Decay pion spectroscopy of electro- produced hypernuclei Tohoku Univ. Kyo Tsukada APFB Aug, 2011 Seoul, Republic of Korea 1

2  Introduction 1. Hypernucleus 2. Concept of decay pion spectroscopy 3. Physics of decay pion spectroscopy

Hypernucleus  Nucleus  many-body system of proton and neutron  Hypernucleus  Hyperon (Y=  here) in a nucleus  a new degree-of-freedom, “strangeness”,   can be introduced deep-inside nucleus (no Pauli effect)  energy level can be measured directly  Y-N interaction can be investigated  Impurity effect for nucleus; shrinkage, clustering, deforming, … n p  Y-N interaction should be investigated carefully and precisely for light hypernuclei. high resolution, high accuracy various nuclei ; wide range, new finding N-N interaction 3

measurements of  (Y) Hypernucleus  e -, π +, K - (e - ’ K + ), K +, π - reaction spectroscopy (B ,mass) JLab MAMI J-PARC γ -ray γ -ray spectroscopy (level splitting) J-PARC emulsion (  ) (mass) J-PARC weak decays (  -, NN)   spectroscopy (mass) JLab MAMI We can measure the mass of various hypernucei by using completely different way with past experiments. examples of processes 4 , p

  spectra of past experiments  It is difficult to achieve both high statistics and resolution. KEK-E287, E326 beam : stop K - target : 7 Li 7 Λ Li 11 Λ B FINUDA Coll. and A. Gal et al., Phys Rev. B 681 (2009) 139 A. Gal, Nucl. Phys. A 828 (2009) 72 high rate and high quality primary electron beam ( Hz, 100  m  ) + thin target ( ̴ 10 mg/cm2) decay   spectroscopy with high resolution and high accuracy 5

e  beam Concept of decay pion spectroscopy Λ p π-π- pion spectroscopy Kaon tag two body decay after stop ] ] Absolute mass of various  hypernuclei pion momentum resolution ̴ 100 keV/c -> mass resolution ̴ 100 keV goal of accuracy ̴ a few 10 keV Fragments 6

Hypernuclei from 9 Be target break-up modeQ value (MeV)  - decay p  (MeV/c) 9  Li- 9 Be +  p + 8  He Li +  n + 8  Li Be +  p + 7  H (B  =6.1) 7 He +  d + 7  He Li +  n + 7  Li Be +  He + 6  H (B  =5.1) 6 He +  H + 6  He Li +  n + 6  Li Be +   + 5  H (B  =4.1) 5 He +  n +  + 4  H He +  He + 3  H He +  Other targets, 7 Li or 12 C or so, should be measured in future. 7

Physics of decay pion spectroscopy  High resolution and accuracy of mass for various light hypernuclei  3  H, 4  H, …, 11  B, 12  B, i.e. A=3-12  Spin-parity (J P ) of the ground state  Charge symmetry breaking (CSB)  ( 4  H 4  He), ( 6  He 6  Li), ( 7  He 7  Li * 7  Be), …  Search for hypernucleus near the neutron drip line  6  H, 7  H, 8  H …  important information for  coupling  … 8

9  Experiment 1. Facilities 2. Experimental apparatus 3. Estimations 4. Run summary 5. Some analysis plots of present conditions

Electron beam facility 10 MAMI-C JLab CEBAFMAMI-C (2006~) Beam energy6.0 GeV1.508 GeV Beam Intensity100 μ A~ 60 μ A Beam size~ 100 μ m (rms) We started the feasibility study for the decay pion spectrometer experiment at Mainz in this year.

MAMI-C (Mainz Microtron) KAOS Spec-ASpec-B Spec-C beam Mainz Frankfurt ̴ 20 km southwest from Frankfurt A1 collaboration 1 st beam time : 24/May/ /Jun/2011 KAOS and SpekC 2 nd beam time : 19/Jul/2011-1/Aug/2011 KAOS and SpekA+SpekC 3 rd beam time : near future 11

spectrometers for decay  spectroscopy KAOS SpekC SpekA target SpekA SpekC Beam dump pre-target beam chicane MeV beam energy -zero-degree kaon tagged by KAOS -decay-pion detection with Spectrometer A & C (  p/p <10 -4 ) Spec A Spec C KAOS Solid Angle28 msr12 msr Ang. accept. (disp)±4 o ±10 o Mom. accept.25 %50 % Δ p/p<10 -4 ~ Path length12 m5.3 m angle wrt beam [degree] Central momentum (1st run) -115 MeV/c 1000 MeV/c Central momentum (2nd run) 125 MeV/c 115 MeV/c 1000 MeV/c 12 2m K+K+  

KAOS KAOS Magnet AC Tagger G-Wall H-Wall G-Wall H-Wall MWPC 13 beam Trigger=H ⊗ G ⊗ Tagger  Some detectors were newly introduced.  TOF wall (H-Wall)  Aerogel Cherenkov detectors (AC)  n =  Tagger counters

Yield estimation  Model : Statistical decay model  Elementary cross section :  b/sr  Initial excited hypernucleus formation prob. : 0.7  Hyperfragment stopping fractions : 0.87  Two-body decay branch :  Spectrometer acceptance : 28msr(SpekA,C), 12msr (KAOS)  Particle decay fractions in flight : 0.2 for  , 0.3 for K + 9 Be target Kaon emission rate : Hz/  A Coincidence rate : hyperfragments/day/  A 14 Phys.Lett.B697 (2011) 222

Peak positions and momentum acceptance 15

Run summary 16 1 st Beam Time2 nd Beam Time Date24/May/ /Jun/201119/Jul/2011-1/Aug/2011 PurposeRate studysame Detector performancenew setup of aerogel counter Trigger optimizationsame Physics datasame Target 9 Be 125um [22.5mg/cm 2 ]same Beam intensity1.5 uA (113 hours, phys. data)2.0uA (190 hours, phys.data) 2.0 uA (23 hours, phys. data) expected yields Kaon emission rate : Hz/  A Coincidence rate : hyperfragments/day/  A

Huge accidental positrons at KAOS 17 y-distribution at G-Wall [mm] Covered by Tagger Covered by Tagger The large acciedental events caused by positrons exists. Singles rate : 3MHz for G-Wall (H-Wall) for I=2.0uA We should avoid and/or remove positron efficiently. accidental positron 1 st + 2 nd polinomial 2 nd polinomial 1 st polinomial

Analysis  Analysis is ongoing.  Particle identification for KAOS and SpekA,C  Momentum reconstruction  Trace-back of particle tracks to target 18 π-π- µ-µ- e-e- time [nsec]  t=10.6ns (11ns for 110MeV/c)  t=7.5ns (6.5ns for 110MeV/c) proton e+,e+, KAOS SpekC

summary  High resolution decay pion spectroscopy for light hypernuclei was proposed.  Mass resolution : ~100 keV  Mass accuracy : ~10 keV  Many light hypernulei including exotic states can be studied via the break-up of highly excited-states.  The 1 st and 2 nd commissioning run were performed at Mainz and the analysis is ongoing now.  The detectors should be improved in order to take data more efficiently with higher beam current. 19

backup 20

Charge symmetry braking (CSB) for 4-body particleDecay mode No of events B Λ (MeV) 4ΛH4ΛHπ- + p + 3 H562.14±0.07 π- + 2 H + 2 H111.92± Λ Heπ- + p + 3 He832.42±0.05 π- + p + p + 2 H152.44±0.09 Large difference ̴ 300 keV Is this difference really CSB effect? [1,2] [3] [1] M. Juric et al., Nucl. Phys. B 52 (1973) 1 [3] E. Hiyama et al., Phys. Rev. C 65 (2001) [2] M. Bedjidian et al., Phys. Lett B 83 (1979) 252 Experimental data were measured only by Emulsion technique. Emulsion data [2] 4H4H 4  He We may confirm this energy by   spectroscopy. 21

Charge symmetry braking (CSB) for 7-body By including CSB parameter and some assumptions, 4-body system can be reproduced. 4H4H 4  He 7  Be by emulsion 7  Li * by emulsion +  spectroscopy 7  He by (e,e’K) BL of 7LHe is much different with 7Li* and 7LBe. CSB parameter decided from 4-body gives worse results for 7-body system. We may confirm this energy by   spectroscopy. 22

 Hypernuclear spectroscopy at JLab  In 2009, we successfully performed the 3 rd generation  hypernuclear spectroscopic experiment via (e,e’K + ).  Coincidence experiment between Hadron arm and Scattered electron arm  Quite huge background associated with bremsstrahlung schematic view of the 3 rd generation reported by T. Gogami, 4 th presentaion in this session reported by T. Gogami, 4 th presentaion in this session 23 -B  [MeV]  0.03  0.2 MeV from α  n n JLab E Li(e,e’K + ) 7 Λ He Preliminar y

SpekA and C  SpekA and SpekC have ideal detector components.  During the first commissioning run in May-Jun/2011, only SpekC was used.  Both SpekA and SpekC were used for second commissioning run in Jul/2011. Q S D D VDC x4 Scinti. Wall x2 (3mm t and 10mm t ) Gas Cerenkov 24

N Z World of matter made of u, d, s quarks N u ~ N d ~ N s Higher density ３ -dimensional nuclear chart ,  Hypernuclei ,  Hypernuclei Strangeness 0 -2 “Stable” by M. Kaneta inspired by HYP06 conference poster Strangeness in neutron stars (  >  0 ) Strange hadronic matter (A → ∞) 25

(e,e’K+) experiment at MAMI-C  Hypernuclear physics at MAMI-C  Upgrade of MAMI : GeV -> GeV (2006 ̴ )  KAOS was introduced in MAMI-C (2008 ̴ ) Kaos Spec- B 縮尺 26

(e,e’K+) experiment at MAMI ~10 MeV (FWHM) ~2.5 MeV (FWHM) JLab MAMI MAMI-CJLab (E05-115) targetliquid H 2 CH 2 target thickness370 mg/cm mg/cm 2 beam intensity1~4 μ A~2 μ A term~3 weeks~ 2 days Kao n magnetKaosHKS dispersive angle21 – 43 deg2 – 12 deg central momentum 0.53 GeV1.2 GeV e’magnetSpec-BHES dispersive angle15 deg3 – 12 deg central momentum 0.33 GeV0.8 GeV 27

Experimental setup – target – target chamber SpecC Kaos 12 C 45 mg/cm 2 Al 2 O 3 beam screen 9 Be 22 mg/cm 2 7 Li (in future) SpecA beam 縮尺 28

今回の実験のまとめ 24 May 7:00 : start beam time 25 May 18:00 ~ : start data taking ~28 May 14:00 : calibration data for paddles ~30 May 11:00 : coincidence data at 500 nA ~1 June 10:00 : coincidence data at 300 nA with MWPC ~1 June 22:00 : improvement of AC radiator (Matsushita -> Russian) ~3 June 13:00 : coin data at 300 nA with MWPC ~7 June 10:00 : coin data at 1500 nA w/o MWPC ~8 June 11:00 : coin data at 2000 nA w MWPC ~14 June 5:00 : coin data at 1500 nA w MWPC target : 125 μ m 9 Be Total Charge : 1.3 C Anselm : 1 counts / μ A / day Sho : 170 counts / 10 μ A / 20days 10 counts stopping hyper fragments 29

Target ターゲットホルダー Be 125 μ m C mg/cm2 Al 2 O 3 beam screen Be 125×4 μ m Li ? mg Scattering chamber empty 上から 冷却水ノズル 横から 4 cm 30

Target target leveler1 leveler2mirror マーカー y, x 軸、合わせ z x z 軸合わせ ビームパイプ mirror leveler2 beam 31

Schematic view of Setup Kaos SpecC 17 deg 124 deg MWPC G-Wall AC target VDC Scinti e-e- GC material : 9 Be thickness : 125 μ m tilt angle : 54 deg Kaon tag Pion spectroscopy TOF ⊗ Tag ⊗ Scinti H-Wall trigger SpecA VDC Scinti GC Pion spectroscopy 32

0 degree (original beam direction) target ( 9 Be 125  m) e  energy : 1508MeV 17 deg 54 deg ] deg SpekC central momentum : 125 MeV/c momentum acceptance : 25% ] deg SpekA central momentum : 130 MeV/c momentum acceptance : 25% ] Kaos central momentum : 1000 MeV/c 33