Progress on JPARC hadron physics in 2016 1

Progress on J-PARC hadron physics in 2016 1 Recent results and future prospects of the decay pion spectroscopy for new mass determination of light hypernuclei Tohoku University Sho Nagao 2016/3/2

Progress on J-PARC hadron physics in 2016/3/2 Contents Ø Introduction ü Hypernuclear BΛ determination ü New experimental method “decay pion spectroscopy” Ø Experiments ü Apparatus ü Data taking ü Result in MAMI 2012 & MAMI 2014 Ø Recent progresses & Feasure prospects ü Beam energy calibration ü Pion spectrometer’s momentum calibration Ø Summary 2

Progress on J-PARC hadron physics in 2016/3/2 3 Hypernuclear chart & BΛ (g. s. ) determinations n Emulsion in 1960~70’s a few 10 ～ several 100 ke. V w/ stat. error Λ potential, Σ mixing, ΛN CSB etc. sys. error is not clear n (e, e’K+) spectroscopy in this decade a few 100 ke. V (total error)

Progress on J-PARC hadron physics in 2016/3/2 4 Issues of light hypernuclei l ΛN Charge Symmetry Breaking (CSB) 3 H ⇔ 3 He mass diff. (strong) : ～ 70 ke. V [R. A. Brandenburg et al. , PRC 37 781 -785 (1988). ] Well consistent with theoretical estimation (ρ0 -ω mixing effect) p n 4 Λ H p n Λ 350± 40 ke. V BΛ (g. s. ) = 2. 04± 0. 04 (⇒ 2. 12± 0. 01) BΛ (1+) = 0. 95± 0. 04 4 Λ He n Λ BΛ (g. s. ) = 2. 39± 0. 03 BΛ (1+) = 1. 24± 0. 06 (⇒ 0. 93± 0. 03) Large symmetry breaking in ground state Spin dependent l Systematic BΛ shift of 12ΛC l Short lifetime of 3ΛH p [M. Juric et al. , NPB 52 (1973) 1. ] [M. Bedjidian et al. , PLB 62(1976)467. ] [M. Bedjidian et al. , PRL 83 (1979) 252. ] [M. Kawachi Doctoral thesis (1997). ] [T. O. Yamamoto et al. PRL. ] [T. Gogami et al. , ar. Xiv: 1511. 04801]

Progress on J-PARC hadron physics in 2016/3/2 New technique “Decay Pion Spectroscopy” eγ* K+ p Kaon tag Fragments Mnucl MHYP M π－ , p π－ Λ Stop Two-body Decay l l πMonochromatic Momentum Pion spectrometer MHYP only from pπ (high resolution) Electro-photo production (high yield) K+ tag for strangeness ID (background suppression) Hyperfragment 5

Progress on J-PARC hadron physics in 2016/3/2 Measurable hypernuclei no 2 -body decay 7 Li 9 Be 12 C 4 4 ΛHe → Li + π Measuring BΛ w/ same setup 6

Progress on J-PARC hadron physics in 2016/3/2 Electron beam accelerator Mainz Microtron (MAMI-C) Ø Beam energy : Max. 1508 Me. V Ø Beam intensity : Max. ~100 μA Ø Duty factor : 100% Ø Energy resolution : ΔE～ 110 ke. V(FWHM) Ø Beam emittance [vertical] : < 1. 2π×µm×mrad (rms) 7

Progress on J-PARC hadron physics in 2016/3/2 A 1 experimental hall Spek-A Spek-C π- π- Spek-C e – beam from MAMI 12 C, 181 Ta 9 Be (125μm, 250μm) Target To Kaos Beam Kaos ～ 2 m K+ to dump to photon dump Target Mover Vacuum Chamber Frame 8

Progress on J-PARC hadron physics in 2016/3/2 9 Pion spectrometers (Spek-A, Spek-C) Spek-A Gas Cherenkov Scintillation Counter π- Drift Chamber 1 m Spek-A Spek-C Mom. Accept 105 -125 Me. V/c 110 -140 Me. V/c Angle ＋90° －126° Mom. res Δp/p ~ 10 -4 (rms) Solid angle 28 msr

Progress on J-PARC hadron physics in 2016/3/2 10 Momentum Calibration Elastic scattering AZ(e, e’)AZ 195. 17 Me. V 12 C, 181 Ta Energy differences of scattered electron 52. 00° 181 Ta 6μm target Function : Landau Gauss + linear FWHM : 200 ke. V/c Momentum calibration Peak shape

Progress on J-PARC hadron physics in 2016/3/2 11 Kaon tagger (Kaos) TOF 2 (H) AC 1 AC 2 TOF 1 (G&I) e +, π +, K +, p Kaos Magnet 1 m Lead wall Mom. Accept 600～ 1200 Me. V/c Angle ~0° Solid angle ~ 15 msr K+ survival ratio ~ 40%

Progress on J-PARC hadron physics in 2016/3/2 12 Data taking Pilot experiment Terms Beam current Kaos rate MAMI 2012 MAMI 2014 25 May – 14 Jun, 24 Oct. - 11 Nov. 2012 26 Jun. – 30 Jul. 2014 19 Jul – 1 Aug 2011 × 10 × 2 2 μA 20 μA ~40 μA × 1/30 × 2/3 1000 k. Hz at 2 μA 30 k. Hz at 20 μA 20 k. Hz at 40 μA Spek-A, C rate 2 k. Hz at 2 μA 30 k. Hz at 20 μA ~60 k. Hz at 40 μA Total charge 1. 4 C 20. 9 C 66. 9 + 10. 8 C Calibration points - 181 Ta : 2 points 181 Ta : 3 points 12 C : 1 point 12 C : 8 points

Progress on J-PARC hadron physics in 2016/3/2 13 Decay pion spectrum (MAMI 2012) 1. 5 Me. V (FWHM) → 4 He + π - Peak significance : 7. 9σ Width : 0. 2 Me. V/c (FWHM) First observation of hypernuclear peak

Progress on J-PARC hadron physics in 2016/3/2 Summary of BΛ (4ΛH [g. s]) BΛ = 2. 12± 0. 01(stat. )± 0. 09(sys. ) Me. V [A. Esser, S. Nagao, F. Schulz et al. PRL 114 (2015) 232501] F. Schulz, Ph. D thesis ü ü ü Consistent result with emulsion data Highest precision Systematic error from reliable estimation Consistent results between 2012 – 2014 runs Large BΛ difference 4ΛH – 4ΛHe 14

Progress on J-PARC hadron physics in 2016/3/2 15 Progressing of decay pion spectroscopy Ø Large systematic error due to precision of e- beam energy in calibration run much more precise measurement of beam energy is necessary. → Mag. field measurement 2 cm Beam pos. monitor m c 0 0 45 Ø ～mid. Feb. 2016 Ø > 10000 data points. Stepping Motor + Hall probe Ø 5～ 50 mm steps [～ 10 μm precision] Ø ΔB < 30 μT

Progress on J-PARC hadron physics in 2016/3/2 Progressing of decay pion spectroscopy Ø Large systematic error due to precision of e- beam energy in calibration run much more precise measurement of beam energy is necessary. → Mag. field measurement → Systematic study of pion spectrometers MAMI 2012 : 2× 181 Ta & 1× 12 C MAMI 2014 : 3× 181 Ta & 8× 12 C Calibration in 2016 Reduction of systematic uncertainties 90 (Me. V) ke. V → a Target few 10 ke. V Beam energy No. of Mom. sets 180 181 Ta + 12 C 10 + 10 195 181 Ta + 12 C + CH 210 181 Ta + 12 C 9 + 9 225 181 Ta + 12 C 8 + 8 450 12 C 1 2 9 + 4 Different angular setting (53. 5, 60, 70 deg) Different beam positions at target (11 points) 16

Progress on J-PARC hadron physics in 2016/3/2 17 Summary Ø Decay pion spectroscopy of electro-produced hypernuclei ü New spectroscopic technique ü BΛ measurement with ~100 ke. V accuracy BΛ (4ΛH [0+]) = 2. 12 ± 0. 01(stat. ) ± 0. 09(sys. ) Me. V [A. Esser, S. Nagao, F. Schulz et al. PRL 114 (2015) 232501] First observation using this method Highest precision for BΛ Reliable estimation for systematic error Large ΛN CSB effect in A=4 hypernuclear system Ø Improvements are on going l Systematic error reduction Precise magnetic field measurement Systematic studies of pion spectrometers Ø Next hypernuclear peak 3 7 ΛH, ΛHe etc. Different target (Lithium etc. )