1. 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

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

3. 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)

4. 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 (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: ]
Short lifetime of 3ΛH

5. 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

6. 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-

7. 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 MeV
Beam intensity : Max. ~100 μA
Duty factor : 100%
Energy resolution : ΔE～110 keV(FWHM)
Beam emittance [vertical] :
< 1.2π×µm×mrad (rms)

8. 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)

9. 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
MeV/c
MeV/c
Angle
＋90°
－126°
Mom. res
Δp/p ~ 10-4 (rms)
Solid angle
28 msr

10. 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
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

11. 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

12. 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 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 C
Calibration points -
181Ta : 2 points
12C : 1 point
181Ta : 3 points
12C : 8 points
×10
×1/30 ×2
×2/3

13. 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

14. 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) ]
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

15. 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
> data points
5～50 mm steps [～10 μm precision]
ΔB < 30 μT
Stepping Motor
+ Hall probe

16. 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
195
181Ta + 12C + CH2
210
9 + 9
225
8 + 8
450
12C 1
Different angular setting (53.5, 60, 70 deg)
Different beam positions at target (11 points)

17. 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) ]
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.)