Study on Λ-hypernuclei at J-PARC with intense pion beams

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1 Study on Λ-hypernuclei at J-PARC with intense pion beams S.Ajimura, H.Bhang, L.Busso, D.Faso, T.Fukuda, T.Kishimoto, Y.Mizoi, O.Morra, H.Noumi, H.Outa, P.K.Saha, A.Sakaguchi, T.Takahashi Osaka, Seoul, Torino, INFN, OsakaEC, INAF-IFSI, KEK, RIKEN, JAEA Collaboration

2 1-2 June, Motivation Intense kaon beams will be available beam intensity is a few X 10 6 kaons/spill with 30GeV, 9μA primary proton beams Provide us also very intense pion beams roughly X1000 higher than kaons a few X 10 7 pions/spill with conventional detectors one order higher than experiments in the past experiments with intense pion beams available even at the beginning of J-PARC

3 1-2 June, Hadron Experimental Hall K1.8 and SKS

4 1-2 June, K1.8 beam line and SKS High intensity π beams (<1.8GeV/c) beam intensity ~10M π-/spill SKS spectrometer move KEK J-PARC Excellent resolution Large acceptance

5 1-2 June, Proposing 2 experiments at J-PARCJ E10 and E22 Production of neutron-rich hypernuclei Double Charge-eXchange (DCX) reaction NCX π + K + DCX π - K + n Λ p p n Λ Study on non-mesonic weak decay Weak decay of A=4 hypernuclei ( 4 Λ He, 4 Λ H) Precise determination of decay amplitudes Neutron-rich rich HY

6 1-2 June, Λ-hypernuclei E10: Neutron-rich hypernuclei N~Z (I=0 or 1/2) Non Charge-Exchange ( K, π ) ( π +, K + ) ordinary nuclei hyperfragments by emulsions exp. N>>Z (I=3/2 or 2) KEK-E521 E521 this proposal ( K, π + ) ( π, K + ) Double CX suggest by Majling

7 1-2 June, Exotic Λ-hypernuclei p Example of hydrogen n 1 H Stable 2 H Stable 3 H Stable Super Heavy Hydrogen 4 H No evidence 5 H Resonance 6 H No evidence Λ 2 Λ H Not bound 3 Λ H Stable 4 Λ H Stable glue like role of Λ 5 Λ H No evidence 6 Λ H Stable? 7 Λ H Stable? We can produce at J-PARC Hyper Heavy Hydrogen

8 1-2 June, Yield estimation: 9 He production Λ Cross section ~10nb/sr (1/1000 of NCX) Major difficulty in this experiment Parameters π - beam momentum π - beam intensity PS acceleration cycle 9 Be target thickness Reaction cross section Spectrometer solid angle Spectrometer efficiency Analysis efficiency Values 1.2 GeV/c 1 x 10 7 /spill 3.4 s/spill 3.5 g/cm 2 10 nb/sr 0.1 sr events in 3 weeks 7 times larger KEK-E521 (47 events) Discussion on level structure possible High intensity beams Large acceptance

9 1-2 June, NNN NNN E22: Non-mesonic weak decay N π Mesonic weak decay (MWD) similar with free decay of Λ Λ properties are predictable I=0 or 1 N N Λ 3 S 1 / 1 S 0 Non-Mesonic weak decay (NMWD) new decay mode in hypernuclei proton- and neutron-stimulated Λp np, Λn nn properties are not well known yet

10 1-2 June, Decay amplitudes Block and Dalitz approach Initial Λ-N in S-wave (s-shell hypernuclei) Introduced 6 independent amplitudes (a ~ f ) spin Initial spin ( 1 S 0 or 3 S 1 ) Final isospin (0 or 1) Parity change (yes or no) isospin parity Branching Ratios S S S 0 ( 1 ( 1 ( I I I = 1) = 0) = 1)

11 1-2 June, Status of amplitudes Status of measurements A=4 and 5 ( 4 ΛH, 4 ΛHe, 5 ΛHe) strong constraint from 5 Λ He other constraints are loose Our prospects Our prospects new measurement of 4 ΛHe np-ratio with 15% accuracy

12 1-2 June, Estimation of 4 He Yield Λ Important factor in design of experiment Tiny branching ratio of Λn nn channel BR( 4 ΛHe,Λn nn) ~ 0.01 (?) BR( 4 ΛHe,Λp np) = 0.16±0.02 Produce 4 ΛHe as much as possible use 4 He(π +,K + ) 4 ΛHe reaction (dσ/dω~10μb/sr) high intensity pion beams (K1.8 beam line) large acceptance spectrometer (SKS) 19,000 4 ΛHe/day 0.5M 4 ΛHe in 4 weeks

13 1-2 June, Setup for decay measurement Large acceptance and high efficiency for NN Good PID capability (n/p/π/γ) n n p p neutron : Ω / 4π 0.4, ε 30% proton : Ω / 4π 0.25, ε 80%

14 1-2 June, Estimation of yield of NMWD Parameters Acceptance for decay proton Acceptance for decay neutron Efficiency for proton Efficiency for neutron Branching ratio of Λp np process Branching ratio of Λn nn process Values large acceptance and high efficiency 1,300 Λp np and 75 Λn nn in 4 weeks in case of 10% BR in case of 1% BR We can achieve 15% statistical error

15 1-2 June, Summary Experiments with intense pion beams Feasible even very early stage of Day-1 Two experimental proposals Production of neutron-rich hypernuclei New neutron-rich hypernuclei ( 9 Λ He and 6 Λ H) Information on ΛN interaction in n-rich hypernuclei Production of exotic hypernucleus 6 Λ H Study on non-mesonic weak decay Detailed study on A=4 hypernuclei ( 4 Λ He and 4 Λ H) Precise determination of decay amplitudes