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

Recent progresses & Feasure prospects Progress on J-PARC hadron physics in 2016 2016/3/2 Contents Introduction Hypernuclear BΛ determination New experimental method “decay pion spectroscopy” Experiments Apparatus Data taking Result in MAMI2012 & MAMI2014 Recent progresses & Feasure prospects Beam energy calibration Pion spectrometer’s momentum calibration Summary

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

Issues of light hypernuclei Progress on J-PARC hadron physics in 2016 2016/3/2 Issues of light hypernuclei ΛN Charge Symmetry Breaking (CSB) 3H ⇔ 3He mass diff. (strong) : ～70 keV [R.A.Brandenburg et al., PRC 37 781-785 (1988).] Well consistent with theoretical estimation (ρ0-ω mixing effect) H 4 Λ He 4 Λ p n Λ p n Λ 350±40 keV BΛ (g.s.) = 2.04±0.04 (⇒ 2.12±0.01) BΛ (g.s.) = 2.39±0.03 BΛ (1+) = 1.24±0.06 (⇒ 0.93±0.03) BΛ (1+) = 0.95±0.04 [M.Juric et al., NPB 52 (1973) 1.] [M.Bedjidian et al., PLB62(1976)467.] [M.Bedjidian et al., PRL83 (1979) 252.] [M.Kawachi Doctoral thesis (1997).] [T.O.Yamamoto et al. PRL.] Large symmetry breaking in ground state Spin dependent Systematic BΛ shift of 12ΛC [T.Gogami et al., arXiv:1511.04801] Short lifetime of 3ΛH

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

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

Electron beam accelerator Mainz Microtron (MAMI-C) Progress on J-PARC hadron physics in 2016 2016/3/2 Electron beam accelerator Mainz Microtron (MAMI-C) Beam energy : Max. 1508 MeV Beam intensity : Max. ~100 μA Duty factor : 100% Energy resolution : ΔE～110 keV(FWHM) Beam emittance [vertical] : < 1.2π×µm×mrad (rms)

A1 experimental hall π - K+ Target Mover Spek-C Spek-A Spek-C Progress on J-PARC hadron physics in 2016 2016/3/2 Kaos Spek-A Spek-C to photon dump e – beam from MAMI to dump Target π - K+ ～2 m A1 experimental hall Target Mover Vacuum Chamber Frame Spek-C Beam To Kaos 12C, 181Ta 9Be (125μm, 250μm)

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

Momentum Calibration Elastic scattering 12C, 181Ta AZ(e,e’)AZ Progress on J-PARC hadron physics in 2016 2016/3/2 Momentum Calibration Elastic scattering AZ(e,e’)AZ 195.17 MeV 12C, 181Ta 𝐸 𝑒′ = 𝐸 𝑒 1+ 𝐸 𝑒 𝑀 𝑡𝑎𝑟 (1−cos⁡( 𝜃 𝑒 )) 52.00° Energy differences of scattered electron 181Ta 6μm target Function : Landau Gauss + linear FWHM : 200 keV/c 𝐸 𝑒′ 𝑐𝑎𝑙𝑐. − 𝐸 𝑒 ′ [𝑒𝑥𝑝.] (MeV/c) Momentum calibration Peak shape

Kaon tagger (Kaos) e+, π+, K+, p TOF2 (H) AC1 AC2 TOF1 (G&I) Lead wall Progress on J-PARC hadron physics in 2016 2016/3/2 Kaon tagger (Kaos) TOF2 (H) AC1 TOF1 (G&I) AC2 1m e+, π+, K+, p Lead wall Mom. Accept 600～1200 MeV/c Angle ~0° Solid angle ~ 15 msr K+ survival ratio ~ 40% Kaos Magnet

Data taking Pilot experiment MAMI 2012 MAMI 2014 Terms Progress on J-PARC hadron physics in 2016 2016/3/2 Data taking Pilot experiment MAMI 2012 MAMI 2014 Terms 25 May – 14 Jun, 19 Jul – 1 Aug 2011 24 Oct. - 11 Nov. 2012 26 Jun. – 30 Jul. 2014 Beam current 2 μA 20 μA ~40 μA Kaos rate 1000 kHz at 2 μA 30 kHz at 20 μA 20 kHz at 40 μA Spek-A, C rate 2 kHz at 2 μA ~60 kHz at 40 μA Total charge 1.4 C 20.9 C 66.9 + 10.8 C Calibration points - 181Ta : 2 points 12C : 1 point 181Ta : 3 points 12C : 8 points ×10 ×1/30 ×2 ×2/3

Decay pion spectrum (MAMI 2012) Progress on J-PARC hadron physics in 2016 2016/3/2 Decay pion spectrum (MAMI 2012) 1.5 MeV (FWHM) Peak significance : 7.9σ Width : 0.2 MeV/c (FWHM) → 4He + π - First observation of hypernuclear peak

BΛ = 2.12±0.01(stat.)±0.09(sys.) MeV Summary of BΛ (4ΛH [g.s]) Progress on J-PARC hadron physics in 2016 2016/3/2 Summary of BΛ (4ΛH [g.s]) BΛ = 2.12±0.01(stat.)±0.09(sys.) MeV [A.Esser, S.Nagao, F.Schulz et al. PRL 114 (2015) 232501] F.Schulz, Ph.D thesis Consistent result with emulsion data Highest precision Systematic error from reliable estimation Consistent results between 2012 – 2014 runs Large BΛ difference 4ΛH – 4ΛHe

Progressing of decay pion spectroscopy Progress on J-PARC hadron physics in 2016 2016/3/2 Progressing of decay pion spectroscopy Large systematic error 4500 cm due to precision of e- beam energy in calibration run 2 cm much more precise measurement of beam energy is necessary. → Mag. field measurement Beam pos. monitor ～mid. Feb. 2016 > 10000 data points 5～50 mm steps [～10 μm precision] ΔB < 30 μT Stepping Motor + Hall probe

Progressing of decay pion spectroscopy Progress on J-PARC hadron physics in 2016 2016/3/2 Progressing of decay pion spectroscopy 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 : 2×181Ta & 1×12C MAMI 2014 : 3×181Ta & 8×12C Reduction of systematic uncertainties 90 keV → a few 10 keV Calibration in 2016 Beam energy (MeV) Target No. of Mom. sets 180 181Ta + 12C 10 + 10 195 181Ta + 12C + CH2 9 + 9 + 4 210 9 + 9 225 8 + 8 450 12C 1 Different angular setting (53.5, 60, 70 deg) Different beam positions at target (11 points)

BΛ (4ΛH [0+]) = 2.12 ± 0.01(stat.) ± 0.09(sys.) MeV Progress on J-PARC hadron physics in 2016 2016/3/2 Summary Decay pion spectroscopy of electro-produced hypernuclei New spectroscopic technique BΛ measurement with ~100 keV accuracy BΛ (4ΛH [0+]) = 2.12 ± 0.01(stat.) ± 0.09(sys.) MeV [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 Improvements are on going Systematic error reduction Precise magnetic field measurement Systematic studies of pion spectrometers Next hypernuclear peak 3ΛH, 7ΛHe etc. Different target (Lithium etc.)