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

CHIRAL05 @RIKEN, 17 Feb. 2005. Search for the omega-mesic nuclei at SPring-8 LEPS. Norihito Muramatsu RCNP, Osaka University. Contents. Concepts of the omega-mesic nuclei search in photoreaction Experimental setups including newly introduced deep-UV laser

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

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

  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. Nuclear Modification of Vector Mesons ρ • 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] ω φ

  4. ω-bound state of nuclei (Amplitude TVN is evaluated by effective Lagrangian.) Binding energy and width 12C (γ, p )ω11B 12C (d,3He)ω11B 12C (π－,n)ω11B

  5. Photoproduction of ω–mesic nuclei γ12C → p ω11B: Accessible by SPring-8 LEPS Carbon ω γ p p γ d

  6. Expected Missing Energy Spectrum Marco and Wise, nucl-th/0012052 Missing energy w/ proton detection： Eγ+mpーEpーmω = Eωーmω+|Bp| 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

  7. Analogy to deeply bound pionic atom search Yamazaki et al., Z. Phys. A355, 219 (1996) • 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

  8. Strategy of Experiment γp→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 Ar laser (351 nm) θp<0.06 rad (3.4 degree) ω momentum [MeV/c] Missing energy [MeV] ω momentum [MeV/c] Photon energy [GeV] Photon energy [GeV] Photon energy [GeV] θp<0.06 rad (3.4 degree) Missing energy [MeV] Missing energy [MeV] ω momentum [MeV/c] Proton polar angle [rad] Proton polar angle [rad] Photon energy [GeV]

  9. The LEPS Collaboration 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

  10. Laser Electron Photon (LEP) Beam • ８ GeV electronｓ 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 ⇒ kmax = 2.40 GeV Deep UV laser (266 nm) klaser = 4.66 eV ⇒ kmax = 2.88 GeV

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

  12. Pump laser Resonator BBO crystal 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 : １M/sec BG (Brems.) : 1-10K/sec • BBO crystal life : 4-7 days

  13. Energy calibration • e (8 GeV) → e’ + γ using Bremsstrahlung γ-rays Tagging Countere+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 Eγ(e+e-) GeV Tagger SSD channel number

  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) LEP Brems. Eγ GeV Eγ GeV

  15. TOF SVTX DC1 AC(n=1.03) Target Dipole Magnet 0.7Tesla DC2 DC3 Start Counter LEPS spectrometer Charged particle spectrometer with forward acceptance PID from momentum and time-of-flight measurements Photons

  16. Missing mass spectra in LH2 data Proton K＋ Λ η´ ∑0 ω Λ(1405)／ ∑0(1385) Λ(1520) η π0 Missing mass (GeV/c2) Missing mass (GeV/c2)

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

  18. 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 Charge Veto (UPV) AC Veto TOF Target γ-ray 10 cm proton Tagger Start Counter (STC) electron 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

  19. 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

  20. Rest proton contribution in K＋and proton missing masses CH2 Carbon X 0.136 K＋missing mass [GeV/c2] Proton missing mass [GeV/c2] ∑(1385) Λ(1405) Λ ∑ Λ(1520) η’ ω η K＋missing mass [GeV/c2] Proton missing mass [GeV/c2]

  21. Rest proton contribution in K＋K－invariant mass and missing mass CH2 Carbon X 0.136 KK invariant mass [GeV/c2] KK missing mass [GeV/c2] proton φ KK invariant mass [GeV/c2] KK missing mass [GeV/c2]

  22. Missing energy spectrum in CH2 data(all tagged energies and θp<0.12) Real data MC (rest proton) CH2 Carbon x 0.136 Missing energy [GeV] Missing energy [GeV]

  23. Momentum measurement vs. Polar angle （w/ Short LH2） θp < 0.06 Missing mass [GeV/c2] Missing mass [GeV/c2] 0.06 < θp < 0.09 Missing mass [GeV/c2] Missing mass [GeV/c2] 0.09 < θp < 0.12 Missing mass [GeV/c2] Missing mass [GeV/c2]

  24. Preliminary ResultComparison by different polar angle region⇒ Not depend on calibration precision Tagger quality cut 3σ PID cut on proton χ2 probability cut No z-vertex cut H contribution~5evnts Polar angle < 0.06 rad No Eγ cut Energy loss correction is applied when plotting missing energy distribution. Very Preliminary θp < 0.06 0.06 < θp < 0.09 X 0.681 (acc. Ratio) Missing energy [GeV] Proton separation energy = 16 MeV

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

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

  27. Energy Dependence Eγ>2.4 GeV Eγ<2.4 GeV Very Preliminary Very Preliminary θp < 0.06 θp < 0.06 0.06 < θp < 0.09 X 0.681 (acc. Ratio) 0.06 < θp < 0.09 X 0.681 (acc. Ratio) Missing energy [GeV] Missing energy [GeV]

  28. 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.

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