Prospects of hypernuclear experiments at MAMI-C
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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
21th Mar. 20143rd Korea-Japan Workshop 3
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
3rd Korea-Japan Workshop 4
Decay pion spectroscopy of Λ hypernuclei
Λp
π- Pionspectrometer
Kaon tag
21th Mar. 20143rd Korea-Japan Workshop 5
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)
21th Mar. 20143rd Korea-Japan Workshop 6
Target thickness optimization
Background suppression in Kaos
Target thickness
21th Mar. 20143rd Korea-Japan Workshop 7
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
21th Mar. 20143rd Korea-Japan Workshop 8
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)
21th Mar. 20143rd Korea-Japan Workshop 9
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)
21th Mar. 20143rd Korea-Japan Workshop 10
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
21th Mar. 20143rd Korea-Japan Workshop 11
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
3rd Korea-Japan Workshop 12
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
21th Mar. 20143rd Korea-Japan Workshop 14
[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)
21th Mar. 20143rd Korea-Japan Workshop 15
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
3rd Korea-Japan Workshop 16
~ 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
21th Mar. 20143rd Korea-Japan Workshop 17
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) ~
21th Mar. 20143rd Korea-Japan Workshop 18
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