheduling.

  37. HKS magnet detail design Enge magnet Photon line Beam Splitter Dipole Q1 Q2 Vacuum extension

  38. Expected accidental coincidence rate • Electron arm singles rate 2.6 MHz • Kaon singles rate 340 Hz • Coincidence time window 2 nsec ( Offline analysis ) At the beam current of 30 mA, we expect Nacc = 1.8 /sec

  39. 荷電対称ハイパー核とクラスター構造 3LH L hyperon Nucleon Alpha 4LH,4LHe 6LHe, 6LLi 7LHe, 7LLi, 7LBe 9LBe 10LBe,10LB 13LC

  40. Spin dependence of the (e,e’K+) reaction Spin independent term f0 f0 spin nonflip Spin dependent term g go spin nonflip g1 g-1 Natural parity states spin flip Unnatural parity states

  41. Elementary electroproduction of a hyperon Virtual photon flux Virtual photon polarization Longitudinal polarization Virtual photon becomes almost real at very forward electron scattering angle Eg = Ee - Ee’

  42. Cross Section View of the HKS Photon line Electron line

  43. Basic experimental conditions of E89-009 • Electron detection including 0 degrees • greater photoproduction cross section of a L hyperon • Eg > 1.2 GeV • Eg = Ee - Ee’, Ee = 1.645 GeV and Ee’~0.285 GeV • K+ detection at forward angle including 0 degrees • PK+ ~ 1.1 GeV/c • flight path as short as possible ~ 8 m • A splitter magnet for e’ and K+ separation at very forward angles • Beam intensity < 1mA • Target thickness ~ 10 mg/cm2

  44. qe’ is aimed about 3o . Virtual process is used in the optical simulation. qe’ (Degrees) The long tails are from the features of tilted Split-pole and momentum dependent fe’ vs qe’ (Degrees)

  45. Accepted e’ from virtual process Collimator • Bremsstrahlung separation • Max. VPF • Min. electron rate Bremsstrahlung/Multiple scattered e’ • Mom. acceptance ~ 180 MeV/c • Average VPF acceptance: ~1.5% DPe’ (%)

  46. HKS Water (or Lucite) Cherenkov counter Tohoku Univ. Florida Int. Univ. Requirement Proton rejection efficiency 410-4of two identical walls with e=0.02 • Water Cherenkov n=1.33 • with and w/o WLS • Lucite Cherenkov n=1.49 • with WLS • w/o WLS • (Total reflection type) Prototypes were built Waiting for R&D beamtime

  47. Focal Plane Correlations Reconstruction from (Xf, Xf’, Yf and Yf’) to (Xt’, Xt’, Yt, Yt’ and d) Xf vs d Yf vs d Xf’ vs d Yf’ vs d

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