1 / 21

omega meson in nucleus, experimental study

omega meson in nucleus, experimental study. K. Ozawa (Univ. of Tokyo). Contents. Physics motivation for w meson Experimental approaches Previous experiments Proposed experiment at J-PARC Summary. Collaboration with, or helped by Prof. R.S. Hayano, Prof. H. Nagahiro,

holmes-meyer
Download Presentation

omega meson in nucleus, experimental study

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. omega meson in nucleus, experimental study K. Ozawa (Univ. of Tokyo)

  2. Contents • Physics motivation for w meson • Experimental approaches • Previous experiments • Proposed experiment at J-PARC • Summary Collaboration with, or helped by Prof. R.S. Hayano, Prof. H. Nagahiro, Prof. S. Hirenzaki, K. Utsunomiya, S. Masumoto, Y. Komatsu, Y. Watanabe I need more helps from you! NQCD symposium, K. Ozawa

  3. Hadrons in QCD • hadron can be undestood as • excitation of QCD vacuum Precise measurements of hadron property at nuclear medium can provide QCD information • many experimental and theoritical efforts to search for and study in-medium modifications of hadrons Mass [GeV] Modification of vector meson mass is expected, even at nuclear density. Figure by Prof. V. Metag I’d like to focus on vector mesons, such as w. NQCD symposium, K. Ozawa

  4. Nucleon Hole Emitted Proton Neutron p, p, g Meson Decay Target Experimental approaches • Meson spectroscopy • Direct measurements of mass spectra PUHF WS, K. Ozawa

  5. Results from LEPS Chiral ’05 N. Muramatsu There some hints of a bound state. Missing mass resolution of ~30MeV/c2 is expected. Forward measurements are essential. Large statistics data and further analysis are waited. NQCD symposium, K. Ozawa

  6. gA   + X after background subtraction p g p0g g  w p0 g g Results from CBELSA/TAPS TAPS, w p0g with g+A D. Trnka et al., PRL 94 (2005) 192203 advantage: • p0g large branching ratio (8 %) • no -contribution (  0 : 7  10-4) disadvantage: • p0-rescattering m =m0 (1 -  /0) for  = 0.13 NQCD symposium, K. Ozawa

  7. TAPS results II Large w width in nuclei due to w-N interaction. M. Kotulla et al, PRL 100 (2008) 192302 Essential: Focus on Small momentum Issue: Yield estimation of decays 60 MeV/c2 even at stopped w. NQCD symposium, K. Ozawa

  8. Nucleon Hole Emitted Neutron p- w p0g decay Target Proposed experiment Two measurements at the same time. • Meson spectroscopy • Direct measurements of mass spectra Clear measurements in small momentum! Bound w state search NQCD symposium, K. Ozawa

  9. J-PARC • Beam Energy： 50ＧｅＶ • (30GeV for Slow Beam) • Beam Intensity: 3.3x1014ppp, 15mA • (2×1014ppp, 9mA) Hadron Hall NQCD symposium, K. Ozawa

  10. NP-HALL 56m(L)×60m(W) Hadron hall NQCD symposium, K. Ozawa

  11. p-A   + N+X n p p0g g  w p0 g g Reaction and Beam momentum Stopped w meson Generate w meson using p beam. Emitted neutron is detected at 0. Decay of w meson is detected. If p momentum is chosen carefully, momentum transfer will be ~ 0. To generate stopped modified w meson, beam momentum is ~ 1.8 GeV/c. (K1.8 can be used.) As a result of KEK-E325, 9% mass decreasing (70 MeV/c2) can be expected. Focus on forward (~2°). 0.4 w momentum [GeV/c] 0.2 4 2 0 0 p momentum [GeV/c] NQCD symposium, K. Ozawa

  12. Note: Forward measurements • Forward proton • Good • High mass resolution • High efficiency • Bad • No separation between proton and p beam. Triggering generated protons is too hard. • Forward 1~2°will be excluded. • Forward neutron • Good • 0 degree measurements • Bad • Need long TOF for high resolution • Low efficiency < 30% NQCD symposium, K. Ozawa

  13. Experimental setup • p-p  wn @ 1.8 GeV/c •  p0g  gg • Target: Carbon 6cm • Small radiation loss • Clear calculation of w bound state • Ca, Nb, LH2 are under consideration. • Neutron Detector • Flight length 7m • 60cm x 60 cm (~2°) • Gamma Detector • Assume T-violation’s • 75% of 4p • SKS for charge sweep Neutron Beam Gamma Detector NQCD symposium, K. Ozawa

  14. Neutron Measurement • Timing resolution • Beam test is done at Tohoku test line • Timing resolution of 80 ps is achieved (for charged particle). • It corresponds to mass resolution of 22MeV/c2. • Neutron Efficiency • Iron plate (1cm t) is placed to increase neutron efficiency. • Efficiency is evaluated using a hadron transport code, FLUKA. • Neutron efficiency of 25% can be achieved. We can not see a clear bound peak. At this moment, there is no beam line at J-PARC to have enough TOF length and beam energy Bound region NQCD symposium, K. Ozawa

  15. Gamma detector • CsI EMCalorimeter • T-violation’s one is assumed. Obtained p meson spectra for stopped K decays （D.V. Dementyev et al., Nucl. Instrum. Meth. A440(2000), 151） Assumed Energy Resolution Muon holes should be filled by additional crystals. Acceptance for w is evaluated as 90%. Fast simulation is tuned to reproduce existing data. NQCD symposium, K. Ozawa

  16. Decay Yield Evaluation Based on measured crosssection of p-p  wn for backward w (G. Penner and U. Mosel, nucl-th/0111024, J. Keyne et al., Phys. Rev. D 14, 28 (1976)) H. Nagahiro et al calculation based on the cross section and known nuclear effects. Assumed potential is consistent with w absorption in nucleus. • Production cross section • 0.02 mb/sr (CM) @ s = 2.0 GeV • 0.17 mb/sr (Lab) @ s = 2.0 GeV • Beam intensity • 107 / spill, 6 sec spill length • Neutron Detector acceptance • Dq = 2°(60 cm x 60 cm @ 7m) • Gamma Detector acceptance • 90% for w • Radiation loss in target 11% • Survival probability in final state interaction • 60% • Beam Time 100 shifts • Branching Ratio 1.3 % • 8.9 % Total No interact Interact w nuclei Large width ~ 60 MeV/c2 NQCD symposium, K. Ozawa

  17. Results for three potentials Generation of w H. Nagahiro et al Large abs. No int. Large abs. Large int. Decay of w (Invariant Mass) 2366 2755 938 NQCD symposium, K. Ozawa

  18. Final Spectrum One can select bound region as Energy of w < E0, which is measured by the forward neutron counter. Bound region Including Background: Main background is 2p0 decays and 1g missing Strong kin. effects Invariant Mass spectrum for the bound region NQCD symposium, K. Ozawa

  19. “Mass” Correlation • Invariant Mass VS Missing Energy • Non-correlated model • Correlated model NQCD symposium, K. Ozawa Correlation analysis will useful for reducing kinematical effects.

  20. Issue • It’s hard to find a bound state peak using forward neutron measurements at J-PARC due to a limited hadron hall space at this moment. • Note: proton measurements are also hard. • Effects of relatively large angle to form a bound state • Effects of beam spread and halo for a trigger. • When we focus on “mass modification” of w meson in nucleus, large nucleus should be used. • In addition, we can measure a large mass width (absorption cross section) of w in nucleus in small momentum range. NQCD symposium, K. Ozawa

  21. Summary • Hadrons can be understood as a excitation of “QCD vacuum” and carried “vacuum” information. • Experimental efforts are underway to investigate this physics. Some results are already reported. • Still, there are problems to extract physics information. • New experiments for obtaining further physics information is being proposed. • Measurement with stopped mesons • Measurement of bound states NQCD symposium, K. Ozawa

More Related