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

Contents Physics motivation for  meson Experimental approaches Previous experiments Proposed experiment at J-PARC Summary 2009/2/22 NQCD symposium, K. Ozawa 2 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!

Hadrons in QCD Mass [GeV] hadron can be undestood as excitation of QCD vacuum Precise measurements of hadron property at nuclear medium can provide QCD information Modification of vector meson mass is expected, even at nuclear density.  many experimental and theoritical efforts to search for and study in-medium modifications of hadrons 2009/2/223 NQCD symposium, K. Ozawa Figure by Prof. V. Metag I’d like to focus on vector mesons, such as .

Experimental approaches –Direct measurements of mass spectra Emitted Proton Neutron p  Nucleon Hole Target Decay Meson –Meson spectroscopy 2009/9/184 PUHF WS, K. Ozawa

Results from LEPS 2009/2/22 NQCD symposium, K. Ozawa 5 Chiral ’05 N. Muramatsu There some hints of a bound state. Missing mass resolution of ~30MeV/c 2 is expected. Forward measurements are essential. Large statistics data and further analysis are waited.

Results from CBELSA/TAPS disadvantage:  0 -rescattering advantage:  0  large branching ratio (8 %) no  -contribution (    0  : 7  )       p  A   + X  00 D. Trnka et al., PRL 94 (2005) after background subtraction TAPS,    0  with +A 2009/2/22 NQCD symposium, K. Ozawa 6 m  = m 0 (1 -   /  0 ) for  = 0.13

TAPS results II 2009/2/22 NQCD symposium, K. Ozawa 7 M. Kotulla et al, PRL 100 (2008) Large  width in nuclei due to -N interaction. 60 MeV/c 2 even at stopped . Essential: Focus on Small momentum Issue: Yield estimation of decays

Proposed experiment Emitted Neutron  Nucleon Hole Target  0  decay  –Meson spectroscopy –Direct measurements of mass spectra 2009/2/228 NQCD symposium, K. Ozawa Clear measurements in small momentum! Bound state search Two measurements at the same time.

J-PARC J-PARC 2009/2/22 NQCD symposium, K. Ozawa 9 Beam Energy ： 50 ＧｅＶ (30GeV for Slow Beam) Beam Intensity:3.3x10 14 ppp, 15A (2×10 14 ppp, 9A) Hadron Hall

2009/2/22 NQCD symposium, K. Ozawa Hadron hall NP-HALL 56m(L)×60m(W) 10

Reaction and Beam momentum 2009/2/22 NQCD symposium, K. Ozawa 11 Stopped  meson       n   A   + N+X  00 To generate stopped modified  meson, beam momentum is ~ 1.8 GeV/c. (K1.8 can be used.) As a result of KEK-E325, 9% mass decreasing (70 MeV/c 2 ) can be expected. Focus on forward (~2°). Generate  meson using beam. Emitted neutron is detected at 0. Decay of  meson is detected. If  momentum is chosen carefully, momentum transfer will be ~ 0.  momentum [GeV/c]  momentum [GeV/c] 0

Note: Forward measurements Forward proton –Good High mass resolution High efficiency –Bad No separation between proton and  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% 2009/2/22 NQCD symposium, K. Ozawa 12

2009/2/2213 NQCD symposium, K. Ozawa Experimental setup  - p   1.8 GeV/c   0    Target: Carbon 6cm Small radiation loss Clear calculation of  bound state Ca, Nb, LH 2 are under consideration. Neutron Detector Flight length 7m 60cm x 60 cm (~2°) Gamma Detector Assume T-violation’s 75% of 4 SKS for charge sweep Beam Neutron Gamma Detector

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 22 MeV/c /2/2214 NQCD symposium, K. Ozawa 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. Bound region 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

Gamma detector CsI EMCalorimeter T-violation’s one is assumed. （ D.V. Dementyev et al., Nucl. Instrum. Meth. A440(2000), 151 ） 2009/2/2215 NQCD symposium, K. Ozawa Assumed Energy Resolution Obtained  meson spectra for stopped K decays Muon holes should be filled by additional crystals. Acceptance for  is evaluated as 90%. Fast simulation is tuned to reproduce existing data.

Decay Yield Evaluation Based on measured crosssection of  - p   n for backward  (G. Penner and U. Mosel, nucl-th/ , J. Keyne et al., Phys. Rev. D 14, 28 (1976)) Production cross section 0.02 mb/sr s = 2.0 GeV 0.17 mb/sr s = 2.0 GeV Beam intensity 10 7 / spill, 6 sec spill length Neutron Detector acceptance  = 2°(60 cm x 60 7m) Gamma Detector acceptance 90% for  Radiation loss in target 11% Survival probability in final state interaction 60% Beam Time 100 shifts Branching Ratio 1.3 % 8.9 % 2009/2/22 NQCD symposium, K. Ozawa 16 H. Nagahiro et al calculation based on the cross section and known nuclear effects. Assumed potential is consistent with  absorption in nucleus. Interact w nuclei No interact Total Large width ~ 60 MeV/c 2

Results for three potentials 2009/2/22 NQCD symposium, K. Ozawa 17 H. Nagahiro et al Generation of  Decay of (Invariant Mass) Large abs. No int. Large abs. Large int.

Final Spectrum 2009/2/22 NQCD symposium, K. Ozawa 18 Including Background: Main background is 2  decays and 1 missing Bound region One can select bound region as Energy of  < E 0, which is measured by the forward neutron counter. Invariant Mass spectrum for the bound region Strong kin. effects

“Mass” Correlation 2009/2/22 NQCD symposium, K. Ozawa 19 Invariant Mass VS Missing Energy Non-correlated model Correlated model Correlation analysis will useful for reducing kinematical effects.

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  meson in nucleus, large nucleus should be used. –In addition, we can measure a large mass width (absorption cross section) of  in nucleus in small momentum range. 2009/2/22 NQCD symposium, K. Ozawa 20

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 2009/2/22 NQCD symposium, K. Ozawa 21