1. Search for the omega-mesic nuclei at SPring-8 LEPS Norihito Muramatsu RCNP, Osaka University CHIRAL05 @RIKEN, 17 Feb. 2005

2. 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

3. 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 ρ ω φ

4. ω-bound state of nuclei (Amplitude T VN is evaluated by effective Lagrangian.) 12 C (γ, p ) ω 11 B 12 C (d, 3 He) ω 11 B 12 C (π －,n) ω 11 B Binding energy and width

5. Photoproduction of ω–mesic nuclei γ 12 C → p ω 11 B : Accessible by SPring-8 LEPS γd p γ p ω Carbon

6. Expected Missing Energy Spectrum 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 ： E γ +m p ー E p ー m ω = E ω ー m ω +|B p |

7. Analogy to deeply bound pionic atom search 208 Pb(d, 3 He) π - 207 Tl reaction at GSI 600 MeV d beam ⇒ π － recoiless kinematics Substitutional reaction （ ΔL=0 ） Calibration by p(d, 3 He)π 0 reaction Yamazaki et al., Z. Phys. A355, 219 (1996)

8. Strategy of Experiment γp→ωp inside nuclei and capturing ω in proton hole =ω-recoiless kinematics at E γ = 2.75 GeV =Extremely forward production of proton New 266 nm laser Photon energy [GeV] Proton polar angle [rad] Photon energy [GeV] ω momentum [MeV/c] Missing energy [MeV] ω momentum [MeV/c] Ar laser (351 nm) θ p <0.06 rad (3.4 degree) θ p <0.06 rad (3.4 degree)

9. 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. Zegers Department of Physics, Pusan National University ： J.K. Ahn, J.Y. Park School of Physics, Seoul National University ： H.C. Bhang, K.H. Tshoo Department 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. Mibe Department 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

10. 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 E e = 7.960 GeV, m e = 0.5110 MeV/c 2 Ar laser (351 nm) k laser = 3.53 eV ⇒ k max = 2.40 GeV Deep UV laser (266 nm) k laser = 4.66 eV ⇒ k max = 2.88 GeV

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

12. 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

13. Energy calibration e (8 GeV) → e’ + γ using Bremsstrahlung γ-rays Tagging Counter e+e- conversion at 0.5 mm-thick Pb E γ =P e+ +P e- based on P-meas. at LEPS spectrometer ⇒ Relation between E γ (e + e - ) and tagger SSD position Tagger SSD channel number E γ (e + e - ) GeV

14. 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) LEPBrems. E γ GeV

15. LEPS spectrometer TOF Dipole Magnet 0.7 Tesla Target Start Counter DC2DC3 DC1SVTX AC(n=1.03) Charged particle spectrometer with forward acceptance PID from momentum and time-of-flight measurements Photons

16. Missing mass spectra in LH 2 data η´ η ω π0π0 Missing mass (GeV/c 2 ) Λ ∑0∑0 Λ(1520) Missing mass (GeV/c 2 ) Λ(1405) ／ ∑ 0 (1385) ProtonK＋K＋

17. Momentum resolution Proton momentum [GeV/c] Momentum resolution [MeV/c] ΔP~25 MeV/c at E γ =2.75 GeV

18. Test Experiment for ω-mesic nuclei search ~8 days run in April and June ， 2003 CH 2 （ 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 proton electron 10 cm Expected Yield (Emiss<0) ≈ ~300[nb/sr]×(π×0.06 2 )×(33.7×10 9 )×3.6[cm] proton polar angle < 3.4°#Tag(Carbon) Thickness ×(6.022×10 23 ×1.730[g/cm 3 ]/12)×0.5 ≈ 20 events Avogadro # density / A transmission

19. Calibrations by rest-proton contribution in CH2 data Basic calibrations were done by LH 2 and LD 2 data with large statistics Precise calibration of SVTX position (Δx~100μm) was done by looking into rest proton contributions in CH 2 data. Carbon Contribution in CH 2 =Carbon Data×0.136 CH 2 （ A=14 ） : 0.967 g/cm 3 ×4.13 cm = 3.99 g/cm 2, #Tag=8.35×10 9 Carbon (A=12): 1.730 g/cm 3 ×3.60 cm = 6.23 g/cm 2, #Tag=33.7×10 9

20. Rest proton contribution in K ＋ and proton missing masses CH 2 Carbon X 0.136 ω η’η’ η Λ ∑ Λ(1520) ∑(1385) Λ(1405) K ＋ missing mass [GeV/c 2 ]Proton missing mass [GeV/c 2 ] K ＋ missing mass [GeV/c 2 ]Proton missing mass [GeV/c 2 ]

21. Rest proton contribution in K ＋ K － invariant mass and missing mass CH2 Carbon X 0.136 φ proton KK invariant mass [GeV/c 2 ]KK missing mass [GeV/c 2 ] KK invariant mass [GeV/c 2 ]KK missing mass [GeV/c 2 ]

22. Missing energy spectrum in CH 2 data (all tagged energies and θ p <0.12) CH 2 Carbon x 0.136 MC (rest proton)Real data Missing energy [GeV]

23. Momentum measurement vs. Polar angle （ w/ Short LH 2 ） 0.06 < θ p < 0.09 θ p < 0.06 0.09 < θ p < 0.12 Missing mass [GeV/c 2 ]

24. Preliminary Result Comparison by different polar angle region ⇒ Not depend on calibration precision Tagger quality cut 3σ PID cut on proton χ 2 probability cut No z-vertex cut H contribution~5evnts Polar angle < 0.06 rad No E γ cut Energy loss correction is applied when plotting missing energy distribution. Proton separation energy = 16 MeV θ p < 0.06 0.06 < θ p < 0.09 X 0.681 (acc. Ratio) Missing energy [GeV] Very Preliminary

25. Same spectrum in － 100 MeV < E miss < 100 MeV with 10 MeV bins Missing energy [GeV] Very Preliminary

26. Missing Energy vs. Polar angle (MC) w/ detector resolution w/ Fermi motion w/ separation energy Missing energy [GeV] 0.06<θ p <0.09 θ p <0.06 Proton polar angle [rad]

27. Energy Dependence E γ >2.4 GeVE γ <2.4 GeV Missing energy [GeV] θ p < 0.06 0.06 < θ p < 0.09 X 0.681 (acc. Ratio) 0.06 < θ p < 0.09 X 0.681 (acc. Ratio) Very Preliminary

28. Summary and prospects Analysis is still on-going, but very preliminary plots show an excess below threshold in comparison of θ p <0.06 rad and 0.06<θ p <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.