Prospects of hypernuclear experiments at MAMI-C

Prospects of hypernuclear experiments at MAMI-C

Tohoku University

Sho NAGAO

21th Mar. 2014

3rd Korea-Japan Workshop 1

Contents

Introduction

Decay pion spectroscopy Experimental setup

Results

Future plan

Summary

21th Mar. 20143rd Korea-Japan Workshop 2

Light hypernuclei


HΛ4HΛ

3 HΛ6

HeΛ4 HeΛ

5 HeΛ6 HeΛ

7 HeΛ8

LiΛ6

BeΛ7

BΛ9

CΛ12

NΛ14

OΛ16

LiΛ7 LiΛ

8 LiΛ9 LiΛ

10

BeΛ8 BeΛ

9 BeΛ10

BΛ11 BΛ

12BΛ10

CΛ13 CΛ

14

NΛ15

hypernuclear chartZ

N

• Expansion of S=-1 floor• Emulsion• (K -,π -),(π+,K+),(e,e’K+) etc.

• ΛN interaction• Effective ΛN interaction• ΛN-ΣN coupling• Three body ΛNN force• Charge symmetry breaking

• Impurity effect• Deeply bound state• Shrinkage effect

Λ-N charge symmetry breaking (CSB)

21th Mar. 2014

3H 3Hepn pp nn ΔB = 760 keV

Coulomb force

≃CSB effect : 71 keV R.A.Brandenburg et al., Phys. Rev. C 37 781-785 (1988).

3H + Λ

-2.04±0.04

-BΛ (MeV) 3He + Λ

Exp.

-1.00±0.06

-2.39 ±0.03

-BΛ (MeV)

Exp.

-1.24±0.06

0+

1+

1+

0+

M. Juric et al., Nucl. Phys. B 52 (1973) 1M. Bedjidian et al., Phys. Lett B 83 (1979) 252

pn Λpp nΛn He4ΛH4Λ350 keV


Decay pion spectroscopy of Λ hypernuclei

Λp

π- Pionspectrometer

Kaon tag


e - K+

New experimental technique Hypernuclear mass spectroscopy with high precision (~30 keV accuracy) Fragmentation probability

Fragments

~20 μA ~20 mg/cm2

Δp/p ~ 10-4

HΛ4HΛ

3 HΛ6

HeΛ4 HeΛ

5 HeΛ6 HeΛ

7 HeΛ8

LiΛ6

BeΛ7

BΛ9

CΛ12

LiΛ7 LiΛ

8 LiΛ9 LiΛ

10

BeΛ8 BeΛ

9 BeΛ10

BΛ11 BΛ

12BΛ10

CΛ13

Z

N

Experimental setup

Spek-A

Spek-B

Spek-C

Kaos

e- Cent.Mom +900 MeV/c

Angle ~0 degree

Solid angle ~ 20 msr

K+ survival ratio ~ 40%

Cent.Mom A:-115, C:-125 MeV/c

Angle A:-90, C:+126 degree

Mom. res Δp/p < 10-4

Solid angle 28 msr

Target

Material 9Be

Thickness 125 μm (54 deg tilted)

9Be

π-

K+

π- Kaos (Kaon tagger)

Spek-A, C (Pion spectrometer)


Target thickness optimization

Background suppression in Kaos

Target thickness


The optimization of target thickness is quite important

Too thin → Less stopping probabilityToo thick → More energy struggling

Worse accuracy

Target thickness (mg/cm2)

Sto

pp

ing

pro

b.

(%)

Resolu

tion

(M

eV

/c)

The estimation of target thickness effect using Geant4

Simulation

Setup in Kaos


Kaos Magnet

TOF2 (H)

AC1

e+, π+, K+, p

1m

AC2

Lead wall

TOF1 (G&I)

Lead wall 10~14 cm thick, e+ absorber

TOF 2 cm thick, σ ~ 250 ps

AC n = 1.05, effπ- ~ 97%

Top view

Setup in Kaos (Lead wal)


Kaos Magnet

TOF2 (H)

AC1

e+, π+, K+, p

1m

AC2

Lead wall

TOF1 (G&I)

Lead wall 10~14 cm thick, e+ absorber

TOF 2 cm thick, σ ~ 250 ps

AC n = 1.05, effπ- ~ 97%

Top viewGeant4 Simulation of Lead wall

Lead thickness (cm)

Su

rviv

al r

atio

e+

π+

K+

p

50 %

0.2 %

• e+ background : Seriously high (~100 MHz/20 μA beam)• Momentum resolution : No relation with mass resolution

Kaos setup (Aerogel Cherenkov)


Rejection efficiency (NPE<2)

Pion 99.9 %Kaon 1.0%

Proton 0.1%

π+ veto in offline analysis

1.5 m

0.5 m

• 6 segments• Hamamatsu 5” PMT• Teflon diffused reflector• Panasonic 3 cm• Refractive index = 1.05 π+

K+

p

NPE

NPE distribution in J-PARC T44

Co

unt

s

0 5 10 15 20 25 30

Decay pion experiment in 2012

Target 9Be (125 μm thickness)Beam current 20 μA

Kaos rate 30 kHz at 20 μASpek-A, C rate 30 kHz at 20 μATotal charge 20.9 C (1.3×1020 electrons)

Typical condition

2nd decay pion experiment

terms : 24 Oct. ~ 11 Nov. in 2012


Coincidence time (ns)

“K+,π-”“K+,μ-”

2012

Identification of decayed pion events

21th Mar. 2014

Coincidence time = Time at target of K+ - Time at target of π -

TOF wall : beta, energy depositMomentum : mass reconstructionAerogel Cherenkov : pion rejection

Coincidence&

Accidental b.g.

Gas Cherenkov : electron rejection

Cuts in Kaon tagger Cuts in Pion spectrometer


Accidental background

counts

/ 5

00 p

s

Coincidence time (ns)

2011

K+ tagged π- momentum spectrum

21th Mar. 2014

Preliminary

accidental background

QF hyperon background

3rd Korea-Japan Workshop

133 MeV/c peak : 4ΛH

width : ~200 keV/c (FWHM)stat. err. : <30 keV/c

13

Formation probability of 4ΛH


[1] Phys. Rev. D 86 (2012) 1328[2] M.M Bloch et al. Proceedings of Int. Conf. on Hyperfragments, CERN-Report 64-1 pp.63[3] D. Bertrand et al. Nucl. Phys. B16 (1970) 77.

[1]

[2,3]

2.0×10-4

Detection ratio of Λ (Simulation)


1. Virtual Photon distribution M. Sotona private communication

2. Fermi motion of proton A. Bodek and J.L. Ritchie, Phys. Rev. D 23 1070-1091 (1981).3. N(γ,K+)Y cross section : Isobar model (K-MAID)4. Acceptance of Kaos & Spek-C

13

2 Kaos

Spek-C

Pio

n m

om

en

tum

(M

eV

/c)

Decayed pion 2D dist.

Pion angle (degree) Pion momentum (MeV/c)

QF ΛQF Σ -

Decayed pion mom. dist.

StoppedQF Σ-

4

http://wwwkph.kph.uni-mainz.de/MAID/kaon/

Future plan

21th Mar. 2014

Taking data with better S/N ratio• Higher yield → Longer beam time & Higher beam intensity• Suppression of background


~ 70% reduction

simulation w/ collimator

Collimator

Pion spectrometer

targetHyperfragments

QFhyperons

~2cm

Accidental b.gOptimization of Lead wall : rate→~1/4 (already checked)Trigger upgrade in Spek-C

QF hyperon b.g

End of May in 2014

Future plan


Material : Tungsten HeavyalloySize : 40H×70L×30T mm3

Tungsten Collimator& Frame

Summary

Decay pion spectroscopy new technique ~ 30 keV mass accuracy in light hypernuclei Hypernuclear formation probability

Pilot experiment The experiments have performed in 2011 & 2012 4

ΛH peak with small statistical err. Formation probability

Future plan Aiming to better S/N ratio

Position optimization of lead wall Collimator to suppress QF hyperon b.g.

Next beam time : The end of May (2014) ~


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Prospects of hypernuclear experiments at MAMI-C