1 / 35

Hypernuclear spectroscopy up to medium mass region through the (e,e’K + ) reaction in JLab

Hypernuclear spectroscopy up to medium mass region through the (e,e’K + ) reaction in JLab. Mizuki Sumihama For HKS collaboration Department of Physics Tohoku university. 2006 HNP. Physics motivation…. p. L. n. L hypernuclei. L N interaction

beyla
Télécharger la présentation

Hypernuclear spectroscopy up to medium mass region through the (e,e’K + ) reaction in JLab

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Hypernuclear spectroscopy up to medium mass region through the (e,e’K+) reaction in JLab Mizuki Sumihama For HKS collaboration Department of Physics Tohoku university 2006 HNP

  2. Physics motivation…

  3. p L n L hypernuclei • LNinteraction • Unified view of baryon-baryon interaction by • including new degree of freedom, strangeness. • Central and spin-dependentLNinteraction. • much smaller than NN interaction. • ex) VLN (~30 MeV) < VNN (~50 MeV) • Unique structure of • hadronic many-body system • Deeply bound states, no Pauli blocking. • Core excited states. • Glue role of aLhyperon in nucleus. Narrow widths of excited states High precision spectroscopy is necessary

  4. Physics issues • 12C 12LB • Precision analysis of core excited states. • p orbit states splitting? • Comparison with the mirror hypernucleus, 12LC (KEK/SKS). • 28Si  28LAl • The first precision spectroscopy beyond the p-shell. • ls splitting in the p, d orbits? • Other targets (6,7Li, 9Be, 10,11B, 51V, 89Y). • Rate study for heavier targets for next exp. • p-shell spectroscopy. • Target mass dependence --- quasifree K+ electroproduction.

  5. p K+ g* e- beam e’ Target nucleus Basic characteristics of (e,e’K+) spectroscopy • Hadron (K or p) beam –BNL/AGS, KEK/SKS..: • Large cross section, • Energy resolution ~ 1.45 MeV, • limited by energy resolution of beam. • Electron beam : • Small cross section, • recovered by high intensity • continuous e beam in JLab. • 400 keV (FWHM) • energy resolution.

  6. The (e,e’K+) reaction • Proton converted to L • Charge symmetry • Neutron rich L hypernuclei • Large momentum transfer Similarly to (p+,K+) reaction • Spin-flip amplitude  Unnatural parity hypernuclear states • 400 keV resolution  High quality primary beam

  7. Previous Experiment…

  8. (1-,2-) (2+,3+) 90 80 (1-,0-) 70 (2-,1-) 60 50 40 -15 -10 -5 0 5 10 15 12LB spectrum of previous exp. Ground state doublet Binding energy BL = 11.4±0.5 MeV Emulsion data BL = 11.37 MeV 1 month Cross section 140±17(stat) ±18(sys) nb/sr ds/dW nb/sr/0.3 MeV Motoba’s calculation 138 nb/sr More statistics and better resolution are required to see more precise structure of core-nucleus excited states. -BL(MeV)

  9. First experiment of X(e,e’K+)LX • Existing Kaon spectrometer in JLab/HallC the energy resolution - 750keV • 0 degree tagging geometry. large backgrounds of electrons/positrons from pair creation. only 1.6 mA beam current with 12C target. • Required improvements for the new experiment. • 1. Reduce the accidental rate in e’ spectrometer. • 2. Improve the energy resolution of Kaon spectrometer.

  10. Improvement in present experiment • New Kaon spectrometer –HKS 200 keV  400 keV (old) in total 400 keV  750 keV (old). • Tilt e’ spectrometer to avoid 0 degree. Tilted angle 7.75o Decrease singles rate  improve signal to accidental ratio. be able to increase beam current.

  11. Present experiment.

  12. Experimental setup e beam e’ K+ Enge HKS

  13. Experimental setup

  14. New spectrometer High resolution Kaon Spectrometer -HKS Configuration Q+Q+D Momentum range 1.0 – 1.4 GeV/c Momentum resolution 2 x 10-4 (FWHM) Dispersion 4.7 cm/% Solid angle 16 msr Momentum acceptance 12.5 % Dipole Q1 Q2 Made in Japan。

  15. HKS detector –Kaon trigger Aerogel cherenkov (n=1.05)  pion rejection 1X 1Y AC 2X WC K+ Dipole Water cherenkov (n=1.33)  proton rejection DC1 DC2 Drift chamber (uu’xx’vv’ wire)  x, x’, y, y’ Plastic scintillator  time-of-flight

  16. Tilt angle of Enge (e’ arm) Accepted region. 7.75 degree Side view

  17. Tilted Enge spectrometer 7.75 degree

  18. Enge detector • 2 layers of hodoscope detect charged particle (e’) make trigger, timing at focal plane. • Drift chamber 10 planes, xx’,uu’,xx’,vv’,xx’ measure positions/angles, x,x’,y,y’ at focal plane.

  19. Data summary • Target 6Li, 7Li, 9Be, 10B, 12C, 28Si, 51V, 89Y, 208Pb, CH2 calibration data / physics data / trigger study • Electron Beam Intensity, I ~ 26 mA for 12C 18 mA for 28Si Energy stability ~ 50 keV

  20. Trigger condition • HKS (Kaon trigger) ---1.2 x 104 Hz 1X x 1Y x 2X x AC x WC ( 1X x 2X : 1.1 x 106 Hz ) Rejection rate by AC / WC is 1/100 • Enge (e’ trigger) ---1.2 x 106 Hz ( 1 x 108 Hz) Hodoscope 1layer x 2layer • Coincidence of K and e’ --- ~500 Hz DAQ dead time ~5% *Rates are with 12C target (100 mg / cm2), 26 mA Previous exp.

  21. Previous vs. Present experiment Old : New • Beam intensity, 1.6 mA : 26 mA • Target thickness, 22 mg/cm2 : 102 mg/cm2 Luminosity, 1 : ~75 • Singles rate of e’ arm, >100 MHz : 1.2 MHz ~10-2 (Coincidence trigger 500 Hz with 5% dead time) • Kaon acceptance, 6 msr : 16 msr • Energy Resolution, 750 keV : 400 keV Kaon arm (Dp/p), 5x10-4 : 2x10-4 Tilt method is quite useful!

  22. Data analysis…

  23. Detector performance Enge (e’ detection) • Drift chamber Position resolution s = 300~370 mm Detection efficiency, ~99% • Hodoscope s~150 ps HKS (K+ detection) • Drift chambers • Position resolution • s~220 mm • Detection efficiency • ~98% • TOF counters s~180 ps • Aerogel cherenkov (veto p) index = 1.05 efficiency > 98% • Water cherenkov (veto p) index = 1.33 efficiency > 98%

  24. Water and aerogel cherenkov Veto conditions are loose in trigger. btof-bK btof-bK Reject pions K+ p K+ p p Off-line analysis Reject protons Sum of WC npe Sum of AC npe Aerogel : Reject pions Water : Reject protons

  25. Time-of-flight • Average TOF resolution : TOF = 1X –2X, 180 ps p K p btof – btrack After cherenkov cut p K p

  26. Coincidence time • Reconstruct timing at target • from timing at detector position. • From coincidence time, select true • Coincidence events (reject accidental events) K+ time at HKS e’ time at Enge Target Beam bunch 2ns (499MHz)

  27. Ratio of true / accidental in coincidence time Previous experiment Present experiment s ~300 ps S/N Improved! With 1mA, CH2 target With 1.5mA, CH2 target

  28. Kaon PID coincidence time (ns) p btof – btrack K p

  29. Target (mg/cm2) p [kHz] K [Hz] π [kHz] e+ [kHz] 12C(100) 21 150 11 4 28Si(65) 32 130 11 11 Particle and Trigger Rate HKS single arm particle rate at 30 uA Trigger rate Beam Current (uA) HKS single (KHz) Enge Single (MHz) Coin (Hz) Target 12C 30 14.8 1.3 740 28Si 18 15.3 1.6 910 89Y 13 15.4 1.8 1040

  30. Calibration data for spectrometer optics • Need new optics parameters for both arms. Enge is tilted. HKS is new. • Angle calibration. Data with sieve slits were taken. • Momentum calibration. p(e,e’K+)L/S0 reactions wirh CH2 target L, S0 masses are well known. 12LB ground state binding energy was measured in the previous experiments.

  31. Calibration data from the p(e,e’K+)L/S0 reactions Previous experiment Present experiment s~930 keV L S/N Improved! 12C(e,e’K+) quasi-free S0 Accidental 210 Lambdas 2000 Lambdas

  32. Coincidence time with 12C target, 26 mA True Accidental Coincidence time (ns)

  33. Carbon (12LB) data s-shell p-shell Very preliminary Accidental events ~ 500 counts (~10/hr) ~2 MeV(FWHM) (Previous exp. 165 counts with 900 keV. HallA 300 counts with 700 keV.)

  34. Coincidence time with 28Si target True/accidental ~ 2 True Accidental Coincidence time (ns)

  35. Summary • Experiment was carried out in JLab/HallC by using ‘tilted ENGE’ and ‘new spectrometer HKS’. • Comparing with the previous experiment, the accidental rate decreases dramatically. We took data with 26 mA for 12C and 18 mA for 28Si. • Physics run with Si target. About 214 hrs. • L/S0 peaks and 12LB ground state are observed. Optics study is in underway. • The data will provide medium-heavier hypernuclear spectra with good statistics and good resolution ever achieved.

More Related