Lambda hypernuclear spectroscopy at JLab Hall-C

Graduate School of Science, Tohoku UniversityToshiyuki Gogami for the HES-HKS collaboration

1.Introduction 2.Physics motivation

M2HY = (Ee + MT - EK+ - Ee’)2 - ( pe - pK+ - pe’ )2

The (e,e’K+) experiment• FWHM ~ 500 keVA few MeV by the (π+,K+), (K-,π-)• P Λn Λ by the (π+,K+), (K-,π-)

Figure.1 : HES-HKS group photo in the experimental hall C in JLab (2009).

Figure.2 : The experimental setup of JLab E05-115 (2009)

Measure with spectrometers

HES HKS

Δp/p ~2×10-4 ~2×10-4

Momentum[GeV/c]

0.844 ± 0.144 1.20± 0.15

Angle (lab)[degree]

3.0 – 9.0 1.0 – 13.0

Beam energy[GeV]

2.344

Target(Hypernuclei)

7Li , 9Be , 10B , 12C , 52Cr (,CH2,H2O)(7

ΛHe, 9ΛLi, 10

ΛBe, 12ΛB, 52

ΛV) (,Λ,Λ)

3.Particle identification

4.Missing Mass

Figure.3 : Picture of HKS detector package

NPE

NPE

Mass square [GeV/c2]2

π+

1 [m]K+

p, π+

K+

p

π+

p

K+

Figure.5 : NPE of Cherenkov detector vs. mass square

Cherenkov detectors -AC,WC-• Aerogel (n=1.05)• Water (n=1.33)

Drift chambers-KDC1,KDC2-

TOF walls -2X,1Y,1X-(Plastic scintillators)

σ ≈ 250 [μm]

TOF σ ≈ 170 [ps]Aerogel (n=1.05)

Water (n=1.33)

Figure.4 : Mass square distributionMass square [GeV/c2]2

After Cherenkov cutK+

Before Cherenkov cut

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.

5.Electro-/photo- production of K+Λ

6.Summary

Figure.11 : The differential cross section of K+Λ productionSAPHIR : 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)• 7

ΛHe, 9ΛLi, 10

ΛBe, 12ΛB and 52

ΛV, 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

p(e,e’K+)Λ~1.8MeV (FWHM)Δm = 19 ± 17 keV/c2

p(e,e’K+)Σ0

~1.8MeV (FWHM)Δm = 73 ± 47 keV/c2

QF Λ from 12C

JLab E05-115CH2, ~ 450 [mg/cm2]~ 2.0 [μA]~ 38 [hours]

The polyethylene target was used as a proton target to optimize energy scale and to study the elementary process of K+Λ production.

Figure.6 : Missing Mass spectrum of Polyethylene (CH2) target Figure.7 : Coincidence time

Accidental coincidence events

Figure.8 : Missing mass spectrum of 12C target.　　　　　　　　　　　　　　　　　 12C(e,e’K+)12

ΛB

Preliminary

Preliminary

pΛ

sΛ

Preliminary

JLab E05-115 (HES-HKS)192±6±89 [ nb / sr ]

Figure.10 : The differential cross section of photo-production of K+Λ ( P.Bydzovsky and T.Mart, Phys. Rev. C 76, 065202 (2007) )

Lack of consistency at forward angles High statistical data have been awaited

Q2 is very small ( ~0.01[GeV/c]2)Almost real photon• W ~ 1.93 GeV• cosθK

CM ~ 0.97

Figure.8 shows preliminary binding energy histogram of 12C(e,e’K+)12

ΛB. 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.

VIII TOURS SYMPOSIUM ON NUCLEAR PHYSICS AND ASTROPHYSICS in Black Forest, Germany (2012)

Figure.9 : Missing mass spectrum of 52Cr target.　　　　　　　　　　　　　　　　　 52Cr(e,e’K+)52

ΛV

Accidental coincidence events

Preliminary

JLab E05-11552Cr, ~154 mg/cm2

~ 7.6 μA~ 227 hours

Figure.9 shows preliminary binding energy histogram of 52Cr(e,e’K+)52

ΛV. 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%.

7ΛHe, 9

ΛLi, 10ΛBe, 12

ΛB, 52ΛV, Λ, Σ0

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

Λ, Σ0

• Elementary production of K+Λ,Σ0

• Contribution of longitudinal terms

• YN interaction(baryon-baryon interaction)• Structure of Λ hypernuclei

Accidental coincidence