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VIII TOURS SYMPOSIUM ON NUCLEAR PHYSICS AND ASTROPHYSICS in Black Forest, Germany (2012)
Lambda hypernuclear spectroscopy at JLab Hall-C
Graduate School of Science, Tohoku University
Toshiyuki Gogami for the HES-HKS collaboration
1.Introduction
2.Physics motivation
9 Li, 10 Be, 12 B, 52 V, Λ, Σ0
He,
Λ
Λ
Λ
Λ
Λ
Λ, Σ0
• Elementary production of K+Λ,Σ0
• Contribution of longitudinal terms
The (e,e’K+) experiment
• FWHM ~ 500 keV
A few MeV by the (π+,K+), (K-,π-)
• PΛ
n Λ by the (π+,K+), (K-,π-)
7
Light Λ hypernuclei (A < ~10)
• ΛN-ΣN interaction
• Charge symmetry breaking
Medium heavy Λ hypernuclei (A=52)
• Mass dependence of Λ single
particle energy
• s-,p-,d-,f-orbit binding energy &
cross section
• ls splitting
Figure.1 : HES-HKS group photo in the experimental hall C in JLab (2009).
HES
HKS
Δp/p
~2×10-4
~2×10-4
Momentum
[GeV/c]
0.844 ± 0.144
1.20± 0.15
Angle (lab)
3.0 – 9.0
1.0 – 13.0
[degree]
Beam energy
2.344
[GeV]
7Li , 9Be , 10B , 12C , 52Cr (,CH ,H O)
Target
2 2
(Hypernuclei) (7ΛHe, 9ΛLi, 10ΛBe, 12ΛB, 52ΛV) (,Λ,Λ)
Figure.2 : The experimental setup of JLab E05-115 (2009)
• YN interaction(baryon-baryon interaction)
• Structure of Λ hypernuclei
4.Missing Mass
M2HY = (Ee + MT - EK+ - Ee’)2 - ( pe - pK+ - pe’ )2
JLab E05-115
CH2, ~ 450 [mg/cm2]
~ 2.0 [μA]
~ 38 [hours]
p(e,e’K+)Λ
Measure with spectrometers
~1.8MeV (FWHM)
Δm = 19 ± 17 keV/c2
3.Particle identification
p(e,e’K+)Σ0
Figure.3 : Picture of HKS detector package
1 [m]
K+
~1.8MeV (FWHM)
Δm = 73 ± 47 keV/c2
Before Cherenkov cut
Accidental coincidence
QF Λ from 12C
p, π+
K+
After Cherenkov cut
Figure.6 : Missing Mass spectrum of Polyethylene (CH2) target
Figure.7 : Coincidence time
The polyethylene target was used as a proton target to optimize
energy scale and to study the elementary process of K+Λ production.
Mass square [GeV/c2]2
Drift chambers
Cherenkov detectors -AC,WC-KDC1,KDC2σ ≈ 250 [μm]
• Aerogel (n=1.05)
TOF walls -2X,1Y,1X• Water (n=1.33)
(Plastic scintillators)
TOF σ ≈ 170 [ps]
NPE
Aerogel (n=1.05)
sΛ
π+
p
K+
NPE
When the Cherenkov and
mass square cuts are
applied to keep ~90%
kaon in the total events,
<2% proton and <1% pion
are contaminated in the
kaon events.
pΛ
Figure.4 : Mass square distribution
Water (n=1.33)
K+
π+
Accidental coincidence events
p
Figure.8 : Missing mass spectrum of 12C target.
12C(e,e’K+)12 B
Λ
JLab E05-115
52Cr, ~154 mg/cm2
~ 7.6 μA
~ 227 hours
Mass square [GeV/c2]2
Figure.5 : NPE of Cherenkov detector vs. mass square
5.Electro-/photo- production of
+
KΛ
Lack of consistency at forward angles
 High statistical data have been awaited
Accidental coincidence events
Figure.9 : Missing mass spectrum of 52Cr target.
52Cr(e,e’K+)52 V
Λ
Figure.8 shows preliminary binding
energy histogram of 12C(e,e’K+)12ΛB.
The peaks of sΛ and pΛ are clearly can
be seen, although the widths are a
few MeV in the current status. The
matrix tuning is on progress not only
to get better energy resolution but
also to keep linearity.
Figure.9 shows preliminary binding
energy histogram of 52Cr(e,e’K+)52ΛV.
450±80 events are in the binding
region (-20 MeV ~ 0 MeV). The
number of events will be increased by
the parameter optimization of the
drift chambers at least by ~10%.
6.Summary
Figure.10 : The differential cross section of photo-production of
K+Λ ( P.Bydzovsky and T.Mart, Phys. Rev. C 76, 065202 (2007) )
Q2 is very small ( ~0.01[GeV/c]2)
 Almost real photon
• W ~ 1.93 GeV
• cosθKCM ~ 0.97
JLab E05-115 (HES-HKS)
192±6±89 [ nb / sr ]
Figure.11 : The differential cross section of K+Λ production
SAPHIR : K.H.Glander et al. , Eur. Phys. J. A 19, 251-273 (2004)
CLAS : R.Bradford et al. , Phys. Rev. C 73, 035202 (2006)
• The (e,e’K+) experiment at JLab Hall-C in 2009 (JLab E05-115)
• 7ΛHe, 9ΛLi, 10ΛBe, 12ΛB and 52ΛV, Λ, Σ0
• Kaon identification
• When the cuts applied to keep ~90% kaon in total events , <2% proton
and <1% pion contaminate in the kaon events.
• Matrix tuning
• In progress not only to get better resolution but also to keep linearity.
• K+Λ elementary production data at very forward angle
• cosθkCM ~ 0.97 , W~1.9 GeV , Q2~0.01 [GeV/c]2