Search for the omega-mesic nuclei at SPring-8 LEPS

Norihito MuramatsuRCNP, Osaka University

CHIRAL05 @RIKEN, 17 Feb. 2005 　　

Contents

Concepts of the omega-mesic nuclei search in photoreaction

Experimental setups including newly introduced deep-UV laser

Very preliminary plots from 1-week test experiment

Summary and prospects

• Chiral symmetry is broken because of quark-antiquark condensates.

• Partial restoration of the chiral symmetry breaking at finite

density. ⇒ Reduction of vector meson mass (~15% at nuclear density)- Brown and Rho, Phys. Rev. Lett. 66, 2720 (1991) [scaling rule]- Hatsuda and Lee, Phys. Rev. C46, 34 (1992) [QCD sum rule]- Klingl, Kaiser and Weise, Nucl. Phys. A624, 527 (1997) [effective Lagransian]- Klingl, Wass and Weise, Nucl. Phys. A650, 299 (1999) [effective Lagransian]

Nuclear Modification of Vector Mesons

)()( LRRLdLRRLudumass ddddmuuuumddmuumL

ρ

ω

φ

ω-bound state of nuclei

(Amplitude TVN is evaluated by effective Lagrangian.)

VNvacVV T :potentialnuclear -

0)( :equationGordon -Klein 222 rmE V

12C (γ, p )ω11B

12C (d,3He)ω11B

12C (π － ,n)ω11B

Binding energy and width

Photoproduction of ω–mesic nucleiγ12C → p ω

11B 　 : Accessible by SPring-8 LEPS

γ d

pγ

p

ωCarbon

Expected Missing Energy Spectrum

)(00

2

ESlab

d

dlab

dEd

d

p

pp

p

BpC

Free cross section ~0.3 μb/sr (SAPHIR)

S(E) includes wave functions of initially bound proton and outgoing proton with distortion functions, and Green function of bound ω

Marco and Wise, nucl-th/0012052

Missing energy w/ proton detection ： Eγ+mp ー Ep ー mω = Eω ー mω+|Bp|

Analogy to deeply bound pionic atom search

• 208Pb(d,3He)π-207Tl reaction at GSI

• 600 MeV d beam ⇒ π － recoiless kinematics• Substitutional reaction （ ΔL=0 ）• Calibration by p(d,3He)π0 reaction

Yamazaki et al., Z. Phys. A355, 219 (1996)

Strategy of Experimentγp→ωp inside nuclei and capturing ω in proton hole =ω-recoiless kinematics at Eγ = 2.75 GeV =Extremely forward production of proton

New 266 nm laser

Photon energy [GeV] Photon energy [GeV]

Proton polar angle [rad] Proton polar angle [rad] Photon energy [GeV]

Photon energy [GeV]

ω m

om

entu

m [

MeV

/c]

Mis

sin

g e

ner

gy

[M

eV]

Mis

sin

g e

ner

gy

[M

eV]

Mis

sin

g e

ner

gy

[M

eV]

ω m

om

entu

m [

MeV

/c]

ω m

om

entu

m [

MeV

/c]

Ar laser (351 nm)

θp<0.06 rad (3.4 degree)

θp<0.06 rad (3.4 degree)

Research Center for Nuclear Physics, Osaka University ： T. Nakano, D.S. Ahn, M. Fujiwara, K. Horie, T. Hotta, K. Kino, H. Kohri, N. Muramatsu, T. Onuma, T. Sawada, A. Shimizu, M. Uchida, R.G.T. ZegersDepartment of Physics, Pusan National University ： J.K. Ahn, J.Y. Park School of Physics, Seoul National University ： H.C. Bhang, K.H. TshooDepartment of Physics, Konan University ： H. Akimune Japan Atomic Energy Research Institute / SPring-8 ： Y. Asano, A. Titov Institute of Physics, Academia Sinica ： W.C. Chang, D.S. Oshuev, Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8 ： H. Ejiri, S. Date', N. Kumagai, Y. Ohashi, H. Ohkuma, H. Toyokawa, T. Yorita Department of Physics and Astronomy, Ohio University ： K. Hicks, T. MibeDepartment of Physics, Kyoto University ： K. Imai, H. Fujimura, T. Miwa, M. Miyabe, Y. Nakatsugawa, M. Niiyama, N. Saito, M. Yosoi Department of Physics, Chiba University ： H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University ： S. Makino Department of Physics and Astrophysics, Nagoya University ： S. Fukui Department of Physics, Yamagata University ： T. Iwata Department of Physics, Osaka University ： S. Ajimura, M. Nomachi, A. Sakaguchi, S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan ： C. Rangacharyulu Department of Physics, Tohoku University ： M. Sumihama Laboratory of Nuclear Science, Tohoku University ： T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University ： T. Matsuda, Y. Toi Institute for Protein Research, Osaka University ： M. Yoshimura National Defense Academy in Japan ： T. Matsumura

The LEPS Collaboration

Laser Electron Photon (LEP) Beam• ８ GeV electron ｓ in SPring8 + UV laser (a few eV ） ⇒ a few GeV photons (Backward Compton Scattering)• Maximum Energy of LEP beam

Ee = 7.960 GeV, me = 0.5110 MeV/c2

Ar laser (351 nm) klaser = 3.53 eV k⇒ max = 2.40 GeV

Deep UV laser (266 nm) klaser = 4.66 eV k⇒ max = 2.88 GeV

laseree

lasere

laseree

laseree

kEm

kEkPEkPEk

4

42)(

max 2

2

Eγ measurement by tagging system

• Photon energy measurement by detecting the direction of recoil electron• 100um-pitch SSD ＋ Plastic Scint.• Energy resolution ~12MeV

Deep UV laser (266 nm)• DeltaTrain (Spectra Physics)• Frequency doubling by

Second Harmonic Generation

Pump laser (532 nm, 5W)

266 nm at BBO crystal (~1W)• #photons

Deep UV : ~200K/sec

Ar : １ M/sec

BG (Brems.) : 1-10K/sec• BBO crystal life : 4-7 days

Pump laser

Resonator

BBO crystal

Energy calibration• e (8 GeV) → e’ + γ using Bremsstrahlung γ-rays

Tagging Counter e+e- conversion at 0.5 mm-thick Pb

• Eγ=Pe++Pe- based on P-meas. at LEPS spectrometer

⇒ Relation between Eγ(e+e-) and tagger SSD position

Tagger SSD channel number

Eγ(

e+e- )

GeV

Energy spectrum• Efficiency correction for tagger plastic scintillators• Compton edge is adjusted to 2.88 GeV by scaling B-field of dipole magnet (momentum calibration ： 1.005)

LEP Brems.

Eγ GeV Eγ GeV

LEPS spectrometer

TOF

Dipole Magnet　 0.7 　 Tesla

Target

Start Counter DC2 DC3

DC1SVTX

AC(n=1.03)

Charged particle spectrometer with forward acceptancePID from momentum and time-of-flight measurements

Photons

Missing mass spectra in LH2 data

η´

η

ω

π0

Missing mass (GeV/c2)

Λ

∑0

Λ(1520)

Missing mass (GeV/c2)

Λ(1405) ／∑0(1385)

Proton K ＋

Momentum resolution

Proton momentum [GeV/c]

Mo

men

tum

res

olu

tio

n [

MeV

/c]

ΔP~25 MeV/cat Eγ=2.75 GeV

Test Experiment for ω-mesic nuclei search

~8 days run in April and June ， 2003

• CH2 （ 41.3 mm ） : 　 ~1.7 M events 　（ for calibrations ）

• Carbon （ 36 mm ） : ~8.7 M events

Target

Start Counter (STC)

AC Veto

Charge Veto(UPV)

Tagger

TOF

γ-ray

protonelectron

10 cm

Expected Yield (Emiss<0) ≈ ~300[nb/sr]×(π×0.062)×(33.7×109)×3.6[cm] proton polar angle < 3.4°#Tag(Carbon) Thickness

×(6.022×1023×1.730[g/cm3]/12)×0.5 ≈ 20 events Avogadro # density / A transmission

Calibrations by rest-proton contribution in CH2 data

Basic calibrations were done by LH2 and LD2 data with large statistics

Precise calibration of SVTX position (Δx~100μm) was done by looking into rest proton contributions in CH2 data.

Carbon Contribution in CH2=Carbon Data×0.136

　　 CH2 （ A=14 ） : 0.967 g/cm3×4.13 cm

= 3.99 g/cm2, 　 #Tag=8.35×109

　　 Carbon (A=12): 1.730 g/cm3×3.60 cm

= 6.23 g/cm2, 　 #Tag=33.7×109

Rest proton contribution in K ＋ and proton missing masses

CH2

CarbonX 0.136

ωη’

η

Λ ∑

Λ(1520)

∑(1385)Λ(1405)

K ＋ missing mass [GeV/c2] Proton missing mass [GeV/c2]

K ＋ missing mass [GeV/c2] Proton missing mass [GeV/c2]

Rest proton contribution in K ＋ K － invariant mass and missing mass

CH2

CarbonX 0.136

φ proton

KK invariant mass [GeV/c2] KK missing mass [GeV/c2]

KK invariant mass [GeV/c2] KK missing mass [GeV/c2]

Missing energy spectrum in CH2 data(all tagged energies and θp<0.12)

CH2

Carbon x 0.136

MC (rest proton)Real data

Missing energy [GeV] Missing energy [GeV]

Momentum measurement vs. Polar angle （ w/ Short LH2 ）

0.06 < θp < 0.09

θp < 0.06

0.09 < θp < 0.12

Missing mass [GeV/c2] Missing mass [GeV/c2]

Missing mass [GeV/c2] Missing mass [GeV/c2]

Missing mass [GeV/c2] Missing mass [GeV/c2]

Preliminary ResultComparison by different polar angle region

Not depend on calibration precision⇒

Tagger quality cut3σ PID cut on protonχ2 probability cutNo z-vertex cut H contribution~5evntsPolar angle < 0.06 radNo Eγ cut

Energy loss correction is applied when plotting missing energy distribution.

Proton separation energy = 16 MeV

θp < 0.06

0.06 < θp < 0.09X 0.681 (acc. Ratio)

Missing energy [GeV]

Very Preliminary

Same spectrum in－ 100 MeV < Emiss < 100 MeV

with 10 MeV bins

Missing energy [GeV]

Missing energy [GeV]

Very Preliminary

Very Preliminary

Missing Energy vs. Polar angle (MC)

w/ detector resolutionw/ Fermi motionw/ separation energy

Missing energy [GeV]

Missing energy [GeV]

Missing energy [GeV]

0.06<θp<0.09

θp<0.06

Pro

ton

po

lar

ang

le [

rad

]

Energy Dependence

Eγ>2.4 GeV Eγ<2.4 GeV

Missing energy [GeV] Missing energy [GeV]

θp < 0.06θp < 0.06

0.06 < θp < 0.09X 0.681 (acc. Ratio)

0.06 < θp < 0.09X 0.681 (acc. Ratio)

Very Preliminary Very Preliminary

Summary and prospects

• Analysis is still on-going, but very preliminary plots

show an excess below threshold in comparison of

θp<0.06 rad and 0.06<θp<0.09 rad.

• Potential problems to be fixed

- e ＋ e － mis-PID contaminations at high momentum

(AC efficiency 99.7%, tighter PID cut for lower side)

- Calibrations, BG shape, …• High statistics data will be collected with

more stable laser (257 nm) this year.