JLab における (e,e'K + ) 反応を用い た 精密ラムダハイパー核分光実験 東北大学理学研究科 後神 利志 Toshiyuki Gogami Strangeness 2010 at KEK JLab Hall-C

Contents Introduction – (e,e’K + ) – JLab, CEBAF JLab E experiment – Motivation – Setup – Analysis Summary Strangeness 2010 at KEK

Spectroscopic experiment via (e,e’K + ) reaction p n γ*γ* Λ K+K+ e-e- e + p ➝ e’ + K + + Λ ee M 2 HY = (E e + M T - E K+ - E e’ ) 2 - ( p e - p K+ - p e’ ) 2 measure target nucleus Feynman diagram u u d u s s u d – p K+K+ Λ γ*γ* Missing mass : Binding energy Cross section

(e,e’K + ) reaction u u d u s s u d ee – p K+K+ Λ γ*γ* u d d d u u s s d u ––π+π+ Λ n u s d d u u d s d u – K-K- Λ n – π-π- e + p ➝ e + K + + Λπ + + n ➝ K + + Λ K+K+ K - + n ➝ π - + Λ (π +, K + )(K -, π - )(e,e’K + ) Momentum transfer (Typical ) ~300 [MeV/c] ~90 [MeV/c] Λ’s Spin At forward angle Λ’s from proton neutron flip ≈ non-flip non-flip Beam primary secondary Target Thin (~100 mg/cm 2 ) (Isotopically enriched) Thick(> a few [g/cm 2 ] ) Reaction Λ can be bounded in deeper orbit Spin dependent structure Mirror lambda hypernuclei High quality, high intensity Fine structure Energy resolution (FWHM) ≤ 500 [keV]1 – 3 [MeV]

JLab CEBAF ( Continuance Electron Beam Accelerator Facility ) (e,e’K + ) experiment 1.Coincidence experiment (K + and e - ) 2.Small cross section ( ~100 [nb/sr] ) 1/ Energy resolution sub MeV (FWHM) 22 nd Indian-summer school (SNP2010) 100 [m] Requirement for accelerator 1.high duty factor 2.high intensity 3.small emittance small ΔE/E CEBAF can satisfy these requirements Thomas Jefferson National Accelerator Facility

(e,e’K + ) experiment in JLab Hall-C Strangeness 2010 at KEK 2000 年 1 st generation exp. JLab E ENGE(e’) + SOS(K + ) 12 Λ B ~ 900 [keV] (FWHM) 2005 年 2 nd generation exp. JLab E ENGE(e’) + HKS(K + ) + Tilt method 7 Λ He, 12 Λ B, 28 Λ Al ~ 500 [keV] (FWHM) 2009 年 3 rd generation exp. JLab E HES(e’) + HKS(K + ) + Tilt method 7 Λ He, 9 Λ Li, 10 Λ Be, 12 Λ B, 52 Λ V ≤ 500 [keV] (FWHM) Luminosity ×137 e’ rate 1/200 S/N ×2.7 Proof of feasibility Establish exp. method Medium heavy

E experimental motivation (1) p-shell( 7 He, 9 Li, 10 Be, 12 B) Charge symmetry breaking Λ-Σ coupling Medium heavy ( 52 V) s-,p-,d-,f-orbit binding energy & cross section Mass dependence of Λ single particle energy l ・ s splitting ∝ 2l Aug – JLab Hall-C (e,e’K + ) reaction Target : 7 Li, 9 Be, 10 B, 12 C, 52 Cr ΛΛ ΛΛ Λ First try B Λ [MeV] It is difficult experimentally. “ b.g. electron due to brems. ∝ ~Z 2 “ A = 52

E experimental motivation(2) 22 nd Indian-summer school (SNP2010) s p d f Photo- and electro production of medium mass Λ-hypernuclei,P.Bydzovsky et al. (2008) FULL(8) 1f 7/2 1d 3/2 FULL(4) ・ ・ ・ ・ ・ ・ s n = 28p = 24 p d f Λ 52 Λ V 52 Cr or ls splitting ∝ 2l+1 ls splitting Core excited

JLab E experimental setup Strangeness 2010 at KEK 2× [msr] 3 – 12 [deg] 2× [msr] 2 – 12 [deg] e + p → e’ + Λ + K + 7 Li, 9 Be, 10 B, 12 C, 52 Cr

HKS detectors Strangeness 2010 at KEK K + p, π + Drift chambers -KDC1,KDC2- TOF walls -2X,1Y,1X- (Plastic scintillators) Cherenkov detectors -AC,WC- Aerogel (n=1.05) Water (n=1.33) 1 [m] June 2009 in JLab Hall-C HKS trigger CP = 1X ×1Y × 2X K = WC × AC  CP × K ~18 [kHz] (8 [μA] on 52 Cr) − π+π+ K+K+ p σ ≈ 250 [μm] TOF σ ≈ 170 [ps]

Strangeness 2010 at KEK HES Detectors Drift chambers - EDC1, EDC2 - TOF walls - EH1, EH2 - (Plastic scintillators) HES D magnet HES trigger EH1 × EH2 ~2 [MHz] (8 [μA] on 52 Cr) e Time Of Flight σ ~ 300 [ps]

TargetHypernucleusThickness [mg/cm 2 ] BeamTypical rate HES/HKS/COIN [kHz] Current [μA]Total charge[C] 7 Li 7 He / 7 / Be 9 Li / 9 / B 10 Be / 1 / C 12 B / 5 / Cr 52 V / 17 / 1.8 Data summary 22 nd Indian-summer school (SNP2010) Λ Λ Λ Λ Λ E ( 2009 Aug – Nov ) TargetHypernucleusThickness [mg/cm 2 ] Beam Current[μA]Total charge[C] CH 2 Λ, Σ H2OH2OΛ, Σ 0 ~ Physics Data Calibration Data

Analysis process tracking x, x’, y, y’ at Reference plane x’, y’, p at target Missing Mass tracking x, x’, y, y’ at Reference plane x’, y’, p at target F2T function particle ID (select K + ) HKS HES tune [mg/cm 2 ] 2.0 [μA] 38 [hours] σ = 2 [MeV/c 2 ] (NOT TUNED) p(e,e’K + )Λ p(e,e’K + )Σ 0

Tracking for high multiplicity Strangeness 2010 at KEK CH 2 target particle CH 2 target mean ~ 2 hit 52 Cr target mean ~ 6 hit 52 Cr target particle KDC1 tracking Blue : selected wires Black: hit wires Multiplicity of typical layer Multiplicity Tracking eff. 52 Cr CH 2 Developing new code Traditional JLab Hall-C tracking code cannot handle with high multiplicity data.

Summary 3 rd generation exp. E experiment – 2009 Aug – Hall C – 7 He, 9 Li, 10 Be, 12 B, 52 V – Spectrometers and Detectors work well – Now analyzing Tracking for high multiplicity first try to measure Λ-hypernuclei up to A=52 via (e,e’K + ) ΛΛΛΛΛ

END ありがとうございました Strangeness 2010 at KEK