Study of charge symmetry breaking via the gamma-ray spectroscopy of hypernuclei

M. UkaiKEK/J-PARC Hadron

for the E13 collaboration

THROUGH THE LOOKING GLASS,AND WHAT FOUND ALICE THERE

J-PARC E13 collaboration

Contents

IntroductionCharge symmetry breaking in 4ΛΛΛΛH/ 4ΛΛΛΛHe

Experiment at J-PARC (E13)

Result of the 2015 physics runNew data on the excitation energy of 4ΛΛΛΛHe(1+)

Future plan

Summary

Charge symmetry breaking (CSB)in NN-interaction

Small CSB effect in NN interaction

G. A. Miller, A. K. Opper,

and E. J. Stephenson,

Ann. Rev. Nucl. Part. Sci. 56, 253 (2006).

Scattering lengthAfter the electromagnetic correction

Level scheme of mirror nuclei 3H / 3He

3H

1/2+

3He

1/2+

764 keV

difference

Major component:

Coulomb contribution

CSB effect = 71 keV

These differences ware explained

by ρρρρ0-ωωωω exchange potential

Unexpectedly large difference in excitation energies (Eγγγγ) and ΛΛΛΛ-binding energies (BΛΛΛΛ)between the mirror hypernuclei.

Charge symmetry breaking (CSB)in ΛΛΛΛN-interaction

+H4

Λ

+He4

Λ

ΛΛΛΛp ≠ ΛΛΛΛn ?

Considering• Coulomb force

( shrink effect of Λ )• 2 body ΛΛΛΛN-ΣΣΣΣN coupling

( ⇒ 3 body ΛN-ΣN mixing )

∆Β∆Β∆Β∆ΒΛΛΛΛ (0+) = 0.35 MeV , ∆Β∆Β∆Β∆ΒΛΛΛΛ (1+) = 0.28 MeV

Level scheme of 4ΛΛΛΛH and 4ΛΛΛΛHe

Many theoretical studies,but inconsistent with data

Need re-examination ofexisting data

A. Nogga, H. Kamada, and W. Gloockle,Phys. Rev. Lett. 88, 172501 (2002)

1.09Eγ =

Eγ =

Large CSB in ΛΛΛΛN-interaction ?

1.4 MeV

[present data]

≠ np

Old experiment for Eγγγγ(4ΛΛΛΛHe)

Only one experiment

• Stopped K- reaction (Li target)• detecting ππππ0→γγ→γγ→γγ→γγ

(with Pb + scinti. sandwich)

for tagging hypernuclei

• Doppler broaden γγγγ peak

• NaI detector• Energy resolution : 120 keV(FWHM)

• Limited statistics

Higher sensitivity and statistics

can be achieved by

• In-flight 4He(K-,ππππ-)4ΛΛΛΛHe reaction• Ge detector (Energy resolution : 0.2%)• High intensity K beam

+ large acceptance spectrometers

Gamma-ray energy spectrumwith detecting ππππ0→γγ→γγ→γγ→γγ decay

reported value : 1.15 (0.04) MeV

M. Bedjidian et al., Phys. Lett. B 83, 252 (1979).

eye guide line (not fitting)

The J-PARC E13 experiment

J-PARC Hadron Experimental Facility

30 GeV proton

K -Experimental target

Au 6 mm thick Primary target

Linac

3GeV synchrotron

30GeV synchrotron

K－－－－

Use high intensity K- beam delivered from J-PARC K1.8 beam line

ππππ−−−−γπ +→ ΛΛ−− ZZZ AAA ＊),(K

Spectrometerfor scat. particle（（（（SksMinus））））

Detect Detect Detect Detect γγγγ ray from ray from ray from ray from hypernucleihypernucleihypernucleihypernuclei・ Hyperball-J

Tag Tag Tag Tag hypernuclearhypernuclearhypernuclearhypernuclear productionproductionproductionproduction

・ Beam line spectrometer・ SksMinus spectrometer

reaction-γ coincidence experiment

Beam linespectrometer

Experimental setup (E13)

Ge detector

array

Hyperball-J

4ΛΛΛΛHe : liq.He target (2.7 g/cm

2)

length : ~23 cm

size : 12cmφφφφpK = 1.5 GeV/c

K－－－－

Use high intensity K- beam delivered from J-PARC K1.8 beam line

ππππ−−−−γπ +→ ΛΛ−− ZZZ AAA ＊),(K

Spectrometerfor scat. particle（（（（SksMinus））））

Detect Detect Detect Detect γγγγ ray from ray from ray from ray from hypernucleihypernucleihypernucleihypernuclei・ Hyperball-J

Tag Tag Tag Tag hypernuclearhypernuclearhypernuclearhypernuclear productionproductionproductionproduction

・ Beam line spectrometer・ SksMinus spectrometer

reaction-γ coincidence experiment

Beam linespectrometer

Experimental setup (E13)

Ge detector

array

Hyperball-J

4ΛΛΛΛHe : liq.He target (2.7 g/cm

2)

length : ~23 cm

size : 12cmφφφφpK = 1.5 GeV/c

J-PARC E13 He run done in 2015 April

Hyperball-J

in air-conditioned hut

SKS

SKS downstream

detectors

Hyperball-J Hyperball-J frameinstalled in K1.8

Hyperball-J frame

SKS magnet

2012.8 @J-PARC K1.8

mounting detectorsto the frame.

with liq.He target

Analysis and Result

Missing mass spectrum4

ΛΛΛΛHe productionMissing mass spectrumfor 4He(K-,ππππ-)X

We can clearly select 4ΛΛΛΛHe bound events.

• Missing mass resolution : 5 MeV (FWHM)• Small mount of B.G. contamination

in “bound region” (10 MeV gate)

Mass gated gamma-ray spectrum

Doppler correction

Mass gate

Gamma rays from non-strange nuclei

(accidental coincidence background)

No peak structure

Mass gated gamma-ray spectrumMass gate

Some gamma rays from non-strange nuclei

(accidental coincidence)

Single peak was observed.

Doppler correction

Revised level scheme and our findingOld level scheme

Revised level scheme

1.09

∆∆∆∆Eγγγγ = Eγγγγ(4ΛΛΛΛHe) - Eγγγγ(4ΛΛΛΛH)= 0.32 ±±±± 0.02 MeV

∆∆∆∆BΛΛΛΛ(1+) = BΛΛΛΛ(4ΛΛΛΛHe(1+)) - BΛΛΛΛ(4ΛΛΛΛH(1+))= 0.03 ±±±± 0.05 MeV

∆∆∆∆BΛΛΛΛ(0+) = 0.35 ±±±± 0.05 MeV

Revised level scheme and our findingOld level scheme

Revised level scheme

1.09

∆∆∆∆Eγγγγ = Eγγγγ(4ΛΛΛΛHe) - Eγγγγ(4ΛΛΛΛH)= 0.32 ±±±± 0.02 MeV

∆∆∆∆BΛΛΛΛ(1+) = BΛΛΛΛ(4ΛΛΛΛHe(1+)) - BΛΛΛΛ(4ΛΛΛΛH(1+))= 0.03 ±±±± 0.05 MeV

∆∆∆∆BΛΛΛΛ(0+) = 0.35 ±±±± 0.05 MeV

Charge symmetry breaking isSpin-dependent

Hint of CSB for 0+/1+ differenceΛΛΛΛN-ΣΣΣΣN mixing effect

Y. Akaishi, et. al.,

Phys. Rev. Lett. 84, 3539 (2000).

Same spin-dependence

with present data

~10 times stronger in 0+

ΛN-ΣN mixingLevel mixing of

Λ and Σ hypernuclear levers

Present result is accepted to PRL

arXiv:1508.00376

Further study

4ΛΛΛΛH(1+→0+) measurement

Previous 4ΛΛΛΛH(1+→0+) measurement

0.9

0.95

1

1.05

1.1

1.15

1.2

1 2 3

average

Previous 4ΛH(1+→0+) datavia stopped K- on Li target

M. Bedjidian et al.Phys. Lett. B 62,467 (1976).

M. Bedjidian et al.Phys. Lett. B 83,252 (1979).

Large Doppler-broadening of γγγγ peak~ 160 keV (FWHM) (with 7%NaI resolution;kawachi)

A. Kawachi, Doctoral thesisUniv. of Tokyo (1997)

160 keV(FWHM) resolution

(~180 keV w/ Doppler broad)

M. May reported high statistics gamma-ray peak

From A= 4 hypernuclei on 7Li(K-, π−γ) dataSmaller Doppler broadening effect

1.108 ±±±± 0.010 MeV with systematic error

They claimed that the peak is sum of4

ΛH(1.05 MeV) and 4

ΛHe(1.15 MeV) gamma-rays

4ΛH (~1.1 MeV) and

4ΛHe(1.4 MeV) can be identify

separately

NaI 74 keV(FWHM) at 1 MeV

1.1 1.4

Possible reaction process; (K-,π-)reaction on α cluster

K- + α α α α + t -> ΛΛΛΛ + 3He + ππππ- + t

Λ+3He -> 4ΛHe (0+ only non-spin-flip) Λ+ t -> 4ΛH (Both 0+/1+ ratio =1:3 expected)

ΛΛΛΛReasonable reaction to produce 4ΛΛΛΛH(1+) state

7Li

M.May, PRL 51(1983)2085

Previous 4ΛH(1+→0+) datavia inflight (K−,π−) on 7Li target

Higly unbound

Bound region

M. May reported high statistics gamma-ray peak

From A= 4 hypernuclei on 7Li(K-, π−γ) dataSmaller Doppler broadening effect

1.108 ±±±± 0.010 MeV with systematic error

They claimed that the peak is sum of4

ΛH(1.05 MeV) and 4

ΛHe(1.15 MeV) gamma-rays

4ΛH (~1.1 MeV) and

4ΛHe(1.4 MeV) can be identify

separately

NaI 74 keV(FWHM) at 1 MeV

1.1 1.4

Possible reaction process; (K-,π-)reaction on α cluster

K- + α α α α + t -> ΛΛΛΛ + 3He + ππππ- + t

Λ+3He -> 4ΛHe (0+ only non-spin-flip) Λ+ t -> 4ΛH (Both 0+/1+ ratio =1:3 expected)

ΛΛΛΛReasonable reaction to produce 4ΛΛΛΛH(1+) state

7Li

M.May, PRL 51(1983)2085

Previous 4ΛH(1+→0+) datavia inflight (K−,π−) on 7Li target

Higly unbound

Bound region

We will confirm this result with high sensitivity by Hyperball-J and J-PARC K1.1 beam line

K1.1 Beam line @ 100 kW

1.1 GeV/c 440 k/spill

0.9 GeV/c 150 k/spill

K1.1 available at ~2018

will move from K1.8 to K1.1π- spectrometer SKS and Ge array Hyperball will move from K1.8 to K1.1

Photo of SKS + Hyperball-J at K1.8

Plan of 4ΛH(1+→0+) measurementvia inflight (K−,π−) on 7Li target at J-PARC

Summary

Study of CSB in ΛΛΛΛN interactionA=4 hypernuclear structure

The first result of γγγγ-ray spectroscopy @J-PARC

Measured excitation energy of 4ΛΛΛΛHe(1+) = 1.406 ±±±± 0.002(stat.) ±±±±0.002(syst.) MeV

Large CSB was confirmeduniquely by γγγγ-ray spectroscopy (compared with Eγ(4ΛH) )

CSB effect is strongly spin-dependent(combined with emulsion data)

Precise measurement of excitation energy of 4ΛΛΛΛH(1+) is

planned at J-PARC K1.1 beam line