Hypernuclear gamma-ray spectroscopy at J-PARC K1.8 Beam line Tohoku Univ. K.Shirotori 東北大学 大学院理学研究科 白鳥昂太郎

2006 JPS in NARA2 Outline  Background of experiments  Requirement on setup  Setup, SKS & Hyperball-J  Detectors in detail, SKS & Veto counters  Summary

2006 JPS in NARA3 Previous hypernuclear gamma-ray experiments Investigation of ΛN interaction by Λ hypernuclei. (π +, K + ) KEK  Good spectrometer SKS (Momentum resolution ～ 1MeV/c)  Low background  Low production rate (K -, π - ) BNL  High production rate  Spectrometer is worse than KEK  Large Background from Beam K - decay Systematic studies of several hypernuclei → J-PARC High production rate +Background rejection Good spectrometer

2006 JPS in NARA4 Proposed “DAY-1” experiment E13  Several light hypernulcear gamma-ray spectroscopy experiments are planed. ( 4 Λ He, 7 Λ Li, 10 Λ B, 11 Λ B, 19 Λ F)  (K -, π - γ) at p K = 1.5 GeV/c (500k/spill) (Out going π - ～ 1.4 GeV/c)  Magnetic spectrometers for (K -, π - ) detection  Hyperball-J for Gamma-ray measurement

2006 JPS in NARA5 HyperBall-J or HyperWall-J Wall TypeBall Type  Single Ge (r.e.70%) ～ 30  PWO background suppression for higher counting rate  Waveform readout LN2 cooling ↓ Mechanical cooling by Pulse tube Target Total photo peak efficiency 1MeV (Geant4 simulation)

2006 JPS in NARA6 Requirement on spectrometer for hypernuclear gamma-ray spectroscopy  To analyze 1.4GeV/c-scattered π - by existing spectrometer system.  Large acceptance ～ 100[msr], θ ～ 20[degree]. →Enough hypernuclear production yield.  Good momentum resolution 2 ～ 4[MeV/c]. →To distinguish excited states of hypernuclei. Modify SKS (Superconducting Kaon Spectrometer )

2006 JPS in NARA7 The K1.8 Beam line and SKS Beam spectrometer ・ BH1,2 : Time-of-flight ・ BAC : π - veto (n=1.03) SKS ・ SAC : K - beam veto (n=1.03) ・ SFV : K - beam veto ・ STOF : Time-of-flight Target : ～ 20 g/cm 2 MWPC & DC : Beam position measurement Background Veto ・ SMF : μ - from K - →μ - +ν ・ SP0 : π - from K - →π - +π 0 Hyperball-J : γray Beam spectrometer SKS

2006 JPS in NARA8 Present SKS to New SKS Momentum resolution 0.1%FWHM ( 0.72 MeV/c 720 MeV/c, 2.2T Maximum central momentum T Acceptance GeV/c θ ～ 20° 2.2T  Scattered particles are not focused and present drift chambers (SDC3,4) are small for large reaction angle (half acceptance). →Large acceptance by large drift chambers  Smaller bending angle(100°→60°) →Momentum resolution gets worse.

2006 JPS in NARA9 Present SKS to New SKS Momentum resolution 0.1%FWHM ( 0.72 MeV/c 720 MeV/c, 2.2T Maximum central momentum T Acceptance GeV/c Parallel scattering 2.7T θ ～ 20°  Scattered particles are not focused and present drift chambers (SDC3,4) are small for large reaction angle (half acceptance). →Large acceptance by large drift chambers  Smaller bending angle(100°→60°) →Momentum resolution gets worse.

2006 JPS in NARA10 Present SKS to New SKS 2.7T  Scattered particles are not focused and present drift chambers (SDC3,4) are small for large reaction angle (half acceptance). →Large acceptance by large drift chambers  Smaller bending angle(100°→60°) →Momentum resolution gets worse. θ ～ 20°

2006 JPS in NARA11 Present SKS to New SKS SBS K - beam directly hit SDC3,4. ↓ Scattering beam particles by heavy material (Pb, W) 20mm cell  Scattered particles are not focused and present drift chambers (SDC3,4) are small for large reaction angle (half acceptance). →Large acceptance by large drift chambers  Smaller bending angle(100°→60°) →Momentum resolution gets worse.

2006 JPS in NARA12 SKS : New configuration SKS ・ SAC : K - beam veto (n=1.03) ・ SFV : K - beam veto ・ STOF : Time-of-flight DC : Beam position measurement Background Veto ・ SMF : μ - from K - →μ - +ν ・ SP0 : π - from K - →π - +π 0 Beam K π

2006 JPS in NARA13 SKS Acceptance & Momentum resolution  Acceptance ～ 120[msr] with large drift chambers (2[m]×1[m]) 100[msr] for present SKS  Momentum resolution 2.1[MeV/c] (bending angle ～ 60° w/ multiple scattering) 0.8[MeV/c] for present SKS Simulation program is checked against previous SKS configuration SKS performance is sufficient for hypernucler gamma-ray spectroscopy

2006 JPS in NARA14 Background rejection  K - →μ - ν (63.4%) ⇒ Muon Filter  K - →π - π 0 (21.1%) ⇒ PiZero Veto Beam K - decay products make serious background K - →π - π - π + (5.58%) K - →e - π 0 ν (4.87%) K - →μ - π 0 ν (3.27%) K - →π - π 0 π 0 (1.73%) Contribution is relatively small ～ 150 trigger Fake trigger ～ 1700/spill True event trigger ～ 700/spill Beam K BACSAC Target 20cm μ νDecay

2006 JPS in NARA15 Muon Filter Thick Material (ex. Iron) μ-μ- π-π- Scintillation counter Scintillation counter Only μ- can be detected. Stopped by hadronic interaction Pass through

2006 JPS in NARA16 Muon Filter After Before  89% of μ can be detected in the trigger  In the offline analysis ～ 100%  Over kill for true π ～ 1.7%

2006 JPS in NARA17 PiZero Veto  70% of π 0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of γ from π 0 hit the SP0) Simulation in progress Before After

2006 JPS in NARA18 Trigger rate  (K -,π - ) Reaction rate ～ 700/spill  K - →μ - ν ～ 1320/spill  K - →π - π 0 ～ 390/spill  K - Beam ～ 10/spill  3-body decay ～ 150/spill ～ 2570/spill w/o Veto counters True trigger ～ 350/spill w/ Ge trigger and fake trigger greatly decreased.  (K -,π - ) Reaction rate ～ 700/spill  K - →μ - ν ～ 140/spill  K - →π - π 0 ～ 120/spill  K - Beam ～ 10/spill  3-body decay ～ 150/spill ～ 1130/spill w/ Veto counters ～ 500/spill w/ Ge trigger (K -, π - γ) at p K = 1.5 GeV/c (500k/spill) Comparable to the present trigger rate

2006 JPS in NARA19 Summary  Several hypernulcear gamma-ray experiments are planed at the J-PARC K1.8 beam line.  SKS is sufficient for hypernuclear gamma- ray spectroscopy.  Simulations in progress show a good veto counter efficiency.  Estimation of background from heavy counter materials is necessary.

Backup

2006 JPS in NARA21 Rough Kawazanyou (compared with BNL E930)  Beam 200k/spill→500k/spill : 2.5 times  Acceptance 60[msr]→120[msr] : 2 times  Hyperball 2.5%→6% : 2.4 times  S/N : 2 times  Cross section 1/3 times (0.9→1.5GeV/c) → 8 times

2006 JPS in NARA22 Proposed “DAY-1” experiment E13  Spin-flip B(M1) measurement and g Λ in a nucleus 7 Λ Li : Least ambiguities exist and most reliable  ΛN interaction study from p-shell hypernuclei 10 Λ B and 11 Λ B : Inconsistency exists. Not enough experimental data  Radial dependence of ΛN interaction from sd-shell hypernuclei 19 Λ F : Simplest in sd-shell  Spin-flip property in hypernuclear production 4 Λ He : Easiest to observe a spin-flip state (K -, π - γ) at p K = 1.5 GeV/c (500k/spill)

2006 JPS in NARA23 Beam Momentum    n  

2006 JPS in NARA24 ΛN effective interaction V(r) = V 0 (r) + V  (r) s N ・ s  + V N (r) l N  ・ s N + V  (r) l N  ・ s  + V T (r) S 12 (Core nucleus ： p-shell 、 Λ ： s-shell) →  Radial Integrals  、 S N 、 S  、 T are determined by previous experiments  = 0.43 S N = S  = T= 0.03 [MeV] Some inconsistencies appear ! Ex. 10 Λ B puzzle → Theory fails to predict energy spacing of ground state doublet To solve these problems and for systematic studies of several hypernuclei → J-PARC

2006 JPS in NARA25 SKS Minus  Time-of-flight : STOF  Position measurement : SDC1 ～ 4  Beam veto : SAC  Beam veto : SFV  Veto counter, μ - from K - →μ - +ν : SMF  Veto counter, π - from K - →π - +π 0 : SP0

2006 JPS in NARA26 Time resolution  Flight time ～ 16[ns]  Path length ～ 4.6[m]  Momentum P k =1.5 GeV/c (ΔP/P=1.4x10 -4 ) P π form (K, π) reaction (ΔP/P=6.3x10 -4 )  Present TOF → 300[ps] w/o PHC  Present BH1,2 → 200[ps] w/ PHC

2006 JPS in NARA27 Beam Veto  SAC efficiency ～ 99% →5k trigger 500k/spill SFV → ～ 10 trigger Reduction of acceptance 7.5%  Beam size σ x =19.8[mm] σ y =3.2[mm] (u=0.02, v=0.002) SBS  SBS K - beam directly hit SDC3,4. ↓ Scattering beam particles by some material (Pb, W) 20mm cell

2006 JPS in NARA28 3-body Decay K - →π - π - π + (5.58%) K - →e - π 0 ν (4.87%) K - →μ - π 0 ν (3.27%) K - →π - π 0 π 0 (1.73%)

2006 JPS in NARA29 Muon Filter  89% of μ can be detected in the trigger  In the offline analysis ～ 100%  Over kill for true π ～ 1.7% After Before

2006 JPS in NARA30 Muon Filter

2006 JPS in NARA31 Iron thickness

2006 JPS in NARA32 PiZero Veto  70% of π 0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of γ from π 0 hit the SP0) Simulation in progress After Before

2006 JPS in NARA33 PiZero Veto  70% of π 0 can be detected by 2 set of 2[cm] lead plate and scintillation counter layer. (75% of γ from π 0 hit the SP0) Simulation in progress After Before Beam K

2006 JPS in NARA34 Percentage of decay in target 25cm

2006 JPS in NARA35

2006 JPS in NARA36 Λ Hypernucleus Λ h ypernucleus → Λ is bound in a nucleus The Baryon which is different from nucleons (p/n) N-N interaction → B-B interaction Deeply bound in a nucleus w/o Pauli effect The property of baryon changing in the nuclear medium  strangeness S= -1  M= MeV  J  =1/2 +  I=0  Mean life=263.2 ps Λ Nucleus Λ hypernucleus

2006 JPS in NARA37 Λ Hypernucleus The Baryon which is different from nucleons (p/n) N-N interaction → B-B interaction Deeply bound in a nucleus w/o Pauli effect The property of baryon changing in the nuclear medium Systematic studies of several hypernuclei → J-PARC Λ Hypernucleus ⇔ ΛN effective interaction

2006 JPS in NARA38 Level scheme of 7 Λ Li

2006 JPS in NARA39 Calculated cross section for 7 Λ Li

2006 JPS in NARA40 B(M1) mesurement